Kermackia texana Slaughter, 1971

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 : 453-455

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/FB113777-7B48-076E-FCB5-FC47285B6000
treatment provided by	Felipe
scientific name	Kermackia texana Slaughter, 1971
status

Treatment

Fig. 8 View Fig , Table 7.

1978 Trinititherium slaughteri Butler, 1978: 10 , fig. 3.

Holotype: SMP−SMU 62398 , Rmx.

Type locality: Butler Farm, north−central Texas, USA.

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

Referred material.— OMNH 67134 View Materials , Rp5 (missing the mesiobuccal corner) ; OMNH 63731 View Materials , Lmx (talonid only) ; OMNH 63893 View Materials , Lmx (trigonid only) ; PM 922 , Rmx ; PM 1046 , Lmx (trigonid only) ; PM 1245 , Rmx ; SMP−SMU 61728 , a left dentary fragment preserving m3 (the holotype of Trinititherium slaughteri Butler, 1978 ) .

Tentatively referred material.— SMP−SMU 62402, RM 1 (missing the mesiobuccal corner).

doi:10.4202/app.2011.0037

Emended diagnosis.—Very small tribosphenidan characterized by the following unique combination of characters: lower molars with a very large, broad metaconid (much larger than the paraconid), distal metacristid hypertrophied such that it meets the cristid obliqua at a notch immediately mesial to the hypoconid (instead of at the base of the trigonid), and large, inflated upper molar paracone.

Description

Upper molar: SMP−SMU 62402 ( Fig. 8A View Fig ) is tentatively referred to Kermackia texana on the basis of size and occlusal fit; the only other taxon from the sample of equivalent size is Slaughteria , but the lower molar morphology of K. texana (described below) suggests that its upper molars are somewhat modified as represented by SMP−SMU 62402. The paracone is very large and inflated, while the metacone is substantially smaller and positioned slightly buccally with respect to the paracone. The postmetacrista is only moderately developed. The parastylar lobe is largely broken, but from the pattern of breakage the stylocone appears to have been very large and closely appressed to the paracone. The ectoflexus was moderately deep, and the parastylar lobe was probably narrower than the metastylar lobe. There is no evidence of stylar cusps other than the stylocone. The protoconal region is well developed (the protocone is as tall as the metacone) and bears both conules. The metaconule is situated close to the protocone, while the paraconule is equidistant from the protocone and paracone. The tooth is heavily abraded, obscuring any other features (including wear facets). This specimen is considered to be a first molar based on the width of the metastylar lobe (tends to be reduced on ultimate molars), and the inferred approximation of the stylocone to the paracone (the parastylar lobe is typically wider on second molars). Kermackia is interpreted to have had three molars (see below).

Lower premolar: OMNH 67134 ( Fig. 8B View Fig ) is a small, semi−molariform premolar broken obliquely at about the midline of the protoconid. The main cusp is large but with heavy apical wear; it is flanked lingually by a mesiodistally broad metaconid. The two cusps are connected by a weak crest. Two additional crests descend distally from the protoconid and meet a crest running mesially from a large heel cusp. A strong notch is present at this juncture; a very similar (and probably serially homologous) notch is found in lower molars of Kermackia texana (see below). The talonid is otherwise undeveloped, except for a faint, low rim enclosing the lingual margin. The small overall size, broad metaconid, and strongly notched heel crest support referral of this specimen to K. texana . The absence of any molarization of the talonid indicates that this premolar is from the adult series, and the presence of a prominent metaconid suggests it is the ultimate premolar. Without material to suggest otherwise, Kermackia is interpreted to possess the primitive tribosphenidan condition of five premolars and three molars (see Davis in press, and references therein).

Lower molars: The lower molars of Kermackia are highly distinctive ( Fig. 8C–G View Fig ), but the limited preservation of the current sample precludes identification of any specimens to locus except the ultimate (interpreted as m3; see below). In occlusal view, the entire crown appears to bow lingually, due to the small size of the paraconid on the mesial end, the poorly−developed lingual margin of the talonid on the distal end, and the hypertrophied distal metacristid on the prominent metaconid in the middle. The trigonid is taller than the talonid and bears a high protoconid and a lower but large, broad metaconid. The paraconid is by far the smallest trigonid cusp and varies from being delicately constructed to low and robust (this likely reflects some positional or intraspecific variation). Cusp f is developed as a shelf but it is limited to the mesial base of the trigonid. Cusp e is present as a distinct ridge projecting from the mesiolingual corner of the paraconid, resembling the keel−like structure characteristic of marsupials ( Cifelli 2004: 70, footnote 2).

The distal metacristid, as defined by Fox (1975) and modified by Davis (in press), typically descends from the apex of the metaconid to the point at which the cristid obliqua meets the distal wall of the trigonid, typically below the protocristid notch. In Kermackia , however, the distal metacristid is modified into a very strong ridge that projects from the apex of the metaconid and descends to meet a foreshortened cristid obliqua immediately mesiolingual to the hypoconid; a well developed notch is present where the two crests meet. The rationale for this interpretation (and the functional implications) is discussed later in the text. As a consequence of the long, ridge−like distal metacristid, the talonid is set much farther distally than would be expected for its small size and degree of development. The hypoconid is the largest cusp, followed by the hypoconulid which is slightly larger than the entoconid. The cusps are evenly spaced, but the entoconid lacks an entocristid so the shallow talonid basin is open lingually (there is substantial space between the entoconid and the trigonid).

The holotype of Trinititherium ( SMP−SMU 61728; Fig. 8G View Fig ) comprises a small dentary fragment bearing a single molar posterior to two alveoli. It also preserves a small portion of the ascending ramus, visible distobuccal to the talonid of the molar. This suggests that the single preserved tooth is the ultimate molar, and accompanying features such as a reduction in the height of the metaconid and a decrease in the size of the talonid (and absence of the entoconid) can account for any differences between this specimen and those otherwise referred to Kermackia . Trinititherium is therefore a junior synonym of Kermackia , and this specimen represents the m3.

Comments.—William Clemens proposed that Trinititherium may be a distal molar of Kermackia (personal communication in Butler 1978: 11), and this view is supported here (see the description). Stratigraphic and geographic range.—Butler Farm, upper

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