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

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. (2006Gaffney et al. ( , 2011. Characters of Sokatra uniting it with the magnafamily Podocnemidera are: quadratebasisphenoid 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.

Imperfect Isolation: Factors and Filters Shaping Madagascar’s Extant Vertebrate Fauna

“…Eremnochelys from the Late Cretaceous of Madagascar [14] supports this scenario; these fossils represent the only Cretaceous occurrence of a genus currently represented in the extant Malagasy vertebrate fauna [10]. The bothremydid turtle Kinkonychelys is also described from the Late Cretaceous [54], as well as Sokatra , a more basal pelomedusoid [55]. Kinkonychelys is interesting biogeographically in that it is nested within a tribe (Kurmademydini) that is otherwise only known from India, thus reflecting the relatively recent physical connections between Madagascar and the Indian subcontinent (at 85–90 Ma).…”

A toothed turtle from the Late Jurassic of China and the global biogeographic history of turtles

“…10a), a landmass named “Northern Gondwana” [44]. Throughout the mid-Cretaceous numerous stem-pelomedusoid “species pairs” are apparent between northern South America and Africa that highlight the faunal ties between these continents (e.g., Araripemydidae, Cearachelyini, and Euraxemydidae [59, 61]), but focused analysis will be necessary to infer vicariance as the direct cause of speciation within these clades (see also [62]). There currently is no evidence that the primary split of Pelomedusoides into the pelomedusid and podocnemidid lineages was caused by vicariance, as the fossil record of freshwater aquatic pan-podocnemidids is broadly distributed across Northern Gondwana [60].…”

“…9) among morphological phylogenies and that is explicitly justified throughout the main body of the text. We then establish biogeographic patterns among turtles by explicit reference to the following literature: Pan-Chelidae [53, 68, 137]; Pan-Pelomedusoides ([59, 60, 68], with additions from [61, 62, 69, 138], and figured material present in [66]); Paracryptodira ([46, 76, 79], with additions from [77, 81, 139, 140]); Pan-Cryptodira/Cryptodira ([16, 46, 84, 85, 87, 141], with additions from [86, 107]); Meiolaniformes ([5, 68]; with additions from [26, 41, 43, 98, 99]); Helochelydridae [100]; and Sichuanchelyidae [16, 102]. …”

Atolchelys lepida, a new side-necked turtle from the Early Cretaceous of Brazil and the age of crown Pleurodira

“…nov., it was included in the most recent published character/ taxon matrix [2], including subsequent additions and modifications proposed [5,11,18]. The cladistic analysis was performed using TNT [19] …”

“…Regardless of the discussion on the phylogeny of stem turtles [1][2][3][4][5][6][7][8], the Triassic Proterochersis robusta has been consistently positioned outside of this clade in recent studies [1,6,8] and the stem lineage is therefore only populated by the clade Platychelyidae [1][2][3][4][5][6][7][8][9][10][11][12].…”