Artiodactyls are the most diverse, large, terrestrial mammals alive today. They are the fifth largest order of mammals, consisting of 10 families, 80 genera, and approximately 210 species. Although the majority of artiodactyls live in relatively open habitats, they can be found in all habitat types, including some aquatic systems, and are native to every continent, excluding Australia and Antarctica. As would be expected in such a diverse group, artiodactyls exhibit exceptional variation in body size and structure. Body mass ranges from 4000 kg in hippos to 2 kg in lesser Malay mouse deer. Height ranges from 5 m in giraffes to 23 cm in lesser Malay mouse deer. (Grzimek, 1990; Grzimek, 2003; Nowak, 1999)
Artiodactyls are paraxonic, that is, the plane of symmetry of each foot passes between the third and fourth digits. In all species, the number of digits is reduced by the loss of the first digit (i.e., pollex), and many species have second and fifth digits that are reduced in size. The third and fourth digits, however, remain large and bear weight in all artiodactyls. This pattern has earned them their name, Artiodactyla, which means "even-toed". In contrast, the plane of symmetry in perissodactyls (i.e., odd-toed ungulates) runs down the third toe. The most extreme toe reduction in artiodactyls, living or extinct, can be seen in antelope and deer, which have just two functional (weight-bearing) digits on each foot. In these animals, the third and fourth metapodials fuse, partially or completely, to form a single bone called a cannon bone. In the hind limb of these species, the bones of the ankle are also reduced in number, and the astragalus becomes the main weight-bearing bone. These traits are probably adaptations for running fast and efficiently. (Feldhamer, et al., 2004; Grzimek, 1990; Grzimek, 2003; Savage and Long, 1986; Simpson, 1984; Vaughn, et al., 2000; Wilson and Reeder, 1993)
Artiodactyls are divided into 3 suborders. Suiformes includes the suids, tayassuids and hippos, including a number of extinct families. These animals do not ruminate (chew their cud) and their stomachs may be simple and one-chambered or have up to three chambers. Their feet are usually 4-toed (but at least slightly paraxonic). They have bunodont cheek teeth, and canines are present and tusk-like. The suborder Tylopoda contains a single living family, Camelidae. Modern tylopods have a 3-chambered, ruminating stomach. Their third and fourth metapodials are fused near the body but separate distally, forming a Y-shaped cannon bone. The navicular and cuboid bones of the ankle are not fused, a primitive condition that separates tylopods from the third suborder, Ruminantia. This last suborder includes the families Tragulidae, Giraffidae, Cervidae, Moschidae, Antilocapridae, and Bovidae, as well as a number of extinct groups. In addition to having fused naviculars and cuboids, this suborder is characterized by a series of traits including missing upper incisors, often (but not always) reduced or absent upper canines, selenodont cheek teeth, a 3 or 4-chambered stomach, and third and fourth metapodials that are often partially or completely fused. (Feldhamer, et al., 2004; Savage and Long, 1986; Simpson, 1984; Vaughn, et al., 2000; Wilson and Reeder, 1993)
Artiodactyls are distributed nearly worldwide and are native to all continents except Antarctica and Australia. Numerous introductions, consisting mainly of domestic species, have occurred in areas outside their normal range. Where introduced in areas with suitable forage, artiodactyls usually thrive. (Grzimek, 1990; Grzimek, 2003)
Artiodactyls are exceptionally diverse and globally distributed. Consequently, they inhabit a broad range of habitat types and can be found anywhere sufficient forage exists. Although artiodactyls occur from deserts to tropical forests to tundra, preferred habitat types fall into four major categories, which are linked to forage abundance and predator defense. Open grasslands provide abundant forage while allowing for early detection of approaching predators. Grasslands or meadows near steep cliffs provide forage while offering safety from potential predators in adjacent rocky ledges and steep terrain. Forests and shrublands provide abundant forage while offering cover from potential predators in dense vegetation. Finally, many species inhabit the ecotone between open areas and forests. While open areas provide abundant forage, adjacent forests provide dense cover from potential predators. Habitat-use patterns in artiodactyls are often linked with body size and taxonomy, with small to medium-sized artiodactyls found mainly in habitats with tall, dense vegetation. Most goat and sheep species (Caprinae) are found in open habitats adjacent to rocky cliffs, where they are specialized for navigating uneven terrain. (Grzimek, 1990; Grzimek, 2003)
In artiodactyls, the structure of the foot is especially diagnostic, specifically the number of toes and the morphology of the astragalus. Most species have either 2 or 4 toes on each foot (for exceptions see Pecari and Tayassu) as the first digit, present in most ancestral mammals, has been lost through evolution and the second and fifth digits have been significantly reduced. As a result, artiodactyls are paraxonic. The unique structure of the astragalus, which consists of a "double-pulley" arrangement of the articular surfaces, completely restricts lateral motion and allows for greater flexion and extension of the hind limb. The astragalus, in conjunction with springing ligaments in the limbs, hard hooves, relatively small feet, and elongated lightweight limbs, allows for highly developed cursorial locomotion in more derived species. In the families Camelidae, Cervidae, Giraffidae, Antilocapridae, and Bovidae, the third and fourth metapodials have become fused to create the cannon bone, which serves as the insertion point for the springing ligament in each of the four limbs. Throughout all of Artiodactyla, the range of fusion between the third and fourth metapodials varies from none to complete. Finally, residents of sandy or snowy habitats often have splayed toes, which distributes an individual's weight over a greater surface area, thereby decreasing movement costs in more fluid terrestrial substrates. (Feldhamer, et al., 2004; Grzimek, 1990; Grzimek, 2003; Rose and Archibald, 2005; Vaughn, et al., 2000)
