Mammalia

mammals

Features
By Matthew Wund and Phil Myers

Diversity

The Class Mammalia includes about 5000 species placed in 26 orders. Systematists do not yet agree on the exact number or on how some orders and families are related to others. The Animal Diversity Web generally follows the arrangement used by Wilson and Reeder (2005). Exciting new information, however, coming from phylogenies based on molecular evidence and from new fossils, is changing our understanding of many groups. For example, skunks have been placed in the new family Mephitidae , separate from their traditional place within the Mustelidae (Dragoo and Honeycutt 1997, Flynn et al., 2005). The Animal Diversity Web follows this revised classification. Whales almost certainly arose from within the Artiodactyla (Matthee et al. 2001; Gingerich et al. 2001). The traditional subdivision of the Chiroptera into megabats and microbats may not accurately reflect evolutionary history (Teeling et al. 2002). Even more fundamentally, molecular evidence suggests that monotremes ( Prototheria , egg-laying mammals) and marsupials ( Metatheria ) may be more closely related to each other than to placental mammals ( Eutheria ) (Janke et al. 1997), and placental mammals may be organized into larger groups (Afrotheria, Laurasiatheria, Boreoeutheria, etc.) that are quite different from traditional ones (Murphy et al. 2001).

All mammals share at least three characteristics not found in other animals: 3 middle ear bones , hair , and the production of milk by modified sweat glands called mammary glands . The three middle ear bones, the malleus, incus, and stapes (more commonly referred to as the hammer, anvil, and stirrup) function in the transmission of vibrations from the tympanic membrane (eardrum) to the inner ear. The malleus and incus are derived from bones present in the lower jaw of mammalian ancestors. Mammalian hair is present in all mammals at some point in their development. Hair has several functions, including insulation, color patterning, and aiding in the sense of touch. All female mammals produce milk from their mammary glands in order to nourish newborn offspring. Thus, female mammals invest a great deal of energy caring for each of their offspring, a situation which has important ramifications in many aspects of mammalian evolution, ecology, and behavior.

Although mammals share several features in common (see Physical Description and Systematics and Taxonomic History), Mammalia contains a vast diversity of forms. The smallest mammals are found among the shrews and bats , and can weigh as little as 3 grams. The largest mammal, and indeed the largest animal to ever inhabit the planet, is the blue whale , which can weigh 160 metric tons (160,000 kg). Thus, there is a 53 million-fold difference in mass between the largest and smallest mammals! Mammals have evolved to exploit a large variety of ecological niches and life history strategies and, in concert, have evolved numerous adaptations to take advantage of different lifestyles. For example, mammals that fly, glide, swim, run, burrow, or jump have evolved morphologies that allow them to locomote efficiently; mammals have evolved a wide variety of forms to perform a wide variety of functions.

Geographic Range

Mammals can be found on all continents, in all oceans, and on many oceanic islands of the world.

Habitat

Different species of mammals have evolved to live in nearly all terrestrial and aquatic habitats on the planet. Mammals inhabit every terrestrial biome, from deserts to tropical rainforests to polar icecaps. Many species are arboreal, spending most or all of their time in the forest canopy. One group ( bats ) have even evolved powered flight, which represents only the third time that this ability has evolved in vertebrates (the other two groups being birds and extinct Pterosaurs).

Many mammals are partially aquatic, living near lakes, streams, or the coastlines of oceans (e.g., seals , sea lions , walruses , otters , muskrats , and many others). Whales and dolphins ( Cetacea ) are fully aquatic, and can be found in all oceans of the world, and some rivers. Whales can be found in polar, temperate, and tropical waters, both near shore and in the open ocean, and from the water's surface to depths of over 1 kilometer.

