Eusmilus
Name: Eusmilus
(Early knife).
Phonetic: Yew-smy-lus.
Named By: Eusmilus - 1876.
Synonyms: Ekgmoiteptecela olsontau,
Eusmilus belli, Hoplophoneus belli, Hoplophoneus cerebralis,
Hoplophoneus sicarius, Machaerodus cerebralis.
Classification: Chordata, Mammalia, Carnivora,
Nimravidae, Hoplophoninae.
Species: E. bidentatus (type), E.
villebramarensis.
Diet: Carnivore.
Size: Up to 2.5 meters long.
Known locations: Eurasia and North America.
Time period: Priabonian of the Eocene to Rupelian of
the Oligocene.
Fossil representation: Multiple specimens.
Out
of all of the nimravids,
mammalian predators better known as the
‘false sabre-toothed cats’, Eusmilus seems to
have been one of the
most dangerous. Not only did Eusmilus grow to be
one of the largest
known nimravids at up to two and a half meters long, but a skull of
its smaller relative Nimravus
has been found with skull damage that is
an almost precise match for the teeth of Eusmilus.
This however may
have been a case of one predator warning another away rather than an
attempt of killing to feed since the wounds on the individual Nimravus
in question actually healed.
As
anyone who is already familiar with nimravids knows, Eusmilus
looked
like one of the later sabre toothed cats, but was in fact no way
related them beyond being a member of the Carnivora. Nimravids like
Eusmilus evolved down a separate genetic line, but
found themselves
living in a world where there was a predatory niche open for cat-like
predators. Growing large and possessing enlarged upper canine teeth
that were almost as long as the skull, Eusmilus
would have been a
hunter of other medium to large sized animals.
The
enlarged canines that are nicknamed ‘sabre-teeth’ were the primary
killing tools employed by Eusmilus and analysis of
the skeleton
supports this. The muscle attachment points on the skull show that
Eusmilus actually had weak jaw closing muscles,
but this was to allow
for a wide jaw opening angle. Reconstructions of Eusmilus
show that
its jaw could open to an impressive ninety degrees wide, thirty
degrees more than a modern African lion (Panthera leo).
However
this still pales in comparison to the later Smilodon
which had the
ability to open its jaws one hundred and twenty degrees wide. These
wide jaw opening angles allow for the sabre-teeth to be brought into
use without the lower jaw getting in the way.
To
compensate the weak bite force, the neck and shoulders were designed
to allow for powerful downward thrusts that drove the sabre-teeth
through its victim without the need for using the jaw muscles. When
these teeth punctured a critical area such as neck, death would come
in a matter of minutes at most for the prey. Despite their awesome
killing power however, the large sabre-teeth of Eusmilus
would have
been quite weak when subjected to side to side movements and it’s
probably that Eusmilus would have had to use its
size and strength to
physically restrain its prey before trying to use its teeth. This
would be a vital precaution to take since if the teeth were broken,
Eusmilus really had no other way of efficiently
killing prey animals.
This
is also why the lower jaw also has two flanges of bone than project
downwards. This is because the canine teeth of Eusmilus
are so large
they would easily clear the bottom of the lower jaw had it not had the
flanges, increasing the likely hood of them being broken should
Eusmilus get hit in the face by a struggling
animal, or colliding
with something while it was running after prey. The concept of
protecting the canine teeth in this way is such an effective and
necessary principal that it occurs in other sabre-toothed mammals such
as the South American Thylacosmilus.
Whereas Eusmilus
is only
distantly related to true cats (members of the Felidae), it is
even more distantly related to Thylacosmilus since
this was a marsupial
mammal, while Eusmilus was a placental mammal,
a type that appeared
after the marsupials. Once again this is another case of convergent
evolution since while Eusmilus and other nimravids
lived in a world
devoid of true cats, Thylacosmilus lived on a
continent not only
devoid of cats but the nimravids as well, yet all of these predators
ended up fulfilling the ecological niche in their habitats.
Further reading
- The Miocene faunas from the Wounded Knee area of western South
Dakota. - Bulletin of the American Museum of Natural History. - J. R.
Macdonald - 1963.
- Functional morphology and the evolution of cats. - Transactions of
the Nebraska Academy of Sciences 8:141-153. - L. D. Martin - 1980.
- Taxonomic and systematic revisions to the North American Nimravidae
(Mammalia, Carnivora). - PeerJ. 4: e1658. - P. Z. Barrett - 2016.
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