Fontainechelon cassouleti, Claude & Tong, 2004, Claude & Tong, 2004

Adán Ṕerez-Garćia, Francisco Ortega & Emiliano Jiménez Fuentes, 2016, Taxonomy, systematics, and diversity of the European oldest testudinids, Zoological Journal of the Linnean Society 177, pp. 648-675 : 662-664

FONTAINECHELON CASSOULETI

( CLAUDE & TONG, 2004) COMB. NOV.

( FIG. 6 D)

Achilemys cassouleti Claude & Tong, 2004

‘ Achilemys ’ cassouleti Gmira et al., 2013 ; Ṕerez- Garćıa & Vlachos, 2014; Ṕerez-Garćıa, 2015

Holotype. MDE-sp37, a specimen preserving the partial carapace, the complete plastron, the right humerus and the left femur ( Fig. 6 D; fig. 3A–E, fig. 3I –N, and plate 3 in Claude & Tong, 2004).

Referred material. MDE-sp90, a right femur (fig. 3F–H in Claude & Tong, 2004), and some unnumbered shell fragments in Claude& Tong, 2004.

Type locality and horizon. Saint-Papoul, Aude, France ( Fig. 1 ). Clays of Saint-Papoul, early Ypresian, MP 8–9, early Eocene (Pérez-Garćıa & de Lapparent de Broin, 2015).

Emended diagnosis. Western European Cenozoic testudinid, with the length of the shell close to 40 cm, differing from all the medium and large European testudinids by the presence of markedly wider than long nuchal, first suprapygal noticeably narrower than the second one, contact between the suprapygals perpendicular to the axial plane, and shorter than wide epiplastra, and characterized by the following exclusive character combination: shallow notch in the anterior carapace margin; eight neurals; hexagonal first neural, with the short sides positioned posteriorly; quadrangular second neural; octagonal third neural; significantly wider than long pygal; dorsally directed distal margins of the anterior and posterior peripherals; smooth outline in the anterior carapacial rim but with the presence of pointed tips in the posterior rim, generating an undulating morphology; presence of a cervical scute; cervical almost as wide as long; third vertebral longer than wide; overlap of the first pair of pleural scutes on the nuchal; third pleurals contacting the seventh to ninth pair of marginals; medial margins of the first marginals not contacting the suture between the first costals and the peripherals; second marginals not contacting the nuchal; fourth marginals medially in contact with the first pleurals; presence of twelve pairs of marginals; overlap of the twelfth marginals on the second suprapygal; anterior plastral lobe as long as the posterior one; straight anterior margin of the anterior plastral lobe; concave dorsal lip of the epiplastra; well-developed gular protrusions; absence of gular pocket; step-like morphology behind the epiplastral lip; sutured contact between all plastral plates; gular scutes not contacting the entoplastron; anterior angle between the sagittal axis and the gularo-humeral sulcus of 65° or more obtuse; contact of the pectorals with the posterior margin of the entoplastron; medially long pectorals scutes; slightly curved diaphyses of the humerus an femur; relatively large angle between the femoral head and the diaphysis of the femur.

Description of the shell. The estimated length of the shell of the holotype and only known shell of F. cassouleti is 370 mm ( Fig. 6 D; fig. 3 and plate 3A–E in Claude & Tong, 2004). Its carapace is relatively high. It shows a granular outer surface. Well-developed carapace growth rings are identified. The morphology of the carapace is subquadrangular. It lacks carapace keels and bumps. The anterior carapace margin has a shallow but wide notch. The nuchal plate is markedly wider than long. This taxon has eight neurals, composing an irregular but continuous series. The first to fifth neurals are longer than wide. The others are wider than long. The first neural is hexagonal, with the short sides positioned posteriorly. The second one is subrectangular, the lateral edges being slightly convex. The third neural is octagonal, with very short latero-anterior and latero-posterior margins. The fourth and fifth neurals are not known. The posterior neurals are hexagonal, their latero-anterior margins being shorter than the latero-posterior. Fontainechelon cassouleti has eight pairs of costals. It shows a well-developed alternating pattern of costals, with the odd costals wider medially, and the even ones wider laterally. The proximal regions of the dorsal ribs are short. Two suprapygals are present. The contact between these plates is perpendicular to the axial plane. The first one is narrower than the second. The first is trapezoidal, wider at the posterior region than at the anterior one. The other suprapygal can be interpreted as subpentagonal. The pygal plate is more than two times wider than long. Eleven pairs of peripherals are present. The distal margins of the anterior and posterior peripherals are dorsally directed. Althought F. cassouleti lacks pointed tips in the anterior carapacial rim, these structures are present in the posterior rim, in the region of contact of the sulci between the marginal scutes and the lateral border of peripherals, generating an undulating morphology.