Physical Description

All mammals have hair at some point during their development, and most mammals have hair their entire lives. Adults of some species lose most or all of their hair but, even in mammals like whales and dolphins , hair is present at least during some phase of ontogeny. Mammalian hair, made of a protein called keratin, serves at least four functions. First, it slows the exchange of heat with the environment (insulation). Second, specialized hairs (whiskers or "vibrissae") have a sensory function, letting an animal know when it is in contact with an object in its environment. Vibrissae are often richly innervated and well-supplied with muscles that control their position. Third, hair affects appearance through its color and pattern. It may serve to camouflage predators or prey, to warn predators of a defensive mechanism (for example, the conspicuous color pattern of a skunk is a warning to predators), or to communicate social information (for example, threats, such as the erect hair on the back of a wolf ; sex, such as the different colors of male and female capuchin monkeys ; or the presence of danger, such as the white underside of the tail of a white-tailed deer ). Fourth, hair provides some protection, either simply by providing an additional protective layer (against abrasion or sunburn, for example) or by taking on the form of dangerous spines that deter predators (porcupines, spiny rats, others).

Mammals are typically characterized by their highly differentiated teeth . Teeth are replaced just once during an individual's life (a condition called diphyodonty ). Other characteristics found in most mammals include: a lower jaw made up of a single bone, the dentary; four-chambered hearts; a secondary palate separating air and food passages in the mouth; a muscular diaphragm separating thoracic and abdominal cavities; a highly developed brain; endothermy and homeothermy; separate sexes with the sex of an embryo being determined by the presence of a Y or 2 X chromosomes; and internal fertilization.

Often, characteristics of skulls and dentition are used to define and differentiate mammalian groups. To make these easier to comprehend within the accounts of lower mammalian taxa, we provide links to dorsal , ventral , and lateral views of the skull of a dog on which the major bones, foramina, and processes have been labelled. Closeups of the basicranial region , orbital region , and lingual and labial views of a mandible are also available. A partially labeled full skeleton of a raccoon has also been prepared.

  • Sexual Dimorphism
  • sexes alike
  • female larger
  • male larger
  • sexes colored or patterned differently
  • female more colorful
  • male more colorful
  • sexes shaped differently
  • ornamentation

Development

There are three major groups of mammals , each is united by a major feature of embryonic development. Monotremes ( Prototheria ) lay eggs, which is the most primitive reproductive condition in mammals. Marsupials ( Metatheria ) give birth to highly altricial young after a very short gestation period (8 to 43 days). The young are born at a relatively early stage of morphological development. They attach to the mother's nipple and spend a proportionally greater amount of time nursing as they develop. Gestation lasts much longer in placental mammals ( Eutheria ). During gestation, eutherian young interact with their mother through a placenta, a complex organ that connects the embryo with the uterus. Once born, all mammals are dependent upon their mothers for milk. Aside from these few generalities, mammals exhibit a diversity of developmental and life history patterns that vary among species and larger taxonomic groups.

Reproduction

Generally, most mammalian species are either polygynous (one male mates with multiple females) or promiscuous (both males and females have multiple mates in a given reproductive season). Because females incur such high costs during gestation and lactation, it is often the case that male mammals can produce many more offspring in a mating season than can females. As a consequence, the most common mating system in mammals is polygyny, with relatively few males fertilizing multiple females and many males fertilizing none. This scenario sets the stage for intense male-male competition in many species, and also the potential for females to be choosy when it comes to which males will sire her offspring. As a consequence of the choices females make and the effort males put into acquiring matings, many mammals have complex behaviors and morphologies associated with reproduction. Many mammal groups are marked by sexual dimorphism as a result of selection for males that can better compete for access to females.

About 3 percent of mammalian species are monogamous, with males only mating with a single female each season. In these cases, males provide at least some care to their offspring. Often, mating systems may vary within species depending upon local environmental conditions. For example, when resources are low, males may mate with only a single female and provide care for the young. When resources are abundant, the mother may be able to care for young on her own and males will attempt to sire offspring with multiple females.

Other mating systems such as polyandry can also be found among mammals. Some species (e.g. common marmosets and African lions ) display cooperative breeding, in which groups of females, and sometimes males, share the care of young from one or more females. Naked mole rats have a unique mating system among mammals. Like social insects ( Hymenoptera and Isoptera ), naked mole rats are eusocial, with a queen female mating with several males and bearing all of the young in the colony. Other colony members assist in the care of her offspring and do not reproduce themselves.

