Pelorochelon eocaenica, Hummel, 1935, Hummel, 1935

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 : 660-661

PELOROCHELON EOCAENICA ( HUMMEL, 1935)

COMB. NOV.

(FIGS 23–28 IN HUMMEL, 1935)

Testudo eocaenica Hummel, 1935

Hadrianus eocaenicus de Broin, 1977

Manouria (Hadrianus) eocaenica Danilov & Averianov, 1997

Hadrianus s.l. eocaenica de Lapparent de Broin, 2001

‘ Hadrianus ’ eocaenica Ṕerez-Garćıa & Vlachos, 2014

Holotype. A complete shell and other elements, corresponding to the specimen 24 in Hummel (1935) (fig. 23 in Hummel, 1935).

Referred material. Several partial shells, corresponding to the specimens 1, 18, 24, 25, and 39 in Hummel (1935) (figs 24–28 in Hummel, 1935). Type locality and horizon. Mücheln, Germany ( Fig. 1 ). Lutetian, MP 11–13, middle Eocene ( Hummel, 1935; de Lapparent de Broin, 2001). Emended diagnosis. A species of Pelorochelon with eight to nine neurals, which differs from P. soriana by: rectangular morphology of the third or fourth neurals; short sides posteriorly positioned in the hexagonal second and third neurals; long gular protrusion; relatively long epiplastral symphysis, being even longer than the entoplastron in some specimens; long dorsal epiplastral lip, longer than half of the length of the epiplastral symphysis; long medial region of the pectoral scutes, almost as long as the entoplastron, or even longer than this plate.

Description of the shell. Pelorochelon eocaenica is a relatively large testudinid, with a shell close to 70 cm in length. Although all known shells are crushed, it is possible to interpret that the height was moderate. The outer surface of all the plates of both the carapace and the plastron is granular. The preserved carapaces show well-developed growth rings. They lack keels. A shallow notch is present in the anterior carapace margin (fig. 23A in Hummel, 1935). The nuchal plate is slightly wider than long. Some specimens of P. eocaenica have eight neurals (fig. 23A in Hummel, 1935). However, the presence of nine neurals is interpreted in other individuals (fig. 28 in Hummel, 1935). The neural series is irregular and continuous, from the contact with the nuchal to that with the suprapygals. The anterior neurals, and those located in the middle region of the neural series, are longer than wide (figs 23A, 27A, and 28 in Hummel, 1935). Some shells of P. eocaenica have all the neurals hexagonal, except the third one, which is rectangular (fig. 27a in Hummel, 1935), whereas the nonhexagonal neural is the fourth in other specimens, being rectangular (fig. 28 in Hummel, 1935). Both the fourth (also rectangular) and the sixth (octagonal) are nonhexagonal neurals in others (fig. 23a in Hummel, 1935). The short sides of the hexagonal first to third neurals are posteriorly positioned (fig. 23a in Hummel, 1935). Nevertheless, the short sides of the hexagonal fourth and fifth neurals are anteriorly positioned (figs 23A, 27A, and 28 in Hummel, 1935). The lengths of the latero-anterior and lateroposterior margins of the posterior neurals are similar to each other. This taxon has eight pairs of noticeably wider than long costals. A well-developed alternating pattern of costals is present (fig. 23a in Hummel, 1935). Two suprapygals are present (figs 23a and 28 in Hummel, 1935). The first one is wider than the second, embrassing it. The known pygal is subtrapezoidal, being slightly wider than long (fig. 23a in Hummel, 1935). Pelorochelon eocaenica has eleven pairs of peripherals. The distal margins of the anterior and posterior plates are dorsally directed. They lack anterior or posterior pointed tips ( Figs 2 A, 3A, B, C, 4C).

