Gingerichia hystrix, 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 : 816-818

Gingerichia hystrix sp. nov.

Figs. 4A–E, 5 , Tables 1–3.

Apheliscinae , new genus and species Youzwyshyn 1988: 209.

Apheliscinae , new genus and species Fox 1990: 59.

Holotype: UALVP 43082 , left p4 ( Fig. 4A).

Type locality: Cochrane 2 in the Porcupine Hills Formation, southwestern Alberta.

Typodigm: UALVP 40796, right p4; UALVP 42544, right p4; UALVP 25053, left p4; UALVP 25061, left p4; UALVP 25062, left p4; UALVP 25065, left p4; UALVP 25066, right m1; UALVP 42642, right m1; UALVP 43087, right m1; UALVP 42634, left m1; UALVP 25057, right m2; UALVP 42406, right m2; UALVP 25068, left dentary fragment with m2 and alveoli for p4–m1 and m3; UALVP 25067, right m3; UALVP 43083, right m3; UALVP 25071, left m3; UALVP 43086, left m3; UALVP 25060, left P4; UALVP 25069, right P4; UALVP 42546, right M?1; UALVP 25058, left M?2; UALVP 43088, left M?2; UALVP 25050, right M1 or M2; UALVP 25051, left M1 or M2; UALVP 25052, right M1 or M2; UALVP 25054, left M1 or M2; UALVP 25059, left M1 or M2; UALVP 25063, right M1 or M2; UALVP 43084, right M1 or M2; UALVP 43085, right M1 or M2.

Derivation of the name: Hystrix , the Latin name for the Old World porcupine. Named in reference to the Porcupine Hills and Porcupine Hills Formation. Obliquely, also a reference to the sharper cusps relative to those of the type species.

Age and distribution.— Gingerichia hystrix is known only from the type locality, Cochrane 2, which is of early Tiffanian (Ti1) age ( Youzwyshyn 1988; Fox 1990; Scott et al. 2002).

Diagnosis.— Gingerichia hystrix is distinguishable from G. geoteretes based on the following characteristics: smaller size (p4 area averages 21% smaller; m1 area averages 18% smaller); more lightly built and less bunodont cheek teeth; p4–m3 more exodaenodont; p4 talonid anteriorly recurved; m1–2 trigonids taller and talonids shorter; retention of connate paraconid on m1–3; M1 more transverse. See Tables 1 and 2 for measurements.

Description.—Lower teeth of Gingerichia hystrix specimens from Cochrane 2 tend to be markedly smaller than those from Douglass Quarry, although the small sample of m2s shows no appreciable size difference.

Lower fourth premolars of G. hystrix are noticeably more gracile and less bunodont than those of G. geoteretes ( Fig. 4). In the type p4, a small but distinct paraconid is retained, as is a subtle metaconid “swelling” near the base of the large, recurved protoconid. Gingerichia hystrix p4s have a less inflated protoconid base than do those of G. geoteretes . The talonid of p4 is less elongate and its cusps taller in G. hystrix than in G. geoteretes . In addition to being taller, talonid cusps of G. hystrix are slightly recurved anteriorly, a feature not found in G. geoteretes . Finally, G. hystrix p4s show somewhat greater ventral extension (exodaenodonty) of buccal enamel than do p4s of G. geoteretes .

Lower molars of G. hystrix show similar differences from G. geoteretes , with G. hystrix having less bunodont molars than the Montana species (compare Figs. 1 , 2 , and 4). Trigonids of G. hystrix molars are relatively higher and more open than those of G. geoteretes . In G. hystrix , a distinct connate paraconid is retained, whereas in G. geoteretes the paraconid is poorly differentiated from the remainder of the paracristid. Finally, molars of G. hystrix have relatively shorter talonids than do those of G. geoteretes .

P4 of G. hystrix is represented by two heavily abraded specimens, which makes comparisons with G. geoteretes difficult. From what is preserved, however, they do not appear to differ substantially. In contrast to the sample of G. geoteretes from Douglass Quarry, which is dominated by specimens from the lower dentition, that of G. hystrix from Cochrane 2 is best represented by M1s and M2s ( Fig. 5 ). As maxillae of Gingerichia have yet to be found, it remains impossible to confidently distinguish M1s from M2s. By analogy with Haplaletes and Litomylus , M1s may differ from M2s in having a hypocone whose base extends further lingually, giving the lingual margin of the crown a straighter margin (compare Fig. 5A 1 with Fig. 5C ). On this basis, a few specimens can be tentatively assigned a locus. The upper molars of Gingerichia closely resemble those of Litomylus , aside from being markedly more transverse. The three primary trigon cusps form an acute triangle, with the paracone and protocone in transverse alignment, and roughly subequal in size. The cusp apices are sharper and less bunodont than in

ZACK ET AL.—NEW APHELISCINE “CONDYLARTH” FROM MONTANA 817

1 mm

Phenacodaptes and Apheliscus . The postparacrista and premetacrista are only moderately developed, and they are not continuous (the anterior end of the premetacrista is slightly offset buccally).

