Skull and Dentition

All three skulls observed displayed the same overall shape: an elongated braincase in the rear with sagittal and occipital crests; sharply pointed postorbital processes; high, wide zygomatic arches; paired infraorbital foramina just posterior to a sudden narrowing of the skull at the muzzle; wide, deep nasal cavities with turbinate bones; and large, frontally oriented orbits. The tooth row ended just posterior to the anterior insertion of the zygomatic arch at the maxilla. Diastema were present between the third upper incisors and the upper canines to accept the cusps of the lower canine teeth, and in some cases were present just after the lower canines as well. There was a palatine fissure between the paired os incivisa and there were two vertical points of bone framing the vomer.

The skull was formed by a number of fused plates (basisphenoid, palatine, zygomatic ventrally; parietal, frontal, temporal, maxilla dorsally), which were roughly correspondent between skulls. A deep sagittal suture bisected each skull along the midline, and a coronal suture bound the frontal and parietal plates. The zygomatic arch was formed by two bones: the jugal process of the maxilla and a process of the temporal bone. The larger skulls had thicker bones and larger ridges, and the canids as a whole had deeper, wider muzzles and nasal cavities than Vulpes. Overall there were not many differences between the wolf and coyote skeletons; the red fox showed the greatest divergence.

The wolf skull was the largest and broadest, with the most rostral dishing and the largest ridges for muscle attachment. It appeared to be an almost extreme adaptation, with the bones extraordinarily heavy in comparison to the coyote and red fox and everything heavily reinforced over articulation points and around the jaw. The temporal fossa were proportionally the widest to admit the enormous masseters. All crests were most pronounced in this species, with the sagittal crest almost horizontal. The skull was 24.3 cm from incisors to foramen magnum and weighed 435.7 g. The muzzle was proportionally widest of the three species. The auditory bulla was nearly round in the wolf; in the other two species it is more oval. The jugular process was more pronounced than in the other two skulls.

The skull of the coyote weighed 167.4 g and was 18.2 cm long. The occipital and sagittal crests were present, but not as pronounced as those in the wolf. The rostrum was less dished than that of the wolf and the overall shape was smaller and lighter. However, the fundamental shape was nearly identical to that of lupus.

The fox skull was the lightest and most slender, weighing 63.2 g. It was 13.8 cm long. There was a dent over the postorbital process and there were distinct temporal crests observed which were not present in the canids. These crests were low and less than 10 mm apart, and are distinct from the ridge connecting the postorbital process to the parietal crest, which is present in all three species. The fox had the largest orbits relative to skull size (2.6 cm/13.8 cm as compared to 2.7/18.2 cm for the coyote and 3.5/24.3 cm for the wolf). There was an extra septum amidst the turbinate bones, which were the lightest and closest-packed of the three specimens. The fox had two post-palatal foramina on the ventral side of the skull, as opposed to three observed in the coyote. The os nasale projected further than the premaxillae, out over the nasal cavity opening. There was no "step" present below the angle of the lower jaw (as is present in Canidae). The tips of the upper canines fell below the anterior mental foramina in the mandible, while in the canids they fell at or above the foramina.

The observed dental formula for all three species was 3/3 1/1 3/3 3/3. The incisors in the canids were "lobed", with three cusps each, and had a single root. The incisors increased in size as they neared the canines, with the root of each tooth pointing into the jaw laterally. The canines curved caudally, with the single root pushed caudolaterally into the skull. The canines of Vulpes were the longest and most slender. The sectoral teeth, or premolars, were relatively reduced in size, with one cusp, directed posteriorly, and two roots (except for the first sectoral, which had one) pointing straight into the skull. The first molar, the carnassial, was oriented front-to-back on both jaws and had three roots and two or three large, slightly caudally curved cusps adapted for shearing meat. The cusps of the upper and lower carnassials came together with the cusps of the lower tooth just inside that of the upper, much like a pair of scissors.

The second molars on both jaws were the largest, with three roots in the upper, two in the lower, both with six cusps. The third (and last) molars were reduced, with three roots in the upper and one in the lower, and five cusps. The upper molars were triangular; the lower molars were more linear. The lower teeth fit entirely inside the upper teeth, and slid quite closely against them.

Note that the dentition of all three animals implies exclusionary or almost-exclusionary carnivory -- the teeth are geared for piercing, grabbing and shearing rather than for the extensive grinding of fibres required by herbivores. Despite the fact that the pattern of dentition is nearly identical, the wolf is the only (almost) complete carnivore in the group. Coyotes and foxes are known to eat fruit, berries and some grasses (albiet occasionally) as part of their natural diet.

< previous   main   next >