Pelorochelon soriana, Adán Ṕerez-Garćia, Francisco Ortega & Emiliano Jiménez Fuentes, 2016
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publication ID |
https://doi.org/ 10.1111/zoj.12381 |
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DOI |
https://doi.org/10.5281/zenodo.5619929 |
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persistent identifier |
https://treatment.plazi.org/id/931F87FC-FFFB-DC5E-FC0D-3544D27F43EB |
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treatment provided by |
Plazi |
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scientific name |
Pelorochelon soriana |
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sp. nov. |
PELOROCHELON SORIANA SP. NOV.
( FIGS 2 View Figure 2 , 3 View Figure 3 , 4, 5 View Figure 5 )
Hadrianus sp. Jiḿenez Fuentes et al., 1988; Jiḿenez Fuentes, 1992, 2003; Cuesta Ruiz-Colmenares & Jiḿenez Fuentes, 1994
? Hadrianus sp. Jiḿenez Fuentes et al., 1989 Holotype. An almost complete shell, STUS 14223 ( Fig. 2 View Figure 2 ).
Paratypes. Forty-four specimens including several almost complete and partial shells, and isolated plates ( Figs 3 View Figure 3 , 4, 5 View Figure 5 ): shells STUS 14224, 14227, 14228, 14229, and 14230; partial carapaces STUS 14225, 14398, and 14399; first neurals STUS 8711, 10840, and 10862; pygals STUS 10785, 10786, and 10841; partial plastra STUS 11697, 11698, and 14226; epiplastra STUS 8707, 10814, 10843, 10849, 10850, 10852, 10853, 10856, 10857, 10860, 10861, 10864, 11693, 11694, 11695, 13736, 13753, 13754, 13762, 13763, and 13802; xiphiplastra STUS 10719, 10851, 10760, 10761, 10787, and 11696.
Etymology. The specific name refers to Soria, the Spanish province where the type locality is situated. Type locality and horizon. Mazateŕon locality ( Fig. 1 View Figure 1 ), Soria Province, Castilla y Léon, Spain. Upper part of the Mazateŕon Formation, early Bartonian, MP 15–16, middle Eocene ( Valero et al., 2012).
Diagnosis. A species of Pelorochelon with eight neurals, which differs from P. eocaenica by: rectangular morphology of the first or second neurals; short sides anteriorly positioned in the hexagonal second and third neurals; relatively short gular protrusion; relatively short epiplastral symphysis; very short dorsal epiplastral lip, in the sagittal plane; relatively short pectoral scutes.
Description of the shell. The length of the shell of the largest known specimens of P. soriana is close to 70 cm ( Fig. 3 View Figure 3 A). All preserved shells are crushed. However, the information available shows that its height was moderate. The outer surface of all the plates is granular. Well-developed carapace growth rings can be observed in all the specimens ( Figs 2 View Figure 2 A1, 3B, 4A1). This taxon lacks medial or lateral carapace keels. A shallow notch is present in the anterior carapace margin ( Figs 2 View Figure 2 A1, 3A, B, C, D). The nuchal plate is slightly wider than long. Pelorochelon soriana has eight neural plates ( Figs 2 View Figure 2 A1, 3B). The neural series is irregular, considering its morphology, but it is continuous, from the contact with the nuchal plate to that with the first suprapygal. All neurals are longer than wide, except the sixth and seventh ones. A dorsal bump is present on the first neural ( Figs 2 View Figure 2 A1, 4D, E, F). The second neural of some specimens is rectangular, being longer than wide ( Figs 2 View Figure 2 A1, 3B). The first neural of these specimens is hexagonal, with their short sides positioned posteriorly. However, the rectangular neural is the first one in other shells ( Figs 3 View Figure 3 B, C, D, 4D, E, F). The other neurals are hexagonal, with the short sides anteriorly positioned. Pelorochelon soriana has eight pairs of costals. All of them are noticeably wider than long. A well-developed alternating pattern of costals, composed by medially alternative long and short plates, versus laterally short and long ones, is present. Pelorochelon soriana has two suprapygals ( Figs 2 View Figure 2 , 3 View Figure 3 A, B, 4C). The first one is wider than the second. The posterior suprapygal is lenticular, and is embrassed by the first one. The morphology of the pygal could be rectangular or trapezoidal, being slightly wider than long or as wide as long ( Figs 2 View Figure 2 , 3 View Figure 3 A, B, 4C, G, H, I). This taxon has eleven pairs of peripherals. The distal margins of the anterior and posterior peripherals are dorsally directed. All of them lack pointed tips on the contact area of the sulci delimiting the marginal scutes with the carapacial rim ( Figs 2 View Figure 2 A, 3A, B, C, 4C).
