Mammuthus exilis - The Channel Islands Mammoth or Pygmy Mammoth
When: Late Pleistocene to Early Holocene (~50,000 to 11,000 years ago)
Where: The Channel Islands off the coast of California, USA.
What: Mammuthus exilis is a tiny mammoth. The largest specimens found stood only 7 feet (~2 meters) tall at the shoulder and smaller full grown individuals reached only 4.5 feet (~1.4 meters). This species of mammoth has been found on several of the Channel Islands, which lie off the coast of Southern California. M. exilis is descendant from the Columbian Mammoth (Mammuthus columbii) which roamed throughout North America.
Yesterday the giant rabbit of Minorca showed an excellent example of one side of the island effect, and this little mammoth gives us the other end of the scale. Giant herbavores become small for a two main reasons: first there is just not enough food on an island to support a population of full sized mammoths for very long, but secondly there is nothing to prey upon the mammoths if they stay small. Therefore, selection pressures only push for smaller and smaller individuals. M. exilis was not a wooly mammoth, and is not closely related to other known examples of dwarf proboscideans. Island dwarfism is something the elephant lineage has undergone time and time again in their evolutionary history.
When the Channel Islands mammoth established a population on the islands they were not the separate land masses of today, but instead were one large island that is called Santa Rosae. At the end of the last glacial event, the waters rose and the modern Channel Islands were formed. It has been proposed that this shrinking habitat and changing vegetation on the islands stressed the pygmy elephant too much.
Mammoth exilis is another great example of allometry; the tiny mammoth is not just a large mammoth shrunken down. It is nothing but head and tusks instead!