Pygmy mammoth

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Pygmy mammoth
Temporal range: Late Pleistocene to Early Holocene, 0.08–0.011 Ma
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Skeleton at the Santa Barbara Museum of Natural History
Model of a pygmy mammoth (front) at the Cleveland Museum of Natural History
Scientific classification Edit this classification
Domain: Eukaryota
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 mammoth native to the northern Channel Islands off the coast of California. It was descended from the Columbian mammoth (M. columbi) of mainland North America.[2]

A case of island or insular dwarfism, from a recent analysis in 2010 it was determined that M. exilis was on average, 1.72–2.02 m (5.6–6.6 ft) tall at the shoulders and 760–1,350 kg (1,680–2,980 lb) in weight,[3][4] in stark contrast to its 3.72–4.2 m (12.2–13.8 ft) tall, 9.2–12.5 t (9.1–12.3 long tons; 10.1–13.8 short tons) ancestor.[4]

This species became extinct at the end of the Late Pleistocene during the Quaternary extinction event in which many megafauna species became extinct due to changing conditions to which the species could not adapt.[5]

Discovery[edit]

Excavation in 1994, Santa Rosa

Mammoth remains have been known on the northern Channel Islands of California since 1856. They were first reported in scientific literature in 1873.[6]

In 1994 the National Park Service called in scientists to inspect an uncovered, unidentified skeleton found on the northeast coast of Santa Rosa Island.[7] They found bones of the axial skeleton of a large land vertebrate and decided to excavate and dig up the skeleton. They recovered 90% of a mature male pygmy mammoth's skeleton.[8] The mammoth was about 50 years old when it died.[7] 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.[8] After the discovery of the skeleton, a pedestrian survey of the island began. This resulted in the discovery of 160 new locations of mammoth remains, the vast majority being found on Santa Rosa Island.[7] This was the first discovery of a nearly complete specimen of the pygmy mammoth. Fortunately, the skeleton 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.[9]

Habitat[edit]

Skeletal restoration of Santa Rosa 1994

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 appears to have survived on the islands until the arrival of the humans[10] associated with Arlington Springs Man around 13,000 years ago[11] and the last known mammoth occurrence was 13–12.9 thousand years ago[8] which predates the later Chumash people's arrival during the early Holocene, between 10,800 and 11,300 years ago.[12]

Mandible

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 Rosa Island; their body size became smaller because it required less food and resources to remain energized and alive. After this evolutionary period, the mammoth had become a distinct species, the pygmy mammoth.[13]

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.[14] 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.[15] These mammoths sometimes modified their habitats, specifically in Channel Islands, where they created more spacious grassland in result of their roaming.[16]

Evolution[edit]

See also: Foster's rule
Size (light orange) compared to a human and other mammoths

The oldest fossils of mammoths on the Channel Islands is a tusk found on a marine terrace on Santa Rosa Island, which has been dated based on surounding corals as 83,800 ± 600 – 78,600 ± 500 years old, and it is suggested that their Columbian mammoths ancestors colonised the islands either around 250,000 or 150,000 years ago, when sea levels were considerably lower than they are today.[17] During these times, the distance to the mainland was reduced to 7 kilometres (4.3 mi).[11] When the Ice Age caused the sea levels to lower, the four northern Channel Islands formed a single island that was closer to the mainland and also larger in size.. Mammoths, like living elephants, were likely capable swimmers able to swim to the new island and adapt to the new environment.[18]

Pygmy mammoth humerus bone, next to that of a Columbian mammoth

The pygmy mammoths lived on Santa Rosae 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 Rosae 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.[19] Also, their mainland predators such as the dire wolves, the Smilodon and the American lion were not present. After this evolutionary period, the mammoth had become a distinct species, the pygmy mammoth.[20] The pygmy mammoth's evolution on Santa Rosae took over 30,000 years.[18][21]

The pygmy mammoth is not the only example of island dwarfism in mammoth: another example is Mammuthus lamarmorai in the Mediterranean island of Sardinia.

Extinction[edit]

The cause of extinction of the pygmy mammoth is unknown, but it could have been caused by over-hunting by humans, wildfires, climate change, or some combination thereof.

Humans[edit]

Human interference often has a greater effect on island species than on continental species, and there is evidence that Native Americans hunted the pygmy mammoth on Santa Rosa.[22] "Mammoths were still extant on the islands when humans arrived" and mammoth remains were associated with charcoal of the same radiocarbon date.[23] Two mammoth skulls with the brain removed were found adjacent to a fire pit, of the 100 fire pits at least a third contained mammoth bones.[24] "More complex ecological explanations involving a combination of climate change and human predation are the most viable."[11] Other authors have argued that there is no direct evidence of human predation on pygmy mammoths.[17]

Wildfires[edit]

"Abrupt ecosystem disruption is evident on the Northern Channel Islands" with the onset of biomass burning and resulting mass sediment wasting of the landscape. "These wildfires coincide with the extinction of the pygmy mammoth."[11]

Climate change[edit]

A shift in sea level driven by climate change likely played a part in the extinction: as the sea level rose, about 61% of the island land-mass was submerged. Some 4,000 years prior to extinction the island had an area of roughly 1,900 square kilometres (730 sq mi) (about the size of the island of Maui). Further increase in sea levels left four smaller islands of nearly eighty percent less total landmass.[25] Post-glacial warming reduced available fresh water and food sources for the pygmy mammoth, pressuring the remnant population and making it vulnerable to other adverse effects.[26]

Comet impact[edit]

Main article: Younger Dryas impact hypothesis

A controversial explanation of the pygmy mammoth's extinction is that of a cosmic impact affecting a large part of the western United States. However, geological data supporting such an impact is lacking,[27] and the hypothesis has been refuted by earth scientists and planetary impact specialists.[28]