Many mammals are seasonal breeders, with environmental stimuli such as day length, resource intake and temperature dictating when mating occurs. Females of some species store sperm until conditions are favorable, after which their eggs are fertilized. In other mammals, eggs may be fertilized shortly after copulation, but implantation of the embryo into the uterine lining may be delayed (“delayed implantation”). A third form of delayed gestation is "delayed development", in which development of the embryo may be arrested for some time. Seasonal breeding and delays in fertilzation, implantation, or development are all reproductive strategies that help mammals coordinate the birth of offspring with favorable environmental conditions to increase the chances of offspring survival.

Some mammals give birth to many altricial young in each bout of reproduction. Despite being born in a relatively underdeveloped state, young of this type tend to reach maturity relatively quickly, soon producing many altricial young of their own. Mortality in these species tends to be high and average lifespans are generally short. Many species that exemplify this type of life history strategy can be found among the rodents and insectivores . At the other end of the life history spectrum, many mammals give birth to one or a few precocial young in each bout of reproduction. These species tend to live in stable environments where competition for resources is a key to survival and reproductive success. The strategy for these species is to invest energy and resources in a few, highly developed offspring that will grow to be good competitors. Cetaceans , primates and artiodactyls are examples of orders that follow this general pattern.

Among mammals, many reproductive strategies can be observed, and the patterns listed above are the extremes of a continuum encompassing this variation. Environmental factors, as well as physiological and historical constraints all contribute to the pattern of reproduction found in any population or species. Differences in these factors among species have led to the diversity of life history traits among mammals.

A fundamental component of mammalian evolution, behavior, and life history is the extended care females must give to their offspring. Investment begins even before a female's eggs become fertilized. All female mammals undergo some form of estrus cycle in which eggs develop and become ready for potential fertilization. Hormones regulate changes in various aspects of female physiology throughout the cycle (e.g., the thickening of the uterine lining) and prepare the female for possible fertilization and gestation. Once fertilization occurs, females nurture their embryos in one of three ways--either by attending eggs that are laid externally ( Prototheria ), nursing highly altricial young (often within a pouch, or "marsupium"; Metatheria ), or by nourishing the developing embryos with a placenta that is attached directly to the uterine wall for a long gestation period ( Eutheria ). Gestation in eutherians is metabolically expensive. The costs incurred during gestation depend upon the number of offspring in a litter and the degree of development each embryo undergoes.

Once the young are born (or hatch, in the case of monotremes) females feed their newborn young with milk, a substance rich in fats and protein. Because females must produce this high-energy substance, lactation is far more energetically expensive than gestation. Once mammals are born they must maintain their own body temperatures, no longer being able to depend on their mother for thermoregulation, as was the case during pregnancy. Lactating females must provide enough milk for their offspring to maintain their body temperatures as well as to grow and develop. In addition to feeding their young, females must protect them from predators. In some species, young remain with their mothers even beyond lactation for an extended period of behavioral development and learning.

Depending upon the species and environmental conditions, male mammals may either provide no care, or may invest some or a great deal of care to their offspring. Care by males often involves defending a territory, resources, or the offspring themselves. Males may also provision females and young with food.

Mammalian young are often born in an altricial state, needing extensive care and protection for a period after birth. Most mammals make use of a den or nest for the protection of their young. Some mammals, however, are born well-developed and are able to locomote on their own soon after birth. Most notable in this regard are artiodactyls such as wildebeest or giraffes . Cetacean young must also swim on their own shortly after birth.

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • pre-independence
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • post-independence association with parents
  • extended period of juvenile learning
  • inherits maternal/paternal territory
  • maternal position in the dominance hierarchy affects status of young

Lifespan/Longevity

Just as mammals vary greatly in size, they also vary greatly in lifespan. Generally, smaller mammals live short lives and larger mammals live longer lives. Bats ( Chiroptera ) are an exception to this pattern, they are relatively small mammals that can live for one or more decades in natural conditions, considerably longer than natural lifespans of significantly larger mammals. Mammalian lifespans range from one year or less to 70 or more years in the wild. Bowhead whales may live more than 200 years.

