Ragechelus sahelica n.

Lapparent, France de, Chirio, Laurent & Bour, Roger, 2020, The oldest erymnochelyine turtle skull, Ragechelus sahelica n. gen., n. sp., from the Iullemmeden basin, Upper Cretaceous of Africa, and the associated fauna in its geographical and geological context, Geodiversitas 42 (25), pp. 455-484 : 466-467

Ragechelus sahelica n. sp.

( Figs 5-9 )

urn:lsid:zoobank.org:act:B201BDDE-1F71-49D9-8904-0D68D9595834

HOLOTYPE. — One skull, MNHN.RA.2018.0078.

ETYMOLOGY. — From Sahel, geographical area of discovery.

TYPE LOCALITY AND HORIZON. — Near Indamane village (or In Daman), at Mont Indamane (Mont Igdaman), 15°26’N, 5°48’E, at altitude 478 m, Tahoua district, southwestern Niger, Iullemmeden basin. Upper Cretaceous, late Maastrichtian. Gypsiferous phosphatic bone bed in the upper part of Lower Sandstones and Mudstones of “Term I” of Greigert (1966), and in the base of the Mosasaurus shales or Farin-Doutchi Formation, FD1 member (see Dikouma [1990] and Dikouma et al. [1994]).

DIAGNOSIS. — A podocnemidid taxon diversified in the continental lineage of Erymnochelyinae posteriorly to the Gondwana break which separated Africa and South America. It is not a member of Stereogenyina because without their smooth, long and medially widened “secondary palate”. Diagnosed as unique: by the meatus quadrati shape, “narrow hot air balloon” shaped, i.e. notable for its great height for its width and inferiorly point-ed, closer to E r ymnochelys madagascariensis and to some of the Neochelys arenarum specimens, instead of wider and rounded in other Erymnochelyinae ; by the flat and narrow anterior meatus wall without precolumellar fossa and with an incurved incisura columellae auris; developed triturating maxillary-palatine surfaces moderately widened, even barely posteriorly, with two strong crests, unique in erymnochelyines because the intermedial one is much less developed than the medial one, contrary to Turkanemys , Dacquemys and Mogharemys . Oblique inclined anterolateral border of the processus trochlearis pterygoideus as in Dacquemys . Long skull (phenotypic category), being longer for its width than in Neochelys , “ N. fajumensis ” and Mogharemys ; moderately wide for its full length (79.20%), with a triangular snout but notably transversally wide anteriorly at the not pointed external naris, long palate and short basicranium (46% of the palate length up to this basicranium); as preserved (and possible when living) moderate postorbital roof cover joining approximately the mid length of the meatus quadrati superior border, with an incurved dorsal posterior notch; not much elevated skull, with a primitive straight oblique roof cover in lateral view, the more similarly with Turkanemys among the longer skulls category where the full roof cover is known, not being posteriorly elevated and rounded as the more globose Erymnochelys skull, and not being anteroposteriorly convex in lateral view and much roofed as Dacquemys . Similarly or not, according to a distribution in mosaic in other erymnochelyines: consistent interorbital width with orbits nearly laterally positioned, and with relatively moderate proportions: orbit height being less great than the interorbital space, maxillae relatively high below the orbits (height less great than the interorbital space) and antorbital space still less great, and shortest inter-premaxillae suture; external naris less wide than the interorbital space but its width greater than the orbit long transversal diameter. Relatively moderately widened carotid foramen, no ventral prootic.

