The puz­zle of how ple­siosaurs swam through oceans

Miami Herald - - FRONT PAGE -

Mil­lions of years ago, when di­nosaurs dom­i­nated the land, leviathans known as ple­siosaurs prowled the oceans. With their long necks and bar­reled bod­ies, these marine rep­tiles — which were not di­nosaurs — re­sem­bled the myth­i­cal Loch Ness mon­ster.

Though not ev­ery ple­siosaur had a neck like “Nessie,” they all had four long flip­pers. Since the first fos­sils of this pre­his­toric sea crea­ture were found about two cen­turies ago, the two nearly iden­ti­cal pairs of aquatic limbs have puz­zled pa­le­on­tol­o­gists.

“Hav­ing four big flip­pers like that is rather strange,” said Luke Mus­cutt, a biomech­a­nist and post­doc­toral re­searcher at the Univer­sity of Southamp­ton in Eng­land. Mus­cutt spent his the­sis de­cod­ing how the ple­siosaur pad­dled, which he said is un­like any other liv­ing ver­te­brate that swims in the ocean. Fish and sharks swim by swing­ing their tails side to side, and whales and dol­phins swing theirs up and down. Even other an­i­mals with flip­pers like sea lions and sea tur­tles do not swim with all four flip­pers, he said.

A study he pub­lished Tuesday in the jour­nal Pro­ceed­ings of the Royal So­ci­ety B pro­vides fur­ther ev­i­dence that the hind flip­pers were key to the ple­siosaur’s un­der­wa­ter moves, and were not just limbs used for steer­ing.

“Ple­siosaurs def­i­nitely used all four flip­pers for propul­sion and that made them more ef­fi­cient and ef­fec­tive swim­mers,” said Mus­cutt. The find­ings, he said, could help set­tle the long-run­ning de­bate on how the ple­siosaur swam. They could also con­tribute to fu­ture de­signs for un­der­wa­ter drones or sub­mersibles.

Mus­cutt used a 3D printer to cre­ate two faux flip­pers to rep­re­sent one side of a ple­siosaur and at­tached them to a me­chan­i­cal de­vice that aimed to mimic how the crea­ture moved. He crafted the foot-long ro­botic flip­pers us­ing pho­to­graphs of ple­siosaur fos­sil spec­i­mens as well as from geo­met­ric data col­lected from to­day’s flip­pered-crea­tures like pen­guins, tur­tles and sea lions.

He put the flip­pers into a large wa­ter tank, and us­ing dif­fer­ent col­ored dyes, ran sev­eral sim­u­la­tions to de­ter­mine un­der what con­di­tions the flip­pers acted most ef­fi­ciently. The sys­tem per­formed best when the front and back flip­pers both flapped.

Ev­ery flap from the front flip­per gen­er­ated a vor­tex, or whirlpool, as it went up and as it went down. When the back flip­pers wove be­tween the whirlpools made by the front flip­pers, they could use that ex­cess en­ergy to move more ef­fi­ciently.

“There’s no other an­i­mal apart from a drag­on­fly which utilizes its own wake in this way,” said Mus­cutt. “It’s like if you duct tape two pen­guins to­gether, that’s what you’re get­ting.”

His col­league Bharathram Gana­p­athisub­ra­mani, a pro­fes­sor of ex­per­i­men­tal fluid me­chan­ics at the Univer­sity of Southamp­ton and co-au­thor on the pa­per, said that the back flip­per scav­enges the en­ergy com­ing from the front flip­per’s vor­tices. It’s sim­i­lar to mi­gra­tory birds fly­ing in a v-for­ma­tion: The birds in the back fly more ef­fi­ciently be­cause of the ef­fort of the birds in the front. When the pair of flip­pers work har­mo­niously, the back flip­per can in­crease its thrust by ap­prox­i­mately 60 per­cent and its ef­fi­ciency by 40 per­cent.

The sci­en­tists now hope to fig­ure out how ple­siosaur mo­tion var­ied by species.

Greg Turk, a com­puter sci­en­tist from the Ge­or­gia In­sti­tute of Tech­nol­ogy who stud­ied ple­siosaur move­ment us­ing a com­puter sim­u­la­tion in 2015, called the pa­per an “in­ven­tive and well-crafted study,” in an email. How­ever, he added that the limb mo­tions were sim­pli­fied and that there was still un­cer­tainty con­cern­ing the range of mo­tion of the ple­siosaur’s hind legs.

“This study has added to our un­der­stand­ing of ple­siosaur swim­ming but we prob­a­bly have not heard the last word about their lo­co­mo­tion,”

he said.

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