Propalaeocastor Borissoglebskaya, 1967

WU, WENYU, MENG, JIN, YE, JIE & NI, XIJUN, 2004, Propalaeocastor (Rodentia, Mammalia) from the Early Oligocene of Burqin Basin, Xinjiang, American Museum Novitates 3461 (1), pp. 1-16 : 2-3

Propalaeocastor Borissoglebskaya, 1967

SYNONYM: Asteneofiber Kretzoi, 1974: 427 .

TYPE SPECIES: Propalaeocastor kazachstanicus Borissoglebskaya, 1967 .

TYPE LOCALITY AND AGE: Kyzylkak, 70 km southwest to City Dzhezkazgan in central Kazakhstan, Early Oligocene.

EMENDED DIAGNOSIS: Primitive, small castorids with brachyodont to mesodont cheek teeth having folded enamel but lacking cement filling; P3 absent; P4 subquadrate; cheek teeth decreasing in size posteriorly; in addition to the five main lophs (anteroloph, protoloph, mesoloph, metaloph, and posteroloph), the metastyle crest, protolophule I and II, and metalophule I and II also present (figs. 1, 3); the paraflexus, mesoflexus, metaflexus, hypoflexus, premesoflexus (or fossette), and postmesoflexus (or fossette) developed; the protolophule II dividing the premesoflexus into the labial flexus (or fossette) and lingual fossette; the short paraflexus about one­third to one­half of the tooth crown width and positioned anterior to the hypoflexus; the hypoflexus about two­fifths of the tooth crown width with its labial end being opposite to the lingual fossette of the premesoflexus; lower teeth having five main lophids (anterolophid, metalophid, mesolo­ phid, hypolophid, and posterolophid), a metastylid crest, and an endostylid crest; the preparafossettid, premesofossettid, and postmesofossettid present in addition to the paraflexid, mesoflexid, metaflexid, and hypoflexid; all main lophs and lophids on the cheek teeth transversely or nearly transversely extended.

INCLUDED SPECIES: Propalaeocastor butselensis ( Misonne, 1957) , P. shevyrevae ( Lytshev and Shevyreva, 1994) , P. aff. shevyrevae ( Lytshev and Shevyreva, 1994) , P. zaissanensis ( Lytshev and Shevyreva, 1994) , and P. irtyshensis , n.sp. Steneofiber aff. dehmi Freudenberg, 1941 is probably a species of Propalaeocastor (see below).

GEOLOGICAL RANGE: Early Oligocene.

Propalaeocastor irtyshensis , new species

Figures 1–4 , table 1

HOLOTYPE: A right maxilla with P4–M3, IVPP ( Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences) V 13690 .

TYPE LOCALITY AND AGE: Locality XJ200203 (=200203 [ Ye et al., 2002], 47°50.454'N, 86°40.883'E), 20 km northwest to Burqin City, Xinjiang. Early Oligocene .

ETYMOLOGY: After the name of the Irtysh River.

DIAGNOSIS: Brachyodont Propalaeocastor with size and dental morphology similar to those of Propalaeocastor butselensis . Differing from Propalaeocastor butselensis in having higher tooth crown, much longer mesoflexus that bends posteriorly, more developed anteroloph, posteroloph, metastyle crest, and paraflexus, more folded enamel, and the lingual end of the mesoflexus connected the lingual premesofossette. Differing from ‘‘ Steneofiber aff. dehmi ’’ in having lower tooth crown, smaller size, shorter mesoflexus and more transversely extended main lophs and flexus. Differing from P. kazachstanicus , P. shevyrevae , and P. aff. shevyrevae mainly in having lower tooth crown. In contrast, P. kazachstanicus possesses longer and anteroposteriorly more stretched mesoflexus; P. shevyrevae has a postmesofossette on the P4 and closed metaflexus to form fossette at all stages of wear on M1–2; P. aff. shevyrevae has the mesoflexus being confluent with the labial premesofossette and has a postmesofossette on P4 and the labially always closed paraflexus on M1–2.

Figures

Fig. 1. Terminology of the upper cheek tooth of Propalaeocastor.

Fig. 2. Sketch showing the maxillary–palatine suture, the posterior palatine foramen, and the groove leading anteriorly from the foramen on the palate of Propalaeocastor irtyshensis, n.sp. (IVPP V13690).

Fig. 3. Line drawing of right P4–M3 of Propalaeocastor irtyshensis, n.sp. (IVPP V13690). A, Labial view; B, occlusal view; C, lingual view.

Fig. 4. Right upper jaw with P4–M3 (IVPP V13690) of Propalaeocastor irtyshensis, n.sp. A, Occlusal view of right P4–M3 (stereograph); B, occlusal view of right P4–M3 (inverse); C, anterior view of P4, showing unihypsodonty; D, lingual view; E, labial (buccal) view. All scale bars = 5 mm.