290
Journal of Paleontology 92(2):289–304
by size and details of tooth morphology. Additional material attributed to L. oregonensis was found in the Mascall Formation (a single upper P4, UCMP 39102; Downs, 1956). Baskin (1998, 2005) interpreted the Leptarctus material from the Olcott Formation of Nebraska (Snake Creek Beds, 17–15 Ma; Tedford et al., 2004) that Matthew (1924) had described as L. primus as belonging in fact to L. oregonensis, thus adding a lower jaw (AMNH 18270) and a nearly complete skull (AMNH 18241) to the material known for L. oregonensis and extending the geographic distribution of the species outside of Oregon. Baskin, (1998) argued that the “smaller P4 with a less prominent hypocone and [the] relatively smaller M1” (Baskin, 1998, p. 158) ofAMNH18241 compared to the holotype of L. primus, which supported its assignment to Leptarctus oregonensis. Lim and Martin (2001a, 2002) and Lim et al. (2001) did not recognize the AMNH skull and the lower jaw as L. oregonensis and, instead, identified these specimens as L. primus. Wang et al. (2004) also identified AMNH 18241 as L. primus. The sizes of the P4 and M1 of AMNH 18241 are intermediate between those of the type specimen of L. primus and the L. oregonensis material from Oregon, and therefore do not allow this debate to be settled (Table 1). Although figured
Table 1. Cranial measurements for Leptarctus oregonensis and other mustelids. Specimen
UOMNH F-35458 L. oregonensis
AMNH 18241 L. oregonensis
AMNH 25258 L. primus
UF 5706 L. ancipidens
LACM (CIT) 206 L. oregonensis
UCMP 39102 L. oregonensis
UNSM 20843 L. martini
UWBM 6418 B. astutus
CM 81783 L. mummorum
UWBM 28348 M. putorius
UWBM 41393 T. taxus
UWBM 41022 G. gulo
UWBM 59961 P. lotor
UWBM 41336 M. mephitis
UWBM 32973† M. meles
UWBM 51603 S. putorius
(Matthew, 1924, fig. 37), AMNH 18241 was only briefly described by Matthew (1924), as well as by Korth and Baskin (2009) who described parts of its zygomatic arch and tympanic projections. The lack of substantial cranial material from Oregon (beyond LACM CIT 206) has prevented an assessment of the differences in cranial morphology between specimens from Nebraska and those from Oregon. We are now able to describe an additional specimen of Leptarctus oregonensis from the Mascall Formation of eastern Oregon, the type formation for this taxon. This new, almost complete skull (UOMNHF-35458) is the first specimen to preserve the morphology of the auditory bulla and its processes. It also includes details of the basi- cranium, previously undescribed for L. oregonensis, which are frequently important in carnivore systematics and should be important in future phylogenetic analyses of the leptarctines. UOMNH F-35458 provides the opportunity for a compre- hensive description of the cranial morphology of this taxon, a revision of the diagnosis of the species, and additions to the long-standing debate concerning intraspecific variation in species of Leptarctus (see Korth and Baskin, 2009). Indeed, despite some morphological differences between the specimens from Oregon and those from Nebraska, we argue here based on
