Mammals of our Saguaro Juniper Zone

Main sources: Nowak, Ronald, 1991, Walker's Mammals of the world, Fifth Edition (two vols.), Baltimore: Johns Hopkins University Press; Hoffmeister, D. F., 1986, Mammals of Arizona, Tucson: University of Arizona Press; Burt, W. & R. Grossenheider, eds., 1976, A Field Guide to the Mammals, Peterson Field Guides: Houghton Mifflin; Eisenberg, John, 1980, The Mammalian Radiations, Chicago: University of Chicago Press; Cockrum, E.L., 1960, The Recent Mammals of Arizona: Their Taxonomy and Distribution, Tucson: University of Arizona Press; Tyburec, Janet, "Bats", and Merlin, Pinau & Peter Siminski, "Shrews", in Steven Phillips and Patricia Comus, eds., 2000, A Natural History of the Sonoran Desert, pp. 461-72 & 492, Arizona-Sonora Desert Museum Press, Tucson; Murie, Olaus, 1974, Animal Tracks, Peterson Field Guides: Houghton Mifflin; Tedford, Richard, 1994, "Key to the Carnivores", Natural History 103:4:74-6; McKenna, Malcolm, 1994, "Early Relatives of Flopsy, Mopsy, and Cottontail", Natural History 103:4:56-8; Johnson et al, 2006, "The late Miocene radiation of Modern Felidae", Science 311:73-7; O'Brien, Stephen, & Warren Johnston, "Evolution of Cats", Scientific American July 2007, pp. 68-75.

Among the terrestrial tetrapods, the mammals are members of the Synapsida -- a great group of vertebrates having a life history of some 300 Million years, the most famous ancestral form of which is probably Dimetrodon grandis, the quadrupedal reptiloid carnivore of the Early Permian period who wore a spectacular vertical sail supported by the elongated dorsal spines of its vertebrae. But of all the classes of Synapsids which have existed since that time, only members of the Class Mammalia survive.

All "Synapsids" possess a single opening on each side of the skull bones, through which pass the muscles closing the jaw (the bones over the opening forming the zygomatic arch, which we humans can feel at the sides of our faces as our "cheek bones").

For example, consider at left this partial skull of a Coati found in October 1996 atop Rabbit Ears Saguaro Hill in Lower Hot Springs Canyon, lacking its lower jaw but otherwise complete. (Click on the image to enlarge it.) The eye socket is visible near the center of the photograph, and just below and running behind it is the zygomatic arch, down through which the muscles working the lower jaw would run in life. These muscles have been ripped out (probably by the predator who killed -- or scavenger who feasted upon -- this animal), but the space where they were formerly attached to the skull is evident in the bare spot of skull behind the eye and flanked by remnant patches of hair.

A better photograph shows the zygomatic arches from above, as in the image at right of a Gray Fox skull found in Sierra Blanca Canyon during July 2004 (Click on the image to enlarge it.). This skeletal feature is characteristic of all Synapsids (that is, today, all mammals -- with the partial exception of the Shrews, in which the arch has become vestigial). (For additional images, click here on Fox Bones.)

True mammals are defined by the possession of three middle-ear bones, though they are named for the milk produced by the mother's mammary glands to feed new-born suckling young. They began to diversify greatly with the breakup of the supercontinent Pangea during the Mesozoic era (between 135-94 MYA), when the Monotremes (egg-layers), Marsupials (pouched mammals), and Eutherians (placental mammals) separated, though nearly all remained small (shrew- to oppossum-sized) until the end-Cretaceous mass extinction episode (66 MYA), after which the great adaptive radiations of mammals occurred and really large ones appeared (even as small ones proliferated).

All our Saguaro Juniper mammals are placental (nurtured within the body of the mother through an organ allowing nutrients and oxygen to be transfered almost directly between mother and developing young -- a more energy-efficient process than is available to non-placental mammals). Placental mammals are a fairly diverse group, comprising some 4,000 species, and our Sonoran Desert contains some 130 species of them.

Worldwide, most of this mammalian diversity is found among the Rodents and the Bats. According to Cockrum (cited above), eight Families of rodents are found in Arizona, and three of bats, but we have not yet observed any of them closely and hence we will deal with them (as well as the Shrews) very briefly here. However, the Bat page has some fairly spectacular images, as you will see.

