Ungulate

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Ungulates, or hoofed mammals, are members of the orders Perissodactyla and Artiodactyla. Ungulates comprise most of the large land mammals on earth and include all of the large domestic animals kept by humans. 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).

Related to ungulates are


(meaning roughly "hoofed" or "hoofed animal") are several groups of mammals most of which use the tips of their toes, usually hoofed, to sustain their whole bodyweight while moving. They make up several orders of mammals, of which six to eight survive. There is some dispute as to whether ungulate should be treated as an actual cladistic (evolution-based) group, or merely a phenetic group (similar, but not necessarily related), in light of the fact that all ungulates do not appear to be as closely related as once believed (see below). Ungulata was formerly considered an order which has been split into Perissodactyla and Artiodactyla. Members of these two orders are called the 'true ungulates' to distinguish them from 'subungulates' (paenungulata) which include members from the Proboscidea, Sirenia, and Hyracoidea orders.[1]

Relationships

The Perissodactyla and Artiodactyla make up the largest portion of ungulates, and also comprise the majority of large land mammals. These two groups first appeared during the late Paleocene and early Eocene (about 54 million years ago), rapidly spreading to a wide variety of species on numerous continents, and have developed in parallel since that time.

Although whales and dolphins (Cetacea) do not possess most of the typical morphological characteristics of ungulates, recent discoveries have suggested that they are likely descended from early artiodactyls, and thus are directly related to other even-toed ungulates such as cattle and hippopotami. As a result of these discoveries, a new order of Cetartiodactyla has also been proposed to include the members of Artiodactyla and Cetacea, to reflect their common ancestry; however, strictly speaking, this is not necessary, as it is possible simply to recognize Cetacea as a subgroup of Artiodactyla.

The Hyracoidea, Sirenia and Proboscidea are the Paenungulata. The Tubulidentata are also thought to be ungulates. The Macroscelidea have been interpreted as ungulates, and there is dental as well as genetic evidence supporting this interpretation. The Macroscelidea and Tubulidentata have recently been united with the Paenungulata in the Pseudungulata. Genetic studies indicate that these animals are not closely related to the artiodactyls and perissodactyls. Instead, the closest relatives of pseudungulates are the Afrosoricida; the Pseudungulata and Afrosoricida make up the Afrotheria.

Ungulate groups represented in the fossil record include the embrithopods, demostylians, mesonychids, "condylarths" and various South American and Paleogene lineages.

In addition to hooves, most ungulates have developed reduced canine teeth, bunodont molars (molars with low, rounded cusps), and an astragalus (one of the ankle bones at the end of the lower leg) with a short, robust head.

Ungulates diversified rapidly in the Eocene, but are thought to date back as far as the late Cretaceous. Most ungulates are herbivores, but a few are omnivores or even predators: the Mesonychia and whales.

Recent developments

That these groups of mammals are most closely related to each other has occasionally been questioned on anatomical and genetic grounds. Molecular phylogenetic studies have suggested that Perissodactyla and Cetartiodactyla are closest to Carnivora and Pholidota rather than to the Pseudungulata.

The Pseudungulata are by some scientists united with the Afrosoricida in the cohort or super-order Afrotheria based on molecular and DNA analysis. This means they are not related to other ungulates.

The extinct South-American ungulates, evolved when the continent was in isolation, are united in the super-order Meridiungulata. They are by some thought to be unrelated to the other ungulates. Instead, they are united with the Afrotheria and the Xenarthra in the supercohort Atlantogenata.

The position of other extinct ungulates is unclear. Embrithopods, Desmostylians and other related groups are seen as relatives of the Paenungulata, thus members of the Afrotheria. The condylarths are, as a result, no longer seen as the ancestors of all ungulates. Instead, it is now believed the condylarths are members of the cohort Laurasiatheria. So it seems that, of all the ungulates, only the Perissiodacyla and Artiodactyla descended from the condylarths—assuming that the animals lumped by scientists into Condylarthra over the years are even related to one another.

As a result of all this, it seems the typical ungulate morphology originated three times independently: in the Meridiungulata, the Afrotheria and the "true" ungulates in the Laurasiatheria. This is a great example of convergent evolution. This is met with scepticism by some scientists, who say there is no morphological evidence to split the ungulates up into so many unrelated clades.

Even-toed ungulates

Even-toed ungulates
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Rocky Mountain Goat, Oreamnos americanus
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Owen, 1848
Families

Antilocapridae
Bovidae
Camelidae
Cervidae
Giraffidae
Hippopotamidae
Moschidae
Suidae
Tayassuidae
Tragulidae
Leptochoeridae † (extinct)
Chaeropotamidae †
Dichobunidae †
Cebochoeridae †
Entelodontidae †
Anoplotheriidae †
Anthracotheriidae †
Cainotheriidae †
Agriochoeridae †
Merycoidodontidae †
Leptomerycidae †
Protoceratidae †
Xiphodontidae †
Amphimerycidae †
Gelocidae †
Merycodontidae †
Dromomerycidae †


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

Odd-toed ungulate

Odd-toed ungulates
00296 zebra.jpg
Plains Zebras
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Perissodactyla
Owen, 1848
Families

Equidae
Tapiridae
Rhinocerotidae
Brontotheriidae † (extinct)
Chalicotheriidae †
Hyracodontidae †



The odd-toed ungulates are browsing and grazing mammals that comprise the order Perissodactyla. They are odd-toed ungulates (animals having an odd number of toes on the hooves), are usually large to very large, and have relatively simple stomachs and a large middle toe.

Evolution

The odd-toed ungulates arose in what is now North America in the late Paleocene, less than 10 million years after the Cretaceous-Tertiary extinction event, in which the non-avian 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 reinvaded 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 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.

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)

The three surviving families of odd-toed ungulate are classified as follows.

  • ORDER PERISSODACTYLA
    • Suborder Hippomorpha
    • Suborder Ceratomorpha
      • Family Tapiridae: tapirs, 4 species in one genus
        • Brazilian Tapir, Tapirus terrestris
        • Mountain Tapir, Tapirus pinchaque
        • Baird's Tapir, Tapirus bairdii
        • Malayan Tapir, Tapirus indicus
      • Family Rhinocerotidae: rhinoceroses, 5 species in 4 genera
        • Black Rhinoceros, Diceros bicornis
        • White Rhinoceros, Ceratotherium simum
        • Indian Rhinoceros, Rhinoceros unicornis
        • Javan Rhinoceros, Rhinoceros sondaicus
        • Sumatran Rhinoceros, Dicerorhinus sumatrensis

References
ISBN 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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  1. Mammology: adaptation, diversity, and ecology, Feldhammer, George A. 1999, p. 312