Ungulate
Ungulates, or hoofed mammals, are members of the orders Perissodactyla and Artiodactyla. Ungulates include most of the large land mammals on earth and all of the large domestic animals kept by humans. They are found naturally on all continents except Antartica and Australia (where they were introduced by humans) and in almost all environments from forests to grasslands to deserts to high mountains to the tundra. They range in size from the Lesser Malay mouse deer, Tragulus javanicus, which weighs 1.5 to 2.5 kg (3.3 to 5.5 lbs) fully grown to the White rhinoceros, Ceratotherium simum, and the Hippotomus, Hippopotamus amphibius, which can weigh over 3,200 kg (7,000 lbs) (Huffman 2006).
Closely related to ungulates are the orders:
- Tubulidentata - Aardvark
- Hyracoidea - Hyraxes
- Proboscidea - Elephants
- Sirenia - Sea cows
- Cetacea - Whales and Dolphins
Ungulate features
The word "ungulate" comes from the Latin word ungula meaning "hoof". A hoof is a claw or nail which protects the toe and enables it to support the weight of the animal. Ungulates stand and run on the tips of their toes. This gives them longer legs which helps them to run faster.
Ungulates are typically herbivores, eating plants; some, such as the pigs, are omnivores, eating a variety of foods including meat.
Perissodactyla: odd-toed ungulates
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 Plains Zebras | ||||||||
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Equidae |
In the Perissodactyla, the odd-toed ungulates, the central axis of the foot passes through the third toe.
Evolution
The odd-toed ungulates arose in what is now North America in the late Paleocene, less than 10 million years after the dinosaurs died out. By the start of the Eocene (55 million years ago) they had diversified and spread out to occupy several continents. The horses and tapirs both evolved in North America; the rhinoceroses appear to have developed in Asia from tapir-like animals and then spread to the Americas during the middle Eocene (about 45 million years ago). There were 12 families, of which only three survive. These families were very diverse in form and size; they included the enormous Brontotheres and the bizarre Chalicotheres. The largest perissodactyl, an Asian rhinoceros called Paraceratherium, reached 11,000 kg (12 tons), more than twice the weight of an elephant.
Perissodactyls were the dominant group of large terrestrial browsers right through the Oligocene. However, the rise of grasses in the Miocene (about 20 million years ago) saw a major change: the even-toed ungulates with their more complex stomachs were better able to adapt to a coarse, low-nutrition diet, and soon rose to prominence. Nevertheless, many odd-toed species survived and prospered until the late Pleistocene (about 10,000 years ago) when they faced the pressure of human hunting and habitat change.
Today there are only 17 species of odd-toes ungulates still living and all of them are in danger of extinction except for the horse and the donkey (UCMP 2006).
Taxonomy
The members of the order fall into two suborders:
- Hippomorpha are odd-toed ungulates that are fast runners with long legs and have only one toe; this suborder has the sole family Equidae (coextensive with the genus Equus), comprising the horse, zebra, donkey, onager, and allied species.
- Ceratomorpha are odd-toed ungulates that have several functional toes and are heavier than and move slower than the Hippomorpha species. This suborder has two families: Tapiridae (tapirs) and Rhinocerotidae (rhinoceroses)
Even-toed ungulates
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| 240px Rocky Mountain Goat, Oreamnos americanus | ||||||||
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Antilocapridae |
The even-toed ungulates form the mammal order Artiodactyla. They are ungulates whose weight is borne about equally by the third and fourth toes, rather than mostly or entirely by the third as in perissodactyls. There are about 220 artiodactyl species, including many that are of great economic importance to humans.
As with many mammal groups, even-toed ungulates first appeared during the Early Eocene (about 54 million years ago). In form they were rather like today's chevrotains: small, short-legged creatures that ate leaves and the soft parts of plants. By the Late Eocene (46 million years ago), the three modern suborders had already developed: Suina (the pig group); Tylopoda (the camel group); and Ruminantia (the goat and cattle group). Nevertheless, artiodactyls were far from dominant at that time: the odd-toed ungulates (ancestors of today's horses and rhinos) were much more successful and far more numerous. Even-toed ungulates survived in niche roles, usually occupying marginal habitats, and it is presumably at that time that they developed their complex digestive systems, which allowed them to survive on lower-grade feed.
The appearance of grasses during the Eocene and their subsequent spread during the Miocene (about 20 million years ago) saw a major change: grasses are very difficult to digest and the even-toed ungulates with their highly-developed stomachs were better able to adapt to this coarse, low-nutrition diet, and soon replaced the odd-toed ungulates as the dominant terrestrial herbivores.
The artiodactyls fall into two groups which, despite underlying similarities, are rather different. The Suina (pigs, hippos, and peccaries) retain four toes, have simpler molars, short legs, and their canine teeth are often enlarged to form tusks. In general, they are omnivores and have a simple stomach (the two hippopotamus species and the babirusa are exceptions). It is possible that Suina is not a natural group. In particular, recent research suggests that the Hippopotamidae (which are likely derived from among the extinct group known as anthracotheres) may be more closely related to the ruminants than to the pigs.
The camelids and the Ruminantia, on the other hand, tend to be longer-legged, to have only two toes, to have more complex cheek teeth well-suited to grinding up tough grasses, and multi-chambered stomachs. Not only are their digestive systems highly developed, they have also evolved the habit of chewing cud: regurgitating partly-digested food to chew it again and extract the maximum possible benefit from it.
Lastly a group of artiodactyls, which molecular biology suggests were most closely related to Hippopotamidae, returned to the sea to become whales. The conclusion is that Artiodactyla, if it excludes Cetacea, is a paraphyletic group. For this reason, the term Cetartiodactyla was coined to refer to the group containing both artiodactyls and whales (though the problem could just as easily be resolved by recognizing Cetacea as a subgroup of Artiodactyla).
- ORDER ARTIODACTYLA
- Suborder Suina
- Family Suidae: pigs
- Family Hippopotamidae: hippos
- Family Tayassuidae: peccaries
- Suborder Tylopoda
- Family Camelidae: camels and llamas
- Suborder Ruminantia
- Suborder Suina
ReferencesISBN links support NWE through referral fees
- Huffman, B. 2006 The Ultimate Ungulate Page Website [1]
- Nowak, R.M. and Paradiso, J.L. 1983. Walker's Mammals of the World. Baltimore, Maryland, USA : The Johns Hopkins University Press
- University of California Museum of Paleontology (UCMP) 2006. "Ungulates: Hoofed Mammals"[2]
- Voelker, W. 1986. The Natural History of Living Mammals. Medford, New Jersey, USA : Plexus Publishing, Inc.
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