Shrews (Order Insectivora, Family Soricidae)

Insectivores are members of the Order Insectivora, which also includes hedgehogs, moles, and solenodons, and are "small, short-legged, mouselike animals with long, pointed noses" (Nowak, cited above, vol. 1, p. 144), primitive teeth, and five-clawed digits on each limb (Walker I:114). As their name implies, most are insectivores, though some are carnivorous. Some members of this order appear to be close to the "generalized, primitive mammalian type", and they appear geologically in the late Cretaceous, more than 65 million years ago (WalkerI:114).

The family Soricidae includes one of the smallest mammals in the world. They are typically nocturnal, and their vision is poorly developed, but hearing and smell are quite acute. (Some of them use echolocation to orient themselves.) While most inhabit moist habitats, a few are found in arid regions (the Notiosorex genus), including: our own:

Desert Shrew (Notiosorex crawfordi) Earliest members of the family Soricidae have been found in North America, dating to the late Eocene Epoch (more than 33 million years ago).

Bats (Chiroptera)

Bats have been flying the nighttime skies for more than 50 million years, and amount to almost 1,000 species around the world today. They are highly diverse in size, color, and in feeding preferences and methods (including true parasitism), and they occuy most regions of both hemispheres except for colder regions (beyond the limits of tree growth) and certain remote oceanic islands. The only mammals that truly fly, their wing membranes are elastic and thin extensions of the skin of the back and belly which extend from tail to neck, supported by the elongated fingers of the forelimbs. Click on the above link for more details.

Rodents (Rodentia)

This order of mammals has far more members worldwide than any other group of mammals. The suborders of rodents (formerly divided into the squirrellike, ratlike, and porcupinelike suborders) are in dispute, but all rodents share certain tooth patterns: all have 4 incisors (2 above, 2 below), which grow throughout life as a segment of a true circle, and are somewhat self-sharpening (features which condemn these creatures to lifetimes of continuous gnawing); no canines or anterior premolars (hence leaving a gap between the incisors and grinding cheek teeth). Rodents in our Saguaro-Juniper area vary in size from the very small (e.g., the Desert Pocket Mouse at a bit over 3" long excluding the tail) to medium size (the American Beaver, about 3.3 feet in length including the tail). Click on the above link for more details.

Pikas, Rabbits, and Hares (Lagomorpha)

Formerly considered a Sub-order of the Rodents, the Lagomorphs are now seen by some as more closely related to the Even-toed Ungulates (Artiodactyls, see below). They "have three pairs of upper incisors at birth; however, the outer one on each side is soon lost. In adults the smaller second upper incisor is located directly behind the first incisor and lacks a cutting edge." (Walker, vol 1, p.540) (Compare the Rodents, above.) So, while Lagomorphs (or their skulls) viewed from the front "look like" rodents -- one sees 2 very prominent incisors above, 2 below -- this appearance conceals a striking morphological difference in tooth pattern -- 2 upper incisors on each side, a smaller one behind the larger. See below, a cottontail rabbit skull photographed (upside down, missing its mandible) on March 19, 2008 on a high terrace above lower Hot Springs Canyon. Its upper incisors (at far right) show these vestigial, secondary teeth behind the primaries:

Click on the image for a closeup of these teeth from another perspective.

This difference from the rodents goes far back in the fossil record: Lagomorph finds from Eocene beds (55 Million Years Ago) in Mongolia show skulls in which the lower incisors also possess the "backup" second incisors, showing that the difference evolved from an ancient one indeed. (Lagomorph fossils of 35 or so MYA are much more like today's animals, possessing for example the also distinctive, rooted cheek teeth used for grinding vegetation with a side-to-side motion which is quite different from that of rodents. (McKenna, pp 56-7)

Lagomorphs are all terrestrials, all eat only vegetation, and they eat their moist-pellet fecal matter, thus gaining a second digestive processing of a given food.

Hares and Rabbits (Leporidae)

In our area, we have the two kinds of Leporidae -- Rabbits and Hares. Hares are generally larger and have black ear tips, and they occupy different habitats and follow different behavioral patterns. See our two main species listed below:

Desert Cottontail Rabbit (Sylvilagus audubonnii)

Black-tailed Jackrabbit (Lepus californicus)

 

Even-toed Ungulates (Artiodactyla)

The "Hoofed Animals" ("ungulates") walk on the terminal bones of their toes, and have enlarged toenails which form hoofs. Many of these evolved adapting to life on open grasslands (walking on the toes led to longer legs, increased running speeds). Among these, the Artiodactyls ("cloven-hooved") have a foot which has an even number of well-developed digits, except in the genus Tayassu (collared and white-lipped peccaries) [see below], in which the hind foot has three digits... The second and fifth (lateral) digits are slenderer than the third and fourth (medial) digits or are vestigial [pig, deer] or absent [camel]." (Walker II:1334) The main body weight is borne on these two medial digits.

