How monsters with 20-foot-long necks ruled our oceans 200 million years ago

By Mark Waghorn via SWNS

Monsters with necks up to 20-feet-long ruled Earth's oceans 200 million years ago, thanks to their massive bodies, according to new research from the UK.

Their size overcame the underwater drag caused by their long necks, which were advantageous for hunting.

How plesiosaurs moved through the water has puzzled evolutionary experts for decades.

They were long-necked predators that swam with four nearly identical flippers - a style unique in nature.

They were around 50 ft and weighed 12 tonnes - more than twice the size of a killer whale.

Now University of Bristol scientists have shown how their huge proportions overcame the excess drag, by combining 3D models and computer simulations.

The legendary creatures differed dramatically from ichthyosaurs - a rival group of marine reptiles.

The latter resembled giant dolphins - which meant they were adapted for speed with a more aerodynamic shape.

Co-author Dr. Colin Palmer, an engineer at the University of Bristol, said: "We showed that although plesiosaurs did experience more drag than ichthyosaurs or whales of equal mass because of their unique body shape, these differences were relatively minor.

"We found when size is taken into account, the differences between groups became much less than the shape differences.

"We also show that the ratio of body length to diameter, which is widely used to classify these aquatic animals as more or less efficient, is not a good indicator of low drag."

Large necks would have added extra drag - but this was compensated by the evolution of large bodies.

Co-author Dr. Susana Gutarra Diaz said: "We created hypothetical 3D models of plesiosaurs with various lengths of necks.

"Simulations of these models reveal past a certain point, the neck adds extra drag, which potentially would make swimming costly. This 'optimal' neck limit lies around twice the length of the trunk of the animal."

The study in the journal Communications Biology debunks the long-standing idea that there is an optimal body shape for low drag.

Tetrapods, or 'four-limbed vertebrates,' have repeatedly returned to the oceans over the last 250 million years.

They range from streamlined modern whales over 80 feet in length to the extinct plesiosaurs and ichthyosaurs - who lived side by side during the Mesozoic Era.

Plesiosaurs with necks over 20 feet long used their enormous four flippers to 'fly' underwater - flapping like penguins. They have no parallel among living animals.

Palaeobiologist Dr. Gutarra Diaz explained: "To test our hypotheses, we created various 3D models and performed computer flow simulations of plesiosaurs, ichthyosaurs, whales, dolphins and porpoises.

"These experiments are performed on the computer, but they are like water tank experiments."

The plesiosaur with the biggest neck was a beast named Elasmosaurus. It reached 23 feet long.

Dr. Gutarra Diaz said: "We were also particularly interested in the necks of elasmosaurs and so, we created hypothetical 3D models of plesiosaurs with various lengths of necks.

Compared to other marine reptiles, pleasiosaurs had a short tail that was only used for steering.

Co-author Dr. Benjamin Moon, a marine reptile expert, said: "When we examined a large sample of plesiosaurs modeled on really well-preserved fossils at their real sizes, it turns out that most plesiosaurs had necks below this high-drag threshold, within which neck can get longer or shorter without increasing drag.

"We showed that plesiosaurs with extremely long necks also had evolved very large torsos, and this compensated for the extra drag."

They were remarkably successful - surviving for about 137 million years until being wiped out by the asteroid strike that killed off the dinosaurs.

Co-author Dr. Tom Stubbs added: "This study shows that, in contrast with prevailing popular knowledge, very long-necked plesiosaurs were not necessarily slower swimmers than ichthyosaurs and whales, and this is in part thanks to their large bodies.

"We found that in elasmosaurs, neck proportions changed really fast. This confirms that long necks were advantageous for elasmosaurs in hunting, but they could not exploit this adaptation until they became large enough to offset the cost of high drag on their bodies."

Plesiosaurus had very sharp teeth and incredibly strong jaws. This allowed them to feed on fish of all sizes and other swimming animals - including ichthyosaurs

Added Professor Mike Benton: "Our research suggests large aquatic animals could afford to have crazy shapes, as in the elasmosaurs.

"But there are limits. Body sizes cannot get indefinitely large, as there are some constraints to very large sizes as well.

"The maximum neck lengths we observe, seem to balance benefits in hunting versus the costs of growing and maintaining such a long neck.

"In other words, the necks of these extraordinary creatures evolved in balance with the overall body size to keep friction to a minimum."