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 für Geologie und Paläontologie, Abhandlungen 261(1): 111-127 - V. Fischer, M. Guiomar & P. Godefroit - 2011.



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