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CENTER for BIOLOGICAL DIVERSITY Because life is good
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Mammals can be identified by the presence in females of mammary glands that produce milk for offspring. Mammals are warm-blooded vertebrates with sweat glands, hair, three middle ear bones and a neocortex region in the brain. Their gradual evolution from mammal-like “reptiles” called “synapsids” spanned about 70 million years. The first clear evidence of fully mammalian jaw joints and middle ears was found about 200 million years ago; mid-Jurassic fossils show early evidence of hair or fur; and lactation occurred in monotremes, egg-layers that urinated, defecated, and reproduced through a single hole, though not at the same time. They are believed to have secreted milk not from nipples but through a hairy patch on their bellies. (The platypus and four echidna species are the sole surviving mammalian egg-layers.) Mammals now encompass approximately 5,400 species, including humans.

Globally, 1,219 species of mammals, or about 22 percent of the total 5,487 described mammal species, were deemed endangered or vulnerable to extinction by the International Union for Conservation of Nature's 2012 Red List. In the United States, 36 mammals are at risk of extinction.

Alexander Archipelago wolf
American pika
American wolverine
Arctic fox
Bearded seal
Black-footed ferret
Black-tailed prairie dog
Bowhead whale
Buena Vista Lake ornate shrew
Canada lynx
Cook Inlet beluga whale
Delmarva Peninsula fox squirrel
Desert kit fox
Eastern small-footed bat
Fisher
Florida bonneted bat
Florida manatee
Florida panther
Gray wolves in the lower 48 states
Great Lakes gray wolf
Grizzly bear
Hawaiian monk seal
Humboldt marten
Iliamna Lake seal
Indiana bat
Island fox
Jaguar
Kenai brown bear
Mexican bobcat
Mexican gray wolf
Mountain caribou
North Atlantic right whale
North Coast red tree vole
North Pacific right whale
Northern long-eared bat
Northern Rocky Mountains gray wolf
Ocelot
Okinawa dugong
Pacific pocket mouse
Pacific walrus
Peninsular bighorn sheep
Plains bison
Polar bear
Preble's meadow jumping mouse
Puget Sound killer whale
Ribbon seal
Ringed seal
San Bernardino flying squirrel
San Bernardino kangaroo rat
San Joaquin kit fox
Sea otter
Sierra Nevada bighorn sheep
Sierra Nevada red fox
Spotted seal
Vaquita
West Virginia northern flying squirrel
Wolves on the West Coast

Photo © Robin Silver