Chacomylus sladei, Williamson & Weil, 2011
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publication ID |
https://doi.org/ 10.4202/app.2009.0147 |
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persistent identifier |
https://treatment.plazi.org/id/1C5AC97D-4858-FF89-FFD9-9ED9FAE12B72 |
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treatment provided by |
Felipe |
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scientific name |
Chacomylus sladei |
| status |
sp. nov. |
Chacomylus sladei sp. nov.
Figs. 3–5, Table 1.
Etymology: In recognition of Warren Slade, long−time NMMNH volunteer and his contributions to New Mexico paleontology.
Holotype: NMMNH P−41208, right M1.
Type locality: NMMNH locality L−4723, head of Willow Wash , San Juan Basin, northwestern New Mexico.
Type horizon: Fossil horizon B ( Williamson 1996), Nacimiento Formation (late Puercan, Pu3).
Material.—NMMNH P−34804, right P4; 38461, left P4; 44353, left M3; 51537, right partial M2; left p3?; 44345, right m2; 55397, left m3.
Diagnosis.—Similar to hyopsodontid and apheliscid “condylarths” (sensu Zack et al. 2005) in its small size and bunodont cheek teeth with a lower molar talonid that is at least about two−thirds the height of the trigonid. Similar in size to Tiuclaenus minutus , but smaller than other hyopsodontids ( Table 1). Differs from all hyopsodontids (the upper dentition is unknown for Tiznatzinia , Bomburia unless Platymastus palantir is a synonym, see Williamson and Carr [2007], and Oxytomodon ) by its lack of a P4 parastyle, rela−
WILLIAMSON AND WEIL—PALEOCENE “CONDYLARTH” MAMMAL FROM NEW MEXICO 249
2 mm
tively more transverse upper molars, and larger protocones. Differs in lower molar morphology from all hyopsodontids, except Litomylus orthronepius and Oxytomodon , in possessing lower molar exodaenodonty. Differs from Litomylus orthronepius in having narrower molar stylar shelves and relatively wider molars. Differs from Oxytomodon in having a more transverse orientation of the distal wall of the trigonid and in having an entocristid that closes the talonid basin lingually. Differs from all hyopsodontids in having development of wear facets that indicates greater enhancement of transverse shearing during mastication. Differs from apheliscids in having the upper molar postcingulum higher above the base of the crown than the precingulum, a relatively less developed hypocone, molar paraconid is lingually positioned, basally fused with, and closely appressed to, the metaconid, and the hypoconulid is lingual to the midline of the tooth and basally fused to the entoconid.
Description.— Chacomylus sladei is known only from isolated teeth. The isolated teeth described in this report are referred to Chacomylus sladei based on size, morphology, pat−
doi:10.4202/app.2009.0147
terns of attritional wear, and occlusal fit. The upper dentition is represented by two P4’s, an M1, a probable M2, and an M3. The lower dentition is represented by an isolated premolar, probably a p3, an m2, and an m3.
P4.—The P4 ( Fig. 3A) is wider than long. The paracone is the tallest cusp and is elongated mesiodistally. A smaller swelling on the crest descending distally from the paracone likely represents the metacone. A low ectocingulum bounds the tooth buccally and widens distally. Mesially, the ectocingulum is narrow. The P4 lacks a parastyle. The protocone is distinct and separated from the paracone by a cleft. A low preprotocrista extends mesiobuccally to the mesial base of the paracone. On the distal face of the protocone, wear has breached the enamel, forming an elongate exposure of dentine ringed by enamel that extends distobuccally. The remnant of a narrow postcingulum is present lingual to this facet on the distal face of the protocone. This obliterates any evidence of a metaconule, if one was originally present. A paraconule is not developed.
M1.—The M1 ( Fig. 3B) is wider than long. The paracone and metacone are subequal in size, closely spaced, and partially fused at their base. The stylar shelf is undeveloped, with only the low ectocingulum bordering the buccal margin of the crown. The parastylar lobe extends mesially and the parastyle has been beveled by wear. The paraconule and metaconule are subequal in size and positioned close to the paracone and metacone. The protocone is large and subequal in height to the para− and metacone. A hypocone is present as a distinct cusp distal to the apex of the protocone. The postmetaconule crista extends to the metastyle. The postcingulum terminates lingual to the metaconule.
