Caninemys tridentata, Meylan & Gaffney & De Almeida Campos, 2009

Meylan, Peter A., Gaffney, Eugene S. & De Almeida Campos, Diogenes, 2009, Caninemys, a New Side-Necked Turtle (Pelomedusoides: Podocnemididae) from the Miocene of Brazil, American Museum Novitates 3639, pp. 1-26 : 4-5

Caninemys tridentata , new species

TYPE SPECIMEN: DNPM-MCT 1496 - R, a nearly complete skull ( figs. 1–4 ) collected by L.I. Price in 1962 .

TYPE LOCALITY: Locality 28 of L.I. Price, Volta de Pedra Pintada , upper Rio Juruá, Acre, Brazil ( fig. 5 ) .

HORIZON: Vertebrate fossils from the upper Rio Juruá are typically found in two beds associated with the Ucayali Unconformity ( Gaffney et al., 1998, Campbell et al., 2000). They come from late Miocene Red Beds of the Contamana Group that lie below the unconformity (‘‘Huayquerian Beds’’ of Lapparent de Broin et al., 1993), or they come from the Acre Conglomerate unit of the Madre de Dios Formation, which overlies the unconformity (Campbell et al., 1985, 2001). Paleochannels filled with younger sediments that are known to produce vertebrate fossils elsewhere in Acre are apparently not accessible along the upper Rio Juruá ( Campbell et al., 2000). It is unlikely that this skull is from a younger horizon. The Acre Conglomerate is also considered to be of late Miocene age by Frailey (1986) and Campbell et al. (2001). Thus, we assign DNPM-MCT 1496- R to a late Miocene age, even though we do not know with certainty from which side of the Ucayali Unconformity it has come.

Lapparent de Broin et al. (1993) included this skull among turtle material they reported from ‘‘Huayquerian Beds’’ and referenced the work of Campos and de Broin (1981). The latter reference lists this material only as coming from the Neogene of Acre. We have not been able to confirm an origin from the ‘‘Huayquerian Beds’’ below the Ucayali Unconformity. Discussion of a lower jaw (see below) that might be assigned to this taxon and other geologic references are in Gaffney et al. (1998).

DIAGNOSIS: Same as for the genus.

ETYMOLOGY: The species epithet is based on the tridentate appearance of the skull that is most clearly seen in anterior view.

DISCUSSION: Although this taxon cannot be differentiated from the shell-based Stupendemys geographicus Wood, 1976 , because there is no overlap in presently known morphology, it is likely that Caninemys is significantly smaller than the Venezuelan Stupendemys . Using skull-shell ratios of recent specimens of Podocnemis expansa and other recent podocnemidid species, it is hypothesized that the shell of Caninemys would be less than 4–5 feet in length rather than the 7-foot plus length of Stupendemys . For comparison, the largest skulls of recent Podocnemis expansa have a condylobasal length of about 12 cm (Williams, 1956) and the Mio-Pliocene Podocnemis bassleri (Williams, 1956; very similar to P. expansa in morphology) is 15.7 cm in length, compared to about 16.5–17.0 cm for Caninemys . It is of course possible that smaller species of Stupendemys were present in the Acre region and that Caninemys is the skull of one of these, but this is only speculation.

Figures

Fig. 1. Caninemys tridentata, new genus and species, DNPM-MCT 1496-R holotype. Partially restored views of skull. A, Dorsal; B, ventral; C, lateral. (B. Degner, del.)

Fig. 2. Caninemys tridentata, new genus and species, DNPM-MCT 1496-R holotype. Partially restored ventral view. (F. Ippolito, del.)

Fig. 3. Caninemys tridentata, new genus and species, DNPM-MCT 1496-R holotype. A, Dorsal; B, ventral; C, right lateral; D, posterior; E, left lateral; F, anterior. (B. Degner, del.)

Fig. 4. Caninemys tridentata, new genus and species, DNPM-MCT 1496-R holotype. A, Dorsal; B, ventral; C, right lateral; D, posterior; E, left lateral; F, anterior. (B. Degner, del.)

Fig. 5. Map of southwestern Amazonia showing the localities for Caninemys and other fossil turtles discussed in the text. 1. Type locality of Stupendemys geographicus (Wood, 1976). 2. L.I. Price locality 28, type locality of Caninemys tridentata (DNPM-MCT 1496-R). 3. LACM locality 5994, source of LACM 141498, a lower jaw that might represent Caninemys (see ‘‘Discussion’’).