Utatsusaurus is the earliest-known form of an
ichthyopterygiaIchthyopterygia was a designation introduced by Sir Richard Owen in 1840 to designate the Jurassic Ichthyosaurs that were known at the time, but the term is now used more often for both true Ichthyosauria and their more primitive early and middle Triassic ancestors .Basal ichthyopterygians...
n (the group of marine reptiles that includes the ichthyosaurs), which lived in the early
TriassicThe Triassic is a geologic period and system that extends from about 251 to 199 Ma . 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...
period (c. 245-250 millions years ago). Unlike the more advanced ichthyosaurs,
Utatsusaurus has no
dorsal finA dorsal fin is a fin located on the backs of some fish, whales, dolphins, and porpoises, as well as the ichthyosaurs. Depending on the species, an animal can have up to three of them. Its main purpose is to stabilize the animal against rolling and assist in sudden turns...
and has a broad
skullThe skull is a bony structure found in the head of many animals. The skull supports the structures of the face and protects the head against injury....
that tapers slowly toward the snout. For the size of the skull, the teeth are rather small, and arranged in a primitive groove.
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Utatsusaurus is the earliest-known form of an
ichthyopterygiaIchthyopterygia was a designation introduced by Sir Richard Owen in 1840 to designate the Jurassic Ichthyosaurs that were known at the time, but the term is now used more often for both true Ichthyosauria and their more primitive early and middle Triassic ancestors .Basal ichthyopterygians...
n (the group of marine reptiles that includes the ichthyosaurs), which lived in the early
TriassicThe Triassic is a geologic period and system that extends from about 251 to 199 Ma . 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...
period (c. 245-250 millions years ago). Unlike the more advanced ichthyosaurs,
Utatsusaurus has no
dorsal finA dorsal fin is a fin located on the backs of some fish, whales, dolphins, and porpoises, as well as the ichthyosaurs. Depending on the species, an animal can have up to three of them. Its main purpose is to stabilize the animal against rolling and assist in sudden turns...
and has a broad
skullThe skull is a bony structure found in the head of many animals. The skull supports the structures of the face and protects the head against injury....
that tapers slowly toward the snout.
For the size of the skull, the teeth are rather small, and arranged in a primitive groove.
Utatsusaurus had small fins, with four toes instead of the usual five found in primitive ichthyosaurs. The tail had a long low fin, suggesting that the animal swam by
undulationUndulation may refer to:* Lateral undulation, the most primitive of vertebrate locomotor patterns* Law of Undulation, an invention of C. S. Lewis* Undulation of the geoid, the separation between the geoid and the reference ellipsoid of the Earth...
, rather than using its paddles and tail. Feeding on a diet of
fishA fish is any aquatic vertebrate animal that is typically ectothermic , covered with scales, and equipped with two sets of paired fins and several unpaired fins...
,
Utatsusaurus reached a length of three meters (nine feet).
Utatsusaurus has been found in
Japanis an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, People's Republic of China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
and
CanadaCanada is a country occupying most of northern North America, extending from the Atlantic Ocean in the east to the Pacific Ocean in the west and northward into the Arctic Ocean...
.
Ryosuke Motani from the
University of California, BerkeleyThe University of California, Berkeley is a public research university located in Berkeley, California, United States. The oldest of the ten major campuses affiliated with the University of California, Berkeley offers some 300 undergraduate and graduate degree programs in a wide range of disciplines...
and Nachio Minoura from
Hokkaido University, or , is a national university of Japan. It is considered as a member of the National Seven Universities. It is situated in downtown Sapporo, just north of Sapporo Station, and stretching approximately 2.4 kilometers northward.-History:...
re-examined the fossils of
Utatsusaurus in 1998 using computer imagery to reverse the
distortionA distortion is the alteration of the original shape of an object, image, sound, waveform or other form of information or representation. Distortion is usually unwanted...
of the original skeleton. They found that
Utatsusaurus was closely related to the
lizardLizards are a very large and widespread group of squamate reptiles, with nearly 5,000 species, ranging across all continents except Antarctica as well as most oceanic island chains...
-like
diapsidDiapsids are a group of reptiles that developed two holes in each side of their skulls, about 300 million years ago during the late Carboniferous period. Living diapsids are extremely diverse, and include all crocodiles, lizards, snakes, and tuatara...
reptiles such as
PetrolacosaurusPetrolacosaurus was a small, long, reptile, and the earliest diapsid known. It lived during the late Carboniferous period, the Joggins strata where it was found are dated to 302 million years old....
, making ichthyopterygians a distant relative to
lizardLizards are a very large and widespread group of squamate reptiles, with nearly 5,000 species, ranging across all continents except Antarctica as well as most oceanic island chains...
s,
snakeSnakes are elongate legless carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic amniote vertebrates covered in overlapping scales...
s and
crocodileA crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all members of the order Crocodilia: i.e...
s.