See also[edit]

Notes[edit]

  1. ^ Chester Stock and E. L. Furlong (1928). "The Pleistocene elephants of Santa Rosa Island, California" (PDF). Science. 68 (1754): 140–141. Bibcode:1928Sci....68..140S. doi:10.1126/science.68.1754.140. PMID 17772244.
  2. ^ Agenbroad 2010, p. 1.
  3. ^ 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.
  4. ^ a b Larramendi, A. (2016). "Shoulder height, body mass and shape of proboscideans" (PDF). Acta Palaeontologica Polonica. 61. doi:10.4202/app.00136.2014. Retrieved November 21, 2015.
  5. ^ Torben 2012, p. 3.
  6. ^ Agenbroad, L.D. (2003). "New absolute dates and comparisons for California's Mammuthus exilis". Deinsea. 9: 1–16.
  7. ^ a b c Agenbroad, L.D.; Johnson J.; Morris D.; Stafford T.W. "Mammoths and Humans as Late Pleistocene Contemporaries on Santa Rosa Island" (PDF). Proceedings of the American Geophysical Union. Spring Meeting 2007.
  8. ^ a b c 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. Archived from the original (PDF) on 2014-02-19. Retrieved 2013-10-23.
  9. ^ anonymous, anonymous. "Stranded on Santa Monica". Discover. 16: 1. ProQuest 206020333.
  10. ^ Fitzgerald, Richard; Rondeau, Michael (2012). "A Fluted Projectile Point from Crystal Cove State Park, Orange County, Alta California". PaleoAmerica. 4 (2): 247–256. doi:10.1179/cal.2012.4.2.247. S2CID 131155806.
  11. ^ a b c d Kennett, D.J.; Kennett, J.P.; West, G.J.; Erlandson, J.M. (2008). "Wildfire and abrupt ecosystem disruption on California's Northern Channel Islands at the Ållerød–Younger Dryas boundary (13.0–12.9 ka)". Proceedings of the National Academy of Sciences. 104 (27–28): 2530–2545. Bibcode:2008QSRv...27.2530K. doi:10.1016/j.quascirev.2008.09.006.
  12. ^ Rocha, Veronica (16 September 2016). "Well-preserved mammoth skull unearthed on Channel Islands puzzles scientists". Los Angeles Times. Retrieved 24 September 2016.
  13. ^ "The pygmy mammoth". Channel Islands National Park. U.S. Department of the Interior National Park Service. 2006-09-01. Retrieved 2008-06-14.
  14. ^ Agenbroad, Larry D.; J. Mead. "Distribution and palaeoecology of central and western North American Mammuthus". National Park Service Paleontological Research.
  15. ^ 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.
  16. ^ Johnson, D. "Landscape evolution on San Miguel Island, California". {{cite journal}}: Cite journal requires |journal= (help)
  17. ^ a b Muhs, Daniel R.; Simmons, Kathleen R.; Groves, Lindsey T.; McGeehin, John P.; Randall Schumann, R.; Agenbroad, Larry D. (2015-05). "Late Quaternary sea-level history and the antiquity of mammoths ( Mammuthus exilis and Mammuthus columbi ), Channel Islands National Park, California, USA". Quaternary Research. 83 (3): 502–521. doi:10.1016/j.yqres.2015.03.001. ISSN 0033-5894. {{cite journal}}: Check date values in: |date= (help)
  18. ^ a b Hollon, Tom. "Two weeks in the Pit as Indiana Jones". The Scientist. 16: 1–2. ProQuest 200018191.
  19. ^ Agenbroad 2001, p. 473.
  20. ^ Agenbroad, p. 473.
  21. ^ "Channel Islands: The Pygmy Mammoth" (web). National Park Service.
  22. ^ Agenbroad 1998, p. 1.
  23. ^ Agenbroad, Larry D; Johnson, John R.; Morris, Don; Stafford Jr., Thomas W. (2005). "Mammoths and humans as late Pleistocene contemporaries on Santa Rosa Island". Proceedings of the Sixth California Islands Symposium. Institute for Wildlife Studies, Arcata, CA: 3–7.
  24. ^ Orr, Phil C; Berger, Rainer (1966). "The Fire Areas on Santa Rosa Island, California". Proc. Natl. Acad. Sci. 56 (5): 1409–1416. Bibcode:1966PNAS...56.1409O. doi:10.1073/pnas.56.5.1409. PMC 219987. PMID 16591389.
  25. ^ Berger, Rainer; Orr, Phil C. (1966). "The Fire Areas on Santa Rosa Island, California, II". Proc. Natl. Acad. Sci. 56 (6): 1678–1682. Bibcode:1966PNAS...56.1678B. doi:10.1073/pnas.56.6.1678. PMC 220154. PMID 16591403.
  26. ^ 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. S2CID 161764677.
  27. ^ Kerr RA (30 October 2010). "Mammoth-Killer Impact Rejected". Science NOW. AAAS. Archived from the original on 17 September 2018. Retrieved 17 September 2018.
  28. ^ Holliday, Vance T.; Daulton, Tyrone L.; Bartlein, Patrick J.; Boslough, Mark B.; Breslawski, Ryan P.; Fisher, Abigail E.; Jorgeson, Ian A.; Scott, Andrew C.; Koeberl, Christian; Marlon, Jennifer; Severinghaus, Jeffrey; Petaev, Michail I.; Claeys, Philippe (2023-07-26). "Comprehensive refutation of the Younger Dryas Impact Hypothesis (YDIH)". Earth-Science Reviews: 104502. doi:10.1016/j.earscirev.2023.104502.

References[edit]

Wikispecies has information related to Mammuthus exilis.
  • 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
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