Beesiiwo cooowuse

Beesiiwo cooowuse is a rhynchosaur named in 2023 from the Popo Agie Formation of Wyoming. Its known sample is small and dominated by jaw bones, yet those fossils carry enough dental and cranial detail to distinguish it from other members of the group. The name Beesiiwo comes from Arapaho and means “big lizard”; the species name refers to the Alcova area. The fossils place a distinct rhynchosaur in a North American Triassic fauna that was long known from an incomplete record. The animal is included in the other fossil reptile catalogue, alongside lineages that are not close relatives.

Quick facts

A new name from the Popo Agie Formation

Adam Fitch and colleagues described Beesiiwo cooowuse in 2023 from the Popo Agie Formation of central Wyoming. The type material is catalogued as USNM 494329. The genus name is derived from Arapaho Beesiiwó, “big lizard”; the species name refers to the Alcova area. The authors worked with several jaw specimens, including referred maxillae from Cottonwood Creek.

The sample is not a buried, complete animal. It consists of separate bones, chiefly from the jaws, collected from a region where Triassic vertebrate remains can be mixed across sites and layers. Assignment to one species depends on matching diagnostic characters, not on geographic proximity alone. The small hypodigm sharply limits claims about the animal's height, limb proportions and total length.

Why the tooth rows matter

Rhynchosaurs had specialised tooth-bearing surfaces that could process plant material. Beesiiwo has jaw features that help separate it from other hyperodapedontines. One detail in the type specimen required careful interpretation: a row of teeth lying medial to two maxillary rows is a fragment of the lower jaw still slotted into a groove, not a third upper row. Several other referred maxillae preserve the expected pattern without that misleading overlap.

This is a useful example of how a fossil's position can create an anatomical illusion. Preparing a specimen and comparing it with other individuals can reveal that apparent extra teeth belong to a different bone. The corrected arrangement affects how researchers describe the jaw and compare it with other rhynchosaur genera.

Relationships and a northern fauna

The original phylogenetic analysis placed Beesiiwo among hyperodapedontine rhynchosaurs and found similarities to the Canadian Oryctorhynchus bairdi. They are close relatives in that analysis, not the same species. The Wyoming animal broadens the known distribution of the group and shows that North America supported both regional and more widely shared rhynchosaur lineages.

Its Carnian age places it in the Late Triassic, when archosauromorphs were diversifying across Pangaea. The Triassic Period saw many reptile groups occupy similar ecosystems. Beesiiwo was a rhynchosaur, not a dinosaur; its presence does not imply that it was an ancestor of later dinosaur groups.

What can be reconstructed?

The jaws directly support a plant-processing feeding apparatus and a taxonomically distinct rhynchosaur. A more complete head is reconstructed by comparison with related animals, and a whole body requires even more inference because no associated limbs or trunk are known for the type. The fossils do not preserve an individual meal, so specific plants remain unknown.

Colour, skin texture, gait and social behaviour are not recorded. An illustration can use the skull profile of related rhynchosaurs to suggest a plausible animal, but it should not make a speculative body look like a complete fossil. Beesiiwo adds a named taxon and a clear jaw anatomy to Wyoming's record; the empty spaces in that record remain scientifically important.