Although exceptions exist (pigs and peccaries), the vast majority of artiodactyls are obligate herbivores, consisting of browsers, grazers and mixed feeders. Although plants provide an abundant and diverse food source, mammals do not possess the enzymes necessary to break down cellulose or lignin. As a result, most artiodactyls rely on microorganisms to help break down these plant compounds. In addition to their true stomach, all artiodactyls have at least one additional chamber in which bacterial fermentation occurs. This chamber, or "false stomach", is located just before the true stomach along the gastrointestinal tract. Cervids and bovids have three false stomachs, hippos, camels, and tragulids have two, while pigs and peccaries have only one small chamber. (Eisenberg, 1983; Feldhamer, et al., 2004; Grzimek, 1990; Grzimek, 2003; Nowak, 1999; Vaughn, et al., 2000)
A majority of artiodactyls having selenodont cheek teeth, however, many species also exhibit lophodont tooth morphology. In general, browsers tend to have brachydont teeth (i.e., low crowned) while grazers have hypsodont teeth (i.e., high crowned). Within Artiodactyla, the families Suidae (pigs) and Tayassuidae (peccaries) are omnivores and have quadrate, bunodont teeth. Often, a diastema occurs between the canine and first premolar, which is especially prevalent in the lower jaw. Bovidae, Cervidae, and Giraffidae have lost their upper incisors, and several groups have lost their upper canines. However, many have retained their incisors (pigs, peccaries, hippos, and camels) and some have developed them as weapons or indicators of mate quality (some suids, cervids and musk deer). While most families have incisiform lower canines, pigs, peccaries, hippos, and camels have conically shaped canines. (Eisenberg, 1983; Feldhamer, et al., 2004; Grzimek, 1990; Grzimek, 2003; Nowak, 1999; Vaughn, et al., 2000)
Artiodactyls exhibit a great deal of variation in physical appearance. Body mass ranges from 4000 kg in hippos to 2 kg in lesser Malay mouse deer. Height ranges from 5 m in giraffes to 23 cm in lesser Malay mouse deer. Most artiodactyls have laterally positioned eyes, often with long eyelashes. They commonly have rotating ears that are round or pointed at the tips and are relatively large in relation to skull size. Most artiodactyls also have elongated and powerful legs. Many families have horns, antlers, or tusks. Horns, always consisting of bone or having a bony core, are common in many families and most often stem from the frontals which are usually larger than the parietals. Similar to horns, antlers arise from the base of the frontals and are entirely bony. Unlike horns, however, antlers are deciduous and used during the breeding season. Horns and antlers are often used in ritualized social interactions, such as male-male competition within species. (Grzimek, 1990; Grzimek, 2003; Nowak, 1999; Vaughn, et al., 2000)
The pelage of artiodactyls typically consists of guard hair and under fur, which together help control heat exchange. Under fur tends to be short and fine and is efficient at trapping heat. Guard hairs are longer and more stout than underfur and act as a barrier against wind, rain, and snow. Pelage color varies from black to white with many shades of brown. Color patterns within the pelage vary from spots to stripes, while most young have distinctly different coats than adults. In some species, males have a ventral ridge of long hairs referred to as a ruff or dewlap and male coat color is often linked to age or social status. Species living in temperate and arctic regions shed their winter coats on a seasonal basis. (Grzimek, 1990; Grzimek, 2003; Nowak, 1999)
The majority of artiodactyls are polygynous, though a few species are seasonally monogamous (e.g., blue duiker). Artiodactyls practice two forms of polygyny, female defense polygyny, and resource defense polygyny. Female defense polygyny occurs when males mate with and defend a single female while she is in estrous. Males may also defend several females (i.e. harem) from other males, courting and mating with each individual during their period of estrous. Males may also defend specific habitat patches that attract mates because they provide abundant resources or safety from predators. This is known as resource defense polygyny and occurs in pronghorn and in many African antelope species. Lekking, a form of resource defense polygyny performed by some artiodactyls (e.g., topi), occurs when a cluster of males remain in close proximity to one another while defending individual plots of land and waiting for females to select among possible mates. (Bronson, 1989; Grzimek, 1990; Grzimek, 2003; Huffman, 2007; Nowak, 1999; Putnam, 1988)
Artiodactyls usually breed only once a year, though some may breed multiple times. They tend to be polyestrous and gestation ranges from 4 to 15.5 months. Aside from Suidae, which can have as many as 12 young in a litter, artiodactyls give birth to one, sometimes two, young per year that can weigh between 0.5 and 80 kg and become sexually mature between 6 and 60 months. Timing of parturition usually coincides with seasonal plant growth. As a result, most species in temperate and arctic regions give birth during early spring, whereas tropical species give birth at the start of the rainy season. Timing of parturition is especially important for the mother, who requires an abundance of high-quality vegetation to offset the physiological costs incurred by lactation. In addition, abundant high-quality vegetation helps young grow more rapidly, which reduces risk of predation. (Bronson, 1989; Grzimek, 1990; Grzimek, 2003; Nowak, 1999)
