Cervidae

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The Cervidae first appear as fossils in the early Miocene of Asia, where they expanded into a wide variety of niches (and were thus able to dominate over the bovids which arrived later). During the Miocene, members of this family migrated to North America. After expanding in the Nearctic region, deer crossed to South America during the Pleistocene, when the Panama land bridge formed.

Antlers are the defining characteristic of this family: all but one species (Hydropotes inermis) possess these cranial appendages, and they are found in no other animal. Unlike the headgear of other Pecorans, antlers are composed entirely of bone and often have elaborate branching patterns. The antlers grow from an extension (the "pedicel") on the skull's frontal bone, joining to the skull in a suture known as a burr. The sutures holding the antlers to the deer's head decalcify on an annual basis (under hormonal control), causing the antlers to fall off (usually in the late fall or early winter in temperate species). After shedding, the antlers soon begin to regrow. During the growth period, the expanding bone is covered with a thin layer of fuzzy skin known as velvet, which helps protect the growing tissue. Because the entire antler is alive, growth is not limited to the base (as in horns) which results in branching patterns which are often species-specific. Unlike the horns of bovids, the regular shedding of antlers makes them a current marker of an animal's status: their size and shape are in direct correlation to age and dominance. In the vast majority of species, antlers are borne only by males - only in the reindeer, Rangifer tarandus, do females regularly grow antlers.

Males of a few species possess enlarged, tusk-like upper canines (Hydropotes, Muntiacus, Elaphodus). In other species the upper canines are either vestigial or absent. The dental formula is thus I 0/3, C 0-1/1, P 3/3, M 3/3 x 2 = 32-34. The molars are selenodont, and usually brachyodont. There are usually two lacrimal canals. Females usually have two pairs of mammae, and the young of most species are spotted. There is no gall bladder.

The Cervid Family Tree

Hydropotinae

Capreolinae

Cervinae

There are 55 species in this family, and they are found in all parts of the world, except for Sub-Saharan Africa, Australia, and Antarctica. The species in this family are found in a wide variety of habitats including forests, grasslands, and on the tundra. All of the species in this family are herbivores and ruminants. They chew their food, swallow it, regurgitate it, and then swallow it again. Their stomachs have four chambers. The first chamber is called the rumen. 

The rumen has bacteria in it that helps break down plant matter. Members of this family have long legs with two toes on each of their their hoofed feet. They have long heads and short tails. In most species, the male has antlers. The species in this family range in size from the tiny Andean Pudu, which is only 16 inches tall and weighs 22 pounds to the largest member of the family, the moose, which can be 7 feet tall and can weigh 1,600 pounds. In North America, there are two subspecies of deer on the endangered species list. The key deer is a subspecies of the white-tailed deer. It is a small deer found only in the Florida Keys. The Columbian white-tailed deer is also a subspecies of the white-tailed deer. It is found in the Columbia River basin of Washington and Oregon

Internal relationships

A 2006 phylogenetic study of the internal relationships in Cervidae by Clément Gilbert and colleagues divided the family into two major clades: Capreolinae (telemetacarpal or New World deer) and Cervinae (plesiometacarpal or Old World deer). Studies in the late 20th century suggested a similar bifurcation in the family. This as well as previous studies support monophyly in Cervinae, while Capreolinae appears paraphyletic. The 2006 study identified two lineages in Cervinae, Cervini (comprising the genera Axis, Cervus, Dama and Rucervus) and Muntiacini (Muntiacus and Elaphodus). Capreolinae featured three lineages, Alceini (Alces species), Capreolini (Capreolus and the subfamily Hydropotinae) and Rangiferini (Blastocerus, Hippocamelus, Mazama, Odocoileus, Pudu and Rangifer species). The following cladogram is based on the 2006 study

Cervidae

Cervinae Muntiacini   Reeves's muntjac     Tufted deer      Cervini       Fallow deer      Persian fallow deer             Rusa     Sambar          Red deer      Thorold's deer     Sika deer           Eld's deer     Père David's deer             Barasingha       Indian hog deer     Chital           Capreolinae Rangiferini   Reindeer (Caribou)          American red brocket        White-tailed deer      Mule deer            Marsh deer     Gray brocket     Southern pudu      Taruca          Capreolini   Roe deer      Water deer      Alceini Moose or Eurasian elk

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

Ruminantia	Tragulina Tragulidae    Pecora   Antilocapridae      Giraffidae        Cervidae        Bovidae      Moschidae