silesaurid
Silesauridae is an extinct family of Triassic dinosauriforms. It is most commonly considered to be a clade of non-dinosaur dinosauriforms, and the sister group of dinosaurs. Some studies have instead suggested that most or all silesaurids compri ...
Late Triassic
The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...
Cooper Canyon Formation
The Cooper Canyon Formation is a geological formation of Norian age in Texas and New Mexico.Weishampel, David B; et al. (2004).Dinosaur distribution (Late Triassic, North America)" In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (e ...
of western Texas.
Etymology
''Soumyasaurus'' is named in honor of Sankar Chatterjee's oldest son, Soumya (likewise, the
shuvosaurid
Shuvosauridae is an extinct family (biology), family of theropod-like pseudosuchians within the clade Poposauroidea. Shuvosaurids existed in North America (United States) and South America (Argentina) during the Late Triassic period (late Carnian ...
pseudosuchian
Pseudosuchia is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely related to crocodilians than to birds. Pseudosuchians are also informally known as "crocodilian-line archosaurs". Prior to ...
''
Shuvosaurus
''Shuvosaurus'' (meaning "Shuvo's lizard") is a genus of beaked reptile from the Late Triassic of western Texas. Despite looking superficially similar to a theropod dinosaur, it is actually more closely related to crocodilians.
Discovery and ...
'' was named for another of Chatterjee's sons, Shuvo). The specific epithet ''aenigmaticus'' derives from the
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
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 anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
, 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
''Asilisaurus'' ( ); from Swahili, ''asili'' ("ancestor" or "foundation"), and Greek, (, "lizard") is an extinct genus of silesaurid archosaur. The type species is ''Asilisaurus kongwe.'' ''Asilisaurus'' fossils were uncovered in the Manda Bed ...
,'' 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 The Meckelian groove (or Meckel's groove, Meckelian fossa, or Meckelian foramen, or Meckelian canal) is an opening in the medial (inner) surface of the mandible (lower jaw) which exposes the Meckelian cartilage.
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 extinct genus of archosauriform from the Middle Triassic of South Africa. It was a small reptile that lived between 245-230 million years ago, and was close to ...
'' 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 ...
The ''Soumyasaurus'' holotype was found in association with other specimens in an assemblage catalogued under TTU P-11254, including a specimen of '' Vancleavea'' (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 mammal has ...
and dentary of ''Technosaurus'' was discovered with posterior jaw bones now known to be from ''
Shuvosaurus
''Shuvosaurus'' (meaning "Shuvo's lizard") is a genus of beaked reptile from the Late Triassic of western Texas. Despite looking superficially similar to a theropod dinosaur, it is actually more closely related to crocodilians.
Discovery and ...
''. It is apparent that the remains labelled TTU P-11254 were brought together in association by similar
taphonomic
Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Efremov t ...
agents, which are inconsistent with previous suggestions of a rapid flooding event.