The dogs and relatives are members of the family Canidae, which includes dogs, wolves, foxes, jackals, and kin. With a few exceptions (none in our area), the dental formula is 3/3, 1/1, 4/4, 2/3 = 42. With the exception of some moderate cursorial adaptations (mostly in the form of digitigrade locomotion and some degree of elongation of limbs), the skeleton is fairly primitive except for the presence of the carnivoran scapholunar in the wrist.
Canids are widespread, absent only from Antarctica on a continental basis, though reaching (probably with humans) Australia in relatively recent times. Most terrestrial habitats from the Arctic to low desert are inhabited.
Unlike the cats, the dogs generally are active hunters depending less on stealth than on quickness and endurance. Several taxa (wolves, Bush Dog, Dhole, and African Hunting Dog) are highly social and cooperate in hunting; others (foxes in general, for example) are pretty much individualistic.
Most canids include a fair amount of vegetal material in their diets and some also may utilize invertebrates extensively. A long rostrum is typical, and molars have a considerable crushing and grinding function; even the lower carnassial (m1) includes a large talonid suitable for crushing.
Five canids occur or historically occurred in area. The Gray Wolf (Canis lupus) occurred throughout the region until locally extirpated from the Southwest by cattle and sheep/goat interests (aided by our tax dollars). Populations hung on considerably later in northern Mexico with occasional individuals swinging north into Texas, New Mexico, and Arizona. The last wild wolf from the region to my memory (I haven't checked the literature, so don't take it too seriously) was in the Fort Davis area in the 1960s. Hidalgo County in the bootheel New Mexico probably had the last wolves in that state, wolves that had most of their range in Mexico. These apparently were gone sometime in the 1940s.
The Southwestern subspecies of wolf has survivors in captivity with an eye to restocking portions of their original range. A related species, Canis rufus (Red Wolf) has been reintroduced into its native geographic range in the southeastern U.S., but remains on the endangered list.
The Coyote (Canis latrans), whose scientific name translates as "barking dog," has done well in competition with humans, expanding its range into areas of eastern North America where it was absent historically and increasing numbers in areas from which wolves have been extirpated (like many carnivores, wolves tend to permanently remove individuals of competing species if they can without undue hazard). Although feeding primarily on prey in the cottontail to jackrabbit size range, small artiodactyls, including the young of large species, can be taken.
Coyotes rely heavily on speed and agility in open habitats; speeds have been recorded up to about 65 km/h. Because of perceived damage to wildlife and game, control measures have long been applied, not only by individuals but also by government at various levels. For example, over 6,300 coyotes were killed in New Mexico in 1963 by state and federal trappers. Such control measures (and payment of bounties) generally do little to control population numbers, apparently mostly reducing the surplus individuals that are produced each breeding season.
Two (or three) species of red foxes (Vulpes) occur in the region. The status of the Swift Fox (V. velox) vs. the Kit Fox (V. macrotis) has fluctuated between being subspecies of one species (V. velox has priority) or being two separate species. Current thinking is that two species are represented. The line between the two taxa in our area occurs at the western edge of the Plains, in the Carlsbad region. Vulpes macrotis is smaller than V. velox, with larger ears and larger auditory bullae, as befits inhabitants of xeric environments. Both are open-country animals—grassland or desert grassland/desert. V. macrotis is the fox of most of our region.
The Red Fox (Vulpes vulpes) is predominantly a northern and eastern animal in North America (the same species occurs in the Old World). In New Mexico, records are from the northern mountains and from the San Juan Valley and environs, with rare records from the eastern plains and Dona Ana County (San Andres and Organ mountains). At one time there was some doubt about Red Foxes being native as opposed to having been introduced for English-style fox hunts. However, archaeological findings confirm that at least the western populations are native, presumably entering North America from Asia during the Pleistocene, as have so many other species found in both the Old and New worlds. Red Foxes are associated primarily with forest habitats, but not entirely limited to such.
The other canid occurring now in our area is the Gray Fox (Urocyon cinereoargenteus—literally the dog-tailed ashy [and thus gray]-silver one). Unlike the Kit Fox, this is an animal primarily of broken country or areas otherwise providing excellent cover, and it is common in the Franklin Mountains and other Southwestern ranges. It is widespread, occurring throughout the eastern half of the U.S. into southern Canada and south into South America. The only appreciable area of the U.S. from which it is absent is the northwestern quadrant. This predator not only is at home among rocks, chaparral, and forests, but is a good climber who often climbs trees and has even been known to climb telephone poles.
As a group in North America, the canids have been very successful. Nevertheless, at least two species have gone extinct or been extirpated from the continent during the Pleistocene ice age: the Dire Wolf (Canis dirus) and the Dhole (Cuon alpinus). The latter, which survives in Asia, is rare as a Pleistocene fossil, but the Dire Wolf was widespread, including within our region. In general, this was a stocky wolf whose heavy dentition has evoked comparisons with the bone-crushing habit of hyaenas.
Smithsonian Field Guide: Canidae.