Many species have horns or antlers. Some are ruminants, with a rumen or paunch which softens grasses and woody materials prior to regurgitation and further chewing. Molar teeth are complexly elaborated. Artiodactyls have a good fossil record back to the Early Eocene.

Deer (Cervidae)

These slim, long-legged Artiodactyls are best characterized by the presence of antlers (borne only by the males), appendages of the skull with a solid bony core and supported on permanent skin-covered pedicles (basal stalks). In the temperate zone antlers begin to grow in summer, covered by thin hairy skin ("velvet"), attaining full size by late summer when the blood supply cuts off, the velvet falls, and the antlers serve as sexual ornaments and weapons. In the northern hemisphere the antlers are shed each year from January to April, following the mating season.

Deer are ruminants, with four-chambered stomachs, their diets herbivorous. Their fossils date from the early Miocene (around 23 million years ago) in North America. Click on the above link for more details.

Mule Deer Odocoileus hemionus

Whitetail (Coues) Deer Odocoileus virginianus couesi

Peccaries (Tayassuidae)

This small Family is found from the southwestern U.S. to Argentina. Peccaries are quite distinct from the Suidae (pigs) in having only 6-9 tail vertebrae (pigs have many more). While the body form is piglike, the legs are long and slim and the hooves are small. The snout is very piglike: elongated, mobile, cartilaginous, with a nearly naked terminal surface. Both genera of Peccaries have a scent gland on the rump in front of the tail, which emits a strong-smelling odor when the animal is excited. The stomach is complex, but non-ruminating. Tayassuidae are found in the early Oligocene in Europe, middle Miocene in North America. A late Pleistocene genus, Platygonus, found throughout the coterminous United States about 12,000 years ago, was much larger than the living genera. (Walker II: 1344-5)

Javelina, or Collared Peccary (Tayassu tajacu)

Carnivores

The Order of Carnivores have four or five clawed digits on each limb, the first of which is not opposable and is sometimes reduced or absent; the brain has well-developed cerebral hemispheres, and the skull is heavy, with strong facial muscles and a jaw designed only for open-and-shut movements. In these jaws are "Nipping incisors, piercing canines, and tight-gripping bladelike premolars [that] are strategically set in skulls of different length and width to take advantage of the muscular force of the bite." (Tedford, p. 74) Unique to true carnivores are the Carnassial premolars/molars -- bladelike teeth which oppose each other top-to-bottom and work like scissors to slice up meat. To illustrate: below left, see the lower jaw of a Gray Fox whose dismembered corpse we found in Sierra Blanca Canyon in July 2004. The carnassial on this animal is the somewhat discolored tooth third from the left. This set of teeth comes from an elderly animal and is greatly worn down, somewhat compromising the image of predatory fierceness. In the Coati image shown toward the top of this page, though the photograph is poor, this was a young animal and the carnassial tooth stands out with its characteristic fierceness. Second, on October 9, 2010, we made the startling discovery of a nearly perfect mandible of what we presume was a baby Gray Fox, below right. Just 3cm long, it is so perfect that we feel the animal must have been swallowed whole by a Great Horned Owl, then regurgitated. See Gray Fox for more details. Again, the carnassial teeth are third from the top in this image. Click on each image to enlarge it.

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The earliest known Carnassial teeth in the fossil record are at least 65 million years old, and may be older.

Some carnivores (canids and felids) walk only on their toes (digitigrade); others (ursids, procyonids) walk on their soles with heels touching the ground (plantigrade). Most live solely or mainly on freshly killed prey -- the body organization is distinctly adapted for predation.

Dogs, Wolves, Coyotes, Foxes (Canidae)

Canids have a lithe, muscular, deep-chested body; usually long, slender limbs; a bushy tail; a long, slender muzzle; and large, erect ears (Walker II:1048). All canids have Carnassial teeth in upper and lower jaws that work both to shear (at the front) and crush (at the rear). They also use molars to chew, enabling them to process a variety of foods -- meat, bones, invertebrates, and plants. This has great survival value, lending ability to shift resources as local conditions dictate. (Tedford p. 75) This canid tooth pattern seems to have been the ancestral development of carnivores. The claws are blunt. These alert, cunning animals are generally active throughout the year, and have acute senses of smell, hearing and sight. Canidae first appear in the late Eocene (more than 33 million years ago) in North America.