Planar wear facets have beveled the mesial and distal sides of the protocone. Similar facets have also truncated the distal face of the paracone and the mesial face of the metacone, forming a V−shaped notch into the centrocrista; the original shape and orientation of the centrocrista have been obliterated. A precingulum may have been present, but this can no longer be determined because of wear to this region of the tooth.
M2.—A probable M2 ( Fig. 3C), missing the metacone and distobuccal corner of the tooth, is represented by NMMNH P−51537. It is similar to the M1, but differs in that the pre− and postcingulum are not completely obliterated by wear. The precingulum originates lingually at a position buccal to the apex of the protocone. It is significantly lower on the protocone than the postcingulum. The postcingulum is expanded distal to the apex of the protocone, but does not support a distinct hypocone. The paracrista extends mesiobuccally from the paracone to the stylocone near the mesio−
WILLIAMSON AND WEIL—PALEOCENE “CONDYLARTH” MAMMAL FROM NEW MEXICO 251
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buccal corner of the tooth. A transverse groove caused by wear separates the stylocone from what may be the parastyle positioned mesial to the paracone. This groove has at least partially obliterated the stylocone and parastyle.
M3.—The M3 ( Fig. 3D), represented by NMMNH P−44353, is smaller than both M1 and M2. The width of the M3 is reduced distally and the metacone is much smaller than the paracone. The distal margin of the protocone is expanded. A paraconule is present and positioned close to the paracone. A wear facet on the posterior face of the protocone that extends buccally to the metacone has largely erased evidence for a metaconule.
p3.—NMMNH P−34838 is tentatively identified as a p3 ( Fig. 4A View Fig ). The crown is bulbous and dominated by the protoconid; a preprotocristid descends mesially from the protoconid, terminating above the swollen base of the crown. A paraconid is not present. Distally, the tooth supports a small talonid basin that lacks distinct cuspids. A ridge extends distobuccally from the protoconid to form the buccal margin of this basin. A small talonid basin is bounded buccally, distally, and lingually by a raised ridge.
m2.—The m2 ( Fig. 4D View Fig ) is nearly rectangular in occlusal view. The trigonid is low so that the talonid is about two−thirds its height The protoconid and metaconid are rounded and subequal in size. The paraconid is high (sensu Zack et al. 2005), lingual and closely appressed to the metaconid, with its base fused to that of the metaconid. The distal wall of the trigonid is strongly worn so that it is oriented nearly transverse. However, we suspect that the distal wall of the metaconid was originally more distally positioned than that of the protoconid and some of it has been removed by wear. The talonid is subequal in width to the trigonid. The hypoconid is the largest of the talonid cuspids followed by the entoconid and the hypoconulid. The talonid is closed lingually by an entocristid that terminates mesially at the base of the metaconid. The hypoconulid is positioned lingual to the midline of the tooth, closely coupled with the entoconid. A distinct notch separates the hypoconulid from the hypoconid. The cristid obliqua intersects the trigonid below the protocristid notch. The tooth is exodaenodont, with the buccal sides of both the trigonid and talonid inflated and overhanging the buccal surfaces of the roots. A small precingulid extends buccally from the hypoconulid and terminates below the hypoconid. A lingual cingulid is not present. A small cuspid in the hypoflexid represents a remnant of the ectocingulid. The distal face of the trigonid and the mesial face of the hypoconid, buccal to the cristid obliqua (wear facets 1 and 3, respectively; sensu Crompton and Kielan−Jaworowska 1978), are heavily worn, with the angle formed between these two planar surfaces closely matching the profile of the M1 paracone and protocone as seen in buccal view ( Fig. 3G).
m3.—The single known m3 (NMMNH P−55397; Fig. 4C View Fig ) closely resembles the m2, but is narrower. The talonid is narrower than the trigonid and more elongate. The hypoconulid is relatively larger and extends further distally.
| NMMNH |
New Mexico Museum of Natural History and Science |
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.