''Balaur bondoc'' is a
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 ...
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 ...
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 late
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 ...
period, in what is now
Romania
Romania ( ; ro, România ) is a country located at the crossroads of Central Europe, Central, Eastern Europe, Eastern, and Southeast Europe, Southeastern Europe. It borders Bulgaria to the south, Ukraine to the north, Hungary to the west, S ...
. It is 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 ...
of the
monotypic
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 ...
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 ...
''Balaur'', after the ''
balaur
A balaur ( pl. ''balauri'') in Romanian folklore is a type of many-headed dragon or monstrous serpent, sometimes said to be equipped with wings. The number of heads is usually around three, but they can also have seven heads or even twelve head ...
'' (), a dragon of
Romanian folklore
The folklore of Romania is the collection of traditions of the Romanians. A feature of Romanian culture is the special relationship between folklore and the learned culture, determined by two factors. First, the rural character of the Romanian ...
. The specific name ''bondoc'' () means "stocky", so ''Balaur bondoc'' means "stocky dragon" in Romanian. This name refers to the greater musculature that ''Balaur'' had compared to its relatives. The genus, which was first described by scientists in August 2010, is known from two partial skeletons (including 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 ...
).
Fossils of ''Balaur'' were found in the
Densuş-Ciula and
Sebeș Formations of
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 ...
Romania
Romania ( ; ro, România ) is a country located at the crossroads of Central Europe, Central, Eastern Europe, Eastern, and Southeast Europe, Southeastern Europe. It borders Bulgaria to the south, Ukraine to the north, Hungary to the west, S ...
which correspond to
Hațeg island
Hațeg Island was a large offshore island in the Tethys Sea which existed during the Late Cretaceous period, probably from the Cenomanian to the Maastrichtian ages. It was situated in an area corresponding to the region around modern-day Hațeg, H ...
, a subtropical island
[Benton, M.J., Csiki, Z., Grigorescu, D., Redelstorff, R., Sander, P.M., Stein, K., and Weishampel, D.B. (2010).]
Dinosaurs and the island rule: The dwarfed dinosaurs from Hațeg Island.
" ''Palaeogeography, Palaeoclimatology, Palaeoecology'', 293(3-4): 438–454. in the European
archipelago
An archipelago ( ), sometimes called an island group or island chain, is a chain, cluster, or collection of islands, or sometimes a sea containing a small number of scattered islands.
Examples of archipelagos include: the Indonesian Archi ...
of the
Tethys sea
The Tethys Ocean ( el, Τηθύς ''Tēthús''), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean that covered most of the Earth during much of the Mesozoic Era and early Cenozoic Era, located between the ancient continents ...
approximately 70 million years ago. Hațeg island is commonly referred to as the "Island of the Dwarf Dinosaurs" on account of the extensive fossil evidence that its native dinosaurs exhibited
island syndrome
Island syndrome describes the differences in morphology, ecology, physiology and behaviour of insular species compared to their continental counterparts. These differences evolve due to the different ecological pressures affecting insular specie ...
, a collection of
morphological,
ecological
Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps wi ...
,
physiological
Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...
and
behavioural
Behavior (American English) or behaviour (British English) is the range of actions and mannerisms made by individuals, organisms, systems or artificial entities in some environment. These systems can include other systems or organisms as well ...
differences compared with their continental counterparts. Examples included
island gigantism
Island gigantism, or insular gigantism, is a biological phenomenon in which the size of an animal species isolated on an island increases dramatically in comparison to its mainland relatives. Island gigantism is one aspect of the more general "i ...
of ''
Hatzegopteryx
''Hatzegopteryx'' ("Hațeg basin wing") is a genus of azhdarchid pterosaur found in the late Maastrichtian deposits of the Densuş Ciula Formation, an outcropping in Transylvania, Romania. It is known only from the type species, ''Hatzegopteryx ...
