Prodipoides burgensis (Korth, 2002)

Korth, William W., 2008, Cranial morphology, systematics and succession of beavers from the middle Miocene Valentine Formation of Nebraska, USA, Acta Palaeontologica Polonica 53 (2), pp. 169-182 : 176-177

publication ID	https://doi.org/ 10.4202/app.2008.0201
persistent identifier	https://treatment.plazi.org/id/03DA87E5-FFCB-FF9E-FFBD-7444FA4FFE97
treatment provided by	Felipe
scientific name	Prodipoides burgensis (Korth, 2002)
status

Treatment

Figs. 5 View Fig , 6A View Fig .

2002 Eucastor burgensis sp. nov.; Korth 2002a: 18, fig. 2. 2007 Prodipoides burgensis ( Korth, 2002a) ; Korth 2007a: 124, fig. 3,

4A.

Holotype: FAM 64975 , mandible with complete lower dentition.

Type locality: Lucht Quarry, Brown County, Nebraska .

Type horizon: Early Clarendonian (Miocene), Burge Member, Valentine Formation.

Material.— UNSM 49029, FAM 64857, 64956, 64957, 64958, 64959, and CM 18875, mandibles with cheek teeth; and FAM 65343, partial skull with right P4 and left M1.

Description.—Only a small portion of the cranium is preserved on FAM 65343. Dorsally, only the frontals are present. The postorbital constriction is 11.39 mm in width, slightly greater than the previously described skull of P. burgensis ( Korth 2007a: table 1). Just posterior to the constriction is a low, but sharp sagittal crest. This part of the cranium is preserved on the skull of P. burgensis from the early Clarendonian, and there is no sagittal crest. Ventrally, there is little information preserved about the morphology. The palate is deeply grooved, but little else can be determined.

P4 is in a moderate state of wear. The hypoflexus and mesoflexus are still open, and the parafossette and metafossette have formed. In all other features, the tooth is similar to those previously described for P. burgensis ( Korth 2002a, 2007a). The single upper molar has the occlusal pattern of a long hypoflexus and a mesofossette. No other fossettes are present.

Both the paraflexid and mesoflexid remain open on p4 of all but one specimen, FAM 64958, which has a greater amount of wear than the other specimens. Otherwise the morphology of p4 is like that previously figured for P. burgensis ( Korth 2002a: fig. 2; Korth 2007a: fig. 4A). On the least worn specimen, FAM 64957, the parastriid is as deep as the mesostriid on the lingual side of the tooth. This is different than on any of the other specimens and the specimens previously described.

The lower molars on all of the specimens are at a state of wear where the mesofossettid has formed and the para− and metafossettids are lost, producing the Dipoides− like S−pattern ( Fig. 5 View Fig ). However, on two specimens, one from the Devil’s Gulch Member ( FAM 64958 ) and one from the Crookston Bridge Member ( FAM 64957 ) there is a minute metafossettid present on the former and a metafossettid and parafossettid on the latter on m2 after the mesofossetid has formed. In both cases, the retained fossettids are minute and will likely disappear after very little additional wear. The m1 on both of these specimens has attained the S−pattern. This indicates that the S−pattern is not yet fully attained on some specimens of m2 of P. burgensis from earlier Valentine horizons .

Discussion.—In a faunal list of the Ogallala fossil quarries of Nebraska, Voorhies (1990a: table 2) listed Eucastor tortus as the only species of castoroidine beaver from the late Barstovian Crookston Bridge Quarry. No tables, figures or descriptions of this material were provided. A reexamination of the material in the University of Nebraska collections from Crookston Bridge and Railway quarries has resulted in the recognition of specimens of Prodipoides burgensis in the samples that were originally referred to E. tortus . The lower dentitions of E. tortus and P. burgensis are similar in having the same degree of crown height and development of lingual striids on the lower premolar and they both generally have the S−pattern on the occlusal surface of the molars. However, P. burgensis is clearly larger than E. tortus ( Voorhies 1990b: A97; Korth 2002a: table 2). Features of the cranium are very distinct between these two species as well ( Korth, 2007a). The specimens referred here to P. burgensis are separable from those of E. tortus in size ( Table 2) as well as the relative length of the diastema, development of the digastric process, and the position of the ascending ramus. In a sample of mandibles of these two species, the relative length of the lower diastema to the alveolar length of the tooth row in E. tortus ranged from 0.77 to 1.00 with a mean of 0.88, whereas in P. burgensis the range was from 0.62 to 0.78 with a mean of 0.71. This is not surprising because the same relationship exists between the upper diastema length and the upper tooth row, where the upper diastema is proportionally longer in Eucastor than in Prodipoides ( Korth 2007a: table 3).

The anterior margin of the ascending ramus on the mandible in specimens of E. tortus begins lateral to m1 and blocks all but the anterodorsal tip of m2 from lateral view ( Stirton 1935: fig. 94). In Prodipoides burgensis , the ascending ramus originates lateral to m2, blocking only the posterior portion of m3 from lateral view ( Fig. 6 View Fig ). It also appears that the digastric process is larger on Prodipoides than on Eucastor . In the case of the two specimens of P. burgensis recognized from quarries in the Crookston Bridge Member, size and these mandibular differences are consistent.

Prodipoides burgensis was originally reported only from the early Clarendonian Burge Member of the Valentine Formation ( Korth 2002a). Previously, no castorids had been reported from the subjacent late Barstovian Devil’s Gulch Member. The presence of P. burgensis from the Crookston Bridge Member along with its occurrence in the Devil’s Gulch extends its known occurrence from the early Clarendonian back into the late Barstovian, overlapping the occurrence of Monosaulax and Eucastor .

Stratigraphic and geographic range.— Previously referred specimens from fossil localities in the early Clarendonian Burge Member of the Valentine Formation, Nebraska ( Korth 2002a). Material described above: UNSM 49029 is from Crookston Bridge Quarry and FAM 64857 is from Railway Quarry A, Cherry County, Nebraska, Crookston Bridge Member, Valentine Formation; FAM 64957, 64958, 64959, 64961, and 65343 are from Meisner Quarry, FAM 64956 is from Devil’s Gulch Horse Quarry, both of the latter quarries are in Cherry County, Nebraska and CM 18875 is from Verdigre Quarry, Knox County, Nebraska; these three quarries are in the Devil’s Gulch Member, Valentine Formation.