DESCRIPTION AND COMPARISONS

Preservation state

The skull is covered by a phosphatic gypsiferous crust that has been partly cleaned but the scute sulci are not visible and the sutures are more or less apparent by places (sometimes more visible under water). Parts of the lateral cheeks and roof (mainly quadratojugal, part of both postorbitary and jugal) are missing, as well as the supraoccipital crest, and a very small part of the right exoccipital at the occipital condyle. The medioanterior palatal part is pushed into the skull by longitudinal breaks in the maxillae while the roof is also moderately pushed into the skull by longitudinal breaks at the maxillary-prefrontal suture and at the parietal suture with the prootic and opisthotic (making the skull a little less high than in life but preserving its oblique straight line of elevation toward the back). However, considering the potential height (from the crushing degree), the skull roof was not much dorso-ventrally elevated. The remaining crust covers the bones by places, making them thicker than in living animal; only a small part of the dorsal roof sutures and a part of the ventral sutures are visible or suspected; at least the dorsal sutures extremities appear at their free border ( Figs 5 , 6 ).

Figures

FIG. 5. — Ragechelus sahelica n. gen., n. sp., Indamane, southwestern Niger, late Maastrichtian; photographs of the skull, holotype MNHN-RA-2018.0031: A-F, dorsal, ventral, left lateral, anterior, right lateral and posterior views. Scale bar: 4 cm.

FIG. 6. — Ragechelus sahelica n. gen., n. sp., Indamane, southwestern Niger, late Maastrichtian. Lateral view of the skull, holotype MNHN-RA-2018.0031. Abbreviations: an sq, antrum squamosum; co, condylus occipitalis; com q, commissura quadrati; fpp; foramen palatinum posterius; fr, frontal; ica+Et, incisura columellae auris with the Eustachian tube; ju, jugal; l pfr, left prefrontal; mq, meatus quadrati; mx, maxilla; na, external nare; pal, palatine; pfr, prefrontal; pmx, premaxilla; paq, processus articularis quadrati; pmx, premaxilla; po, postorbital; ppo, processus paroccipitalis opisthotici; pro, prootic; pter, pterygoid; ptp, processus trochlearis pterygoideus; q, quadrate; r paq, right processus articularis quadrati; r pter, right pterygoid; soc, supraoccipital; sq, squamosal; V, foramen trigemini; black arrow, position of the foramen stapediotemporale; blue and green dotted lines, hypothetic positions for the skull lateral notch border; red line, border of the palatal medial crest. Scale bar: 4 cm.

FIG. 7. — Ragechelus sahelica n.gen.,n. sp.,Indamane,southwestern Niger,late Maastrichtian;interpretative drawing of the skull,holotype MNHN-RA-2018.0031. Abbreviations:aaq, area articularis quadrati;boc, basioccipital; bsph, basiphenoid;car c, carotid canal; cav pter, cavum pterygoideum; co, condylus occipitalis; col-Et, columella auris with the Eustachian tube passage; cq, commissura quadrati; fpp, foramen palatinum posterius; fp, fenestra postotica; imc, intermediate maxillo-palatine crest; ju, jugal; mc, medial maxillo-palatine crest; ms, muscle insertion zone; mx, maxilla; pal, palatine; pmx, premaxilla; po, postorbital; ppo, processus paroccipitalis opisthotici; pter w, pterygoid wing; ptp, processus trochlearis pterygoideus; q, quadrate. Ventral view. Scale bar: 4 cm.

FIG. 8. — Ragechelus sahelica n. gen., n. sp., Indamane, southwestern Niger, late Maastrichtian;detail of the skull,holotype MNHN-RA-2018.0031,showing the rounded carotid foramen for entrance in te besicranium,at the back of the deep cavum pterygoideum, below the (broken here) podocnemidid pterygoid wing;Abbreviations:boc, basioccipital;bsph, basisphenoid;car can, enlarged carotid foramen; cav pter, cavum pterygoideum; pw, break of the pterygoid wing at its posterior base; q, quadrate; q art, area articularis quadrati. Ventral view. Scale bar: 2 cm.

FIG. 9. — Ragechelus sahelica n. gen., n. sp., Indamane, southwestern Niger, late Maastrichtian; detail of the skull, cavum tympani area, holotype MNHN- RA-2018.0031. Abbreviations: ant, antrum squamosum; cq, commissura quadrati; ica+Et, incisura columellae auris with Eustachian tube. Left lateral view. Scale bar: 2 cm.