'',
island dwarfism
Insular dwarfism, a form of phyletic dwarfism, is the process and condition of large animals evolving or having a reduced body size when their population's range is limited to a small environment, primarily islands. This natural process is disti ...
of the
titanosaur
Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still th ...
''
Magyarosaurus dacus
''Magyarosaurus'' (" Magyar lizard") is a genus of dwarf sauropod dinosaur from late Cretaceous Period (early to late Maastrichtian) in Romania. It is one of the smallest-known adult sauropods, measuring only in length and in body mass. The ...
'', and a
reduction in flight capacity in ''Balaur'' (''Balaur'' is currently believed to be a basal
avialan
Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative definitions are occasionally used ...
, a group that includes modern
birds
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 ...
, based on
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 ...
analysis, despite being previously grouped within the
dromaeosaurid
Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...
dinosaurs
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 ...
, a group which includes ''
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 ...
''). This reduction in flight capacity is also seen in extant island birds including the
ratites
A ratite () is any of a diverse group of flightless, large, long-necked, and long-legged birds of the infraclass Palaeognathae. Kiwi, the exception, are much smaller and shorter-legged and are the only nocturnal extant ratites.
The systematics o ...
and insular
barn owls
The barn owl (''Tyto alba'') is the most widely distributed species of owl in the world and one of the most widespread of all species of birds, being found almost everywhere except for the polar and desert regions, Asia north of the Himalayas ...
as well as the extinct
moa
Moa are extinct giant flightless birds native to New Zealand.
The term has also come to be used for chicken in many Polynesian cultures and is found in the names of many chicken recipes, such as
Kale moa and Moa Samoa.
Moa or MOA may also refer ...
of
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
and the extinct
dodo
The dodo (''Raphus cucullatus'') is an extinct flightless bird that was endemic to the island of Mauritius, which is east of Madagascar in the Indian Ocean. The dodo's closest genetic relative was the also-extinct Rodrigues solitaire. The ...
of
Mauritius
Mauritius ( ; french: Maurice, link=no ; mfe, label=Mauritian Creole, Moris ), officially the Republic of Mauritius, is an island nation in the Indian Ocean about off the southeast coast of the African continent, east of Madagascar. It incl ...
.
Discovery and naming
![Balaur](https://upload.wikimedia.org/wikipedia/commons/7/79/Balaur.png)
The first small bones belonging to ''Balaur bondoc'' consisted of six elements of the front limbs. Named specimens FGGUB R. 1580–1585, these were discovered in 1997 in
Romania
Romania ( ; ro, România ) is a country located at the crossroads of Central Europe, Central, Eastern Europe, Eastern, and Southeast Europe, Southeastern Europe. It borders Bulgaria to the south, Ukraine to the north, Hungary to the west, S ...
by
Dan Grigorescu
Dan or DAN may refer to:
People
* Dan (name), including a list of people with the name
** Dan (king), several kings of Denmark
* Dan people, an ethnic group located in West Africa
**Dan language, a Mande language spoken primarily in Côte d'Ivoir ...
, but the morphology of the arm was so unusual that scientists could not correctly combine them,
mistaking them for the remains of an
oviraptorosaur
Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period (geology), Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like s ...
. The first partial skeleton was discovered in September 2009 in Romania, approximately 2.5 kilometers north of Sebeș, along the
Sebeș river in the
Sebeș Formation dating from the early
Maastrichtian
The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...
, and was given the preliminary field number ''SbG/A-Sk1''. Later it received the
holotype
A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...
inventory number EME VP.313. The discovery was made by the
geologist
A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, althou ...
and
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 ...
Mátyás Vremir of the
Transylvanian Museum Society of Cluj Napoca who sent them for analysis to
Zoltán Csiki of the
University of Bucharest
The University of Bucharest ( ro, Universitatea din București), commonly known after its abbreviation UB in Romania, is a public university founded in its current form on by a decree of Prince Alexandru Ioan Cuza to convert the former Princel ...
