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Cetartiodactylacetaceans and artiodactyls

By Allison Poor

Diversity

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. (Boisserie, et al., 2005; Gatesy, et al., 1996; Gatesy, et al., 1999; Gatesy, 1997; Graur and Higgins, 1994; Milinkovitch and Thewissan, 1997; Montgelard, et al., 1997; Naylor and Adams, 2001; O'Leary and Geisler, 1999; Shimamura, et al., 1997; Thewissen, et al., 2001)

Geographic Range

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. (Nowak, 1999; Rice, 1984; Simpson, 1984)

Habitat

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. (Nowak, 1999; Rice, 1984; Simpson, 1984)

Physical Description

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. (Nowak, 1999; Rice, 1984; Simpson, 1984)

  • Sexual Dimorphism
  • sexes alike
  • female larger
  • male larger
  • ornamentation

Reproduction

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. (Nowak, 1999; Rice, 1984; Simpson, 1984)

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. (Nowak, 1999; Rice, 1984; Simpson, 1984)

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. (Nowak, 1999; Rice, 1984; Simpson, 1984)

  • 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

Lifespan/Longevity

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. (Carey and Judge, 2002; George, et al., 1999)

Behavior

Most cetartiodactyls are highly social animals. Some live in large herds or pods numbering hundreds or even thousands of individuals. Group living commonly results in the formation of dominance hierarchies among both male and female cetartiodactyls. A few species, such as greater mouse-deer (Tragulus napu) and river dolphins (Platanista) are solitary. Many cetartiodactyl species migrate seasonally or are nomadic, and some bovid species (Bovidae) are territorial. Different species vary in their timing of daily activities: some are diurnal, some are nocturnal, some are crepuscular, and some are active at any time of the day or night. (Nowak, 1999; Rice, 1984; Simpson, 1984)

Communication and Perception

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. (Nowak, 1999; Rice, 1984; Simpson, 1984)

Food Habits

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). (Nowak, 1999; Rice, 1984; Simpson, 1984)

Predation

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. (Nowak, 1999; Rice, 1984; Simpson, 1984)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

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. (Nowak, 1999; Rice, 1984; Roberts and Janovy, Jr., 2000)

Mutualist Species
Commensal/Parasitic Species

Economic Importance for Humans: Positive

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. (Nowak, 1999)

  • Positive Impacts
  • food
  • body parts are source of valuable material
  • ecotourism
  • research and education
  • produces fertilizer

Economic Importance for Humans: Negative

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. (Nowak, 1999)

Conservation Status

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)

  • IUCN Red List [Link]
    Not Evaluated

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Allison Poor (author), University of Michigan-Ann Arbor.

Glossary

Arctic Ocean

the body of water between Europe, Asia, and North America which occurs mostly north of the Arctic circle.

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

Nearctic

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.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

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.

carnivore

an animal that mainly eats meat

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

chaparral

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.

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cosmopolitan

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.

crepuscular

active at dawn and dusk

cryptic

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.

desert or dunes

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.

diurnal
  1. active during the day, 2. lasting for one day.
dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

echolocation

The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.

ecotourism

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.

endothermic

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.

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

fertilization

union of egg and spermatozoan

filter-feeding

a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.

folivore

an animal that mainly eats leaves.

food

A substance that provides both nutrients and energy to a living thing.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

freshwater

mainly lives in water that is not salty.

frugivore

an animal that mainly eats fruit

herbivore

An animal that eats mainly plants or parts of plants.

holarctic

a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.

World Map

Found in northern North America and northern Europe or Asia.

insectivore

An animal that eats mainly insects or spiders.

internal fertilization

fertilization takes place within the female's body

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

iteroparous

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).

migratory

makes seasonal movements between breeding and wintering grounds

molluscivore

eats mollusks, members of Phylum Mollusca

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

mycophage

an animal that mainly eats fungus

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

nomadic

generally wanders from place to place, usually within a well-defined range.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

pelagic

An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).

piscivore

an animal that mainly eats fish

planktivore

an animal that mainly eats plankton

polar

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.

polyandrous

Referring to a mating system in which a female mates with several males during one breeding season (compare polygynous).

