Evidences from Biogeographical Distribution
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Evidences from Biogeographical Distribution
Evidences of Evolution of Class 12
Earlier whole land mass of Globe was one piece called Panagea. 200 - 300 million years ago it got divided as follows :
Earlier whole land mass of Globe was one piece called Panagea. 200 - 300 million years ago it got divided as follows :
Sclater (1858) first divided globe in six zoogeographical realms on the basis of avian fauna.
A.R.Wallace (1876) divided more scientifically on the basis of entire flora and fauna as :
- Oriental region – Asia (lower China, West Asia, Malaysia, Indonesia)
- Australian region – Australia, New Zealand, New Guinea
- Ethiopian region – Africa continent, Madagascar, Egypt
- Palaearctic region – Europe, Most part of China, Japan, USSR, Siberia
- Nearctic region – North America continent (USA, Canada, Alaska, Greenland)
- Neotropical region – South America continent (Mexico, Galapagos island)
Wallace’s Line divides Oriental and Australian region.
Darwin (1831) during his expedition on H.M.S. Beagle visited Galapagos Islands (900 Km off West coast of South America) and found many endemic (restricted) species. He studied 13 different subspecies of finches (Darwin’s finches by David Lack 1947) with different eating habits (originally seed-eating). He reasoned it as suitable adaptation brought by environmental conditions and called the islands as “ living laboratory of evolution ”. Discontinuous (Allopatric) distribution : When closely related genera are found in different regions. This indicated that after arising from common stock they were geographically separated and evolved differently. Due to the geographical barrier they remained isolated and evolved as genera Examples:
Lung fishes (Dipnoi) Flightless bird (Ratitae)
Protopterus — Africa Ostrich — Africa
Lepidosiren — S. America Rhea — S. America
Ceratodus — Australia Emu — Australia
Alligator only in South East USA and Eastern China Cassowaries — Australia
Kiwi — New Zealand
Magnolia, Tulips and Sassafras, now grow only in eastern China
Continuous (Sympatric) distribution : When closely related genera are found in the same or connected region. Eg. Prototheria and Metatheria are found only in Australian region. Sometimes referred as restricted distribution. endemic fauna.
