''Psittacosaurus'' ( ; "
parrot
Parrots, also known as psittacines (), are birds of the roughly 398 species in 92 genera comprising the order Psittaciformes (), found mostly in tropical and subtropical regions. The order is subdivided into three superfamilies: the Psittacoid ...
lizard
Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...
") is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
extinct
Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
ceratopsia
Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. ...
n
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
from the Early
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
of what is now
Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...
, existing between 126 and 101
million years ago
The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds.
Usage
Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago). ...
. It is notable for being the most
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
-rich non-avian dinosaur genus. Up to 12 species are known, from across
China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
,
Mongolia
Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million, ...
,
Russia
Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...
, and
Thailand
Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is bo ...
. The species of ''Psittacosaurus'' were obligate
bipeds
Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' a ...
at adulthood, with a high skull and a robust beak. One individual was found preserved with long filaments on the tail, similar to those of ''
Tianyulong
''Tianyulong'' (Chinese: 天宇龍; Pinyin: ''tiānyǔlóng''; named for the Shandong Tianyu Museum of Nature where the holotype fossil is housed) is an extinct genus of heterodontosaurid ornithischian dinosaur. The only species is ''T. confuc ...
''. ''Psittacosaurus'' probably had complex behaviours, based on the proportions and relative size of the brain. It may have been active for short periods of time during the day and night, and had well-developed senses of smell and vision.
''Psittacosaurus'' was one of the earliest ceratopsians, but closer to ''
Triceratops
''Triceratops'' ( ; ) is a genus of herbivore, herbivorous Chasmosaurinae, chasmosaurine Ceratopsidae, ceratopsid dinosaur that first appeared during the late Maastrichtian stage of the Late Cretaceous Period (geology), period, about 68 m ...
'' than ''
Yinlong
''Yinlong'' (, meaning "hidden dragon") is a genus of basal ceratopsian dinosaur from the Late Jurassic Period of central Asia. It was a small, primarily bipedal herbivore.
Discovery and species
A coalition of American and Chinese paleontologis ...
''. Once in its own family, Psittacosauridae, with other genera like ''Hongshanosaurus'', it is now considered to be
senior synonym
The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently.
* In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linnae ...
of the latter and an early offshoot of the branch that led to more
derived
Derive may refer to:
* Derive (computer algebra system), a commercial system made by Texas Instruments
* ''Dérive'' (magazine), an Austrian science magazine on urbanism
*Dérive, a psychogeographical concept
See also
*
*Derivation (disambiguatio ...
forms. The genera closely related to ''Psittacosaurus'' are all from Asia, with the exception of ''
Aquilops'', from
North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
. The first species was either ''P. lujiatunensis'' or closely related, and it may have given rise to later forms of ''Psittacosaurus''.
''Psittacosaurus'' is one of the most completely known dinosaur genera. Fossils of hundreds of individuals have been collected so far, including many complete skeletons. Most age classes are represented, from
hatchling
In oviparous biology, a hatchling is a newly hatched fish, amphibian, reptile, or bird. A group of mammals called monotremes lay eggs, and their young are hatchlings as well.
Fish
Fish hatchlings generally do not receive parental care, similar to ...
through to adult, which has allowed several detailed studies of ''Psittacosaurus'' growth rates and
reproductive
The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are als ...
biology
Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...
. The abundance of this dinosaur in the
fossil record
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...
has led to the labelling of Lower Cretaceous sediments of
east Asia
East Asia is the eastern region of Asia, which is defined in both geographical and ethno-cultural terms. The modern states of East Asia include China, Japan, Mongolia, North Korea, South Korea, and Taiwan. China, North Korea, South Korea and ...
the ''Psittacosaurus''
biochron A biochron (from the Greek ''bios'', life; and ''khronos'', time) is the length of time represented by a biostratigraphic zone. Biochrons are named after characteristic fossil organisms or taxa
In biology, a taxon (back-formation from ''taxon ...
.
History of discovery
![Psittacosaurus mongoliensis - AMNH - DSC06312](https://upload.wikimedia.org/wikipedia/commons/5/50/Psittacosaurus_mongoliensis_-_AMNH_-_DSC06312.JPG)
''Psittacosaurus'' was first described as a genus in 1923, by
Henry Fairfield Osborn
Henry Fairfield Osborn, Sr. (August 8, 1857 – November 6, 1935) was an American paleontologist, geologist and eugenics advocate. He was the president of the American Museum of Natural History for 25 years and a cofounder of the American Euge ...
. He named the
type species
In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...
''P. mongoliensis'', for the location of its discovery in
Mongolia
Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million, ...
, placing it in the new family Psittacosauridae. Remains of this dinosaur were first discovered the year before, on the third
American Museum of Natural History
The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 inter ...
expedition to the
Gobi Desert
The Gobi Desert (Chinese: 戈壁 (沙漠), Mongolian: Говь (ᠭᠣᠪᠢ)) () is a large desert or brushland region in East Asia, and is the sixth largest desert in the world.
Geography
The Gobi measures from southwest to northeast an ...
of Mongolia, when one of the expedition's drivers, Wong, found the
type specimen
In biology, a type is a particular wiktionary:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to a ...
(AMNH 6254), which preserves a nearly complete skull, as well as a post cranial skeleton lacking sections of the limbs.
This same expedition turned up the remains of many other famous Mongolian dinosaurs, including ''
Protoceratops
''Protoceratops'' (; ) is a genus of small protoceratopsid dinosaurs that lived in Asia during the Late Cretaceous, around 75 to 71 million years ago. The genus ''Protoceratops'' includes two species: ''P. andrewsi'' and the larger ''P. hellenik ...
'', ''
Oviraptor
''Oviraptor'' (; ) is a genus of oviraptorid dinosaur that lived in Asia during the Late Cretaceous period. The first remains were collected from the Djadokhta Formation of Mongolia in 1923 during a paleontological expedition led by Roy Chapma ...
'', and ''
Velociraptor
''Velociraptor'' (; ) is a genus of small dromaeosaurid dinosaur that lived in Asia during the Late Cretaceous epoch, about 75 million to 71 million years ago. Two species are currently recognized, although others have been assigned in the pa ...
''.
Many later expeditions by various combinations of Mongolian, Russian, Chinese, American, Polish, Japanese, and Canadian paleontologists also recovered specimens from throughout Mongolia and northern China. In these areas, ''Psittacosaurus mongoliensis'' fossils are found in most
sedimentary
Sedimentary rocks are types of rock (geology), rock that are formed by the accumulation or deposition of mineral or organic matter, organic particles at Earth#Surface, Earth's surface, followed by cementation (geology), cementation. Sedimentati ...
strata
In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...
dating to the
Aptian
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), a ...
to
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0.9 M ...
stages
Stage or stages may refer to:
Acting
* Stage (theatre), a space for the performance of theatrical productions
* Theatre, a branch of the performing arts, often referred to as "the stage"
* ''The Stage'', a weekly British theatre newspaper
* S ...
of the Early
Cretaceous Period
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of t ...
, or approximately 125 to 100 mya. Fossil remains of over 75 individuals have been recovered, including nearly 20 complete skeletons with skulls.
[ Individuals of all ages are known, from ]hatchling
In oviparous biology, a hatchling is a newly hatched fish, amphibian, reptile, or bird. A group of mammals called monotremes lay eggs, and their young are hatchlings as well.
Fish
Fish hatchlings generally do not receive parental care, similar to ...
s less than long, to very old adults reaching nearly in length.[
]
When describing ''Psittacosaurus mongoliensis'' in 1923, Osborn also gave the name ''Protiguanodon mongoliense'' to another skeleton found nearby, believing it to represent an ancestor of the ornithopod
Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (), that started out as small, bipedal running grazers and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous wo ...
''Iguanodon
''Iguanodon'' ( ; meaning 'iguana-tooth'), named in 1825, is a genus of iguanodontian dinosaur. While many species have been classified in the genus ''Iguanodon'', dating from the late Jurassic Period to the early Cretaceous Period of Asia, Eu ...
