Pygmy mammoth

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Pygmy mammoth
Temporal range: Late Pleistocene to Early Holocene, 0.06–0.011Ma
Mammuthus exilis.jpg
Skeleton
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Proboscidea
Family: Elephantidae
Genus: Mammuthus
Species: M. exilis
Binomial name
Mammuthus exilis
(Stock & Furlong, 1928)[1]

The pygmy mammoth or Channel Islands mammoth (Mammuthus exilis) is an extinct species of dwarf elephant descended from the Columbian mammoth (M. columbi) of mainland North America.[2] This species went extinct during the Quaternary extinction event in which many megafauna species went extinct due to changing conditions to which the species could not adapt.[3] 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,[4] in stark contrast to its 4.3 m (14 ft) tall, 9,100 kg (20,100 lb) ancestor.[5]

Discovery[edit]

Excavation in 1994

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.[6] B. Agenbroad, L. Agenbroad, D. Morris, S. Morris, T. Rockwell and L. Roth [6] found bones of 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 dig up the skeleton. They recovered 90% of a mature male Pygmy Mammoth's skeleton.[7] The mammoth was about 50 years old when it died.[6] The small bones were preserved in life position, which represented that it had died where it was found rather than being scattered around the island. The bones were returned to the Santa Barbara Museum of Natural History.[7] 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.[6] This was the first discovery of a nearly complete specimen of the pygmy mammoth. Fortunately enough, the skeleton of the mammoth was only missing a foot, a tusk, and a couple of vertebrae. The remains were covered by a sand dune, which prevented the bones from scattering and kept them intact. Since the bones were undisturbed, it is predicted he simply died of old age.[8]

Habitat[edit]

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).[7]

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 wolf, 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.[5]

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.

The Pygmy mammoth was able to thrive in all of the many different ecosystems found on Santa Rosae, such as high elevation plateaus to dune, grassland, riparian and steppe-tundra ecosystems.[7] Their fossils are found in the Channel Islands and in the California Channel. The evidence of their habituation in all of those diverse dwellings is revealed by the pollen and plant pieces found in sediments and in dung. In addition, each habitat has a specific isotope mark from the unique types of soil, plants and water.[9] These mammoths sometimes modified their habitats, specifically in Channel Islands, where they created more spacious grassland in result of their roaming.[6]

Evolution[edit]

Land bridges have been theorized to be on the channel island during the time of ancestral elephants because it was assumed the mammoths could not swim. However, evidence of there ever being land bridges is not very high. New evidence shows that elephants are skilled enough to swim and do it to cross bodies of water. Modern elephants are believed to swim much faster, at speeds that range from 0.96–2.70 km/hr.[6] Pygmy mammoths are thought to be descendants of Columbian mammoths that swam to the Channel Islands. When the Ice Age caused the sea levels to lower, the four Channel Islands formed a single island that was closer to the mainland and also larger in size. The Columbian mammoths were capable swimmers, and were able to swim to the new island and adapt to the new environment.[10]

The pygmy mammoths lived on Santa Rosa island which was beginning to shrink due to rising sea levels. The pygmy mammoths evolved through generations in order to survive on the ever-shrinking Santa Rosa Island. Smaller bodies require less food and resources to remain healthy in a smaller territory and allowed for less competition among the species, which is an example of island dwarfism.[11] 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.[12] Despite popular belief, the evolution and dwarfing of the Pygmy mammoth took a long period of time. The process took over 30,000 years but as the mammoths adapted to the new land and restricted food supply they slowly became only as half as tall as their Columbian mammoth predecessors.[10][13][14]

Like most elephant species, the male pygmy mammoth is dominance. The males also have a somewhat larger skeletal structure, especially in the legs, skull and tusks.[7] The female pygmy elephant has a different pelvic structure, allowing her to give birth.[15]

Extinction[edit]

The cause of extinction of the pygmy mammoth is unknown, but it could have been caused by over-hunting by humans, climate change, a comet's impact, or some combination thereof. While human interference often has a greater effect on island species than on continental species, there is no evidence that humans on Santa Rosa hunted the pygmy mammoth.[16] Climate change likely played a part in the extinction, as the environment in and around the Santa Rosa landmass was changing dramatically. The island was broken into four smaller islands, and the landmass of the islands shrank by nearly eighty percent. Post-glacial warming reduced the available fresh water and food sources for the pygmy mammoth, putting a great strain on the population, and making them vulnerable to other adverse effects.[17] A controversial explanation of the pygmy mammoth's extinction is that of a cosmic impact. Kennet Douglas hypothesized that an impact may have caused rapid ecosystem disruption, triggering extinctions of megafauna and reducing the population of the pygmy mammoth. However, geological data supporting or contradicting the an impact is inconclusive.[18]

See also[edit]

Notes[edit]

  1. ^ 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. PMID 17772244. 
  2. ^ Agenbroad 2010, p. 1.
  3. ^ Torben 2012, p. 3.
  4. ^ 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. 
  5. ^ 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. 
  6. ^ a b c d e f Agenbroad, L.D.; Johnson J.; Morris D.; Stafford T.W. "Mammoths and Humans as Late Pleistocene Contemporaries on Santa Rosa Island" (PDF). American Geophysical Union. Spring Meeting 2007. 
  7. ^ a b c d e Agenbroad, Larry D.; Don P. Morris. "Giant Island/Pygmy Mammoths:The Late Pleistocene Prehistory of Channel Islands National Park" (PDF). National Park Service Paleontological Research 4: 35–39. 
  8. ^ anonymous, anonymous. "Stranded on Santa Monica" (PDF). "Discover" 16: 1. 
  9. ^ Koch, P. L. (1988). "The diet of Pleistocene proboscideans and its role in their extinction.". Geological Society of America 1988 Centennial Celebration Program 21: A378. 
  10. ^ a b Hollon, Tom. "Two weeks in the Pit as Indiana Jones" (PDF). The Scientist 16: 1–2. 
  11. ^ Agenbroad 2001, p. 473.
  12. ^ Agenbroad, p. 473.
  13. ^ "Channel Islands: The Pygmy Mammoth" (web). National Park Service. 
  14. ^ "Mammuthus exilis a.k.a. pygmy mammoth and Channel Islands mammoth". Prehistoric Wildlife. Retrieved 2013-10-23. 
  15. ^ Shoshani, J. "Understanding proboscidean evolution: a formidable task. Trends in Ecology and Evolution" 13. pp. 480–487. doi:10.1016/s0169-5347(98)01491-8. 
  16. ^ Agenbroad 1998, p. 1.
  17. ^ Rick, Torben C.; Hoffman, C. A.; Braje, T. J.; Maldonado, J. E.; Sillett, T. S.; Danchisko, K.; Erlandson, J. M. (2012). "Flightless ducks, giant mice and pygmy mammoths: Late Quaternary extinctions on California's Channel Islands". World Archaeology 44: 3–20. doi:10.1080/00438243.2012.646101. 
  18. ^ Douglas, Kennett (2009). "Shock-synthesized hexagonal diamonds in Younger Dryas boundary sediments" (PDF). Proceedings of the National Academy of Sciences of the United States of America 106: 1–6. doi:10.1073/iti0109106. 

References[edit]

  • 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
  • Torben, Rick (2012). "Flightless ducks, giant mice and pygmy mammoths: Late Quaternary extinctions on California’s Channel Islands, 3