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he Erymnochelys group of turtles (Pleurodira, Podocnemididae) in the Eocene of Europe: New taxa and paleobiogeographical implications

Adán Pérez-García, France de Lapparent de Broin, and Xabier Murelaga

Plain Language Abstract

Two fundamental groups of turtles continue to be part of the current biodiversity: Pleurodira (turtles that bend the neck in a horizontal plane for its retraction within the shell) and Cryptodira (those with a vertically bent neck). Pleurodires are now only present in intertropical regions, most of them being exclusively freshwater forms. The freshwater extant Malagasy Erymnochelys madagascariensis is the only representative of Erymnochelyinae (Pleurodira) alive today. Additionally, it is a member of the Erymnochelys group, a group that originated in Africa by the late Cretaceous. Only sparse information on most of the fossil representatives of this group is available. Thus, the oldest unambiguous generic diagnoses heretofore established belong to uppermost Miocene-Pliocene forms. The poorly-known French middle Eocene 'aff. Erymnochelys' eremberti is studied here in detail and attributed to a new genus, Eocenochelus. Eocenochelus is the first genus of the Erymnochelys group to be defined outside of Africa. It is identified as the only known hyaline tolerant coastal form of the Erymnochelys group, and this probably facilitated its spread from Africa to Europe in the Eocene. Eocenochelus is also recognized in the European lower and upper Eocene record by two new species described here.

Resumen en Español

El grupo de tortugas Erymnochelys (Pleurodira, Podocnemididae) en el Eoceno de Europa: nuevos taxones e implicancias paleobiogeográficas

El grupo de tortugas Erymnochelys es un linaje de Erymnochelyinae, tortugas pleurodiras que se originaron en África, con un registro fósil que se extiende desde el Cretácico Tardío. Actualmente se encuentra representada por una única especie, la magadascarí Erymnochelys madagascariensis. La información respecto a la mayoría de sus representantes fósiles es escasa. De hecho, las determinaciones genéricas inequívocas más antiguas hasta ahora establecidas dentro del grupo son las de Turkanemys y Kenyemys, ambas del Mioceno más tardío-Plioceno de Kenia. Aquí se completa la descripción e ilustración de la especie francesa del Eoceno medio 'aff. Erymnochelys' eremberti, y se propone por primera vez una diagnosis para esta especie. Se atribuye a un nuevo género, Eocenochelus, el primer género del grupo Erymnochelys en ser definido fuera de África. Eocenochelus también se reconoce en el registro europeo del Eoceno inferior a superior con dos nuevas especies, Eocenochelus lacombianus y Eocenochelus farresi, respectivamente. Por ende, Eocenochelus es un taxón nuevo con una amplia distribución en Europa durante el Eoceno y es relativamente diverso. Éste también es el caso de la continental Neochelys, el único otro género de podocnemídidos reconocido hasta ahora en el registro paleógeno europeo. Exclusivamente identificado en depósitos costeros, Eocenochelus es la única forma del grupo Erymnochelys encontrada en sedimentos marino marginales. Sus adaptaciones anatómicas probablemente facilitaron su propagación de África a Europa.

Palabras clave: tortugas de cuello de serpiente; Erymnochelyinae; linaje africano; nuevo género; nueva especie

Traducción: Diana Elizabeth Fernández

Résumé en Français

Le groupe de tortues Erymnochelys (Pleurodira, Podocnemididae) de l'Éocène d'Europe : nouveaux taxons et implications paléobiogéographiques

