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

Eugene S. Gaffney,David W. Krause

doi:10.1206/3728.2

Eugene S. Gaffney, David W. Krause

Open Access

https://doi.org/10.1206/3728.2

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Abstract

Sokatra antitra, n. gen. et sp., is a new side-necked turtle from the Maastrichtian (Upper Cretaceous) Maevarano Formation, Mahajanga Basin, northwestern Madagascar. Sokatra antitra is based on a series of incomplete skulls: a partial skull that lacks the premaxillae and some of the basicranium, a partial skull that has a complete ear region and partial basicranium, and other isolated specimens, including dentaries. Although this species exhibits some features of the North African and Brazilian Euraxemydidae, it does not belong to this family, but instead it is the sister taxon of the magnafamily Podocnemidera of Gaffney et al. (2006, 2011). Characters of Sokatra uniting it with the magnafamily Podocnemidera are: quadrate-basisphenoid contact, ventral covering of processus interfenestralis of opisthotic, and at least half of prootic covered ventrally The laterally open foramen jugulare posterius and the distinct accessory ridge on the maxilla are characteristic, but not unique, features shared with members of the Euraxemydidae. The presence of a small wall posterior to the columellae auris and medial to the incisura columellae auris and the formation of the foramen posterius canalis carotici interni by both the prootic and quadrate are unique to Sokatra. In a PAUP analysis using the character matrix from Gaffney et al. (2006), Sokatra resolves as: (Pelomedusidae, Araripemys (Sokatra (Euraxemydidae (Bothremydidae, Podocnemididae)))). The deep phylogenetic roots of Sokatra indicates the presence of its lineage on Madagascar prior to the beginning of the Late Cretaceous.

Highlights

Turtles split into two main groups, cryptodires and pleurodires, before the Late Triassic (Galfney, 1990; Galfney et al, 2006; Galfney and Jenkins, 2010)
The recently discovered morphological diversity of pleurodiran skulls demonstrates a level of eco¬ logical diversity previously unknown (Gaffney et al, 2006, 2011)
Sokatra antitra is the fourth pleurodiran taxon to be recognized from the Late Cretaceous of Madagascar, the others being relatively derived forms (Gaffney and Forster, 2003; Gaffney et al, 2009)

Summary

Introduction

Turtles split into two main groups, cryptodires and pleurodires, before the Late Triassic (Galfney, 1990; Galfney et al, 2006; Galfney and Jenkins, 2010). Structures of vertical plate: The maxilla in Sokatra is similar to that in pelomedusids and euraxemydids, forming the ventral margin of the orbit, the lateral margin of the apertura narium externa, and the anterior margin of the cheek emargination. Structures on ventral surface: In the quadrates of FMNH PR 2649 and UA 9769, there is a notch for the foramen posterius canalis carotici interni that is formed between the quadrate posteriorly and the prootic anteriorly.

Results

Conclusion