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The Antilopinae is a diverse assemblage of small and medium-sized antelopes
native to open, arid environments in Africa and Eurasia. While widespread
in Africa, this subfamily also has a dozen species spread across Eurasia
(only one other Aegodontia subfamily remains successful outside of Africa).
The Antilopinae arose 17-16 million years ago; the first fossils appear
in Eurasia, with evidence in African deposits beginning 13.5 million years
ago.
Several features unite the species within this group, notably the skull
structure, dentition (closely resembling fossils from 12 million years ago),
and presence of solid horn cores. The preorbital glands are well developed
in most species: they are composed of a spherical mass of glandular tissue
located in front of each eye. These glands secrete a sticky black substance
which is carried by a central duct to a circular patch of bare skin. The
opening of this duct is covered by a purse-like fold of skin which can be
opened wide during the deposition of secretions.
There are two traditionally recognized tribes, each of which is discussed
separately below:
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Antilopini - gazelles and relatives
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Neotragini - dwarf antelope
The Antilopini (gazelles) are medium-sized bovids which are highly evolved
for a cursorial (running) existence in open environments. There is
little sexual dimorphism in body size or coloration. Horns are generally
present in both sexes of this tribe, but they are lacking in females of some
genera. There are often striking markings on the face, flanks, and/or
rump. The mating system of all species is polygynous. The Antilopini
traditionally includes the genus Procapra. However, the three
species in this genus appear to be as different from the gazelles as they
are from the dwarf antelope - no new tribe has yet been ascribed to these
antelope.
The Neotragini have traditionally been grouped together on the basis of small
body size (all species weigh less than 30 kg); all genera also possess
"primitive" characteristics. However, following molecular analysis,
this classification seems to be erroneous. While most of the dwarf
antelope are closely related, the genera Neotragus and
Oreotragus, while clearly within the Aegodontia, do not have clear
evolutionary affinities with any subfamily, including the Antilopinae.
Indeed, it has been proposed that both of these genera are unique lineages,
and may have diverged from other bovids during the early Miocene. They
are shown in the phylogeny below as basal to the subfamily Antilopinae in
order to put this discussion into perspective: as of yet, there is no consensus
as to the names of their respective subfamilies. With the exclusion
of Neotragus and Oreotragus, the traditional tribe Neotragini
is now polyphyletic. Naming conventions have not yet been resolved
(can there be a Neotragini that excludes the genus Neotragus?), and
thus the classical names are still used here.
Neotragus is a primarily forest-dwelling genus, with a hare-like build
and backward-slanting horns (the preorbital glands lack a surface fold of
skin). Oreotragus is a specialized rock-dweller, inhabiting
kopjes and cliffs adjacent to savannahs. The remaining dwarf antelopes
(Dorcatragus, Madoqua, Ourebia, and Raphicerus,
which DO form a taxonomically-valid grouping) all inhabit relatively arid
environments (savannahs and scrub mosaic), and have several adaptations for
conserving water, notably nasal panting. All are selective feeders
and rarely (if ever) need to drink. Unlike the Antilopini, they often
form monogamous pairs. Short, vertical, spike-like horns are found
only in males (never in females). |