Behavior

Mammalian behavior varies substantially among species. As endotherms, mammals require more energy intake than ectotherms of a similar size, and mammalian activity patterns reflect their high energy demands. For example, thermoregulation plays an important role in dictating mammalian behavior. Mammals that live in colder climates must keep warm, while mammals that live in hot, dry climates must keep cool and conserve water. Behavior is an important way for mammals to help maintain physiological balance.

There are mammal species that exhibit nearly every type of lifestyle, including fossorial, aquatic, terrestrial, and arboreal lifestyles. Locomotion styles are also diverse: mammals may swim, run, bound, fly, glide, burrow, or climb as a means of moving throughout their environment.

Social behavior varies considerably as well. Some mammals live in groups of tens, hundreds, thousands or more individuals. Other mammals are generally solitary except when mating or raising young.

Activity patterns among mammals also cover the full range of possibilities. Mammals may be nocturnal, diurnal, or crepuscular.

Communication and Perception

Generally, olfaction, hearing, tactile perception, and vision are all important sensory modalities in mammals. Olfaction plays a key role in many aspects of mammalian ecology, including foraging, mating and social communication. Many mammals use pheromones and other olfactory cues to communicate information about their reproductive status, territory, or individual or group identity. Scent-marking is commonly used to communicate among mammals. They are often transmitted through urine, feces, or the secretions of specific glands. Some mammals even use odors as defense against mammalian predators (e.g. skunks ), which are especially sensitive to foul-smelling chemical defenses.

Typically, mammalian hearing is well-developed. In some species, it is the primary form of perception. Echolocation, the ability to perceive objects in the external environment by listening to echoes from sounds generated by an animal, has evolved in several groups. Echolocation is the main perception channel used in foraging and navigation in microchiropteran bats ( Chiroptera ) and many toothed whales and dolphins ( Odontoceti ), and has also evolved to a lesser degree in other species (e.g., some shrews ).

Many mammals are vocal, and communicate with one another or with heterospecifics using sound. Vocalizations are used in communication between mother and offspring, between potential mates, and in a variety of other social contexts. Vocalizations can communicate individual or group identity, alarm at the presence of a predator, aggression in dominance interactions, territorial defense, and reproductive state. Communication using vocalizations is quite complex in some groups, most notably in humans.

Mammals also perceive their environment through tactile input to the hair and skin. Specialized hairs (whiskers or "vibrissae") have a sensory function, letting an animal know when it is in contact with an object in its external environment. Vibrissae are often richly innervated and well-supplied with muscles that control their position. The skin is also an important sensory organ. Often, certain portions of the skin are especially sensitive to tactile stimuli, aiding in specific functions like foraging (e.g., the fingers of primates and the nasal tentacles of star-nosed moles ). Touch also serves many communication functions, and is often associated with social behavior (e.g., social grooming).

Vision is well-developed in a large number of mammals, although it is less important in many species that live underground or use echolocation. Many nocturnal animals have relatively large, well-developed eyes. Vision can be important in foraging, navigation, entraining biological rhythms to day length or season, communication, and nearly all aspects of mammalian behavior and ecology.

Food Habits

As a group, mammals eat an enormous variety of organisms. Many mammals can be carnivores (e.g., most species within Carnivora ), herbivores (e.g., Perissodactyla , Artiodactyla ), or omnivores (e.g., many primates ). Mammals eat both invertebrates and vertebrates (including other mammals), plants (including fruit, nectar, foliage, wood, roots, seeds, etc.) and fungi. Being endotherms, mammals require much more food than ectotherms of similar proportions. Thus, relatively few mammals can have a large impact on the populations of their food items.