All artiodactyls give birth to precocial young that are capable of walking within a few hours after birth. The young of some species are even capable of running within 2 to 3 hours of birth. Females are the primary caregivers and nurse until young are weaned, 2 to 12 months after birth. Artiodactyls can be placed into two different categories based on maternal care: hiders and followers. "Hider young" tend to have camouflaged coats and remain hidden while their mother leaves to forage during the day. Prior to leaving, hider mothers lead their young in a secluded area in which young will choose a place to hide. Hider mothers periodically return throughout the day to nurse and clean their young. When hider young become more capable of escaping potential predators, they begin to accompany their mother during foraging bouts, which occurs immediately after birth in follower species. Hiders tend to live in smaller groups, in areas that provide adequate shelter for young. Followers tend to be larger species that live in open habitats with little shelter for young. Both are likely forms of antipredator defenses related to the size of the young and the amount of exposure in the local environment. Offspring frequently stay with their mother for months or even years after they are weaned, and in some species of sexually segregating Bovidae and Cervidae, daughters remain with their natal herd, even after reaching sexual maturity. Female red deer, which are matriarchal, may transfer social status and part of their range to their daughters. (Darling, 1937; Grzimek, 1990; Grzimek, 2003; Jarman, 2000; Nowak, 1999)
The lifespan of artiodactyls ranges from 8 to 40 years. Numerous studies have shown that adult male survival is lower and more variable over time than female survival. Sex-biased mortality in artiodactyls is most often attributed to sexual selection and evidence suggests a positive correlation between size-biased mortality rates and the degree of sexual dimorphism, with the larger sex exhibiting higher mortality rates (for exceptions see alpine ibex and mouflon). The correlation between mortality rates and size-dimorphism is thought to be the result of increased polygyny, resulting in increased male-male competition. It has also been hypothesized that the larger sex in sexual-size dimorphic species have higher absolute energy requirements and therefore are more susceptible to starvation. Studies also show that senescence induced mortality begins around age eight for some artiodactyl species, regardless of sex. (Grzimek, 1990; Loison, et al., 1999; Toigo and Gaillard, 2003)
Although some artiodactyls are solitary, most are gregarious. Living in large groups is thought to increase the per-capita forage intake by decreasing the per-capita time spent scanning for predators. As a result, gregarious animals yield benefits through increased predator detection and increased forage intake. However, as groups size increases, the degree of intraspecific competition increases as well. Herds are often sexually segregated, which may help reduce intersexual resource competition for food. In size-dimorphic species, evidence suggests that gender differences in the length of the gastrointestinal tract may result in different dietary requirements, further reducing dietary overlap of males and females. (Caro, 2005; Darling, 1937; Du Toit, 2005; Grzimek, 1990; Grzimek, 2003; Huffman, 2007; Nowak, 1999; Putnam, 1988)
Artiodactyls have many different ways of dealing with encounters of conspecifics and predators. To avoid fighting, some species use displays, which may include posturing and vocalizing. Posturing often incorporates physical attributes, such as coloration of fur, horns, antlers, or tusks. Some artiodactyls make themselves appear larger to their opponent by exhibiting a broadside display or through piloerection (i.e., raising the hairs on their neck or back). Though most displays are used to avoid physical confrontation, some artiodactyls use threat displays, which communicate the desire to fight. For example, suids grit their teeth to express a desire for combat. When physical confrontation is unavoidable, horns, antlers, and tusks are important tools of defense for artiodactyls. Commonly, artiodactyls use these weapons when competing with conspecifics for mates or territory rather than defending themselves or their young from predators. (Caro, 2005; Grzimek, 1990; Grzimek, 2003; Huffman, 2007; Jarman, 2000; Nowak, 1999)
Similar to other endothermic animals, many artiodactyl species migrate according to proximal cues, such as photoperiod. These proximal cues serve as indicators for various ultimate factors, such as changes in season, which can affect the abundance of pests, predators, and forage. Although the costs of migration can be great, benefits often include increased individual survival rates and increased reproductive fitness. Two of the best-studied cases of artiodactyl migration include barren-ground caribou and Serengeti wildebeest, which travel annual distances of more than 500 and 1700 km, respectively. Unfortunately, seasonal migrations of many artiodactyl species are cued by photoperiod while plant-growing seasons are cued by temperature. If the growing season of species-specific resources is not precisely matched to the initiation of migration, changes in plant phenologies may detrimentally impact the long-term survival of migratory animals. For example, increasing mean spring temperatures in West Greenland appear to have resulted in a mismatch between caribou migratory cues and the onset of spring growing season for important forage plants. Evidence suggests that caribou migrations are not advancing at a comparable rate with forage plants and as a result, calf production in West Greenland caribou has decreased by a factor of four. (Darling, 1937; Feldhamer, et al., 2004; Grzimek, 1990; Grzimek, 2003; Nowak, 1999; Post and Forchhammer, 2008; Scott, 1988; Vaughn, et al., 2000)
Many artiodactyl species use glandular secretions to communicate with conspecifics. Pheromones are produced my epithelial glands, which are most often located on either side of the body and some artiodactyls use pedal glands to mark trails or bedding areas. In general, artiodactyls use pheromones to communicate danger, their own physical state, to establish their presence, or to attract potential mates. For example, some members of Cervidae rake their antlers on understory vegetation to make their presence known to conspecifics. Many artiodactyls use urine or feces to mark territory, contribute to mating rituals, and may incorporate excretory actions into physical displays. For example, camels excrete feces and urine when in the presence of conspecific rivals, and some species of cervid spray urine to attract mates. (Grzimek, 1990; Grzimek, 2003; Huffman, 2007; Morris and Beer, 2003; Nowak, 1999; Theodor and Smith, 2009)
