Theretairus antiquus Simpson, 1926

Herrera-Flores, Jorge A., Stubbs, Thomas L. & Sour-Tovar, Francisco, 2022, 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, Acta Palaeontologica Polonica 67 (3), pp. 623-630 : 628

Theretairus antiquus Simpson, 1926

Fig. 2E .

Material. — USNM 26088 , a fragment of a left dentary with remains of two caniniform teeth, one of them complete from Quarry 9, Como Bluff , Wyoming, USA; upper Kimmeridgian / lower Tithonian (Upper Jurassic) .

Description. —USNM 26088 is a fragment of the symphyseal region of a left dentary, that preserves remains of two large caniniform teeth and four or five smaller alternate hatchling teeth. The mesialmost caniniform tooth is broken at the base of the tooth crown, but remains of the tooth neck are well preserved and show an oval and slightly curved shape ( Fig. 2E ). The distalmost caniniform is complete and with a marked conical blade-like shape; it is a high, pointy, slightly striated and notably curved element, with a curvature of about 70°. Serrations on the mesial and distal cutting edges of the caniniform tooth are not present. Alternate teeth are small, conical and all of them are broken at the top of the crown. The mandibular symphysis is robust, curved and with a marked ventral projection, pointy and curved. In labial view, five mental foramens are present, the three foramens closer to the mandibular symphysis are small and rounded, and the other two are larger and oval. In lingual view, the Meckelian groove is open and notably wide. Length as preserved is 5.7 mm.

Stratigraphic and geographic range.—Upper Kimmeridgian–lower Tithonian (Upper Jurassic), Quarry 9, Como Bluff, Wyoming, USA

Figures

Fig. 2. Teeth of rhynchocephalians Opisthias sp. (A–D) and Theretairus antiquus Simpson, 1926 (E) from Quarry 9, Como Bluff, Wyoming, USA, Upper Jurassic. A. USNM 6126, right dentary fragment with a relatively complete coronoid process in labial view. B. USNM 26080, fragment of palatine in?lingual view with four teeth attached. C. USNM 508532, rock matrix with fragments of right maxilla in lingual view (C1), close-up detail (C2), maxillary teeth (C3). D. USNM 7767 and USNM 26086, fragments of a right dentary, in lingual (D1), labial (D2), and occlusal (D3) views, close-up detail of the four distalmost additional teeth (D3), close-up detail of the four distalmost additional teeth in labial (D4) and lingual (D5) views. E. USNM 26088, anterior fragment of a left dentary, in labial (E1), lingual (E2), and occlusal (E3) views.