. The findings were described on August 31, 2010, in the ''
Proceedings of the National Academy of Sciences
''Proceedings of the National Academy of Sciences of the United States of America'' (often abbreviated ''PNAS'' or ''PNAS USA'') is a peer-reviewed multidisciplinary scientific journal. It is the official journal of the National Academy of Sci ...
''.
The 1997 specimens indicate an individual about 45% longer than the holotype; they were also found in a younger
stratum
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 ...
.
The
generic name ''
Balaur
A balaur ( pl. ''balauri'') in Romanian folklore is a type of many-headed dragon or monstrous serpent, sometimes said to be equipped with wings. The number of heads is usually around three, but they can also have seven heads or even twelve head ...
'' (three syllables, stressed on the second /a/) is from the
Romanian
Romanian may refer to:
*anything of, from, or related to the country and nation of Romania
**Romanians, an ethnic group
**Romanian language, a Romance language
***Romanian dialects, variants of the Romanian language
**Romanian cuisine, traditional ...
word for a dragon of
Romanian folklore
The folklore of Romania is the collection of traditions of the Romanians. A feature of Romanian culture is the special relationship between folklore and the learned culture, determined by two factors. First, the rural character of the Romanian ...
, while the
specific epithet
In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...
''bondoc'' (pronounced like "boned oak", meaning "a squat, chubby individual") refers to the small, robust shape of the animal. As the ''balaur'' is a winged dragon, the name additionally hints at the close relation of ''Balaur'' to the birds within
Panaves
Avemetatarsalia (meaning "bird metatarsals") is a clade of diapsid reptiles containing all archosaurs more closely related to birds than to crocodilians. The two most successful groups of avemetatarsalians were the dinosaurs and pterosaurs. D ...
. ''Bondoc'' was chosen by the discoverers also because it is derived from the
Turkish
Turkish may refer to:
*a Turkic language spoken by the Turks
* of or about Turkey
** Turkish language
*** Turkish alphabet
** Turkish people, a Turkic ethnic group and nation
*** Turkish citizen, a citizen of Turkey
*** Turkish communities and mi ...
''bunduk'', "small ball", thus alluding to the probable Asian origin of the ancestors of ''Balaur''.
Description
![Balaur bondoc scalechart 2015](https://upload.wikimedia.org/wikipedia/commons/8/81/Balaur_bondoc_scalechart_2015.png)
''Balaur'' 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
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 estimated to have lived about years ago in the late Cretaceous (
Maastrichtian
The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...
), and contains the single species ''B. bondoc''.
The bones of this species were shorter and heavier than those of basal paravians. While the feet of most early paravians bore a single, large "sickle claw" on the second toe which was held retracted off the ground, ''Balaur'' had large retractable sickle claws on both the first and second toes of each foot.
In addition to its strange feet, the type specimen of ''Balaur'' is unique for its status of being the most complete theropod fossil from the late Cretaceous of Europe. It also possesses a great number of additional
autapomorphies
In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to t ...
, including a reduced and presumably nonfunctional third finger, consisting of only one rudimentary phalanx.
The partial skeleton was collected from the red floodplain
mudstone
Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...
of the
Sebeș
Sebeș (; German: ''Mühlbach''; Hungarian: ''Szászsebes''; Transylvanian Saxon dialect: ''Melnbach'') is a city in Alba County, central Romania, southern Transylvania.
Geography
The city lies in the Mureș River valley and straddles the rive ...
Formation of Romania. It consists of a variety of
vertebrae
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 i ...
, as well as much of
pectoral
Pectoral may refer to:
* The chest region and anything relating to it.
* Pectoral cross, a cross worn on the chest
* a decorative, usually jeweled version of a gorget
* Pectoral (Ancient Egypt), a type of jewelry worn in ancient Egypt
* Pectoralis ...
and
pelvic girdles
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 p ...
, and a large part of the limbs. It is the first reasonably complete and well-preserved theropod from the Late Cretaceous of Europe.
![Balaur bondoc as avialan](https://upload.wikimedia.org/wikipedia/commons/6/69/Balaur_bondoc_as_avialan.jpg)
It is similar in size to ''
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 ...