Many artiodactyls attract mates, defend territory, establish and defend hierarchical position, and send messages to conspecifics by creating a variety of sounds or vocalizations. For example, male okapis create a quiet moan to attract females, whereas hippopotami make roaring sounds in response to conspecific challengers. During mating season, American bison make guttural vocalizations (i.e., bellows) that indicate mate quality and physical condition to females. Communication among conspecifics is especially important in gregarious species. (Grzimek, 1990; Grzimek, 2003; Huffman, 2007; Morris and Beer, 2003; Nowak, 1999; Wyman, et al., 2008)
Highly developed senses of smell, hearing, and vision help artiodactyls detect disturbances in their environment. Often, when an individual becomes aware of a disturbance they send an immediate message to conspecifics by using physical displays. Physical displays are especially important in gregarious artiodactyls, warning herd members of the presence of a threat, thereby reducing surprise attacks. For example, Grant's gazelles piloerect the hairs on their hind legs to alert fellow herd members of potential threats, and white-tailed deer lift and wave their tail from side to side to warn others of potential threats. (Grzimek, 1990; Grzimek, 2003; Huffman, 2007; Morris and Beer, 2003; Nowak, 1999)
With the exception of the suborder Suinae, artiodactyls are obligate herbivores. Typical forage includes grass, leaves, fruits, flowers, twigs, aquatic vegetation, roots, and nuts. In Suidae and Tayassuidae, diets may also include insect larvae, grubs, and eggs. Although obligate herbivores, some species of artiodactyls are opportunistic feeders (e.g., deer and giraffes), occasionally feeding on carrion. Artiodactyls with low quality diets (i.e., high fiber and low protein) are forced to compensate by ingesting large amounts of forage, chewing their cud (i.e., ruminating), and devoting a majority of their time to feeding. In addition, because mammals do not possess the enzymes needed to digest cellulose and lignin, most artiodactyls depend upon bacterial fermentation to break down these compounds. (Colby, 1966; Dagg and Foster, 1976; Donkin, 1985; Grzimek, 1990; Mochi and Carter, 1974; Prins, 1996; Whitaker and Hamilton, 1998)
In addition to the true stomach, or abomasum, all artiodactyls have at least one additional chamber, or false stomach, in which bacterial fermentation takes place. In the suborder Ruminantia, the digestion of poor-quality food occurs via four different pathways. First, gastric fermentation extracts lipids, proteins, and carbohydrates, which are then absorbed and distributed throughout the body via the intestines. Second, large undigested food particles form into a bolus, or ball of cud, which is regurgitated and re-chewed to help break down the cell wall of ingested plant material. Third, cellulose digestion via bacterial fermentation results in high nitrogen microbes that are occasionally flushed into the intestine and are subsequently digested by their host. These high-nitrogen microbes serve as an important protein source for many artiodactyls, especially ruminants. Finally, ruminants can store large amounts of forage in their stomachs for later digestion. All ruminants chew their cud, have three or four-chambered stomachs, and support microorganisms that breakdown cellulose. (Gentry, 1994; Grzimek, 1990; Prins, 1996; Van Soest, 1994; Whitaker and Hamilton, 1998)
Within the order Artiodactyla, only the suborder Suiformes is considered omnivorous. However, many species diverge from this broad classification and are considered specialized herbivores. For example, babirusas (Babyrousa babyrussa), giant forest hogs (Hylochoerus meinertzhageni), and warthogs (Phacochoerus aethiopicus) are all considered specialized herbivores. In general, suids have large heads and snouts that are used to root for food. Suidae is the most omnivorous of the three extant Suiformes families, and when given the opportunity, kill and eat small animals including rodents, snakes, and bird eggs and nestlings. Although the family Tayassuidae (i.e., javelinas and peccaries) is considered omnivorous, evidence suggests that javelinas and peccaries rely more heavily on plants than suids. Similar to suids, most tayassuids have large heads and mobile snouts that are used while rooting for food. The two species that comprise the family Hippopotamidae, Hippopotamous amphibius and Hexaprotodon liberiensis, are more specialized herbivores than either sister family. Hippopotamous amphibius individuals forage primarily on grass, while H. liberiensis also consumes leaves and fruit. Suidae and Tayassuidae have one false stomach and Hippopotamidae has two. (Feldhamer, et al., 2004; Grzimek, 2003; Vaughn, et al., 2000)
Species in the suborder Tylopoda are extensively specialized for dry arid habitats. As such, they can easily digest plants with high salt content (i.e., halophytes) that other artiodactyls find intolerable. Camelids are ruminating grazers and can survive in habitats with sparse vegetation. They have two false stomachs and a short, simple cecum. (Feldhamer, et al., 2004; Grzimek, 2003; Vaughn, et al., 2000)
Humans hunt artiodactyls for their meat and skins, and as trophies. In the wild, felids and canids are the main predators of artiodactyls. With the exception of humans, felids, and canids, large artiodactyls have few predators. However, juveniles are highly vulnerable and are often targeted by smaller predators. Due to an inability to escape enclosures, livestock are vulnerable to predation and are often targeted by predators during periods of scarcity. (Dagg and Foster, 1976; Grzimek, 1990; Grzimek, 2003; Whitaker and Hamilton, 1998)
Many artiodactyls have some form of ornamentation, and although ornamentation is used primarily during conspecific interactions, horns, antlers, and tusks are also used during predator defense. They also use their powerful legs and sharp hooves to defend against predators. Frequently, artiodactyls use their speed to outrun predators and their sharp senses of smell, sight, and hearing detect potential threats. They often live in groups for protection and make themselves appear larger through piloerection or laterally positioning relative to predators. During a predation event, gregarious artiodactyls may stand in defensive formations that help decrease individual and group vulnerability. For example, musk oxen stand adjacent to one another in head to tail formation or in a circular formation when approached by a predator. Predators most often target old, juvenile, or sick individuals. In conjunction with feeding behavior, predation pressure has lead to important morphological adaptations resulting in cursorial, unguligrade locomotion. (Gentry, 1994; Grzimek, 1990; Gentry, 1994; Grzimek, 1990; Caro, 2005; Dagg and Foster, 1976; Gentry, 1994; Grzimek, 1990; Grzimek, 2003; "UCMP webserver", 1994)
