Calede et al.—Ecomorphology of Leptarctus oregonensis
Table 2. Ratios of dental measurements used in assessing likely diet of Leptarctus oregonensis. Genus
Aonyx Arctonyx
Bassariscus Eira
Enhydra Gulo Gulo
Ictonyx
Leptarctus Lontra Martes Meles
Mellivora Mephitis Mephitis Mustela Mydaus Neovison Procyon Spilogale Taxidea Taxidea
collaris astutus barbara lutris gulo gulo
striatus
Species capensis
Source 1
oregonensis canadensis americana meles
capensis mephitis mephitis putorius
javanensis vison lotor
putorius taxus taxus
1 2 1 1 1 3 1 4 1 1 1 1 1 5 6 1 1 7 8 1 9
Diet
Invertivore Invertivore Omnivore
Vertivore/invertivore Invertivore
Hypercarnivore Hypercarnivore
Vertivore/invertivore —
Vertivore/invertivore Vertivore Omnivore
Vertivore/invertivore Invertivore Invertivore
Vertivore/invertivore Invertivore Vertivore Omnivore Omnivore
Vertivore/invertivore Vertivore/invertivore
1.36 1.41 1.47 0.72 1.72 1.82 1.74 1.41 1.26 1.65 1.26 1.27 1.29 1.34 1.86 1.35 1.68 1.04 1.74 1.17 1.21
295
P4LB/P4W P4PM/P4W PRBL/P4W M1BL/M1W M1LL/M1W 1.27
0.75 0.7
0.77 0.74 0.34 0.71 0.75 1.09 1.08 0.7
1.04 0.82 0.77 0.51 0.6
0.91 0.79 0.65 0.76 0.93 0.89 0.85 0.95 0.42 1.01 0.59 0.57
0.41 0.42 0.49 0.63 1.02 0.43 0.87 0.51 0.79 0.66 0.41 1.1
0.44 0.97 0.73 0.91 1.02
0.81 1.05 0.74 0.46 0.59 0.51 0.51 0.45 1.17 0.75 0.51 0.96 0.4 0.9
0.87 0.61 1.16 0.51 1.02 0.95 0.62 0.68
0.78 1.08 0.48 0.62 0.67 0.56 0.58 0.44 0.92 0.75 0.59 1.18 0.63 0.82 0.79 0.51 0.96 0.62 0.9
0.69 1.09 1.11
Abbreviations: P4LB, length of P4; P4W, width of P4; P4PM, length of basin of P4; PRBL, length of shearing blade of P4; M1BL, length of shearing surface of M1; M1LL, length of M1; M1W, width of M1. Sources: 1: Species average from Popowics (2003), 2: UWBM 6418, 3: UWBM 41022, 4: UOMNH F-35458, 5:UWBM 41336, 6: UWBM28348, 7: UWBM 59961, 8: UWBM 51603, 9: UWBM 41393. New measurements were taken following the guidelines of Popowics (2003). All measurements are in mm. Diet data are taken from Long (1973), Popowics (2003), Nowak (2005), Figueirido et al. (2011), and Myslajek et al. (2013).
The skull is medio-laterally broad and anteroposteriorly short (Figs. 1, 2). It exhibits the strong parasagittal crests and zygomatic arches characteristic of Leptarctus (Korth and Baskin, 2009). It is smaller in both length and width (SL and WZA, Table 1) than L. ancipidens, L. mummorum, L. supremus, L. primus, L. martini, L. neimenguensis, L. webbi,and L. wortmani (see Olsen, 1958; Zhai, 1964; Lim andMiao, 2000; Lim et al., 2001; Baskin, 2005; Korth and Baskin, 2009). Based on an occiput to orbit length of 60.9mm,we calculated amass of 2.2kg for L. oregonensis,which is comparable to the mass of Mephitis mephitis Schreber, 1776, the striped skunk, which weighs up to 2.5kg (Nowak, 2005), or the mass of a medium-sized Martes (martens and sable; Nowak, 2005).At itswidest point the skull is 60–65% as wide as it is long, although the skull is broken anteriorly and the total length of the skull is therefore unknown. The bones of the skull are overall well fused such that the sutures can hardly be observed. The cranial morphology of UOMNH F-35458 is broadly similar to AMNH 18241, a skull of L. oregonensis from the Olcott Forma- tion, although the UOMNH specimen is not as deformed taphonomically. The frontals are smooth and convex dorsally (Figs. 1.1, 3).
They are slightly flatter in UOMNH F-35458 than in AMNH 18241. They are fused medially in a groove extending anteroposteriorly. The frontals are damaged in UOMNH F-35458 but can be observed in AMNH 18241 in which they display a mid-sagittal ridge originating in the groove between the paired frontals and extending posteriorly to the fusion between the lambdoidal crests. The fossae on either side of this mid-sagittal ridge can be observed in UOMNH F-35458. Anteriorly, the infraorbital foramen is round in UOMNH F-35458 (Fig. 3) and more teardrop-shaped in AMNH 18241, with the broad end lateral and the acute angle medial. The jugal is very strong and thickened dorsally and posteriorly to the infraorbital foramen (Fig. 2.1). The roots of the cheek teeth extend dorsally, into the upper jaw, up to the ventral margin of this
thickening. The orbit is small relative to skull size and round (Table 1, Fig. 3). The postorbital processes of the frontal and jugal are triangular with those of the frontal longer andmore acute than those of the jugal (Fig. 1.1). They are not as strong as the postorbital process of L. mummorum (Korth and Baskin, 2009). The suture between the jugal and the squamosal cannot be easily distinguished in UOMNH F-35458 but is apparent in AMNH 18241 posteriorly to the postorbital process of the jugal. The dorso-ventrally tallest point of the zygomatic arch is part of the squamosal. Both specimens display a concavity in the squamosal ventral to the tallest point of the zygomatic arch and a convexity (bump) ventral to the postorbital process of the jugal (Fig. 3). The zygomatic arch is dorsally curved. It is also medio-
laterally thickened ventrally (Fig. 1.2). This strong zygomatic arch is the origin for an enlargedmassetermuscle, a jaw-closingmuscle (Hall, 1926; Davis, 1964; Riley, 1985). The glenoid fossa of the squamosal ismedio-laterally broad, extending fromthe lateral end of the squamosal medially to the middle of the auditory bulla and aligned with the buccal cusps of M1. The robust pre- and post- glenoid processes support a strong articulation with the dentary (Peigné et al., 2005). The post-glenoid process is stronger than the pre-glenoid and the glenoid fossa is frontally oriented. The posterior end of the zygomatic arch contacts the anterior edge of the bulla as well as the anterolateral end of the lambdoidal crest, which ends at a ball-like structure: the mastoid process. The mastoid process is connected by a ridge of bone extending posteriorly to a process located posteriorly to the auditory bulla. The external opening of the auditorymeatus is located just anterior to themastoid process and surrounded ventrally by a thickened lip of bone. The mastoid process is larger in UOMNH F-35458 than in AMNH 18241. The foramina of the orbital region could only be
observed on UOMNH F-35458 and cannot be described in AMNH 18241. The lacrimal bears two foramina dorsal to the infraorbital foramen. The nasolacrimal foramen is round and
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