Holoclemensia texana Slaughter, 1968b

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 : 450-453

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/FB113777-7B4D-076C-FFB9-F83C2FF9659B
treatment provided by	Felipe
scientific name	Holoclemensia texana Slaughter, 1968b
status

Treatment

Figs. 6, 7 View Fig , Table 6.

1989 Comanchea hilli Jacobs, Winkler, and Murry, 1989: 4992 , fig. 1. Holotype: SMP−SMU 61997 , RM2 missing the protoconal region. Type locality: Butler Farm , north−central Texas, USA.

Type horizon: Upper Antlers Formation (Aptian–Albian)

Referred material.— PM 1000, LM1 (missing protoconal region); PM 1004, RM 1 (missing paracone, parastylar lobe, and protoconal region); PM 886, RM 2 (missing paracone, parastylar lobe, and protoconal region); SMP−SMU 62009, RM 3; SMP−SMU 61727, Lm1; PM 887, Rm1 (trigonid only); PM 966, Lm1 (trigonid only); PM 1005, Rm2; PM 3877, Lm2 (trigonid only); SMP−SMU 62131, Lm2; SMP−SMU 62721, Rm2; OMNH 62412, Rm3; OMNH 62414, Lmx (talonid only); OMNH 63894, Rmx (talonid only); SMP−SMU 62722, Rmx (talonid only).

Tentatively referred material.— SMP−SMU 61948 , LP4 ; SMP−SMU 71848 , LDP5 (holotype of Comanchea hilli ); SMP−SMU 62399 , Lp5.

Emended diagnosis.—Basal eutherian mammal differing from all other basal eutherians in presence of a very large central stylar cusp (= mesostyle); differs from stem tribosphenidans in very small size of stylocone, the presence of a very large mesostyle, relatively narrow metastylar lobe at all loci, a prominent, flange−like parastylar lobe on mesial molars, very tall, bulbous metaconid on lower molars, and highly mesiodistally compressed trigonid; differs from deltatheroidans in presence of three molars, relatively weak postmetacrista, small stylocone, and small, inclined paraconid; differs from Slaughteria in larger size, presence of metaconid on p5, metaconid taller than paraconid on molars, and absence of distal metacristid; differs from Pappotherium in

DAVIS AND CIFELLI — REAPPRAISAL OF THE EARLY CRETACEOUS TRINITY “THERIANS” 451

1 mm

presence of three molars, shallower ectoflexus, more separated paracone and metacone, narrower metastylar lobe, metaconid taller than paraconid, and absence of distal metacristid.

Description

Upper premolars: Two upper premolars are tentatively referred to Holoclemensia texana . SMP−SMU 61948 ( Fig. 6G) is a very large, trenchant premolar, complete except for some minor breakage along the lingual margin. Both Slaughter (1968{a,b?}: 135) and Butler (1978: 14) interpreted this breakage to indicate the presence of a small protocone on this specimen; whether this was indeed the case or if simply a lingual cingulum was present is impossible to judge. Separate mesiobuccal and distobuccal cingula each bear a small cuspule (the distal one is larger). The size and morphology of the principal cusp on this specimen strongly suggest that it is a p4 (see the discussion of serial homology in Davis 2011). H. texana is the largest tribosphenidan known from the Trinity Group, and the only taxon appropriate in size for referral of this specimen. However, the possibility that another larger, unknown taxon was present in the fauna cannot be excluded.

SMP−SMU 71848 ( Fig. 6F) is a worn and fragmentary upper molariform tooth, established as the holotype of Comanchea hilli by Jacobs et al. (1989), who implicitly regarded it to be a molar. However, it possesses features that are more consistent with a deciduous premolar, especially in light of the upper molar morphology of H. texana . The paracone is large and swollen, and the metacone is very small and well separated from the paracone. A very weak preparacrista connects to a very small parastyle, which is the first in a line of four stylar cusps. An equally small stylocone is immediately distal to the parastyle, and it is followed by a very large mesostyle (equal in size to the metacone), positioned distobuccal to the paracone. A weak ridge connects the mesostyle with a smaller cusp (possibly equivalent to stylar cusp D). The protoconal region is transversely narrow but somewhat long mesiodistally; a distinct but small paraconule is present. This specimen compares well with the morphology of the upper molars of H. texana , except in ways that are characteristic of deciduous premolars ( Cifelli 1999a): the parastylar and protoconal regions are reduced, and the paracone is large and swollen relative to the metacone. Considering how strongly molariform this specimen is and how much smaller it is than the referred P4, it is most likely a DP5.

Upper molars: All specimens except for the M3 are missing the protoconal region of the crown. The M1s ( Fig. 6A, B) are heavily worn, but together they provide morphology for the entire buccal half of the crown. The paracone was clearly larger than the metacone. The preparacrista appears to have been low, but observation is difficult due to wear and breakage. The postmetacrista is much weaker than in Pappotherium or deltatheroidans. The stylocone is small and positioned at the buccal margin of a wide, wing−like parastylar lobe which projects beyond the buccal extent of the metastylar lobe (in a similar fashion to but to a greater extent than doi:10.4202/app.2011.0037

in Prokennalestes ; see Kielan−Jaworowska and Dashzeveg 1989). The mesostyle is much larger than the stylocone but not as tall as the metacone, and is positioned at or just mesial to the middle of the centrocrista; a low bulge just distal to it indicates the presence of another stylar cusp (in the position of stylar cusp D). An ectoflexus is lacking. The preprotocrista is obliterated by wear in PM 1000, but it probably participated in the large parastylar lobe. The postprotocrista does not extend buccally past the base of the metacone.