Le groupe Erymnochelys est une lignée d'Erymnochelyinae, des tortues pleurodires originaires d'Afrique, avec un registre fossile commençant au Crétacé récent. Ce groupe n'est actuellement représenté que par une seule espèce malgache, Erymnochelys madagascariensis. Les données sur la plupart des représentants fossiles sont rares. De fait, les déterminations génériques certaines les plus anciennes pour ce groupe étaient jusqu'à présent celles des genres Turkanamys et Kenyemys, tous les deux du Miocène terminal-Pliocène du Kenya. La description et l'illustration d'une espèce de l'Éocène moyen de France, 'aff. Erymnochelys' eremberti, sont présentées ici, et une diagnose de cette espèce est proposée pour la première fois. Elle est attribuée au nouveau genre Eocenocelus gen. nov., le premier genre du groupe Erymnochelys à être défini en dehors d'Afrique. Eocenochelus gen. nov. est également identifié dans le registre européen avec deux nouvelles espèces Eocenochelus lacombianus gen. et sp. nov. et Eocenochelus farresi gen. et sp. nov., respectivement dans l'Éocène inférieur et supérieur. Eocenochelus gen. nov. est donc un taxon avec une vaste distribution en Europe pendant l'Éocène et est relativement diversifié. C'est également le cas du genre continental Neochelys, le seul autre genre de podocnémididé identifié jusqu'à présent dans le registre paléogène européen. Identifié exclusivement dans des dépôts côtiers, Eocenochelus gen. nov. est la seule forme connue du groupe Erymnochelys trouvée dans des sédiments de marge marine. Ses adaptations anatomiques ont probablement facilité sa dispersion d'Afrique vers l'Europe.

Mots-clés : tortues pleurodires ; Erymnochelyinae ; lignée africaine ; nouveau genre ; nouvelle espèce

Translator: Antoine Souron

Deutsche Zusammenfassung

Die Erymnochelys-Gruppe der Schildkröten (Pleurodira, Podocnemididae) im Eozän von Europa: neue Taxa und paläobiogeographische Folgerungen

Die Erymnochelys-Gruppe ist eine Linie der Erymnochelyinae, pleurodire Schildkröten, die in Afrika entstanden und einen Fossilrekord bis in die späte Kreide aufweisen. Die Gruppe wird gegenwärtig durch eine einzige Art repräsentiert, der madagassischen Erymnochelys madagascariensis. Über die meisten fossilen Vertreter gibt es nur spärliche Informationen. Tatsächlich sind die ältesten unzweifelhaften Gattungen innerhalb dieser Gruppe bisher Turkanemys und Kenyemys, beide aus dem späten Miozän-Pliozän von Kenia. Hier wird die Beschreibung und Illustration der französischen mitteleozänen Art 'aff. Erymnochelys' vervollständigt und es wird zum ersten Mal eine Diagnose für diese Art vorgestellt. Sie wird einer neuen Gattung, Eocenochelus, zugeteilt, der ersten Gattung der Erymnochelys-Gruppe außerhalb Afrikas. Eocenochelus wird ebenso durch die zwei neuen Arten, Eocenochelus lacombianus und Eocenochelus farresi, im europäischen unteren und oberen Eozän anerkannt. Daher ist Eocenochelus ein Taxon mit einer weiten Verbreitung in Europa während des Eozäns und es ist relativ divers. Dies ist ebenso der Fall mit dem kontinentalen Neochelys, der einzigen anderen podocnemididen Gattung, die bis jetzt im Paläogen von Europa erkannt wurde. Ausschließlich in Küstenablagerungen identifiziert, ist Eocenochelus die einzige Form aus der Erymnochelys-Gruppe, die in randmarinen Sedimenten gefunden wurde. Ihre anatomischen Adaptionen erleichterten möglicherweise die Verbreitung von Afrika nach Europa.

Schlüsselwörter: Halswender-Schildkröten; Erymnochelyinae; Afrikanische Linie; neue Gattung; neue Art

Translator: Eva Gebauer

Arabic

Translator: Ashraf M.T. Elewa

 

 

TABLE 1. Comparison of some cranial and postcranial characters of three podocnemidids: the new European Eocene genus Eocenochelus (represented by the three species studied here, Eocenochelus lacombianus sp. nov., Eocenochelus eremberti comb. nov. and Eocenochelus farresi sp. nov.), the Malagasy Erymnochelys (represented by the extant species Erymnochelys madagascariensis) and the European Eocene Neochelys (represented by ten species). For more information and detailed comparisons see the text.