Artiodactyls play an integral role in the structure and function of the ecosystems in which they reside and many species have been shown to alter the density and composition of local plant communities. For example, on Isle Royale National Park, moose (Alces alces) have been shown to alter the density and composition of foraged aquatic plant communities and as a result, fecal nitrogen transferred from aquatic to terrestrial habitats via the ingestion of aquatic macrophytes increases terrestrial nitrogen availability in summer core areas. Foraging by artiodactyls has been shown to have a significant impact on plant succession and plant diversity is greater in areas subjected to foraging. As a result, foraging by artiodactyls might lead to shifts from one plant community type to another (e.g., hardwoods to conifers). In addition, moderate levels of foraging by artiodactyls may increase habitat suitability for conspecifics. For example, litter from browsed plants decomposes more quickly those not subject to browsing, thus increasing nutrient availability to the surrounding plant community. Moreover, nutrient inputs from urine and feces have been shown to contribute to longer stem growth and larger leaves in the surrounding plant community, which are preferred during foraging bouts. Finally, research has shown that the decomposition of large artiodactyl carcasses can result in elevated soil macronutrients and leaf nitrogen for a minimum of two years. (Bowyer, 1997; Bump, et al., 2009; Flanagan and Van Cleve, 1983; Molvar, et al., 1993; Pastor, et al., 1993; Peek, 2007; Risenhoover and Maass, 1987)
Artiodactyls are host to a diverse array of endo and ectoparasites. Many species of parasitic flatworms (Cestoda and Trematoda) and roundworms (Nematoda) spend at least part of their lifecycle in the tissues of artiodactyl hosts. Artiodactyls are also vulnerable to various forms of parasitic arthropods including ticks (Ixodoidea), lice (Phthiraptera), mites (Psoroptes and Sarcoptes), keds (Hippoboscidae), fleas (Siphonaptera), mosquitoes (Culicidae), and flies (Diptera). Artiodactyls also host various forms parasitic protozoa, including trypanosomatids, coccidians, piroplasmids, and numerous species of Giardia. In addition, various forms of bacterial and viral pathogens play an important role in artiodactyl health and population dynamics. For example, Brucella abortus, the bacteria that causes brucellosis, affects many artiodactyls and rhinderpest, also known as cattle plague, is a highly contagious viral disease caused by paramyxovirus (Morbillivirus) that is especially prevalent in ruminants. Unfortunately, evidence suggests that recent climate change is altering host-parasite dynamics across the globe, increasing transmission rates between populations of conspecifics and hybridization rates between host specific parasite forms. (Dagg and Foster, 1976; Escalante and Ayala, 1995; Kutz, et al., 2005; Whitaker and Hamilton, 1998)
Although artiodactyls can serve as host to numerous species of pathogenic bacteria and protozoa, in conjunction with anaerobic fungi, these organisms are one of the major reasons that artiodactyls are as abundant and diverse as they are today. Bacteria comprise between 60 and 90% of the microbial community present in the ruminant's gastrointestinal (GI) tract and help break down cellulose. Ciliated protozoa, which makes up 10 to 40% of the microbe community within the rumen, help bacteria break down cellulose, while also feeding on starches, proteins and bacteria. The presence of anaerobic fungi in the rumen has only been known since the early 1970's. These fungi make up between 5 to 10% of the rumen's microbial abundance and are thought to help break down the cell wall of ingested plant material. Bacteria and protozoa that pass from the upper to the lower regions of the GI tract represent a significant portion of the dietary nitrogen required by their host. (Van Soest, 1994)
Humans and their ancestors have subsisted by hunting and gathering for the majority of their evolutionary history. Artiodactyls likely served as an important food source during a significant majority of this time and continue to be important parts of the human diet. Between 72,000 and 42,000 years ago, humans began wearing clothes, which probably included the skins of many artiodactyl species. In the near east, around 10,000 years ago, goats and sheep were domesticated for subsistence purposes, followed by the domestication of cows (7,500 years ago), pigs (7,500 years ago), llamas and alpacas (6,500 years ago), and camels (3,500 years ago). The domestication of artiodactyls for subsistence purposes lead to one of the most important cultural changes in human history, the transition from a purely hunter-gatherer society to a pastoral and agricultural societies. (Colby, 1966; Dagg and Foster, 1976; Donkin, 1985; Bates, 2005; Colby, 1966; Dagg and Foster, 1976; Donkin, 1985; Feldhamer, et al., 2004; Gentry, 1994; Grzimek, 1990)
Economically, cattle are the most important domesticated animal world wide. In 2001, the global population of domestic artiodactyls was greater than 4.1 billion, more than 31% of which consisted of cattle. In the United States, one of the worlds top 4 beef producers, beef production is the country's fourth largest industry. In addition to meat production, artiodactyls are used for their milk, fur, skin, bone, and feces and sport hunting generates millions of dollars in North America and Europe annually. However, trophy hunting can alter the evolutionary dynamics of wild populations by imposing unnatural selective pressures for decreased ornamentation. Finally, artiodactyls play an important role in the global ecotourism movement as various species of ungulates are readily observable throughout much of their native habitat. (Colby, 1966; Dagg and Foster, 1976; Donkin, 1985; Grzimek, 1990; Grzimek, 2003)