Fontainechelon cassouleti has a cervical. In dorsal view, this scute is almost as wide as long. However, its visceral length is short (plate 3C–E and fig. 3 in Claude & Tong, 2004). Five relatively narrow vertebral scutes are present. The first is approximately as wide as long. It has an anterior rounded outline but their latero-posterior margins are substraight, constituting slightly divergent margins. The second to fourth vertebrals are longer than wide. The third one is the longest in the vertebral series. The second and third are subrectangular but the fourth is subhexagonal. The fifth is the widest, being substantially wider than long. The first pair of pleurals overlaps the latero-posterior region of the nuchal plate. Fontainechelon cassouleti lacks contact between the second pleurals and the fourth marginals, as well as between the third pleurals and the sixth marginals. The anterior marginals do not contact the suture between the costals and the peripherals. However, the contact between the marginals and the pleurals coincides with that suture from the third marginals. The second marginals do not contact the nuchal plate nor the vertebral series. This taxon lacks supracaudal scute. Therefore, twelve pairs of marginals are present. The twelfth marginals overlap the posterior region of the second suprapygal.

The anterior plastral lobe is as long as the posterior one ( Fig. 6 D; fig. 3 and plate 3A, B in Claude & Tong, 2004). The length of the plastral bridge is greater than that of each of the lobes. The anterior lobe is subtrapezoidal. It lacks medial notch. Its anterior margin is straight, perpendicular to the axial axis. The lateral margins are rounded. This taxon has well-developed gular protrusions. A well-developed dorsal lip of the epiplastra is observed. This lip is concave. Its medial length is greater than half of the length of the epiplastral symphysis. The symphysis is relatively long, its length being greater than half of that of the entoplastron. The epiplastra are noticeably wider than long. Fontainechelon cassouleti lacks gular pocket. However, a relatively well-developed change in the visceral relief of the epiplastra, behind the lip, is present. The suture between the epiplastra and the hyoplastra is subperpendicular to the axial axis. The entoplastron is subrombic. This plate is posteriorly elongated. The hyoplastra are longer that the hypoplastra. The axillary and inguinal buttresses are in contact with the lateral region of the costal series: the axillary buttresses contacting with the lateral region of the first pair of costals, and the inguinals contacting with the lateral region of the fifth pair of costals. The xiphiplastra are shorter that the hypoplastra but slightly longer than the entoplastron. This taxon lacks plastral hinges. It has a wider than long anal notch. The lateral margins of the xiphiplastra, and those of the anal notch, are subrounded. A slight protrusion is identified in the lateral margin of the xiphiplastra, in the contact region with the femoro-anal sulcus.

The gular scutes of F. cassouleti not contact with the entoplastron ( Fig. 6 D; fig. 3 and plate 3A, B in Claude & Tong, 2004). The anterior angle between the sagittal axis and the gularo-humeral sulcus is higher than 65°. The pectorals contact with the posterior margin of the entoplastron. Medially, the humero-pectoral sulcus is perpendicular to the axial plane. However, it shows a well-developed lateral change of curvature. The pectorals are medially long, being almost as long as the entoplastron. These scutes contact with the posterior margin of the entoplastron. The longer scutes are the abdominals. Medially, the sulcus between the pectoral and the abdominal scutes is subperpendicular to the axial axis. However, the abdomino-femoral sulcus is medially concave. That between the femoral and the anal scutes is convex.

