Side-Necked Turtle Lower Jaws (Podocnemididae, Bothremydidae) from the Late Cretaceous Maevarano Formation of Madagascar

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.

Evolution of the Side-Necked Turtles: The Family Podocnemididae

“…As part of our Podocnemididae project, the reader is directed to earlier papers on podocnemidids in this series: Gaffney et al (1998), , Gaffney and Wood (2002), Gaffney and Forster (2003), Gaffney et al (2006), Gaffney et al (2008), and Meylan et al (2009). The cranial morphology of turtles and an illustrated compilation of morphologic terminology can be found in Gaffney (1972Gaffney ( , 1979.…”

“…Discussion: This character is described and discussed in Gaffney et al (2006: 617; see also Gaffney et al, 1998;Gaffney and Forster, 2003). The long, posteroventrally directed processus retroarticularis is a feature of the epifamily Podocnemidinura.…”

Sokatra, a New Side-Necked Turtle (Late Cretaceous, Madagascar) and the Diversification of the Main Groups of Pelomedusoides

“…It includes a close relative of Erymnochelys madagascariensis but also shows the presence of at least two species of the extinct family Bothremydidae (Gaffney and Forster, 2003;Gaffney et al, 2009). In this paper we add to the diversity of Late Cretaceous pleurodirans from Madagascar by describing a new member of the Pelomedusoides, Sokatra antitra.…”

“…The fossil record of pleurodires from Madagascar (Lapparent de Broin, 2000;Gaffney and Forster, 2003;Gaffney et al, 2009) is essentially restricted to the Late Cretaceous (but see Samonds et al, 2009, for report of unidentified Eocene turtles). It includes a close relative of Erymnochelys madagascariensis but also shows the presence of at least two species of the extinct family Bothremydidae (Gaffney and Forster, 2003;Gaffney et al, 2009).…”

“…The classification is abbreviated in that not all taxa included in Gaffney et al (2006) are shown. For those interested in Madagascar, however, we include the three other known turtle taxa previously identified from the Late Cretaceous of Madagascar; they are all podocnemidids or bothremydids (Gaffney and Forster, 2003;Gaffney et al, 2009). Sokatra is not placed in a new higher taxon in this classification; it is indicated as the sister group to the remaining Podocnemidera by indentation.…”