Procoptodon
Name:
Procoptodon
(forward hill tooth).
Phonetic: Pro-cop-toe-don.
Named By: Richard Owen 1874.
Classification: Chordata, Mammalia, Marsupiala,
Diprotodontia, Macropodidae, Sthenurinae.
Species: P. cegsai, P. goliah, P.
maddocki, P. mccoy, P. pusio, P. texasensis, P. ussys.
*Note, the number of valid species varies depending upon source and
some are disputed.
Diet: Herbivore.
Size: 2 meters tall.
Known locations: Australia.
Time period: Calabrian through to Tarantian of the
Pleistocene.
Fossil representation: Multiple specimens.
During
the Pleistocene Australia had a variety of animals that loosely
resembled those still living today but on a much grander scale, from
giant three meter long wombats like Diprotodon
to four meter plus
goannas like Varanus
priscus. Procoptodon for its
part was
essentially a giant kangaroo, although its full size has been the
subject of mis-interpretation by some authors. Procoptodon
itself
stood no more than two metres high, but it could use its long arms to
reach up to three meters high, a figure that has in the past been
erroneously presented as the full height of the animal.
Procoptodon
seems to have been one of the more abundant members of the Australian
Pleistocene megafauna and seems to have been active in different
habitats wherever there was ample growth of plants to support the
population. These areas included the growth of tall plants, shrubs
and trees that would have been out of reach for many of the animals of
the time, and this is where the large size of Procoptodon
comes in.
First by being tall, the shoulders are higher up off the ground,
which immediately gives Procoptodon a reach
advantage over smaller
kangaroos. The long arms also had hands that had two enlarged fingers
tipped with curved claws which could quite conceivably have been used
to wrap around tall branches and pull them down to the mouth, much
like how the giant ground sloths of the Americas lived during this
time. Procoptodon also had forward facing eyes
which would have
granted it the all-important depth perception that would have been
required so that it knew exactly how far it had to reach in order to
pull down the next branch.
How
Procoptodon ate can also be revealed in the shape
and proportions of
the skull. Shorter faced animals usually have the adaptation of a
shorter snout so that they can more easily process food with the rear
teeth. This is a simple principal where the point of jaw articulation
is actually the fulcrum of the mechanism that allows an animal to open
and close its mouth and allows the jaw closing muscles to focus more
force upon shearing through food. In Procoptodon
this food could have
been parts of sclerophyll plants that were soft and nutritious within,
but had a tough exterior to protect the inner parts from drying in the
harsh Australian climate. The dentary (lower jaw) was fused and
well developed so that it could easily withstand the stresses of the
more powerful jaw action. The teeth were also well adapted for this
with low crowns that exhibited extra folds to increase their food
processing potential.
Despite
its large size, Procoptodon would have been prey
to the larger
predators of the time such as Thylacoleo,
better known as the
marsupial lion, that is often envisaged as dropping down from trees
to hit is prey from above. Also was the aforementioned Varanus
priscus, a huge monitor lizard that could have lain in
denser areas
of vegetation to surprise any unsuspecting Procoptodon
that ventured
too close. Procoptodon was not completely
defenceless however,
although its best defence against predators would have been speed.
Most of the metatarsals of the foot were reduced with the exception of
the fourth digit that had become so enlarged that in life Procoptodon
would have been seen to have but a single toe. This single toe was
actually stronger and would have been less susceptible to injury that
several toes that would have meant more but smaller and weaker bones.
The leg bones were also proportionately more robust than those of
smaller kangaroos with the larger surface areas providing enlarged
anchor points of tendons that attached to the proportionately more
powerful leg muscles that would have been necessary to propel the
larger and heavier body. Used correctly these legs would have also
been a considerable weapon against predators, as well as rival
Procoptodon since kangaroos can be observed today
balancing on their
tails while kicking out at an opponent or something they perceive as a
threat.
The
disappearance of Procoptodon from Australia seems
to coincide with the
arrival of the first humans on the continent, although the precise
date remains a matter of debate with some sources claiming that
Procoptodon may have survived to as recently as just
under twenty
thousand years ago, while others remain steadfast to the
disappearance occurring forty to fifty thousand years ago. The cause
of their extinction is also debated, but the main theory is effects
of people that comes in two parts. The first is that Procoptodon
may
have been hunted by early humans for food, although it seems unlikely
that people would or even could have hunted one of the most common
large marsupials of the time into extinction. A contributing effect
is that of fire stick farming where vast expanses of land are set
alight to encourage fresh growth of plants that are more easily
consumed than the existing growths already there. This would cause a
shift in the availability of plant types that may have suited other
herbivorous animals better than Procoptodon,
leading to increased
strain upon the species.
Further reading
- Systematics and Evolution of the Sthenurine Kangaroos - University of
California Publications in Geological Sciences 146: 1–642 - Gavin
Prideaux - 2004.
- Ecological and evolutionary significance of sizes of giant extinct
kangaroos - Australian Journal of Zoology 54 (4) - K. M. Helgen, R. T.
Wells, B. P. Kear, W. R. Gerdtz & T. F. Flannery - 2006.
- Extinction implications of a chenopod browse diet for a giant
Pleistocene kangaroo - Proceedings of the National Academy of Sciences
106.28 (2009) - Gavin J. Prideaux, Linda K. Ayliffe, Larisa R. G.
DeSantis, BlaineW. Schubert, Peter F. Murray, Michael K. Gagan
& Thure E. Cerling - 2009.
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