The M2 ( Fig. 6C, D) is larger than the M1. The paracone is taller than the metacone and relatively well separated from it, and the preparacrista, postmetacrista, and centrocrista are all low. The stylocone is very small (equal in size to the parastyle), and positioned mid−way on a wide, mesiobuccally projecting parastylar lobe; it anchors the preparacrista. The mesostyle is large and centrally positioned, as on the M1. The metastylar lobe is much narrower than the parastylar lobe, but relatively wider than on the M1. There is weak evidence of a small cuspule on the distal stylar shelf, and an ectocingulum is absent. The postprotocrista has the same extent as on the M1.

SMP−SMU 62009 ( Fig. 6E) represents the M3 and is the most complete upper molar, missing only the lingual portion of the protocone. The crown is transversely wide and mesiodistally compressed, with substantial reduction to the metacone and metastylar lobe, as is typical for ultimate molars. The paracone is large and dominant, while the metacone is low and thin; the preparacrista is oriented toward the parastyle, but terminates prior to reaching it. The parastylar lobe is short and wide, with a large, sharp parastyle and a much smaller stylocone. The mesostyle is delicate and spire−like as compared to the other molars. The protocone is also tall, about two−thirds the height of the paracone, and is flanked by a small paraconule and metaconule. The conules are closely appressed to the protocone. The preprotocrista is interrupted for a brief stretch mesial to the paracone.

Lower premolar: SMP−SMU 62399 ( Fig. 7A View Fig ) is a semi−molariform premolar. The protoconid is rounded much like that on a typical molar, and a low but distinct metaconid is present directly lingual to the protoconid. The mesialmost portion of the crown is broken, but there is no evidence that a paraconid was present. A weak ridge runs down the distal face of the metaconid, parallel to a stronger crest from the protoconid, bounding a wide trough; the crests meet at a single, very low heel cusp. The heel bends slightly lingually (in occlusal view); the distobuccal portion of the crown is basally expanded, and bears a very small isolated cuspule. While it agrees well morphologically with the expected p5 for H. texana , it is considerably mesiodistally shorter than the referred lower molars; its referral to this taxon is therefore tentative. An additional premolar from Butler Farm, SMP−SMU 61947 (see Butler 1978: fig. 4G), may also represent the p5 for H. texana (Alexander Averianov personal communication, 2011). This specimen is better preserved than SMP−SMU 62399, but it does not differ appreciably in morphology and was unavailable for study at the time of this project.

Lower molars: Specimens representing all three lower molar loci are known for H. texana . In general, all share a mesiodistally compressed trigonid bearing a large metaconid and a much smaller, somewhat procumbent paraconid. The m1 ( Fig. 7B, C View Fig ) is characterized by less inflation of the metaconid relative to the other loci, and less height and transverse width differential between the trigonid and talonid. The hypoconid is very prominent (it would likely have been taller than the paraconid), while the other two talonid cusps are subequal in size. The talonid basin is deep but not well enclosed mesiolingually due to the absence of a prominent entocristid.

The trigonid of the m2 ( Fig. 7D View Fig ) is much taller than the talonid, and it is transversely much wider than mesiodistally long. The metaconid is heavy and inflated (more obvious in lingual view). The paraconid is small, slightly inclined, and set somewhat buccal to the metaconid. The protocristid is more prominent and more strongly notched than in Pappotherium . The morphology (and presence) of the e and f cusps are variable; cusp e is either absent or represented by two very tiny cuspules on the mesiolingual base of the paraconid. Cusp f is much more prominent, and varies from a strong, oblique ridge to a short flange. The cristid obliqua meets the trigonid below the protocristid notch, and a distal metacristid is absent. The three talonid cusps are evenly spaced, though the hypoconid is again by far the tallest cusp. The entoconid is slightly smaller than the hypoconid, and lacks a strong entocristid.

One heavily worn and abraded specimen is referred to the m3 ( OMNH 62412; Fig. 7E View Fig ). In trigonid morphology, it clearly represents Holoclemensia but it demonstrates typical trends in distal molar loci, and resembles what would be appropriate for an ultimate molar of this taxon. The crown is smaller overall than the other specimens. The trigonid is more strongly mesiodistally compressed than the other loci, and while the major cusps are largely broken it is clear that the metaconid was very large and the paraconid was much smaller and set buccally. The protocristid was strong and notched. Cusp e is apparently absent (breakage of the paraconid could have removed it), and cusp f is represented by a strong, worn cingulid that occupies the entire mesial face of the trigonid and extends to the buccal side of the protoconid. The talonid is heavily worn such that no individual cusps can be discerned. The basin is, however, open mesiolingually as in the other referred specimens (due to a weak entocristid).

Stratigraphic and geographic range.— Butler Farm, upper Antlers Formation (Aptian–Albian), north−central Texas, USA ; Greenwood Canyon (Triconodont Gully, Turtle Gully), upper Antlers Formation (Aptian–Albian), north−central Texas, USA ; Pecan Valley Estates ( SMP−SMU locality 157), Paluxy Formation (Albian); Tomato Hill ( OMNH V706 ), middle Antlers Formation (Aptian–Albian), southeastern Oklahoma, USA ; Willawalla, upper Antlers Formation (Aptian–Albian), north−central Texas, USA .