1a. Oviparous; mammary glands internal duct to the surface thru a slit; no nipples; no mammae.
MONOTREMATA: monotremes, platypus, spiny ant eaters.

1b. Viviparous; mammary glands developed as mammae with a nipple.......................................2

2a. Marsupium present, or a marsupial fold in most species; epipbis present (vestigial in some).
MARSUPALIA: kangaroos, wallabys, wombats, possums, koala, gliders, bandicoots and others.

2b. No marsupium; epipubis absent .......................................3

3a. Hind limbs vestigial or absent; never externally visible.......................................4

3b. Hind limbs well developed and visible.......................................5

4a. No lips; the skin covering the jaws not developed as muscular flaps; teeth homodont if present.
CETACEA: whales, dolphins, porpoises.

4b. Lips present; upper lips with muscular lateral flap on each side. SIRENIA: dugongs, sea
cows, manatees.

5a. Forelimbs not developed for flight (there are some gliding mammals); fingers shorter
than forearm.......................................6

5b. Forelimbs not developed for flight (there are some gliding mammals); fingers shorter
than forearm.......................................6

6a. Underparts furred; head and body and tail more or less completely covered with large,
overlapping epidermal scales. PHOLIDOTA: pangolins.

6b. Body furred all over, or more or less fully covered with dermal bony plates
and/or rings/ no epidermal scales* .......................................7

7a. Nose developed as a long muscular trunk which almost reaches to ground when the
elephant is standing. PROBOSCIDEA: elephants.

7b. Nose short, never long enough to reach the ground when the animal
is standing....................................... 8

8a. Aquatic: limbs modified as flippers. PINNIPEDIA: seals, sea lions, and walruses.

8b. Terrestrial or amphibious; limbs not modified as flippers.......................................9

9a. Orbits enclosed by a bony ring, walled off from the temporal fossa behind. PRIMATES: lemurs,
spectral tarsiers, moneys apes, man.

9b. Orbits open to temporal fossa behind.......................................10

10a. Unguiligrade, standing on tips of fingers with 1 or 2 hooves; horns and/or antlers commonly
present on head or snout.......................................11

10b. Plantigrade, semiplantigrade or subdigitigrade or digitigrade, walking on the palm or
3 or more fingers; claws or nails present; no horns nor antlers.......................................12

11a. Walking on the tip of the 3rd finger (mesaxonic) with a single hoof. PERISSODACTYLA: horses,
zebras, asses, tapirs, rhinos.

11b. Walking on the tips of 3rd and 4th digits with 2 hooves (paraxonic). ARTIODACTYLA: sheep,
goats, cattle, antelopes, gazelles, pigs, peccaries, hippos, giraffes, okapi, deer, elk, moose,
reindeer, pronghorn.

12a. Teeth absent, or reduced or all more or less alike homodont, molariform, cylindrical or peg-like.......................................13

12b. Teeth heterodont; incisors and molars always present in one or both jaws; canines
often present .......................................15

13a. Body covered more or less completely with bony plates and rings. EDETATA in part. Armadillos.*

14b. Forefeet with 4 digits; claws more or less equally developed; long tubular snout; long
rabbit-like ears; heavy tail. TUBULIDENTATA: aardvarks.

15a. A prominent diastem in tooth row; canines absent.......................................16

15b. No diastem; canines present.......................................17

16a. Simplicidont; incisors 1/1 in a single row. RODENTIA: rats, mice, jumping mice, kangaroo
rats, jerboas, sewellel, squirrels, chipmunks, gophers, beavers, capybaras, gerbils, hamsters,
guinea pigs, chinchillas, lemmings, and others.

16b. Duplicidont; inciors 2/1, upper incisors in 2 rows, one behind the other. LAGOMORPHA: hairs,
rabbits, pikas.

17a. Canines and incisors about equally developed. INSECTIVORA: moles, shrews of many types
and hedgehogs. In some groups teeth chestnut pigmented.

17b. Canines much larger than incisors. CARNIVORA: dogs, wolves, foxes, coyotes, bears, pandas,
raccoons, cats, weasels, skunks, otters, martins, minks, civets, mongooses, hyaenas, and badgers.