LR RW WZA HZA SL POC PW OW LP2 WP2 LP3 WP3 LP4 WP4 LM1 WM1 30.2* — 57.6 12.6 74.0* 19.9 14.1 11.2 —— 3.9 2.8
— 21.79 62.5 — 88.0 19.2 —— 3.2 ——— — — — ——— — — —
— —
— —
— 22.3 —— 94.6* —— — ——— — 100.3 —— — 4.0
— — —
2.2 4.7 3.3
— —
7.2 7.1
— 3.8 — 7.0 — —
2.2
7.6 64.5 17.1 11.2 9.9 2.2 3.9 77.6 16.4 9.4 17.4 3.8
53.1 33.8 73.6 14.1 123.1 27.2 17.8 18.1 3.9 66.4 36.6 93.0 27.1 149.1 30.7 26.2 16.3 6.4 55.5 25.8 10.4 19.0 114.0 25.1 21.1 19.4 4.4 27.6 22.4 51.6 11.1 20.3 12.3 34.6
5.8 56.1 13.0 8.0 9.1 2.0 78.7 19.4 14.1 12.5 2.0
2.9 1.4 1.8 2.6 4.3 2.6 1.3 1.3
5.0 3.9
5.4 4.8 3.6 1.9 4.0 2.2
— 6.8 — 7.3 9
8.8 6.5 7.1
5.1 5.4 5.0
7.0 7.5 7.2
7.7 8
6.05 7.3 7.0
5.7 —— 6.4 7
58.9 35.6 85.7 — 129.1 28.4 20.9 —— — 6.5 5.7 11.5 10.8 12.31 —— 70.2 — 98.8 —— — 3.9 25.9 14.7 38.7 19.3 13.9 46.9
9.5 3.5 5.1
6.4 4.8 11.2 9.3
7.9 7.4 6.2
7.6 5.5 3.6
7.4 8.8
10.3
8.9 10.2 3.4 5.8 6.7
5.6 7.8 9.8
8.9 5.5 19.9 10.9 6.8 13.2 5.7 3.9 3.8 2.8 3.1 1.6
8.9 7.1 5.0
8.7 8.2 5.2
55.5 28.8 75.1* 16.5 127.6 24.8 17.8 15.9 —— 4.9 3.15 —— — —
UOMNHF-35458, L. oregonensis;AMNH18241, L. oregonensis (from Wang et al., 2004 and based on UCMP 27295); LACM (CIT 206), L. oregonensis; UCMP 39102, L. oregonensis; AMNH 25258, L. primus (from Lim and Martin, 2002); UF 5706, L. ancipidens (from Lim and Martin, 2001; Lim and Martin, 2002); CM 81783, L. mummorum (from Korth and Baskin, 2009); UNSM 20843, L. martini (from Lim and Miao, 2000; Lim and Martin, 2001); UWBM 28348, Mustela putorius; UWBM 6418, Bassariscus astutus; UWBM 41393, Taxidea taxus; UWBM 41022, Gulo gulo; UWBM 59961, Procyon lotor; UWBM 41336, Mephitis mephitis; UWBM 51603, Spilogale putorius; UWBM 32973, Meles meles. Abbreviations: LR, Length of rostrum from posterior to the postorbital process of the jugal anteriorly; RW, width of rostrum at canines; WZA, width of skull across zygomatic arches; HZA, total height of zygomatic arches; SL, skull length; POC, width of skull at postorbital constriction;PW, width of palate between M1s;OW, maximum width of orbits; LP2, length of P2;WP2, width of P2; LP3, length of P3; WP3, width of P3; LP4, length of P4; WP4, width of P4 across protocone; LM1, length of M1; WM1, width of M1. Measurements of the P4 and M1 were taken following the guidelines of Popowics (2003). Measurements in mm.
* = Broken feature, measurement approximate; 1one of the two measurements given in the original publication; †specimen’s cheek teeth are too worn to be accurately measured.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166 |
Page 167 |
Page 168 |
Page 169 |
Page 170 |
Page 171 |
Page 172 |
Page 173 |
Page 174 |
Page 175 |
Page 176 |
Page 177 |
Page 178 |
Page 179 |
Page 180 |
Page 181 |
Page 182 |
Page 183 |
Page 184 |
Page 185 |
Page 186 |
Page 187 |
Page 188 |
Page 189 |
Page 190 |
Page 191 |
Page 192 |
Page 193 |
Page 194 |
Page 195 |
Page 196 |
Page 197 |
Page 198 |
Page 199 |
Page 200 |
Page 201 |
Page 202 |
Page 203 |
Page 204
