Plesiosaurs doubled their neck length by acquiring new vertebrae

New research suggests that plesiosaurs, marine reptiles known for their long necks, evolved these unique features within five million years, about 250 million years ago.

Plesiosaurs developed their distinctive long necks quickly, evolving over a period of five million years, and a recent study revealed the introduction of a new ancestor, Chosaurus xiangensis.

Research suggests that plesiosaurs evolved their distinctive long necks in a remarkably short period of time.

These long necks are thought to have been used to chase fast-moving fish, and they evolved rapidly over five million years about 250 million years ago.

The results were recently published in the journal BMC ecology and evolution, Conducted by scientists in China and the United Kingdom, it shows that A Classify Known as the pachypleurosaur, it lengthened their necks mainly by adding new vertebrae. This type had 25 vertebrae, while some were later Cretaceous period Plesiosaurs like Elasmosaurus had up to 72, and their neck was five times as long as their torso.

New origins and discoveries

These creatures first appeared early Triassic, just four million years after the end-Permian mass extinction, which led to the disappearance of nearly 90% of species on Earth. This period was characterized by rapid transformations in the wake of this catastrophic event.

In the study, the researchers describe a new, short-necked ancestor of plesiosaurs called Chosaurus xiangensis From the Early Triassic of Hubei Province, China. His neck began to lengthen, but only half the length of his torso compared to 80% or higher in later relatives.

Rapid evolution of plesiosaurs

Image showing rapid development rates and samples. Research suggests that plesiosaurs, marine reptiles known for their long necks, evolved these unique features within five million years, about 250 million years ago. Credit: Chi-Ling Liu

“We were lucky enough to find two complete skeletons of this new monster,” said Chi-Ling Liu, from the China University of Geosciences in Wuhan, who led the project. “It’s small, less than half a meter long, but it was close in origin to an important group of marine reptiles called Sauropterygia.

“We have new reptiles, Chausaurus, is a pachypleurosaur, one of a group of small marine predators that were very important in the Triassic period. I wasn’t sure at first if this dinosaur was a pachypleurosaur, because its neck seemed very short.

Context and comparisons

Dr Li Tian, ​​from the China University of Geosciences in Wuhan, who co-supervised the project, said: ‘The fossils come from the Nanchang-yuan’an fauna in Hubei. “This has been studied very intensively in recent years as one of the oldest groups of marine reptiles from the Triassic. We have good quality radiometric dates that show the animals date back to 248 million years ago.

Collaborating Professor Michael Benton from University of Bristol“The end-Permian mass extinction was the largest mass extinction ever recorded, and only one in twenty species survived,” the UCL School of Earth Sciences said.

“The early Triassic was a recovery period and marine reptiles evolved very quickly at that time, and most of them were predators of shrimp, fish and other marine organisms. They arose right after the extinction, so we know that their rates of change were very rapid in the post-crisis New World.”

“Bashipleurosaurus “They lengthened their necks mainly by adding new vertebrae,” said Professor Qing Long, from the Wuhan Geological Survey of China, a co-supervisor.

“usually, vertebrates Like reptiles and mammals (and us) they have seven vertebrae in the neck. Chausaurus It actually had 17, while the later pachypleurosaur had 25. Some plesiosaurs of the Late Cretaceous such as The osmosaurus Even when he was 72 years old, his neck was five times the length of his torso. With so many vertebrae, these long necks must have been very snake-like and would presumably have snapped the neck to catch fishy prey while keeping the body stable.

Various evolutionary tactics

Dr Tom Stubbs from the Open University in the UK added: “Not all long-necked animals do this in the same way. For example, giraffes retain the standard seven neck vertebrae, but each one is so long that they can reach the tops of trees. Flamingos also have long necks so they can reach water to feed, due to their long legs. They have additional vertebrae, up to twenty, but each vertebra is also long.

Dr Ben Moon, also from the University of Bristol, added: “Our study shows that pachypleurosaurs doubled the length of their necks over five million years, and then the rate of increase slowed.” “Presumably they have reached some sort of ideal neck length for their lifestyle.

“We think that, as small predators, they probably fed primarily on shrimp and small fish, so their ability to sneak into small shoals, then hover in the water, and throw their head behind fast-swimming prey was a great way to survive.” But there would have been additional costs in having a much longer neck, so I settled on a length equal to the length of the torso.

Reference: “Rapid neck elongation in Sauropterygia (Reptilia: Diapsida) revealed by a new basal pachypleurosaur from the Lower Triassic of China” by Qi-Ling Liu, Long Cheng, Thomas L. Stubbs, Benjamin C. Moon, Michael J. Benton and Li Tian, ​​August 31, 2023, BMC ecology and evolution.
doi: 10.1186/s12862-023-02150-s

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