[Aztlan] Stegomastodons in Patagonia

[Bruce Rogers]

Listeros,

>The bones of a stegomastodon, a prehistoric 
>elephant that lived 13,000 years ago, were found 
>in 2007 in Patagonia at a site called La Plata.

The following may be more than you ever wanted to 
know about these Big Guys (and Gals).

Stegomastodon ("roof nipple tooth" in Latin) is 
an extinct genus of gomphotheres, a family of 
proboscideans (elephant-like animals = big 
noses).  Most stegomastodons stood about 2.8 
meters (9 ft) tall, weighed in at about 6,000 kg 
(6.5 tons), and looked like a robust version of 
the modern day elephant, but with a massive neck 
and "Quasimodo" shoulder hump.  In common with 
modern elephants, it had two tusks.  Other 
closely related proboscideans had four tusks and 
upper and lower jaws of varying length and 
function (The Shovel-tusked mastodon Amebelodon 
fricki had a greatly elongated lower jaw with 
stubby, shovel-like lower tusks and a shortened 
upper jaw evolved to feed on aquatic roots and 
the like at lake margins and marshes). The 
Stegomastodon's 3.5 m (11 ft.) long tusks curved 
out roughly parallel and somewhat upwards. Its 
enameled molars had a complex pattern of ridges 
and knobby protrusions on them, giving the 
creature a large chewing surface that enabled it 
to eat grasses. All mastodon teeth consist of a 
series of paired conical cusps. When seen in 
profile, these mound-shaped cusps resemble a 
woman's breasts; hence the name mastodon was 
derived from the Greek masto (breast) and  don 
(tooth). Its brain weighed about 5 kg (roughly 11 
lbs.).

Mastodons evolved in the Miocene Epoch (26 to 9 
million years ago) and continued to thrive 
through the Pleistocene Epoch or Ice Ages (1.8 
million to 10 thousand years ago). Mastodons were 
in the mainline of proboscidean evolution and 
were probably descended from Moeritherium that 
inhabited what is now Egypt in the Early 
Oligocene Epoch (38 million to 26 million years 
ago). It migrated east and south via Eurasia and 
Beringia to live in both North and South America. 
From about 5 million years ago onwards, they were 
slowly replaced by modern elephants, but the very 
last South American species did not finally 
become extinct until possibly as recently as 400 
years ago.  Gomphotheres also survived in 
Mesoamerica until the end of the Pleistocene Ice 
Ages, roughly 10,000 to 7,000 years ago and may 
have been the critter BBQ-ed by the proto-Maya at 
Actun Loltún in the Sierrita de Ticul, Yukatan, 
some 8,800 years ago.

The two South American species arrived from North 
America following the Great American Interchange, 
an event starting about 9 million years ago and 
climaxing about 3 million yeas ago.   This 
tectonic event closed the Isthmus of Panama, thus 
separating the Pacific and Atlantic Oceans, by 
both uplifting the adjacent sea floor and 
building of volcanic islands chains and land 
masses.

The Stegomastodons introduced to South America 
were initially mixed feeders; Waring's 
Stegomastodon (Stegomastodon waringi) evolved 
towards grazing, while the Platen Stegomastodon 
(S. platensis) evolved towards tree and brush 
browsing. The two Stegomastodon species occupied 
warmer, lower-altitude habitats east of the Andes 
Mountains, while the related gomphothere 
Cuvieronius hyodon occupied the cooler, 
higher-altitude habitats; this fellow finally was 
extirpated about 9,100 years ago.

Read all about these fascinating animals in:

Alberdi, M. T.; Prado, J. L.; Ortiz-Jaureguizar, 
E.; Posadas, P.; Donato, M., 2007, Historical 
biogeography of Trilophoont gomphotheres 
(Mammalia, Proboscidea) reconstructed applying 
dispersal-vicariance analysis in Díaz-Martínez, 
E.; Rábano, I., eds., Proceedings of the 4th 
European Meeting on the Paleontology and 
Stratigraphy of Latin America, Zaragoza, Spain 
17-19 September 2007, Madrid: Instituto Geológico 
y Minero de España, p. 9-14, (ISBN 
978-84-7840-707-1) 

	Graham, R. W., 2001, The world of 
elephants: Proceedings of the 1st International 
Congress, Rome, October 16-20, 2001, Consiglio 
Nazionale delle Ricerche, p. 707-709.

	Osborn, Henry Fairfield, 1933, Serbelodon 
burnhami, a new shovel-tusker from California: 
American Museum Novitates, v. 639,  p. 1-5.

Palmer, D., ed., 1999, The Marshall Illustrated 
Encyclopedia of Dinosaurs and Prehistoric 
Animals: London, Marshall Editions, p. 239-242. 
(ISBN 1-84028-152-9)

Prado, J. L.; Alberdi, M. T.; Azanza, B.; 
Sánchez, B.; Frassinetti, D. , 2005, The 
Pleistocene Gomphotheriidae (Proboscidea) from 
South America: Quaternary International, v. 
126-128, p. 21-30. 
(doi:10.1016/j.qiaint.2004.04.012).

While it may be that this concentration of bone 
material is the work of early South American 
immigrants as at Chile's Monte Verde, it is also 
possible the concentration had another cause.  If 
there was a favorite spring bog/marsh in the 
grassy plains, then weak or careless tuskers may 
have become bogged down in the relatively small, 
muddy wallows and died in large numbers.  Such 
sites are known from the central and eastern US. 
That said, it is also possible that early 
migrants preyed upon the dead animals much like a 
do-it-yourself butcher shop.

Indeed, we await further work to confirm this 
site as an early wo/man hunting/scavenging site 
or a natural death trap.

Cheers,
Bruce Rogers, earth scientist on decidedly not vegetarian days