Name:
Castoroides.
Phonetic: Cass-tor-oy-dees.
Named By: John Wells Foster - 1838.
Synonyms: Castoroides nebrascensis,
Burosor efforsorius.
Classification: Chordata, Mammalia, Rodentia,
Castoridae, Castoroidinae, Castoroidini.
Species: C. ohioensis
(type), C. dilophidus.
Diet: Herbivore.
Size: Largest individuals up to 2.2 meters
long, not including the tail.
Known locations: Canada - Ontario, Yukon.
USA - Alabama, Florida, Georgia, Illinois, Iowa,
Kansas, Michigan, Nebraska, New Jersey, Ohio, Oklahoma,
Pennsylvania, South Carolina, Tennessee, Virginia.
Time period: Mid Calabrian of the Pleistocene
through to the early Holocene.
Fossil representation: Multiple individuals.
Castoroides
is another example of how back in the Pleistocene animals were just
bigger than they were today. Also known as the ‘giant beaver’,
Castoroides is not just the largest beaver that we
currently know
about, but it is the largest rodent known to have ever lived on the
North American continent. At the time of writing the only rodents
known to have been bigger than Castoroides are
Phoberomys
and
Josephoartigasia
from South America.
Unfortunately
no clear irrefutable evidence exists that proves that Castoroides
built
dams like modern beavers. Structures that might represent the
prehistoric remains of such structures can also be explained away as
other things such as flood deposits or naturally occurring accretions.
Available evidence actually supports the theory that Castoroides
did
not build dams given that their incisors were not as well suited to
cutting into wood as modern beavers have. However related genera do
seem to have built lodges, which by association might indicate that
Castoroides too also built lodges.
The
extinction of Castoroides has for a long time been
shrouded in
mystery. While the disappearance of much of the North American
Megafauna has been attributed to such factors as extreme glaciations,
climate change, super volcanic eruptions, asteroid strikes,
human hunting and combinations of all the above, Castoroides
populations are actually known to have been in decline before this mass
extinction took place. This has meant that the exact cause for the
extinction of Castoroides has been unknown for
almost two hundred
years, but there may now be one idea which might go some way to
explaining things. A 2011 paper by J. T. Faith detailed how
nitrogen levels in the soil were declining at the time that Castoroides
numbers were also declining.
Reduced
levels of nitrogen in the soil cause a reduction in growth and
nutritional quality of plants that require high nutrient levels.
Herbivorous animals that rely upon such plants end up having to eat
even greater amounts of them to maintain there population, but this
results in even less nitrogen going back into the soil as leaf litter.
This further reduces the crop of nitrogen rich plants the following
year, which means even more had to be eaten, and again this made
the problem much worse again the following year, and so on and on
again until the ecosystem collapses and is unable to support the
presence of such herbivorous. It Castoroides
preferred eating plants
that required high levels of nitrogen, then they would over
successive seasons and generations slowly deplete available food plant
supplies. Thus, unable to adapt to eating different plants,
Castoroides may have ended up starving themselves
into extinction.
Further reading
- Two New Records of the Pleistocene Beaver, Castoroides
ohioensis. -
American Midland Naturalist 12 (12): 529–532. - William L. Engels -
1931.
- Taxonomy of the giant Pleistocene beaver Castoroides
from Florida. -
Journal of Paleontology 43 (4): 1033–1041. - Robert A. Martin - 1969.
- A giant beaver (Castoroides ohioensis Foster)
fossil from New
Brunswick, Canada. - Atlantic Geology 36 (1): 1–5. - R. F. Miller, C.
R. Harrington & R. Welch - 2000.
- Paleoecology of Northeast Indiana Wetland Harboring Remains of the
Pleistocene Giant Beaver (Castoroides Ohioensis). -
Proceedings of the
Indiana Academy of Science 110: 151. - Anthony L. Swinehart, Ronald L.
Richards - 2001.
- Additional records of the giant beaver, Castoroides,
from the
Mid-South: Alabama, Tennessee, and South Carolina. - Smithsonian
Contribution to Paleobiology 93:65-71. - P. W. Parmalee & R. W.
Graham - 2002.
- Giant Beaver, Castoroides ohioensis, remains in
Canada and an
overlooked report from Ontario. - Canadian Field-Naturalist. 121 (3):
330–333. - C. R. Harington - 2007.
- Late Pleistocene Climate Change, Nutrient Cycling, And The
Megafaunal Extinctions In North America. - Quaternary Science
Reviews 30: 1675–1680. - J. Tyler Faith - 2011.