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The first fossil skull of Chelus (Pleurodira: Chelidae, Matamata turtle) from the early Miocene of Colombia

Edwin A. Cadena and Carlos A. Jaramillo

Plain Language Abstract

The Matamata turtle is considered one of the weirdest turtles in the world, because it has a very particular flat head covered with a very rugose and decorated skin. Today the Matamata turtle (Chelus fimbrita) can only be found at the Orinoco and Amazon rivers in South America. In this study, we present and describe the first and only so far known skull for a Matamata turtle group, discovered at the Guajira Peninsula, Castilletes, Colombia.

Resumen en Español

El primer cráneo fósil de Chelus (Pleurodira: Chelidae, tortuga matamata) del Mioceno temprano de Colombia

Se describe el primer cráneo fósil conocido para el género de tortuga Chelus del Mioceno temprano (~ 16 M.a.), Formación Castilletes, Península de la Alta Guajira, Cuenca Cocinetas, Colombia. El cráneo se conserva parcialmente, incluyendo la mayor parte de la base del cráneo (huesos pterigoideo- basioccipital) y los elementos más dorsales como el parietal, pterigoideo y porciones del escamoso, supraoccipital y del cuadrado más dorsal. El cráneo se conserva en tres dimensiones, sin evidencia de roturas por aplastamiento, permitiendo la observación de la morfología de la caja craneal interna mediante microtomografía computarizada. Las comparaciones con el cráneo de la única especie existente para el género Chelus fimbriata (tortuga matamata) nos han permitido concluir que durante los últimos 16 millones años la morfología del cráneo de este género se ha mantenido casi invariable, constatándose únicamente una compresión ligeramente más alta de la más caja craneal más anterior en comparación con lo que se observa en las especies existentes. Debido a su condición fragmentaria, no es posible una identificación más precisa más allá de la de género (Chelus sp.); sin embargo, la anatomía general del cráneo indica que la forma fósil pudo haber tenido las mismas adaptaciones ecológicas y tróficas de su pariente actual.

Palabras clave: Chelidae; Testudines; Colombia; Sudamérica; La Guajira

Traducción: Enrique Peñalver

Résumé en Français

Le premier crâne fossile de Chelus (Pleurodira : Chelidae, tortue Matamata) du Miocène ancien de Colombie

Nous décrivons dans cet article le premier crâne fossile connu jusqu'à présent du genre de tortue Chelus, provenant du Miocène ancien (~ 16 Ma) de la formation de Castilletes, péninsule d'Alta Guajira, bassin de Cocinetas, Colombie. Le crâne est préservé partiellement, incluant la plus grande partie du basicrâne (os du ptérygoïde-basioccipital) et des éléments du toit crânien incluant le pariétal, le ptérygoïde et des parties du squamosal, le supraoccipital, et la partie la plus dorsale du carré. Le crâne est préservé en trois dimensions, sans indications d'écrasement, ce qui permet d'observer la morphologie interne de la boîte crânienne en utilisant la tomographie assistée par micro-ordinateur. Des comparaisons avec le crâne de la seule espèce actuelle du genre, Chelus fimbriata (tortue Matamata), nous permettent de conclure que la morphologie du crâne de ce genre est restée presque inchangée pendant les derniers 16 millions d'années, avec seulement une compression légèrement plus importante de la partie la plus antérieure de la boîte crânienne chez l'espèce actuelle. En raison du caractère fragmentaire, une identification plus précise au sein du genre (Chelus sp.) n'est pas possible. Cependant, l'architecture globale du crâne indique que l'espèce fossile pourrait avoir eu les mêmes adaptations en termes d'écologie et de régime alimentaire que l'espèce actuelle apparentée.