'', in the new subfamily Protiguanodontinae. ''Protiguanodon mongoliense'', AMNH 6523, measured long, and was known from much of the skeleton, although at the time of description the neck vertebrae were still covered by matrix
Matrix most commonly refers to:
* ''The Matrix'' (franchise), an American media franchise
** ''The Matrix'', a 1999 science-fiction action film
** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchis ...
. Osborn diagnosed his taxa on the basis of features of the teeth and snout. However, modern taxonomists find these features insignificant, instead placing ''Protiguanodon mongoliense'' within ''Psittacosaurus mongoliensis''.[ When the skeleton was prepared further, it became clear that it was nearly identical to ''Psittacosaurus mongoliensis''.][ In 1958, Chinese paleontologist ]Yang Zhongjian
Yang Zhongjian, also Yang Chung-chien (; 1 June 1897 – 15 January 1979), courtesy name Keqiang (), also known as C.C. (Chung Chien) Young, was a Chinese paleontologist and zoologist. He was one of China's foremost vertebrate paleontologists. H ...
(better known as C. C. Young) renamed the skeleton ''Psittacosaurus protiguanodonensis''. Today the specimen is generally referred to as the species ''Psittacosaurus mongoliensis'' and the names ''Protiguanodon mongoliense'' and ''Psittacosaurus protiguanodonensis'' are considered junior synonym
The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently.
* In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linna ...
s of the name ''Psittacosaurus mongoliensis'', which was coined first.[
In 1931, C. C. Young named a new species of ''Psittacosaurus'' for a partial skull discovered in ]Inner Mongolia
Inner Mongolia, officially the Inner Mongolia Autonomous Region, is an autonomous region of the People's Republic of China. Its border includes most of the length of China's border with the country of Mongolia. Inner Mongolia also accounts for a ...
, China. The skull was named ''P. osborni'' after Henry Fairfield Osborn. The validity of this species is now considered equivocal. Sereno (1990) considered it a synonym of ''P. mongoliensis'', which is found in nearby strata of the same age. You and Dodson (2004) listed it as valid in a table, but not in their text.[ In a 2010 review, Sereno again regarded ''P. osborni'' as a synonym of ''P. mongoliensis'', but noted it was tentative because of the presence of multiple valid psittacosaur species in Inner Mongolia.][ Young also described the species ''P. tingi'' in the same 1931 report which contained ''P. osborni''. It is based on several skull fragments.][ He later synonymised the two species under the name ''P. osborni''.][ You and Dodson (2004) followed this in a table,][ but Sereno regarded both species as synonyms of ''P. mongoliensis'';][ a table in the latter reported ''P. tingi'' as a '']nomen dubium
In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application.
Zoology
In case of a ''nomen dubium'' it may be impossible to determine whether a s ...
'', however.[ The front half of a skull from ]Guyang County
Guyang County (Mongolian language, Mongolian: ''Güyaŋ siyan''; ) is a county in western Inner Mongolia, People's Republic of China. It is under the administration of Baotou City, the downtown of which is to the south-southwest.
Climate
Re ...
in Inner Mongolia was described as ''Psittacosaurus guyangensis'' in 1983. Disarticulated postcranial remains representing multiple individuals were found at the same locality and were assigned to the species. While it differs from the type specimen of ''P. mongoliensis'', it falls within the range of individual variation seen in other specimens of that species and is no longer recognised as a valid species.[ You and Dodson (2004) included ''P. guyangensis'' in a table of valid taxa, but did not include it as such in their text.][
]
Assigned species
Seventeen species have been referred to the genus ''Psittacosaurus'', although only nine to eleven are considered valid today. This is the highest number of valid species currently assigned to any single non-avian dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
. In contrast, most other dinosaur genera are monospecific
In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...
, containing only a single known species. The difference is most likely due to artifacts of the fossilisation process. While ''Psittacosaurus'' is known from hundreds of fossil specimens, most other dinosaur species are known from far fewer, and many are represented by only a single specimen. With a very high sample size, the diversity of ''Psittacosaurus'' can be analysed more completely than that of most dinosaur genera, resulting in the recognition of more species. Most extant
Extant is the opposite of the word extinct. It may refer to:
* Extant hereditary titles
* Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English
* Extant taxon, a taxon which is not extinct, ...
animal genera are represented by multiple species, suggesting that this may have been the case for extinct dinosaur genera as well, although most of these species may not have been preserved. In addition, most dinosaurs are known solely from bone
A bone is a Stiffness, rigid Organ (biology), organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red blood cell, red and white blood cells, store minerals, provid ...
s and can only be evaluated from a morphological standpoint, whereas extant species often have very similar skeletal morphology but differ in other ways which would not normally be preserved in the fossil record, such as behaviour, or colouration. Therefore, actual species diversity may be much higher than currently recognised in this and other dinosaur genera. As some species are known only from skull material, species of ''Psittacosaurus'' are primarily distinguished by features of the skull and teeth. Several species can be recognised by features of the pelvis
The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton).
The ...
as well.[
;''P. sinensis''
In the 1950s, a new Chinese species of ''Psittacosaurus'' was found in the Aptian-Albian Qingshan Formation of ]Shandong Province
Shandong ( , ; ; alternately romanized as Shantung) is a coastal province of the People's Republic of China and is part of the East China region.
Shandong has played a major role in Chinese history since the beginning of Chinese civilizatio ...
, southeast of Beijing
}
Beijing ( ; ; ), alternatively romanized as Peking ( ), is the capital of the People's Republic of China. It is the center of power and development of the country. Beijing is the world's most populous national capital city, with over 21 ...
. C. C. Young called it ''P. sinensis'' to differentiate it from ''P. mongoliensis'', which had originally been found in Mongolia.[ Fossils of more than twenty individuals have since been recovered, including several complete skulls and skeletons, making this the most well-known species after ''P. mongoliensis''.][ Chinese paleontologist ]Zhao Xijin
Zhao Xijin (赵喜进; born c. 1935 died July 21, 2012) was a Chinese paleontologist notable for having named numerous dinosaurs. He was a professor at Beijing's Institute of Vertebrate Paleontology and Paleoanthropology.
Biography
Zhao Xijin was ...
named a new species after his mentor, C. C. Young, in 1962. However, the type specimen of ''P. youngi'' (a partial skeleton and skull) was discovered in the same rocks as ''P. sinensis'' and appears to be very similar, so ''P. youngi'' is generally considered a junior synonym of that better-known species.[ As with ''P. guyangensis'' and ''P. osborni'', You and Dodson (2004) listed it as valid in a table, but not in their text.][
;''P. xinjiangensis''
In 1988, Zhao and American paleontologist ]Paul Sereno
Paul Callistus Sereno (born October 11, 1957) is a professor of paleontology at the University of Chicago and a National Geographic "explorer-in-residence" who has discovered several new dinosaur species on several continents, including at sites ...
described ''P. xinjiangensis'', named after the Xinjiang Autonomous Region
Xinjiang, SASM/GNC: ''Xinjang''; zh, c=, p=Xīnjiāng; formerly romanized as Sinkiang (, ), officially the Xinjiang Uygur Autonomous Region (XUAR), is an autonomous region of the People's Republic of China (PRC), located in the northwest ...
in which it was discovered. Several individuals of different ages were discovered in the early 1970s by Chinese paleontologists and described by Sereno and Zhao, although the holotype and most complete skeleton belonged to a juvenile. An adult skeleton was later discovered at a different locality in Xinjiang.[ These specimens come from the upper part of the ]Tugulu Group
The Tugulu Group () is a geological Group in Xinjiang, China whose strata date back to the Early Cretaceous
The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name), is the ...
, which is regarded as Aptian-Albian in age.[
;''P. meileyingensis''
]
A second species described in 1988 by Sereno and Zhao, along with two Chinese colleagues, was ''P. meileyingensis'' from the Jiufotang Formation
The Jiufotang Formation ( Chinese: 九佛堂组, pinyin: ''jiǔfótáng zǔ'') is an Early Cretaceous geological formation in Chaoyang, Liaoning which has yielded fossils of feathered dinosaurs, primitive birds, pterosaurs, and other organisms (see ...
, near the town of Meileyingzi, Liaoning Province
Liaoning () is a coastal provinces of China, province in Northeast China that is the smallest, southernmost, and most populous province in the region. With its capital at Shenyang, it is located on the northern shore of the Yellow Sea, and i ...
, northeastern China. This species is known from four fossil skulls, one associated with some skeletal material, found in 1973 by Chinese scientists.[ The age of the Jiufotang in Liaoning is unknown, but in the neighbouring province of Inner Mongolia, it has been dated to about 110 Ma, in the Albian stage of the Early Cretaceous.]
;''P. sattayaraki''
French paleontologist Eric Buffetaut
The given name Eric, Erich, Erikk, Erik, Erick, or Eirik is derived from the Old Norse name ''Eiríkr'' (or ''Eríkr'' in Old East Norse due to monophthongization).
