Horses and zebras, members of the Equidae
family, share common anatomical traits such
as hard hooves, strong spinal columns, muscular
arching necks, sloping shoulders, wide hindquarters,
high-crowned teeth, slender legs, and elongated
heads. Size and coloration varies according
to specific horse breeds developed through selective
breeding. Similar differences in zebra species
have evolved due to natural selection and environment.
Horses and zebras are related to wild
asses and donkeys and represent five species of
the genus Equus.
Anatomy Development
Eohippus was the ancestor of both domestic and
wild horse species.Aleaf-eatingmammalas small
as a fox, Eohippus lived during the Eocene epoch
and had several toes on its feet. Descendants gradually
grew larger, lost toes, and became grass
grazers. Przewalski's horse, indigenous to Mongolia
but not seen in the wild since 1968, links
ancient and modern horses. Because it has sixtysix
chromosomes and domestic horses have sixtyfour,
Przewalski's horse is a separate wild horse
species and not an ancestor of modern horses.
A hybrid produced by a horse and a Przewalski
has sixty-five chromosomes and is fertile.
Modern horses and zebras are distinguished
by a single hoof on each foot. Vestigial remains of
prehistoric toes are located above hooves. Horses
and zebras have long skulls and jaws that hold approximately
forty to forty-four permanent teeth,
including incisors to bite grass and molars to
chew roughage. The teeth have long crowns that
slope with age and can be examined to determine
how old an animal is. Horses use their teeth to eat,
groom, and fight.
The horse's digestive system is bigger and
more efficient than that of carnivores, and has approximately
40 meters (131 feet) of intestines with
a meter-long cecum attached to the colon. Horses
and zebras live on grasslands ranging between
sea level and mountains and eat mostly fibrous
food such as hay, grain, and oats. Food ferments in
the cecum, which can hold as much as thirty-eight
liters (ten gallons). Horses eat an average of sixteen
hours per day to sustain their systems.
The average horse's heart weighs about 3 kilograms
(6.6 pounds), and the surface area of a
horse's lungs measures approximately 2,500
square meters (8,200 square feet). Horses' weight
varies from minimums of nearly 500 kilograms
(1,000 pounds) to maximums of more than 908 kilograms
(1 ton). Fifty-one vertebrae are in horses'
spines from the top of the skull to the base of the
tail.
Horses' eyes are placed on the sides of their
heads, enabling them to see the horizon without
moving their head. Their eyesight is better than
that of dogs. Horses depend on hearing more than
sight, but rely most on the sense of smell. The
flehmen response is when the horse raises its upper lip to indicate it has smelled something interesting.
Social Behavior
Depending on the age, female horses are called fillies
and mares, and males are colts, stallions, and
geldings. Horses attain sexual maturity at two to
three years old and usually produce a single foal
after eleven months of gestation. Multiple births
are rare, with twins occurring on average once per
1,500 births. Foals are able to stand within an hour
of birth. Stallions fight while competing for mares,
and one stallion may mate with several mares
during a season. Mares usually come into heat one
week after giving birth. Foals are weaned before
they are one year old.
Horses are herd animals and rely on this social
relationship, as well as on speed and endurance,
as protection from predators. Domesticated
horses enjoy the companionship of horses and
other animals.Wild horses form a family group of
one stallion, several mares, and their offspring.
Young stallions sometimes form a bachelor group
led by an older stallion. These groups forage in an
area where they can find food, water, and shelter,
and a pecking order maintains a hierarchy of rank
within the group. Several groups often share the
same range. Horses communicate by whinnying
and nickering.
Vulnerable to wild animals, horses can run an
average speed of forty-five to sixty kilometers
(twenty-eight to thirty-seven miles) per hour.
Their legs are slender and angled forward so that
their weight is carried forward to enhance quick
motion. Horses' shoulders absorb shock, while
their powerful hindquarters provide impulsion.
Horses naturally move at the gaits of
walk (four beat), trot and pace (two
beat), canter (three beat), and gallop
(an extended canter), with several
other natural gaits including pacing
and the running walk.
Appearance
Domesticated horses are described by
three types: heavy or draft, light, and
pony. Humans genetically developed
specific breeds for different tasks and
degrees of hardiness, stamina, and
versatility. Most horse breeds are derivatives
of Arabians and thoroughbreds.
Draft horses (often referred to
as cold-blooded, which is not physiologically
accurate), usually stand over
sixteen hands high at the withers (the
ridge between the shoulder blades)
and have sturdy, thick dimensions,
useful for pulling loads. Light horses,
sometimes called hot bloods, are at
least 14.2 hands high and tend to
be streamlined. Ponies are shorter
than 14.2 hands and vary in conformation
according to breed.Welsh ponies
tend to be more delicate, while
Shetland ponies are more rotund. Miniature
horses are extremely small ponies that are often
less than one meter tall.