  Eocenochelus Erymnochelys Neochelys
Snout Short Prominent Prominent
Premaxillary beak Absent Present Absent
Suborbital space height Greater than the orbits height Less than the orbits height Less than the orbits height
Interorbital space Wider than the orbits length Narrower or as narrow as the orbits length Narrower or as narrow as the orbits length
Cheek emargination Absent. Filled by a ventral expansion of the jugal Small. In large part filled by the jugal or jugal and quadratojugal ventral expansion Largely present between the maxilla and the quadratojugal
Interparietal scute anterior extension Not contacting the frontals Overlapping the frontals Overlapping the frontals
Interparietal anterior concavity Present Absent Present
Mandibular symphysis length About 40% of the lower jaw length About 30% of the lower jaw length About 25% of the lower jaw length
Lower jaw Very robust Relatively robust Slender
Number of neurals 6 to 7 6 6 to 7
Plastral lobes Posterior lobe narrower than the anterior Posterior lobe narrower than the anterior Subequal width of both lobes
Anterior lobe morphology Subrounded Subrounded to subtrapezoidal Subrounded to subtrapezoidal
Intergular length Long, reaching or overlying the entoplastron Short, not reaching the entoplastron Long, reaching or overlying the entoplastron
Medial contact of the gulars Present. Intergular not contacting the humerals Present. Intergular not contacting the humerals Absent. Intergular contacting the humerals, and contacting or not the pectorals

 

TABLE 2. Comparison of shell characters of three representatives of the new European Eocene genus Eocenochelus recognized here: the lower Eocene Eocenochelus lacombianus sp. nov., the middle Eocene Eocenochelus eremberti comb. nov., and the upper Eocene Eocenochelus farresi sp. nov. For more information and detailed comparisons see the text.

  Eo. eremberti Eo. lacombianus Eo. farresi
Number of neurals Al least 7 7 6
Width of the neurals Relatively narrow for their length Relatively wide for their length Relatively narrow for their length
Pubic scar Long and narrow Short and oval Unknown
Posterior branch of the ischiatic scar Poorly-developed Well-developed in the xiphiplastral point but not reaching its extremity Well-developed, reaching the xiphiplastral point extremity
Epiplastral symphysis Relatively long Relatively long Very short
Intergular anterior border Much narrower than that of each gular Almost as wide as that of each gular Almost as wide as that of each gular
Latero-posterior region of the humerals on the hyoplastra Relatively short overlap Relatively short overlap Long
Posterior plastral lobe Relatively wide. Subrounded lateral margins Narrow. Slightly concave lateral margins Narrow. Slightly convex lateral margins
Anal notch Wide and short, the length being about half of the width. Rounded borders Wide and short, the length being about half of the width. Straight borders Deep, being almost as long as wide. Rounded borders
 

FIGURE 1. Stratigraphic and paleobiogeographical distributions of the currently accepted members of Erymnochelyinae, including the European taxa described here, i.e., the representatives of the new genus Eocenochelus, belonging to the Erymnochelys group. The shell and skull symbols accompanying the name of each taxon indicate which of these elements are known. The star indicates continental Stereogenyina, and the pentagon indicates continental or littoral Stereogenyina.

 figure1a

FIGURE 2. Geographic locations of the type localities of the European Eocene representatives of the podocnemidid Eocenochelus gen. nov.: Soulane (Jonquières, Aude, France), type locality of the lower Eocene (Ypresian) Eocenochelus lacombianus sp. nov.; Saint-Germain-en-Laye (Yvelines, Île-de-France, France), type locality of the middle Eocene (Lutetian) Eocenochelus eremberti comb. nov.; Can Beuloví (Sobremunt, Barcelona, Spain), type locality of the upper Eocene (Priabonian) Eocenochelus farresi sp. nov.

 figure2

FIGURE 3. Skull of the holotype of Eocenochelus eremberti comb. nov., MNHN.F CGR 101, from the middle Eocene (Lutetian) of Saint-Germain-en-Laye (Yvelines, Île-de-France, France), in dorsal (1-2), ventral (3-4) and right lateral (5-6) views. Abbreviations: ane, apertura narium externa; ang, angular; bo, basioccipital; bs, basisphenoid; cm, condylus mandibularis; cpt, cavum pterygoidei; cv, cervical vertebra; den, dentary; ex, exoccipital; fct, foramen anterius chorda tympani; fo, fossa orbitalis; fpo, fenestra postotica; fpp, foramen palatinum posterius; fr, frontal; FR, frontal scute; fst, foramen stapedio-temporale; IP, interparietal scute; ju, jugal; MS, masseterian scute; mx, maxilla; MX, maxillary scute; op, opisthotic; pa, parietal; PA, parietal scute; pal, palatine; pf, prefrontal; pm, premaxilla; po, postorbital; pr, prootic; pt, pterygoid; ptp processus trochlearis pterygoidei; pw, pterygoid wing; q, quadrate; qj, quadratojugal; so, supraoccipital; SO, subocular scute.