Predation

Predation is a significant source of mortality for many mammals. Except for those few species that are top predators, mammals are preyed upon by many other organisms, including other mammals. Other groups that typically eat mammals are predatory birds and reptiles . Many species cope with predation through avoidance strategies such as cryptic coloration, by restricting foraging to times when predators may not be abundant, or through their sociality. Some mammals also have defensive chemicals (e.g., skunks ) or bear some type of protective armor or physical defense (e.g., armadillos , pangolins , New World porcupines and Old World porcupines ).

Ecosystem Roles

The ecological roles, or niches, filled by the nearly 5000 mammal species are quite diverse. There are predators and prey, carnivores, omnivores, and herbivores, species that create or greatly modify their habitat and thus the habitat and structure of their communities [e.g., beavers damming streams, large populations of ungulates ( Artiodactyla and Perissodactyla ) grazing in grasslands, moles digging in the earth]. In part because of their high metabolic rates, mammals often play an ecological role that is disproportionately large compared to their numerical abundance. Thus, many mammals may be keystone predators in their communities or play important roles in seed dispersal or pollination. The ecosystem roles that mammals play are so diverse that it is difficult to generalize across the group. Despite their low species diversity, compared to other animal groups, mammals have a substantial impact on global biodiversity.

Economic Importance for Humans: Positive

Mammals are a vital economic resource for humans. Many mammals have been domesticated to provide products such as meat and milk (e.g., cows and goats ) or fiber ( sheep and alpacas ). Many mammals are kept as service animals or pets (e.g., dogs , cats , ferrets ). Mammals are important for the ecotourism industry as well. Consider the many people who travel to zoos or to all corners of the world to see animals like elephants , lions , or whales . Mammals (e.g., bats ) often help control populations of crop pests. Some species like Norway rats and domestic mice are vitally important in medical and other scientific research; because humans are mammals, other mammals can serve as models in human medicine and research.

  • Positive Impacts
  • pet trade
  • food
  • body parts are source of valuable material
  • ecotourism
  • research and education
  • produces fertilizer
  • controls pest population

Economic Importance for Humans: Negative

Some mammal species are considered to have a detrimental impact on human interests. Many mammals that eat fruit, seeds, and other types of vegetation are crop pests. Carnivores are often considered to be a threat to livestock or even to human lives. Mammals that are common in urban or suburban areas can become a problem if they cause damage to automobiles when they are struck on the road, or can become household pests. A few species coexist exceptionally well with people, including some feral domesticated mammals (e.g., rats , house mice , pigs , cats , and dogs ). As a result of either intentional or unintentional introductions near human habitation, these animals have had considerable negative impacts on the local biota of many regions of the world, especially the endemic biota of oceanic islands.

Many mammals can transmit diseases to humans or livestock. The bubonic plague is perhaps the most well-known example. Plague is spread via fleas that are carried by rodents . Rabies, which can be transmitted among mammalian species, is also a significant threat to livestock and can kill humans as well.

Conservation Status

Overexploitation, habitat destruction and fragmentation, the introduction of exotic species, and other anthropogenic pressures threaten mammals worldwide. In the past five centuries at least 82 mammal species have gone extinct. Currently, the International Union for Conservation of Nature and Natural Resources (IUCN) has listed about 1000 species (roughly 25% of all known mammals), as being at some risk of extinction. Several factors contribute to a species' vulnerability to human-induced extinction. Species that are naturally rare or require large home ranges are often at risk due to habitat loss and fragmentation. Species that are seen to threaten humans, livestock, or crops may be directly targeted for extirpation. Those species that are exploited by humans as a resource (e.g., for their meat or fur) but are not domesticated are often depleted to critically low levels. Finally, global climate change is adversely affecting many mammals. The geographic ranges of many mammals are shifting, and these shifts often correlate with changes in local temperatures and climate. As temperatures rise, which is especially pronounced in polar regions, some mammals are unable to adjust and are consequently at risk of losing their environment.

Encyclopedia of Life

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Matthew Wund (author), University of Michigan-Ann Arbor, Phil Myers (author), Museum of Zoology, University of Michigan-Ann Arbor.

