This is a brief overview of the type of zoogeographic distributions of animals, such as cosmopolitan, discontinuous, endemic, isolated, and bipolar distributions.

1. SYED MUHAMMAD KHAN (BS HONS. ZOOLOGY)
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Types of Animal Distribution
Animals constantly try to expand their habitat. No space on Earth is free of animals if it can
support life.
“Animal distribution is the range on Earth occupied by an animal species.”
Types of Animal Distribution
There are five types of distribution patterns exhibited by animals:
(1) Cosmopolitan Distribution: It is a type of distribution in which animals are distributed
almost worldwide, i.e. in all suitable habitats. Such animals have certain adaptations to
overcome environmental barriers, they are called Eurytopic animals. Some animals with
cosmopolitan distribution are humans (Homo sapiens), Killer whales (Orcinus orca), wasps,
cats, dogs, etc. The term cosmopolitan distribution usually should not be taken literally,
because it is often applied loosely in various contexts. Commonly the intention is not to include
Polar Regions, extreme altitudes, oceans, deserts, or small, isolated islands. For example, the
housefly is nearly as cosmopolitan as any animal species, but it is neither oceanic nor polar
in its distribution.
Figure: Cosmopolitan distribution of Killer whale (Orcinus orca), highlighted blue.
(2) Discontinuous Distribution: It is a type of distribution in which animals are present in
certain areas but absent from other areas without any continuity. Animals with restricted /
discontinuous distribution are called Stenotopic animals. These animals cannot cross the
environmental barriers because they are adapted and specialized for specific environmental
conditions. Some examples are as follows:
 Flightless Birds: Ostriches are found in Africa and Arabia, cassowaries and emus are found
in Australia, kiwis are found in New Zealand, and rheas are found in South America.

2.  Alligators: They occur only in North America (American Alligator) and China (Chinese
Alligator).
 Lungfish: There are three genera of lungfish: (1) Protopterus is found in the marshes and
swamps of Africa, (2) Lepidosiren is found in the marshes and swamps of South America,
while (3) Neoceratodus is found in the rivers of Queensland, Australia.
 Marsupials: They are found in Australia (which is their real home) and the Americas (South,
Central, and North).
 Elephants & Rhinoceroses: They are found in Asia and Africa.
 Llamas: They are found only in South America.
 Tapirs: They are found in Java, Sumatra, and Central and South America.
Figure: Discontinuous distribution of flightless birds.
Distribution changes over time: The distribution of a group of animals today will not necessarily
remain the same tomorrow because new species are always originating and they in turn
migrate from the centers of origin and spread to different areas as their predecessors have
done in the past. The succession of fauna is a complicated phenomenon involving evolution,
adaptive radiation, and the extinction of dominant groups and their replacement by other
dominant elements of fauna. Many animals had a continuous distribution in the past, as
indicated by their fossil record but today they exhibit a discontinuous distribution, such animals
which once had a worldwide distribution but are now confined to some areas are referred to
as the “relics of the past”.
Darlington’s views on Discontinuous Distribution: There are several arguments to explain the
occurrence of discontinuous distribution. According to Darlington, a group of animals can
become discontinuously distributed in three ways:
 By reaching oceanic islands across the water (oceanic islands are in deep water and have
never had any connection with the mainland).
 By the extinction of species in between two ranges or two areas (due to unfavorable
conditions such as predation, habitat destruction, climate change, etc.; or due to
competition with highly advanced and aggressive forms).
 By submergence of land-masses in between two ranges.

3. SYED MUHAMMAD KHAN (BS HONS. ZOOLOGY)
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Figure: Discontinuous distribution of extant and extinct lungfish.
Evidence of Evolution: Discontinuous distribution provides very good evidence for evolution. It
indicates that in the past, various physical, chemical, and climatic changes occurred which
affected the distribution of animals.
(3) Endemic Distribution: It is a type of distribution in which animals are confined to the areas
in which they evolved, i.e. they are endemic to those regions. Their confinement may be due
to physical barriers to dispersion or to the fact that they have only recently evolved and have
not yet had time to spread from their centers of origin. Examples include nilgai (endemic to
the Indian subcontinent), giraffe (endemic to Africa), sloth (endemic to South America), and
armadillos (endemic to South and Central America). The Neotropical region has a maximum
number of endemic vertebrates.
Figure: Endemic distribution of Brown-throated Three-toed Sloth.
(4) Isolated Distribution: It is a type of distribution in which animals are found in certain
isolated regions of the world, i.e. monotremes/prototherians (egg-laying mammals) are found
in the Australian region, whereas Tuatara (Sphenodon punctatus) is found only in New

4. Zealand (it is a type of lizard). These animals are small in number and primitive, they survive
due to the absence of their enemies or predators.
Figure: Isolated distribution of Duck-billed Platypus in Eastern parts of Australia.
(5) Bipolar Distribution: It is a type of interrupted distribution in which the same species,
genus, or family lives in the temperate latitudes of the northern and southern hemispheres but
is absent in the tropics. Some species, because they are adapted to the cold arctic climate,
cannot migrate to the warmer areas and are hence restricted to the Polar Regions. Polar
bears, arctic fox, lemmings, coyotes, and reindeers are found in the northern Polar Regions
while penguins are restricted to the Antarctica region. Bipolar distribution is particularly
characteristic of marine organisms: several marine invertebrates (for example, mussels),
marine fish (the anchovy, Pacific saury, basking shark, and porbeagle sharks), some
mammals (southern whale, gray dolphin), and many species of marine algae (kelp and fucus).
The occurrence of bipolar distribution is caused by the conditions that prevailed in the ice age,
when the temperature in the tropics dropped and northern organisms were able to spread to
the tropics and reach the southern hemisphere. Later when the temperature rose, these
organisms died out in the tropics, thereby giving rise to an interrupted range.
Figure: Bipolar distribution of Basking shark, found only in the northern and southern
temperate latitudes (shaded dark blue).