Eurhinosaurus
Name:
Eurhinosaurus
(Well nosed lizard).
Phonetic: Yoo-rye-noe-sore-us.
Named By: Abel - 1909.
Classification: Chordata, Reptilia,
Ichthyosauria, Leptopterygiidae.
Species: E. longirostris (type),
E. costini.
Diet: Piscivore.
Size: Around 6.4 meters long.
Known locations: England and Germany.
Time period: Sinemurian through to the Toarcian of
the Jurassic.
Fossil representation: Specimens for identification
of two species, at least one specimen is of a complete individual.
Eurhinosaurus
is one member of what still appears to be a small group of ichthyosaurs
that had specialised asymmetrical jaws. What this means in more
detail is that the rostrum of the upper jaw extended beyond the lower
jaw to give Eurhinosaurus a head and set of jaws
that resemble a modern
day swordfish. For an ichthyosaur this is quite unusual as normally
both jaws are of roughly equal length to provide a longer ‘catch
area’ which makes trapping prey like fish between the jaws much
easier. In addition to being longer than the lower jaw, the
elongated snout also had side wards pointing teeth.
Eurhinosaurus
has especially well developed frontal fins, something that suggests
it may have been a fast swimmer. This is a simple principal where the
thrashing of the tail pushes the animal through the water, but it
does not counter the body weight so that the animal actually ends up
pitching down into the depths. As such the more powerful the tail and
faster the swim, the greater the downwards pitching effect becomes.
The front fins counter this problem by acting as hydroplanes that can
be adjusted to keep the animal level and pointed in the desired
direction. The larger the fins the greater the benefit and the faster
that said animal can swim.
With
the above principal in mind, Eurhinosaurus may
have been one of the
fastest marine reptiles of its time, and was probably faster than the
related Excalibosaurus
which had proportionately shorter limbs. With
a nose like a sword fish, and possibly speed like a swordfish,
Excalibosaurus may have also hunted like a
swordfish. Eurhinosaurus
probably devolved these fast swimming features to chase down fast
swimming fish, but these would be difficult to catch by just the
mouth. By using the elongated rostrum to swipe at fish in front of
it, Eurhinosaurus could cause injury to their
flanks, severely
hampering the prey’s ability to swim out of danger, making capture by
the mouth easier for Eurhinosaurus to accomplish.
This is where the
side wards pointing teeth would come into play; whereas a swordfish
can lash against fish, Eurhinosaurus would tear
into the flanks as
well, the teeth causing even worse injuries to the prey.
Aside
from Excalibosaurus, Eurhinosaurus
is also related to Leptonectes
which is actually the type genus of the Leptopterygiidae group of
ichthyosaurs to which Eurhinosaurus belongs.
Further reading
- First record of the leptonectid ichthyosaur Eurhinosaurus
longirostris from the Early Jurassic of Switzerland and its
stratigraphic framework. - Swiss Journal of Geosciences 104(2):
211-224. - A. G. Reisdorf, M. W. Maisch & A. Wetzel - 2011.
- New data on the palaeobiogeography of Early Jurassic marine reptiles:
the Toarcian ichthyosaur fauna of the Vocontian Basin (SE France). -
Neues Jahrbuch f�r Geologie und Pal�ontologie, Abhandlungen 261(1):
111-127 - V. Fischer, M. Guiomar & P. Godefroit - 2011.
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