Turkanemys Wood, 2003

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 : 38

Turkanemys Wood, 2003

TYPE SPECIES: Turkanemys pattersoni Wood, 2003 .

INCLUDED SPECIES: Turkanemys pattersoni Wood, 2003 .

DISTRIBUTION: Late Miocene Nawata Formation, early Pliocene Kanapoi Formation, and Mio-Pliocene sediments west of Ekora, northwestern Kenya ( Wood, 2003).

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 present but not reaching to dorsal edge of orbit; postorbital large in contrast to Podocnemis ; medial expansion of triturating surface, median maxillary ridge, present; two accessory ridges present on triturating surface in contrast to Erymnochelys and Peltocephalus , ridges deep in contrast to all other Erymnochydand; vomer absent; fossa precolumellaris present and shallow as in Peltocephalus but in contrast to Erymnochelys ; foramen jugulare posterius closed; jugal-quadrate contact absent in contrast to Erymnochelys and Peltocephalus ; horizontal occipital present in contrast to Erymnochelys and Peltocephalus ; chorda tympani enclosed in processus retroarticularis.

Postcrania with cervical centra saddle shaped but not identical to those in Peltocephalus ; nuchal bone width greater than length; six neurals extending to costal six; first neural four sided; pectoral scales do not contact mesoplastra, but do contact entoplastron and epiplastra.

DISCUSSION: Turkanemys provides anoth- er glimpse of the podocnemidid record in the African Miocene providing further evidence that there is much to be learned about the relationships of Erymnochelys and Peltocephalus from the fossil record. The shell of Turkanemys is very similar to that of Erymnochelys , particularly in the classically influential area of the anterior plastral lobe, in that it has medially meeting gular scales rather than separated ones as in Peltocephalus . In our resolution, the MPC shows Turkanemys as the sister taxon to ( Erymnochelys , Peltocephalus ) + remaining magnatribe Erymnochelydand. A close alternative would be Turkanemys as the sister taxon to ( Erymnochelys , Peltocephalus ). Unfortunately some potentially decisive characters in Turkanemys are missing due to lack of preparation, in particular the condition of the anterior opening of the cavum ptergoidei. So future work may resolve these relationships. Nonetheless, Turkanemys is clearly a member of the magnatribe Erymnochelydand, with close similarities to both Erymnochelys and Peltocephalus .

Cervical vertebrae 4–7 of both Erymnochelys and Turkanemys are very similar to each other in being wider than high and differ from other Podocnemidinae (as defined here) in lacking the well-developed heterocoely or saddle-shaped centra. This condition could be interpreted as an intermediate between the Podocnemis fully heterocoelous centra that wrap around posterolaterally and the condition seen in the basal podocnemidid, Bauruemys . Nonetheless, our analysis still places Turkanemys outside Erymnochelys + Peltocephalus requiring the wide articular condition to be acquired twice, despite the proximity of these taxa in the cladogram. Again, this is only a few steps away from a group containing Erymnochelys , Peltocephalus , and Turkanemys . We feel that although our MPC resolves these three taxa, in view of the missing data for Turkanemys it would be more realistic to conclude that the three are an unresolved trichotomy at present.

Another as yet incompletely described piece of the Erymnochelys-Peltocephalus puzzle may be a specimen from Kenya. Witmer (1990) published an abstract announcing a new fossil from the lower Miocene of Rusinga Island, Kenya. This well-preserved specimen, KNM-RU 18401, consists of an articulated skull, shell, cervicals, and appendicular elements, and has been examined by us in the KNM. This as yet unnamed specimen has what appears to be a quadratejugal contact that partially closes the check emargination, similar to that seen in Erymnochelys and Peltocephalus . It has a shallow fossa precolumellaris and a posterior cervical that is almost identical with one from Turkanemys . The Rusinga skull has a surface coating of matrix obscuring sutures, which needs to be removed before the very tentative sutures reported here can be accepted. Because of this and the fact that the lower jaws are still attached to the skull by matrix, we feel that there are insufficient characters to use this specimen in our character matrix. Although Witmer mentions the presence of an interorbital groove characteristic of Podocnemis , our own examination suggests that the widely spaced orbits of the Rusinga skull have a shallow midline depression not homolgous to the distinctly formed, interorbital groove seen between the very closely spaced orbits of Podocnemis . Nonetheless, we agree completely with Witmer’s conclusions (1990: 49A): ‘‘the Rusinga turtle is a member of a clade that was relatively diverse on mainland Africa, but that today exhibits a relict distribution.’’