'', with ''Balaurs recovered skeletal elements suggesting an overall length of around and a body mass of .
''Balaur'' had re-evolved a functional first toe used to support its weight, which bore a large claw that could be hyperextended. It had short and stocky feet and legs, and large muscle attachment areas on the pelvis which indicate that it was adapted for strength rather than speed.
Csiki ''et al.'' describe this "novel body plan" as "a dramatic example of aberrant morphology developed in island-dwelling taxa."
The stocky feet are exemplified by the length of the
metatarsus
The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the med ...
being only two times its width. It is 1.5 times wider than the lower leg. Both traits are unique in the
Theropoda
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 ca ...
. The skeleton of ''Balaur'' also shows extensive fusion of limb bones. Wrist bones and the
metacarpals
In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeleton, skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpa ...
are fused into a carpometacarpus. The pelvic bones are fused. The shinbone, calf bone and the upper ankle bones have been fused into a tibiotarsus and the lower ankle bones and the
metatarsals
The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medi ...
into a tarsometatarsus. The degree of fusion is typical for the
Avialae
Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative definitions are occasionally used ...
, the evolutionary branch of the birds and their direct relatives.
Classification
![Balaur holotype pes and tibia](https://upload.wikimedia.org/wikipedia/commons/d/d6/Balaur_holotype_pes_and_tibia.jpg)
The position of ''Balaur'' relative to other bird-like dinosaurs and early birds has been difficult to determine. The initial
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 ...
analysis placed ''Balaur bondoc'' closest to the Asiatic mainland
dromaeosaurid
Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...
species ''
Velociraptor mongoliensis
''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 ...
''. A 2013 study by Brusatte and colleagues, using a modified version of the same data, found it in an unresolved close relationship with the dromaeosaurids ''
Deinonychus
''Deinonychus'' ( ; ) is a genus of dromaeosaurid theropod dinosaur with one described species, ''Deinonychus antirrhopus''. This species, which could grow up to long, lived during the early Cretaceous Period, about 115–108 million ye ...
'' and ''
Adasaurus
''Adasaurus'' ( ; meaning "Ada lizard") is a genus of dromaeosaurid dinosaur that lived in Asia during the Late Cretaceous period about 70 million years ago. The genus is known from two partial specimens found in the Nemegt Formation of Mongolia ...
'', with some possible alternative trees suggesting it branched off before the common ancestor of ''
Deinonychus
''Deinonychus'' ( ; ) is a genus of dromaeosaurid theropod dinosaur with one described species, ''Deinonychus antirrhopus''. This species, which could grow up to long, lived during the early Cretaceous Period, about 115–108 million ye ...
'' 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 ...
'', while others maintained it as the closest relative of ''
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 ...
'', with ''
Adasaurus
''Adasaurus'' ( ; meaning "Ada lizard") is a genus of dromaeosaurid dinosaur that lived in Asia during the Late Cretaceous period about 70 million years ago. The genus is known from two partial specimens found in the Nemegt Formation of Mongolia ...
'' as their next closest relative.
[Brusatte, S. L. et al. (2013). "The Osteology of ''Balaur bondoc'', an Island-Dwelling Dromaeosaurid (Dinosauria: Theropoda) from the Late Cretaceous of Romania"'' Bulletin of the American Museum of Natural History ''374: 1-100. ]
More recent analyses using different sets of anatomical data have since cast doubt on a dromaeosaurid classification for ''Balaur''. In 2013, a larger analysis containing a wide variety of coelurosaurs found that ''Balaur'' was not a dromaeosaurid at all, but a basal
avialan
Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative definitions are occasionally used ...
