Utatsusaurus

Utatsusaurus hataii is the earliest-known ichthyopterygian. It lived during the Early Triassic period, about 245–250 million years ago. It was about 2.5 to 3 metres long and had a slender body. The first fossil of Utatsusaurus was found in Utatsu-cho, a place that is now part of Minamisanriku-cho, in Miyagi Prefecture, Japan.

This dinosaur is the only species in its genus, called Utatsusaurus. It is also the only member of the family Utatsusauridae. The name Utatsusaurus comes from the city where the first fossils were found. More fossils have been found in the Early Triassic Osawa Formation in Miyagi Prefecture, Japan, as well as in British Columbia, Canada.

Utatsusaurus is considered one of the most basic types of ichthyosaurs. This makes it very important for scientists who study these ancient creatures.

Description

Utatsusaurus was a small ancient sea creature that lived about 245–250 million years ago. It was about 2.5–3 metres (8.2–9.8 ft) long and weighed around 57.8 kg (127 lb).

Utatsusaurus with a human to scale.

Unlike later sea reptiles, Utatsusaurus did not have a dorsal fin on its back and had a broad skull. Its snout was gently pointed, unlike the rounded snouts of later relatives. It had small teeth arranged in grooves along its jaw. The creature had small fins with five digits, and extra finger bones in those digits. Its tail had a long, low fin, which suggests it swam by moving its body from side to side, rather than just using its paddles and tail.

Utatsusaurus showed features that were in between land reptiles and later sea reptiles. Its body was not well-built for moving on land like land reptiles, and its front and back legs were almost the same length, unlike later sea reptiles which had longer front legs. Its back legs also seemed a bit larger than its front legs. Scientists studied its family tree and found that these ancient sea reptiles were closely related to two important groups of reptiles.

Paleobiology

Restoration

Utatsusaurus ate fish. It had about 40 bones in its upper body that were shaped like cylinders. These bones probably helped it move through the water, similar to how an eel moves.

Classification

Scientists from the University of California, Berkeley and Hokkaido University studied the fossils of Utatsusaurus in 1998. They used special computer tools to learn more about the bones. They found that Utatsusaurus was closely related to lizard-like reptiles called diapsids, like Petrolacosaurus. This means ichthyopterygians, the group Utatsusaurus belongs to, are distant relatives of modern lizards, snakes, and crocodiles.

Fossil of Utatsusaurus hataii. Exhibit in the National Museum of Nature and Science, Tokyo.

In 2013, scientists from the University of Calgary in Canada did more research. They found that ichthyopterygians are a special group of related animals. They showed that Utatsusaurus and another animal called Parvinatator were among the earliest members of this group.

Destruction of the Gyoryū-kan

Minamisanriku-cho in Japan is known for its many fossils of ichthyosaurs, including the first example of Utatsusaurus. A museum named Gyoryū-kan, meaning "a house of fish-dragons," was built there to protect and show these fossils. Many people visited it each year.

Unfortunately, on Friday, March 11, 2011, the museum was destroyed during the 2011 Tōhoku earthquake and tsunami. The fossils of Utatsusaurus were safe in another location at the time, and most of the other fossils were also saved. However, the museum has not been rebuilt or reopened yet.