The last marine pelomedusoids (Testudines: Pleurodira): a new species of Bairdemys and the paleoecology of Stereogenyina - PubMed (original) (raw)
The last marine pelomedusoids (Testudines: Pleurodira): a new species of Bairdemys and the paleoecology of Stereogenyina
Gabriel S Ferreira et al. PeerJ. 2015.
Abstract
The extinct Stereogenyina turtles form a relatively diverse Podocnemididae lineage, with twelve described and phylogenetically positioned species. They are characterized by a wide geographic and temporal range, from the Eocene of Africa to the Pleistocene of Southeast Asia, and a peculiar palate morphology, with a secondary palate that is unique among side-necked turtles. Here, we describe a new Stereogenyina species, based on an almost complete skull from the middle Miocene Capadare Formation, of Venezuela. A new phylogenetic analysis supports the assignment of the new species to the genus Bairdemys. Based on geometric morphometrics analyses, we related the development of the stereogenyin secondary palate with the acquisition of a durophagous diet. Based on a review of the sedimentary environments where their fossils are found, we also propose that stereogenyins were a marine radiation of podocnemidid turtles, as corroborated by previous studies of fossil eggs and limb morphology. These two inferences allowed us to hypothesize that stereogenyins occupied an ecological niche similar to that of the extant Carettini sea turtles, and that the rise of the latter group may be related to the Stereogenyina diversity fall in the end of the Miocene.
Keywords: Bairdemys; Durophagy; Marine pelomedusoides; Miocene; Paleoecology; Podocnemididae; Stereogenyina; Venezuela.
Conflict of interest statement
The authors declare there are no competing interests.
Figures
Figure 1. Maps of the type location of the holotype of Bairdemys thalassica.
(A) Surface geology map of the Falcón state, Venezuela, showing the location of the El Miedo Cave, where the holotype of Bairdemys thalassica was found, and (B) map of South America showing Venezuela (light gray) and Falcón state (black).
Figure 2. Bairdemys thalassica sp. nov.
Holotype skull IVIC-P-2908 in (A) dorsal, (B) ventral, (C) rostral, (D) caudal, (E) left, and (F) right lateral views.
Figure 3. Bairdemys thalassica sp. nov.
Drawing of the holotype skull IVIC-P-2908 in (A) dorsal, (B) ventral, (C) rostral, (D) caudal, (E) left, and (F) right lateral views. Abbreviations: bo, basioccipital; bs, basisphenoid; cc, cavum cranii; cm, condylus mandibularis; co, condylus occipitalis; cpt, cavum pterygoidei; cso, crista supraoccipitalis; ct, cavum tympani; eap, entrance of the antrum postoticum; et, eustachian tube; ex, exoccipital; fjp, foramen jugulare posterius; fnh, foramina nervi hypoglossi; fnt, foramen nervi trigemini; fo, fossa orbitalis; fpo, fenestra postotica_;_ fr, frontal; ica, incisura columellae auris; ju, jugal; msp, midline cleft of the secondary palate; mx, maxilla; mxr, maxillary ridge; op, opisthotic; pa, parietal; pal, palatine; po, postorbital; ppo, processus paroccipitalis; pt, pterygoid; ptf, pterygoid flange; ptp, processus trochlearis pterygoidei; qj, quadratojugal; qu, quadrate; so, supraoccipital; sq, squamosal.
Figure 4. Bairdemys thalassica sp. nov.
Dermal scales of the skull in (A) dorsal and (B) lateral view. On the identification of each scale (in lower case latin numbers, from i to viii) there is after the “=” mark the preliminary homology assessment in relation to the Sterli & de la Fuente (2013) system (see Dermal scales of the skull section).
Figure 5. Phylogenetic relations of Stereogenyina based on the single most parsimonious tree obtained in the present study.
Node numbers are indicated above each node and GC bootstrap values above 40 in front of them. Squares indicate the synapomorphies of the respective clade (black = 0 to 1, gray = 0 to 2, white = 1 to 0).
Figure 6. Landmarks used in the geometric morphometric analyses.
Landmarks shown in the palates of (A) Peltocephalus dumerilianus and (B) Bairdemys winklerae, and in the lower jaws of (C) Peltocephalus dumerilianus and (D) Bairdemys venezuelensis. For the description of the landmarks see Supplemental Information 3.
Figure 7. Results of the geometric morphometric analyses.
Principal component analysis (A and C) derived from the first two principal components (PC1 and PC2) and comparison of the mean values of the coordinates (B and D) for the upper (A and B) and the lower jaws (C and D). D’Arcy Thompson grids correspond to extreme shape variation. Durophagous taxa are represented in blue, non-durophagous in green, and fossil taxa with unknown diet in purple.
Figure 8. Cladogram calibrated on a time scale and species diversity plot.
Cladogram calibrated on a time scale (A and D) and species diversity plot based on the count of lineages on each age (B and C), from the Eocene to the present, for Stereogenyina (A and B) and Carettini turtles (C and D, cladogram based on Parham & Pyenson, 2010). Layout modified from Romano et al. (2014)).
Figure 9. Inference for salt glands in Stereogenyina turtles.
(A) cross section of a generalized Stereogenyina skull, indicating (red arrow) the position of the “posterior pocket on septum orbitotemporale”; (B) distribution of character 19 “fossa orbitalis caudal pocket” (left tree) and inferred paleoenvironment (right tree) in the phylogenetic hypothesis presented here. The coding of the character 19 is based on personal observations and on Gaffney et al. (2011) coding. Abbreviations: ane, apertura narium
externa; cc, cavum cranii; ju, jugal; msp, midline cleft of the secondary palate; mx, maxilla; pa, parietal; pal, palatine; pm, premaxilla; po, postorbital; pt, pterygoid; ptp, processus trochlearis pterygoidei; sot, septum orbitotemporale.
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Grants and funding
This research was supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) scholarships to GSF (2012/11604-1) and research funding to MCL (2014/03825-3), and by Venezuelan education university, science, and technology Ministry (MEUCT), research fundings IVIC-1096 and PEII2012-456 to ADR and AS. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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