''Heishanosaurus'' is an extinct genus of

choristodere Choristodera (from the Greek χωριστός ''chōristos'' + δέρη ''dérē'', 'separated neck') is an extinct order of semiaquatic diapsid reptiles that ranged from the Middle Jurassic, or possibly Triassic, to the Miocene (168 to 20 or p ...

reptile from the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

of China. The type and currently only known species is ''Heishanosaurus pygmaeus''. It is unusual as it is much more primitive than other known choristoderes from the Early Cretaceous of Asia, and retains many

plesiomorphic 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, an ...

characters.

Discovery

The type specimens are represented by the blocks IVPP V25322, 25323 and 25324, were discovered in September 2003 at the Badaohao locality, in

Heishan County Heishan () is a county of north-central Liaoning, People's Republic of China. It is under the administration and occupies the northeastern corner of Jinzhou City. Administrative divisions Source: There are 17 towns, six townships, and two ethni ...

Liaoning Province ) , image_skyline = , image_alt = , image_caption = Clockwise: Mukden Palace in Shenyang, Xinghai Square in Dalian, Dalian coast, Yalu River at Dandong , image_map = Liaoning in China (+all claims hatched).svg , ...

, China, in sediments belonging to the Shahai Formation. The Shahai Formation is generally thought to overlie the

Jiufotang Formation The Jiufotang Formation () is an Early Cretaceous geological formation in Chaoyang, Liaoning which has yielded fossils of feathered dinosaurs, primitive birds, pterosaurs, and other organisms (see Jehol Biota). It is a member of the Jehol group. T ...

and has an uncertain

Aptian The Aptian is an age (geology), age in the geologic timescale or a stage (stratigraphy), stage in the stratigraphic column. It is a subdivision of the Early Cretaceous, Early or Lower Cretaceous epoch (geology), Epoch or series (stratigraphy), S ...

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

age, based on the

radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to Chronological dating, date materials such as Rock (geology), rocks or carbon, in which trace radioactive impurity, impurities were selectively incorporat ...

of the Jiufotang Formation. The remains are disarticulated inside the blocks, and were scanned using microcomputed tomography.

Description

Remains include disarticulated skull bones, along with limited postcranial remains. Based on the size of the skull, the animal likely around 16 cm long, similar in size to ''

Cteniogenys ''Cteniogenys'' is a genus of choristodere, a morphologically diverse group of aquatic reptiles. It is part of the monotypic family Cteniogenidae. The type and only named species, ''C. antiquus'', was named in 1928 by Charles W. Gilmore. The h ...

''. The skull retains an open lower

temporal fenestra Temporal fenestrae are openings in the temporal region of the skull of some amniotes, behind the orbit (eye socket). These openings have historically been used to track the evolution and affinities of reptiles. Temporal fenestrae are commonly (al ...

, as in ''Cteniogenys'', ''

Coeruleodraco ''Coeruleodraco'' is an extinct genus of choristoderan known from the Late Jurassic ( Oxfordian) Tiaojishan Formation in China. ''Coeruleodraco'' is significant as the most complete Jurassic choristodere taxon, as the only other named Jurassic ch ...

'' and neochoristoderes, but which is closed in the majority of Early Cretaceous Asian "non-neochoristoderans".

Phylogeny

In a strict consensus phylogenetic analysis, it was recovered as a basal choristodere, more derived than ''Cteniogenys'', but more primitive than neochoristoderes or the weakly supported clade containing all other Asian Early Cretaceous "non-neochoristoderans" with closed lower temporal fenestrae, which was informally named the "allochoristoderes" in the study. ''Heishanosaurus'' was recovered in a

polytomy An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tree ...

with the Late Jurassic ''Coeruleodraco'', despite its much younger age.

References

{{Taxonbar , from= Q105477518 Choristodera Fossil taxa described in 2020 Prehistoric reptile genera