 figure3

FIGURE 4. Some elements of the carapace of the holotype of Eocenochelus eremberti comb. nov., MNHN.F CGR 101, from the middle Eocene (Lutetian) of Saint-Germain-en-Laye (Yvelines, Île-de-France, France). 1-2, plates of the carapace, in dorsal and ventral views. 3-4, reconstruction of the dorsal view of the shell, showing the position of all these elements of the carapace. 4-6, details of the outer surface of some plates of the carapace: the second left peripheral (4), the distal region of the sixth right costal (5), and the proximal region of the fourth left costal (6). Abbreviations: c, costal; M, marginal scute; n, neural; p, peripheral; PL, pleural scute; py, pygal; V, vertebral scute.

 figure4

FIGURE 5. Plastron of the holotype of Eocenochelus eremberti comb. nov., MNHN.F CGR 101, from the middle Eocene (Lutetian) of Saint-Germain-en-Laye (Yvelines, Île-de-France, France), in ventral (1-2) and dorsal (3-4) views. Abbreviations: AB, abdominal scute; AN, anal scute; en, entoplastron; ep, epiplastron; FE, femoral scute; GU, gular scute; hp, hypoplastron; HU, humeral scute; hy, hyoplastron; IG, intergular scute; M, marginal scute; ms, mesoplastron; PC, pectoral scute; xi, xiphiplastron.

 figure5

FIGURE 6. Fragmentary skeletal bones of the holotypes of Eocenochelus eremberti comb. nov., MNHN.F CGR 101, from the middle Eocene (Lutetian) of Saint-Germain-en-Laye (Yvelines, Île-de-France, France) (1-49), and Eocenochelus lacombianus sp. nov., MNHN.F EBA 534, from the lower Eocene (Ypresian) of Soulane (Jonquières, Aude, France) (50-57). 1-4, left hyoid horn, second branchial horn, in dorsal (1), medial (2), ventral (3) and lateral (4) views. 5-9, acromion of the right scapula with the partial glenoid articular region, in posterior (5), ventral (6), anterior (7) and dorsal (8) views, and articular part in ventrolateral view (9). 10-14, acromion of the left scapula with the partial glenoid articular region, in posterior (10), ventral (11), anterior (12) and dorsal (13) views, and proximal articular section (14). 15-19, left coracoid in dorsal (15), posteroventral (16), ventral (17) and anterior (18) views, and articular-glenoid facet part, in proximal view (19). 20-25, left ischium, in anterior (20), medial (21), posterior (22) and distal (23) views, and dorsal (24) and ventral (25) sections. 26-31, right ilium, in posterior (26), lateral (27), anterior (28) and medial (29) views, and dorsal (30) and ventral (31) sections. 32-37, left pubis, in anterior (32), medial (33), posterior (34) and lateral (35) views, proximal articular-acetabular region in dorsal view (36), and ventral section (37). 38-43, left humerus, in anterior (38), ventral (39), posterior (40) and dorsal (41) views, and proximal (42) and distal (43) sections. 44-49, right femur, in anterolateral (44), ventral (45), posteromedial (46) and dorsal (47) views, and proximal (48) and distal (49) sections. 50-53, right hemipelvis, in lateral (50), posterior (51), anterior (52) and medioventral (53) views. 54-57, left hemipelvis, in lateral (54), posterior (55), anterior (56) and medial (57) views.