The first element, ''ei-'' may be derived from the older Proto-Norse ''* ain ...
and a Thai colleague, Varavudh Suteethorn
Varavudh Suteethorn, or Warawut Suteethorn ( Thai:วราวุธ สุธีธร; born 10 October 1948) is a Thai geologist and palaeontologist. He is the current director of the Palaeontological Research and Education Centre, Mahasarakham ...
, described a partial upper and lower jaw from the Aptian-Albian Khok Kruat Formation of Thailand
Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is bo ...
in 1992, giving it the name ''P. sattayaraki''. In 2000, Sereno questioned the validity of this species, citing its eroded and fragmentary nature, and noted an absence of features characteristic of the genus ''Psittacosaurus''.[ However, in 2002 the original authors published new images of the fossil which seem to show teeth in the lower jaw that exhibit the bulbous vertical ridge characteristic of psittacosaurs.] Other authors have also defended its validity,[ while some continue to regard it as dubious.][ Sereno (2010) proposed that the best assignment for the type material may be Ceratopsia '']incertae sedis
' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...
''.[
;''P. neimongoliensis'' and ''P. ordosensis''?
Two new species of ''Psittacosaurus'' were described by Canadian ]Dale Russell
Dale Alan Russell (27 December 1937 – 21 December 2019)
was an American-Canadian geologist and palaeontologist. Throughout his career Russell worked as the Curator of Fossil Vertebrates at the Canadian Museum of Nature, Research Professor a ...
and Zhao in 1996. The first was named ''P. neimongoliensis'', after the Mandarin Chinese
Mandarin (; ) is a group of Chinese (Sinitic) dialects that are natively spoken across most of northern and southwestern China. The group includes the Beijing dialect, the basis of the phonology of Standard Chinese, the official language of ...
name for Inner Mongolia. It is based on a nearly complete fossil skeleton, including most of the skull, found in the Early Cretaceous Ejinhoro Formation
The Ejinhoro Formation () is a geological Formation (geology), formation in Inner Mongolia, north People's Republic of China, China, whose strata date back to the Early Cretaceous period (Aptian/Albian age.Sereno, P.C. (2010). "Taxonomy, cranial mo ...
with seven other individuals.[ Russell and Zhao also named ''P. ordosensis'' in 1996, after the ]Ordos Ordos may refer to:
Inner Mongolia
* Ordos City, Inner Mongolia, China
**Ordos Ejin Horo Airport
* Ordos Loop of the Yellow River, a region of China
**Ordos Plateau or "the Ordos", land enclosed by Ordos Loop
*Ordos Desert, in Inner Mongolia
*Ordos ...
prefecture of the Inner Mongolia Autonomous Region. The type specimen is a nearly complete skeleton, including part of the skull. However, only the skull, lower jaw, and foot have been described. Three other specimens were referred to this species but remain undescribed. Like ''P. neimongoliensis'', this species was discovered in the Eijnhoro Formation.[ Sereno (2010) found the species as described to be indistinguishable from ''P. sinensis'', another small species, but suggested that additional study of ''P. ordosensis'' might reveal diagnostic features. He provisionally designated ''P. ordosensis'' a ''nomen dubium''.][
;''P. mazongshanensis''?
Xu Xing, another Chinese paleontologist, named a new species of ''Psittacosaurus'' in 1997, based on a complete skull with associated ]vertebra
The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
e and a forelimb. This material was recovered in Gansu Province
Gansu (, ; alternately romanized as Kansu) is a province in Northwest China. Its capital and largest city is Lanzhou, in the southeast part of the province.
The seventh-largest administrative district by area at , Gansu lies between the Tibeta ...
, near the border with Inner Mongolia. This species is named ''P. mazongshanensis'' after the nearby mountain called Mazongshan (Horse Mane Mountain) and has been described in a preliminary manner. Unfortunately, the skull was damaged while in the care of the Chinese Institute of Vertebrate Paleontology and Paleoanthropology The Institute of Vertebrate Paleontology and Paleoanthropology (IVPP; ) of China is a research institution and collections repository for fossils, including many dinosaur and pterosaur specimens (many from the Yixian Formation). As its name suggest ...
(IVPP), and several fragments have been lost, including all of the teeth.[ The remains were found in the Lower Xinminbao Formation, which have not been precisely dated, although there is some evidence that they were deposited in the late ]Barremian
The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma (million years ago) and 121.4 ± 1.0 Ma). It is a subdivision of the Early Cretaceous Epoch (or Lower Cretaceous Series). It is preceded ...
through Aptian stages. Sereno suggested in 2000 that ''P. mazongshanensis'' was a ''nomen dubium'', with no unique features that separate it from any other species of ''Psittacosaurus''.[ However, more recent authors have noted that it can be distinguished by its proportionally long snout compared to other species of ''Psittacosaurus'', as well as a prominent bony protuberance, pointing outwards and downwards, on the maxilla of the upper jaw.][ The maxillary protuberance is also now missing.][ Other features originally used to distinguish the species have been recognised as the results of the deformation of the skull after fossilisation.][ Sereno (2010) remained unconvinced of its validity.][
;''P. sibiricus''
Beginning in the 1950s, Russian paleontologists began excavating ''Psittacosaurus'' remains at a locality near the village of Shestakovo in the ]oblast
An oblast (; ; Cyrillic (in most languages, including Russian and Ukrainian): , Bulgarian: ) is a type of administrative division of Belarus, Bulgaria, Kazakhstan, Kyrgyzstan, Russia, and Ukraine, as well as the Soviet Union and the Kingdom of ...
of Kemerovo
Kemerovo ( rus, Ке́мерово, p=ˈkʲemʲɪrəvə) is an industrial city and the administrative center of Kemerovo Oblast, Russia, located at the confluence of the Iskitimka and Tom Rivers, in the major coal mining region of the Kuznetsk Ba ...
in Siberia
Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part of ...
. Two other nearby localities were explored in the 1990s, one of which produced several complete skeletons. This species was named ''P. sibiricus'' in 2000 in a scientific paper written by five Russian paleontologists, but credit for the name is officially given to two of those authors, Alexei Voronkevich and Alexander Averianov. The remains were not completely described until 2006. Two nearly complete, articulated skeletons and a variety of disarticulated material from other individuals of all ages are known from the Ilek Formation
The Ilek Formation is a Lower Cretaceous geologic formation in Western Siberia. Many different fossils have been recovered from the formation. It overlies the Late Jurassic Tyazhin Formation and underlies the Albian Kiya Formation.
The formation ...
of Siberia, which ranges from the Aptian to Albian stages of the Early Cretaceous.[ The Species can grow up to 2.5 meters in length
;''P. lujiatunensis''
''P. lujiatunensis'', named in 2006 by Chinese paleontologist Zhou Chang-Fu and three Chinese and Canadian colleagues, is one of the oldest-known species, based on four skulls from the lower beds of the ]Yixian Formation
The Yixian Formation (; formerly transcribed as Yihsien Formation) is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the late Barremian and early Aptian stages of the Early Cretaceous. It is known for its ex ...
, near the village of Lujiatun.[ While this bed has been dated differently by different authors, from 128 Ma in the Barremian stage,] to 125 Ma in the earliest Aptian,[ revised dating methods have shown them to be about 123 million years old.] ''P. lujiatunensis'' was contemporaneous with another psittacosaurid species, ''Hongshanosaurus houi'', which was found in the same beds. It is potentially synonymous with ''H. houi''; Sereno (2010), who proposed that ''Hongshanosaurus'' is a synonym of ''Psittacosaurus'', opted to leave ''P. lujiatunensis'' and ''H. houi'' separate species due to the inadequacies of the latter's type specimen.[
;''P. major''
One nearly complete skeleton of ''P. lujiatunensis'' from the same lower beds of the Yixian Formation had previously been classified in its own species, ''Psittacosaurus major'', named for the large size of its skull by Sereno, Zhao and two colleagues in 2007.][ You and colleagues described an additional specimen and concurred that it was distinct from ''P. lujiatunensis''.][ ''P. major'' was originally characterised by a proportionately large skull, which was 39% of the length of its torso, compared to 30% in ''P. mongoliensis'', and other features. However, a 2013 study utilising morphometric analysis showed that the supposed differences between ''P. lujiatunensis'' and ''P. major'' were due to differences in preservation and crushing. The study concluded that both represented a single species.][
;''P. houi''?
