Fossils of short-necked ancient marine reptile found in China

The two intact bones of Chusaurus, the short-necked ancestor of plesiosaurs, were discovered in the Nanzhang-Yuan'an Fauna of Hubei Province, China, dating back to the Early Triassic period.
Mrigakshi Dixit
Representational image of a plesiosaur group species.
Representational image of a plesiosaur group species.

Daniel Eskridge/iStock 

Plesiosaurs were a group of ancient marine reptiles that existed from the early Triassic Period to the late Cretaceous Period.  

These creatures possessed unique physical morphology that helped them adapt to life in the ocean. 

Their fossil remains revealed a long neck, a barrel-shaped torso, and four paddle-like flippers. The long neck took up a large percentage of their entire body length and comprised several vertebrae, allowing for flexible movement underwater.

Paleontologists have been particularly curious in unraveling the evolutionary mystery behind their remarkably long necks, setting them apart from other marine creatures.

A new study led by an international team of experts from the United Kingdom and China has now illuminated the origins of their extraordinarily elongated necks.

As per the official statement, their distinctive lengthy neck underwent rapid growth over a span of five million years, approximately 250 million years ago. Subsequently, the rate of this development began to decelerate.

The fossil remains of short-neck ancestors 

Plesiosaurs exhibited a wide range of diversity in terms of their size, physical characteristics, and adaptability. As an illustration, the Elasmosaurus, belonging to this group, boasted a remarkable 72 vertebrae in its anatomy, a feature that emerged during the Late Cretaceous period.

With its massive vertebrae size, this species' neck easily surpassed the length of its trunk – by over five times. 

In this new study, the scientists analyzed and described the fossilized bones of a new species named Chusaurus xiangensis.

The two complete bones of this newfound plesiosaur ancestor were unearthed from China's Nanzhang-Yuan'an Fauna of Hubei Province. 

Chusaurus was the short-necked ancestor of plesiosaurs during the Early Triassic period. The radiometric dating technique found that the Nanzhang-Yuan'an Fauna dates back 248 million years ago, making the Triassic marine fossil one of the oldest known.

During this time, the species' neck grew longer, although it was still relatively short, with just 17 vertebrae compared to its later cousins.

"Our new reptile, Chusaurus, is a pachypleurosaur, one of a group of small marine predators that were very important in the Triassic," said Qi-Ling Liu from the China University of Geosciences in Wuhan, who led the study. 

Fossils of short-necked ancient marine reptile found in China
Image showing fast rates of evolution and the specimens

Pachypleurosaurs, ancient marine reptiles resembling lizards, predominantly thrived during the Triassic era. Notably, members of this group extended their necks by augmenting their vertebrae count, possessing more than 25 vertebrae.

Chusaurus’ neck suggests they were well-suited for capturing prey from water, particularly the fast-moving fish. 

“We think, as small predators, they were probably mainly feeding on shrimps and small fish, so their ability to sneak up on a small shoal, and then hover in the water, darting their head after the fast-swimming prey was a great survival tool,” described Ben Moon from the University of Bristol.

Typically, creatures like reptiles and mammals, which includes humans, possess a set of seven neck bones referred to as cervical vertebrae. Giraffes, too, have seven neck vertebrae; however, each of these vertebrae is exceptionally elongated, allowing them to reach high into the trees.

The Great Dying mass extinction

Around 252 million years ago, the end-Permian mass extinction wiped off over 90 percent of Earth's life.

These marine reptiles appeared in the Early Triassic era, some four million years after this catastrophic global extinction event, also known as the "Great Dying." 

This event had far-reaching ecological implications, paving the way for the emergence of new life forms throughout the following Triassic period.

"The Early Triassic was a time of recovery, and marine reptiles evolved very fast at that time, most of them predators of the shrimps, fishes, and other sea creatures. They had originated right after the extinction, so we know their rates of change were extremely rapid in the new world after the crisis," said Michael Benton of the University of Bristol. 

The findings have been reported in the journal BMC Ecology and Evolution. 

Study Abstract:

Neck elongation has appeared independently in several tetrapod groups, including giraffes and sauropod dinosaurs on land, birds and pterosaurs in the air, and sauropterygians (plesiosaurs and relatives) in the oceans. Long necks arose in Early Triassic sauropterygians, but the nature and rate of that elongation has not been documented. Here, we report a new species of pachypleurosaurid sauropterygian, Chusaurus xiangensis gen. et sp. nov., based on two new specimens from the Early Triassic Nanzhang-Yuan’an Fauna in the South China Block. The new species shows key features of its Middle Triassic relatives, but has a relatively short neck, measuring 0.48 of the trunk length, compared to > 0.8 from the Middle Triassic onwards. Comparative phylogenetic analysis shows that neck elongation occurred rapidly in all Triassic eosauropterygian lineages, probably driven by feeding pressure in a time of rapid re-establishment of new kinds of marine ecosystems.

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