Various forms of zoonotic pathogens use artiodactyls during critical portions of their life or viral cycle. For example, pigs can harbor several influenza virus strains simultaneously, which can hybridize and result in new and virulent strains of influenza (e.g., H1N1). In addition, artiodactyls can transmit zoonotic diseases (e.g. Mad Cow disease) to humans through meat, milk, or direct physical contact. Artiodactyls also present a potential threat to various forms of agriculture by damaging and consuming crops, serving as a potential vector of zoonotic diseases for domestic artiodactyl populations (e.g., brucellosis), and competing with livestock for resources. (Colby, 1966; Dagg and Foster, 1976; Donkin, 1985; Pulliam and Dushoff, 2009)
Extinction threatens nearly half of all artiodactyls and risk of extinction increases in areas with decreased economic development. Humans have hunted many species without regulation to near extinction. One of the greatest threats to artiodactyls is habitat loss. For example, the native swamp habitat of Pere David's deer was largely destroyed 3500 years ago due to the draining and cultivation. Fortunately, large herds of Pere David's deer live in numerous parks and reserves throughout their native range. In some cases, conservation efforts to increase local population growth have been so effective that population control has become necessary (e.g., Giraffa camelopardalis). In addition to habitat loss, climate change has begun to contract species ranges and forced many species move poleward. For example, moose (Alces alces), which are an important ecological component of the boreal ecosystem, are notoriously heat intolerant and are at the southern edge of their circumpolar distribution in the north central United States. Since the mid to late 1980's, demographic studies of this species have revealed sharp population declines at its southernmost distribution in response to increasing temperatures. (Colby, 1966; Dagg and Foster, 1976; Feldhamer, et al., 2004; Lenarz, et al., 2009; Murray, et al., 2006; Price and Gittleman, 2007)
The IUCN Red List of Threatened Species lists 168 artiodactyl species. Seven are listed as "extinct" and two are listed as "extinct in the wild". Twenty-six species are listed as “endangered,” one is “near threatened,” and data is lacking for thirteen other species. The remaining 73 species are listed as “lower risk”. Within the United States, the U.S. Fish and Wildlife Service has listed wood bison (Bison bison athabascae), woodland caribou (Rangifer tarandus caribou), Columbian white-tailed deer (Odocoileus virginianus leucurus), key deer (Odocoileus virginianus clavium), Sonoran pronghorn (Antilocapra americana sonoriensis), Peninsular bighorn sheep (Ovis canadensis nelsoni), and Sierra Nevada bighorn sheep (Ovis canadensis sierrae) as endangered throughout at least part of their native U.S. range. (Grzimek, 1990; Grzimek, 2003; IUCN, 2010; U. S. Fish and Wildlife Service, 2011)
Artiodactyls are an important food source for a number of different carnivores. As artiodactyl populations decline, so too will those animals that depend on them. For example, the decline of cheetahs is often attributed habitat loss. However, cheetahs primarily prey upon small to medium sized ungulates, specifically gazelles. According to the IUCN Red List of Threatened Species, 2 species of gazelle are extinct, while 10 more are listed as vulnerable, endangered or critically endangered. In north Africa, as preferred prey species have declined, more and more cheetahs are turning to livestock for prey. Consequently, these cheetahs are then killed as pests. As a result, one of the major directives for cheetah conservation is restoration of wild prey species, most of which are small to medium-sized artiodactyls. (IUCN, 2010; Ray, et al., 2005)
Erika Etnyre (author), University of Michigan-Ann Arbor, Jenna Lande (author), University of Michigan-Ann Arbor, Alison Mckenna (author), University of Michigan-Ann Arbor, John Berini (author, editor), Animal Diversity Web Staff, Phil Myers (editor), University of Michigan-Ann Arbor.
Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
living in the southern part of the New World. In other words, Central and South America.
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
uses sound to communicate
living in landscapes dominated by human agriculture.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
helps break down and decompose dead plants and/or animals
a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.
either directly causes, or indirectly transmits, a disease to a domestic animal
Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.
uses smells or other chemicals to communicate
used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.
having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
parental care is carried out by females
an animal that mainly eats leaves.
A substance that provides both nutrients and energy to a living thing.
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
an animal that mainly eats fruit
an animal that mainly eats seeds
An animal that eats mainly plants or parts of plants.
referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
a species whose presence or absence strongly affects populations of other species in that area such that the extirpation of the keystone species in an area will result in the ultimate extirpation of many more species in that area (Example: sea otter).
marshes are wetland areas often dominated by grasses and reeds.
makes seasonal movements between breeding and wintering grounds
Having one mate at a time.
having the capacity to move from one place to another.
This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
generally wanders from place to place, usually within a well-defined range.
islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.
an animal that mainly eats all kinds of things, including plants and animals
found in the oriental region of the world. In other words, India and southeast Asia.
an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death
the business of buying and selling animals for people to keep in their homes as pets.
chemicals released into air or water that are detected by and responded to by other animals of the same species
the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.
having more than one female as a mate at one time
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them
scrub forests develop in areas that experience dry seasons.