]
A third species of Lujiatun psittacosaur, the first to be named, was described as ''Hongshanosaurus houi'' in 2003. The generic name ''Hongshanosaurus'' was derived from the Mandarin Chinese
Mandarin (; ) is a group of Chinese (Sinitic) dialects that are natively spoken across most of northern and southwestern China. The group includes the Beijing dialect, the basis of the phonology of Standard Chinese, the official language of ...
words 紅 (''hóng'': "red") and 山 (''shān'': "hill"), as well as the Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
word ''sauros'' ("lizard"). This name refers to the ancient Hongshan culture
The Hongshan culture () was a Neolithic culture in the West Liao river basin in northeast China. Hongshan sites have been found in an area stretching from Inner Mongolia to Liaoning, and dated from about 4700 to 2900 BC.
The culture is named aft ...
of northeastern China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
, who lived in the same general area in which the fossil skull of ''Hongshanosaurus'' was found. The type and only named species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
, ''H. houi'', honours Hou Lianhai, a professor at the IVPP in Beijing, who curated the specimen. Genus and species were both named by Chinese paleontologist
Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
s You Hailu
In Modern English, ''you'' is the second-person pronoun. It is grammatically plural, and was historically used only for the dative case, but in most modern dialects is used for all cases and numbers.
History
''You'' comes from the Proto- ...
, Xu Xing, and Wang Xiaolin
Wang may refer to:
Names
* Wang (surname) (王), a common Chinese surname
* Wāng (汪), a less common Chinese surname
* Titles in Chinese nobility
* A title in Korean nobility
* A title in Mongolian nobility
Places
* Wang River in Thailand ...
in 2003. Sereno (2010) regarded its distinct proportions as due to crushing and compression of the ''Hongshanosaurus'' skulls.[ He regarded ''Hongshanosaurus'' as a ]junior synonym
The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently.
* In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linna ...
of ''Psittacosaurus'', and potentially the same as ''P. lujiatunensis''. He did not synonymise the two species because of difficulties with the holotype skull of ''H. houi'', instead considering new combination ''P. houi'' a ''nomen dubium
In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application.
Zoology
In case of a ''nomen dubium'' it may be impossible to determine whether a s ...
'' within ''Psittacosaurus''.[ Sereno's hypothesis was supported by a morphometric study in 2013, which found ''P. houi'' and ''P. lujiatunensis'' to be synonymous. While ''P. houi'' is the oldest available name, the researchers argued that because the type specimen of ''P. lujiatunensis'' was better preserved, the correct name for this species should be ''P. lujiatunensis'' rather than ''P. houi'', which would normally have priority.]
;''P. gobiensis''
''P. gobiensis'' is named for the region it was found in 2001, and first described by Sereno, Zhao and Lin in 2010. It is known from a skull and partial articulated skeleton with gastroliths.[ Many other specimens either cannot be determined to belong to any particular species, or have not yet been assigned to one. These specimens are generally all referred to as ''Psittacosaurus'' sp., although it is not assumed that they belong to the same species.][ More than 200 specimens of ''Psittacosaurus'' have been found in the Yixian Formation, which is famous for its fossils of ]feathered dinosaur
A feathered dinosaur is any species of dinosaur possessing feathers. While this includes all species of birds, there is a hypothesis that many, if not all non-avian dinosaur species also possessed feathers in some shape or form.
It has been su ...
s. The vast majority of these have not been assigned to any published species, although many are very well preserved and some have already been partially described. Nearly 100 ''Psittacosaurus'' skeletons were excavated in Mongolia during the summers of 2005 and 2006 by a team led by Mongolian paleontologist Bolortsetseg Minjin
Bolortsetseg Minjin is a Mongolian paleontologist known for her work in fossil repatriation and dinosaur-themed science outreach. She is a recipient of the WINGS WorldQuest Women of Discovery Award for Earth, National Geographic Explorer, and ...
and American Jack Horner from the Museum of the Rockies in Montana
Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columbi ...
. Although only ''P. mongoliensis'' has been described from Mongolia so far, these specimens are still in preparation and have not yet been assigned to a species.[
;''P. amitabha''
''P. amitabha'' was named by Napoli ''et al.'' in 2019 from a complete skull and partial skeleton. recovered in the Barremian Andakhuduk Formation of Mongolia. It is named after Amitabha.
]
Description
The species of ''Psittacosaurus'' vary in size and specific features of the skull
The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...
and skeleton, but share the same overall body shape. The best-known—''P. mongoliensis''—can reach 2 metres (6.5 ft) in length. The maximum adult body weight was most likely over 20 kilogramme
The kilogram (also kilogramme) is the unit of mass in the International System of Units (SI), having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo colloquially. ...
s (44 lb) in ''P. mongoliensis''. Several species approach ''P. mongoliensis'' in size (''P. lujiatunensis'', ''P. neimongoliensis'', ''P. xinjiangensis''), while others are somewhat smaller (''P. sinensis'', ''P. meileyingensis''). The smallest known species, ''P. ordosensis'', is 30% smaller than ''P. mongoliensis''.[ The largest are ''P. lujiatunensis'' and ''P. sibiricus'', although neither is significantly larger than ''P. mongoliensis''.] ''Psittacosaurus'' postcranial skeletons are more typical of a 'generic' bipedal ornithischian.[ There are only four digits on the manus ('hand'), as opposed to the five found in most other ornithischians (including all other ceratopsians), while the four-toed hindfoot is very similar to many other small ornithischians.]
The skull of ''Psittacosaurus'' is highly modified compared to other ornithischia
Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek s ...
n dinosaurs of its time. Extremely tall in height and short in length, the skull has an almost round profile
Profile or profiles may refer to:
Art, entertainment and media Music
* ''Profile'' (Jan Akkerman album), 1973
* ''Profile'' (Githead album), 2005
* ''Profile'' (Pat Donohue album), 2005
* ''Profile'' (Duke Pearson album), 1959
* '' ''Profi ...
in some species. The portion in front of the orbit
In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...
(eye socket) is only 40% of total skull length, shorter than any other known ornithischian. The lower jaws of psittacosaurs are characterised by a bulbous vertical ridge down the centre of each tooth. Both upper and lower jaws sport a pronounced beak, formed from the ''rostral'' and ''predentary'' bones, respectively. The bony core of the beak may have been sheathed in keratin
Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ho ...
to provide a sharp cutting surface for cropping plant
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...
material. As the generic name suggests, the short skull and beak superficially resemble those of modern parrots. ''Psittacosaurus'' skulls share several adaptations with more derived
Derive may refer to:
* Derive (computer algebra system), a commercial system made by Texas Instruments
* ''Dérive'' (magazine), an Austrian science magazine on urbanism
*Dérive, a psychogeographical concept
See also
*
*Derivation (disambiguatio ...
ceratopsians, such as the unique rostral bone at the tip of the upper jaw, and the flared jugal
The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species.
Anatomy ...
(cheek) bones. There is still no sign of the bony neck frill or prominent facial horns which would develop in later ceratopsians.[ Bony horns protrude from the skull of ''P. sibiricus'', but these are thought to be an example of ]convergent evolution
Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
.[
]
Soft tissue and coloration
The integument
In biology, an integument is the tissue surrounding an organism's body or an organ within, such as skin, a husk, shell, germ or rind.
Etymology
The term is derived from ''integumentum'', which is Latin for "a covering". In a transferred, or ...
, or body covering, of ''Psittacosaurus'' is known from a Chinese specimen, which most likely comes from the Yixian Formation
The Yixian Formation (; formerly transcribed as Yihsien Formation) is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the late Barremian and early Aptian stages of the Early Cretaceous. It is known for its ex ...
of Liaoning Province
Liaoning () is a coastal provinces of China, province in Northeast China that is the smallest, southernmost, and most populous province in the region. With its capital at Shenyang, it is located on the northern shore of the Yellow Sea, and i ...
, China. The specimen, which is not yet assigned to any particular species, was likely illegally exported from China and was donated to the Senckenberg Museum
The Naturmuseum Senckenberg is a museum of natural history, located in Frankfurt am Main. It is the second-largest of its type in Germany. The museum contains a large and diverse collection of birds with 90,000 bird skins, 5,050 egg sets, 17,0 ...
in Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
. It was described while awaiting repatriation; previous repatriation attempts were unsuccessful.[
Most of the body was covered in ]scales
Scale or scales may refer to:
Mathematics
* Scale (descriptive set theory), an object defined on a set of points
* Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original
* Scale factor, a number w ...
