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 compr ...
dinosauriform
Dinosauromorpha is a clade of avemetatarsalian archosaurs (reptiles closer to birds than to crocodilians) that includes the Dinosauria (dinosaurs) and some of their close relatives. It was originally defined to include dinosauriforms and lager ...
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 ...
(
Norian
The Norian is a division of the Triassic Period. It has the rank of an age ( geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.
Stratigraphic ...
)
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 (ed ...
of western Texas.
Etymology
''Soumyasaurus'' is named in honor of Sankar Chatterjee's oldest son, Soumya (likewise, the shuvosaurid
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'' was named for another of Chatterjee's sons, Shuvo). The
specific epithet
In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...
''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 ...
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
Archosauriformes (Greek for 'ruling lizards', and Latin for 'form') is a clade of diapsid reptiles that developed from archosauromorph ancestors some time in the Latest Permian (roughly 252 million years ago). It was defined by Jacques Gauthie ...
''
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 t ...
'' 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
Dinosauromorpha is a clade of avemetatarsalian archosaurs (reptiles closer to birds than to crocodilians) that includes the Dinosauria (dinosaurs) and some of their close relatives. It was originally defined to include dinosauriforms and lage ...
.
Taphonomy
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''. 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 Efrem ...
agents, which are inconsistent with previous suggestions of a rapid flooding event.