There is a strong cingulum wrapping from the anterolingual margin of the paracone to the posterolingual margin of the metacone. This buccal cingulum is continuous with the paracingulum and preparaconule crista anteriorly and the metacingulum and postmetaconule crista posteriorly. The parastyle is low and more shelflike than connate. The metastyle is somewhat more distinct, and is located at the posterior end of a well−defined postmetacrista. The preparacrista, though present, is relatively more weakly developed. The parastyle and metastyle produce winglike extensions of the buccal cingulum at the anterior and posterior corners of the molars, respectively, resulting in a weak ectoflexus. Both the paraconule and metaconule are present, but the paraconule is more strongly developed and is displaced slightly lingual relative to the metaconule. Additionally, while both internal conular cristae are present, the postparaconule crista is much stronger than the premetaconule crista. Strong pre− and postprotocristae connect the conules to the protocone.

A small anterior cingulum, which extends for the entire breadth of the protocone, ends just anterior to the paraconule and does not contact the buccal cingulum. There is a strong hypocone, which arises out of a moderate posterior cingulum. This posterior cingulum does not contact the buccal cingulum, but rather dives under it at the point where the postmetaconule crista and the buccal cingulum become continuous.

Discussion.—The distinctiveness of the Cochrane 2 material was first recognized by Youzwyshyn (1988) as Apheliscinae n. gen. and sp. in an unpublished masters thesis. We maintain that there is sufficient justification for separating the known specimens of Gingerichia into two species, centered on the Cochrane 2 and Douglass Quarry populations. In area, Gingerichia p4s and m1s from Cochrane 2 are markedly smaller than those from Douglass Quarry (see Table 3 for summary statistics on each species). Particularly in p4, the specimens from Douglass Quarry are noticeably larger than the Cochrane 2 specimens. Additionally, the p4 talonid is relatively more elongate in the Douglass Quarry specimens. In the Cochrane 2 Gingerichia specimens, p4 and the lower molars show greater distention of buccal enamel than do the Douglass Quarry specimens, and the p4 talonid cusps are recurved anteriorly. Lower molars from Cochrane 2 have relatively higher and more open trigonids and shorter talonids than do specimens from Douglass Quarry, and retain a connate paraconid (whereas in the Douglass Quarry specimens it is nearly indistinguishable from the paracristid). Finally, the cheek teeth in the Douglass Quarry specimens are more bunodont than in the Cochrane 2 sample.

The size and morphological distinctions between Cochrane 2 and Douglass Quarry specimens of Gingerichia are sufficiently great to warrant their separation into two species. Differences between the two samples are consistent with those recently used to distinguish species of other apheliscid genera, particularly species of Apheliscus ( Gingerich 1983, 1994; Penkrot 2002). In fact, the morphological differences between the Douglass Quarry and Cochrane 2 samples exceed the morphological differences between some apheliscid species (e.g., Aletodon mellon – A. gunnelli ; Haplomylus speirianus – H. scottianus ; Gingerich 1983, 1994).

Where they differ morphologically, G. hystrix is generally less specialized than G. geoteretes . In particular, p4s of G. hystrix are less simplified and inflated. This suggests that G. hystrix may have been ancestral to G. geoteretes , which in turn would suggest that Cochrane 2 is somewhat older than Douglass Quarry. This is consistent with Youzwyshyn’s (1988) assessment that other elements of the fauna are more primitive than those at Douglass Quarry.

Figures

Fig. 5. Upper teeth of Gingerichia hystrix gen. et sp. nov. from the early Tiffanian Cochrane 2 locality, Alberta, Canada. A. Right M1?, UALVP 42546 in occlusal (A1), posterior (A2), and lingual (A3) views. B. Right M1 or M2, UALVP 25063 in buccal view. C. Left M2? (reversed), UALVP 43088 in occlusal view. D. Right M1 or M2, UALVP 43084 in anterior view.

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.