It is estimated that research groups such as Tokyo City University discovered fossils from the eastern strata of Russia that were relatively old as ichthyosaurs, which are "reptiles" that lived in the sea, and reached a total length of about 5 meters. From this, it is possible that the ichthyosaurs grew larger and reigned at the top of the marine ecosystem faster than previously thought.
The ichthyosaur, a "reptile" that lived in the sea, appeared about 252 million years ago and has been thought to have grown in size over about 8 million years.
Research groups such as Associate Professor Yasutoshi Nakajima of Tokyo City University discovered five fossil bones from the strata on the islands of eastern Russia, about 3 million years after their appearance, which is relatively old for ichthyosaurs.
One of them is a fossil of the front fin of an ichthyosaur, which has a similar bone shape to the later enlarged ichthyosaur and is relatively large at that time, with a length of about 13 cm. It is estimated that the total length of the ichthyosaur reached about 5 meters.
Furthermore, when examining the inside of the bone, it is said that it had a sponge-like structure and had characteristics similar to those of a whale bone, and that it could have been able to dive deeply.
Based on these facts, the research group believes that ichthyosaurs grew in size in about 3 million years, which was earlier than previously thought, and reigned at the top of the marine ecosystem.
Associate Professor Nakajima says, "Ichthyosaurs may have been able to grow in size rapidly because the mass extinction of organisms occurred just before the number of large sharks and others decreased."