Urocyon minicephalus Martin, 1974

TEDFORD R. H., WANG X. & TAYLOR B. E., 2009, Phylogenetic Systematics Of The North American Fossil Caninae (Carnivora: Canidae), Bulletin of the American Museum of Natural History 2009 (325), pp. 1-218 : 75-77

Urocyon minicephalus Martin, 1974 Figure 7, 30; appendices 2, 3

Type: UF 13146 (fig. 30A, D–E), nearly complete skull except for premaxillaries, broken nasals and zygomae, with P1–M2 from Coleman IIA Loal Fauna (late Irvingtonian), Sumter County, Florida.

Referred from the Type Locality: UF 67849 and 67852, two left maxilla with P4– M1 ; UF 67851 , left premaxilla and partial maxilla with I1–I3 alveoli, C–P2 ; UF 67850 , left partial maxilla with P4–M2 ; UF 13148 , left partial premaxilla and maxilla and right partial maxilla with P3–P4 and detached teeth of two or more individuals including two right upper P4s ; UF 13143 * and 67848*, two postorbital crania ; UF 67855 *, right edentulous ramus ; UF 67863 *, left posterior part of ramus ; UF 67856 , left partial ramus with p1 alveolus–m2 ; UF 67854 , right ramus with C, P1–P2 alveoli, P3–M2, m3 alveolus ; UF 13140 ( Fig. 30B–C), right partial ramus with c, p1–p2 alveoli, p3–p4, m1–m2, and m3 alveolus ; UF 67858 , left partial ramus with p2–m1 ; UF 67857 , left partial ramus with p2– m1 ; UF 67857 , left partial ramus with p3 (broken)–m2 ; UF 67861 *, left partial ramus with i1–i3 alveoli, c–p1, and p2–p3 alveoli ; UF 67862 *, left partial ramus with p2 and c– p1, and p3–m2 alveoli ; UF 67859 , left partial ramus with m1 and m2–m3 alveoli ; UF 67860 , left partial ramus with p2–p4 and c– p1, p3, and m1 all alveoli ; UD 67853, right ramus with c–p1 alveoli, p2–m1, and m2–m3 alveoli.

McLeod Lime Rock Mine, Smith Pit, pocket ‘‘A’’ (late Irvingtonian), Levy County, Florida: F:AM 67296, left partial maxilla with P4; F:AM 67297, right ramus with c–m1 and m2–m3 alveoli; F:AM 95190, partial scapula; F:AM 68024, left humerus; F:AM 68024A, left humerus; F:AM 68024B, left partial humerus; F:AM 68024C, right radius; F:AM 68024D, left partial radius; F:AM 68024E, right distal part of tibia: F:AM 68024G, right calcaneum.

Distribution: Only known from the late Irvingtonian of Florida.

Revised Diagnosis: Derived relative to U. progressus in shorter parietals. Differs from U. citrinus in possessing the following apomorphies: m1 less elongate, and m2 relatively smaller with shorter trigonid, paraconid absent, and shorter and angled subangular lobe. Differs from U. galushai in the following apomorphies: smaller, lower crowned premolars; m2 trigonid shorter, smaller paraconid shelf, stronger anterolabial cingulum, stronger protostylid; and mandibular ramus less elongate with less expanded masseteric fossa and angled subangular lobe. Differs from U. cinereoargenteus floridanus in the following plesiomorphies: smaller skull, narrower frontals, greater postorbital constriction, narrower braincase, less widely separated frontoparietal crests, narrower occiput; M1 with lower crowned paracone and metacone, weaker labial cingulum, smaller paraconule; smaller metaconule; m1 protostylid weaker; and m2 metaconid less posterior and almost directly opposite protoconid, protostylid weaker. Differs from U. c. scotti in the following plesiomorphies: small- er skull with relatively wider muzzle, narrow- er frontals, greater postorbital constriction, narrower braincase, less lyrate parasagittal crests, narrower occiput. Apomorphies that distinguish U. minicephalus from U. c. scotti are: P4 stronger protocone, stronger anterolabial cingulum; M2 metaconule greatly reduced or absent; and m2 less elongate, relatively wider, shorter trigonid, stronger anterolabial cingulum, stronger protostylid.

Description and Comparison: Martin (1974: 70) described the skull of U. minicephalus as differing from the living gray fox ‘‘in the relatively closely allied sagittal crests and narrower occiput.’’ Additional primitive characters that distinguish the skulls of U. minicephalus from those of U. c. floridanus are wider muzzle, narrower frontals, and a less expanded braincase. The upper dentition of U. minicephalus is very similar to that of U. c. floridanus except the P 4 in which the protocone is larger than the average Florida gray fox and the anterolabial cingulum is stronger. In the P4 of the type of U. minicephalus this cingulum is produced into a small, but distinct, parastyle that is present in some of the living gray foxes examined. The M1 and M2 of U. minicephalus are more primitive in being more complex than those of U. c. floridanus with a smaller paraconule of both upper molars, and the M2 bears a small metaconule.

The lower dentition of U. minicephalus averages smaller than that of U. c. floridanus, and the m1 is primitive in being less robust with a weaker protostylid. Two jaws ( UF 67855, 67856) of U. minicephalus with unworn m2s have an extremely short trigonid with the metaconid directly opposite the protoconid. In contrast, the more apomorphic m 2 in U. c. floridanus has a larger metaconid that is situated slightly posterior to the protoconid, making the trigonid longer and the lingual border of m2 more convex.

The morphology of the lower dentition of U. minicephalus is more like that of U. c. floridanus than that of U. c. scotti or even U. citrinus from the early Irvingtonian of Florida. The premolars, especially p4, of U. minicephalus are more robust, and the p2–p3 diastema is shorter than in the type jaw of U. citrinus . Except for a slightly stronger protostylid, the m1 is very similar to that of U. citrinus . Derived features separating U. minicephalus from U. citrinus are seen in the m2, which in U. minicephalus is less elongate with the trigonid shorter and the paraconid absent. Furthermore, the talonid in U. minicephalus is also shorter and lacks the distinct entoconulid.

No morphological features were observed to distinguish the limbs of U. minicephalus from the McLeod Lime Rock Mine from those of U. cinereoargenteus .

Discussion: Although the morphology of the skull of U. minicephalus is primitive and differs markedly from that of U. c. floridanus, the dentition is derived and very similar to that of the latter. The dentition of the late Irvingtonian U. minicephalus is more like that of the recent eastern race of the gray fox than that of the more primitive U. citrinus from the early Irvingtonian of Florida or the living western race, U. c. scotti.