Ophthalmosaurus

*Ophthalmosaurus icenicus*

***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 large eyes. It has a graceful 6 meter long dolphin-shaped body, and its almost toothless jaw was well adapted to catch squid. Major fossils have been found in Europe and North America.

## Description

*Ophthalmosaurus* had a certain resemblance to the swordfish due to its long snout and end. The head was round with two large eyes adapted to night hunting. It had fins instead of legs, as well as the tail of a fish and a dorsal fin.

Relative to its body size, *Ophthalmosaurus* had the largest eyes of any vertebrate. Its eyes, 4 inches in width, took up most of the space in the skull. They were protected by bony plates, which most likely helped to keep the shape of the eyeballs against water pressure at depth.

## Discovery and species

*Apatodontosaurus*, *Ancanamunia*, *Baptanodon*, *Mollesaurus‎*, *Paraophthalmosaurus‎*, *Undorosaurus* and *Yasykovia‎* were all deemed as synonyms of *Ophthalmosaurus* by Maisch & Matzke, 2000, but newer studies found that *Mollesaurus periallus* from Argentina is a valid genus of ophthalmosaurid. *Ophthalmosaurus natans* is likely not a kind of *Ophthalmosaurus* either, for which the genus name *Baptanodon* Marsh, 1880 is available. *Undorosaurus's* is now deemed valid by most authors, even by Maisch (2010) who once thought the synonymy and the two other Russian taxon might be valid too. *Ophthalmosaurus chrisorum* Russell, 1993 was moved to its own genus, *Arthropterygius*, in 2010 by Maxwell.

In Ophthalmosauridae, *Ophthalmosaurus* was viewed to be most closely related to *Aegirosaurus*. However, most recent studies found *Ophthalmosaurus* to nest in a clade with *Acamptonectes* and *Mollesaurus*. *Aegirosaurus* was found to be more closely related to *Platypterygius*, and thus it doesn't belong to the Ophthalmosaurinae.

## Classification

### List of species

* *Ophthalmosaurus icenicus* Seeley, 1874 (type species)
* *Ophthalmosaurus natans*
* *Ophthalmosaurus saveljeviensis*
* *Ophthalmosaurus yasykovi*
* *Ophthalmosaurus gorodischensis*
* *Ophthalmosaurus periallus*

## Paleobiology

Like all ichthyosaurs, *Ophthalmosaurus* gave birth to its pups tail-first so it won't drown them. Skeletons of unhatched young have been found in more than 50 females on fossil finds, and litter sizes ranged from 2 to 11 pups.

The size of the eyes and the bony plates suggests that *Ophthalmosaurus* hunted at a depth where there is not much light or that it may have hunted at night when prey was more active.

Estimates suggest that a typical *Ophthalmosaurus* could stay submerged for about 20 minutes or more. The swimming speed of *Ophthalmosaurus* has been estimated at 2.5 m/s or greater. Even taking a conservative speed of 1 m/s, an *Ophthalmosaurus* would be able to dive to 600 meters and back to the surface in 20 minutes.

## Dinosaur Field Guide Description

Ophthalmosaurus ("eye lizard") was shaped like a dolphin. It had flippers for hands and feet, which it used for steering through the water. It had a dorsal fin on top of its body, and a half-moon-shaped tail fin, which would have helped make it a very fast swimmer. Ophthalmosaurus was one of the ichthyosaurs, or fish lizards. They were neither fish nor lizards, but were related to the plesiosaurs. Although dolphins and ichthyosaurs look similar, there are many important differences. Dolphins are a kind of mammal, whereas ichthyosaurs were reptiles. Dolphins primarily use sonar (sending out and listening for special sound waves) to tell where objects are underwater: There is no evidence that ichthyosaurs used sonar, but they did have enormous eyes to see their prey. Ichthyosaurs ate mainly squid and they probably ate some fish. Ichthyosaurs would not have been able to support themselves on land to lay their eggs. Instead, as fossils show us, their babies grew inside the body of the mother until they were large enough to
swim on their own. Then, like dolphins, they were born tail first.

## Fun Facts

The largest ichthyosaur had eyes over 10 inches (26 cm) across the largest eyes of any known animal in the history of the Earth!

## Trivia

Ophthalmosaurus may have been able to dive almost a mile (1.6 km) down
in the water while chasing after its food.

## References

1. ↑ University of California Museum of Natural History: Motani's ichthyosaur page [1]
2. ↑ Maisch MW, Matzke AT. 2000. The Ichthyosauria. Stuttgarter Beiträge zur Naturkunde Serie B (Geologie und Paläontologie) 298: 1-159.
3. ↑ 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.
4. ↑ Fischer, Valentin; Edwige Masure, Maxim S. Arkhangelsky and Pascal Godefroit (2011). "A new Barremian (Early Cretaceous) ichthyosaur from western Russia". Journal of Vertebrate Paleontology 31 (5): 1010–1025. doi:10.1080/02724634.2011.595464.
5. ↑ Valentin Fischer, Michael W. Maisch, Darren Naish, Ralf Kosma, Jeff Liston, Ulrich Joger, Fritz J. Krüger, Judith Pardo Pérez, Jessica Tainsh and Robert M. Appleby (2012). "New Ophthalmosaurid Ichthyosaurs from the European Lower Cretaceous Demonstrate Extensive Ichthyosaur Survival across the Jurassic–Cretaceous Boundary". PLoS ONE 7 (1): e29234. doi:10.1371/journal.pone.0029234.
6. ↑ 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.
7. ↑ 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
8. ↑ Michael W. Maisch (2010). "Phylogeny, systematics, and origin of the Ichthyosauria – the state of the art". Palaeodiversity 3: 151–214.
9. ↑ 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.
10. ↑ 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.
11. ↑ Fernández M. 2007. Redescription and phylogenetic position of Caypullisaurus (Ichthyosauria: Ophthalmosauridae). Journal of Paleontology 81 (2): 368-375.
12. ↑ Fischer, Valentin; Edwige Masure, Maxim S. Arkhangelsky and Pascal Godefroit (2011). "A new Barremian (Early Cretaceous) ichthyosaur from western Russia". Journal of Vertebrate Paleontology 31 (5): 1010–1025. doi:10.1080/02724634.2011.595464.
13. ↑ Valentin Fischer, Michael W. Maisch, Darren Naish, Ralf Kosma, Jeff Liston, Ulrich Joger, Fritz J. Krüger, Judith Pardo Pérez, Jessica Tainsh and Robert M. Appleby (2012). "New Ophthalmosaurid Ichthyosaurs from the European Lower Cretaceous Demonstrate Extensive Ichthyosaur Survival across the Jurassic–Cretaceous Boundary". PLoS ONE 7 (1): e29234. doi:10.1371/journal.pone.0029234.
14. ↑ University of California Museum of Natural History: Motani's ichthyosaur page [2]