''Agkistrognathus'' is an extinct genus of

thalattosaur Thalattosauria (Greek for "sea lizards") is an extinct order of marine reptiles that lived during the Triassic Period. Thalattosaurs were diverse in size and shape, and are divided into two superfamilies: Askeptosauroidea and Thalattosauroidea. ...

ian which lived in the early to middle

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

. There is only one species known in this genus, ''Agkistrognathus campbelli''. The genus name translates to "hook jaw" while the species name refers to Bob Campbell, who discovered the only known specimen.

Description

''Agkistrognathus'' is a thalattosaurian, a group of marine reptiles with long, paddle-like tails and independently movable digits. ''Agkistrognathus'' can be distinguished from other thalattosaurians due to having conical, closely spaced teeth which are smallest in the middle of the jaw and deep

dentaries 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 i ...

with hooked front ends. These features may have given it a powerful bite . The dentaries are also bifurcated at their posterior ends, with both forks being the same length but the dorsal one being much deeper. This combination is unique to ''Agkistrognathus''. ''Agkistrognathus'' is probably closely related to ''

Thalattosaurus ''Thalattosaurus'' (pronounced: , from and ) is an extinct genus of marine reptile in the family Thalattosauroidea. Known exclusively from the Triassic period, it was a long shellfish-eating diapsid with paddle-like limbs and a down-turned ros ...

'' and ''

Paralonectes ''Paralonectes'' is an extinct genus of thalattosaurian reptile which lived in the Early or Middle Triassic of what is today British Columbia. The type and only species is ''P. merriami''. The genus name is derived from Ancient Greek and means " ...

'' due to having conical teeth at the

mandibular symphysis In human anatomy, the facial skeleton of the skull the external surface of the mandible is marked in the median line by a faint ridge, indicating the mandibular symphysis (Latin: ''symphysis menti'') or line of junction where the two lateral ha ...

History

''Agkistrognathus'' was discovered in the

Sulphur Mountain formation The Sulphur Mountain Formation is a geologic formation of Early to Middle Triassic age. It is present on the western edge of the Western Canada Sedimentary Basin in the foothills and Rocky Mountains of western Alberta and northeastern British Co ...

in eastern British Columbia. It was described in a 1993 article along with several other new thalattosaurs from the same locality: ''Thalattosaurus borealis, Paralonectes merriami'', an additional specimen referred to ''Paralonectes'', and an unnamed species. Based on the

conodont Conodonts, are an extinct group of marine jawless vertebrates belonging to the class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning " cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known from their hard ...

fauna, this locality is believed to be early to mid triassic in age, probably from the late

Anisian In the geologic timescale, the Anisian is the lower stage (stratigraphy), stage or earliest geologic age, age of the Middle Triassic series (stratigraphy), series or geologic epoch, epoch and lasted from million years ago until million years ag ...

to early

Ladinian The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between Ma and ~237 Ma (million years ago). The Ladinian was preceded by the Anisian and succeeded by the Carnian (part of the Upper or Late Triassic ...

. Thus, these species may be the oldest thalattosaurians known. The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

of ''Agkistrognathus campbelli'', TMP 89.127.6, is a disarticulated skull including a

maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...

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 ...

vomer The vomer (; ) is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones. The vomer forms ...

, dentaries, angular,

splenial The splenial is a small bone in the lower jaw of reptile Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology ...

, and other unidentified fragments.

References

{{Taxonbar, from=Q3606585 Thalattosauria Middle Triassic reptiles of North America Prehistoric reptile genera