figure6 

FIGURE 7. Shell of the holotype of Eocenochelus lacombianus sp. nov., MNHN.F EBA 534, from the lower Eocene (Ypresian) of Soulane (Jonquières, Aude, France). 1-2, carapace, in dorsal view. 3-4, carapace, in ventral view. 5, reconstruction of the dorsal view of the shell, showing the position of the preserved elements of the carapace. 6-7, plastron, in ventral view. 8-9, plastron, in dorsal view. Abbreviations: AB, abdominal scute; AN, anal scute; c, costal; en, entoplastron; ep, epiplastron; FE, femoral scute; GU, gular scute; hp, hypoplastron; HU, humeral scute; hy, hyoplastron; IG, intergular scute; M, marginal scute; ms, mesoplastron; n, neural; nu, nuchal; p, peripheral; PC, pectoral scute; PL, pleural scute; py, pygal; V, vertebral scute; xi, xiphiplastron.

 figure7

FIGURE 8. Shell of the holotype of Eocenochelus farresi sp. nov., MGSB 74.641-GLV.T.45, from the upper Eocene (Priabonian) of Can Beuloví (Sobremunt, Barcelona, Spain), in dorsal (1-2) and ventral (3-4) views. Abbreviations: AB, abdominal scute; AN, anal scute; c, costal; en, entoplastron; ep, epiplastron; FE, femoral scute; GU, gular scute; hp, hypoplastron; HU, humeral scute; hy, hyoplastron; IG, intergular scute; M, marginal scute; ms, mesoplastron; n, neural; p, peripheral; PC, pectoral scute; PL, pleural scute; py, pygal; V, vertebral scute; xi, xiphiplastron.

 figure8

FIGURE 9. Reconstruction of the dorsal and ventral views of the shells of the three Podocnemididae species studied here, Eocenochelus lacombianus sp. nov. (1-2), Eocenochelus eremberti comb. nov. (3-4), and Eocenochelus farresi sp. nov. (5-6), compared to those of the extant Malagasy Erymnochelys madagascariensis (7-8), and the European Eocene Neochelys liriae (9-10).

figure9

 

 

perezAdán Pérez-García. Grupo de Biología Evolutiva, Facultad de Ciencias, Universidad Nacional de Educación a Distancia, Paseo de la Senda del Rey 9, 28040 Madrid, Spain. This email address is being protected from spambots. You need JavaScript enabled to view it.

Adán Pérez-García is a paleontologist working on several clades of reptiles, mainly on Testudinata. He obtained his PhD on the fossil turtles from the Iberian Peninsula in 2012, at the Universidad Complutense de Madrid. He is now a researcher at the Universidad Nacional de Educación a Distancia (Madrid). His main work focuses on the study of the systematics, paleobiogeography and diversity of Mesozoic and Cenozoic faunas of turtles from the Jurassic to the Holocene, including both European and African clades. He described several new taxa corresponding to pan-pleurodiran and pan-cryptodiran forms.

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lapparentFrance de Lapparent de Broin. Centre de Recherche sur la Paléodiversité et les Paléoenvironnements, Muséum national d’Histoire naturelle, 57 rue Cuvier, CP 38, 75231 Paris cedex 5, France. This email address is being protected from spambots. You need JavaScript enabled to view it.

France de Lapparent de Broin is an expert on extinct crocodiles (among which the giant Cretaceous Sarcosuchus) and turtles who has made them known to the paleoherpetological community over almost 50 years. Her studies have dealt with fossils from the Mesozoic (mostly the Cretaceous) and the Cenozoic (mainly the Eocene and Miocene but up to the Holocene from Africa included). She has been interested in faunas originating from all continents and she produced large reviews of turtles from South America, Europe and Africa. She erected several taxa, mostly of turtles. Among these taxa are some strange forms that appear to represent unique morphological feeding type.

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murelagaXabier Murelaga. Departamento de Estratigrafía y Paleontología, Facultad de Ciencia y Tecnología, Universidad del País Vasco, UPV/EHU, Apartado 644, 48080 Bilbao, Spain. This email address is being protected from spambots. You need JavaScript enabled to view it.

Xabier Murelaga is a palaeontologist whose research covers a variety of subjects like taxonomy of Tertiary and Quaternary fossil microvertebrates and taxonomy and evolution of Mesozoic and Cenozoic turtles. Xabier is Assistant Lecturer in the Department of Stratigraphy and Palaeontology in the University of Basque Country.

 

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