Ophthalmosaurus

Ophthalmosaurus Temporal range: Middle - Late Jurassic, 165–145 Ma PreЄ Є O S D C P T J K Pg N
Ophthalmosaurus icenicus skeleton
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	†Ichthyosauria
Family:	†Ophthalmosauridae
Genus:	†Ophthalmosaurus Seeley, 1874
Species
†O. icenicus Seeley, 1874 (type species) ?†O. natans (Marsh, 1879 [originally Sauranodon nom. praeocc.]) †O. saveljeviensis (Arkhangelsky, 1997 [originally Paraophthalmosaurus]) †O. yasykovi (Efimov, 1999 [originally Yasykovia])
Synonyms
see text

Ophthalmosaurus (meaning “eye lizard” in Greek) is an ichthyosaur of the Middle to Late Jurassic period (165 to 145 million years ago), named for its extremely large eyes. It had a graceful 6 metre long dolphin-shaped body, and its almost toothless jaw was well adapted for catching squid. Major fossil finds of this genus have been recorded in Europe and North America.

Discovery and species

Ophthalmosaurus yasikovi.

Ophthalmosaurus with a human to scale

The genera Apatodontosaurus, Ancanamunia, Baptanodon, Mollesaurus‎, Paraophthalmosaurus‎, Undorosaurus and Yasykovia‎ were all considered junior synonyms of Ophthalmosaurus by Maisch & Matzke, 2000.^[1] However, all recent cladistic analyses found that Mollesaurus periallus from Argentina is a valid genus of ophthalmosaurid.^[2][3] Ophthalmosaurus natans is probably not a species of Ophthalmosaurus either,^[2] for which the generic name Baptanodon Marsh, 1880 is available. Undorosaurus's validity is now accepted by most authors, even by Maisch (2010) who originally proposed the synonymy.^{[4][5][6][7][3]} and the two other russian taxon might be also valid.^[6][3] Ophthalmosaurus chrisorum Russell, 1993 was moved to its own genus Arthropterygius in 2010 by Maxwell.^[8]

Within Ophthalmosauridae, Ophthalmosaurus is most closely related to Aegirosaurus.^[9]

Palaeobiology

Like other ichthyosaurs, Ophthalmosaurus gave birth to its pups tail-first to avoid drowning them. Skeletons of unhatched young have been found in over fifty females on fossil finds, and litter sizes ranged from two to eleven pups.

Ophthalmosaurus had a body shaped like a tear-drop and a caudal fin like a half-moon. Its forelimbs were more developed than the hind ones, which suggests that the front fins did the steering while the tail did the propelling. Ophthalmosaurus' chief claim to fame is its eyes which, at 4 inches in diameter, were extremely large in proportion to its body. The eyes occupied almost all of the space in the skull and were protected by bony plates (sclerotic rings), which most likely assisted to maintain the shape of the eyeballs[2] against water pressure at depth. The size of the eyes and the sclerotic rings suggests that Ophthalmosaurus hunted at a depth where there is not much light or that it may have hunted at night when a prey species was more active.

Calculations suggest that a typical Ophthalmosaurus could stay submerged for approximately 20 minutes or more[3]. The swimming speed of Ophthalmosaurus has been estimated at 2.5 m/s or greater, but even assuming a conservative speed of 1 m/s, an Ophthalmosaurus would be able to dive to 600 meters and return to the surface within 20 minutes.

In the bone joints of Ophthalmosaurus skeletons traces of decompression sickness (the bends) have been found, possibly caused as a result of evasive tactics. Modern whales have been known to get the bends when ascending rapidly to escape predators.^[10]

In popular culture

• Ophthalmosaurus was featured in the third episode of the BBC television series Walking with Dinosaurs, with a male pup being one of the main characters.
• An Ophthalmosaurus named "Mo" was a featured character in the movie The Land Before Time IX: Journey to Big Water

See also

• List of ichthyosaurs

Paleontology portal

References

1. ^ Maisch MW, Matzke AT. 2000. The Ichthyosauria. Stuttgarter Beiträge zur Naturkunde Serie B (Geologie und Paläontologie) 298: 1-159.
2. ^ ^{a b} Patrick S. Druckenmiller and Erin E. Maxwell (2010). "A new Lower Cretaceous (lower Albian) ichthyosaur genus from the Clearwater Formation, Alberta, Canada". Canadian Journal of Earth Sciences 47 (8): 1037–1053. doi:10.1139/E10-028. http://rparticle.web-p.cisti.nrc.ca/rparticle/AbstractTemplateServlet?calyLang=eng&journal=cjes&volume=47&year=0&issue=8&msno=e10-028. 
3. ^ ^{a b c} Fischer, V.; Masure, E.; Arkhangelsky, M.S.; and Godefroit, P. (2011). "A new Barremian (Early Cretaceous) ichthyosaur from western Russia". Journal of Vertebrate Paleontology 31 (5): 1010–1025. doi:10.1080/02724634.2011.595464. http://www.tandfonline.com/doi/abs/10.1080/02724634.2011.595464. 
4. ^ Storrs, Glenn W.; Vladimir M. Efimov and Maxim S. Arkhangelsky (2000). "Mesozoic marine reptiles of Russia and other former Soviet republics". In Benton, M.J.; Shishkin, M.A.; and Unwin, D.M.. The Age of Dinosaurs in Russia and Mongolia. Cambridge: Cambridge University Press. pp. 140–159. ISBN 052154582X, 9780521545822. 
5. ^ McGowan C, Motani R. 2003. Ichthyopterygia. – In: Sues, H.-D. (ed.): Handbook of Paleoherpetology, Part 8, Verlag Dr. Friedrich Pfeil, 175 pp., 101 figs., 19 plts; München
6. ^ ^{a b} Michael W. Maisch (2010). "Phylogeny, systematics, and origin of the Ichthyosauria – the state of the art". Palaeodiversity 3: 151–214. http://www.palaeodiversity.org/pdf/03/Palaeodiversity_Bd3_Maisch.pdf. 
7. ^ Fischer, V.; A. Clement, M. Guiomar and P. Godefroit (2011). "The first definite record of a Valanginian ichthyosaur and its implications on the evolution of post-Liassic Ichthyosauria". Cretaceous Research 32 (2): 155–163. doi:10.1016/j.cretres.2010.11.005. http://www.sciencedirect.com/science/article/pii/S0195667110001114. 
8. ^ Maxwell, E.E. (2010). "Generic reassignment of an ichthyosaur from the Queen Elizabeth Islands, Northwest Territories, Canada". Journal of Vertebrate Paleontology 30 (2): 403–415. doi:10.1080/02724631003617944. 
9. ^ Fernández M. 2007. Redescription and phylogenetic position of Caypullisaurus (Ichthyosauria: Ophthalmosauridae). Journal of Paleontology 81 (2): 368-375.
10. ^ Cannon, John. 2007. Why Do Whales Get the Bends?. ScienceNOW Daily News. [1].

External links

• Walking With Dinosaurs - Fact File: Ophthalmosaurus