Coyote (Canis latrans)

Gray Fox (Urocyon cinereoargenteus)

Mexican Wolf (Canis lupus baileyi) -- while not currently known for our area, some information on this Canid is provided in the Coyote page.

Bears (Ursidae)

These are large animals: head and body length run from nearly 4 feet (1000mm) to 9 feet (2,800mm), weight runs from 72 lbs (27 kg) to 2100 lbs (780 kg). Males are considerably larger than females. Bears have a big head, a large, heavily built body, short, powerful limbs, a short tail, and small eyes. Their teeth have evolved away from a more Canid-like pattern to emphasize crushing and masticating processes, and Bears have become more fully omnivorous and herbivorous. The coat is long and shaggy, usually of one color. Hearing and eyesight are mediocre, but sense of smell is excellent. They characteristically walk plantigrade, but can walk upright (bipedal) for short distances, and while they are slower-moving than the Canids, they are surprisingly agile and many species can outrun humans. Bears become fat during autumn and sleep through the winter in dens (except for non-pregnant polar bears). Ursidae first appear in the Late Eocene of Europe, the late Miocene (more than 5.3 million years ago) in North America.

Black Bear (Ursus americanus)

Below left: Black Bear tracks along the San Pedro River. This image shows the front paws, and you can see imprints of the claws. Below right: a hind paw track from Sierra Blanca Canyon Wash, also showing some claw marks, though this animal was slipping and sliding in fresher mud, just after a flood. Click on the images to enlarge.

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Raccoons, Ringtails, Coatis, and Pandas (Procyonidae)

This Family includes one genus found in the Himalayas and eastern Asia, and six which occur in tropical and temperate North and Central America. Procyonidae often have facial markings and tails ringed with light and dark bands. Their teeth, like those of the Bears, have developed somewhat away from the Canid pattern. Each limb bears 5 digits, the third being the longest. They walk on the sole of the foot, are good climbers, and most are omnivorous. The Procyonidae first appear in the Late Eocene of Europe, the Early Oligocene (around 30 million years ago) in North America.

Raccoon (Procyon lotor)

Coati (Nasua narica)

Ringtail (Bassaricus astutus)

Weasels, Badgers, and Otters (Mustelidae)

Mustelids are a very old family, very diverse and indeed genetic memberships remain unclear (see further below). They vary widely in size and behavior. Generally, their limbs are short and bear five digits each, and they walk on digits or partially on soles. Claws are compressed, curved, and nonretractile. Ears are short and round, and they have thick fur. Most genera have well developed anal scent glands, but these are used for signaling and marking territory rather than defence. Mustelids are mainly flesh-eaters, hunting by scent though sight and hearing are also well developed. Mustelidae first appear in the Eocene of Europe, the early Oligocene (about 30 million years ago) in North America.

While our initial construction of this page placed them in this Family, recent DNA studies suggest that skunks are sufficiently separated from the other Mustelidae (differing DNA, differing proteins) to warrant their own separate Family. We follow that suggestion here, so our sole resident member of the Mustelidae in the Cascabel area is the

Badger (Taxidea taxus).

Skunks (Mephitidae)

Mephitidae has the meaning of “stinks”. While all carnivores have scent glands (which they smear on objects to mark their scents), these animals aim a controlled, misting spray aimed with nozzles (located beside the anal sphincter) at other animals deemed threatening. When the spray enters the eyes, it burns. It is also highly flammable and can cause vomiting.

Skunks are largely fearless carnivores, and do not run from threats (for example, from approaching vehicles, hence their high rates of death due to automobiles). They also pursue very eclectic diets, and may attack snakes (rattlers become silent when they smell skunks, since the snake is likely to lose such combat). One of the few animals to eat stink bugs (first rolling them in sand until the spray-tanks are empty), skunks also scratch beehives and lick up individual bees (accepting stings during the act). They favor complex, mixed ecologies, and thrive in the vicinity of humans.

Individual skunks may travel several miles a night while searhing for food (they are primarily nocturnal), and each one may store knowledge of a number of dens, each of which it will occasionally use. They do not hold exclusive territories, and may share dens during the winter. Mothers stay close to their kits, since male skunks may kill them.