. Larger scales were arranged in irregular patterns, with numerous smaller scales occupying the spaces between them, similarly to skin impressions known from other ceratopsians, such as ''Chasmosaurus
''Chasmosaurus'' ( ) is a genus of ceratopsid dinosaur from the Upper Cretaceous Period of North America. Its name means 'opening lizard', referring to the large openings ( fenestrae) in its frill (Greek ''chasma'' meaning 'opening' or 'hollow' ...
''. A series of what appear to be hollow, tubular bristle-like structures, approximately long, were also preserved, arranged in a row down the dorsal
Dorsal (from Latin ''dorsum'' ‘back’) may refer to:
* Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism
* Dorsal, positioned on top of an aircraft's fuselage
* Dorsal c ...
(upper) surface of the tail. These were confirmed by the authors, as well as an independent scientist, to not represent plant material.[ The bristle-like integumentary structures extend into the skin nearly to the vertebrae, and were likely circular or tubular before being preserved. Under ]ultraviolet light
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
, they gave off the same fluorescence as scales, providing the possibility they were keratin
Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ho ...
ized. The study stated that, "at present, there is no convincing evidence which shows these structures to be homologous to the structurally different integumentary filaments of theropod
Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...
dinosaurs". However, they found that all other feather-like integument from the Yixian Formation could be identified as feathers.[
In 2008, another study was published describing the integument and ]dermis
The dermis or corium is a layer of skin between the epidermis (with which it makes up the cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from stress and strain. It is divided i ...
of ''Psittacosaurus'' sp., from a different specimen. The skin remains could be observed by a natural cross-section to compare them to modern animals, showing that dinosaurian dermal layers evolved in parallel to those in many other large vertebrates. The collagen
Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole ...
tissue fibres in ''Psittacosaurus'' are complex, virtually identical to all other vertebrates in structure but having an exceptional thickness of about forty layers. As the sections of dermis were collected from the abdomen, where the scales were eroded, the tissue may have assisted with the musculature of the stomach and intestines and offered protection against predators.
As described in a 2016 study, examination of melanosomes preserved in the specimen of ''Psittacosaurus'' preserved with integument indicated that the animal was countershaded
Countershading, or Thayer's law, is a method of camouflage in which an animal's coloration is darker on the top or upper side and lighter on the underside of the body. This pattern is found in many species of mammals, reptiles, birds, fish, a ...
, likely related to living in a dense forest habitat with little light, much like many modern species of forest-dwelling deer and antelope; stripes and spots on the limbs may represent disruptive coloration
Disruptive coloration (also known as disruptive camouflage or disruptive patterning) is a form of camouflage that works by breaking up the outlines of an animal, soldier or military vehicle with a strongly contrasting pattern. It is often comb ...
. The specimen also had dense clusters of pigment on its shoulders, face (possibly for display), and cloaca
In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, a ...
(which may have had an antimicrobial function), as well as large patagia
The patagium (plural: patagia) is a membranous body part that assists an animal in obtaining lift when gliding or flight. The structure is found in extant and extinct groups of flying and gliding animals including bats, birds, some dromaeosau ...
on its hind legs that connected to the base of the tail. Its large eyes indicate that it also likely had good vision, which would have been useful in finding food or avoiding predators. The authors pointed out that there might have been variation in coloration across the range of the animal, depending on differences in the light environment. The authors were unable to determine which species of Jehol Formation ''Psittacosaurus'' the specimen belonged to due to the way the skull is preserved, but ruled out ''P. mongoliensis'', based on hip features.
Another 2016 study used laser-stimulated fluorescence imaging to analyze the internal structure of the bristles. The highly cornified bristles were arranged in tight clusters of three to six individual bristles, with each bristle being filled with pulp. The authors considered the bristles as being most similar to the quills of ''Tianyulong
''Tianyulong'' (Chinese: 天宇龍; Pinyin: ''tiānyǔlóng''; named for the Shandong Tianyu Museum of Nature where the holotype fossil is housed) is an extinct genus of heterodontosaurid ornithischian dinosaur. The only species is ''T. confuc ...
'', and the sparsely distributed elongated broad filamentous feathers (EBFFs) of '' Beipiaosaurus''. Similar, non-feather-derived bristles are found in a few extant birds such as the "horn" on the horned screamer
The horned screamer (''Anhima cornuta'') is a member of a small family of birds, the Anhimidae, which occurs in wetlands of tropical South America. There are three screamer species, the other two being the southern screamer and the northern scr ...
and the "beards" of turkeys
The turkey is a large bird in the genus ''Meleagris'', native to North America. There are two extant turkey species: the wild turkey (''Meleagris gallopavo'') of eastern and central North America and the ocellated turkey (''Meleagris ocellat ...
; these structures differ from feathers in that they are unbranched, heavily cornified and do not develop from a follicle, but instead arise from discrete cell populations that exhibit continuous growth. A 2016 study by Ji Qiang and colleagues was published in the Journal of Geology. Their conclusion was that these were actually highly modified scales because the morphology and anatomy did not resemble feathers. A darkened soft-tissue structure was also found near the jugal horn; this may represent a keratinous sheath or a skin flap.
A 2020 study of SMF R 4970 identified it as an approximately 6–7 year old subadult, and found it preserves the first cloaca
In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, a ...
known from a non-avalian dinosaur. The positioning of the individual when it died means that both sides of the structure can be seen, although the right side is better preserved. ''Psittacosaurus cloaca is comparable to those of crocodilians', with a "longitudionally opening vent" and a "rosette pattern of cloacal scales and 129 transverse rows of quadrangular ventral scale", as opposed to the naked area around the cloaca of birds. Like modern crocodilians and birds, dinosaur genitalia
A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, a ...
were positioned internally. Since SMF R 4970 was not fully sexually mature when it died, unfortunately the fully matured structure, as well as the sex of the individual and any coacal phallus
A phallus is a penis (especially when erect), an object that resembles a penis, or a mimetic image of an erect penis. In art history a figure with an erect penis is described as ithyphallic.
Any object that symbolically—or, more precisel ...
that may have been present in life, are undetermined.
Species characteristics
Skulls of ''P. mongoliensis'' are flat on top, especially over the back of the skull, with a triangular depression, the antorbital fossa
An antorbital fenestra (plural: fenestrae) is an opening in the skull that is in front of the eye sockets. This skull character is largely associated with archosauriforms, first appearing during the Triassic Period. Among extant archosaurs, birds ...
, on the outside surface of the maxilla
The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...
(an upper jaw bone). A flange is present on the lower edge of the dentary
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...
(the tooth-bearing bone of the lower jaw), although it is not as prominent as in ''P. meileyingensis'' or ''P. major'' (=''P. lujiatunensis''). ''P. mongoliensis'' is among the largest known species. The skull of the type specimen, which is probably a juvenile,[ is 15.2 centimetres (6 in) long, and the associated ]femur
The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...
is 16.2 centimetres (6.4 in) in length. Other specimens are larger, with the largest documented femur measuring about 21 centimetres (8.25 in) long.
''P. sinensis'' is readily distinguished from all other species by numerous features of the skull. Adult skulls are smaller than those of ''P. mongoliensis'' and have less teeth. Uniquely, the premaxilla
The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...
ry bone contacts the jugal
The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species.
Anatomy ...
(cheek) bone on the outside of the skull. The jugals flare out sideways, forming 'horns Horns or The Horns may refer to:
* Plural of Horn (instrument), a group of musical instruments all with a horn-shaped bells
* The Horns (Colorado), a summit on Cheyenne Mountain
* ''Horns'' (novel), a dark fantasy novel written in 2010 by Joe Hill ...
' proportionally wider than in any other known ''Psittacosaurus'' species except ''P. sibiricus'' and ''P. lujiatunensis''. Because of the flared cheeks, the skull is actually wider than it is long. A smaller 'horn' is present behind the eye, at the contact of the jugal and postorbital
The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some ve ...
bones, a feature also seen in ''P. sibiricus''. The mandible
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...
(lower jaw) lacks the hollow opening, or ''fenestra
A fenestra (fenestration; plural fenestrae or fenestrations) is any small opening or pore, commonly used as a term in the biological sciences. It is the Latin word for "window", and is used in various fields to describe a pore in an anatomical st ...
'', seen in other species, and the entire lower jaw is bowed outwards, giving the animal the appearance of an underbite
In orthodontics, a malocclusion is a misalignment or incorrect relation between the teeth of the upper and lower dental arches when they approach each other as the jaws close. The English-language term dates from 1864; Edward Angle (1855-1930), ...
