The even-toed ungulates (Artiodactyla or Paraxonia) have an unusual ankle with an extra joint made
possible by a modified astragalus bone that has two pulley-like facets.
The axis of support runs between the third and fourth toes. The small early palaeodonts gave rise
to the piglike Suina, the Tylopoda (including oreodonts and camels, and the Ruminantia.
The ruminants are the most successful group; their digestion involves a partitioned stomach
from which food is regurgitated and repeatedly chewed as a cud.
For defense, many of the Suina rely upon canine tusks, while most ruminants rely
either on bony antlers or on keratinous horns.
The earliest whales were derived from artiodactyls in coastal Asia and quickly specialized for marine life.
The primitive Archaeoceti gave rise to the fish-eating Odontoceti (toothed whales with asymmetrically altered skulls)
and the giant plankton-feeding Mysticeti, in which the teeth have been replaced by horny plates of baleen.
- Order Artiodactyla:
- Artiodactyl characters and evolutionary trends
- Artiodactyl classification
- Suborder Palaeodonta
- Suborder Suina
- Suborder Tylopoda
- Suborder Ruminantia
- Order Cetacea:
- Origin of whales
- Archaeoceti
- Odontoceti
- Mysticeti
Illustrations
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