Name: Mesonyx
(Middle claw).
Phonetic: Mee-son-icks.
Named By: Edward Drinker Cope - 1872.
Classification: Chordata, Mammalia, Mesonychia,
Mesonychidae.
Species: M. obtusidens
(type) M. nuhetingensis, M. uqbulakensis. M.
lanius and M. uintensis are also sometimes mentioned but
their validity is uncertain as their appearance is not universal.
Diet: Carnivore.
Size: Between 1.25 and 1.5 meters long, depending upon species.
Known locations: USA - Colorado, Utah and
Wyoming. China.
Time period: Ypresian to Lutetian of the Eocene.
Fossil representation: Many specimens.
Mesonyx
has been repeatedly identified as a wolf-like predator due to its
similar size and overall appearance to modern wolves; although it’s
important to mention that it was not directly related to modern wolves
as Mesonyx appeared (and disappeared) long
before the direct
ancestors of them. Still, Mesonyx probably
filled the same
ecological niche of a predator that runs down its prey which could have
included everything from small to medium sized mammals. It is unknown
if Mesonyx hunted in groups, but current thinking
and fossil evidence
suggests that pack hunting in mammals evolved with the higher levels of
brain power and intelligence that are hall marks of the later members
of the Carnivora group of mammals. Earlier mammalian hunters like
Mesonyx are usually attributed as acting from raw
instinct rather than
developing sophisticated behaviour.
The
high sagittal crest that runs across the top of the skull would have
allowed for the attachment of larger jaw closing muscles. This would
allow for the placement of larger jaw closing muscles that would in
turn proportionately increase the bite force of Mesonyx.
This would
give Mesonyx a crushing bite allowing it to quickly
kill smaller prey
as well as hold on to larger animals that Mesonyx
may have been able to
weaken with successive bites. Mesonyx, along
with other members of
the Mesonychidae were likely some of the top predators of their day.
However the emergence of creodonts such as Hyaenodon
and Sarkastodon
seems to have signalled the extinction for mesonychids as their remains
disappear from the fossil record during the late Eocene.
As
the type genus of the Mesonychia, Mesonyx is
often credited as being
ancestral to whales,
or at the very least closely related to their
ancestors. This is based upon the interpretation that mesonychids
have several similarities with whales, particularly of note,
triangular molar teeth that are also present in many of the earliest
whales, the archaeocetids. However this is an antiquated notion as
later discoveries have found that the earliest whales are more likely
descended from hippopotamids due to much closer skeletal
characteristics.
Mesonyx
was used as the basis for early reconstructions of Andrewsarchus
which
is so far only known from a skull. Because the skull of Mesonyx
is
smaller in life, it was scaled up to a comparable size so that the
increased skeleton could be used as a stand in for the missing
Andrewsarchus remains. This led to Andrewsarchus
being estimated at
six meters long and being declared one of if not the largest meat
eating land mammal of all time. However, modern study has since
cast doubt upon Mesonyx being a good body model as
the skull of
Andrewsarchus is more like that of an enteledont in
proportion. While
this has had greater ramifications for Andrewsarchus,
the wider
paleontological community no longer considers Mesonyx
to be that
closely related to Andrewsarchus as previously
thought.
Further reading
- Descriptions of some new Vertebrata from the Bridger Group of the
Eocene. - Proceedings of the American Philosophical Society 12:460-465.
- Edward Drinker Cope - 1872.
- Skeletons of terrestrial cetaceans and the relationship of whales to
artiodactyls. - Nature 413:277-281. - J. G. M. Thewissen, E. M.
Williams & S. T. Hussain - 2001.
- New mesonychid (Mammalia) material from the Lower Paleogene of the
Erlian Basin, Nei Mongol, China. - Vertebrata PalAsiatica 50 (3):
245–257. - Xun Jin - 2012.