.[ The skull of an adult ''P. sinensis'' can reach 11.5 centimeters (4.5 in) in length.][
''P. sibiricus'' is the largest-known species of ''Psittacosaurus''. The skull of the type specimen is 20.7 centimetres long (8.25 in), and the femur is 22.3 cm (8.75 in) in length. It is also distinguished by its ]neck frill
A neck frill is the relatively extensive margin seen on the back of the heads of reptiles with either a bony support such as those present on the skulls of dinosaurs of the suborder Marginocephalia or a cartilaginous one as in the frill-necked ...
, which is longer than any other species, at 15 to 18% of skull length. A very striking feature of ''P. sibiricus'' is the number of 'horns' around the eyes, with three prominences on each postorbital, and one in front of each eye, on the palpebral
An eyelid is a thin fold of skin that covers and protects an eye. The levator palpebrae superioris muscle retracts the eyelid, exposing the cornea to the outside, giving vision. This can be either voluntarily or involuntarily. The human eye ...
bones. Similar horns found on the postorbital of ''P. sinensis'' are not as pronounced but may be homologous. The jugal has extremely prominent 'horns' and may contact the premaxilla, both features also seen in the possibly related ''P. sinensis''. There is a flange on the dentary of the lower jaw, similar to ''P. mongoliensis'', ''P. meileyingensis'', and ''P. sattayaraki''. It can be told apart from the other species of ''Psittacosaurus'' by a combination of 32 anatomical features, including six that are unique to the species. Most of these are skull details, but one unusual feature is the presence of 23 vertebrae between the skull and pelvis, unlike the 21 or 22 in the other species where the vertebrae are known.[
''P. xinjiangensis'' is distinguished by a prominent jugal 'horn' that is flattened on the front end, as well as some features of the teeth. The ilium, one of the three bones of the pelvis, also bears a characteristically long bony process behind the ]acetabulum
The acetabulum (), also called the cotyloid cavity, is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint.
Structure
There are three bones of the ''os coxae'' (hip bone) that c ...
(hip socket).[ An adult femur has a published length of about 16 centimetres (6.3 in).][ ''P. meileyingensis'' has the shortest snout and ]neck frill
A neck frill is the relatively extensive margin seen on the back of the heads of reptiles with either a bony support such as those present on the skulls of dinosaurs of the suborder Marginocephalia or a cartilaginous one as in the frill-necked ...
of any species, making the skull nearly circular in profile. The orbit
In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...
(eye socket) is roughly triangular, and there is a prominent flange on the lower edge of the dentary, a feature also seen in specimens of ''P. lujiatunensis'', and to a lesser degree in ''P. mongoliensis'', ''P. sattayaraki'', and ''P. sibiricus''.[ The complete type skull, probably adult, is 13.7 centimetres (5.5 in) long.][ The dentary of ''P. sattayaraki'' has a flange similar to that found in ''P. mongoliensis'', ''P. sibiricus'', ''P. lujiatunensis'' and ''P. meileyingensis'', although it is less pronounced than in those species. The material appears to be roughly the same size as ''P. sinensis''.][ The ]frontal bone
The frontal bone is a bone in the human skull. The bone consists of two portions.''Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, par ...
of ''P. neimongoliensis'' is distinctly narrow compared to that of other species, resulting in a narrower skull overall. The bone of the pelvis is also longer than the femur
The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...
, which differs from other species in which these bones are known.[ The type specimen has a skull length of 13.2 centimetres (5.2 in) and a femoral length of 13 centimetres (5.1 in), but is not fully grown. An adult ''P. neimongoliensis'' was probably smaller than ''P. mongoliensis'', with a proportionately longer skull and tail.][ ''P. ordosensis'' can be distinguished by numerous features of the jugals, which have very prominent 'horns'.][ It is also the smallest known species. One adult skull measures only 9.5 centimeters (3.75 in) in length.][
The type skull of ''P. lujiatunensis'' measures 19 cm (7.5 in) in length, while the largest-known skull is 20.5 centimetres (8 in) long, so this species was similar in size to ''P. mongoliensis'' and ''P. sibiricus''. There is a fossa in front of the eye, as in ''P. mongoliensis''. The jugal bones flare outwards widely, making the skull wider than it is long, as seen in ''P. sinensis''. Widely flared jugals are also found in ''P. sibiricus''. Overall, this species is thought to exhibit several primitive characteristics compared to other species of ''Psittacosaurus'', which is consistent with its greater geological age.][ ''P. gobiensis'' was small-bodied ( long) and differs from other species of ''Psittacosaurus'' by "significant, but structurally minor, details." These include the presence of a pyramidal horn on the ]postorbital
The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some ve ...
, a depression on the postorbital-jugal contact, and enamel thickness. ''P. mongoliensis'' was a contemporary.
Classification
''Psittacosaurus'' is the type genus
In biological taxonomy, the type genus is the genus which defines a biological family and the root of the family name.
Zoological nomenclature
According to the International Code of Zoological Nomenclature, "The name-bearing type of a nominal f ...
of the family Psittacosauridae, which was also named by Osborn in 1923. Psittacosaurids were basal to almost all known ceratopsians except ''Yinlong
''Yinlong'' (, meaning "hidden dragon") is a genus of basal ceratopsian dinosaur from the Late Jurassic Period of central Asia. It was a small, primarily bipedal herbivore.
Discovery and species
A coalition of American and Chinese paleontologis ...
'' and perhaps the Chaoyangsauridae
Chaoyangsauridae is a family (biology), family of ceratopsian dinosaurs. They are among the earliest known marginocephalian dinosaurs, with remains dating to about 160 million years ago, during the Late Jurassic period. Members of this group had ...
. While Psittacosauridae was an early branch of the ceratopsian family tree, ''Psittacosaurus'' itself was probably not directly ancestral to any other groups of ceratopsians. All other ceratopsians retained the fifth digit of the hand, a plesiomorphy
In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades.
Plesiomorphy, symplesiomorphy, apomorphy, and ...
or primitive trait, whereas all species of ''Psittacosaurus'' had only four digits on the hand. In addition, the ''antorbital fenestra
An antorbital fenestra (plural: fenestrae) is an opening in the skull that is in front of the eye sockets. This skull character is largely associated with archosauriforms, first appearing during the Triassic Period. Among extant archosaurs, bird ...
'', an opening in the skull between the eye socket and nostril
A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbi ...
, was lost during the evolution
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
of Psittacosauridae, but is still found in most other ceratopsians and in fact most other archosaur
Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian d ...
s. It is considered highly unlikely that the fifth digit or antorbital fenestra would evolve a second time.[
In 2014, the describers of a new taxon of basal ceratopsian published a phylogenetic analysis encompassing ''Psittacosaurus''. The below cladogram is from their analysis, placing the genus as one of the most primitive ceratopsians. The authors (Farke ''et al.'') noted that all taxa outside of ]Leptoceratopsidae
Leptoceratopsidae is an extinct family of neoceratopsian dinosaurs from Asia, North America and Europe. Leptoceratopsids resembled, and were closely related to, other neoceratopsians, such as the families Protoceratopsidae and Ceratopsidae, but t ...
and Coronosauria
Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. ...
with the exception of their genus '' Aquilops'' are from Asia, meaning the group likely originated there.
Although many species of ''Psittacosaurus'' have been named, their relationships to each other have not yet been fully explored and no scientific consensus exists on the subject.[ Several ]phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
analyses have been published, with the most detailed being those by Alexander Averianov and colleagues in 2006,[ Hai-Lu You and colleagues in 2008,] and Paul Sereno
Paul Callistus Sereno (born October 11, 1957) is a professor of paleontology at the University of Chicago and a National Geographic "explorer-in-residence" who has discovered several new dinosaur species on several continents, including at sites ...
in 2010.[ The middle one is shown below.
In 2005, Zhou and colleagues suggested that ''P. lujiatunensis'' is basal to all other species. This would be consistent with its earlier appearance in the fossil record.][
]
Paleobiology
The brain of ''P. lujiatunensis'' is well known; a study on the anatomy and functionality of three specimens was published in 2007. Until the study, it was generally thought the brain of ''Psittacosaurus'' would have been similar to other ceratopsians with low Encephalisation Quotients. Russell and Zhao (1996) believed "the small brain size of psittacosaurs implies a very restrictive behavioural repertoire relative to that of modern mammals of similar body size". However, the 2007 study dispelled this theory when it found the brain to be more advanced. There is generally negative allometry
Allometry is the study of the relationship of body size to shape, anatomy, physiology and finally behaviour, first outlined by Otto Snell in 1892, by D'Arcy Thompson in 1917 in ''On Growth and Form'' and by Julian Huxley in 1932.