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
one of the sexes (usually males) has special physical structures used in courting the other sex or fighting the same sex. For example: antlers, elongated tails, special spurs.
associates with others of its species; forms social groups.
digs and breaks up soil so air and water can get in
places a food item in a special place to be eaten later. Also called "hoarding"
living in residential areas on the outskirts of large cities or towns.
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
uses touch to communicate
Coniferous or boreal forest, located in a band across northern North America, Europe, and Asia. This terrestrial biome also occurs at high elevations. Long, cold winters and short, wet summers. Few species of trees are present; these are primarily conifers that grow in dense stands with little undergrowth. Some deciduous trees also may be present.
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
Living on the ground.
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.
A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.
A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.
A terrestrial biome with low, shrubby or mat-like vegetation found at extremely high latitudes or elevations, near the limit of plant growth. Soils usually subject to permafrost. Plant diversity is typically low and the growing season is short.
living in cities and large towns, landscapes dominated by human structures and activity.
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
young are relatively well-developed when born
the Regents of the University of California. 1994. "UCMP webserver" (On-line). Accessed February 09, 2009 at http://www.ucmp.berkeley.edu/mammal/artio/artiolh.html.
Bates, D. 2005. Human Adaptive Strategies: Ecology, Culture, and Politics (Third Edition). Boston, MA: Pearson, Allyn, and Bacon.
Bowyer, R. 1997. The role of moose in landscape processes: Effects of biogeography, population dynamics and predation. Pp. 265-287 in J Bissonette, ed. Wildlife and landscape ecology: effects of pattern and scale. New York, NY: Springer-Verlag.
Bronson, F. 1989. Mammalian Reproductive Biology. Chicago: The University of Chicago Press.
Bump, J., R. Peterson, J. Vucetich. 2009. Wolves modulate soil nutrient heterogeneity and foliar nitrogen by configuring the distribution of ungulate carcasses. Ecology, 90: 3159-3167.
Caro, T. 2005. Antipredator Defenses in Birds and Mammals. Chicago, IL: University of Chicago Press.
Colby, C. 1966. Wild Deer. New York: Duell, Sloan, and Pearce.
Dagg, A., J. Foster. 1976. The Giraffe: Its Biology, Behavior, and Ecology. New York: Van Nostrand Reinhold Co..
Darling, F. 1937. A Herd of Red Deer: A Study in Animal Behavior. London: Oxford University Press.
Donkin, R. 1985. The Peccary- With Observations on the Introductions of Pigs to the New World. Independence Square, Philadelphia: American Philosophical Society.
Du Toit, J. 2005. Sex differences in the foraging ecology of large mammalian herbivores. Pp. 35-52 in K Ruckstuhl, P Neuhaus, eds. Sexual Segregation in Vertebrates: Ecology of the Two Sexes. Cambridge: Cambridge University Press.
Eisenberg, J. 1983. The Mammalian Radiations: An Analysis of Trends in Evolution, Adaptation, and Behavior. Chicago, IL: The University of Chicago Press.
Escalante, A., F. Ayala. 1995. Evolutionary origin of Plasmodium and other Apicomplexa based on rRNA. Proceedings from the National Academy of Science, 92: 5793-5797.
Feldhamer, G., L. Drickamer, S. Vessey, J. Merritt. 2004. Mammalogy: Adaptation, Diversity, Ecology. New York: McGraw Hill.
Flanagan, P., K. Van Cleve. 1983. Nutrient cycling in relation to decomposition and organic-matter quality in taiga ecosystems. Canadian Journal of Forest Research, 13: 795- 817.
Gentry, A. 1994. "Artiodactyla" (On-line). Encyclopedia Britannica Online. Accessed March 09, 2009 at http://www.britannica.com/EBchecked/topic/37203/artiodactyl/51680/Areas-of-distribution.
Grzimek, B. 2003. Artiodactyla (Even-toed ungulates). Pp. 263-417 in M Hutchins, D Kleiman, V Geist, M McDade, eds. Grzimek's Animal Life Encyclopedia, Vol. 15, Mammals IV, 2nd Edition. Farmington Hills, Michigan, USA: Gale Group.
Grzimek, B. 1990. Artiodactyla. Pp. 1-639 in S Parker, ed. Grzimek’s Encyclopedia of Mammals, Vol. 5, 1st Edition. New York: McGraw-Hill.
Huffman, B. 2007. "Ungulates of the World" (On-line). The Ultimate Ungulate Page. Accessed February 17, 2009 at http://www.ultimateungulate.com/ungulates.html.
IUCN, 2010. "Mammals" (On-line). IUCN Red List of Threatened Species. Accessed March 23, 2011 at http://www.iucnredlist.org/initiatives/mammals.
Jarman, P. 2000. Antelopes, Deer, and Relatives. New Haven: Yale University Press.
Kurpius, J., R. Guralnick, J. Johnson, A. Monk, J. Scotchmoor, M. Stefanski. 2008. "Understanding Geologic Time" (On-line). University of California Museum of Paleontology. Accessed March 22, 2011 at http://www.ucmp.berkeley.edu/education/explorations/tours/geotime/guide/geologictimescale.html.
Kutz, S., E. Hoberg, L. Polley, E. Jenkins. 2005. Global warming is changing the dynamics of Arctic host–parasite systems. Proceedings from the Royal Society B, 272/1581: 2571-2576.
