|Ruminants - so named for their habit of ruminating or "chewing the cud"
(regurgitating and rechewing their food) - are considered to be the most
advanced artiodactyls, and they are certainly the most numerous and widespread
of the world's modern-day ungulate fauna. Their great success is due to a
very specialized digestive tract, which allows these ungulates to thrive
on relatively poor vegetation.
Learn more about the process of rumination HERE
All ruminants have a four-chambered stomach. The dental formula is generally I 0/3, C 0/1, P 3/3, M 3/3 x 2 = 32, although in members of the Tragulidae, Moschidae, and some Cervidae the upper canine may be present (total teeth 34). The cheek teeth have selenodont (crescent-shaped) ridges, which grind food efficiently with the side-to-side chewing motion characteristic of this group. The bones in the feet (metapodials) are fused to form a cannon bone, although in Hyemoschus (Tragulidae) this does not occur until after maturity. The navicular and cuboid bones are always fused. Only the third and fourth digits are well developed; the second and fifth are vestigial or absent.
Within the Ruminantia, two infraorders are recognized:
The infraorder Tragulina displays several ancestral characteristics (notably a lack of fusion of the limb bones until adulthood and a poorly-developed omasum), and the chevrotains probably resemble the ancestors of the other ruminants. The Pecora are a much more diverse group, all of which have an advanced ruminating stomach. All members of the Pecora display cranial appendages (except for two genera: Hydropotes and Moschus), but this characteristic has evolved independently among the different Pecoran families.
The basal divergence between the Pecora and Tragulina is well-supported by morphological and molecular evidence. All six of the ruminant families are accepted as monophyletic, but the interrelationships within the infraorder Pecora are still controversial and under review. Different analyses have arrived at vastly different relationships between the five modern Pecoran families; this phylogenetic instability is likely the result of rapid diversification in the late Oligocene and early Miocene, and is compounded by parallel evolution within the groups (e.g., the evolution of cranial appendages and the loss of upper canines). Although the family tree shown below is a general consensus, recent studies have suggested that the Moschidae may ally more closely with the Bovidae than the Cervidae.
(Hernandez-Fernandez and Vrba, 2005; Price, Bininda-Emonds, and Gittleman, 2005)
or jump to the Ruminantia Species List