Odd-toed ungulates: horses, tapirs and rhinoceroses
To the odd-toed ungulates belong three famlies of quite different
animals. These are the horses, donkeys and zebras (together called
equus on this page); the tapirs that resemble pigs, and the
rhinoceroses. They have a common feature, i.e. their odd number of
toes: horses have 1, rhinoceroses 3 and tapirs have 4 on their forelegs
and 3 on their hind legs. They are all hind gut
fermenters; digestion is for a large part behind the stomach.
All animals have large ears. 7 species
of equus, 4 tapirs and 5 rhinoceroses are distinguished.
On the page horse - pig - cow
the horse is discussed in detail. Horses, donkeys and zebras resemble
each other in many ways. Horses, donkeys and zebras are trotting
animals with long legs. Zebras populate the plains of Africa in
large numbers, horses come from the plains of Asia and Europe and
donkeys live in small herds in the semi-deserts of Asia and Africa.
They are closely related and can interbreed (a
horse and a donkey produce a mule, a zebra and a horse a hebra or a
zorse), but the offspring is infertile.
Horses and donkeys have been domesticated, which did not succeed with
zebras. There is much internal aggression with zebras,
which is why they cannot be kept. Moreover, they accept no
leader, especially when it is not a zebra. In imminent danger horses
flight headlong. Donkeys stay where they are until they have analysed
the (dangerous) situation and chosen the best escape route.
This is important because a donkey cannot run as fast as a horse. When
the danger is not great (just a door slamming or something
that glimmers in the sun) the donkey stays where it is. Is the
danger real then it runs away. Donkeys put their feet down with more
confidence than horses. Horses accept orders, donkeys need
to be asked.
Tapirs look like big pigs with long legs. They live in the tropical
rainforest, mostly in the neighbourhood of water like rivers and
swamps. They spend much of their time in the water and are excellent
swimmers. When threatened, some species go into the water and they
can dive and stay under for some minutes, others dive into the
vegetation and defend themselves by biting. The Indian tapir can walk
on the bottom of a river, just like the hippopotamus. Tapirs may
copulate in - or out of the water. They are especially active
during the night. Tapirs are solitary animals.
In the water the digestive activity increases and tapirs let their
faeces drop in or next to water, again, just like hippopotamuses. They
are good climbers of steep banks and mountain slopes. Tapirs follow
fixed paths, which they mark with urine.
Brazilian or Lowland tapir with offspring
Mountain tapir - overview
Rhinoceroses live mainly solitary. The big white rhinoceros is the most
social species living in small groups. The Asiatic species can
behave aggressively, whereas the African species try to avoid contact.
Especially the white rhinoceros is a good-natured and introverted
animal. The black rhinoceros may charge at people when it smells them,
to stop a few meters before them, because then it suddenly
sees what it was charging at.
In areas where rhinoceroses live, dungheaps lie along the paths the
animals use. They let some droppings fall every time they pass. Even
when they are fleeing, they take some time for that procedure.
All horses, donkeys and zebras have the same bodyshape: the head is
high, the neck is long with a mane and the legs are long, straight and
slender. The hind part is somewhat higher
then the middle of the back. There are some differences: horses have a
relatively heavy head and the neck is thicker.
Wild donkeys are less heavy than the Przewalski horse, but
just as long. Compared
to the Przewalski horse, donkeys are also more slender,
which applies to the neck as well. It seems as if the head is kept
higher. The legs are a bit longer and the legs are straighter.
The mane of the donkey is relatively shorter.
The zebra has shorter legs than the horse and the body is more
thick-set, it seems more massive. Its body is longer than the
horse's body and weighs less (with the exception of the
Grevy-zebra). The head is longer and more slender than the
horse's. The mane is longer than the donkey's.
The mane of the zebra is harder and stiffer than that of the
donkey and softer and thinner than that of the horse. From donkey via
zebra to horse, the mane goes from soft to hard, from flexible to stiff
and from thin to thick.
Tapirs look like big pigs with long legs. Their body is massive and
thick-set; the back is a bit higher than the shoulders. The backline is
arched. There is no distinct neck, but there is some transitional form
from body to head. The body is agile and mobile. Tapirs are
about 2 meters long and 1 meter high and weigh 225 to 300
kilos. Some species have a mane in the neck.
The legs are short and stout (compared to horses). The front legs have
4 and the hind legs have 3 toes, of which 1 has grown bigger. All toes
have hooves and each foot has a callous cushion, that supports part of
the weight; they do not walk on the hooves only.
The upperlip is developed into a short, fleshy, prehensile proboscis,
with which they sniffingly seek their way through the rainforest and
pull twigs towards them.
Rhinoceroses (800 – 3500 kilo) have a big elongated body.
They are up to 4 meters long and 2 meters high. The body seems
especially long. The bigger species have a high shoulder and the
anterior part of the body is higher than the posterior part. The neck
is rather long and thick. The head is heavy and measures up to 1/3 of
the total body length. The head is kept low and is under the backline.
While walking, the mouth is only a few centimeters from the
ground. The skin is thick and hairless with most species.
The skin of the Indian rhinoceros makes huge creases over its body, as
if it is armoured.
The legs are short and muscular and have 3 hooves. The middle hoove is
larger than the other two and carries most of the weight. Despite their
weight and short legs, they can run up to 50 km per hour.
On the head, in the middle behind the nose, is one horn.
The biggest species even have two horns behind each other. The anterior
horn can be as long as 1.5 meters, de posterior stays shorter. Horns
are made of keratin, a formation of the epidermis, which also makes
nails and hair. Horns keep growing during
the rhinoceros's whole life. If cut off, they grown back on again.
