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Gross morphology and microstructure of type locality ossicles of Psephophorus polygonus Meyer, 1847 (Testudines, Dermochelyidae)

Massimo Delfino, Torsten M. Scheyer, Francesco Chesi, Tamara Fletcher, Richard Gemel, Stewart Macdonald, Marton Rabi and Steven W. Salisbury
Gross morphology and microstructure of type locality ossicles of Psephophorus polygonus Meyer, 1847 (Testudines, Dermochelyidae)
Geological Magazine (September 2013) 150 (5): 767-782

Abstract

Psephophorus polygonus Meyer, 1847, the first fossil leatherback turtle to be named, was described on the basis of shell ossicles from the middle Miocene (MN6-7/8?) of Slovakia. The whereabouts of this material is uncertain but a slab on display at the Naturhistorisches Museum Wien is considered the neotype. We rediscovered further type locality ossicles in four European institutions, re-evaluated their gross morphology and described for the first time their microstructure by comparing them with Dermochelys coriacea, the only living dermochelyid turtle. The gross morphology is congruent with that already described for P. polygonus, but with two significant exceptions: the ridged ossicles of P. polygonus may have a distinctly concave ventral surface as well as a tectiform shape in cross-section. They do not develop the external keel typical of many ossicles of D. coriacea. Both ridged and non-ridged ossicles of P. polygonus are characterized by compact diploe structures with an internal cortex consisting of a coarse fibrous meshwork, whereas the proportionately thinner ossicles of D. coriacea tend to lose the internal cortex, and thus their diploe, during ontogeny. The ossicles of both P. polygonus and D. coriacea differ from those of other lineages of amniotes whose carapace is composed of polygonal ossicles or platelets, in having growth centres situated at the plate centres just interior to the external bone surface and not within the cancellous core or closer to the internal compact layer. The new diagnosis of P. polygonus allows us to preliminarily re-evaluate the taxonomy of some of the Psephophorus-like species. Despite some macro- and micromorphological differences, it seems likely that Psephophorus was as cosmopolitan as extant Dermochelys and had a broadly similar ecology, with a possible difference concerning the dive depth.


ISSN: 0016-7568
EISSN: 1469-5081
Coden: GEMGA4
Serial Title: Geological Magazine
Serial Volume: 150
Serial Issue: 5
Title: Gross morphology and microstructure of type locality ossicles of Psephophorus polygonus Meyer, 1847 (Testudines, Dermochelyidae)
Affiliation: Universita di Torino, Dipartimento di Scienze della Terra, Turin, Italy
Pages: 767-782
Published: 201309
Text Language: English
Publisher: Cambridge University Press, London, United Kingdom
References: 43
Accession Number: 2013-069428
Categories: Vertebrate paleontology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
N47°45'00" - N49°40'00", E16°49'00" - E22°30'00"
Secondary Affiliation: Universitaet Zuerich, CHE, SwitzerlandUniversita di Firenze, ITA, ItalyUniversity of Queensland, AUS, AustraliaNaturhistorisches Museum Wien, AUT, AustriaJames Cook University, AUS, AustraliaEotvos Lorand Tudomany Egyetem, HUN, Hungary
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Cambridge University Press. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201341
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