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Ophthalmosaurus

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Ophthalmosaurus
Temporal range: Middle-Late Jurassic
~165–160 Ma
↓
O. icenicus skeleton
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: †Ichthyosauria
Family: †Ophthalmosauridae
Subfamily: †Ophthalmosaurinae
Genus: †Ophthalmosaurus
Seeley 1874
Type species
Ophthalmosaurus icenicus
Species
Synonyms
  • Ancanamunia Rusconi 1942
  • Khudiakovia Arkhangelsky 1999

Ophthalmosaurus (meaning “eye lizard” in Greek) is an ichthyosaur of the Middle Jurassic period (165-160 million years ago), named for its extremely large eyes. It had a graceful 6 m (19.5 ft) 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 and South America.

Description

Ophthalmosaurus with a human to scale

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 (some reaching about 9 inches or 220–230 mm in diameter) [2][3] which 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 [4] 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.

Discovery and species

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][4] Ophthalmosaurus natans has been recovered as closer to other ophthalmosaurines than to the Ophthalmosaurus type species,[2][4][5] necessitating resurrection of Baptanodon Marsh, 1880 as the only available generic name. Undorosaurus's validity is now accepted by most authors, even by Maisch (2010) who originally proposed the synonymy.[3][6][7][8][9] and the two other Russian taxa might be also valid.[3][8] Ophthalmosaurus chrisorum Russell, 1993 was moved to its own genus Arthropterygius in 2010 by Maxwell.[10] On the other hand, Paraophthalmosaurus and Yasykovia are apparently valid and distinct from Ophthalmosaurus.[11][12]

Classification

O. icenicus in Tubingen

Within Ophthalmosauridae, Ophthalmosaurus was once considered most closely related to Aegirosaurus.[13] However, many recent cladistic analyses found Ophthalmosaurus to nest in a clade with Acamptonectes and Mollesaurus. Aegirosaurus was found more closely related to Platypterygius, and thus does not belong to the Ophthalmosaurinae.[3][4]

The cladogram below follows Fischer et al. 2012.[4]

Thunnosauria 

Palaeobiology

Restoration

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. [citation needed]

Ophthalmosaurus could likely dive for around 20 minutes. Assuming a conservative crusing speed of 1 metre per second (3.3 ft/s) (2 metres per second (6.6 ft/s) being more likely), Ophthalmosaurus could reach depths of 600 metres (2,000 ft) or more during a dive, reaching the mesopelagic zone.[15]

Scientists have found evidence of decompression sickness (the bends) in the bone joints of Ophthalmosaurus skeletons, possibly caused by evasive tactics. Modern whales have been known to get the bends when they ascend rapidly to escape predators.[16]

See also

References

  1. ^ Maisch MW, Matzke AT. 2000. The Ichthyosauria. Stuttgarter Beiträge zur Naturkunde Serie B (Geologie und Paläontologie) 298: 1-159.
  2. ^ a b "A new Lower Cretaceous (lower Albian) ichthyosaur genus from the Clearwater Formation, Alberta, Canada". Canadian Journal of Earth Sciences. 47 (8): 1037–1053. 2010. Bibcode:2010CaJES..47.1037D. doi:10.1139/E10-028. {{cite journal}}: Unknown parameter |authors= ignored (help)[permanent dead link‍]
  3. ^ a b c d Fischer, Valentin; Edwige Masure; Maxim S. Arkhangelsky; 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.
  4. ^ a b c d Valentin Fischer; Michael W. Maisch; Darren Naish; Ralf Kosma; Jeff Liston; Ulrich Joger; Fritz J. Krüger; Judith Pardo Pérez; Jessica Tainsh; 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. Bibcode:2012PLoSO...729234F. doi:10.1371/journal.pone.0029234. PMC 3250416. PMID 22235274.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  5. ^ Ilaria Paparella; Erin E. Maxwell; Angelo Cipriani; Scilla Roncacè; Michael W. Caldwell (2017). "The first ophthalmosaurid ichthyosaur from the Upper Jurassic of the Umbrian–Marchean Apennines (Marche, Central Italy)". Geological Magazine. 154 (4): 837–858. doi:10.1017/S0016756816000455.
  6. ^ Storrs, Glenn W.; Vladimir M. Efimov; Maxim S. Arkhangelsky (2000). "Mesozoic marine reptiles of Russia and other former Soviet republics". The Age of Dinosaurs in Russia and Mongolia. Cambridge: Cambridge University Press. pp. 140–159. ISBN 9780521545822. {{cite book}}: Unknown parameter |editors= ignored (|editor= suggested) (help)
  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. ^ a b "Phylogeny, systematics, and origin of the Ichthyosauria – the state of the art" (PDF). Palaeodiversity. 3: 151–214. 2010. {{cite journal}}: Unknown parameter |authors= ignored (help)
  9. ^ Fischer, V.; A. Clement; M. Guiomar; 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. ^ Storrs, Glenn W., Maxim S. Arkhangel'skii, and Vladimir M. Efimov. 2000. Mesozoic marine reptiles of Russia and other former Soviet republics. In: Michael J. Benton, Michael A. Shishkin, David M. Unwin, and Evgenii N. Kurochkin (eds.), The Age of Dinosaurs in Russia and Mongolia, Cambridge University Press, pp. 187-210.
  12. ^ N. G. Zverkov, M. S. Arkhangelsky and I. M. Stenshin (2015) A review of Russian Upper Jurassic ichthyosaurs with an intermedium/humeral contact. Reassessing Grendelius McGowan, 1976. Proceedings of the Zoological Institute 318(4): 558-588
  13. ^ Fernández M. 2007. Redescription and phylogenetic position of Caypullisaurus (Ichthyosauria: Ophthalmosauridae). Journal of Paleontology 81 (2): 368-375.
  14. ^ Arkhangel’sky, M. S., 1998, On the Ichthyosaurian Genus Platypterygius: Palaeontological Journal, v. 32, n. 6, p. 611-615.
  15. ^ Motani, Ryosuke (2005). "Evolution of fish-shaped reptiles (Reptilia: Ichthyopterygia) in their physical environments and constraints" (PDF). Annual Review of Earth and Planetary Sciences. 33: 395–420. Bibcode:2005AREPS..33..395M. doi:10.1146/annurev.earth.33.092203.122707.
  16. ^ Cannon, John. 2007. Why Do Whales Get the Bends?. ScienceNOW Daily News. [1].
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