Paleotomus junior, S.Scott & C.Fox & P.Youzwyshyn, 2002
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publication ID |
https://doi.org/ 10.5281/zenodo.13285980 |
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persistent identifier |
https://treatment.plazi.org/id/039F87B0-0D6A-FF89-AA5B-FB87FA92FA64 |
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treatment provided by |
Felipe |
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scientific name |
Paleotomus junior |
| status |
sp. nov. |
Genus Paleotomus Van Valen, 1967 Paleotomus junior sp. nov.
Fig. 4; Table 5.
Holotype: UALVP 28556 , left m3, Fig. 4C 1 –C View Fig 3 View Fig .
Type horizon and locality: Cochrane 2, Paskapoo Formation, southwestern Alberta.
Etymology: In reference to the small size of this species and to its occurrence with P. senior at Cochrane 2.
Age and distribution: Earliest Tiffanian of Alberta (type locality) .
Material.—UALVP 28564, P4; UALVP 28558, p3; UALVP 28566–28568, dp4s; UALVP 126, 45096, m1s; UALVP 28557, 28559, m3s.
Diagnosis.—Smallest species of the genus; differs from Paleotomus senior ( Simpson, 1937) , Paleotomus milleri Rigby, 1980 , Paleotomus radagasti ( Van Valen, 1978) , and Paleotomus carbonensis Secord, 1998 in its significantly smaller dental dimensions (approximately 40 percent less than Paleotomus senior , 20 percent less than Paleotomus milleri , 50 percent less than Paleotomus radagasti , and 35 percent less than Paleotomus carbonensis ); differs further from P.milleri in m1 lacking an entoconulid and mesoconid.
Description.—p3: The crown of p3 is dominated by the large protoconid; a small, unicuspate heel is developed posteriorly. A small, conical paraconid arises from the anterolingual base of the protoconid and projects anteriorly.No metaconid is de − veloped.Two prominent crests, one anterior, the other poste − rior, descend from the apex of the protoconid; the posterior crest continues posteriorly to the heel.A short crest runs anterolingually from the apex of the talonid cusp and meets the posterobasal part of the protoconid to form a shallow talonid basin.
dp4: dp4 is molariform, with a well−developed trigonid and talonid.The crown is dominated by a tall, subconical protoconid and a slightly shorter and smaller metaconid.The paraconid is positioned well anterior to both the metaconid and protoconid.A large secondary cusp arises anterolingual to the paraconid; the size and position of this cusp creates the appearance of a “twinned” paraconid.The metaconid is positioned posterolingual to the protoconid, and the two are joined for almost half their heights.The paracristid and protocristid are notched medially.The talonid is large and robust, slightly wider than the trigonid, with three distinct, well−separated cusps: the hypoconid is the largest talonid cusp, followed by a smaller entoconid and hypoconulid.The hypoconid and hypoconulid are subcrescentic in occlusal view, whereas the entoconid is more nearly circular.A tiny entoconulid is present on a low entocristid, and a swelling interpreted as a mesoconid occurs on the cristid obliqua.The talonid notch is broad and open lingually.The cristid obliqua is high at the hypoconid, but descends anteriorly and strikes the postvallid low and slightly labial to the medial notch in the protocristid.Labial exodaenodonty ( Krause 1977) is present over the anterior and posterior roots.
m1: The trigonid is taller and of subequal width compared to the talonid.The protoconid is the largest and tallest trigonid cusp; its lingual face is concave.The metaconid is tall, slightly shorter than the protoconid, and convex along its anterior face.The paraconid is smaller and in a slightly more labial position than the metaconid; in occlusal view, the trigonid cusps form a nearly equilateral triangle.The para − cristid is moderately high and notched.The protocristid is broadly V−shaped in labiolingual dimensions, and deeply notched medially, but well above the level of the talonid.The precingulid is prominent and shelf−like.A minor swelling is sometimes present at the base of the paraconid.The talonid is open lingually, and the cusps are well developed and spaced equidistantly from each other; although wear has reduced the original sizes of the cusps, they appear to have been nearly equal in height, but from the dimensions of its base, the hypoconid was probably more massive than either the entoconid or hypoconulid.The hypoconid is subcrescentic in occlusal view, whereas the entoconid and hypoconulid are more nearly circular.Neither an entoconulid nor mesoconid are developed.The talonid crests are sectorial; the cristid obliqua meets the postvallid ventral to the protocristid notch.
m3: As in other species of Paleotomus , the protoconid on m3 is smaller relative to the metaconid than on m1 or m2. The paracristid and protocristid notches are distinct but weakly developed.The talonid cusps are robust and well de − fined, and both the mesoconid and entoconulid are absent.
Remarks.— Simpson (1937) described the pantolestid “ Palaeosinopa ” senior on the basis of an isolated m3 (AMNH 33990) and two upper molars (AMNH 33828 and 33991) from the early Tiffanian Scarritt Quarry, Montana. Van Valen (1967) later erected the genus Paleotomus , which he considered to be a didelphodontine palaeoryctid, for the m3, and named a new species, “ Palaeosinopasimpsoni ”, based on the upper molars. Gingerich (1980) subsequently synonymized “ Palaeosinopa simpsoni ” with Paleotomus senior and returned this taxon to the Pantolestidae ; better−preserved specimens referable to Paleotomus senior from Douglass Quarry, Montana, supported this revision ( Krause and Gingerich 1983). McKenna and Bell (1997) subsequently returned Paleotomus to the Didelphodonta, consistent with Van Valen’s (1967) original classification.It is clear from the repeated taxonomic shuffling that the suprageneric affinities of Paleotomus are not well understood; for the present, we consider the taxon best referred to Eutheria, incertae sedis.
Until the discovery of P. junior , the late Torrejonian P. milleri from Swain Quarry, Wyoming, and P. carbonensis from Grayson Ridge and Halfway Hill localities, Wyoming, were the smallest recognized species of the genus. P. junior occurs with the much larger P. senior at Cochrane 2.
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