Camptognathosaurus parisiensis

Augé, Marc Louis, Dion, Michaël & Phélizon, Alain, 2021, The lizard (Reptilia, Squamata) assemblage from the Paleocene of Montchenot (Paris Basin, MP 6), Geodiversitas 43 (17), pp. 645-661 : 653

cf. Camptognathosaurus parisiensis Folie, Smith & Smith, 2013

MATERIAL EXAMINED. — MNHN.F.MTC238 ( Fig. 7 ), posterior part of a left dentary (L = 3.2 mm); it preserves only two tooth positions with one complete tooth.

DESCRIPTION

The sulcus Meckeli (its posterior part) opens widely and faces medio-ventrally. This fossa is divided by a well-developed, subvertical intramandibular septum that separate the alveolar canal from the Meckelian canal; Its ventral margin is fused with the internal, ventral wall of the dentary and the septum terminates at, or near, the level of the posteriormost tooth (see discussion on this position in Čerňanský 2019). Its posterior margin is deeply incised.

Overhanging the Meckelian fossa, the subdental shelf is not arched, its mesial border is nearly vertical and terminates at the level of the last tooth position. Immediately behind this tooth, the dentary bears a strong coronoid process that projects posterodorsally.

The single preserved tooth (certainly the penultimate one) is heavily built, subcylindrical and slightly tapers towards the crown. The tooth base is broad and nearly half of the tooth height projects above the dental parapet. The apex is somewhat eroded and it seems rather rounded. The tooth implantation is pleurodont and a sulcus dentalis may run along the medial side of the tooth raw although the presence of sediment casts some doubts on this observation.

DISCUSSION AND COMPARISONS

Despite the fragmentary nature of this fossil, the presence of a well-developed intramandibular septum fused with the ventral wall of the dentary and of a strongly developed coronoid process are features common to many amphisbaenian lizards, though they may be present in some skinks like Ophiomorus (Čerňanský pers. comm.). In addition, the robust tooth shows typical amphisbaenian morphology ( Čerňanský et al. 2015) with simplification of the tooth crown ( Smith 2009), features obviously absent in scincid lizards As a last point, this dentary is very similar to other dentaries from the late Paleocene of Rivecourt Petit Pâtis and Cernay-lès-Reims attributed to the amphisbaenian taxon Camptognathosaurus parisiensis ( Folie et al. 2013) . The dentary from Montchenot shares two diagnostic features with this species: teeth bulbous that project above the dental parapet nearly half of their height. However, due to the fragmentary nature and the poor preservation of the specimen, this referral cannot be accepted without some reservations.

Figures

FIG. 7. — Cf.CamptognatosaurusparisiensisFolie,Smith & Smith,2013,posterior part of a left dentary,MNHN.F.MTC238:A, labial view;B, lingual view.Scale bar:1 mm.