Lenarz, M., M. Nelson, M. Schrage, A. Edwards. 2009. Temperature mediated moose survival in northeastern Minnesota. Journal of Wildlife Management, 73: 503-510.
Loison, A., M. Festa-Bianchet, J. Gaillard, J. Jorgenson, J. Jullien. 1999. Age-specific survival in five populations of ungulates: evidence of senescence. Ecology, 80/8: 2539-2554.
Mochi, U., T. Carter. 1974. Hoofed Mammals of the World. NY: Lutterworth Press.
Molvar, E., R. Bowyer, V. Van Ballenberghe. 1993. Moose herbivory, browse quality and nutrient cycling in an Alaskan tree line community. Oecologia, 94: 472-479.
Morris, P., A. Beer. 2003. World of Mammals: Mammals 6: Ruminant (Horned) Herbivores. Danbury, CT: Grolier.
Murray, D., E. Cox, W. Ballard, H. Whitlaw, M. Lenarz, T. Custer, T. Barnett, T. Fuller. 2006. Pathogens, nutritional deficiency, and climate influences on a declining moose population. Wildlife Monographs, 166: 1-30.
Nowak, R. 1999. Walker’s Mammals of the World. Baltimore and London: The Johns Hopkins University Press.
Pastor, J., B. Dewey, R. Naiman, P. McInnis, Y. Cohen. 1993. Moose browsing and soil fertility in the boreal forests of Isle Royale National Park. Ecology, 74: 467-480.
Peek, J. 2007. Habitat Relationships. Pp. 351-376 in A Franzmann, C Schwartz, eds. Ecology and Management of North American Moose, Second Edition. Boulder, CO: University Press of Colorado.
Post, E., M. Forchhammer. 2008. Climate change reduces reproductive success of an Arctic herbivore through trophic mismatch. Philosophical Transactions of the Royal Society B, 363: 2367-2373.
Price, S., J. Gittleman. 2007. "Hunting to extinction: biology and regional economy influence extinction risk and the impact of hunting in artiodactyls" (On-line). Accessed February 07, 2009 at http://journals.royalsociety.org/content/835104w3v3727236/fulltext.pdf.
Prins, H. 1996. Ecology and Behaviour of the African Buffalo. Great Britain: Chapman and Hall.
Pulliam, J., J. Dushoff. 2009. "Ability to Replicate in the Cytoplasm Predicts Zoonotic Transmission of Livestock Viruses" (On-line). Chicago Journals. Accessed March 11, 2009 at http://www.journals.uchicago.edu/doi/full/10.1086/596510?cookieSet=1.
Putnam, R. 1988. Natural History of Deer. Ithaca, New York: Comstock Publishing Associates.
Ray, J., K. Redford, R. Steneck, J. Berger. 2005. Large Carnivores and the Conservation of Biodiversity. Washington D. C.: Island Press.
Risenhoover, K., S. Maass. 1987. The influence of moose on the composition and structure of Isle Royale forests. Canadian Journal of Forest Resources, 17: 357-364.
Rose, K., D. Archibald. 2005. The Rise of Placental Mammals. Baltimore, Maryland: The John Hopkins University Press.
Savage, R., M. Long. 1986. Mammal Evolution, an Illustrated Guide. New York: Facts of File Publications.
Scott, J. 1988. The Great Migration. London: Elm Tree Books.
Simpson, C. 1984. Artiodactyls. Pp. 686 in S Anderson, J Jones, Jr., eds. Orders and Families of Recent Mammals of the World. New York: John Wiley and Sons.
Theodor, J., D. Smith. 2009. "Introduction to the Artiodactyla" (On-line). The University of California Museum of Paleontology. Accessed February 17, 2009 at http://www.ucmp.berkeley.edu/mammal/artio/artiodactyla.html.
Toigo, C., J. Gaillard. 2003. Causes of sex-biased adult survival in ungulates: sexual size dimorphism, mating tactic or environment harshness. Oikos, 101: 376-384.
U. S. Fish and Wildlife Service, 2011. "Mammalian species report" (On-line). U.S. Fish and Wildlife Service, Endangered Species Program. Accessed March 23, 2011 at http://www.fws.gov/endangered/species/us-species.html.
University of California Museum of Paleontology (UCMP), 2011. "Geologic Time Scale" (On-line). Accessed March 20, 2011 at http://www.ucmp.berkeley.edu/education/explorations/tours/geotime/guide/geologictimescale.html.
Van Soest, P. 1994. Nutritional Ecology of the Ruminant, Second Edition. Ithaca, NY: Cornell University Press.
Vaughn, T., J. Ryan, N. Czaplewski. 2000. Mammalogy, Fourth Edition. Fort Worth: Brooks/Cole.
Whitaker, J., W. Hamilton. 1998. Mammals of the Eastern United States. Ithaca, New York: Cornell University Press. Accessed February 09, 2009 at http://books.google.com/books?id=5fVymWAez-YC&printsec=copyright&dq=artiodactyla+diet.
Wilson, D., D. Reeder. 1993.
Mammal Species of the World, A Taxonomic and Geographic Reference. 2nd edition. Washington D. C.: Smithsonian Institution Press.
Wyman, M., M. Mooring, B. McCowan, M. Penodos, L. Hart. 2008. Amplitude of bison bellows reflects male quality, physical condition and motivation. Animal Behaviour, 76: 1625-1639.