Tiny Mammoths
Along with dinosaurs, mammoths are some of the most charismatic extinct animals. Recently, they have been on the news quite a bit due to Colossal Biosciences’ plan to bring them back from extinction1. These elephant relatives are usually associated with their massive sizes, but a species of pygmy mammoths also existed. They provide a good case study of the power of evolutionary forces, as well as how animals are affected by their ecology.
Santa Rosa Island off the coast of California was home to these pygmy mammoths (Mammuthus exilis), which on average were around 1.7 meters tall and 750 kilograms 2. These dimensions are tiny compared to their closest relative which they evolved from, the Columbian mammoth (Mammuthus columbi), which stood at 4 meters tall and 12 tons.
Drawing made by Susan Morris showing the articulated skeleton found in 1994 in Santa Rosa Island.
The Columbian mammoths swam to Santa Rosa Island during glacial periods, when sea levels were lower because water was trapped in glaciers. After the end of this ice age, sea levels rose once more and the mammoths were trapped in the island.3
There are several reasons why these mammoths confined to the island evolved to become smaller 3:
Santa Rosa Island did not have any large predators that posed a threat to mammoths, so there wasn't as much advantage to being large for protection compared to the mainland where predators like saber-toothed cats roamed
Santa Rosa Island did not have as much vegetation as mainland California, so the available resources could no longer support the energy needs of an enormous body.
Over 100 fossils of pygmy mammoths have been found in this island. Dates of human arrival and mammoth remains have some overlap, so some researchers believe they might have become extinct due to human contact.
This story is textbook island dwarfism and provides an interesting example of geological events affecting the evolution of a species. Evolution does not happen in a vacuum. It is shaped by geology, ecology, and environmental chemistry.
De-extinction is a very interesting topic that I will probably discuss in the future. If you haven’t yet, check out the dire wolf story! Just look up "dire wolf"↩
Agenbroad, L. D. (2009). Mammuthus exilis from the California Channel Islands: Height, mass, and geologic age. In C. C. Damiani & D. K. Garcelon (Eds.), Proceedings of the 7th California Islands Symposium (pp. 15–19). Institute for Wildlife Studies.↩
Agenbroad, L. D., & Morris, D. P. (1999). Giant island/pygmy mammoths: The Late Pleistocene prehistory of Channel Islands National Park. In V. L. Santucci & L. McClelland (Eds.), Paleontological research (Technical Report NPS/NRGRD/GRDTR-99/03, pp. 55–57). U.S. Department of the Interior, National Park Service, Geological Resource Division.↩