The only bears within the conterminous USA are the Black Bear (Ursus americanus) and the Brown Bear (Ursus arctos, which includes the Grizzly Bear, Big Brown Bear and Kodiak Bear). Black Bears, despite the common name, often are of various shades, most of which approach either black or cinnamon. The two species can be distinguished perhaps most easily by the general body form, with the shoulder region of the grizzly being much higher than other parts of the body and, frequently, the head is held high; the Black Bear has shoulders about the height of the rest of the body (or even lower) and the head habitually is held lower than the rest of the body.
Both the Black Bear and the Grizzly Bear are omnivorous, feeding on various fruits in season and taking animal material both through scavenging and through active hunting. Because of its great size, the grizzly is able to take larger prey than the other species and reports of the killing of horses and cattle were common. Because of stock depredations and possible danger to people, strong efforts were made to eliminate grizzlies from their native, western range. The last grizzly in New Mexico probably was killed in the 1930s; in northern Mexico, they may have lasted into the 1960s in the Sierra del Nido of Chihuahua. Both forested country and grasslands were inhabited by the grizzly. Populations survive in the Yellowstone region and in much of Alaska and western Canada. On the other hand, the Black Bear occurs throughout our area in montane forests and woodlands and on rare occasion roves through lower country. One entered the El Paso portion of Fort Bliss some years ago, for example.
Black Bears tend to be active during the dark hours and hole up in a protected area during the day. Mating occurs in June or July, but delayed implantation occurs, with the embryos not implanting until late fall and birth occurring in late January. Thus, although copulation occurs some 7 months before birth, actual embryological development has taken little more than 2 months. At the time of birth, the mother is in "hibernation" (the quotes are because this is not true hibernation in the sense of a drop of body temperature to within a few degrees of the ambient temperature; however, most physiological processes do slow down greatly), and the young are only about 6 - 8" long at birth. By the time they leave the den in early to mid spring, they may weight in the neighborhood of 6 - 8 pounds; they remain with the mother until the following spring. The mother breeds only every other year. The young usually do not breed until about their fourth year. The life span may extend to as much as a quarter of a century.
The Grizzly Bear is a relatively late comer to North America (or at least the portion south of the Pleistocene ice sheets). There appears to be only one Pleistocene site known where this species and the extinct Giant Short-faced Bear (Arctodus simus) co-occur. In common with other late comers, the Grizzly Bear is deemed to be conspecific with Old World relatives. It has, however, had a stormy nomenclatural history. As is frequent with large mammals (and particularly those that tend to stick close to home), differences from one place to another were interpreted as being marking different species. As a result, some 94 names have been applied to North American populations. With extermination of most of these populations, little evidence is available as to the specific status other than the biologically commonsense stance that everything in evolutionary theory indicates one species alone. Much of the moderately old literature will treat the North American forms as Ursus horribilis.
Smithsonian Field Guide: Ursidae.
These three families collectively are called pinnipeds and are an interesting group that's been pushed around in regard relationships.
The pinnipeds have a large number of specializations for aquatic life. They generally are large (from about 35 kg to some 3,600 kg [that's well over 3 tons for the conversion challenged]) apparently as an adaptation for a cold environment (remember that body mass increases more rapidly than surface area as size increases; thus a large body has a large mass generating heat and a relatively small surface area through which to lose it). In addition, the body usually has a thick layer of insulating blubber. Additional adaptations are for streamlining to reduce friction and turbulence during swimming. These include reducing or hiding external projections (the ears are small or absent and the external genitalia and nipples are withdrawn from the surface of the body; the limbs are partially buried within the body, with only those parts distal to the elbow and knee protruding. The tail is extremely small.
Other adaptations for aquatic life include nostrils in which the default condition is closed and muscular effort is required to open them. Clavicle and vertebral zygapophyses are absent, allowing great flexibility. The thumb (pollex) is the longest digit of the manus, forming the leading edge of a fully webbed, flipper-like structure. Likewise, the pes is fully webbed, but the first and fifth digits share length honors. The main bones of the forelimb are short and robust, while the femur is flattened. The more specialized seals probably have gone about as far as they can in limb specialization since, unlike the whales, they have to haul out onto land to breed and raise young—a certain degree of mobility, then, must be retained.
Generally speaking, the cheek teeth are homodont or nearly so and two-rooted, often conical (though usually with some development of accessory cusps in phocids), and vary in number from 12 to 24. Nothing resembling a carnassial pair is present.
The otariids (eared seals such as the Sea Lion) and phocids (true or fur seals) have gone in somewhat different directions in their adaptations. In otariids, enlarged cervical and thoracic vertebrae and a large scapula provide support for forelimb musculature, the forelimb providing most of the propulsive force. In phocids, the hind limbs are more important for propulsion, with enlarged lumbar vertebrae and less emphasized thoracic girdle and limbs. Along with these differences, the otariids have maintained the ability to twist the hind feet to where they are pointing forward, whereas phocids have lost this ability. Other differences include the loss of external ears in the phocids. Both families are marine, but some phocids also occur in freshwater and estuarine situations. Sexual dimorphism is particularly well developed in the otariids, with some species having the male some five times the weight of the female.
Last Update: 23 Jan 2008
Centennial Museum and Department of Biological Sciences, The University of Texas at El Paso