Cetartiodactyla is a group comprised of two orders of mammals that are superficially quite different and that, until recently, were recognized as two separate monophyletic clades. These orders are Artiodactyla, even-toed ungulates, including animals such as cows (Bovidae), camels (Camelidae), and deer (Cervidae), and Cetacea, a group of mammals that are highly specialized for an aquatic lifestyle, including baleen whales and toothed whales. Recent molecular evidence suggests that Cetacea evolved from artiodactyl ancestors, making Artiodactyla non-monophyletic unless Cetacea is included. Experts suggest the monophyletic clade representing artiodactyls and cetaceans be called Cetartiodactyla.
Cetartiodactyls are found the world over, from north of the Arctic Circle to the waters surrounding Antarctica. Artiodactyls are native to all continents except Antarctica and Australia, and some artiodactyls are domesticated and have been introduced around the world by humans. Cetaceans inhabit all of the world's oceans and some freshwater lakes and rivers in South America, North America, and Asia.
Biogeographic Regions: nearctic (Introduced , Native ); palearctic (Introduced , Native ); oriental (Introduced , Native ); ethiopian (Introduced , Native ); neotropical (Introduced , Native ); australian (Introduced ); arctic ocean (Native ); indian ocean (Native ); atlantic ocean (Native ); pacific ocean (Native ); mediterranean sea (Native )
Other Geographic Terms: holarctic ; cosmopolitan
Because cetaceans are so highly specialized for their aquatic lifestyle, they bear little resemblance to their artiodactyl ancestors. They have nearly hairless, fusiform bodies. They lack hind limbs except for tiny internal pelvic vestiges, and the forelimbs are modified into streamlined flippers. The tail bears a flattened fluke. In addition, cetacean skulls are highly modified so that the nares are located on the top of the head. On the other hand, most artiodactyls are specialized for cursorial locomotion, with long, hoofed limbs, and they lack the extreme aquatic specializations found in cetaceans. Most cetartiodactyls are relatively large animals, but there is an enormous range of body sizes in this group. Blue whales, Balaenoptera musculus, are the largest animals on earth, growing over 27 meters in length and weighing over 190,000 kg, whereas the smallest artiodactyl, the lesser mouse deer (Tragulus javanicus), is just 45 cm long and weighs 2 kg. Many species of cetartiodactyls exhibit sexual dimorphism, with males larger than females or vice versa. Also, male artiodactyls often bear antlers or large horns, and some male cetartiodactyls (narwhals (Monodon monoceros), tragulids, and suids) bear large tusks.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: sexes alike; female larger; male larger; ornamentation
Most artiodactyls live entirely on land and reside in a range of terrestrial habitats, such as savannah, forest, mountains, desert, and farmland. One artiodactyl family, Hippopotamidae, is semi-aquatic and can be found in freshwater lakes, ponds, streams, and rivers. Cetaceans, on the other hand, are exclusively aquatic and inhabit the world's oceans, as well as some freshwater rivers and streams.
Habitat Regions: temperate ; tropical ; polar ; terrestrial ; saltwater or marine ; freshwater
Terrestrial Biomes: tundra ; taiga ; desert or dune ; savanna or grassland ; chaparral ; forest ; rainforest ; scrub forest ; mountains
Aquatic Biomes: pelagic ; lakes and ponds; rivers and streams; coastal
Other Habitat Features: agricultural ; riparian ; estuarine
As a group, cetartiodactyls consume a wide array of terrestrial and aquatic food items. Most artiodactyls are herbivores, consuming grass, leaves, bark, and other plant parts. Those in the family Suidae are omnivorous, and eat small mammals, reptiles, amphibians, insects and other invertebrates, fruit, bulbs, rhizomes, fungi, carrion, and bird eggs. Cetaceans consume plankton, fish, squid, crustaceans, and aquatic birds and mammals (including other cetaceans).
Foraging Behavior: filter-feeding
Primary Diet: carnivore (Eats terrestrial vertebrates, Piscivore , Eats eggs, Insectivore , Eats non-insect arthropods, Molluscivore , Scavenger ); herbivore (Folivore , Frugivore , Lignivore); omnivore ; planktivore ; mycophage
Cetartiodactyls are primary, secondary, and higher-level consumers, filling roles of predator (most cetaceans) and prey (most artiodactyls). Terrestrial cetartiodactyls are plagued by ectoparasites such as fleas, lice, and bot flies. Cetaceans, though aquatic, are not free from external parasites either, and are host to barnacles, copepods, and whale lice. Both terrestrial and aquatic species host internal parasites as well, such as tapeworms, flukes, and nematodes. Interestingly, birds have evolved commensal relationships with both aquatic and terrestrial cetartiodactyls. Seagulls follow schools of dolphins and consume small fish stirred up by the cetaceans, and cowbirds follow herds of cattle and consume insects stirred up by the hooves of the artiodactyls. Also, some cetartiodactyl species are mutualists with animals that feed on their ectoparasites: topsmelt (Atherinops affinis) consume whale lice that live on the skin of gray whales (Eschrichtius robustus), while oxpeckers (Buphagus) remove fleas and other parasites from the skin of various African artiodactyls.
