Gingerichia geoteretes, Zack & Penkrot & Krause & Maas, 2005

Zack, Shawn P., Penkrot, Tonya A., Krause, David W. & Maas, Mary C., 2005, A new apheliscine “ condylarth ” mammal from the late Paleocene of Montana and Alberta and the phylogeny of “ hyopsodontids ”, Acta Palaeontologica Polonica 50 (4), pp. 809-830 : 812-815

Gingerichia geoteretes sp. nov.

Figs. 1–3 , Tables 1–3.

Hyopsodontidae , new genus and species Krause and Maas 1990: 84.

Holotype: UM 83932 ( Fig. 1A ), left dentary with p 4m 1–3 and alveoli for p2–3. Collected by E.M. Schloeder.

Type locality: Douglass Quarry in the eastern Crazy Mountains Basin, south−central Montana, USA.

Hypodigm: UM 83933, right dentary with p 4m 1–3 and alveoli for p2–3; UM 84535, right dentary with p 4m 1–3; UM 83939, right dentary with m2–3 and alveoli for p 2–3m 1; UM 83937, right p2 or p3; UM 83934, right p4; UM 83938, left m1; UM 54888 right m2; UM 83935, right m2; UM 83936, right m2; UM 84536, left m2; UM 84539, left M?2; UM 54889 left M1 or M2 ( Figs. 1B , 2A, C ).

Derivation of the name: Greek geios (of the earth) and teretes (keeper, watcher) ( Brown 1956), in reference to the EARTHWATCH organization, whose volunteers found several specimens of this new species. Gender: masculine.

Referred material.—Glennie Quarry, eastern Crazy Mountains Basin, south−central Montana: UM 54890, left p 4 in dentary fragment; UM 54891, right P4; UM 54894, right P4; UM 54893, left P4; UM 54892, right M?1 ( Figs. 2B , 3 ).

Age and distribution.— Gingerichia geoteretes is known from Douglass Quarry (the type locality) and from Glennie Quarry, both of which are of early Tiffanian (Ti1) age ( Krause and Gingerich 1983; Hartman and Krause 1993).

Diagnosis.— Gingerichia geoteretes is distinguishable from G. hystrix based on the following characteristics: larger size (see diagnosis of G. hystrix , Tables 1 and 2); more robust and bunodont cheek teeth; less exodaenodonty in p4–m3; p4 talonid erect, not anteriorly recurved; m1–2 trigonids lower and talonids more elongate; m1–3 paraconids crestiform; M1 more quadrate. See Tables 1 and 2 for measurements.

Description.—The dentary is shallow, approximately 3.4 mm deep below m1 ( Fig. 1 ). The four alveoli anterior to p4 preserved in UM 83933 are small and closely appressed, presumably for two−rooted p2 and p3. Two mental foramina are preserved on UM 83933, one below the anterior part of the posterior alveolus for p3 and the other below the anterior part of the posterior alveolus for p2.

An isolated, two−rooted p2 or p3 (UM 83937) is referred to G. geoteretes on the basis of its size and morphological similarity to p4 ( Fig. 2C ). It is about 60% the length of p4 ( Table 1). The trigonid has a single, prominent, bulbous cusp, the protoconid, which has an apical wear facet. There is no vestige of an anterior cingulid, paraconid, or metaconid. A faint ridge extends down the anterolingual face of the protoconid from the cusp tip and bends slightly more lingually at the base, where it becomes more prominent. Posteriorly, a ridge extends from the tip of the protoconid, down the postvallid, and slightly lingually to the base of the single, prominent, posterolingual talonid cusp.

The fourth lower premolar is the largest mandibular tooth in length and height; its width is exceeded only by that of m2 ( Figs. 1 , 2 , Table 1). The two roots are widely separated. The trigonid, which is considerably higher than the talonid, is unicuspid with a large, bulbous protoconid located centrally; there is no trace of either a paraconid or metaconid. An anterior cingulid is present on p4 of the type specimen, feebly developed on UM 83933 , and absent on UM 84534 and UM 84535 . In lateral profile, the anterior border of the trigonid is markedly convex and the posterior border is concave. A ridge descends posteriorly from the apex to the base of the protoconid, lingual to the midline. Wear is largely confined to the apex of the protoconid; postvallid wear facets are absent. The talonid is transversely broad. On the type specimen ( UM 83932 ) and UM 83933 there is a single, low, lingual talonid cusp, but on UM 83934 and UM 84535 a second small cusp can be distinguished, just lingual to the main talonid cusp. The cristid obliqua is short and distinct on UM 83932 , UM 83933 , and UM 83934 , but faint on UM 84535 . It extends anteriorly from the main talonid cusp and ends buccal to the termination of the ridge that extends posteriorly from the protoconid. On the buccal surface of the tooth, the enamel beneath the talonid of p4 extends further ventrally that does the enamel beneath the trigonid .

The molar proportions of G. geoteretes are distinctive ( Fig. 1 ). The second lower molar is longer than m1 but slightly shorter than m3, and broader than either m1 or m3 ( Table 1). The trigonid and talonid of both m1 and m2 are subequal in width; the m3 trigonid is markedly broader than the talonid ( Table 1).