Remarks. As has been indicated, the previous generic attribution of the testudinid from the French locality of Saint-Papoul (early Eocene), Achilemys, has been refuted ( Gmira et al., 2013; Ṕerez-Garćıa & Vlachos, 2014; Ṕerez-Garćıa, 2015). Achilemys was defined by a specimen, from the middle Eocene of Wyomming ( USA) ( Hay, 1908). This specimen is the holotype of the species A. allabiata ( Cope, 1872b), the only known specimen of this genus. It is a partial shell, represented by the right half of the anterior plastral lobe, two anterior peripherals, three posterior peripherals, a portion of the pygal, and a portion of the last suprapygal. Therefore, the information available for this North American taxon is very limited. That specimen was first attributed to Hadrianus (i.e. Hadrianus allabiatus ) ( Cope, 1872b) and, subsequently, recognized as belonging to a new genus, Achilemys, based on the thin and short epiplastral lip, probably being concave; the absence of contact of the posterior margin of the fifth vertebral with the pygal plate; and the presence of recurved posterior peripherals ( Hay, 1908). The identification of these three characters in the testudinid from Saint- Papoul ( Fig. 6 D) led Claude & Tong (2004) to propose that cogeneric attribution. However, it is now known that these character states are also present in other testudinids, including European forms, as has been previously stated. Thus, as can be observed in the cladistic analysis performed here, the epiplastral lip may be shorter in some European taxa than in F. cassouleti (e.g. P. soriana ). The last pair of marginal scutes (or the supracaudal scute) is superimposed on the posterior region of the second suprapygal in all European taxa analyzed here. The presence of recurved posterior peripherals, observed in F. cassouleti , is also shared with several European taxa, as is the case of the Pelorochelon members and Ta. gigas. Claude & Tong (2004) indicated that the pygal plates of A. allabiata and F. cassouleti were wider than long, supporting the cogeneric relationship. As a result of its preservation, the ratio between the width and the length of the pygal plate of the North American taxon is not known. However, a similar ratio to that being part of the variability of some European testudinids can be interpreted (compare the pygal plate of the holotype of A. allabiata, in fig. 482 of Hay, 1908; with those of the P. soriana specimens in Figs 1 A, 2B). Therefore, the most accurate knowledge about the Paleogene forms shows that all the characters previously considered as exclusively shared between A. allabiata and the Saint-Papoul taxon are also shared with other testudinids.

Most of the limited characters available in the holotype of A. allabiata, several of them recognized here and other recent studies as having relevant systematic value ( Gmira et al., 2013; Ṕerez-Garćıa & Vlachos, 2014; Ṕerez-Garćıa, 2015), are not shared with the Saint-Papoul taxon: absence of undulating posterior carapace margin, absence of gular protrusion, short epiplastral symphysis, longer than wide epiplastra, antero-laterally directed suture between the epiplastra and the hyoplastra, elongated anterior half of the entoplastron, absence of the morphology of the epiplastral lip described for F. cassouleti , gular scutes on the anterior region of the entoplastron, anterior angle between the sagittal axis and the gularo-humeral sulcus approximately 45°, gularo-humeral sulcus almost reaching the anterior plastral margin. Therefore, the previously proposed attribution of ‘ Achilemys ’ cassouleti to a new genus ( Gmira et al., 2013; Ṕerez- Garćıa & Vlachos, 2014; Ṕerez-Garćıa, 2015) is supported here. The review of several European Paleogene testudinids performed here, as well as the comparison with North American forms, allows us to characterize this new genus (i.e. Fontainechelon ). In addition to the comparisons between the shell of F. cassouleti and those of other European taxa performed here, Ṕerez-Garćıa & Vlachos (2014) indicated some differences corresponding to appendicular bones. The appendicular bones so far described in the European taxa analyzed here are the humerus and femur of F. cassouleti and numerous elements of Titanochelon. As Ṕerez-Garćıa & Vlachos (2014) indicated, the humerus and femur of Titanochelon show a more curved diaphysis compared with those of F. cassouleti . Moreover, the longer diameter of the femoral head of F. cassouleti is developed with an acute angle, much lower than that observed in Titanochelon.

Figures

Figure 1. Geographical position of the type localities of the European Eocene testudinids discussed here. 1, Llamaquique (Asturias, Spain), middle-late Eocene, type locality of ‘ Asturichelys multicostatus ’. 2, Mazateŕon (Soria, Spain), middle Eocene, type locality of Pelorochelon soriana. 3, Falaise de Baby (Gironde, France), late Eocene, type locality of Cheirogaster maurini. 4, Castrais (Tarn, France), middle Eocene, type locality of ‘ Testudo castrensis ’. 5, Saint-Papoul (Aude, France), early Eocene, type locality of Fontainechelon cassouleti. 6, Salzburg (Austria), middle Eocene, type locality of ‘ Cheirogaster steinbacheri ’. 7, Mücheln (Germany), middle Eocene, type locality of Pelorochelon eocaenica.