The Cetartiodactyla encompasses all even toed ungulates (pigs, hippos, camels, llamas, deer, etc) and all cetaceans (whales and dolphins). Morphological evidence suggests that whales are the closest relatives of the Artiodactyla and most molecular data place whales entirely within the Artiodactyla Order.
The Cetacea are subdivided into two Suborders; the Mysticeti (baleen whales) and the Odontoceti (toothed whales, including porpoises and dolphins). All whales have an elongated hairless body with front flippers and a tail flipper. Their hind limbs are greatly reduced and no longer external, but can be seen as atavisms in skeletons. They breathe air just as all mammals do and so although they are fully aquatic, they need to come to the surface of the water to breathe. The length of time they can stay under water is species dependant but generally tends to be linger, the larger the species.
The baleen whales comprise the grey whale, the rorquals (including the humpback whale and the blue whale) and right whales. They are grouped based on their filter feeding mechanism which utilises two rows of baleen plates that are attached to either side of the upper jaw.
The toothed whales are far more diverse and comprise almost 90% of all whale species. The group includes dolphins, river dolphins, the killer whale, white whales, sperm whales and beaked whales. They are generally a lot smaller than the baleen whales, although the sperm whale can grow up to 18 m in length. The toothed whales, just like the baleen whales, are grouped together based in their feeding habits. Instead of large rows of baleen plates, they have jaws filled with conical, pointed teeth used for catching prey. The teeth are not divided into canines and incisors, etc like other mammals, but are all relatively uniform in size and shape, with a slight curve on some and a straight shaft on others. Killer whales prey on other whales in packs, whereas most toothed whales hunt fish, squid and other non-mammalian prey. The majority of toothed whales live in groups called pods and are very sociable mammals. They are the only known mammal apart from humans who have sex for fun and not just to produce offspring.
Length: 1.9-4 m
Weight: 500 kg
Social unit: Variable
Region: Worldwide (except polar regions)
Hoofed mammals are divided into two orders; the Artiodactyla
(which are more closely related to whales) and the Perissodactyla.
Although superficially similar, the two are not closely related
but are nevertheless frequently grouped together under the name
ungulates (hoofed mammals). The Artiodactyla are even toed hoofed
mammals that include pigs, hippopotamuses, camels, deer, giraffe,
okapi, sheep, goats and all species of cattle. The vast majority
of artiodactyls live in large social groups with a safety in numbers
motive as ungulates are the most common prey of many carnivores.
Most are terrestrial with only the hippo being semi-aquatic. The
hippo is thought to be the link between whales and other even
toed ungulates. Ungulates are the most dominant terrestrial herbivores
and have become such a highly successful group due to their speed
and endurance. Their limbs are embedded within the body wall as
far down as the elbow or knee joint. This increased lower limb
plus the increased movement in the shoulder joint allow the ungulates
to have an extremely long stride length which in turn gives more
speed when running. Most large predators will give up a chase
if the ungulate manages to outrun them for only relatively short
periods of time as carnivores overheat quickly and have low endurance
levels. The artiodactyls and perrisodactyls also have fewer toes,
thus fewer muscles and tendons which in turn decreases the amount
of energy required to move quickly. Unlike predators, ungulates
run on their toes, which are encased in sturdy hooves.
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Author: Emma-Louise Nicholls
Last updated: 20th November 2005
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