On m1 a distinct, curved paracristid connects the protoconid with a small, terminal paraconid, which lies anterior and slightly buccal to the metaconid. The metaconid is subequal in size to the protoconid and both are much larger than the paraconid. Both metaconid and protoconid have broad, bulbous bases and are closely appressed. Both the anterior and posterior cingulids are poorly developed (particularly so in UM 83933), and there is no vestige of a buccal cingulid. The hypoconulid is the smallest and lowest of the three talonid cusps and is situated approximately midway between, and slightly posterior to, the hypoconid and entoconid. The talonid is deeply basined and is bounded buccally by a cristid obliqua that meets the trigonid slightly buccal to the midline and to the notch between metaconid and protoconid. The postcristid is continuous between the three major talonid cusps ( Fig. 2 ).

The m2 paracristid turns more sharply at midlength than on m1 and terminates in a small paraconid that is more medial in position than on m1. The paraconid lies slightly lingual to the midline and anterior to the notch between metaconid and protoconid. It is closely appressed to both the metaconid and protoconid; consequently the paracristid is short and the trigonid anteroposteriorly compressed. As in m1 the metaconid and protoconid are subequal in size, broad−based, and closely appressed, there is no buccal cingulid, and the posterior cingulid is indistinct. The anterior cingulid is slightly more pronounced than on m1. The relative size, shape, and position of the three major talonid cusps are virtually identical with those on m1. An entoconulid, absent on the available specimens of m1, is evident on two (UM 83933 and UM 83935) of the eight m2s.

The m3 paracristid, as on m2, is angled but it is more prominent than on m2 and terminates in a larger, more lingually placed paraconid. The protoconid and metaconid are subequal in size but less bulbous and closely appressed than on m1 or m2. The hypoconulid is much more prominent than on the more anterior molars. It is taller than either the hypoconid or entoconid, and more lingual than the m1–2 hypoconulids. An entoconulid is present on two of four specimens. The cristid obliqua curves buccally, in contrast to the straight cristid obliqua on m1 and m2.

The P4 of Gingerichia is similar to that of other apheliscids in being dominated by a large, inflated paracone, and a small protocone (roughly one−third to one−half the height of the paracone), also with a bulbous base ( Fig. 3 ). The protocone is positioned slightly anterior to the center of the paracone. A tiny metacone is present, but is essentially fused to the base of the large paracone, and is located along the postparacrista. A small but distinct parastyle is present. The P4 of Gingerichia has both an anterior and a posterior cingulum, but these cingula do not meet as the buccal margin of the paracone and the lingual margin of the protocone lack cingula. The posterior cingulum is elevated adjacent to the metacone, where it continues above the level of the rest of the posterior cingulum. Mirroring the posterolingually recurved protoconid of the p4, the P4 paracone is also distinctively recurved posterolingually. Although on a much smaller scale, the parastyle shares this posterolingual recurvature.

Upper molars of G. geoteretes are limited to two fragmentary specimens from Douglass Quarry and a complete but worn molar from Glennie Quarry ( Fig. 3 ). Based on the limited material available, the upper molars of G. geoteretes do not appear to differ appreciably in morphology from those of G. hystrix (see below). The probable M1 from Glennie Quarry (UM 54892) is somewhat less transverse than a probable M1 of G. hystrix , indicating more quadrate upper molars in G. geoteretes .

Discussion.—Aside from material from the type locality, a small but significant collection of isolated teeth from Glennie Quarry, which lies stratigraphically below Douglass Quarry, is referred to G. geoteretes . The Glennie Quarry sample is of importance because it includes well−preserved P4s, which are otherwise represented for the genus by two poorly preserved specimens of G. hystrix (see below). Referral of the Glennie Quarry sample to G. geoteretes rather than to G. hystrix is based on the close match in size and morphology of the single p 4 in the Glennie Quarry sample to the type sample from Douglass Quarry.

Figures

Fig. 1. Dentaries of Gingerichia geoteretes gen. et sp. nov. from the early Tiffanian Douglass Quarry, Montana, USA. A. Holotype, left p4–m3, UM 83932 in occlusal (A1, stereophotograph) and buccal (A2) views. B. Right p4–m3 (reversed), UM 84535 in occlusal (B1, stereophotograph) and buccal (B2) views.

Fig. 2. Lower teeth of Gingerichia geoteretes gen. et sp. nov. from the early Tiffanian Douglass (A, C) and Glennie (B) quarries, both Montana, USA. A. Left m2, UM 84536 in buccal (A1), occlusal (A2), lingual (A3), anterior (A4) and posterior (A5) views. B. Left p4, UM 54890 in buccal (B1), occlusal (B2), and lingual (B3) views. C. Right p2 or p3 (reversed), UM 83937 in buccal (C1), occlusal (C2), and lingual (C3) views.

Fig. 3. Upper teeth of Gingerichia geoteretes gen. et sp. nov. from the early Tiffanian Glennie Quarry, Montana, USA. A. Right M1?, UM 54892 in occlusal view. B. Right P4, UM 54891 in occlusal (B1), posterior (B2), and buccal (B3) views.