- topsmelt Atherinops affinis
- oxpeckers Buphagus
- fleas Siphonaptera
- lice Anoplura
- bot flies Oestridae
- barnacles Cirripedia
- copepods Copepoda
- whale lice Cyamidae
- tapeworms Cestoda
- flukes Trematoda
- nematodes Nematoda
- birds Aves
Artiodactyls are an important food source for many large mammalian carnivores, notably felids, canids, and ursids. Cetaceans, on the other hand, have few natural predators, save other cetaceans (killer whales, Orcinus orca), sharks, and occasionally walruses (Odobenus rosmarus). Group living ("safety in numbers") and camouflage are two defenses often employed by cetartiodactyls against predation.
- large mammalian carnivores (Carnivora)
- sharks (Chondrichthyes)
- walruses (Odobenus rosmarus)
Anti-predator Adaptations: cryptic
Life History and Behavior
Cetartiodactyls perceive the world through visual, tactile, auditory, and chemical means. Some cetaceans, the Odontoceti, navigate and hunt using echolocation. Terrestrial cetartiodactyls often communicate with scent; many species, such as those in the family Cervidae, have specialized glands for doing so. Communication in cetaceans is accomplished largely by sound, as sound waves travel well in water. Low frequency sounds produced by baleen whales (Mysticeti) may travel for hundreds of kilometers, allowing individuals to communicate with one another over great distances.
Communication Channels: visual ; tactile ; acoustic ; chemical
Other Communication Modes: scent marks
Perception Channels: visual ; tactile ; acoustic ; echolocation ; chemical
Cetartiodactyls are relatively long-lived mammals. Most species live for at least a decade in the wild, and captivity usually prolongs life expectancy by several years. Cetaceans are especially long-lived; 116-year-old fin whales (Balaenoptera physalus) have been reported from the wild and bowhead whales (Balaena mysticetus) may live up to 200 years.
Cetartiodactyls are monogamous, polyandrous, polygynandrous, or polygynous. Polygyny, in which social groupings consist of adult females and their young and one or a few adult males, is a common cetartiodactyl strategy. It occurs in species as different as elk (Cervus elaphus) and killer whales (Orcinus orca). Sexual dimorphism in ornamentation (such as antlers) and body size indicates intense male-male competition for mates in many species.
Mating System: monogamous ; polyandrous ; polygynous ; polygynandrous (promiscuous)
In general, cetartiodactyls are not highly prolific, giving birth to just one or two young every one or two years. However, some members of the family Suidae may have 12 or more young at a time. Breeding may be either seasonal or year-round. At least one species, the minke whale (Balaenoptera acutorostrata) regularly experiences a postpartum estrus. Gestation periods are as short as four months in small artiodactyls to as long as 17 months in Baird's beaked whales (Berardius bairdii), and youngsters are weaned between 2 1/2 and 24 months of age. Age at sexual maturity varies widely as well, from 5 months to more than 10 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); viviparous ; post-partum estrous
Most cetartiodactyls have precocial young, as it is necessary for them to be able to walk or swim from the moment of birth. Young stay with their mothers for at least four months. In some species, such as bottlenosed dolphins (Tursiops truncatus), young remain with their mothers for up to five years, long after they are weaned. Males may care for their offspring indirectly by defending family groups, but they generally do not help females raise their young.
Parental Investment: precocial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Male, Female); pre-independence (Provisioning: Female, Protecting: Male, Female); post-independence association with parents; extended period of juvenile learning; maternal position in the dominance hierarchy affects status of young
Currently, the IUCN classifies 54 cetartiodactyl species as data deficient, 146 as lower risk, 40 as vulnerable, 32 as endangered, 14 as critically endangered, 7 as extinct, and 2 as extinct in the wild. The biggest threats to many terrestrial species are habitat loss and fragmentation and overhunting. Several large cetacean species were hunted nearly to extinction until an international treaty banned commercial whaling in the 1980s. Populations of many large, commercially-valuable whales remain severely depleted. Today, cetaceans face threats associated with global climate change, which could have widespread impacts on their food supply in the near future.
- IUCN, 2004. "2004 IUCN Red List of Threatened Species" (On-line). Accessed September 14, 2005 at www.redlist.org.
Relevance to Humans and Ecosystems
Artiodactyls, especially domesticated species, sometimes carry diseases that are transmissible to humans or other domestic animals. Wild artiodactyls sometimes interfere with farming operations by eating crops.
Negative Impacts: injures humans (carries human disease); crop pest; causes or carries domestic animal disease
Cetartiodactyls are of immense economic importance to humans. They have been hunted for thousands of years, for food, for sport, and for various body parts. They are important for ecotourism, be it a whale-watching boat off the coast of Maine or a safari on the African savannah. Several artiodactyl species have been domesticated for thousands of years and are used to produce meat, milk, leather and wool, and their dung is used as a fertilizer. Cetaceans are sometimes kept in captivity and taught to perform tricks. Many cetartiodactyls are the focus of research programs that help us to better understand many aspects of evolution, physiology, and behavior.
Positive Impacts: food ; body parts are source of valuable material; ecotourism ; research and education; produces fertilizer
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