Cordichelys antiqua ( Andrews, 1903 ) Gaffney & Meylan & Wood & Simons & De Almeida Campos, 2011

Gaffney, Eugene S., Meylan, Peter A., Wood, Roger C., Simons, Elwyn & De Almeida Campos, Diogenes, 2011, Evolution Of The Side-Necked Turtles: The Family Podocnemididae, Bulletin of the American Museum of Natural History 2011 (350), pp. 1-237 : 49-51

Cordichelys antiqua ( Andrews, 1903) , n. gen.

Podocnemis antiqua Andrews, 1903

Podocnemis stromeri Reinach, 1903a

Shweboemys antiqua Wood, 1970

Stereogenys cromeri Andrews, 1906 (in part) ‘‘ Pod. Stromeri var. major ,’’ Reinach, 1903a

TYPE SPECIMEN: CGM 10038 ( Andrews,

1903: pl. 8, figs. A, B; more detailed description with same figure in Andrews, 1906), a nearly complete shell so heavily coated with gypsum that none of the scute sulci and only some of the bone sutures can be recognized.

TYPE LOCALITY: ‘‘north of Birket el- Qurun’’ Andrews (1906: 289).

TYPE HORIZON: ‘‘Qasr el-Sagha beds (Middle Eocene)….’’ Andrews (1906: 289); now regarded as late Eocene ( Holroyd et al., 1996; Seiffert, 2006).

DIAGNOSIS: Genus is monotypic.

REFERRED SPECIMEN: YPM 7457 (formerly YPM 6205; field number 67-502, accession 7152; skull drawings published by Gaffney, 1979: fig. 136 as YPM 6205), associated skull and shell (figs. 53–57); ‘‘Eocene, Qasr el-Sagha Fm., Zeuglodon Valley, Egypt, collected Lloyd Tanner, 1966–67’’ (label and YPM database, original accession data states only ‘‘Zeuglodon Valley’’). According to P. Holroyd (personal commun.) the Qasr el-Sagha Fm. does not outcrop in Zeuglodon Valley and the source is more likely the Birket Qarun Fm. However, Moustafa (1974: fig. 4) shows a ‘‘ Podocnemis antiqua ’’ partial shell in situ in the Qasr el-Sagha Fm. that may be YPM 7457 (P. Holroyd, personal commun.).

DISCUSSION: Considering the large number of commonly shared characters evident in the shells of Cordichelys antiqua and ‘‘ Podocnemis stromeri , ’’ i.e., the pointed xiphiplastra, straight outer borders of the posterior plastral lobe, short anterior plastral lobe, indentation at the front end of the carapace, same number of neurals, and in general the similar configurations of bone sutures and scute sulci; it seems reasonable to conclude that all these specimens belong to a single species. Therefore, we have synonymized ‘‘ Podocnemis stromeri ’’ Reinach, 1903a, including ‘‘ Pod. Stromeri var. major ,’’ with Cordichelys antiqua .

DESCRIPTION: Although the type specimen of ‘‘ Podocnemis ’’ antiqua (CGM 10038) consists of a fairly complete shell, it is so heavily coated with gypsum that none of the scute sulci and only some of the bone sutures can be recognized. The Yale specimen (YPM 7457, figs. 56, 57), which forms the basis for the following description, now permits a much fuller account to be given of the shell of this poorly known species as well as of its skull.

Andrews (1906: 289) commented regarding the type of ‘‘ Podocnemis ’’ antiqua that: ‘‘The carapace in this species is flatter posteriorly than in front, where it seems to have been highly arched. The nuchal border is straight, without a trace of any emargination.’’ Crushed bone may have misled Andrews in reconstructing the only specimen he had available for study. Inspection of the Yale specimen confirms only part of this description. The entire carapace was apparently rather flat and more or less low arched in cross section. No evidence of a more pronounced arching toward the front can be detected in the Yale specimen. In addition, a definite emargination in the anterior edge of the nuchal is clearly discernible, producing an unusual cordiform shell.