, more closely related to modern birds than to
Jeholornithiformes
Jeholornithidae is a family of avialan theropods whose taxonomy is controversial, whose remains are found in fossil deposits of what is now China. The controversy stems from whether most of the taxa in the group are just specimens of ''Jeholornis ...
but more basal than
Omnivoropterygiformes
Omnivoropterygidae (meaning "omnivorous wings") is a family of primitive avialans known exclusively from the Jiufotang Formation of China, though putative omnivoropterygids are known from the Maevarano Formation of the Maastrichtian of Madagascar ...
.
A study published in 2014 found ''Balaur'' to be sister to
Pygostylia
Pygostylia is a group of avialans which includes the Confuciusornithidae and all of the more advanced species, the Ornithothoraces.
Definition
The group Pygostylia was intended to encompass all avialans with a short, stubby tail, as opposed to t ...
.
An independent analysis using an expanded version of the original data set (the one that found ''Balaur'' to be a dromaeosaurid) drew a similar conclusion in 2014.
In 2015, researchers Andrea Cau, Tom Brougham, and Darren Naish published a study which specifically attempted to clarify which theropods were close relatives of ''Balaur''. While their analysis could not completely rule out the possibility that ''B. bondoc'' was a dromaeosaurid, they concluded that this result was less likely than the classification of ''Balaur'' as a non-
pygostylia
Pygostylia is a group of avialans which includes the Confuciusornithidae and all of the more advanced species, the Ornithothoraces.
Definition
The group Pygostylia was intended to encompass all avialans with a short, stubby tail, as opposed to t ...
n avialan based on several important bird-like features. Many of the presumed unique traits would in fact have been normal for a member of the Avialae. Typical bird features included the degree of fusion of the limb bones, the functional first toe, the first toe claw not being smaller than the second claw, a long penultimate phalanx of the third toe, a small fourth toe claw and a long fifth metatarsal.
On the other hand, some recent studies continue to place ''Balaur'' within the Velociraptorinae.
Paleobiology
Diet and lifestyle
![Balaur bondoc](https://upload.wikimedia.org/wikipedia/commons/b/bb/Balaur_bondoc.jpg)
Little is known about the behavior of ''Balaur''. Because of the lack of skull material, it is impossible to determine by the shape of the teeth whether ''Balaur'' was a carnivore or a herbivore. The original description assumed it was carnivorous because it had been found that it was closely related to ''
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 ...
''. Csiki speculated in 2010 that it may have been one of the
apex predator
An apex predator, also known as a top predator, is a predator at the top of a food chain, without natural predators of its own.
Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the highest trophic lev ...
s in its limited
island ecosystem Island ecology is the study of island organisms and their interactions with each other and the environment. Islands account for nearly 1/6 of earth’s total land area,Paulay, G. 1994. Biodiversity on Oceanic Islands: Its Origin and Extinction. ''A ...
, as neither the skeletons nor teeth of larger theropods have been discovered in Romania. He also believed that it likely used its double sickle claws for slashing prey, and that the atrophied state of its hands indicates that it probably did not use them to hunt. One of the original discoverers indicated that it "was probably more of a kickboxer than a sprinter" compared to ''
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 ...
'', and was probably able to hunt larger animals than itself.
However, more recent studies by Denver Fowler and others have shown that the foot anatomy of paravians like ''Balaur'' indicate that they used their large claws to grip and pin prey to the ground while flapping with their proto-wings to stay on top of their victim. Once it was worn out, they might have proceeded to feast while it was still alive as some modern birds of prey still do. Due to the shape of the claws, they would not have been effective in slashing attacks.
The very short, fused metatarsus of ''Balaur'' and enlarged first claw, strange even by true dromaeosaur standards, are thought to be consistent with these newer studies, lending further support to the idea that ''Balaur'' was a predator.
Italian paleontologist Andrea Cau has speculated that the aberrant features present in ''Balaur'' may have been a result of this theropod being
omnivorous
An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nutri ...
or
herbivorous
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
rather than carnivorous like most non-avian theropods. The lack of the third finger may be a sign of reduced predatory behavior, and the robust first toe could be interpreted as a weight-supporting adaptation rather than a weapon. These characteristics are consistent with the relatively short, stocky limbs and wide, swept-back pubis, which may indicate enlarged intestines for digesting vegetation as well as reduced speed. Cau referred to this as the "Dodoraptor" model. However, in light of the research done by Fowler et al., Cau has remarked that the anatomy of ''Balaur'' may be more congruent with the hypothesis that ''Balaur'' was predatory after all.