Overview
Allom ...
for brain size with development in vertebrates, but this was shown not to be true in ''Psittacosaurus''. The EQ score for ''P. lujiatunensis'' is 0.31, significantly higher than genera such as ''Triceratops''. A higher EQ correlates with more complex behaviour, and various dinosaurs have high EQs, similar to birds, which range from 0.36 to 2.98. Thus, ''Psittacosaurus'' behaviour could have been as complex as that in ''Tyrannosaurus
''Tyrannosaurus'' is a genus of large theropoda, theropod dinosaur. The species ''Tyrannosaurus rex'' (''rex'' meaning "king" in Latin), often called ''T. rex'' or colloquially ''T-Rex'', is one of the best represented theropods. ''Tyrannosa ...
'', whose EQ ranges from 0.30 to 0.38. Behaviours influenced by high EQs include nest-building, parental care, and bird-like sleeping, some of which have been shown to be present in ''Psittacosaurus''.
The senses of ''Psittacosaurus'' can be inferred from the endocast
An endocast is the internal cast of a hollow object, often referring to the cranial vault in the study of brain development in humans and other organisms. Endocasts can be artificially made for examining the properties of a hollow, inaccessible sp ...
. Large olfactory bulb
The olfactory bulb (Latin: ''bulbus olfactorius'') is a grey matter, neural structure of the vertebrate forebrain involved in olfaction, the sense of odor, smell. It sends olfactory information to be further processed in the amygdala, the orbitof ...
s are present, indicating the genus had an acute sense of smell. The size of these bulbs are comparable to large predatory theropods, although they likely evolved to avoid predators instead of to seek out prey. The sclerotic ring
Sclerotic rings are rings of bone found in the eyes of many animals in several groups of vertebrates, except for mammals and crocodilians. They can be made up of single bones or multiple segments and take their name from the sclera. They are bel ...
s in reptiles directly show the size of the eyeball. The rings are not well preserved in ''Psittacosaurus'', with one individual preserving them likely contracted postmortem, but if they are similar to those of ''Protoceratops
''Protoceratops'' (; ) is a genus of small protoceratopsid dinosaurs that lived in Asia during the Late Cretaceous, around 75 to 71 million years ago. The genus ''Protoceratops'' includes two species: ''P. andrewsi'' and the larger ''P. hellenik ...
'', ''Psittacosaurus'' would have had large eyes and acute vision. The curvature of the semicircular canals
The semicircular canals or semicircular ducts are three semicircular, interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the horizontal, superior and posterior semicircular canals.
Structure
The ...
is related to the agility of reptiles, and the large curved canals in ''Psittacosaurus'' show that the genus was much more agile than later ceratopsians. Comparisons between the scleral rings of ''Psittacosaurus'' and modern birds and reptiles suggest that it may have been cathemeral
Cathemerality, sometimes called metaturnality, is an organismal activity pattern of irregular intervals during the day or night in which food is acquired, socializing with other organisms occurs, and any other activities necessary for livelihood ar ...
, active throughout the day and for short intervals at night.
Ford and Martin (2010) proposed that ''Psittacosaurus'' was semi-aquatic, swimming with its tail like a crocodile, and paddling and kicking. They based their interpretation on evidence including: the lacustrine (lake) depositional setting of many specimens; the position of the nostrils and eyes; interpretations of the motions of the arms and legs; tails with long chevrons
Chevron (often relating to V-shaped patterns) may refer to:
Science and technology
* Chevron (aerospace), sawtooth patterns on some jet engines
* Chevron (anatomy), a bone
* '' Eulithis testata'', a moth
* Chevron (geology), a fold in rock l ...
(and with the bristles on the tail interpreted as possibly skin-covered, forming a fin), providing a propulsive surface; and the presence of gastroliths
A gastrolith, also called a stomach stone or gizzard stone, is a rock held inside a gastrointestinal tract. Gastroliths in some species are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. In oth ...
, interpreted as ballast. They further suggested that some species of ''Psittacosaurus'' were more terrestrial than others.
Diet
Psittacosaurs had self-sharpening teeth that would have been useful for cropping and slicing tough plant material. Unlike later ceratopsians, they did not have teeth suitable for grinding or chewing their food. Instead, they used gastroliths—stones swallowed to wear down food as it passed through the digestive system. Sometimes numbering more than fifty, these stones are occasionally found in the abdominal cavities of psittacosaurs, and may have been stored in a gizzard
The gizzard, also referred to as the ventriculus, gastric mill, and gigerium, is an organ found in the digestive tract of some animals, including archosaurs (pterosaurs, crocodiles, alligators, dinosaurs, birds), earthworms, some gastropods, so ...
, as in modern birds.[
Unlike many other dinosaurs, psittacosaurs had akinetic skulls: that is to say, the upper and lower jaws each behaved as a single unit, without internal joints. The only joint was the jaw joint itself, and psittacosaurs could slide their lower jaws forward and backward on the joint, permitting a shearing action. Unlike most ceratopsians, their beaks did not form curved tips, but were instead rounded and flattened. If the jaws were aligned, the beaks could be used to crop objects, but if the lower jaw was retracted so that the lower beak was inside the upper beak, the jaws may have served a nutcracking function. A nut- or seed-rich diet would also match well with the gastroliths often seen in well-preserved psittacosaur skeletons.][
]
Limb function
Studies by Phil Senter in 2007 conducted on ''P. neimongoliensis'' and ''P. mongoliensis'' concluded that the forelimbs of these taxa (and likely those of other ''Psittacosaurus'' species) were too short (only about 58% as long as the hindlimbs) to reach the ground, and their range of motion indicates they could neither be pronated
Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...
nor generate propulsive force for locomotion, suggesting that ''Psittacosaurus'' was entirely bipedal. The forelimbs were also too short to be used in digging or bringing food to the mouth, and Senter suggested that if ''Psittacosaurus'' needed to dig depressions in the ground it may have used its hindlimbs instead. The forelimbs could be used for two-handed grasping of objects or scratching the body, but due to their extremely limited flexibility and reach, they could have only been used to grasp objects very close to the belly or sides of the animal and could have scratched only the belly, flank and knees. Even though the hands could not reach the mouth, ''Psittacosaurus'' could have still used them to carry nesting material or food to a desired location.
However, ''Psittacosaurus'' may not have been entirely bipedal for its entire lifespan. Taking sections from the limb bones of 16 specimens of ''Psittacosaurus'', ranging in age from less than a year old to ten-year-old adults, Qi Zhao from the University of Bristol found that ''Psittacosaurus'' was probably secondarily bipedal. The infants' front limbs grew at faster rates than the hind limbs at between birth and three years of age. At the age of between four and six years, arm growth slowed and leg growth accelerated as the animal became mature. At this stage, ''Psittacosaurs'' would switch to a bipedal stance. These findings further reveal that the ancestor of ''Psittacosaurus'' was likely quadrupedal and eventually gained the ability to become bipedal as it evolved, with the young retaining the quadrupedal gait of the ancestor in question. These findings also lead to the hypothesis that many such dinosaur families may have evolved along this path at some point in their evolution.
Growth rate
Several juvenile ''Psittacosaurus'' have been found. The smallest is a ''P. mongoliensis'' hatchling conserved in the American Museum of Natural History
The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 inter ...
(AMNH), which is only 11 to 13 centimetres (4–5 inches) long, with a skull in length. Another hatchling skull at the AMNH is only long. Both specimens are from Mongolia. Juveniles discovered in the Yixian Formation are approximately the same age as the larger AMNH specimen.
A histological
Histology,
also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures vis ...
examination of ''P. mongoliensis'' has determined the growth rate of these animals. The smallest specimens in the study were estimated at three years old and less than , while the largest were nine years old and weighed almost . This indicates relatively rapid growth compared to most reptiles and marsupial
Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a po ...
mammals, but slower than modern bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
s and placental
Placental mammals (infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupial
Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsup ...
mammals.[ An age determination study performed on the ]fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
ized remains of ''P. mongoliensis'' by using growth ring counts suggest that the longevity of the basal ceratopsian was 10 to 11 years.[
]
Gregarious juveniles
The find of a herd of six ''Psittacosaurus'' individuals killed and buried by a volcanic mudflow indicates the presence of at least two age groups from two distinct clutches gathered together. This find has been taken as evidence for group fidelity and gregariousness
Sociality is the degree to which individuals in an animal population tend to associate in social groups (gregariousness) and form cooperative societies.