A horse is
uniformly brown, the underside is lighter. The colour of donkeys is
lighter than that of horses with more white on the underside
and farther up on the sides with a clear boundary. Both have a white
area around the mouth. Donkeys may have stripes on their legs.
Zebras are striped. Only the Grevy-zebra has stripes on the
underside as well.
a tough skin with short light- to dark-brown hair. The Indian tapir is
Young animals are born with horizontal stripes, like wild boar.
are solid grey. The skin is very thick (1.5 - 5 cm) and bald.
eat young, highly nutricious grass and leaves. They bite it off with
their chisel-like incisors. They eat 60-80% of the day.
are grazers and
browsers. They eat grass, waterplants, leaves, buds and fruit. In the
same way as horses, they bite off grass. They remove leaves from twigs
by pulling the twig along their teeth with their proboscis.
Sometimes they eat animal food. They go for hours along well-known
paths through the vegatation with their proboscis to the ground,
searching for food.
live from grass (white and Indian rhinoceros) and branches with leaves
(black and Javan rhinoceros) and sometimes fruit (Sumatran rhinoceros).
They eat approx. 2% of their body weight in dry matter per day, that is
100 to 120 kilos, and they drink about 100 liters a day.
have a big blind gut (cecum) and colon (large intestine) for the
fermentation of their food. The digestive tract is 15 x their body
have a smaller blind gut, they digest their food in the large intestine
digest their food in the colon. The white rhinoceros has a small cecum
and an enlarged large intestine (colon). The digestive tract
is 9 - 10 x its body length.
have large incisors, mares have no canines, stallions small canines.
Male zebras have pointed canines. The molars are big and ridged.
The teeth of tapirs
resemble those of horses, but are not specialized for grazing. The
teeth are low-crowned. The incisors are
chisel-like, the outer upper incisors are long and the canines are
conical, relatively long (compared to horses) and stand close to the
The big rhinoceros
species lack incisors and canines. The Asiatic species do have
incisors, but nor canines, and the Sumatran rhinoceros has both
incisors and canines. All species have large molars.
have larger eyes
and longer ears than horses. They taste small differences in food. The
ears of zebras are rounder than horses' ears. All species
have a sensible skin.
The sense of smell of Tapirs
is good, their hearing is somewhat less developed. The eyes
are small and their vision is badly developed.
have a bad
vision. At a distance of 30 meter they are not able to see an upright
person. Because their eyes are at the sides of their head, they have to
turn their head to see what is in front of them. Hearing is well
developed. They can locate where sounds come from by directing
their movable, funnel-shaped ears. The skin is not very sensible. The
most important sense organ is the nose, their sense of smell is good.
In the group of the odd-toed ungulates the equus-species are
the animals with the long, straight limbs. They have the most
specialized legs, with only one hoof. They are animals
of plains that trot and run a lot. They eat young, relative
rich grass, that is bitten off with their chisel-like incisors. They
have large senses, too. Equus have the most powerful lower jaw (which
is the limbs part of the skull (see here for an explanation)).
Of these animals the donkeys
have a white underside, the largest senses, they can taste food well
and they seem to observe
and analyse a situation before they do something. They
have the most developed nerve-sense system.
cannot be kept, behave aggressively, the males have sharp
canines. They have the characteristics of the heart-lung system. That
could explain their stripes, too (as stripes and
dots on the fur is a characteristic of carnivores and
heart-lung animals in general).
have a less white underside. They are sturdier. Horses and donkeys
are able to learn. Horses have the characteristics of the
Tapirs resemble pigs in body-characteristics and behaviour; they have a
plump body and a prehensile proboscis. They have relatively big canines
and eat, besides grass and leaves, fruit and sometimes meat. The young
Rhinoceroses are enormous animals with a length up to 4 meters and a
weight to 3500 kilos. They have a long body with a long head, which is
lower than the backline. The senses are small and the eyes are badly
developed. They eat great quantities of nutrient low grass.
- The equus-species are the nerve-sense animals of this
group (head is high above the backline, big senses, can learn, long
legs, eat relatively nutricious, young grass).
- The tapirs are the heart-lung animals with their
pig-like appearance, relatively large canines, their diet with some
fruit and meat and striped young.
- The rhinoceroses are the metabolic-limbs animals with
their massive, long body, head kept low, not very well
developed senses and low-quality food.
The equus-species have developed their limbs most. The
rhinoceroses have developed their metabolism most. It seems as if the
process of the limbs (which gives straight, long forms) works in the
entire body of the rhinoceroses, and has an elongated form as a result.
long legs, head high
||stocky, head on a
level with backline
||big, long body, head
long en low, horns
||long and massive
||incisors and canines
||most species no
incisors, big molars
fruit, some meat
||curious, can learn
||1 striped young
||sees badly; smell,
of odd-toed ungulates
Zebra: a striped and aggressive horse
Tapir: pig-like with its short proboscis and long legs
A white rhinoceros: a massive animal of 3500 kg
and a length of 4 meters
The kiang, the Asiatic donkey, the white of the belly is not limited to
The African ass (light colour, white underparts, stripes on the legs)
with a foal
A striped young of a tapir
A Sumatran rhinoceros with young
The skull of a horse with the powerful and long lower jaw
The skull of a tapir: chisel-like incisors and a relatively
large canine before the diastema
The skull of a white rhinoceros: two big horns on the nose and big
molars; the canines and incisors are lacking
The toes and hooves of a tapir: 4 front and 3 behind
The armoured skin of a rhinoceros
A Malayan tapir: black and white
Zebras and wildebeest at the plain of the Ngorongoro Crater
Two white rhinoceroses