Hippopotamus
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Pod of hippos, Luangwa
Valley, Zambia |
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Scientific classification |
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Binomial name |
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Hippopotamus amphibius |
The Hippopotamus (Hippopotamus
amphibius), from the Greek ‘ιπποπόταμος (hippopotamos, hippos
meaning "horse" and potamos meaning "river"), is a
large, plant-eating African mammal, one of only two extant, and three or four recently
extinct, species in the family Hippopotamidae.
Hippopotamuses (hippopotami
is also accepted as a plural form by the OED), also sometimes called hippos,
are gregarious, living in groups of up to 40 animals, called a pod, herd,
school or bloat. A male hippopotamus is known as bull, a
female as cow, and a baby as calf. A hippo's lifespan is
typically 40 to 50 years. Female hippos will reach sexual maturity at 5 to 6
years, and have a gestation period of 8 months.
Hippos average 3.5 meters
(11 ft) long, 1.5 m (5 ft) tall at the shoulder, and weigh from
1500 kg to 3200 kg (3,300 to 7,000 lb). They are approximately the
same size as the White Rhinoceros, and experts are split on which is the next
largest land animal after the elephant. Male hippos appear to continue growing
throughout their lives, whereas the females reach a maximum weight at around
the age of 25. Females are smaller than their male counterparts, and normally
weigh no more than 1500 kg. The value given above of 3200 kg is often
quoted as being the upper limit of weight for a male hippo. However, larger
specimens than this have been documented, including one which weighed about
10,000 lb (4,500 kg) and measured about 16 feet (5 m) long. Their
skin weighs a ton, it is 4cm thick, bullet-proof and accounts for 25% of their
weight. Even though they are bulky animals, hippopotamuses can run faster than
a human on land. There are estimates of their running speed varying from
30 km/h (18 mph) to 40 km/h (25 mph), or even 50 km/h
(30 mph). The hippo can maintain these higher estimates for only a few
hundred metres or yards.
A
hippopotamus' teeth are used for eating and for defense
The eyes, ears, and
nostrils of the hippo are placed high on the roof of the skull. This allows
them to spend most of the day with the majority of their body submerged in the
waters of tropical rivers to stay cool and prevent sunburn. Indeed apart from
whales and dolphins, hippos are the only other mammal that gives birth under
water. For additional protection from the sun, their skin secretes a natural sunscreen
substance which is red-colored. This secretion is sometimes referred to as
"blood sweat," but is neither blood nor sweat. This secretion starts
out colorless and turns red-orange within minutes, eventually becoming brown.
There are two distinct pigments
that have been identified in the secretions, red and orange. The two pigments
are highly acidic compounds. They are known as red pigment hipposudoric acid
and orange one norhipposudoric acid. The red pigment was found to
inhibit the growth of disease-causing bacteria, lending credence to the theory
that the secretion has an antibiotic effect. The light absorption of both
pigments peaks in the ultraviolet range, creating a sunscreen effect. Hippos
all over the world secrete the pigments so it does not appear that food is the
source of the pigments. Instead, the animals may synthesize the pigments from precursors
such as the amino acid tyrosine. (Saikawa, et al., 2004)
As indicated by the name,
ancient Greeks considered the hippopotamus to be related to the horse. Until
1985, naturalists grouped hippos with pigs, based on molar patterns. However
evidence, first from blood proteins, then from molecular systematics, and more
recently from the fossil record, show that their closest living relatives are cetaceans
– whales, porpoises and the like .[1] Hippopotami have
more in common with whales than they do with other artiodactyls (even-toed ungulates),
such as pigs. Thus, the common ancestor of hippos and whales existed after the
branch-off from ruminants, which occurred after the divergence from the rest of
the even-toed ungulates, including pigs. While the whale and hippo are each
other's closest living relatives, their lineages split very soon after
their divergence from the rest of the even-toed ungulates.