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

polygynous

having more than one female as a mate at one time

rainforest

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.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

scavenger

an animal that mainly eats dead animals

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

sexual ornamentation

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.

social

associates with others of its species; forms social groups.

solitary

lives alone

tactile

uses touch to communicate

taiga

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.

temperate

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).

terrestrial

Living on the ground.

territorial

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

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

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.

savanna

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.

temperate grassland

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.

tundra

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.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year

young precocial

young are relatively well-developed when born

References

Boisserie, J., F. Lihoreau, M. Brunet. 2005. The position of Hippopotamidae within Cetartiodactyla. Proceedings of the National Academy of Sciences, 102: 1537-1541.

Carey, J., D. Judge. 2002. "Longevity Records: Life Spans of Mammals, Birds, Amphibians, Reptiles, and Fish" (On-line). Accessed September 14, 2005 at http://www.demogr.mpg.de/.

Gatesy, J. 1997. More DNA support for a Cetacea/Hippopotamidae clade: The blood-clotting protein gene Y-Fibrinogen. Molecular Biology and Evolution, 14(5): 537-543.

Gatesy, J., C. Hayashi, M. Cronin, P. Arctander. 1996. Evidence from milk casein genes that cetaceans are close relatives of hippopotamid artiodactyls. Molecular Biology and Evolution, 13(7): 954-963.

Gatesy, J., M. Milinkovitch, V. Waddell, M. Stanhope. 1999. Stability of cladistic relationships between Cetacea and higher-level artiodactyl taxa. Systematic Biology, 48(1): 6-20.

George, J., J. Bada, J. Zeh, L. Scott, S. Brown. 1999. ge and Growth Estimates of Bowhead Whales (Balaena mysticetus) Via Aspartic Acid Racemization. Canadian Journal of Zoology, 78: 1182-1198.

Graur, D., D. Higgins. 1994. Molecular evidence for the inclusion of cetaceans within the order Artiodactyla. Molecular Biology and Evolution, 11(3): 357-364.

IUCN, 2004. "2004 IUCN Red List of Threatened Species" (On-line). Accessed September 14, 2005 at www.redlist.org.

Milinkovitch, M., J. Thewissan. 1997. Even-toed fingerprints on whale ancestry. Nature, 388: 622-624.

Montgelard, C., F. Catzeflis, E. Douzery. 1997. Phylogenetic relationships of artiodactyls and cetaceans as deduced from the comparison of cytochrome b and 12S rRNA mitochondrial sequences. Molecular Biology and Evolution, 14(5): 550-559.

Naylor, G., D. Adams. 2001. Are the fossil data really at odds with the molecular data? Morphological evidence for Cetartiodactyla phylogeny reexamined. Systematic Biology, 50(3): 444-453.

Nowak, R. 1999. Walker's Mammals of the World, vol. II. Baltimore and London: The Johns Hopkins University Press.

O'Leary, M., J. Geisler. 1999. The position of Cetacea within Mammalia: Phylogenetic analysis of morphological data from extinct and extant taxa. Systematic Biology, 48(3): 455-490.

Rice, D. 1984. Cetaceans. Pp. 447-490 in S Anderson, J Jones Jr., eds. Orders and Families of Recent Mammals of the World. New York: John Wiley and Sons.

Roberts, L., J. Janovy, Jr.. 2000. Foundations of Parasitology. New York: McGraw-Hill.

Shimamura, M., H. Yasue, K. Ohshima, H. Abe, H. Kato, T. Kishiro, M. Goto, I. Munechika, N. Okada. 1997. Molecular evidence from retroposons that whales form a clade within even-toed ungulates. Nature, 388: 666-670.

Simpson, C. 1984. Artiodactyls. Pp. 563-587 in S Anderson, J Jones Jr., eds. Orders and Families of Recent Mammals of the World. New York: John Wiley and Sons.

Thewissen, J., E. Williams, S. Hussain. 2001. Skeletons of terrestrial cetaceans and the relationship of whales to artiodactyls. Nature, 413: 277-281.

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