In the area of Cascabel, the following four species of skunk may be expected (given the distributions indicated in Grossenheider (cited above): the Spotted Skunk (Spilogale gracilis), the Striped Skunk (Mephitis mephitis), the Hooded Skunk (Mephitis macroura), and the Hognosed Skunk (Conopatus leuconotis). We think we may have seen all four, and the Spotted Skunk is so distinctive that we know it and give it a separate page, listed directly below.

Spotted Skunk (Spilogale gracilis)

But the other three yield less readily to our infrared camera evidence so far. We have therefore grouped them within a single page, and we present our photographic and background-documentary evidence with some diffidence.

Striped Skunk, Hooded Skunk, and Hognosed Skunk

Cats (Felidae)

See also O'Brien & Johnson, "Evolution of Cats", Scientific American July 2007, pp. 68-75.

Cats generally have a lithe, muscular, compact, deep-chested body. In most species the claws are retractile (to prevent blunting of these weapons), sharp, and strongly curved (which aids in holding prey). Pads of the feet are naked, but the rest of the foot is well haired to assist silent stalking of prey.

The head is round and shortened (see left), and the teeth are designed for seizing and cutting rather than for grinding -- for example, unlike wolves, who have lower molars for crushing and grinding as well as the carnivore "Carnassial" molars for shearing meat, lions have only the Carnassial lower molars. The tongue is "covered with sharp-pointed, recurved, horny paipillae" (Walker II:1187), suiting it for laceration and retaining food within the mouth. The eyes have pupils that contract vertically.

Cats, in sum, are "hypercarnivores" -- they prey on almost any mammal or bird they can overpower, and sometimes even fish or reptiles. Nearly all of them stalk their prey. Catlike carnivores first appeared in the Oligocene epoch (about 35 million years ago [Ma]), "and evolved into one of the world's most successful carnivore families, inhabiting all the continents except Antarctica" (Johnson et al, p. 73). Like humans, they mostly have wide ranges and tend to explore new territories as opportunities arise. Hence the very wide geographic spread of cat lineages described below.

Knowledge of the evolution of cats (family Felidae) has expanded rapidly with the application of genetic analyses, the latest and most systematic of which (Johnson et al, cited above) confirms a division into 8 major lineages into which all 38 identified species can be fit. According to this interpretation, while the earliest known cat-like ancestors appeared in the Oligocene, "All living cats trace back to a pantherlike predator that lived in Southeast Asia 10.8 Million years ago." The divergence or radiation of the cats began thereafter first with the separation of the Panthera Genus, the "great roaring cats" which today include not only lions, tigers, and leopards of the Old World, but also the Jaguar of North America. Divergence of the other seven lineages proceeded thereafter, first with the Baycat lineage of Asia, then the Caracal lineage of Africa, then, after migration into the New World, the Ocelot lineage of South America. Then followed separation of the Lynx lineage of North America (which includes not only the North American Lynx and our own Bobcat but also both Eurasian and Iberian Lynxes) and the Puma lineage of North America (and later, Africa), which includes not only our Mountain Lion but also the African Cheetah. The Lynx and Puma lineages diverged around 7 Ma. Johnson et al correlate these divergences with changes in global sea levels during the late Miocene Epoch (10.5 to 5 Ma), which fostered some 10 migrations in various directions across the continents during these times.

The final divergence, which occurred some 6 Ma, was a lineage that includes today's Asian leopard cats and various wild cats of Eurasia and Africa, which in turn split into two lineages, the Leopard Cat lineage and what Johnson et al call the Domestic Cat lineage -- since this line led first to European Wild Cats (Felis sylvestris) and out of that species, to our own domestic Felis catus.

Mountain Lion (Puma concolor)

Bobcat (Lynx rufus)

Jaguar (Felis onca) -- rarely reported for our area

Jaguarundi (Herpailurus yaguarondi) -- rarely reported for our area

Domestic Cat (Felis catus) -- where feral, has the status of an "invasive species"

Below left & center: Mountain Lion tracks in mud (the Diversion Tank, September 2000); in both images you can see that the claws are retracted, hence do not show in the mud. This marks a sharp contrast with Canid tracks. At right, tracks in dry silt near Rabbit Ears Hill in Hot Springs Canyon, January 2003. Click on each image to enlarge.

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