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Pecora is an infraorder of with digestion. Most members of Pecora have cranial appendages projecting from their ; only two extant genera lack them, and . The name "Pecora" comes from the Latin word pecus, which means "cattle".Bubenik, A. Epigenetical, Morphological, Physiological, and Behavioral Aspects of Evolution of Horns, Pronghorns, and Antlers. in Horns, Pronghorns, and Antlers. G. Bubenik and A. Bubenik eds. Springer-Verlag. New York. 1990 Although most pecorans have cranial appendages, only some of these are properly called "horns", and many scientists agree that these appendages did not arise from a common ancestor, but instead evolved independently on at least two occasions.Janis, C., K. Scott. The Interrelationships of Higher Ruminant Families with Special Emphasis on the Members of the Cervoidea. American Museum Novitates. 2893: 1-85. 1987. http://digitallibrary.amnh.org/dspace/handle/2246/5180 Likewise, while Pecora as a group is supported by both molecular and morphological studies, morphological support for interrelationships between pecoran families is disputed.


Evolutionary history
The first fossil appeared in the and were small, likely , forest-dwellers. Molecular dating studies estimate that split into the two Pecora and around 45 million years ago, during the . However, it was not until 15 million years later, at around 30 million years ago during the , that the evolutionary radiation of Pecora began and the five families appeared (, , , , and ).

The appearance of many Pecoran fossils during the suggests that its rapid diversification may correspond to the climate change events of that epoch, as this time period was marked by much of Earth's forest habitats being replaced by grasslands due to widespread cooling and drying.

It is likely that the antelopes, giraffids, and pronghorns evolved in an open environment while the cervids, including the caribou, evolved in a woodland habitat. The type of gallop in Pecorian species is shown to be closely related to their environment and anatomy, where light Pecorian species use both flexed and extended suspensions in their fast gallops. The white-tail and mule-deer have been observed to primarily use the extended suspension, since in this phase of their gallop they leap over bushes and logs that are present in their brush environment. However, heavy Pecorian species do not use extended suspensions as most have backs that slope downward with shorter hind legs.


Taxonomy and classification
Pecora is an infraorder within the larger suborder , and is the to the infraorder (of which is the only surviving family).

Pecora's placement within can be represented in the following :(see e.g. Fig S10)

Current attempts to determine the relationships among pecoran families (as well as all artiodactyls) rely on molecular studies, as little consensus exists in morphological studies. Different families within Pecora are recognized as valid by different groups of scientists.and sources therein, pp. 4–5

Until the beginning of the 21st century it was understood that the family (musk deer) was to . However, a 2003 study by Alexandre Hassanin (of National Museum of Natural History, France) and colleagues, based on and nuclear analyses, revealed that and form a sister to . According to the study, Cervidae diverged from the Bovidae-Moschidae clade 27 to 28 million years ago. The following is based on the 2003 study.

Infraorder Pecora ("horned ruminants", "higher ruminants")


Anatomy
Pecorans share characteristics with other artiodactyls, including a four-chambered stomach, and a paraxonic foot, meaning that it supports weight on the third and fourth digits. Several characteristics distinguish Pecora from its sister taxon, : an with parallel sides, a loss of the trapezium, and differences in parts of the skull such as the petrosal bone.

The distinguishing features of most pecoran families are cranial appendages. Most modern pecorans (with the exception of the ) have one of four types of cranial appendages: horns, antlers, ossicones, or pronghorns.

  • True horns have a bone core that is covered in a permanent sheath of . They are indicative of Bovidae. Horns develop in the over the frontal bone, and can be curved or straight. Surface features on the keratin sheath (e.g., ridges or twists) are thought to be caused by differential rates of growth around the bone core.
  • are bony structures that are shed and replaced each year in members of the family . They grow from a permanent outgrowth of the frontal bone called the pedicle. Antlers can be branched, as in the white-tailed deer ( Odocoileus virginianus), or palmate, as in the moose ( ).
  • are permanent bone structures that fuse to the frontal or parietal bones during the lifetime of an animal. They are found only in the and closely related extinct clades, represented in modern animals by the giraffe ( Giraffa camelopardalis) and the okapi ( ).
  • are similar to horns in that they have keratinous sheaths covering permanent bone cores; however, these sheaths are deciduous and can be shed like antlers. Very little is known about the development of pronghorns, but they are generally presumed to have evolved independently. The only extant animal with pronghorns is the pronghorn antelope ( Antilocapra americana).


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