Peradectes chesteri (Gazin, 1952)

Murphey, Paul C., 2019, PE Note: Corrigenda to Murphey et al. 2018, Palaeontologia Electronica (25 A) 21 (2), pp. 1-54 : 22-24

Peradectes chesteri (Gazin, 1952)

Figure 13.1-4 , Table 3

1952 Peratherium chesteri ; Gazin, p. 18, pl. 1, figure 1.

1962 Peratherium chesteri ; Gazin, p. 21.

1973 Peratherium innominatum , in part; West, p. 79.

1980 Peradectes chesteri : Bown, p. 131.

1982 Peratherium sp. , cf. P. innominatum ; Bown, p. A43.

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

1983b Peradectes chesteri ; Krishtalka and Stucky, p. 249, figure 5.

1984 Peradectes chesteri ; Krishtalka and Stucky, p. 37, figure 3.

1994 P eradectes chesteri ; Bown et al., p. 4, tab. 1.

1998 Peradectes chesteri ; Gunnell, p. 88.

2008 Peradectes chesteri ; Korth, p. 43.

Referred specimens. From locality UCM 92189 : LM1, UCM 68427 ; partial maxilla with LM2-3 , UCM 95781; Lm2 or 3 , UCM 78458. From locality SDSNH 5842: partial RM 1 , SDSNH 110418. From locality DMNH 4672: RdP3, DMNH 75275 .

Description. DMNH 75275 is identified as a dP3 ( Figure 13.1 ) because of its nearly equilateral dimensions (just slightly longer than wide), very elongated posterior metastylar wing, and reduced anterior parastylar shelf. It is significantly smaller than the M2-3. The paracone and metacone are equal in size and height. The protocone and talon basin are reduced as compared to those of the M2- 3. The paraconule is weakly developed with very short, vestigial pre- and post paraconulecristae, whereas a metaconule is lacking. Stylar cusp C is represented by an elongated, weak bulge along the labial rim of the stylar shelf approximately opposite of the metacone apex, whereas stylar cusps A, B, D, and E are lacking. The ectoflexus is very shallow. The posterior cingulum (postcingulum) is weakly developed and an anterior cingulum (precingulum) is lacking.

An isolated M1 (UCM 68427, Figure 13.2 ) is compatible in size and very similar in occlusal morphology to the associated M2-3 (UCM 95781, Figure 13.3 ) described below, both of which were recovered from UCM Locality 92189. It differs from M2-3 by the following: 1) slightly longer relative to its width (slightly less transversely broad); 2) a weakly-developed stylar cusp (probably cusp D) present on the stylar shelf posterior of the metacone apex and anterior to the labial terminus of the metastylar wing; 3) a shallower ectoflexus; and 4) a metacone slightly larger than the paracone. All of these differences are typically used to separate the M1 from the M2-3 of Peradectes (McGrew, 1939; Lillegraven, 1976; Krishtalka and Stucky, 1983b). Like the M2-3, UCM 68427 is lacking stylar cusps A, C, and E, and a protoconule and metaconule, and has a non-dilambdodont centrocrista with the metacone slightly taller than the paracone.

UCM 95781 ( Figure 13.3 ) consists of a partial right maxilla with fragments of the M1 due to its crown being broken off, a nearly complete M2 with only the apex of the paracone broken off, and a complete M3. Although the occlusal morphologies of the M2 and M3 are quite similar, the M3 differs by being more transverse and by having a slightly deeper, more defined ectoflexus and a significantly more anteroposteriorly compressed protocone. The M2-3 have the paracone and metacone subequal in size, with the former slightly lower in height. A protoconule and metaconule are lacking. Stylar cusp B is moderately developed and connected lingually to the preparacrista on M2, but on the M3 it is isolated from the labial terminus of the preparacrista by a very shallow, narrower valley. Stylar cusps A, C, D, and E are lacking. The stylar shelf is relatively wide and the ectoflexus relatively deep, especially on M3. Anterior and posterior cingula are lacking.

An isolated left lower molar, either m2 or 3 ( Figure 13.4 ), was recovered from the same locality as the partial maxilla with M2-3. Its trigonid and talonid are equal in width. The primary cusps of the trigonid (protoconid, metaconid, and paraconid) are robust, with the paraconid about one-half the height of the protoconid and the metaconid just slightly lower in height than the protoconid. The paracristid is straight, connecting the paraconid and metaconid. The entoconid is about equal in size to the hypoconulid, closely positioned to it, and separated from it by a shallow notch. The cristid obliqua extends from the hypoconid apex to terminate on the posterior wall of the trigonid, just below the protocristid notch. The anterior and posterior cingula are moderately distinct. The labial border between the trigonid and talonid is almost straight with very little emargination.

Remarks. Crochet (1979) erected the tribe Peradectini , based primarily on North American species of Peradectes . Subsequent investigators have either elevated its rank to the subfamily level as Peradectinae (e.g., Korth, 2008) or family level as Peradectidae (e.g., Reig et al., 1985; Johanson, 1996; Rothecker and Storer, 1996; Case et al., 2005; Horovitz et al., 2009; Rose, 2010) or used both ranks (e.g., Korth, 1994). Williamson et al. (2012) regarded " Peradectidae " sensu lato as an unranked clade composed a basal polytomy of species, which also included certain Cretaceous Eurasian and Paleocene South American taxa. Following Horovitz et al. (2009), we regard Peradectidae as a familial rank.

Peradectes is characterized by the following (Krishtalka and Stucky, 1983b; Korth, 2008): 1) the M1-3 paracone and metacone subequal in size and not dilambdodont; 2) the M1-3 stylar cusps, protoconule and metaconule weakly developed and in some species all stylar cusps, except B, vestigial or absent; 3) the M1-3 posterolingual base of the protocone unexpanded; 4) the m1-3 talonid relatively short with a labially positioned cristid obliqua and a low entoconid; and 5) the m1-3 hypoconulid and entoconid subequal in size, positioned relatively close to each other, and separated by a weak notch. The TBM specimens exhibit the above diagnostic characters of Peradectes and can be confidently assigned to the genus.

The holotype of Peradectes chesteri , a partial right dentary with m3 (USNM 19199), came from the late Wasatchian (biochron Wa7) Wasatch Formation near La Barge, Wyoming (Gazin, 1952).

Subsequently, Peradectes chesteri has also been recorded from earliest Bridgerian (biochron Br1a) through the early Uintan (biochron Ui1b), resulting in a geochronologic range of about 7 Ma (West, 1973; Krishtalka and Stucky, 1983a, 1983b; Gazin, 1976; Walsh, 1996; Gunnell, 1998; Gunnell et al., 2009).

Peradectes chesteri is characterized by having the following (Krishtalka and Stucky, 1983a, 1983b, 1984): 1) small size; 2) M1-3 with a moderately reduced stylar cusp B and other stylar cusps vestigial or absent; 3) M1-3 paracone taller than protocone and stylar cusp B; 4) M1-3 paraconule and metaconule greatly reduced (vestigial); 5) M2- 3 ectoflexus well defined and moderately deep; 6) M3 with a highly compressed protocone and more transversely broadened than M2; 7) p3 with short talonid that is lower in height than m1; 8) m1-3 narrow in proportion to length with little to no labial emargination between the trigonid and talonid; 9) m1 smaller than m2-3; and 10) m4 talonid shorter than trigonid. The specimens from the TBM are indistinguishable in size and occlusal morphology from those of Peradectes chesteri and are referred 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.