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Ancient sea monster may have cared for its young

Aug. 12, 2011
Courtesy of the Nat­u­ral His­to­ry 
Mu­se­um of Los An­ge­les Coun­ty
and World Science staff

Some of the mon­strous rep­tiles that lorded it over the oceans dur­ing the Age of Di­no­saurs might have cared for their young, and even in­ter­acted a bit like dol­phins, re­search­ers are re­port­ing.

The claim is based on a fos­sil of a preg­nant mem­ber of a rep­til­i­an line­age known as ple­siosaurs. De­tails of the ob­ject sug­gest the beast would have giv­en birth to a sin­gle, live off­spring, the sci­en­tists say.

With long necks, small heads, dagger-like teeth and pad­dle-shaped limbs, ple­siosaurs prowled the seas snap­ping up smaller crea­tures for mil­lions of years be­fore dy­ing out along with the di­no­saurs some 65 mil­lion years ago. 

Artist's con­cept of a moth­er and juve­nile ples­io­saur. (Cour­tesy U.S. Nat'l Science Found­ation)


Oth­er line­ages of aquat­ic rep­tiles from this era are known to have birthed live young. But wheth­er ple­siosaurs al­so did so has been un­known, pa­le­on­tol­ogists say. Rob­in O’­Keefe of Mar­shall Uni­vers­ity in Hun­ting­ton, W. Va. and Lu­is Chi­appe of the Nat­u­ral His­to­ry Mu­se­um of Los An­ge­les Coun­ty an­a­lyzed the fos­sil, disco­vered in 1987 and archived at the mu­se­um. Their find­ings are pub­lished in the Aug. 12 is­sue of the re­search jour­nal Science.

The fe­tus’ large size sug­gests that rath­er than giv­ing birth to mul­ti­ple smaller young, as oth­er live-bearing ma­rine rep­tiles of the age did, ple­siosaurs made one, large ba­by, the re­search­ers pro­pose. Oth­er ma­rine spe­cies that give birth this way, such as whales, care for their young ex­ten­sive­ly, they not­ed. Though more ev­i­dence is needed, they con­tin­ued, ple­siosaurs may al­so have done so.

The 78-mil­lion-year-old, 15.4-foot-long adult spec­i­men is iden­ti­fied as a spe­cies of ple­si­o­saur called Poly­coty­lus latip­pi­nus. The em­bry­on­ic ske­l­e­ton with­in shows much of the de­vel­op­ing body, in­clud­ing ribs, 20 ver­te­brae, shoul­ders, hips, and pad­dle bones.

"Sci­en­tists have long known that the bod­ies of ple­siosaurs were not well suit­ed to climb­ing on­to land and lay­ing eggs in a nest," O'­Keefe said. "So the lack of ev­i­dence of live birth in ple­siosaurs has been puz­zling. This fos­sil doc­u­ments live birth in ple­siosaurs for the first time, and so fi­nally re­solves this mys­tery. Al­so, the em­bry­o is very large in com­par­i­son to the moth­er, much larg­er than one would ex­pect in com­par­i­son with oth­er rep­tiles. Many of the an­i­mals alive to­day that give birth to large, sin­gle young are so­cial and have ma­ter­nal care. We spec­u­late that ple­siosaurs may have ex­hib­ited si­m­i­lar be­hav­iors, mak­ing their so­cial lives more si­m­i­lar to those of mod­ern dol­phins than oth­er rep­tiles."

Ple­siosaurs have no known liv­ing rel­a­tives, thought they were com­mon in their day. They are thought to have ranked among the top preda­tors in the West­ern In­te­ri­or Sea­way, a vast body of wa­ter that split North Amer­i­ca dur­ing the Cre­ta­ceous era when wa­ters from the Arc­tic Ocean and the Gulf of Mex­i­co flood­ed on­to the con­ti­nent and met.


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Some of the monstrous reptiles that lorded it over the oceans during the Age of Dinosaurs might have cared for their young, and even interacted a bit like dolphins, researchers are reporting. The claim is based on a fossil of a pregnant member of a reptilian lineage known as plesiosaurs. Details of the object suggest the beast would have given birth to a single, live offspring, the scientists say. With long necks, small heads, dagger-like teeth and paddle-shaped limbs, plesiosaurs prowled the seas snapping up smaller creatures for millions of years before dying out along with the dinosaurs some 65 million years ago. Other lineages of aquatic reptiles from this era are known to have birthed live young. But whether plesiosaurs also did so has been unknown, paleontologists say. Robin O’Keefe of Marshall University in Huntington, W. Va. and Luis Chiappe of the Natural History Museum of Los Angeles County analyzed the fossil, discovered in 1987 and archived at the museum. The fetus’ large size suggests that rather than giving birth to multiple smaller young, as other live-bearing marine reptiles of the age did, plesiosaurs made one, large baby, the researchers propose. Other marine species that give birth this way, such as whales, care for their young extensively, they noted. Though more evidence is needed, they continued, plesiosaurs may also have done so. The 78-million-year-old, 15.4-foot-long adult specimen is identified as a species of plesiosaur called Polycotylus latippinus. The embryonic skeleton within shows much of the developing body, including ribs, 20 vertebrae, shoulders, hips, and paddle bones. "Scientists have long known that the bodies of plesiosaurs were not well suited to climbing onto land and laying eggs in a nest," O'Keefe said. "So the lack of evidence of live birth in plesiosaurs has been puzzling. This fossil documents live birth in plesiosaurs for the first time, and so finally resolves this mystery. Also, the embryo is very large in comparison to the mother, much larger than one would expect in comparison with other reptiles. Many of the animals alive today that give birth to large, single young are social and have maternal care. We speculate that plesiosaurs may have exhibited similar behaviors, making their social lives more similar to those of modern dolphins than other reptiles." Plesiosaurs have no known living relatives, thought they were common in their day. They are thought to have ranked among the top predators in the Western Interior Seaway, a vast body of water that split North America during the Cretaceous era when waters from the Arctic Ocean and the Gulf of Mexico flooded onto the continent and met.