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

introduced

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

native range

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

Palearctic

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

World Map

introduced

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

native range

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

oriental

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

World Map

introduced

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

native range

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

Ethiopian

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

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introduced

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

native range

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

Neotropical

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

World Map

introduced

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

native range

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

Australian

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

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introduced

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

native range

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

Antarctica

lives on Antarctica, the southernmost continent which sits astride the southern pole.

native range

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

oceanic islands

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.

introduced

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

native range

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

Arctic Ocean

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

native range

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

native range

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

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

native range

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

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

native range

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

native range

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

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.

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).

tropical

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

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.

terrestrial

Living on the ground.

saltwater or marine

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

freshwater

mainly lives in water that is not salty.

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.

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.

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.

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.

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.

forest

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

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.

scrub forest

scrub forests develop in areas that experience dry seasons.

mountains

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

pelagic

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

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

coastal

the nearshore aquatic habitats near a coast, or shoreline.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

marsh

marshes are wetland areas often dominated by grasses and reeds.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

bog

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.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

suburban

living in residential areas on the outskirts of large cities or towns.

agricultural

living in landscapes dominated by human agriculture.

riparian

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

estuarine

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

intertidal or littoral

the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.

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.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

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.

polymorphic

"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

venomous

an animal which has an organ capable of injecting a poisonous substance into a wound (for example, scorpions, jellyfish, and rattlesnakes).

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.

monogamous

Having one mate at a time.

polyandrous

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

polygynous

having more than one female as a mate at one time

polygynandrous

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

cooperative breeder

helpers provide assistance in raising young that are not their own

eusocial

the condition in which individuals in a group display each of the following three traits: cooperative care of young; some individuals in the group give up reproduction and specialize in care of young; overlap of at least two generations of life stages capable of contributing to colony labor

semelparous

offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.

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).

seasonal breeding

breeding is confined to a particular season

year-round breeding

breeding takes place throughout the year

sexual

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

induced ovulation

ovulation is stimulated by the act of copulation (does not occur spontaneously)

fertilization

union of egg and spermatozoan

internal fertilization

fertilization takes place within the female's body

viviparous

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

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

delayed fertilization

a substantial delay (longer than the minimum time required for sperm to travel to the egg) takes place between copulation and fertilization, used to describe female sperm storage.

delayed implantation

in mammals, a condition in which a fertilized egg reaches the uterus but delays its implantation in the uterine lining, sometimes for several months.

embryonic diapause

At about the time a female gives birth (e.g. in most kangaroo species), she also becomes receptive and mates. Embryos produced at this mating develop only as far as a hollow ball of cells (the blastocyst) and then become quiescent, entering a state of suspended animation or embryonic diapause. The hormonal signal (prolactin) which blocks further development of the blastocyst is produced in response to the sucking stimulus from the young in the pouch. When sucking decreases as the young begins to eat other food and to leave the pouch, or if the young is lost from the pouch, the quiescent blastocyst resumes development, the embryo is born, and the cycle begins again. (Macdonald 1984)

arboreal

Referring to an animal that lives in trees; tree-climbing.

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

saltatorial

specialized for leaping or bounding locomotion; jumps or hops.

natatorial

specialized for swimming

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

active during the night

crepuscular

active at dawn and dusk

parasite

an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death

motile

having the capacity to move from one place to another.

nomadic

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

migratory

makes seasonal movements between breeding and wintering grounds

sedentary

remains in the same area

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

solitary

lives alone

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

social

associates with others of its species; forms social groups.

colonial

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.

dominance hierarchies

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

visual

uses sight to communicate

tactile

uses touch to communicate

acoustic

uses sound to communicate

chemical

uses smells or other chemicals to communicate

mimicry

imitates a communication signal or appearance of another kind of organism

duets

to jointly display, usually with sounds in a highly coordinated fashion, at the same time as one other individual of the same species, often a mate

choruses

to jointly display, usually with sounds, at the same time as two or more other individuals of the same or different species

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

scent marks

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

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

tactile

uses touch to communicate

acoustic

uses sound to communicate

ultrasound

uses sound above the range of human hearing for either navigation or communication or both

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.

vibrations

movements of a hard surface that are produced by animals as signals to others

chemical

uses smells or other chemicals to communicate

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

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.

aposematic

having coloration that serves a protective function for the animal, usually used to refer to animals with colors that warn predators of their toxicity. For example: animals with bright red or yellow coloration are often toxic or distasteful.