A small cervical scute is present (fig. 23a in Hummel, 1935). It is almost as wide as long. The second to fourth vertebrals are relatively narrow, being longer than wide. The fourth vertebral is wider than the third one in some specimens (fig. 23a in Hummel, 1935) but not in others (fig. 28 in Hummel, 1935). The fifth vertebral is the widest (fig. 23a in Hummel, 1935). Therefore, the first one is narrower than that vertebral but it is wider than the others. The lateroposterior margins of the first vertebral are divergent towards the anterior region. The latero-anterior margins of the fifth vertebral are markedly divergent towards the posterior region. The first pair of pleurals contacts with the first to fifth marginals. The second pair contacts with the fifth to seventh marginals. The third pair contacts with the sixth to ninth marginal. The last pair of pleurals contacts with the ninth to eleventh marginal. The medial margins of the marginals do not contact with the costo-peripheral suture. Pelorochelon eocaenica lacks a supracaudal scute as a result of the absence of fusion between the scutes of the last pair of marginals. The first pair of marginals is significantly wider than long. This taxon lacks contact of the second marginals with the nuchal plate. The only pair of marginals in contact with the first vertebral is the first one. The anterior region of the last pair of marginals overlaps the posterior area of the second suprapygal.

The anterior plastral lobe is narrower than the posterior, being slightly longer (figs 23b, 24, and 26 in Hummel, 1935). The anterior lobe is medially notched. The lateral margins of the known epiplastra are subrounded. The dorsal epiplastral lip of this taxon is concave. It shows a well-developed visceral relief in the latero-anterior region of the epiplastra. In the sagittal plane, the dorsal epiplastral lip is longer than half of the length of the epiplastral symphysis. The epiplastral symphysis is relatively long, being even longer than the entoplastron in some specimens (figs 24 and 25a in Hummel, 1935). This taxon has a relatively long gular protrusion. It lacks gular pocket, as well as a well-developed change of relief in the posterior margin of the epiplastral lip. The epiplastra are almost as wide as long. The entoplastron is subrhombic, wider than long in some specimens (figs 24 and 25a in Hummel, 1935) but longer than wide in others (fig. 26 in Hummel, 1935). The hyoplastra are longer that the hypoplastra. The axillary buttresses are in contact with the lateral region of the first pair of costals. The inguinal buttresses contact the lateral region of the fifth pair of costals. The xiphiplastral are shorter that both hyoplastra and hypoplastra. No plastral hinges are developed in this taxon, all constacts between the plates being well sutured. The anal notch is wider than long, with straight to subrounded margins (figs 23b, 24, 26, and 27b in Hummel, 1935). The morphology of the lateral margins of the xiphiplastra are subrounded, with a welldeveloped contrition in the region of contact with the femoro-anal sulcus.

The gular scutes of some individuals contact with the anterior end of the entoplastron (figs 23b and 26 in Hummel, 1935). However, the gulars of other specimens are shorter, lacking this contact (figs 24 and 25a in Hummel, 1935). In all the specimens, the anterior angle between the sagittal axis and the gularo-humeral sulcus is higher than 65°. The humero-pectoral sulcus is perpendicular to the axial plane in the medial area in some specimens (figs 23b and 26 in Hummel, 1935) but not in others (figs 25a and 27b in Hummel, 1935). The medial region of the pectoral scutes of P. eocaenica is relatively long. In this sense, it can be as long as the entoplastron in some specimens (fig. 25a in Hummel, 1935), or even longer than this plate in others (fig. 24 in Hummel, 1935). The relationship between the pectoral scutes and the entoplastron of P. eocaenica is subject to variability. Although these elements are not in contact in some specimens (figs 24, 25a, and 27b in Hummel, 1935), the pectorals of some individuals contact with the posterior margin of the entoplastron (fig. 23b in Hummel, 1935) or overlap the posterior region of this plate (fig. 26 in Hummel, 1935). The medial region of the sulcus between the abdominal and the femoral scutes can be concave (figs 26 and 27b in Hummel, 1935), subperpendicular to the axial plane (fig. 23b in Hummel, 1935), or convex (fig. 24 in Hummel, 1935). However, the sulcus between the femoral and the anal scutes is convex in all known specimens. In the plastron, the abdominal scutes are the longest.

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.

Figure 2. STUS 14223, holotype of Pelorochelon soriana, from the early Bartonian (middle Eocene) of the Spanish site of Mazateŕon (Soria Province), in dorsal (A) and ventral (B) views. Scale bar = 10 cm.