Keratin – a group of scleroproteins that form the structural bases of hair, wool, nails, and other epidermal structures in animals

Keystone Species – a species on which other species in an ecosystem largely depend, such that if it were removed the ecosystem would change drastically

Kingdom – a taxonomic category of the highest rank, grouping together all forms of life having certain fundamental characteristics in common

Kleptoparasitism – a form of feeding in which one animal takes prey or other food from another that has caught, collected, or otherwise prepared the food

Lagomorph – group of mammals characterized by two pairs of continually-growing incisors and fully furred feet

Larva – the stage in the life cycle of an animal during which it is motile and capable of feeding itself that occurs after hatching from the egg and prior to the reorganizations involved in becoming adult

Lateral Line – a system of receptors embedded in special grooves in the skin that is capable of detecting vibrations in the water surrounding the animal

Lek – territory that is held and defended against rivals by males of certain species during the breeding season

Leucism – a condition in which there is partial loss of pigmentation in an animal resulting in white, pale, or patchy coloration of the skin, hair, feathers, scales, or cuticle, but not the eyes

Ligament – a sheet or band of tough fibrous tissue connecting bones together

Machairodont – any member of various extinct groups of predatory mammals that were characterized by long, curved, saber-shaped teeth

Mammal – a class of warm-blooded animals characterized by a covering of hair on the skin and, in the female, milk-producing mammary glands for nourishing young

Mandibles – in arthropods, one of the pair of mouth-parts most commonly used used for seizing and cutting food

Marginocephalian – a group of dinosaurs characterized by a bony shelf at the back of the skull

Marsupial – a mammal that raises its young in a pouch

Marsupium – a pouch

Matriarchal – a social group that is led by the dominant female

Megafauna – large or giant animals whose weight is in excess of 44 kg (100 lb) or in excess of 1000 kg (2200 lb). depending on sources used

Melanism – an increased amount of black or nearly black pigmentation

Melon Organ – mass of adipose tissue found in toothed whales that focuses and modulates the animal’s vocalizations and aides in communication and echolocation

Mesocarnivore – a carnivore whose diet is between 25% and 70% vertebrate flesh

Mesozoic – the middle of three eras of geologic time from about 248 to 65 million years ago and characterized by the presence of dinosaurs as the dominant fauna

Metamorphosis – biological process by which an animal physically develops after birth or hatching and involving a conspicuous and relatively abrupt change in the animal’s body structure through cell growth and differentiation

Migration -the movement of animals from one area to another

Mimicry – the similarity of one organism to another that has evolved because the resemblance is selectively favored by the behavior of a shared signal revceiver that can respond to both

Molar – one of the posterior teeth, used for crushing and characterized by the presence of multiple roots and a biting surface formed from patterns of projections and ridges

Mollusk – a class of invertebrates characterized by a soft, unsegmented body usually enclosed in a calcareous shell

Monotreme – the most primitive order of mammals, characterized by the presence of a cloaca and hatching young from eggs

Morph – domesticated reptile displaying skin patterning and/or coloration that has been selectively bred for

Musk – a substance secreted in a glandular sac under the skin of certain animals and possessing a strong odor

Musth – the frenzied state of a male elephant during the mating season

Mutualism – an interaction between members of two species that benefits both

Myotoxin – toxin that causes muscle necrosis and paralysis

Myriapod – a class of arthropods characterized by an elongated, segmented body

Nail – a horny covering on the upper surface of the tip of the digits in primates

Natural Selection – a complex process in which the total environment determines which members of a species survive to reproduce and so pass on their genes to the next generation

Neurotoxin – toxin that affects the functioning of the nervous system

Niche – the functional position of an organism in its environment compromising the habitat in which the organism lives, the periods of time during which it occurs and is active there, and the resources it obtains there

Nocturnal – an animal that is active at night

Olfaction – the sense of smell

Omnivore – an animal that feeds on both plants and animals

Operculum – a bony plate that covers a fish’s gills

Opposable – applied to a digit that can be turned so that its pad makes contact with the pad of each of the other digits on the same limb

Ornithopod – a group pf dinosaurs characterized by three-toed feet, a horny beak, and an elongated pubis

Ossicone – hornlike protuberances on the heads of giraffes and their relatives that are derived from ossified cartilage rather than living bone and covered in skin rather than keratin

Osteoderm – a bony plate embedded in the skin

Osteophagy – the practice of eating bones

Oviparous – reproducing by laying eggs

Ovipositor – specialized egg-laying organ found in most insects

Ovoviviparous -reproducing by having young develop from eggs retained with the mother’s body but separated from it by egg membranes

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