Toxodon
Name: Toxodon
(Bow tooth).
Phonetic: Tocks-oh-don.
Named By: Richard Owen - 1837.
Classification: Chordata, Mammalia, Toxodontidae.
Species: T. platensis (type),
T. burmeisteri, T.
chapadmalensis, T. darwini, T. ensenadense, T. expansidens, T.
gracilis.
Diet: Herbivore.
Size: 2.7 meters long, 1.5 meters high.
Known locations: South America.
Time period: Late Piacenzian of the Pliocene through
to the late Tarantian of the Pleistocene.
Fossil representation: Multiple specimens.
Toxodon
was a
large herbivorous mammal that was similar in proportion to a
rhinoceros, but also possessed other features that were similar to
hippopotamuses and possibly even elephants. The post cranial skeleton
has a very robust construction which suggests that in life Toxodon
was
a very heavy animal. The feet were plantigrade which means that
Toxodon walked with the flat of its foot so that it
could better
support its body weight. The body was wide which suggests that
Toxodon had an extensive digestive system for
processing plant matter.
The hind legs were much longer than the fore legs which meant that the
main body sloped down towards the front. This also meant that the
head was carried closer to the ground where Toxodon
could feed upon low
growing vegetation. The neural spines of the anterior dorsal
vertebrae were enlarged, either providing anchor points for neck
muscles that supported the heavy skull, or supported the formation
of a fatty hump that served as storage for leaner times.
Toxodon
has been envisioned
as both a grazer, an animal that eats grasses, and as a browser,
an animal that feeds on the foliage of shrubs and low growing trees.
It’s quite possible that Toxodon was a generalist
that did both as the
wide mouth could have easily been used to do either method. Although
so far not known for certain, some researchers have considered the
possibility that Toxodon had a prehensile lip. This could have been
used to guide vegetation into the mouth, allowing Toxodon
to adapt to
whatever was available.
Many
reconstructions of
Toxodon have seen it set as a semi aquatic animal
similar to hippo that
submerged itself in water to support the bulk of its body while feeding
upon aquatic plants. However since the twentieth century this has
been considered an antiquated view that gives a false representation of
the habitats that Toxodon frequented. First and
most obvious is that
Toxodon remains have always been found in arid
ecosystems, something
to be expected since most of South America was covered by steppe and
grassy plains during the Pleistocene. Additionally an animal that has
its head carried low on its body would not be able to completely
submerge itself otherwise it would not be able to get its head above
the water to breathe, which means that Toxodon
could not have tried
to use water to support its weight for risk of drowning.
During
the Pleistocene
Toxodon seems to have been one of the most common
herbivores across
South America, and lived at the time of the Great American
Interchange. This is where the formation of the Isthmus of Panama
created a land bridge that joined North and South America, allowing
previously isolated animals to intermix and spread out into new
locations. As such Toxodon probably did not have
to worry about being
attacked by phorusrhacids,
popularly known as terror birds, since
they were largely extinct by the time it appeared. Unfortunately
however this extinction seems to have been brought about by the spread
of North American predators such as the sabre toothed cat Smilodon.
North American populations of Smilodon seem to
have had a preference
for hunting large bison, and it’s not inconceivable that some may
have adapted to killing Toxodon.
The
final nail in the
proverbial coffin however seems to have been the arrival of human
hunters. Arrowheads found with Toxodon remains
virtually prove that
this was a prey animal for early human hunters, and the theory of
overkill of Toxodon populations has been repeatedly
used to explain the
disappearance of much of the megafauna animals at the end of the
Pleistocene. However while hunting would have certainly been a
contributing factor to their extinction, there are other theories
such as on-going climate change, diseases and even comets exploding
in the air above the planet (similar to the 1908 Tunguska event
but on a larger scale) that have been proposed to explain the
disappearance of the megafauna.
Further reading
.
- ESR dating of a Toxodon tooth from a Brazilian
karstic cave. Applied
Radiation and Isotopes 52 (5): 1345–1349. - O. Baffa, A. Brunetti, I.
Karmann & C. M. Dias Neto - 2000.
- Microstructural defects and enamel hypoplasia in teeth of Toxodon
Owen, 1837 from the Pleistocene of Southern Brazil. - Lethaia. 47 (3):
418–431. - P. R. Braunn, A. M. Ribeiro & J. Ferigolo - 2014.
- Ancient proteins resolve the evolutionary history of Darwin's South
American ungulates. - Nature. 522 (7554): 81–4. - Welker, Frido;
Collins, Matthew J.; Thomas, Jessica A.; Wadsley, Marc; Brace, Selina;
Cappellini, Enrico; Turvey, Samuel T.; Reguero, Marcelo; Gelfo, Javier
N.; Kramarz, Alejandro; Burger, Joachim; Thomas-Oates, Jane; Ashford,
David A.; Ashton, Peter D.; Rowsell, Keri; Porter, Duncan M.; Kessler,
Benedikt; Fischer, Roman; Baessmann, Carsten; Kaspar, Stephanie Olsen,
Jesper V.; Kiley, Patrick; Elliott, James A.; Kelstrup, Christian D.;
Mullin, Victoria; Hofreiter, Michael; Willerslev, Eske; Hublin,
Jean-Jacques; Orlando, Ludovic; Barnes, Ian; Macphee, Ross D. E. - 2015.
- Ancient collagen reveals evolutionary history of the endemic South
American 'ungulates'. - Proceedings. Biological Sciences. 282 (1806):
20142671. - M. Buckley - 2015.
- Isotopic paleoecology (δ13C, δ18O) of Late Quaternary megafauna from
Mato Grosso do Sul and Bahia States, Brazil. Quaternary Science
Reviews. 221: 105864. - T. R. Pansani, F. P. Muniz, A. Cherkinsky, M.
L. Pacheco & M. A. Dantas - 2019.
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