''Soumyasaurus'' is a small silesaurid dinosauriform from the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...

(

Norian The Norian is a division of the Triassic geological period, Period. It has the rank of an age (geology), age (geochronology) or stage (stratigraphy), stage (chronostratigraphy). It lasted from ~227.3 to Mya (unit), million years ago. It was prec ...

) Cooper Canyon Formation of western Texas.

Etymology

''Soumyasaurus'' is named in honor of Sankar Chatterjee's oldest son, Soumya (likewise, the shuvosaurid pseudosuchian '' Shuvosaurus'' was named for another of Chatterjee's sons, Shuvo). The

specific epithet In Taxonomy (biology), taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin gramm ...

''aenigmaticus'' derives from the

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

word ''aenigma'', meaning "enigma or riddle", referring to the poor preservation of the fossil.

Description

The only known element of ''Soumyasaurus'' is a small (less than 3 cm long), poorly preserved left

dentary In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone ...

, missing its anterior end and containing some teeth with an estimated tooth count of at least 15. ''Soumyasaurus'' is mostly characterised by its teeth, which are fused to the jaw bone by a rim fibrous bone at their bases (ankylothecodont), a characteristic trait of silesaurids. Unlike the typically leaf-shaped teeth of other silesaurids, the teeth of ''Soumyasaurus'' are smooth and conical, resembling those of '' Asilisaurus,'' and are readily distinguishable from the uniquely triangular, possibly tricuspid teeth of the contemporary silesaurid '' Technosaurus''. Unfortunately, it is unknown if ''Soumyasaurus'' had small serrations like ''Asilisaurus'', as these portions of the teeth are either missing or badly damaged, and is only distinguished from it by the lower position of the Meckelian groove on the inside of the jaw. The tip of the jaw, known to be toothless and possibly supporting a beak in other silesaurids, is missing and so its shape is unknown for ''Soumyasaurus''. ''Soumyasaurus'' was described as "minute" by Sarıgül and colleagues, inferring a small body size from the length of the preserved dentary, certainly smaller in size than the contemporary ''Technosaurus''.

Classification

A phylogenetic analysis was performed which recovered ''Soumyasaurus'' as a silesaurid, however its relationships amongst Silesauridae were unresolved. The coeval ''Technosaurus'' was not included in this analysis, as including the two taxa together unusually resulted with the archosauriform ''

Euparkeria ''Euparkeria'' (; meaning "Parker's good animal", named in honor of W. K. Parker) is an Extinction, extinct genus of archosauriform reptile from the Triassic of South Africa. ''Euparkeria'' is close to the ancestry of Archosauria, the reptile gro ...

'' as the

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to a polytomy containing the two dinosauriforms.

Taphonomy

The ''Soumyasaurus'' holotype was found in association with other specimens in an assemblage catalogued under TTU P-11254, including a specimen of ''

Vancleavea ''Vancleavea'' is a genus of extinct, armoured, non-archosaurian archosauriforms from the Late Triassic of western North America. The type species, type and only known species is ''V. campi'', named by Robert Long & Phillip A Murry in 1995 in pa ...

'' (TTU P-11254a), indeterminate archosauromorph remains (TTU P-11254c-e), and remains indeterminate beyond Sauria (TTU P-11254f-i). This is similar to another assemblage at the Post Quarry where the holotype

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 mammals h ...

and dentary of ''Technosaurus'' was discovered with posterior jaw bones now known to be from '' Shuvosaurus''. It is apparent that the remains labelled TTU P-11254 were brought together in association by similar taphonomic agents, which are inconsistent with previous suggestions of a rapid flooding event.

References

{{Taxonbar, from=Q56233078 Silesauridae Norian genera Late Triassic archosaurs of North America Triassic geology of Texas Fossil taxa described in 2018