Ancient plesiosaurs, often claimed to be the Loch Ness Monster, gained their long necks over a relatively short space of time.
A new find of a short-necked ancestor shows that it was not long before the species added vertebrae to end up with Elasmosaurus, whose neck was five times the length of its trunk.
Researchers from the UK and China, say their lengthy necks, used for chasing fast-moving fishes, developed quickly over a five million period around 250 million years ago.
The study in the journal BMC Ecology and Evolution shows that a species known as pachypleurosaur lengthened its necks mainly by adding new vertebrae.
This species had 25 vertebrae, while some Late Cretaceous plesiosaurs such as the Elasmosaurus had as many as 72.
Humans and most mammals, even giraffes, have seven.
The animals originated in the Early Triassic, four million years after the end-Permian mass extinction wiped out around 90 percent of Earth’s species and during a time of rapid change following the disaster.
The team from the University of Bristol and China University of Geosciences in Wuhan describe a new, short-necked plesiosaur ancestor called Chusaurus xiangensis.
Living in Hubei Province, China in the Early Triassic its neck had begun to lengthen was only half the length of the trunk of its body compared to 80 percent or higher in its later relatives.
Dr. Qi-Ling Liu, who led the project said: “We were lucky enough to find two complete skeletons of this new beast.
“It’s small, less than half a meter long, but this was close to the ancestry of the important group of marine reptiles called Sauropterygia.
“Our new reptile, Chusaurus, is a pachypleurosaur, one of a group of small marine predators that were very important in the Triassic.
“I wasn’t sure at first whether it was a pachypleurosaur though because the neck seemed to be too short.”
Dr. Ben Moon from Bristol University said: “Our study shows that pachypleurosaurs doubled the lengths of their necks in five million years, and the rate of increase then slowed down.
“They had presumably reached some kind of perfect neck length for their mode of life.
“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.
“But there might have been additional costs in having a much longer neck, so it stabilized at a length just equal to the length of the trunk.”
Collaborator Professor Michael Benton of the University of Bristol’s School of Earth Sciences said: “The end-Permian mass extinction had been the biggest mass extinction of all time and only one in twenty species survived.
“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.”
Professor Cheng Long added: “The pachypleurosaur lengthened their necks mainly by adding new vertebrae.
“Normally, vertebrates like reptiles and mammals and us have seven neck vertebrae.
“Chusaurus already had 17, whereas later pachypleurosaur had 25. Some Late Cretaceous plesiosaurs such as Elasmosaurus even had 72, and its neck was five times the length of its trunk.
“With so many vertebrae, these long necks must have been super-snakey and they presumably whipped the neck around to grab fishy prey while keeping the body steady.”
Dr. Tom Stubbs of the Open University UK added: “Not all long-necked animals do it in the same way.
“Giraffes for example keep the standard seven neck vertebrae, but each one is very long, so they can reach high into the trees.
“Flamingos also have long necks so they can reach the water to feed, because of their long legs, and they have extra vertebrae, up to twenty, but each one is also long.”
Produced in association with SWNS Talker