[Cau, A (2011)]
The Extinction of Dodoraptor (?)
Theropoda, December 30, 2011.
In 2015, Cau et al. reconsidered the ecology of ''Balaur'' again in their reevaluation of its phylogenetic position, arguing that if ''Balaur'' was an avialan, it would be
phylogenetically bracketed by taxa known to have been herbivorous, such as ''
Sapeornis
''Sapeornis'' is a monotypic genus of avialan which lived during the early Cretaceous period ( late Barremian to early Aptian, roughly 125-120 mya). ''Sapeornis'' contains only one species, ''Sapeornis chaoyangensis''.
Description
''Sapeornis' ...
'' and ''
Jeholornis
''Jeholornis'' (meaning "Jehol bird") is a genus of avialans that lived between approximately 122 and 120 million years ago during the early Cretaceous Period in China. Fossil ''Jeholornis'' were first discovered in the Jiufotang Formation in Heb ...
''. This suggests a non-hypercarnivorous lifestyle to be a more parsimonious conclusion and supports Cau's initial interpretations of its specializations. This is also indicated by the reduced third finger, the lack of a gynglymoid lower articulation of the second metatarsal and the rather small and moderately recurved second toe claw. ''Balaur'' had a broad pelvis, a broad foot, a large first toe, and broad lower ends of the metatarsals relative to the articulation surfaces; such a combination can in the remainder of the Theropoda only be found with the herbivorous
.
Island syndrome
![Balaur in Hateg environment](https://upload.wikimedia.org/wikipedia/commons/a/ae/Balaur_in_Hateg_environment.jpg)
During the
Maastrichtian
The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...
age, much of Europe was fragmented into islands, and a number of the bizarre
morphologies of ''Balaur'' are thought to be a result of
Island syndrome
Island syndrome describes the differences in morphology, ecology, physiology and behaviour of insular species compared to their continental counterparts. These differences evolve due to the different ecological pressures affecting insular specie ...
.
This describes the differences in the
morphology
Morphology, from the Greek and meaning "study of shape", may refer to:
Disciplines
*Morphology (archaeology), study of the shapes or forms of artifacts
*Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...
,
ecology
Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps wi ...
,
physiology
Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...
and
behaviour
Behavior (American English) or behaviour (British English) is the range of actions and mannerisms made by individuals, organisms, systems or artificial entities in some environment. These systems can include other systems or organisms as wel ...
of island species like ''Balaur'' compared to their continental counterparts as a result of the different selection pressures that act on island species.
One common effect is
Foster's rule
Fosters or Foster's may refer to:
Places
* Fosters, Alabama
* Fosters, Michigan
* Fosters, Ohio
Television
* ''The Fosters'' (British TV series), a short-lived British sitcom that ran from 1976 to 1977
* ''The Fosters'' (American TV series), ...
which describes how small mainland species become larger and large mainland species become smaller. This is seen in other taxa from
Hațeg island
Hațeg Island was a large offshore island in the Tethys Sea which existed during the Late Cretaceous period, probably from the Cenomanian to the Maastrichtian ages. It was situated in an area corresponding to the region around modern-day Hațeg, H ...
including the
pterosaur
Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 to ...
''
Hatzegopteryx
''Hatzegopteryx'' ("Hațeg basin wing") is a genus of azhdarchid pterosaur found in the late Maastrichtian deposits of the Densuş Ciula Formation, an outcropping in Transylvania, Romania. It is known only from the type species, ''Hatzegopteryx ...
'' which exhibited
island gigantism
Island gigantism, or insular gigantism, is a biological phenomenon in which the size of an animal species isolated on an island increases dramatically in comparison to its mainland relatives. Island gigantism is one aspect of the more general "i ...
and the
titanosaur
Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still th ...