Eleven peripherals that extend along either side of the carapace from the nuchal back to the pygal are preserved on one side or the other of YPM 7457. Contrary to Andrew’s observation (1906: 290) that ‘‘The last marginals [peripheral bones] and pygals are somewhat enlarged,’’ these elements appear to be roughly equivalent in size to the anterior peripherals, and it would appear that the middle peripherals in the series are actually the largest. Numbers seven, eight, and nine are larger than the others, being not only longer but also wider than the others. The nuchal is much wider than long and, as noted above, is indented along the anterior margin. Andrews (1906: 289) mentioned that ‘‘at the point of junction of the nuchal, first neural, and first costal there is a small opening through the shell.’’ Apparently he regarded this as a natural fenestration. No similar structure is evident on the Yale specimen, and in view of the poor state of preservation of the type it is reasonable to assume that the holes that Andrews observed can be attributed to distortion caused by crushing. Six neurals are present, the first one abutting directly against the posterior end of the nuchal. The first neural is fusiform in shape, while the following four are hexagonal and elongate anteroposteriorly. The last neural is pentagonal in outline and as wide as it is long. Intervening between the last neural and the suprapygal are three costals (numbers six, seven, and eight) that meet in the midline. Of the eight costals, the first is the largest and there is a progressive decrease in size posteriorly. The suprapygal is pentagonal, its borders abutting against the last pair of costals, the 11th pair of peripherals, and the pygal. In typical pleurodiran fashion, the pelvic girdle was fused to the carapace and plastron. However, because of severe weathering in the area of the iliac attachment, it is not possible to determine the outline of the scars representing the point of fusion between pelvis and carapace.

There are five vertebral scales, all roughly hexagonal in outline. The first is slightly wider at its widest point than the nuchal bone underlying it. It converges anteriorly and is narrower than the nuchal where it reaches the anterior margin of the shell. This species is unique among Pelomedusoides in that the first vertebral extended forward to the anterior margin of the carapace, preventing the first pair of marginal scales from meeting in the midline (fig. 56). Four pairs of pleural scales are arranged along either side of the vertebrals. Extending around the fringe of the carapace are 12 marginal scales. The first pair do not meet at the front of the shell, as noted above, because of the interposition of the first vertebral scale. The sulci between the pleurals and marginals are situated well down on the peripheral bones, more or less midway between their distal and proximal ends.

In the plastron of the type, the scale sulci are unrecognizable, and the pattern of bone sutures on the outer surface is obscured. What Andrews (1906: 290) described was actually the bone suture pattern on the inner surface of the plastron. The Yale shell (YPM 7457) confirms his general description, however. The posterior lobe of the plastron is narrower than the anterior one, and it extends much farther from the bridge than does the anterior lobe. The exterior surface of the plastron is completely flat except for a slight upward curve at the posterior tip of the acutely pointed xiphiplastra. Situated rather more anteriorly than in most other pleurodires, the diamond-shaped entoplastron permits only a narrow contact between the epiplastra at the anterior margin of the plastron. From the outer angles of the entoplastron, sutures separating the epiplastra from the hyoplastra extend to the outer border on a line approximately perpendicular to the long axis of the shell. The complex pattern of these sutures, which Andrews described, is characteristic only of the inner surface of the plastron. The sutures between the hyoplastra and hypoplastra bisect the middle of the bridge and terminate laterally in a junction with the mesoplastral sutures. No mesoplastra have been preserved, but from the notch between the lateral borders of the hyo- and hypoplastron it is possible to determine that they were relatively small and probably hexagonal. The suture between the hypoplastra and the xiphiplastra is situated about one-third of the distance from the posterior end of the bridge to the posterior end of the plastron. A V-shaped notch is excavated into the posterior border of the xiphiplastra. The relative position and orientation of the ischial and pubic scars are not very different from those of recent specimens of Pelusios , Pelomedusa , and Podocnemis . Possibly, however, in Cordichelys antiqua the ischial scar may be relatively larger than the pubic scar as compared to the living forms. The pelvis itself has not been preserved.

Interposed between the gulars is a narrow triangular intergular that extends posteriorly onto the entoplastron and separates the small triangular gulars at the midline. Along the posterior part of their midline borders, the humerals meet each other, but anteriorly they too are separated by the intergular. For the most part, the lateral portions of the humero-pectoral sulcus coincide with the epi-hyoplastral suture. The pectoral-abdominal sulcus does not cross the mesoplastra; the position of this and the remaining plastral sulci are indicated in figure 56.