Pygmy mammoth
| Pygmy mammoth Temporal range: Late Pleistocene to Early Holocene,
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| Species: | M. exilis
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| Mammuthus exilis (Stock & Furlong, 1928)[1]
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The pygmy mammoth or Channel Islands mammoth (Mammuthus exilis) is an extinct species of dwarf elephant descended from the Columbian mammoth (M. columbi). A case of island or insular dwarfism, from a recent analysis in 2010 it was determined that M. exilis was on average, 1.72 m (5.6 ft) tall at the shoulders and 760 kg (1,680 lb) in weight.[2] A stark contrast to its 4.3 m (14 ft) tall, 9,100 kg (20,100 lb) ancestor.[3]
Remains of M. exilis have been discovered on three of the northern Channel Islands of California since 1856: Santa Cruz, Santa Rosa, and San Miguel, which together with Anacapa were the highest portions of the now mostly submerged superisland of Santa Rosae. The late Pleistocene elephant may have lived on the islands until the arrival of the Chumash people during the early Holocene, between 10,800 and 11,300 years ago. Radiocarbon dating indicates M. exilis existed on the island for at least 47,000 years prior (which is the approximate limit of the dating method).[4]
Modern elephants are excellent swimmers, and the ancestors of M. exilis most likely swam the 4 mi (6.4 km) to Santa Rosae. As the population of mammoths increased, the lack of large predators such as the dire wolves, smilodon and the american lion and the loss of habitat caused by the rise of sea levels at the end of the ice age as Santa Rosae split into four islands favored smaller animals. Because of this, the pygmy mammoths began evolving through generations as a survival mechanism to stay alive on the ever-shrinking Santa Rose Island, their body size became smaller in order to require less food and resources to keep them energized and alive. After this evolution is when the species became its own distinct species, the pygmy mammoth.[3]
M. exilis should not be confused with the mammoths of Wrangel Island or Saint Paul Island, which were small races of the woolly mammoth (M. primigenius) and which died out around 1700 B.C. and 4000 B.C., respectively.
1994 Discovery
In July 1994, L. Agenbroad was called by the National Park Service to inspect an uncovered, unidentified skeleton found on the northeast coast of Santa Rosa Island. [5]B. Agenbroad, L. Agenbroad, D. Morris, S. Morris, T. Rockwell and L. Roth [5] found bones representing the axial skeleton of a large land vertebrate on the Santa Rosa Island. On August 1994, they decided there was enough evidence to start excavate and salvage the skeleton. They recovered 90% of a mature male Pygmy Mammoth's skeleton. [4] The mammoth was about 50 years old when it died. [5]The small bones were preserved in life position, which indicated it had died where it was found rather than being scattered around. The bones were returned to the Santa Barbara Museum of Natural History.[4] After the discovery of the skeleton, a pedestrian survey of the island was started, which resulted the discovery of 160 new locations of mammoth remains, the vast majority being found on Santa Rosa Island. [5]
Land Bridges/Swimming
Land bridges have been hypothesized on the channel island during the time of ancestral elephants because it was assumed they could not swim. However, the geological evidence of there ever being land bridges is low. New evidence shows that elephants are skilled enough to swim and cross water gaps. Modern Elephants are believed to swim much faster at speeds that range from 0.96–2.70 km/hr. This is reason to be popular belief because of there motive to cross watergaps that lead modern elephants in Asia and Africa to cross water gaps. [5]
Extinction
It is unknown how exactly the pygmy mammoth went extinct, although generally human interference is thought to have a greater impact on the extinction of island-dwelling species. It has been debated whether their extinction was caused by human overkill, climate change or an extraterrestrial impact. While there is currently no evidence supporting that the earliest peoples inhabiting the island hunted mammoths, there were likely significant climate changes happening in the area during the existence of mammoths. After rising sea levels broke Santarosae into four landmasses sometime between 18,000 and 7,000 years ago, the land area of the northern Channel Islands shrank by almost eighty percent. Postglacial warming changed the freshwater and food sources for the pygmy mammoth, which may have had a negative effect. It has also been suggested that wildfires caused by a comet landing could have caused the mammal's extinction, but this is highly disputed.[6]
Dwarfing
The pygmy mammoths lived on the Santa Rose island which was beginning to shrink because of the ice plates that were covering a lot of the ocean on the northern hemisphere were melting and the sea levels were rising. The pygmy mammoths began evolving through generations as a survival mechanism to stay alive on the ever-shrinking Santa Rosa Island, their body size became smaller in order to require less food and resources to keep them energized and alive and because the population of pygmy elephants stayed the same while the amount of land they had to roam became smaller and more habitable for smaller species. [7]Also, their mainland predators such as the dire wolves, the smilodon and the american lion were not prominent on Santa Rose allowing them to evolve for multiple generations. After this evolution is when the species became its own distinct species, the pygmy mammoth.[8]
Notes
- ^ Chester Stock and E. L. Furlong (1928). "The Pleistocene elephants of Santa Rosa Island, California". Science. 68 (1754): 140–141. Bibcode:1928Sci....68..140S. doi:10.1126/science.68.1754.140.
- ^ Agenbroad, L. D. (2010). ". Mammuthus exilis from the California Channel Islands: Height, Mass and Geologic Age" (PDF). Proceedings of the 7th California Islands Symposium. p. 17. Retrieved 13 June 2012.
- ^ a b "The pygmy mammoth". Channel Islands National Park. U.S. Department of the Interior National Park Service. 2006-09-01. Retrieved 2008-06-14.
- ^ a b c Agenbroad, L. D. (2001-10-19). "Channel Islands (USA) pygmy mammoths (Mammuthus exilis) compared and contrasted with M. columbi, their continental ancestral stock" (PDF). La terra delgli Elefanti: Atti del 1st Congresso Internazionale (The World of Elephants: Proceedings of the 1st International Congress). Roma: Consiglio Nazionale delle Ricerche. pp. 473–475. ISBN 88-8080-025-6. Retrieved 2008-06-14.
{{cite conference}}: Cite has empty unknown parameter:|coauthors=(help); Unknown parameter|booktitle=ignored (|book-title=suggested) (help) Cite error: The named reference "Agenbroad" was defined multiple times with different content (see the help page). - ^ a b c d e Agenbroad, L.D. ""Mammoths and Humans as Late Pleistocene Contemporaries on Santa Rosa Island"" (PDF). American Geophysical Union. Spring Meeting 2007.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) Cite error: The named reference "Johnson" was defined multiple times with different content (see the help page). - ^ Rick, Torben C. ""Flightless ducks, giant mice and pygmy mammoths: Late Quaternary extinctions on California's Channel Islands"" (PDF). World Archaeology. 44: 3–20.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Agenbroad 2001, p. 473.
- ^ Agenbroad, p. 473.
References
Agenbroad, L.D. (2001). "Channel Islands (USA) pygmy mammoths (Mammuthus exilis) compared and contrasted with M. columbi, their continental ancestral stock", World of Elephants, 473
See also
References
[Prehistoric Wildlife 1]
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