''Archaeornithoides'' is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of
maniraptora
Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to ''Ornithomimus velox''. It contains the major subgroups Avialae, Deinonychosauria, Oviraptoros ...
n
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 ...
of the
Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...
of
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, ...
.
Discovery and naming
In 1965, a Polish-Mongolian paleontological expedition found a fossil of a small dinosaur at
Bayn Dzak,
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, ...
. In 1983, the find was reported by
Andrzej Elzanowski. The remains were named as 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 specime ...
''Archaeornithoides deinosauriscus'' by Elzanowski and
Peter Wellnhofer
Peter Wellnhofer (born Munich, 1936) is a German paleontologist at the Bayerische Staatssammlung fur Paläontologie in Munich. He is best known for his work on the various fossil specimens of ''Archaeopteryx'' or "Urvogel", the first known bird. W ...
in 1992.
In 1993, they were described in more detail by the same authors.
The generic name (''Archaeornithoides'') means “shaped like an ancient bird” in
Ancient Greek
Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic p ...
, from ἀρχαῖος, ''archaios'', "ancient"; ὄρνις, ''ornis'', "bird"; and εἶδος, ''eidos'', "form". The
specific descriptor ''deinosauriscus'', "little dinosaur", alludes to the animal's small size for a dinosaur.
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 sever ...
, ZPAL MgD-II/29, was discovered in Late Cretaceous river sandstones of the
Djadokhta Formation
The Djadochta Formation (sometimes transcribed and also known as Djadokhta, Djadokata, or Dzhadokhtskaya) is a highly fossiliferous geological formation situated in Central Asia, Gobi Desert, dating from the Late Cretaceous period, about 75 mill ...
beds, dating from the late
Campanian
The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campani ...
. It consists of an articulated but fragmentary skull and lower jaws comprehending paired
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. T ...
e, a partial
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 ...
, palate bones and dentaries. The specimen represents a juvenile individual.
Description
![Archaeornithoides](https://upload.wikimedia.org/wikipedia/commons/d/d9/Archaeornithoides.jpg)
The holotype of ''Archaeornithoides'' was a very small individual. The head fragment as preserved measures just twenty-seven millimetres in length, indicating an original skull length of about five centimetres. The body length was estimated at fifty to sixty centimetres,
making the ''Archaiornithoides'' type one of the smallest known non-avian dinosaurs. Adult length is uncertain.
The snout of ''Archaeornithoides'' features a long
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 ...
, stretching over three quarters of the length of the maxilla. The maxilla bears at least eight teeth. These are small, conical and smooth, lacking wrinkles, serrations or carinae. The
palatine bone seems to show the presence of a secondary fenestra.
Classification
Elżanowski & Wellnhofer (1993) claimed that ''Archaeornithoides'' was the closest known relative to birds or
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 use ...
. This conclusion rested on key bird-like features; an interdigitated suture between the premaxilla and maxilla, broad palatal shelves, pneumatic sinuses, lack of interdental plates, and unserrated teeth. Since publication, though, all of these features have been discovered in new fossils of adult and/or juvenile
troodonts and
dromaeosaur
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 ...
s.
[Clark, James M., Norell, Mark A., Makovicky, Peter J. (2002) "Cladistic approaches to the relationships of birds to other theropods" pp.31-61 in “Mesozoic Birds: Above the Heads of Dinosaurs” Chiappe&Witmer ed. ] The describing authors in 1993 also concluded that ''Archaeornithoides'' was closely related to troodontids,
Spinosauridae
The Spinosauridae (or spinosaurids) are a clade or family of tetanuran theropod dinosaurs comprising ten to seventeen known genera. They came into prominence during the Cretaceous period. Spinosaurid fossils have been recovered worldwide, in ...
and ''
Lisboasaurus'', all these taxa together with birds forming a
clade, showing that birds originated from a more basal position than normally assumed.
However, subsequent research has not supported a close relationship between spinosaurids and troodontids and ''Lisboasaurus'' was later shown to be a lizard or a
crocodylomorph
Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction.
During Mesozoic and early Cenozoic times, cro ...
.
Some scientists had suggested that the juvenile specimen of ''Archaeornithoides'' may belong to a previously known species of Mongolian troodontid, either ''
Saurornithoides
''Saurornithoides'' ( ) is a genus of troodontid maniraptoran dinosaur, which lived during the Late Cretaceous period. These creatures were predators, which could run fast on their hind legs and had excellent sight and hearing. The name is deri ...
'' or ''
Byronosaurus''. However, studies of a juvenile ''Byronosaurus'' skull showed that theropod dinosaurs possess many distinctive adult characteristics even as hatchlings or embryos, and that the lack of characters solidly linking ''Archaeornithoides'' to known adult specimens shows that it is probably a distinct species. Bever and Norell (in 2009) found no evidence to support the placement of ''Archaeornithoides'' close to Avialae, and only weak support for the idea that it is a juvenile troodontid.
Paleobiology
Paleopathology
Elzanowski and Wellnhofer noted that the specimen has distinct bite marks while the back of the head fragment was ragged, and suggested that the jaws were bitten off from its braincase by a ''
Deltatheridium
''Deltatheridium'' (meaning ''triangle beast'' or ''delta beast'') is an extinct species of metatherian. It lived in what is now Mongolia during the Upper Cretaceous, ''circa'' 80 million years ago. A study in 2022 strongly suggested that De ...
'' mammal the size of a weasel (adding that these are common in the Bayn Dzak assemblage).
Clark and colleagues (2002) noted that it may have also passed through the digestive tract of the predator before fossilization. If true, this may be the first known evidence 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 Cretace ...
mammals feeding on dinosaurs (see ''
Repenomamus
''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 ...
'').
References
External links
{{Taxonbar, from=Q780065
Prehistoric paravians
Late Cretaceous dinosaurs of Asia
Taxa named by Andrzej Elżanowski
Taxa named by Peter Wellnhofer