Side-necked turtle lower jaws (Podocnemididae, Bothremydidae) from the late Cretaceous Maevarano Formation of Madagascar. American Museum novitates ; no. 3397

Abstract

Two lower jaws from the upper part (early Maastrichtian) of the late Cretaceous Maevarano Formation in the Mahajanga Basin, northwestern Madagascar, are identified as belonging to side-necked turtles (Pleurodira). A nearly complete lower jaw is identified as cf. Erymnochelys because of its close resemblance to the living Malagasy Erymnochelys madagascariensis. Both uniquely possess the combination of a posteriorly directed processus retroarticularis and a nearly identical triturating surface that is narrow anteriorly with a horizontal labial ridge and a dorsally rising lingual ridge. A second specimen, consisting of an incomplete symphyseal region, is questionably identified as Bothremydidae on the basis of a thick wedge-shaped symphysis with partial or complete pits on the rami. The cf. Erymnochelys specimen is the oldest record of Erymnochelys or a taxon very similar to it, and it indicates the persistence of a Mesozoic element in the extant Malagasy turtle fauna. The possible bothremydid jaw suggests a more cosmopolitan element now extinct.