Oklatheridium minax, Davis & Cifelli, 2011

Davis, Brian M. & Cifelli, Richard L., 2011, Reappraisal of the tribosphenidan mammals from the Trinity Group (Aptian-Albian) of Texas and Oklahoma, Acta Palaeontologica Polonica 56 (3), pp. 441-462 : 446-447

publication ID	https://doi.org/ 10.4202/app.2011.0037
publication LSID	lsid:zoobank.org:pub:5990F90D-CD8B-4BB2-96FB-466D8794E29D
persistent identifier	https://treatment.plazi.org/id/F13FECC3-7B86-4E48-A304-3177D567F680
taxon LSID	lsid:zoobank.org:act:F13FECC3-7B86-4E48-A304-3177D567F680
treatment provided by	Felipe
scientific name	Oklatheridium minax
status	sp. nov.

Treatment

Oklatheridium minax sp. nov.

1997 Tribosphenida indet.; Cifelli 1997: fig. 3

2008? Oklatheridium sp. ; Davis, Cifelli, and Kielan−Jaworowska 2008: fig. 1.3

Fig. 3F–H View Fig , Table 3.

Etymology: From the Latin for “threatening”, in reference to the strongly−developed shearing crests in this taxon, and its larger size compared to the other deltatheroidans of the Trinity Group.

Holotype: OMNH 33455 View Materials , LM2 missing the metacone and metastylar lobe.

Type locality: Tomato Hill (OMNH V706), southeastern Oklahoma, USA.

Type horizon: Middle Antlers Formation (Aptian–Albian).

Referred material.—PM 884, LM1 (missing the protoconal region); OMNH 63727, RM3 (missing the parastylar lobe and protoconal region).

Diagnosis.—Species of Oklatheridium differing from O. szalayi in overall larger size, relatively heavier stylocone, and in less relative size difference between M1 and M2.

Description

Upper molars: PM 884 ( Fig. 3F View Fig ) is a large, somewhat abraded molar with a very heavy stylocone. The relatively narrow parastylar lobe and shallow ectoflexus indicate this to be an M1. The metacone is lower and broader than the paracone, features consistent with Oklatheridium . The paracone and stylocone are connected by a strongly notched preparacrista. The parastyle is large and positioned slightly lingual to the stylocone. While this molar is substantially larger than the M1 referred to O. szalayi ( Table 2), it is still smaller than the M2 of O. minax and is therefore referred to that species.

OMNH 33455 ( Fig. 3G View Fig ) was initially described by Cifelli (1997: 10), and referred to? Oklatheridium sp. by Davis et al. (2008). Comparisons with the proportions of the M2 of O. szalayi suggest that this specimen represents the M2 (as proposed by Davis et al. 2008). The stylocone is very large and separated from the parastyle by a strong notch. The protoconal region is broad, bearing large conules. The paraconule is more buccally positioned than the metaconule, and there is no evidence of internal cristae. The paracone is mostly broken, but it appears to have been much heavier than in all other deltatheroidans.

The M3 of O. minax, OMNH 63727 ( Fig. 3H View Fig ), was originally referred to O. szalayi by Davis et al. (2008). However, it appears to be too large for that species (as is evident from comparisons between the M2 and M3 of the morphologically similar Deltatheridium ; see Davis et al. 2008: fig. 1.8). The parastylar lobe of this specimen is broken but the remaining portion suggests that it would likely have been very wide; the metastylar lobe is reduced in width but still retains a prominent shelf. The metacone is much lower than the paracone but is only slightly shorter mesiodistally. The centrocrista is formed by very sharp crests. The pattern of breakage suggests that the protoconal region would have been large, comparable to but slightly smaller than that in OMNH 33455 (see hypothetical restoration in Davis et al. 2008: fig. 1.8).

DAVIS AND CIFELLI—REAPPRAISAL OF THE EARLY CRETACEOUS TRINITY “THERIANS” 447

1 mm

Stratigraphic and geographic range.— Greenwood Canyon (Triconodont Gully), upper Antlers Formation (Aptian– Albian), north−central Texas, USA ; Tomato Hill ( OMNH V706 ), middle Antlers Formation (Aptian–Albian), southeastern Oklahoma, USA .