Mots-clés : Chelidae ; Testudines ; Colombie ; Amérique du Sud ; La Guajira

Translator: Antoine Souron

Deutsche Zusammenfassung

Der erste fossile Schädel von Chelus (Pleurodira: Chelidae, Matamata Schildkröte) aus dem frühen Miozän von Kolumbien

Im Folgenden beschreiben wir den ersten bisher bekannten fossilen Schädel der Gattung Chelus aus dem frühen Miozän (~ 16 Mio.J.), Castilletes Formation, Alta Guajira Peninsula, Cocinetas Becken, Kolumbien. Der Schädel ist partiell erhalten und beinhaltet die meisten Teile des Basicraniums (Pteygoid-Bassioccipital-Knochen) und die Schädeldachelemente wie das Parietale, Pterygoid und Teile des Squamosums, Supraoccipitale und den dorsalen teil des Quadratums. Der Schädel ist dreidimensional erhalten, ohne Hinweis auf Verdrückung, und erlaubt so eine Untersuchung der inneren Hirnschädelmorphologie mit Mikrocomputertomographie. Vergleiche mit der einzigen heute noch lebenden Art der Gattung Chelus fimbriata (Matamata Schildkröte) lassen darauf schließen, dass die Schädelmorphologie dieser Gattung während der letzten 16 Millionen Jahre nahezu unverändert blieb, bis auf die etwas höhere Stauchung des anterioren Hirnschädels bei der heutigen Art. Wegen des fragmentarischen Zustands ist eine Identifikation über die Gattung hinaus (Chelus sp.) nicht möglich. Jedoch weist das allgemeine Schädelmuster darauf hin, dass die fossile Art dieselben ökologischen Anpassungen und Nahrungsgewohnheiten gehabt haben könnte wie die heutige Verwandte.

Schlüsselwörter: Chelidae; Testudines; Kolumbien; Südamerika; La Guajira

Translator: Eva Gebauer

Arabic

Translator: Ashraf M.T. Elewa

 

 

APPENDIX 1.

List of specimens of Chelus frimbiata directly examined by the senior author. Abbreviations: ICN, Instituto Colombiano de Ciencias Naturales, Universidad Nacional de Colombia, Bogotá, Colombia; MNHN, Muséum National d’Histoire Naturelle, Paris, France; NMW, Naturhistorisches Museum Wien, Vienna, Austria; Herpetological Collection, Senckenberg Museum, Frankfurt, Germany; USNM, Smithsonian National Museum of Natural History, Washington D.C., USA.

 

ICN 1767, 1776, 1780, 1781, 6411, D-75, and D-90
MNHN 1930-365, 1973-8381, 1991-2581B, 9406, A5171, A5200, A9940
NMW 1859, 39830
SM 57977, 37178
USNM 064154, 117455, 301989, 301991, 301992

APPENDIX 2.

Chelus sp. MUN-STRI-dbid 38473 CT dynamic cutaways sagittal. Click on image to run animation.

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APPENDIX 3.

Chelus sp. MUN-STRI-dbid 38473 CT dynamic cutaways coronal. Click on image to run animation.

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APPENDIX 4.

Chelus sp. MUN-STRI-dbid 38473 CT dynamic cutaways horizontal. Click on image to run animation.

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APPENDIX 5.

Chelus fimbriata SM 37178 CT dynamic cutaways sagittal. Click on image to run animation.

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APPENDIX 6.

Chelus fimbriata SM 37178 CT dynamic cutaways coronal. Click on image to run animation.

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APPENDIX 7.

Chelus fimbriata SM 37178 CT dynamic cutaways horizontal. Click on image to run animation.

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cadenaEdwin A. Cadena
Center for Tropical Paleoecology and Archaeology
Smithsonian Tropical Research Institute
Balboa, Ancon
Panama
and Senckenberg Museum
Department of Paleoanthropology and Messel Research
603025 Frankfurt
Germany
This email address is being protected from spambots. You need JavaScript enabled to view it.

Dr. Edwin Cadena is a geologist/vertebrate paleontologist. His research focuses on the evolution of turtles, principally from Central America and Northern South America, as well as patterns of preservation of bone cells in fossil record and their paleobiological and evolutionary implications. He completed an MSc in Geology at the University of Florida in 2009 and a PhD at the North Carolina State University in 2012, and currently is finishing a postdoctoral fellowship at the Senckenberg museum of Natural History in Frankfurt, Germany.

