[Aztlan] Stegomastodons in Patagonia

[Mike]

Hi Bruce and fellow Listeros,
I just wanted to say what a fascinating post that was. Thank you very much 
Bruce, and keep'em coming.
Regards,
Mike Reed (U.K.)

----- Original Message ----- 
From: "Bruce Rogers" <bwrogers at dslextreme.com>
To: <aztlan at lists.famsi.org>
Sent: Sunday, August 09, 2009 7:05 PM
Subject: [Aztlan] Stegomastodons in Patagonia


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 =ig
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
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