Sinovenator

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Sinovenator
Temporal range: Early Cretaceous, 125Ma
Fossil Japan.jpg
Specimen IVPP V14322
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Dinosauria
Order: Saurischia
Suborder: Theropoda
Family: Troodontidae
Genus: Sinovenator
Xu et al., 2002
Species
  • S. changii Xu et al., 2002 (type)

Sinovenator (meaning "Chinese hunter") is a genus of troodontid dinosaur from China. It is from the early Cretaceous Period.

Discovery and naming[edit]

Two fossils were originally found in the Lujiatun Beds of the lower Yixian Formation in China, dating from about 125 million years ago (Ma) during the Aptian age.[1]

The type species, Sinovenator changii, was named and described by Xu Xing, Mark Norell, Wang, Makovicky and Wu in 2002.[2] The generic name is derived from the Latin words venator, meaning "hunter" and Sinae, "the Chinese". The specific name honours the Chinese paleontologist Meemann Chang.[2] As Chang is a female researcher, the epithet should have been "changae". However, such mistakes cannot be emended according to the rules of the ICZN and therefore forms such as "Sinovenator changae" or "Sinovenator changiae" that sometimes appear in the literature, are incorrect.

The type specimen or holotype of Sinovenator changii is IVPP 12615, a partial skull and disarticulated skeleton. An additional specimen was by the original publication scientifically described and assigned as the paratype of the species: an incomplete but articulated postcranial skeleton, numbered IVPP 12583. A third specimen was referred: IVPP V14322, a fragmentary skeleton. All three are in the collection of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, China. However, Sinovenator fossils appear to be common in the Lujiatun Beds. In a 2006 survey of the Jehol Biota, Xu and Norell reported that hundreds of undescribed specimens are known.[3] The fossils have been preserved three-dimensionally, not strongly compressed on a slab.

In 2014, the wrist of one specimen was described, IVPP V14009, an adult.[4]

Description[edit]

Size of Sinovenator compared to a human

The holotype individual of Sinovenator was about the size of a chicken, less than a metre long.[2] In 2010, Gregory S. Paul estimated the weight of a one metre long individual at 2.5 kilogrammes.[5] However, the holotype and paratype are subadults; specimens are known with about twice their length.

In the original description some distinguishing traits or autapomorphies were established. The front edge of the antorbital fenestra, the large skull opening in front of the eye socket, is straight and vertically oriented. The frontal bone shows a vertical ridge touching the lacrimal bone. The surangular in the lower jaw has a T-shaped cross-section. The shinbone has a vertical ridge on the upper outer side, the crista cnemialis, touching a lower vertical ridge, the crista fibularis.[2]

There is a number of other notable traits. The upper branch of the praemaxilla excludes the maxilla from the nostril. The premaxillary teeth lack denticles; those on the maxillary teeth are small. The maxillary tooth row is positioned at some distance from the jaw rim. A fenestra promaxillaris is present. The branch of the jugal towards the postorbital is long, slender and inclined to the rear. The foramen magnum is much larger than the occipital condyle. The braincase lacks a recessus suboticus and a crista otosphenoidalis. The rear of the pterygoid has a secondary, rod-like, process. The front dentary teeth are closely packed. The rear of the surangular is extraordinarily deep.[2]

Five sacrals are present, those of the middle being clearly larger. The ilium is relatively small. The ischium is bird-like: small with a low obturator process and processes on the upper and lower rear edge. The shinbone is wide at the top and has a roughly rectangular lower joint surface. The fourth metatarsal is not strongly developed but the second metatarsal is small. The third metatarsal is pinched at the top but still visible at the upper front of the metatarsus, conforming to the subarctometatarsal condition.[2]

Phylogeny[edit]

Sinovenator was in 2002 placed in the Troodontidae.

Sinovenator is a basal or "primitive" troodontid, and shares features with the most basal dromaeosaurids and Avialae. It thus was one of the first fossil specimens conclusively demonstrating the close relation of these three groups in the over-arching Paraves. A typical basal trait is the orientation of the pubic bone to the rear, similar to the situation in the Dromaeosauridae and basal birds. This proves that the orientation to the front with later troodontids, is a reversal and not a trait directly inherited from older theropods that also possess a forward pointing pubic bone. Another basal character is the lack of a bulla, a swollen region on the underside of the braincase. This indicates that the similar bulla with the Ornithomimosauria presents a case of parallel evolution and is not a proof for a Bullatosauria, an earlier presumed close relationship between troodontids and ornithomimosaurs.

Originally, the basal position of Sinovenator seemed to be corroborated by a very high age, the fossils being assumed to date from the Hauterivian. Later research however, indicated that the layers were younger.

The cladogram below shows the position of Sinovenator in the evolutionary tree according to an analysis from 2012 by Turner, Makovicky and Norell.[6]

Paraves

Epidexipteryx




Avialae


Deinonychosauria

Dromaeosauridae


Troodontidae


Anchiornis



Xiaotingia




Jinfengopteryginae

IGM 100/1323




IGM 100/1126



Jinfengopteryx







Mei




Sinovenator



Xixiasaurus






IGM 100/44




Byronosaurus




Sinornithoides




Troodon




Saurornithoides



Zanabazar













References[edit]

  1. ^ Zhou, Z. (2006). "Evolutionary radiation of the Jehol Biota: chronological and ecological perspectives." Geological Journal, 41: 377–393.
  2. ^ a b c d e f Xu, Xing, Norell, Mark A., Wang, Xiao-Lin, Makovicky, Peter J., Wu, Xiao-Chun. (2002) "A basal troodontid from the Early Cretaceous of China". Nature 415: 780-784. 14 February 2002
  3. ^ Xu, X. and Norell, M.A. (2006). "Non-Avian dinosaur fossils from the Lower Cretaceous Jehol Group of western Liaoning, China."Geological Journal, 41: 419–437.
  4. ^ Xing Xu, Fenglu Han & Qi Zhao, 2014, "Homologies and homeotic transformation of the theropod ‘semilunate’ carpal", Scientific Reports 4, Article number: 6042 Doi:10.1038/srep06042
  5. ^ Paul, G.S., 2010, The Princeton Field Guide to Dinosaurs, Princeton University Press p. 140
  6. ^ Turner, A. H.; Makovicky, P. J.; Norell, M. A. (2012). "A Review of Dromaeosaurid Systematics and Paravian Phylogeny". Bulletin of the American Museum of Natural History 371: 1. doi:10.1206/748.1.  edit

External links[edit]