''
Magyarosaurus dacus
''Magyarosaurus'' (" Magyar lizard") is a genus of dwarf sauropod dinosaur from late Cretaceous Period (early to late Maastrichtian) in Romania. It is one of the smallest-known adult sauropods, measuring only in length and in body mass. The ...
'' which exhibited
island dwarfism
Insular dwarfism, a form of phyletic dwarfism, is the process and condition of large animals evolving or having a reduced body size when their population's range is limited to a small environment, primarily islands. This natural process is disti ...
.
However, ''Balaur'' appears to have had comparable body size to other basal
avialans
Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative definitions are occasionally used ...
and closely related
dromaeosaurid
Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...
dinosaurs
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 ...
. ''Balaur'' appears to have exhibited other features of island syndrome, most notably a
reduced capacity for flight compared to other basal
avialans
Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative definitions are occasionally used ...
. This reduction in flight capacity is also seen in extant island birds including the
ratites
A ratite () is any of a diverse group of flightless, large, long-necked, and long-legged birds of the infraclass Palaeognathae. Kiwi, the exception, are much smaller and shorter-legged and are the only nocturnal extant ratites.
The systematics o ...
and insular
barn owls
The barn owl (''Tyto alba'') is the most widely distributed species of owl in the world and one of the most widespread of all species of birds, being found almost everywhere except for the polar and desert regions, Asia north of the Himalayas ...
as well as the extinct
moa
Moa are extinct giant flightless birds native to New Zealand.
The term has also come to be used for chicken in many Polynesian cultures and is found in the names of many chicken recipes, such as
Kale moa and Moa Samoa.
Moa or MOA may also refer ...
of
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
and the extinct
dodo
The dodo (''Raphus cucullatus'') is an extinct flightless bird that was endemic to the island of Mauritius, which is east of Madagascar in the Indian Ocean. The dodo's closest genetic relative was the also-extinct Rodrigues solitaire. The ...
of
Mauritius
Mauritius ( ; french: Maurice, link=no ; mfe, label=Mauritian Creole, Moris ), officially the Republic of Mauritius, is an island nation in the Indian Ocean about off the southeast coast of the African continent, east of Madagascar. It incl ...
.
In addition to island syndrome, species isolated on islands are also affected by
genetic drift
Genetic drift, also known as allelic drift or the Wright effect, is the change in the frequency of an existing gene variant (allele) in a population due to random chance.
Genetic drift may cause gene variants to disappear completely and there ...
and the
founder effect
In population genetics, the founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population. It was first fully outlined by Ernst Mayr in 1942, using ...
to a greater degree due to the small effective population size. This can magnify the effects of mutations which may otherwise be diluted in a larger population and may have given rise to some of the neomorphies seen in ''Balau'' like the retractable claw on its first toe.
In 2010, the increased robustness of ''Balaur'' was compared to parallel changes seen in isolated herbivorous mammals.
In 2013, it was claimed that ''Balaur'' was the only predatory vertebrate known to have become more robust after invading an island niche and it was suggested that its broad feet had evolved to improve postural stability.
The 2015 interpretation of ''Balaur'' as an omnivorous member of the Avialae, suggested it was the descendant of a flying species that had developed a larger size similar to the development in several other island herbivores. This would then be a rare instance of
secondary flightlessness in a paravian to resemble a
dromaeosaurid
Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...
, as predicted by
Gregory S. Paul
Gregory Scott Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology, and more recently has examined sociology and theology. He is best known for his work and research on theropod dino ...
.
References
External links
{{Taxonbar, from=Q132853
Prehistoric avialans
Maastrichtian life
Late Cretaceous dinosaurs of Europe
Cretaceous Romania
Fossils of Romania
Hațeg fauna
Fossil taxa described in 2010
Taxa named by Stephen L. Brusatte
Taxa named by Mark Norell