Sphenacodontidae, Marsh, 1878 sensu Benson, 2012

Falconnet, Jocelyn, 2015, The sphenacodontid synapsid Neosaurus cynodus, and related material, from the Permo-Carboniferous of France, Acta Palaeontologica Polonica 60 (1), pp. 169-182 : 174

Sphenacodontidae indet. 3

Figs. 3C, D .

Material.—UM 5903, partial right tooth-bearing dentary. Two flat and a rod-like unidentified bones of unknown affinity

“?” in Fig. 3C 2, D 2 ) and a tiny xenacanthid tooth were found during the preparation of UM 5903 . Collected the 9 th of September 1986, by Paul Ellenberger from Saint-Julien, Le Bosc Commune, Hérault Department, Languedoc Region , southern France; α or β bone breccia, lower Viala Formation, Autunian Group, Lodève Basin; Sakmarian, early Permian (see above) .

Description

Dentary.—UM 5903 consists of an incomplete dentigerous posterior portion of a dentary ( Fig. 3C, D ). Its anterior end has been displaced dorsally along two vertical fractures. The deep ventral lamina displays a slight medial curvature that forms the medial wall of the Meckelian canal ( Fig. 3C 2, D 2 ). Dorsally the dentary thickens abruptly to form a slightly ventrally bowed alveolar ridge with a squarish cross section. Its medial surface is covered with numerous, parallel anteroposterior striations of a sutural scar for the coronoids. The anterodorsally oriented line of contact between the anterior and posterior coronoids is preserved on the medial surface of the alveolar ridge. The lateral surface of the dentary is smooth where it is well preserved ( Fig. 3C 1 , D 2 ).

Dentition.—A series of four teeth are preserved as well as three empty alveoli mesial to them, indicating a minimal count of seven teeth. The dentition is subthecodont. Resorption pits are visible at the bases of the first and third preserved teeth and at the mesial, unoccupied position. The teeth show a basal neck constriction below a bulbous, distally recurved crown. The mesiodistal expansion of the crown results in sharp and apparently unserrated edges. The crowns are asymmetrical, with a more bulbous aspect labially than lingually. Distally there is a steady serial decrease in tooth size, which is paralleled by a decrease in recurvature and labiolingual compression of the crowns. Consequently, the most distal tooth has a more conical, bulbous aspect than the others.

Figures

Fig. 3. Unidentified sphenacodontids. A. Sphenacodontidae indet. 1, left dentary (MNHN.F.LOD213), from Saint-Julien, Sakmarian, in lateral view. B. Sphenacodontidae indet. 2, right dentary (UM 5902), from Le Capitoul, Sakmarian, in medial view. C, D. Sphenacodontidae indet. 3, right dentary (UM 5903), from Saint-Julien, Sakmarian, in lateral (C) and medial (D) views. Photographs (C1, D1), explanatory drawings (C2, D2).

Fig. 2. Sphenacodontid synapsid Neosaurus cynodus (Gervais, 1869), holotype (HN004 2009-00-1), from Moissey, Late Gzhelian–Asselian. Schematic comparison between the structure preserved in bone and impression.

Fig. 1. Sphenacodontid synapsid Neosaurus cynodus (Gervais, 1869), holotype, from Moissey, Late Gzhelian–Asselian. A. Left maxilla (HN004 2009- 00-1A) in lateral view. B. Corresponding impression (HN004 2009-00-1B) in lateral view. Drawings by Peggy Vincent.