Everything about Ungulate totally explained
Ungulates (meaning roughly "being
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 Ungulata are a
cladistic (evolution-based) group, or merely a
phenetic group (similar, but not necessarily related), because not all ungulates appear as closely related as once believed. Ungulata was considered an order which has been split into
Perissodactyla,
Artiodactyla,
Tubulidentata,
Hyracoidea,
Sirenia, and
Proboscidea. Members of the orders
Perissodactyla,
Artiodactyla, and
Cetacea are called the 'true ungulates' to distinguish them from '
subungulates' (
paenungulata) which include members from the
Proboscidea,
Sirenia,
Hyracoidea, and
Tubulidentata orders.
Commonly known examples of ungulates living today are the
horse,
zebra,
donkey,
cattle/
bison,
rhinoceros,
camel,
hippopotamus,
goat,
pig,
sheep,
giraffe,
deer,
tapir,
antelope, and
gazelle.
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) don't possess most of the typical morphological characteristics of ungulates, recent discoveries have suggested that they're 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 isn't necessary, as it's 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's dental as well as genetic evidence supporting this interpretation. Some recent studies link Tubulidentata with the Paenungulata in the
Pseudoungulata. 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.
Another characteristic of most ungulates is the fusion of the front forelimbs. In ungulates, the
radius and
ulna are fused along the length of the forelimb. This is a trait of most modern ungulates, as early ungulates, such as the
arctocyonids didn't share this unique skeletal structure. The fusion of the radius and ulna prevents an ungulate from rotating its forelimb. Since this skeletal structure has no specific function in ungulates, it's considered to be a homologous characteristic that ungulates share with other mammals. This trait would have been passed down from a common ancestor.
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.
This is the family tree of the ungulates (notice below, it's excluding the paenungulates, but including the whales and the South American ungulates, and the common ancestor, as some scientists believe).
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're not related to other ungulates.
The orders of the extinct South-American ungulates, which arose when the continent was in isolation some time during the mid to late
Paleocene, are united in the super-order
Meridiungulata. They are by some thought to be unrelated to the other ungulates. Instead, they're 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's 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's no morphological evidence to split the ungulates up into so many unrelated clades.
Further Information
Get more info on 'Ungulate'.
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