Sociality is a survival response to evolutionary pressures. For example, when a mother wasp ...
extending beyond the nest; the earliest such evidence for any ceratopsian. Even very young psittacosaur teeth appear worn, indicating they chewed their own food and may have been precocial
In biology, altricial species are those in which the young are underdeveloped at the time of birth, but with the aid of their parents mature after birth. Precocial species are those in which the young are relatively mature and mobile from the mome ...
.[ Another juvenile-only cluster shows that specimens of different ages grouped together. These juveniles may have associated together as a close knit, mixed-age herd either for protection, to enhance their foraging, or as putative helpers at the parental nest. There is no evidence for parental care.]
In 2004, a specimen found in the Yixian Formation was claimed as evidence for parental care in dinosaurs. The specimen DNHM D2156 consists of 34 articulated juvenile ''Psittacosaurus'' skeletons, closely associated with the skull of an adult. The juveniles, all approximately the same age, are intertwined in a group underneath the adult, although all 34 skulls are positioned above the mass of bodies, as they would have been in life. This suggests that the animals were alive at the time of burial, which must have been extremely rapid, perhaps due to the collapse of a burrow
An Eastern chipmunk at the entrance of its burrow
A burrow is a hole or tunnel excavated into the ground by an animal to construct a space suitable for habitation or temporary refuge, or as a byproduct of locomotion. Burrows provide a form of sh ...
.[ However, a 2013 paper pointed out that the adult specimen did not belong with the nest, its skull having no sedimentary connection to the main slab where the juveniles occurred, but had been glued onto it. This artificial association led to the inference that the skull belonged to an individual, possibly a "mother", that was providing parental care for the 34 juveniles—a claim that is unfounded. Furthermore, the adult was also shown to be six years old, whereas histological studies have shown ''P. mongoliensis'' was unable to breed until it reached ten years of age. It is also unlikely that a single female would have so many offspring at one time.]
A 2014 analysis of the same specimen supported the association and concluded that the proximity of the six-year-old specimen to the post-hatchlings may indicate post-hatchling cooperation, making the six-year-old specimen a possible caretaker.
Pathology
Out of the hundreds of known ''Psittacosaurus'' specimens, only one has been described to possess any sort of pathology
Pathology is the study of the causes and effects of disease or injury. The word ''pathology'' also refers to the study of disease in general, incorporating a wide range of biology research fields and medical practices. However, when used in ...
. The specimen in question, consisting of a complete adult skeleton and tentatively assigned to ''P. mongoliensis'', was found in the lower beds of the Yixian Formation. There is no sign of a bone fracture
A bone fracture (abbreviated FRX or Fx, Fx, or #) is a medical condition in which there is a partial or complete break in the continuity of any bone in the body. In more severe cases, the bone may be broken into several fragments, known as a '' ...
, but very clear signs of an infection
An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...
can be seen near the midpoint of the right fibula
The fibula or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity is ...
. The bone exhibits a large round pit, evidence of necrosis
Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...
due to a lack of blood
Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the c ...
supply to the region. The pit is surrounded by a massive amount of swelling along the lower third of the bone. This large amount of bone deposited around the injury indicates that the animal survived for quite a while despite the injury and subsequent infection. As psittacosaurids were bipedal animals, a similar injury to a weight bearing In orthopedics, weight-bearing is the amount of weight a patient puts on an injured body part. Generally, it refers to a leg, ankle or foot that has been fractured or upon which surgery has been performed, but the term can also be used to refer to ...
bone in the leg would most likely have been fatal. Unlike the femur and tibia
The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...
, the fibula is not a weight-bearing bone, so this animal would still have been able to walk to some extent. The source of the injury remains unknown.
Predation
Another fossil from the Yixian Formation provides direct evidence of ''Psittacosaurus'' as a prey
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...
animal. One skeleton of ''Repenomamus robustus
''Repenomamus'' (Latin: "reptile" (reptilis), "mammal" (mammalis)) is a genus of opossum- to badger-sized gobiconodontid mammal containing two species, ''Repenomamus robustus'' and ''Repenomamus giganticus''. Both species are known from fossils ...
'', a large triconodont
Eutriconodonta is an order of early mammals. Eutriconodonts existed in Asia, Africa, Europe, North and South America during the Jurassic and the Cretaceous periods. The order was named by Kermack ''et al.'' in 1973 as a replacement name for the p ...
mammal, is preserved with the remains of a juvenile ''Psittacosaurus'' in its abdominal cavity. Several of the juvenile's bones are still articulated, indicating that the carnivorous
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other sof ...
mammal swallowed its prey in large chunks. This specimen is notable in that it is the first-known example of Mesozoic
The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...
mammals preying on live dinosaurs. Heavy predation on juvenile ''Psittacosaurus'' may have resulted in R-selection
In ecology, ''r''/''K'' selection theory relates to the selection of combinations of traits in an organism that trade off between quantity and quality of offspring. The focus on either an increased quantity of offspring at the expense of individ ...
, the production of more numerous offspring to counteract this loss.
Paleochronology
''Psittacosaurus'' is known from hundreds of individual specimens, of which over 75 have been assigned to the type species, ''P. mongoliensis''. All ''Psittacosaurus'' fossils discovered so far have been found in Early Cretaceous
The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma.
Geology
Pro ...
sediments in Asia, from southern Siberia
Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part of ...
to northern China, and possibly as far south as Thailand. The most common age of geologic formation
A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...
s bearing ''Psittacosaurus'' fossils is from the late Barremian
The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma (million years ago) and 121.4 ± 1.0 Ma). It is a subdivision of the Early Cretaceous Epoch (or Lower Cretaceous Series). It is preceded ...
through Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0.9 M ...
stages of the Early Cretaceous, or approximately 126 to 101 mya (million years ago
The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds.
Usage
Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago). ...
). Many terrestrial sedimentary
Sedimentary rocks are types of rock (geology), rock that are formed by the accumulation or deposition of mineral or organic matter, organic particles at Earth#Surface, Earth's surface, followed by cementation (geology), cementation. Sedimentati ...
formations of this age in Mongolia and northern China have produced fossils of ''Psittacosaurus'', leading to the definition of this time period in the region as the ''Psittacosaurus'' biochron.
The earliest known species is ''P. lujiatunensis'', found in the lowest beds of the Yixian Formation.[ Over 200 specimens attributed to this genus have been recovered from these and other beds of the Yixian, the age of which is the subject of much debate.][ Although many early studies using ]radiometric dating
Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares t ...
put the Yixian in the Jurassic Period
The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
, tens of millions of years outside of the expected temporal range of ''Psittacosaurus'', most recent work dates it to the Early Cretaceous. Using argon–argon dating
Argon–argon (or 40Ar/39Ar) dating is a radiometric dating method invented to supersede potassiumargon (K/Ar) dating in accuracy. The older method required splitting samples into two for separate potassium and argon measurements, while the newer ...
, a team of Chinese scientists dated the lowest beds
A bed is an item of furniture that is used as a place to sleep, rest, and relax.
Most modern beds consist of a soft, cushioned mattress on a bed frame. The mattress rests either on a solid base, often wood slats, or a sprung base. Many be ...
in the formation to about 128 mya, and the highest to approximately 122 mya. A more recent Chinese study, using uranium–lead dating
Uranium–lead dating, abbreviated U–Pb dating, is one of the oldest and most refined of the radiometric dating schemes. It can be used to date rocks that formed and crystallised from about 1 million years to over 4.5 billion years ago with routi ...
, suggests that the lower beds are younger, approximately 123.2 mya, while agreeing with an age of 122 mya for the upper beds.
See also
* Timeline of ceratopsian research
This timeline of ceratopsian research is a chronological listing of events in the history of paleontology focused on the ceratopsians, a group of herbivorous marginocephalian dinosaurs that evolved parrot-like beaks, bony frills, and, later, spe ...
References
External links
*
{{featured article
Ceratopsians
Feathered dinosaurs
Early Cretaceous dinosaurs of Asia
Cretaceous Mongolia
Fossils of Mongolia
Cretaceous China
Paleontology in Shandong
Paleontology in Gansu
Yixian fauna
Cretaceous Thailand
Fossils of Thailand
Fossil taxa described in 1923
Taxa named by Henry Fairfield Osborn
Ornithischian genera