Two living suborders:
tapirs and rhinoceroses.
There is also a third, now extinct, suborder-
(Ý denotes an extinct group).
Perissodactyls are characterised chiefly by:
- mesaxonic feet
(line of symmetry down third digit);
- a full set of
- greatly molarised pre-molars.
They were once a very
widespread and diverse group, but have been on the wane since the
late Miocene as the artiodactyls have prospered.
This suborder was very successful in the Eocene and
Oligocene, when there were several different families of rhinoceroses
and tapirs. Today there are only two families.
FAMILY TAPIRIDAE: THE TAPIRS.
A Brazilian tapir
terrestris). Note the short
All four living tapirs belong to the genus
Tapirus, an ancient
taxon present in the northern hemisphere at least 20MY ago. The
primitive features of the tapir demonstrate its antiquity. Digit
reduction has only taken place on the hind feet - despite being
mesaxonic the forefoot still has four toes. The legs are short and
the body is heavy with a curved back. Compare the body shape with
that of the peccary (Order Artiodactyla, Family Tayassuidae). Both
have converged on a similar body shape as a result of their sharing a
similar lifestyle and habitat.
Today, tapirs are found only in South East Asia (the
Malaysian peninsula and the island of Sumatra) and in parts of South
and and Central America. The remaining range of this genus is a
relict of a distribution that once encompassed the northern
The Tapiridae as a whole were once very diverse. In
the early Tertiary a variety of forms evolved in Asia before being
superseded by the artiodactyls. These included horse-like and
Tapirs are usually found in forested habitats and
rarely far from water. Their diet includes fruit, leaves, buds and
grass, collected by their prehensile proboscis. The tapir's teeth are
also specialised - most of the pre-molars are molarised, and the
molars are quite high-crowned with crests. A diastema is
The presence of the nasal bones midway up the face
indicates the presence of a proboscis. This allows the evolution of
the proboscis in extinct tapirs to be traced.
The striking colouration of the Malayan tapir and the
coarse manes of the Amazonian and Baird's tapir are anti-predator
Tapirs are hunted for their skins, their meat and for
sport. However, undoubtedly the biggest threat to their future is the
destruction of their habitats.
A Brazilian tapir with
calf. Note the cryptic colouring of
the calf. The stripes and spots help to break up its outline
in the forest. Infant tapirs of all four species are
coloured like this, regardless of their colour as an
FAMILY RHINOCEROTIDAE : THE RHINOCEROSES.
A black rhinoceros
bicornis) from Africa. This species
is highly endangered and will probably be extinct shortly
after the turn of the century.
There are 5 types of living rhinoceroses - 2 in Africa and 3
in south Asia. All are currently at risk of immediate extinction
except perhaps the white rhino which is protected in South Africa.
Rhinoceroses have been hunted for centuries for the supposed
medicinal effects of the horn (pharmacologically unproven) and to
make horn-handled daggers in the Yemen.
The plight of the rhino is not helped by their
solitary lifestyle. Indian rhinoceroses of both sexes live in a home
range containing all necessary resources and are hostile to other
members of the same sex.
The skull of the Indian rhinoceros shows high
crowned, crested molars associated with a browsing/grazing habit. The
Indian rhino eats mostly short grass, also browses with its
prehensile lip. Unlike African rhinoceroses, incisors are present.
Only Sumatran rhinoceroses have canines. Heavily built, the skull
would carry a large horn made of keratin, not bone, attached to a
roughened area on the skull.
The head of the white rhinoceros, from
Africa, shows the massive horns.
Rhinoceros limbs are mesaxonic, like all
perissodactyls, and show little reduction in the number of digits -
adapted as they are more for supporting the rhinoceros' huge weight
rather than making it fleet of foot. Despite this, African white
rhinoceroses have an impressive turn of speed.
Two white rhinoceroses lying down. Although
the skin of the rhinoceroses looks very thick it is actually
quite thin and sensitive. Rhinoceroses look after their skin
by taking frequent 'mud-baths'.
The earliest rhinoceros,
Hyrachyus, was similar
the first horse and probably did not look too different to the hyrax
of today. Extinct rhinoceroses include
largest land mammal ever, but rhinoceroses similar to today's
probably appeared in the Miocene epoch.
There were once three families in this suborder, of
which only the equids (horses) have survived. The other two died out
over 30 million years ago.
Equids: The earliest horse, Hyracotherium, was remarkably similar to the earliest rhinoceroses and titanotheres.
The earliest perissodactyl cannot have been much different. The
evolutionary history of the horses is very well understood. A clear
lineage can be traced through the fossil record from
Hyracotherium to the
modern horse, Equus.
There were many 'side-branches' to this lineage of other grazing and
Eocene/early Oligocene group of huge rhinoceros-like beasts, were
driven to extinction by the rhinoceroses themselves who possessed
less primitive teeth and were better able to adapt to a grazing
habit. Unlike the rhinoceroses, the titanotheres had horns made of
bone covered in skin.
closely related to the horses, this predominantly European group of
perissodactyls may well have evolved from Hyracotherium. In the
absence of tapirs the palæotheres became medium-sized, robust
browsers. Parallel evolution even led to the evolution of a short
proboscis similar to that found in
A plains zebra
burchelli) and foal.
There are seven members currently found in this
family, all genus
Equus : the domestic
horse, wild horse, 3 zebras and two asses.
A domestic horse
The family is typified by large, long heads on long
necks and slender legs. Horses are very much a product of the
grasslands. Their dentition copes with the silica found in grasses
and their unguligrade limbs allow swift travel across the plains.
As hindgut fermenters, horses can live on poorer
forage than ruminants. The higher throughput rate allows more to be
taken. However, large quantities must be eaten - about 16 hours a day
are spent foraging.
Except for the plains zebra all the wild horses are
rare. Preszwalski's horse is found only in zoos, and is vulnerable to
genetic dilution as a result of interbreeding with domestic
XH18-1.16 Equus burchelli (Zebra)
All members of the genus have similar skulls - a deep
lower jaw; upper and lower incisors; a long diastema; high crowned,
ridged pre-molars and molars; eyes far back in the skull providing
binocular vision and a wide field of view.
A herd of zebra, East
Two families: the advanced Chalicotheriidae and the
more primitive Eomoropidae (the latter intermediate between the
chalicotheres and the most primitve perissodactyls).
Chalicotheres: an unusual family of ungulates with
claws instead of hooves. They had primitive teeth, but were
horse-like aside from their elongated front limbs. Although never
very abundant, these strange animals were fairly successful. Prior to
their extinction barely 12,000 years ago the chalicotheres had been
relatively unchanged for the previous 25 million years.
The claws are often thought to indicate a diet of
roots and underground plant parts, but there is no evidence that the
feet were used for digging. The fairly long neck of the chalicotheres
and their long fore arms to help raise the head and shoulders suggest
that they were browsers.