A small cervical scute, that is almost as wide as long, is present ( Figs 2 View Figure 2 A1, 3B, C). This element is very short in visceral view ( Figs 2 View Figure 2 A2, 3A). This taxon has five relatively narrow vertebral scutes, the second to fourth being longer than wide. The third vertebral is slightly wider than the second, and both are wider than the fourth. The first one is wider that these vertebrals. The latero-posterior margins of this pentagonal vertebral are divergent towards the anterior region ( Figs 2 View Figure 2 A1, 3B, C, D, 4A1). The wider vertebral scute is the fifth, their latero-anterior margins being markedly divergent towards the posterior region. The first pair of pleurals is not in contact with the nuchal plate ( Figs 2 View Figure 2 A1, 3B, C, D). This pair of scutes contacts with the first to fifth marginals. The second pair contacts with the fifth to seventh marginals. The third pair contact with the sixth to ninth marginal. The last pair of pleurals contact with the ninth to eleventh marginal. Pelorochelon soriana lacks coincidence between the medial margins of the marginals and the costo-peripheral suture ( Figs 2 View Figure 2 A1, 3B, C). Twelve pairs of marginals are present. Thus, this taxon lacks a supracaudal scute. The first pair is significantly wider than long ( Figs 2 View Figure 2 A1, 3B, C, D). Therefore, this taxon lacks contact of the second marginals with the nuchal. The only marginals in contact with the first vertebral are those of the first pair. The anterior region of the last pair of marginals overlaps the posterior area of the second suprapygal ( Figs 2 View Figure 2 A1, 3B, 4C).
The plastral lobes are relatively short and wide ( Figs 2 View Figure 2 A2, 3A, 4A2, B). The anterior one is almost as long as the posterior. The anterior lobe is medially notched ( Figs 2 View Figure 2 A2, 3A, C2, D2, 4A2, B, 5A–W). The morphology of the lateral margins of the epiplastra is recognized as subject to variability, this area being substraight in some specimens ( Fig. 5 View Figure 5 J, M, Q) but subrounded in others ( Fig. 5 View Figure 5 D, E, H). The well-developed dorsal epiplastral lip is concave. It shows a welldeveloped visceral relief in the latero-anterior region of the epiplastra. The epiplastral symphysis is relatively short, being shorter than the length of the entoplastron. In the sagittal plane, the dorsal epiplastral lip is very short, generally being much shorter than half of the length of the epiplastral symphysis. This taxon has relatively short gular protrusions. It lacks gular pocket, as well as a well-developed change of relief in the posterior margin of the epiplastral lip ( Fig. 5 View Figure 5 A–W). The epiplastra are almost as wide as long. The entoplastron is subrhombic. 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 xiphiplastra are shorter that the hypoplastra. Pelorochelon soriana lacks plastral hinges. It has a wider than long anal notch ( Figs 2 View Figure 2 A2, 3A, 4A2, B, J– O). The morphology of the lateral margins of the xiphiplastra, and that of the lateral margins of the anal notch, are also subject to variability (compare the two specimens in Fig. 3 View Figure 3 A, one of them with straight margins but subrounded margins in the other).
The gular scutes of P. soriana do not overlap the entoplastron. These scutes contact the anterior margin of the entoplastron in some specimens ( Figs 2 View Figure 2 A2, 4B2) but other individuals lacks this contact ( Figs 3 View Figure 3 A, 3C2, 4A2). 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 but shows a well-developed lateral change of curvature. The pectoral scutes are relatively short in the medial region, being considerably shorter than the entoplastron in most of the specimens. These scutes do not contact the entoplastron. The concavity of the sulcus between the abdominal and the femoral scutes is anteriorly directed, in the medial region, whereas that between the femoral and anal scutes is posteriorly directed ( Figs 2 View Figure 2 A2, 3A, 4A2, B2). The abdominal scutes are the longest. The second longer scutes are the humerals.
Remarks. The comparison between the material of P. eocaenica and the specimens attributable to the genus Pelorochelon from Mazateŕon allows their assignment to two different species. Jiḿenez Fuentes (1992, 2003) indicated that the morphology of the dorsal region of the epiplastra of the taxon from Mazateŕon was different from that observed in the other European specimens of ‘ Hadrianus ’. However, Jiḿenez Fuentes (1992, 2003) did not describe those epiplastra, and he did not indicate what were these differences.
The neural formula of P. eocaenica and P. soriana is different. Some shells of P. eocaenica have all the neurals hexagonal, except the third one, which is rectangular, whereas, in other specimens, the nonhexagonal neurals are the fourth (rectangular) and the sixth (octagonal). In some specimens of P. soriana , all neurals are hexagonal, except the second one (rectangular), although the nonhexagonal neural is the first one (rectangular) in other individuals. The second neural of P. eocaenica is always hexagonal, their short sides being posteriorly positioned (as in H. corsoni ). The specimens of P. soriana in which the second neural is hexagonal possess the short sides anteriorly positioned. The presence of a rectangular second neural, recognized in other specimens of P. soriana , is shared with Fontainechelon cassouleti . The third neural P. soriana is always hexagonal, their short sides being anteriorly positioned. However, the short sides are posteriorly positioned in the specimens of P. eocaenica in which the third neural is hexagonal. The presence of a rectangular fourth neural, recognized in other specimens of P. eocaenica , is shared with H. corsoni , Ch. maurini , ‘ Erginemys ’ bruneti and the members of Titanochelon, being longer than wide in P. eocaenica , H. corsoni and Ch. maurini .
The gular protrusion of P. eocaenica is much longer than that of P. soriana . For this reason, the length of the epiplastral symphysis is much longer in the first of these two taxa, being even longer than the entoplastron in some specimens. The presence of a very short dorsal epiplastral lip in P. soriana , in the sagittal plane, contrasts with the long lip observed in P. eocaenica , longer than half of the length of the epiplastral symphysis.
The medial region of the pectoral scutes of P. eocaenica is long. In this sense, it can be as long as the entoplastron, or even longer than this plate in some specimens. This condition is shared with F. cassouleti . The pectoral scutes of P. soriana are shorter than those of P. eocaenica .
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