Researchers from China and Canada have discovered a new large ichthyosaur, called Baisesaurus robustus, from southwest China, thus extending the known geographic range of this group. We tell you more here!

Ichthyosaurs are a group of successful Mesozoic marine reptiles that have a worldwide distribution, but their evolutionary origin is still unclear. In recent years, many new marine reptiles related to ichthyosaurs, called primitive ichthyosaurs, have been found in rocks from the early Triassic and shed light on the origin of ichthyosaurs.

These early ichthyosauromorphs were discovered in many countries, but most of them are from China, including Cartorhynchus, Chaohusaurus, and several members of an ichthyosauromorph subgroup called the Hupehsuchia. They are generally small (about 1 meter long) and come from eastern and central China.

However, in a new paper published in the journal PeerJ, researchers from China and Canada report a new large primitive ichthyosauromorph, called Baisesaurus robustus, from southwest China.

In 2017, researchers from the Guizhou Geological Survey found some vertebrate bones exposed in limestone in the Zhebao region of southwest China’s Guangxi province and invited researchers from the China Geoscience University (Wuhan) to join them in the specimen study.

The Specimen

Baisesaurus Robustus

Jiang and Han, researchers at the China University of Geosciences, confirmed that the fossil was from a marine reptile, possibly a relative of ichthyosaurs. The specimen was collected by the joint investigation team in 2018 and was prepared at the Wuhan Center of the China Geological Survey.

The specimen comprises only the front part of the torso skeleton, including some vertebrae and ribs, a limb bone, and abdominal bones called gastralia (abdominal rib).

This made classification difficult, but the researchers compared the fossil comprehensively with other early Triassic marine reptiles and eventually identified it as an ichthyosauromorph. In general, Baisesaurus robustus shares more similarities with Japan’s Utatsusaurus, another early ichthyosauromorph, than with other marine reptiles.

The researchers also found some unusual features that were unknown in other early ichthyosauromorphs, such as deep depressions on the sides of the vertebrae and a robust radius with two distinct articular facets for contact with the wrist bones. These new features indicate that the fossil belongs to a previously unknown species, which the researchers named Baisesaurus robustus.

Furthermore, Baisesaurus is estimated to be around 3 meters long, making this newly discovered marine reptile significantly larger than any other ichthyosauromorph from China’s Early Triassic.

Finally, Baisesaurus has a more robust radius than many other early ichthyosaurs, suggesting strong swimming abilities that may have been used in long-distance migrations along the eastern edge of an ancient ocean known as Paleo-Tethys.

According to study co-author Corwin Sullivan, Baisesaurus may be a kind of reminder that much remains to be discovered about the tremendous evolutionary explosion in vertebrate diversity that occurred in the Triassic.

Source: With Agencies