Andrewsarchus
Name:
Andrewsarchus
(Andrew's ruler)
Phonetic: An-dru-sar-kus.
Named By: Discovered by Kan Chuen Pao in 1923,
Henry Fairfield Osborn wrote the description in 1924.
Classification: Chordata, Mammalia, Artiodactyla, Cetancodontamorpha.
Species: A. mongoliensis (type).
Diet: Carnivore.
Size: Total size uncertain due to lack of remains.
Skull is 83 centimetres long.
Known locations: Mongolia.
Time period: Lutetian through to Priabonian of the
Eocene.
Fossil representation: Skull.
In
popular culture, especially at the turn of the twentieth and
twenty-first centuries, Andrewsarchus has been
presented as a huge
predator, similar in form to other quadrupedal meat eating mammals,
but powerfully built like a big cat or even a bear. However despite
this reconstruction becoming very familiar in the public
consciousness, palaeontologists are far more cautious as so far only
the skull of this animal is known.
The
popular reconstruction is based upon the concept that for a long time
Andrewsarchus was envisioned as a larger relative of
Mesonyx,
a meat
eating predator that is often described as wolf-like, although it
actually appeared long before the emergence of true wolves. Later
interpretations of Andrewsarchus however (one of
best known being a
2009 study by Michelle Spaulding, Maureen A. O’Leary and John
Gatesy) have since concluded that Andrewsarchus
probably isn’t that
closely related to Mesonyx. In fact today Andrewsarchus
has been
widely considered to be closer to primitive hippos or even enteledonts
due to the long jaws with wide cheek bones.
The
exact diet of Andrewsarchus has also been
questioned as the previous
older apex predator theories don’t carry as much weight as they used
to. Although the jaws would have had tremendously powerful muscles
(as indicated by the size of the cheek bones), most of the teeth
in the mouth are not particularly well adapted for any one purpose.
The forward canines are the largest and are most useful for getting a
grip on things, or perhaps in the case of a carnivore to deliver a
killing bite such as puncturing the cranium of a prey animal. Because
the type specimen skull was found in what would have been a coastal
environment during the Eocene, Andrewsarchus has
been presented as a
beach comber. Here Andrewsarchus may have had a
durophagus diet that
means it ate shellfish that it dug out with its forward teeth,
although it may have included animals like turtles as well as washed
up carrion. However while this skull proves that Andrewsarchus
was
active in coastal areas, it would be a mistake to assume that it
was limited to them without the evidence of further remains.
Aside
from the skull being similar in form this has also led to some claiming
that the behaviour of Andrewsarchus was similar to
what has been
proposed for enteledonts. This would see Andrewsarchus
living the
life of an opportunistic omnivore, as while Andrewsarchus
is on paper
capable of killing its own prey, it may have scavenged carcasses as
well as driven off other predators from their kills. The forward
teeth could also have been capable of digging up plant tubers that
Andrewsarchus could have then eaten.
Since
Andrewsarchus had a large skull it would need strong
neck muscles to
provide ample support. Although we still do not know for certain,
it’s possible that the anterior dorsal vertebrae had enlarged neural
spines (bony projections that rise upwards from the individual
vertebra) that provided increased areas for muscle attachment.
This is similar to how some other creatures with large skulls such as
enteledonts supported their heads. If true then Andrewsarchus
would
in life have powerful powerfully built fore quarters which may have
given rise to a small hump above its shoulders from the increased
muscle mass from this area.
When
Andrewsarchus was first compared to Mesonyx
its missing body was
estimated by scaling up the skull of Mesonyx to
that of Andrewsarchus.
This led to early size estimates of up to six meters long, something
that saw Andrewsarchus being treated as possibly
the largest meat
eating mammal to ever walk the earth. However there are a number of
problems with this estimate, the most obvious being the general
consensus that Andrewsarchus was not like Mesonyx
at all which
automatically makes this size comparison flawed. Second is that it is
impossible to say how heavily built Andrewsarchus
was without
seeing how things like muscles could attach to the skeleton.
For
example the dire
wolf (Canis dirus) is skeletally not
much
larger
that the grey wolf (Canis lupus), but the
bones are thicker and
the muscle attachment points are much more strongly developed which
indicates that it had a larger muscle mass making it a bigger animal.
Also other large meat eating mammals such as the short faced bear
Arctodus
are very large, but have comparatively lightweight builds so
that their immense size does not weigh them down. This is where the
confusion about Andrewsarchus lies, as a
terrestrial predator with a
physically large skeleton needs some way to reduce its weight otherwise
it’s simply too slow to catch anything. This might not be such a
problem if Andrewsarchus could hunt large and
equally slow prey, but
this first needs to be available in sufficient quantities to keep the
large body going, as well as a population to continue the species.
Another argument that counts against Andrewsarchus
being the largest
ever carnivore is comparison to similarly large skulled animals like
enteledonts. These animals also have large skulls and shoulder areas
to support the head, but the main body itself is very gracile so as
not to put too much strain upon the intake of food. Of course without
more complete remains we will never know how large Andrewsarchus
was,
but while it is still treated by some as being one of if not the
largest mammalian predator, most researchers prefer to consider
large bears as the biggest terrestrial mammalian predators.
Like
with many mammals the demise of Andrewsarchus may
have been brought
about by a combination of climate change and new animals appearing on
the landscape. The rising Himalaya Mountains resulted in much of Asia
becoming a drier expanse of plains which in turn created a shift
towards different types of potential prey. Enteledonts also started
to become widespread although they were mostly smaller varieties when
compared to their giant forms of the early Miocene. New predators
such as creodonts like Hyaenodon
and the bear-like Sarkastodon
were
also beginning to fill the top predator niches.
Andrewsarchus was named in honour of Roy Chapman Andrews.
Further reading
- Andrewsarchus, giant mesonychid of Mongolia. - American Museum
Novitates 146:1-5. - H. F. Osborn - 1924.
-
Relationships of Cetacea (Artiodactyla) Among Mammals: Increased Taxon
Sampling Alters Interpretations of Key Fossils and Character Evolution.
- PLoS ONE. 4 (9): e7062. - M. Spaulding, M. A. O’Leary & J.
Gatesy
- 2009.
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