Erymnochelys Baur, 1888

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 : 39-40

Erymnochelys Baur, 1888

TYPE SPECIES: Dumerilia madagascariensis Grandidier (1867) .

INCLUDED SPECIES: Erymnochelys madagascariensis .

DISTRIBUTION: Recent of Madagascar, possibly Miocene-Pliocene of eastern Africa. There have been a number of records of shell material identified as Erymnochelys sp. or as something similar to Erymnochelys (see Lapparent de Broin, 2000a, for summary and literature). Most of these are relatively fragmentary and, as far as can be determined from the publications, lack generic level diagnostic characters. However, Hirayama (1992) described shells and a posterior cervical from the Mio-Pliocene Sinda beds of the Democratic Republic of Congo (formerly Zaire) that are better preserved. The shells have a small intergular with medially meeting gular scales, diagnostic of Erymnochelys among the Recent fauna. The cervical is nearly identical to one of the cervicals in Erymnochelys , in that it is wider than high and lacks the saddle-shaped centra. However, considering the more recent additions to the fossil record, particularly Turkanemys and possibly related taxa, it is less likely that the Sinda material can be reliably identified as Erymnochelys . Among the published records, it is clear that the magnatribe Erymnochelydand has a long record in Africa that is only now being documented. The relatively conservative shell morphology in this group must be kept in mind when identifying shell material.

There is, however, undescribed skull material that can possibly be identified as Erymnochelys . Partial skulls and shell material in the MAC identified by label as coming from Miocene beds in the Sinda/Mohari region, western rift valley, Democratic Republic of Congo, consist of MAC RG1368A, MAC RG2626, MAC RG13686B, and MAC uncataloged. All are anterior portions of the skull, and all unfortunately lack any part of the cheek or basicranium. Although the preserved areas agree closely with the Recent Erymnochelys , the diagnostic characters of the cheek and basicranium are missing, making it possible that these specimens represent a taxon different from Erymnochelys .

DIAGNOSIS: A podocnemidid known from the skull and postcrania; skull relatively high and narrow in contrast to Bauruemys ; orbits facing laterally in contrast to Podocnemis ; interorbital groove such as found in Podocnemis absent; temporal emargination less than in Podocnemis ; parietal-quadratojugal contact long; cheek emargination absent; postorbital large in contrast to Podocnemis ; medial expansion of triturating surface, median maxillary ridge, present; accessory ridge or ridges present in triturating surface; vomer absent; fossa precolumellaris deep and well defined as in Podocnemis unifilis ; foramen jugulare posterius closed; jugal-quadrate contact present in contrast to all other podocnemidids except Peltocephalus and UCMP 42008; cavum pterygoidei with large anterior opening and foramen cavernosum in roof; horizontal occipital shelf absent; chorda tympani enclosed in processus retroarticularis.

Postcrania with cervical centra not saddle shaped but not the same as in Bauruemys ; nuchal bone width greater than length; six neurals extending to costal six; first neural four sided; axillary buttress reaches peripheral two in contrast to Peltocephalus ; axillary musk duct in buttress not in bridge; pectoral scales do not contact mesoplastra, but do contact entoplastron and epiplastra; gular scales meet on midline.

DISCUSSION: Use of Erymnochelys and Peltocephalus goes back to Dumeril and Bibron (1835) and Baur (1888), but it was the synonymization with Podocnemis by the influential Boulenger (1889) catalog that curtailed their use, despite Baur’s (1890) argument against synonymy, until Williams (1954c) began their more recent resurrection. In that paper Williams, agreeing with Baur (1890), Siebenrock (1902), and Müller (1935), proposed that Peltocephalus was allied with the African forms and not with the other South American ones, differing from the hypotheses of Dacqué (1912) and Zangerl (1948). Later, more widespread use of the three genera by Frair et al. (1978), Gaffney (1979), and others normalized the revival of the three genera.

Baur (1890: 483) published the following comparative diagnoses of the osteology of the three Recent podocnemidid genera in opposition to Boulenger’s sinking of them into Podocnemis :

‘‘ Podocnemis, Wagler

Jugal and quadrate bones separated; articular faces of anterior cervicals saddle shaped; first intercentrum small and free. Type: P. expansa, Schweigg.

‘‘ Peltocephalus, Dum. and Bib.

Jugal and quadrate in contact. articular faces of anterior cervical saddle shaped; first intercentrum large and suturally united with neuroids and centrum of atlas. Interparietal shield triangular with base behind. Type: P. tracaxa, Spix.

‘‘ Erymnochelys, Baur

Jugal and quadrate in contact; articular faces of cervicals not saddle shaped; first intercentrum large and suturally united with neuroids and centrum of atlas. Interparietal shield triangular with base in front. Tpye [sic]: E. madagascariensis, Grand. ’’

Despite examining specimens, we have been unable to substantiate the atlas character in Podocnemis . The other characters became very influential systematically and appear in nearly all phylogenetic treatments of the Podocnemididae over the past 120 years, including the present one.