Saturday, December 26, 2015

[Paleontology • 2015] Leyvachelys cipadi • The First South American Sandownid Turtle from the Lower Cretaceous of Colombia


Leyvachelys cipadi  Cadena, 2015

Abstract

Sandownids are a group of Early Cretaceous-Paleocene turtles that for several decades have been only known by cranial and very fragmentary postcranial elements. Here I report and describe the most complete sandownid turtle known so far, including articulated skull, lower jaw and postcranial elements, from the Early Cretaceous (upper Barremian-lower Aptian, >120 Ma), Paja Formation, Villa de Leyva town, Colombia. The new Colombian sandownid is defined here as Leyvachelys cipadi new genus, new species and because of its almost identical skull morphology with a previously reported turtle from the Glen Rose Formation, Texas, USA, both are grouped in a single and officially (ICNZ rules) defined taxon. Phylogenetic analysis including L. cipadi supports once again the monophyly of Sandownidae, as belonging to the large and recently redefined Pan-Chelonioidea clade. The morphology of L. cipadi indicates that sandownids were not open marine turtles, but instead littoral to shallow marine durophagous dwellers. Leyvachelys cipadi not only constitutes the first record of sandowinds in South America, but also the earliest global record for the group.


Systematic Paleontology

TESTUDINES Batsch, 1788
PAN-CRYPTODIRA Cope, 1868

SANDOWNIDAE sensu Tong & Meylan, 2013

Leyvachelys gen. nov.

Etymology. Combining ‘Leyva’ (from Villa de Leyva, town of where the discovery took place) and ‘chelys’ (Greek, turtle).

Leyvachelys cipadi sp. nov.

Etymology. cipadi’ (dedicated to the CIP, Centro de Investigaciones Paleontológicas)

Holotype. FCG-CBP-71 (housed at the CIP, Villa de Leyva, Colombia, Fig. 1C), articulated skull and lower jaw, nearly complete carapace, three cervical vertebrae, right humerus and coracoid, both femora, tibiae, and pelvic girdle, and two caudal vertebrae.


Paleoecology and paleobiogeography of sandownids

The morphology of the shell of Leyvachelys cipadi (FCG-CBP-71 specimen), allows the support of previously hypothesized habitat adaptations for sandownids; in particular, that they inhabited littoral to near-shore shallow marine environments Tong & Meylan (2013), and that their general body-plan was not designed for leading an open marine lifestyle. They nevertheless potentially shared niches with open marine turtles, as evidenced by the occurrence of protostegids from the same stratigraphical horizons (Cadena & Parham, 2015). The abundant occurrence of mollusks, principally ammonites, some of them preserved associated with the carapace of L. cipadi, suppose a potential source of food for its durophagous diet adaptation which could have also included artropods, as for example crabs.

Leyvachelys cipadi not only expands back to the upper Barremian-lower Aptian (>120 Ma) the fossil record of sandownids, but also expands their paleogeographical distribution, being the first record of sandownids in South America. Paleotectonic reconstructions for the Barremian-Aptian of the Gulf of Mexico and the porto-caribbean (Pindell & Kennan, 2009; Blakey, 2011) (Figs. 1E and 10), suggest the existence of an almost continuous littoral areas between the Gulf of Mexico and northern South America, which could have served as a corridors for the dispersion or migrations of marine-littoral vertebrates including Leyvachelys cipadi giving explanation to its occurrence in Glen Rose Formation of Texas and Paja Formation of Colombia. As mentioned by Tong & Meylan (2013), the evolutionary history and dispersion of sandownids (now with a Barremian to Paleocene stratigraphic range and a geographical distribution including South America, North America, Europe, and Africa) was influenced by the opening of the Atlantic Ocean. This seems to be also the case for other groups of littoral to costal turtles, as for example the bothermydid pleurodires (Gaffney, Tong & Meylan, 2006; Cadena, Bloch & Jaramillo, 2012).


Cadena E. 2015. The First South American Sandownid Turtle from the Lower Cretaceous of Colombia. PeerJ. 3:e1431 DOI: 10.7717/peerj.1431

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