Excalibosaurus

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Excalibosaurus
Temporal range: Early Jurassic
Excalibosaurus costini (dark fossil at rear), Lyme Regis, England, Early Jurassic - Royal Ontario Museum - DSC09979.JPG
Fossil, Royal Ontario Museum
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Order: Ichthyosauria
Suborder: Eurhinosauria
Family: Leptopterygiidae
Genus: Excalibosaurus
McGowan, 1986
Binomial name
Excalibosaurus costini
McGowan, 1986

Excalibosaurus (meaning "Excalibur's lizard") is a monotypic genus of marine prehistoric fish-like reptiles (ichthyosaurs) that lived during the Sinemurian stage (approximately 196.5 ± 2 Ma to 189.6 ± 1.5 Ma (million years ago)) of the Early Jurassic period in what is now England. It is characterized by the extreme elongation of the rostrum, with the lower jaw about three fourth of the length of the upper jaw, giving the animal a swordfish-like look. The only known species is Excalibosaurus costini.

Description[edit]

Excalibosaurus costini
Both specimens of Excalibosaurus with a human to scale

This relatively rare animal is known from two skeletons. The holotype, discovered in 1984 near a beach on the Somerset coast, consists of the skull, forefin, part of the pectoral girdle and some vertebrae and ribs. It has been described in 1986 by McGowan.[1] The fossil is hosted in the Bristol City Museum and Art Gallery. The second specimen is an almost complete skeleton collected in the same area in 1996, and was purchased by the Royal Ontario Museum. It was described again by McGowan in 2003.[2]

Excalibosaurus is related to two other genera of ichthyosaurs, Leptonectes from the Rhaetian (Late Triassic) to the Sinemurian (Early Jurassic) of England and Eurhinosaurus from the Toarcian (Early Jurassic) of Germany. The three genera are grouped in the family Leptopterygiidae[3] and the suborder Eurhinosauria.[4] It was once thought that Excalibosaurus was a junior synonym of Eurhinosaurus,[5] but the description of the 1996 specimen show many morphological differences such as the shape of the forefin (much shorter and broader in Excalibosaurus), the slender shape of the body, that clearly differentiate the two genera.[2] The estimate body length of the 1996 specimen is 7 m with a 1.54 m long skull. The holotype specimen was much smaller, with a skull length of 0.785 m and an estimated body length of 4 m, indicating that it was a juvenile.

References[edit]

  1. ^ McGowan, C. (1986). "A putative ancestor for the swordfish-like ichthyosaur Eurhinosaurus". Nature 322 (6078): 454–456. doi:10.1038/322454a0. 
  2. ^ a b McGowan, C. (2003). "A new Specimen of Excalibosaurus from the English Lower Jurassic". Journal of Vertebrate Paleontology 23 (4): 950–956. doi:10.1671/1860-20. 
  3. ^ Maisch, M. W. (1998). "A new ichthyosaurian genus from the Posidonia Shale (Lower Toarcian, Jurassic) of Holzmaden, SW-Germany, with comments on the phylogeny of post-Triassic ichthyosaurs". Neues Jahrbuch fu¨r Geologie und Pala¨ontologie, Abhandlungen 209: 47–78. 
  4. ^ Motani, R. (1999). "Phylogeny of the Ichthyopterygia". Journal of Vertebrate Paleontology 19 (3): 473–496. doi:10.1080/02724634.1999.10011160. 
  5. ^ Maisch, M. W.; A. T. Matzke (2000). "The Ichthyosauria". Stuttgarter Beitrage zur Naturkunde Serie B (Geologie und Palaeontologie) 298: 1–159.