Coat colors range from shades of brown and
red to solid black and white, with some horses,
such as Appaloosas and pintos, having spots and
others being gray or roan. Spotted patterns are
linked to genes that also often produce mottled
noses, eyelids, and genitalia, blue eyes, and
striped hooves. Lipizzans are born black and turn
completely white by age two years. Some horses
have dorsal stripes and zebra stripes on their legs.
Various white facial and leg markings also distinguish
horses.
African Cousins
Zebras belong to the horse family and are represented
by three species, the plains, Grevy's, and
mountain zebras. Several subspecies exist according
to geographic range, herd behavioral differences,
and physical variations such as dewlaps.
Zebras are smaller than horses and have erect
manes, longer ears, and thinner tails. The average
zebra stands 140 centimeters (55 inches) high and
weighs 300 kilograms (660 pounds). These striped
animals exist in herds that graze in southeastern
Africa's grasslands and also live in nearby
deserts.
Each zebra species is determined by a specific
stripe pattern of black, brown, and white markings.
Individual zebras have unique striping
somewhat like the uniqueness of human fingerprints.
Scientists have determined that zebras,
fromthemomentof birth, are drawn to striped objects,
a type of imprinting which has led to speculation
that stripes might be a factor in herd cohesiveness
and sociability. Previous hypotheses that
stripes are for camouflage and to confuse predators
have been discredited. The exact purpose of
stripes remains a scientific mystery. Researchers
are aware that abnormally striped zebras are often
shunned by herds, which threatens their survival.
Herds can include several zebras, often a male
and females with their offspring or a group of
young males. Herds can expand to hundreds of
zebras. Typically passive animals, male zebras occasionally
fight for females during breeding season
by kicking, biting, and shoving each other. Female
zebras attain sexual maturity at age three
and usually reproduce annually throughout their
lives, while males reach breeding age at five years.
Gestation lasts approximately eleven to thirteen
months, and twins are rarely foaled. The life span
of wild zebras can extend to twenty-two years,
and zebras kept in captivity can live longer.
Zebra foals weigh approximately thirty-two to
thirty-six kilograms (seventy to eighty pounds) at
birth. Able to stand soon after being born, zebra
foals eat grass which adds about 0.45 kilograms
(1 pound) of body weight per day until they reach
physical maturity. Zebra foals develop more
quickly than horse foals and become independent
sooner.
Defense Mechanisms
The herd protects zebras from predators, primarily
large cats, such as lions and cheetahs, in addition
to hyenas. Humans also hunt zebras for their
hides. While other zebras sleep, a guard zebra
watches for potential hazards and is aided by its
keen night vision, comparable to an owl's, and tall
ears which can rotate to pick up sounds. Zebras'
primary defense mechanism is to run away from
danger, and they can reach speeds as high as sixtyfive
kilometers (forty miles) per hour, which is
much slower than most of their enemies.
Zebras also are at risk from reduced water resources
and grasslands due to ranching and farming
and compete with livestock for basic nutritional
needs. While the common zebra remains
abundant, the Grevy's zebra and the mountain zebra
are considered endangered species and another
type of zebra, the quagga, became extinct in
1883.Acentury later, the Quagga Breeding Project
attempted to revive the quagga because genetic
researchers determined that quagga and plains
zebra deoxyribonucleic acid (DNA) was similar,
and hypothesized that the quagga was not a separate
species but rather a variation of the plains zebra.
Zebroids are horse-zebra hybrids that are
sterile.
Classification:
Kingdom: Animalia
Subkingdom: Metazoa
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Subclass: Eutheria
Order: Perissodactyla
Suborder: Hippomorpha
Family: Equidae
Genus: Equus
Subgenera: Equus (horses), Asinus (asses), Hippotigris (zebras),
Dolichohippus (zebras)
Species: Equus przewalskii (Przewalksi's horse), Equus caballus
(domestic horse), Equus africanus (African ass), Equus
hemionus (Asiatic ass), Equus burchelli (plains zebra), Equus
zebra (mountain zebra), Equus grevyi (Grevy's zebra)
Geographical location: Horses can be found on all continents
except Antarctica; zebras live in southeastern Africa
Habitat: Grasslands in tropical, temperate, and subarctic regions
Gestational period: Eleven months for horses; thirteen months
for some zebras
Life span: Tento twenty-five years,upto thirty-five in captivity
Special anatomy: One-toed feet, high-crowned teeth
Copyright © 2014 Animalia Life | All rights reserved