Oklatheridium szalayi Davis, Cifelli, and Kielan−Jaworowska, 2008

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 : 445-446

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/FB113777-7B40-0765-FF73-FEEE2C3F64EB
treatment provided by	Felipe
scientific name	Oklatheridium szalayi Davis, Cifelli, and Kielan−Jaworowska, 2008
status

Treatment

Fig. 3A–E View Fig , Table 2.

Holotype: OMNH 62410 View Materials , LM2 missing the protoconal region of the crown.

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

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

Referred material.—OMNH 62411, LM1 (missing the protocone); PM 1238, LM1 (missing the protoconal region); OMNH 61180, LM1 (missing the protoconal region); OMNH 63986, RM3 (missing the metastylar lobe and protoconal region).

Emended diagnosis.—Species of Oklatheridium differing from O. minax in smaller size, relatively smaller stylocone, and greater relative size difference between M1 and M2.

Description

Detailed descriptions of the molars of Oklatheridium szalayi can be found in Davis et al. (2008), and will not be repeated here. However, the identification of a second species of Oklatheridium based on upper molars ( O. minax sp. nov.) has led to the removal of all lower molars from the hypodigm of O. szalayi . These specimens are here referred to Oklatheridium sp. (see below). The upper molar morphology of O. szalayi is summarized to facilitate comparisons between the various tribosphenidan taxa described in this paper.

Upper molars: The upper molars of O. szalayi are in many ways similar to those of Pappotherium , and are distinguished primarily by relative proportions of the paracone and metacone. In both species of Oklatheridium , there is less height differential between these cusps than in Pappotherium , and the metacone is slightly broader than the paracone (the opposite is true in Pappotherium ). The parastylar lobe increases substantially in width between the M1 and the M3, and the parastyle is prominent. The metastylar lobe is long doi:10.4202/app.2011.0037

and bears a very strong, notched postmetacrista. There is some variation in the depth of the ectoflexus, but it is quite deep on the holotype (similar to that seen in the M2 of Deltatheridium ). The stylocone is the only stylar cusp (typical of deltatheroidans, despite the variable presence of cuspules or crenulations in Sulestes ; see Averianov et al. 2010), but there is a small cuspule present immediately distal to the stylocone on one M2 (OMNH 61180) and the referred M3 (OMNH 63986).

The M3 originally referred to O. szalayi by Davis et al. (2008), OMNH 63727, appears to belong instead to O. minax sp. nov. (see below). A different specimen, OMNH 63986 ( Fig. 3E View Fig ), is a better match for M3 of O. szalayi , in terms of size. This molar is fragmentary, preserving only the paracone, parastylar lobe, and the mesial base of the metacone. The stylocone is large and well separated from the paracone; the parastylar lobe is much wider than any specimen referred to Pappotherium (see below). There is a prominent cuspule along the ectocingulum immediately distal to the stylocone, and the ectocingulum appears to have been strong, as in other specimens of this taxon.

Comments.—The presence of Oklatheridium in the Greenwood Canyon sample, a taxon otherwise only known from Tomato Hill, was originally suggested by Alexander Averianov (personal communication to BMD, 2007) in reference to PM 1238, a LM1 originally referred to Pappotherium by Butler (1978).

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 .