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jaramilloCarlos A. Jaramillo
Center for Tropical Paleoecology and Archaeology
Smithsonian Tropical Research Institute
Balboa, Ancon
Panama
This email address is being protected from spambots. You need JavaScript enabled to view it.

Carlos Jaramillo is a staff scientist with the Smithsonian Tropical Research Institute in Panama. His research investigates the causes, patterns, and processes of tropical biodiversity at diverse scales of time and space. He is also interested in Cretaceous-Cenozoic biostratigraphy of low latitudes, developing methods for high-resolution biostratigraphy and the paleobiogeography of Tethys.

 

 

FIGURE 1. Geographical and stratigraphical occurrence of Chelus sp. MUN-STRIdbid 38473. 1, map of the northernmost portion of South America, showing the location of Castilletes, on the Guajira Peninsula of Colombia. 2, stratigraphic column for the lower segment of the Castilletes Formation, Kaitamana section, including the horizon where Chelus sp. MUN-STRI-dbid 38473 was found, redrawn from Moreno et al. (2015). 3, landscape photograph of the locality where Chelus sp. MUN-STRI-dbid 38473 was found. 4, complete skeleton of Chelus fimbriata NMW 1859, orange shadowed area in the skull, represents the area preserved in the fossil Chelus sp. MUN-STRI-dbid 38473, down is the anterior view of the head of Ch. fimbriata (photo credit, Stuart Hamilton).

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FIGURE 2. Skulls of Chelus fimbriata SM 37178 and Chelus sp. UNT-STRI-dbid 38473. Photographs and interpretative drawings. Chelus fimbriata SM 37178. 1-2, dorsal view; 3-4, ventral view; 5-6, posterior view. Chelus sp. MUN-STRI-dbid 38473 fossil from Castilletes Formation, Colombia. 7-8, dorsal view; 9-10, ventral view; 11-12, right lateral view; 13-14, posterior view. Abbreviations: bo, basioccipital; bs, basisphenoid; ex, exoccipital; fjp, foramen jugulare posterius; fm, foramen magnum; fn, foramen nervi hypoglossi, fp, fenestra postotica; fpcci, foramen posterior canalis caroticus cerebralis; fpp, foramen palatinum posterior; fr, frontal; fst, foramen stapedio temporalis; fts, fossa temporalis superior; ju, jugal; mx, maxilla; op, opisthotic; pa, parietal; pf, prefrontal; pl, palatine; pm, premaxilla; po, postorbital; pr, prootic; pt, pterygoid; qu, quadrate; so, supraoccipital; sq, squamosal; vo, vomer. Dotted line in 2 indicates sulci of skull scutes. Light grey areas in 8 indicate preservation of the dorsalmost surface of the bones. Scale bar applies for all figures.

figure2

FIGURE 3. CT images of Chelus sp. MUN-STRI-dbid 38473. 1, skull in dorsal view, arrows indicate the position of the cuts shown in 4-7. 2, horizontal cut on the lower portion of the skull, anterior to the foramen magnum. 3, horizontal cut at the level of the widest portion of the skull. 4, sagittal cut on the left portion of the skull. 5, sagittal cut at the midline of the skull. 6, coronal cut very close to the level of the basisphenoid-basioccipital contact. 7, coronal cut on the anterior portion of the skull. Abbreviations are as in Figure 2, plus apb (anterior process of basisphenoid).

figure3

FIGURE 4. CT images of Chelus sp. and the extant C. fimbriata in sagittal view. These figures show the difference in the height of the endocranium between the fossil skull described here and juveniles and adults of the extant representative of Chelus ; all cuts are located at the midline of the skull. 1, Chelus sp. MUN-STRI-dbid 38473 (adult); 2, C. fimbriata SM 37178 (adult); 3, C. fimbriata UMA R-1376 (hatchling-juvenile?); 4, C. fimbriata SM 57977 (juvenile). The basisphenoid bone is delimited by light blue color.

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FIGURE 5. Comparison between height of the endocranium at the anterior (h1) and posterior (h2) end of the basisphenoid for three extant Chelus fimbriata specimens (black dots) vs the fossil Chelus sp. described here (red dot).

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