Excalibosaurus
Encyclopedia
Excalibosaurus is a monotypic genus
of marine
prehistoric fish-like reptile
s (ichthyosaur
s) 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.
, 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. 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.
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
and the suborder Eurhinosauria. It was once thought that Excalibosaurus was a junior synonym of Eurhinosaurus, 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. 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.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of marine
Marine biology
Marine biology is the scientific study of organisms in the ocean or other marine or brackish bodies of water. Given that in biology many phyla, families and genera have some species that live in the sea and others that live on land, marine biology classifies species based on the environment rather...
prehistoric fish-like reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s (ichthyosaur
Ichthyosaur
Ichthyosaurs were giant marine reptiles that resembled fish and dolphins...
s) that lived during the Sinemurian
Sinemurian
In the geologic timescale, the Sinemurian is an age or stage in the Early or Lower Jurassic epoch or series. It spans the time between 196.5 ± 2 Ma and 189.6 ± 1.5 Ma...
stage (approximately 196.5 ± 2 Ma to 189.6 ± 1.5 Ma (million years ago)) of the Early Jurassic
Early Jurassic
The Early Jurassic epoch is the earliest of three epochs of the Jurassic period...
period in what is now England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
. It is characterized by the extreme elongation of the rostrum
Rostrum (anatomy)
The term rostrum is used for a number of unrelated structures in different groups of animals:*In crustaceans, the rostrum is the forward extension of the carapace in front of the eyes....
, with the lower jaw about three fourth of the length of the upper jaw, giving the animal a swordfish
Swordfish
Swordfish , also known as broadbill in some countries, are large, highly migratory, predatory fish characterized by a long, flat bill. They are a popular sport fish of the billfish category, though elusive. Swordfish are elongated, round-bodied, and lose all teeth and scales by adulthood...
-like look. The only known species is Excalibosaurus costini.
Description
This relatively rare animal is known from two skeletons. The holotypeHolotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
, discovered in 1984 near a beach on the Somerset
Somerset
The ceremonial and non-metropolitan county of Somerset in South West England borders Bristol and Gloucestershire to the north, Wiltshire to the east, Dorset to the south-east, and Devon to the south-west. It is partly bounded to the north and west by the Bristol Channel and the estuary of the...
coast, consists of the skull, forefin, part of the pectoral girdle and some vertebrae and ribs. It has been described in 1986 by McGowan. The fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
is hosted in the Bristol City Museum and Art Gallery
Bristol City Museum and Art Gallery
The Bristol City Museum and Art Gallery is a large museum and art gallery in Bristol, England. It is run by the city council with no entrance fee. It holds designated museum status, granted by the national government to protect outstanding museums...
. The second specimen is an almost complete skeleton collected in the same area in 1996, and was purchased by the Royal Ontario Museum
Royal Ontario Museum
The Royal Ontario Museum is a museum of world culture and natural history in Toronto, Ontario, Canada. With its main entrance facing Bloor Street in Downtown Toronto, the museum is situated north of Queen's Park and east of Philosopher's Walk in the University of Toronto...
. It was described again by McGowan in 2003.
Leptonectes
Leptonectes is a genus of ichthyosaur that lived in the Late Triassic to Early Jurassic . Fossils have been found in Belgium, England, Germany and Switzerland....
from the Rhaetian
Rhaetian
The Rhaetian is in geochronology the latest age of the Triassic period or in chronostratigraphy the uppermost stage of the Triassic system. It lasted from 203.6 ± 1.5 to 199.6 ± 0.6 million years ago...
(Late Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
) to the Sinemurian (Early Jurassic) of England and Eurhinosaurus
Eurhinosaurus
Eurhinosaurus is an extinct genus of ichthyosaur from the Early Jurassic of Europe...
from the Toarcian
Toarcian
The Toarcian is, in the ICS' geologic timescale, an age or stage in the Early or Lower Jurassic. It spans the time between 183.0 Ma and 175.6 Ma...
(Early Jurassic) of Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
. The three genera are grouped in the family Leptopterygiidae
Leptopterygiidae
Leptopterygiidae is a family containing three kinds of ichthyosaurs. They were all small to medium sized creatures, most noted for their very long, swordfish-like snouts, which could have been used like a weapon, slashing through schools of fish....
and the suborder Eurhinosauria. It was once thought that Excalibosaurus was a junior synonym of Eurhinosaurus, 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. 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.