Opisthiamimus

Opisthiamimus (lit. 'Opisthias mimic') is an extinct genus of small-bodied eusphenodontian rhynchocephalian from the Upper Jurassic Morrison Formation of Northern Wyoming, United States. The type species, O. gregori, is known from four specimens, which together preserve a nearly complete skeleton. It is amongst the smallest known rhynchocephalians, with a skull length of 2.05 centimetres (0.81 in) and a snout–vent length (the length from the tip of the snout to the cloaca) of around 8.5 centimetres (3.3 in). The genus was described in 2022 by David DeMar, Marc E. H. Jones, and Matthew Carrano. It was found that it was only distantly related to Eilenodon, Theretairus and Opisthias, the other known rhynchocephalians from the Morrison Formation.^[1]

Opisthiamimus Temporal range: Tithonian PreꞒ Ꞓ O S D C P T J K Pg N
Restored skull in lateral view
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Rhynchocephalia
Suborder:	Sphenodontia
Infraorder:	Eusphenodontia
Genus:	†Opisthiamimus DeMar, Jones & Carrano, 2022
Type species
†Opisthiamimus gregori DeMar, Jones & Carrano, 2022[1]

Phylogeny

Cladogram following Sues and Schoch, 2023:^[2]

Rhynchocephalia Wirtembergia hauboldae Gephyrosaurus bridensis Sphenodontia Diphydontosaurus avonis Acrosphenodontia Planocephalosaurus robinsonae Rebbanasaurus jaini Godavarisaurus lateefi Theretairus antiquus Eusphenodontia Polysphenodon mulleri Opisthiamimus gregori Clevosauridae Clevosaurus convallis Clevosaurus brasiliensis Clevosaurus hadroprodon Clevosaurus bairdi Clevosaurus hudsoni Clevosaurus cambrica Neosphenodontia