Acta Palaeontologica Polonica

Redescription of the type specimens for the Late Jurassic rhynchocephalian Opisthias rarus and a new specimen of Theretairus antiquus from Quarry 9, Morrison Formation, Wyoming, USA

Jorge A. Herrera-Flores, Thomas L. Stubbs, and Francisco Sour-Tovar

Acta Palaeontologica Polonica in press
available online 15 Jun 2022 doi:

We reexamine and redescribe the type specimens and other associated material of the Late Jurassic rhynchocephalian Opisthias rarus, from Quarry 9 of the Morrison Formation. We rediscover and describe a fragment of rock matrix belonging to the holotype that is presented for the first time, and we also comment on undescribed material from Quarry 9 that possibly belongs to an unnamed species of Opisthias. In addition, we describe a new specimen of Theretairus antiquus that helps to reject its proposed status as a junior synonym of O. rarus, and contributes to increase the knowledge of the microvertebrate fauna of the Late Jurassic of North America.

Key words: Lepidosauria, Rhynchocephalia, Morrison Formation, Jurassic, Wyoming, USA.

Jorge A. Herrera-Flores [] and Francisco Sour-Tovar [], Museo de Paleontología, Facultad de Ciencias, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04510, Ciudad de México, Mexico. Thomas L. Stubbs [], School of Earth Sciences, University of Bristol, Queens Road, Bristol, BS8 1RJ, UK.

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