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.

biodegradation

helps break down and decompose dead plants and/or animals

soil aeration

digs and breaks up soil so air and water can get in

keystone species

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).

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

food

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

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.

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).

causes or carries domestic animal disease

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

carnivore

an animal that mainly eats meat

piscivore

an animal that mainly eats fish

sanguivore

an animal that mainly eats blood

insectivore

An animal that eats mainly insects or spiders.

molluscivore

eats mollusks, members of Phylum Mollusca

scavenger

an animal that mainly eats dead animals

herbivore

An animal that eats mainly plants or parts of plants.

folivore

an animal that mainly eats leaves.

frugivore

an animal that mainly eats fruit

granivore

an animal that mainly eats seeds

nectarivore

an animal that mainly eats nectar from flowers

omnivore

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

planktivore

an animal that mainly eats plankton

mycophage

an animal that mainly eats fungus

coprophage

an animal that mainly eats the dung of other animals

References

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Apfelbach, R. 1990. Body Functions. Pp. 85-106 in Grzimek's Encyclopedia of Mammals , Vol. 1, 1st Edition. New York: Mcgraw-Hill.

Dragoo, J., R. Honeycutt. 1997. Systematics of mustelid-like carnivores. Journal of Mammalogy , 78: 426-443.

Flynn, J., J. Finarelli, S. Zehr, J. Hsu, M. Nedbal. 2005. Molecular phylogeny of the Carnivora (Mammalia): assessing the impact of increased sampling on resolving enigmatic relationships. Systematic Biology , 54/2: 317-337.

Gingerich, P., M. ul Haq, I. Zalmout, I. Khan, M. Malkani. 2001. Origin of whales from early artiodactyls: Hands and feet of Eocene Protocetidae from Pakistan. Science , 293: 2239-2242.

Grzimek, B. 1990. General Introduction. Pp. 4-5 in Grzimek's Encyclopedia of Mammals , Vol. 1, 1st Edition. New York: Mcgraw-Hill.

Janke, A., X. Xu, U. Arnason. 1997. The complete mitochondrial genome of the wallaroo (Macropus robustus) and the phylogenetic relationship among Monotremata, marsupialia, and Eutheria. Proc. National Academy of Sciences , 94: 1276-1281.

Keil, A., N. Sachser. 1998. Reproductive benefits from female promiscuous mating in a small mammal. Ethology , 104: 897-903.

Klima, M., W. Maier. 1990. Body Structure. Pp. 58-84 in Grzimek's Encyclopedia of Mammals , Vol. 1, 1 Edition. New York: Mcgraw-Hill.

Lazaro-Perea, C., C. Castro, R. Harrison, A. Araujo, M. Arruda, C. Snowdon. 2000. Behavioral and demographic changes following the loss of the breeding female in cooperatively breeding marmosets. Behavioral Ecology and Sociobiology , 48: 137-146.

Matthee, C., J. Burzlaff, J. Taylor, S. Davis. 2001. Mining the mammalian genome for artiodactyl systematics. Systematic Biology , 50: 367-390.

Murphy, W., E. Eizirik, S. O'Brien, O. Madsen, M. Scally, C. Douady, E. Teeling, O. Ryder, M. Stanhope, W. de Jong, M. Springer. 2001. Resolution of the early placental mammal radiation using Bayesian phylogenetics. Science , 294: 2348-2351.

Nowak, R. 1991. Walker's Mammals of the World . Baltimore: Johns Hopkins University Press.

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To cite this page: Wund, M. and P. Myers 2005. "Mammalia" (On-line), Animal Diversity Web. Accessed {%B %d, %Y} at https://animaldiversity.org/accounts/Mammalia/

Last updated: 2005-00-27 / Generated: 2025-10-03 01:04

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