Asian Elephants Evolution and Evolutionary Distinctivness
Evolution of Asian Elephants:
The Asian elephant once roamed from the Tigris and Euphrates rivers in western Asia as far east as China's Yangtze River. No longer. Now a highly endangered species, it has been eliminated from western Asia completely, from substantial parts of the Indian subcontinent and Southeast Asia, and almost entirely from China. Exceedingly adaptable in diet and behavior, elephants can survive anywhere from grasslands to rain forests, but they must migrate across large areas to find water and suitable food at different times of the year. Such vast ranges have become extremely rare in densely populated, rapidly developing Asia.
The Asian elephant (Elephas maximus) and the African elephant (Loxodonta africana) are the only ele-phant species remaining from a formerly diverse evolutionary radiation. A third proboscidean species, the woolly mammoth (Mammuthus primigenius), survived into early historical time. This group is thought to have originated in Africa during the Eocene (some 50-60 million years ago) and subsequently spread to Europe, Asia, and North and South America.
Two main lineages had evolved by the early Pliocene: the Elephantidae, to which the two living species belong, and the extinct mastodons of the families Mastodontidae and Stegodontidae. The Asian ele-phant and mammoth lineage dispersed from Africa during the mid-late Pliocene, spread throughout Europe and Asia, and became restricted to Asia by the late Pleistocene.
The closest living relatives of the two elephant species are the sea cows (manatees and dugongs), whose ancestors diverged from the Proboscidea during the Palaeocene (50-60 million years ago).
First elephant-like animals discovered in Moroccan rocks (Gheerbrant 1996, 2009)
- 55 million year-old Phosphatherium weighed 15 kg (33 lbs)
- 60 million year-old Eritherium weighed 4 to 5 kg (8.8 to 11 lbs)
Over time, there have been 10 or 11 families in the Order Proboscidea
- Have tusks, modified upper lips and noses,
- Evolutionary trend for size increase from dog-sized to over 4 meters (13 ft.)
Mastodons diverged from elephant family 24 to 28 million years ago
- Belong to a separate family only distantly related to modern elephants
- Found in Europe, Greece, North America and Central America
Molecular data: African elephants separate from Asian elephants and mammoths 7.6 million years ago
New discovery: earliest Asian elephants found in 6.7–5.2 million-year-old rocks in Kenya.
Mammoths (Mammuthus) belong to an extinct genera of the elephant family
- Widespread in Europe, northern Asia, North America and central Mexico, but not South America
- DNA reveals mammoths closer relationship to Asian elephants than to African elephants
- The woolly mammoth (M. primigenius) occupied Europe, British Isles, northern Asia, and as far south as Kansas in the United States
After arriving in North America, some populations returned to Asia.
- The Columbian mammoths (M. columbi) spread throughout North America into Central America
- A dwarf form of the Columbian mammoth survived on the Channel Islands of California.
Extinct about the time of early human contact 12,000 to 13,000 years ago. Extinct pygmy mammoth skeletons found on Mediterranean island of Crete and Sardinia. DNA and morphology shows closer relationship to Mammuthus than to Elephas.
Modern genera Loxodonta and Elephas both originated in East Africa.
- Loxodonta migrated throughout Africa
- Elephas migrated to Asia and Eurasia
- Extinct pygmy elephants on islands of Cyprus and Tilos islands in Mediterranean (Pou-lakakis et al 2006).
- DNA more like modern Elephas
- Not known if pygmy elephants on Sicily and Malta more like mammoths or modern elephants
Elephants' closest living relatives: hyrax, sea cows, golden moles
- Grouped into proposed new taxon which originated in Africa, Afrotheria, together with aardvarks, elephant shrews, tenrecs
- Close relationships based on molecular evidence, shared anatomy, earth history of plate tectonics