A review of the fossil record of turtles of the clade Thalassochelydia

Abstract

POSTPRINTThis is a postprint of the following peer-reviewed publication: AbstractThe Late Jurassic (Oxfordian to Tithonian) fossil record of Europe and South America has yielded a particularly rich assemblage of aquatic pan-cryptodiran turtles that are herein tentatively hypothesized to form a monophyletic group named Thalassochelydia. Thalassochelydians were traditionally referred to three families, Eurysternidae, Plesiochelyidae, and Thalassemydidae, but the current understanding of phylogenetic relationships is insufficient to support the monophyly of either group. Given their pervasive usage in the literature, however, these three names are herein retained informally. Relationships with marine turtles from the Cretaceous have been suggested in the past, but these hypotheses still lack strong character support. Thalassochelydians are universally found in near-shore marine sediments and show adaptations to aquatic habitats, but isotopic evidence hints at a broad spectrum of specializations ranging from freshwater aquatic to fully marine. A taxonomic review of the group concludes that of 68 named taxa, 27 are nomina valida, 18 are nomina invalida, 18 are nomina dubia, and 5 nomina oblita.

New material of named fossil turtles from the Late Jurassic (late Kimmeridgian) of Wattendorf, Germany

“…, a partial skeleton consisting of the skull, the left forelimb, and the left anterior portions of the shell [11, pl. 17.5], designated by [1].…”

“…Diagnosis. Eurysternum wagleri can most easily be differentiated from all other known representatives of Thalassochelydia by the following combination of characteristics: a thin, pentagonal shell of intermediate size (carapace length up to 50cm), a deep pygal notch, reduced carapacial fontanelles in adults, contribution of vertebral V to posterior margin of shell, a ligamentous bridge, well developed plastral fontanelles, and poor connection of the epi/entoplastron with the hyoplastra (for a more extensive diagnosis see [1]).…”

“…Late Jurassic deposits across Europe have yielded an astounding array of fossil turtles since the 19th century (see [1,2] for recent summaries) that were recently united into the clade Thalassochelydia [1]. Several factors have hindered a meaningful synthesis of this fauna.…”

“…Several factors have hindered a meaningful synthesis of this fauna. First, fossil turtle taxa were often named over the course of the 19th century based on highly fragmentary material [3,4,5], but generations of workers have been reluctant to ignore the resulting dubious names [6,7] resulting in a pantheon of poorly diagnosed taxa [1]. Second, many Late Jurassic turtles have been recovered as partial to complete skeletons from platy limestones, but the associated cranial material is typically crushed and specimens only prepared from one side (e.g., [8][9][10][11][12][13][14]), making comparison difficult with three-dimensionally preserved specimens from other localities and specimens preserved in opposite views (dorsal versus ventral).…”

“…Third, significant collections of Late Jurassic turtles were mentioned and named in the literature (e.g., [15]), but never figured, making it impossible for the greater community to evaluate their morphology. Finally, although some comparisons were made across borders, there was a certain tendency over the course of the 19th century to recognize local faunas defined by national boundaries [1]. A revived interest in the turtles of the Late Jurassic of Europe has recently been able to clarify the morphology of much historic material [16][17][18][19][20][21][22][23] and to establish a network of occurrences across Europe [21,22,24,25], but the morphology, status, and distribution of many taxa remains unresolved.…”