Peradectes californicus ( Stock, 1936 )

Murphey, Paul C., 2019, PE Note: Corrigenda to Murphey et al. 2018, Palaeontologia Electronica (25 A) 21 (2), pp. 1-54 : 24-25

Peradectes californicus ( Stock, 1936) Figure 13.5 , Table 3

1936 Peratherium californicum ; Stock, p. 123, figures 2, 2a.

1975 Nanodelphys cf. N. minutus , in part; Setoguchi, p. 269.

1976 Nanodelphys californicus ; Lillegraven, p. 91, pl. 5, figure 3, pl. 6, figures 1a-c, pl. 7, figures 1a-c, 2a-c, pl. 8, figures 1a-c, pl. 9, figures 1a-c, 2a-c, 3a-c, pl. 10, figures 1a-c, 2a-c, 3a-c, 4a-c.

1983a Peradectes californicus ; Krishtalka and Stucky, p. 219.

1983b Peradectes californicus ; Krishtalka and Stucky, p. 247.

1984 Peradectes californicus ; Storer, p. 21, figures 1k.

1990 Peradectes californicus ; Kelly, p. 8.

1994 Peradectes californicus ; Kelly and Whistler, p. 2, figure 1.

1996 Peradectes californicus ; Rothecker and Storer, p. 773, figure 1o-q.

2008 Peradectes californicus ; Korth, p. 43.

2010 Peradectes californicus ; Kelly, p. 160, figure 1b-f.

2013 Peradectes californicus ; Kelly, p. 58, figure 2c.

Referred specimen. From locality SDSNH 5844: Rm2 or 3, SDSNH 110432.

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Description. The lower molar trigonid is slightly wider than the talonid. The primary cusps of the trigonid are robust, with the protoconid larger and slightly taller than the metaconid. The paraconid and metaconid are subequal in size, with the paraconid about one-half the height of the protoconid. The paracristid extends anterolabially from the protoconid apex and then turns more directly labially to join the paraconid apex, giving it a curved appearance in occlusal view. The entoconid and hypoconulid are subequal in size, closely positioned to one another and separated by a shallow notch. The cristid obliqua extends anterolabially from the hypoconid apex to terminate on the posterior wall of the trigonid, between the paracristid notch and the protoconid apex. The labial margin between the trigonid and talonid is distinctly emarginated. The anterior cingulid is robust, whereas the posterior cingulid is slightly less developed.

Remarks. One lower molar, either m2 or 3 (SDSNH 110432, Figure 13.5 ), that came from the highest fossil yielding level in the TBM, can be eliminated as belonging to Herpetotherium or Copedelphys by having the following combination of characters: 1) small size; 2) the entoconid and hypoconulid about equal in size and height, positioned close to each other and separated by a weak notch; and 3) the hypoconulid cuspate (not shelf-like) and not projecting well posterior of the entoconid. This talonid morphology is typical of members of the Peradectes - Nanodelphys lineage (Krishtalka and Stucky, 1983b; Korth, 1994).

As discussed above, the taxonomic history of Peradectes californicus is complicated. The holotype, a partial right dentary with p3-m2 (LACM [CIT] 1943), came from the late Uintan (biochron Ui3) part of the Sespe Formation, Ventura County, California ( Stock, 1936). Peradectes californicus has also been recorded from the late Uintan Mission Valley and Santiago Formations of San Diego County, California, the late Duchesnean (biochron Du) part of the Sespe Formation, California, the medial Uintan to early Duchesnean (biochrons Ui2- Du) Wagon Bed Formation of the Wind River Basin, Wyoming, the Duchesnean (biochron Du) Tepee Trail Formation of Wyoming, and late Uintan to Duchesnean (biochrons Ui3- Du) Cypress Hills Formation of Saskatchewan ( Setoguchi, 1975; Lillegraven, 1976; Krishtalka and Stucky, 1983b; Storer, 1984; Rothecker and Storer, 1996; Korth, 2008; Kelly, 2010, 2013).

Peradectes californicus is similar in size to Peradectes chesteri , but differs by the following (Lillegraven, 1976; Krishtalka and Stucky, 1983a, 1983b, 1984): 1) M1-3 length shorter relative to width (ap and tr nearly equal); 2) M1-3 paraconule, metaconule usually slightly better developed, but still weak; 3) M1-3 with very small stylar cusps C and D commonly present; 3) M3 less transverse with less compression of protocone; 4) p3 talonid absent; and 5) m1-3 wider relative to length and with a distinct labial emargination between the trigonid and talonid. As in Peradectes californicus, SDSNH 110432 exhibits a very distinct emargination between the trigonid and talonid and its width relative to its length is wider (tra/ap = 0.62) than that of the m2 or 3 referred above to Peradectes chesteri from lower in the TBM (tra/ap = 0.51).

Setoguchi (1973) originally assigned certain specimens from the Uintan and Duchesnean Tepee Trail Formation at Badwater Creek to two informal species of Nanodelphys ; Nanodelphys sp. , cf. N. minutus and Nanodelphys sp. nov. Later, Setoguchi (1975) subsumed the sample of Nanodelphys sp. nov. into his Nanodelphys sp. , cf. N. minutus . Krishtalka and Stucky (1983b) determined that Setoguchi's (1975) sample of Nanodelphys sp. , cf. N. minutus actually consisted of three species; Peradectes californicus , Peratherium innominatum (= Copedelphys innominata , see Rothecker and Storer [1996]), and Nanodelphys sp. , cf. N. minutus (= Nanodelphys sp. nov. of Setoguchi [1973]). Korth (1994) noted that the upper molars that Krishtalka and Stucky (1983b) retained in Nanodelphys sp. , cf. N. minutus may represent a new species of Peradectes because their length to width ratios are intermediate between those of Nanodelphys and Peradectes , and they have less reduction of the stylar cusps than that of Nanodelphys . Korth (1994) also noted that the lower molars of Nanodelphys differ from those of Peradectes by having relatively narrower and more elongated trigonids and straighter paracristids. In SDSNH 110432, the paracristid is slightly curved posteriorly and the ratio for its trigonid length/ap is 0.54, whereas that for the mean m2-3 trigonid length/ap of Nanodelphys hunti is 0.64 (Korth, 1994).

Based on the above comparisons, SDSNH 110432 can be eliminated as representing either Peradectes chesteri or Nanodelphys . sp., cf. N. minutus , but is indistinguishable from the lower molars of Peradectes californicus and is assigned to that species.

Figures

FIGURE 13. Upper and lower dentition of Peradectes from TBM. 1-4, Peradectes chesteri: 1, RdP3, DMNH 75275; 2, LM1, UCM 68427; 3, LM2-3, UCM 95781; 4, Lm2 or 3, UCM 78458. 5, Peradectes californicus, Rm2 or 3, SDSNH 110432. All occlusal views. Scale bar = 1 mm.