''Arvinachelys goldeni'' is an extinct baenid

turtle Turtles are an order of reptiles known as Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked tu ...

from the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...

. ''A. goldeni'' is notable among turtles for the presence of two nasal openings instead of one, giving it a vaguely pig-nosed appearance in life.

Description

The holotype, UMNH VP 21151, is a largely completed skeleton, including the shell and skull, belonging to an animal about 60 centimeters long. Remains previously ascribed to other baenid turtles are now recognised to belong to the animal.

Phylogenetics

''Arvinachelys'' bears most of the synapomorphies characteristic of

Baenidae Baenidae is an extinct family of paracryptodiran turtles known from the Early Cretaceous to Eocene of North America. While during the Early Cretaceous they are found across North America, during the Late Cretaceous they are only found in Laramidi ...

. It is described as a sister taxon to '' Hayemys''; given the latter's position as a

lazarus taxon In paleontology, a Lazarus taxon (plural ''taxa'') is a taxon that disappears for one or more periods from the fossil record, only to appear again later. Likewise in conservation biology and ecology, it can refer to species or populations tha ...

basal to the rest of Baenidae, ''Arvinachelys''' discovery extends its branch of the family tree back into the

Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campanian s ...

. However, ''Arvinachelys''' discovery may indicate that a reevaluation of Baenidae as a whole is necessary, as several remains from the region have been reassigned to this genus.

Biology

''Arvinachelys'', like typical baenids, was an aquatic or semi-aquatic animal, bearing typical characteristics of aquatic turtles, including a hydrodynamic shell and broad, paddle-like limbs. Baenids are the most diverse type of turtle in the north hemisphere during the

, being extremely speciose and probably occupying a variety of ecological niches. Its nostrils, superficially reminiscent of a pig's snout, are highly atypical for baenids and turtles in general, and might have played a role in its lifestyle.

Ecology

''Arvinachelys'' hails from the

Kaiparowits Formation The Kaiparowits Formation is a sedimentary rock formation found in the Kaiparowits Plateau in Grand Staircase–Escalante National Monument, in the southern part of Utah in the western United States. It is over 2800 feet (850 m) thick, and is Ca ...

, which also includes several

dinosaurs Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

such as ''

Teratophoneus ''Teratophoneus'' ("monstrous murderer"; Greek: ''teras'', "monster" and ''phoneus'', "murderer") is a genus of tyrannosaurid dinosaur which lived during the late Cretaceous period (late Campanian age, about 77 to 76 million years ago) in what i ...

'' and ''

Parasaurolophus ''Parasaurolophus'' (; meaning "near crested lizard" in reference to '' Saurolophus)'' is a genus of herbivorous hadrosaurid ornithopod dinosaur that lived in what is now North America and possibly Asia during the Late Cretaceous Period, abou ...

''. In particular, ''Arvinachelys'' showcases further the high endemism of the local fauna, implying some sort of biogeographical isolation.

References

{{Taxonbar, from=Q21402882 Baenidae Prehistoric turtle genera Campanian genera Late Cretaceous turtles of North America Paleontology in Utah Kaiparowits Formation Fossil taxa described in 2015