Did mosasaurs do the breast stroke?

Date:  September 23, 2019

Source:  Geological Society of America

Mosasaurs were true sea monsters of late Cretaceous seas. These marine lizards -- related to modern snakes and monitor lizards -- grew as long as fifty feet, flashed two rows of sharp teeth, and shredded their victims with enormous, powerful jaws.

Now, new research suggests that mosasaurs had yet another potent advantage: a muscular breast stroke that may have added ambush-worthy bursts of speed.

"We know that mosasaurs most likely used their tails for locomotion. Now we think that they also used their forelimbs, or their tail and forelimbs together," explains lead author Kiersten Formoso, a Ph.D. student in vertebrate paleontology at the University of Southern California. That dual swimming style, she says, could make mosasaurs unique among tetrapods (four limbed creatures), living or extinct.

Previous studies noted that mosasaurs had an unusually large pectoral girdle -- the suite of bones that support the forelimbs. But most assumed the creature's swimming was mainly driven by their long tails, something like alligators or whales. That smooth, long distance-adapted swimming style is called "cruising," as opposed to "burst" motion. "Like anything that swims or flies, the laws of fluid dynamics mean that burst versus cruising is a tradeoff," explains co-author Mike Habib, Assistant Professor of Anatomical Sciences at USC. "Not many animals are good at both."

To dive in more closely on whether mosasaurs were burst-adapted, cruise-adapted, or an unusual balance of both, Formoso and co-authors focused on the oversized pectoral girdle. They studied a fossil Plotosaurus, a type of mosasaur, at the Natural History Museum of Los Angeles County. In addition, they used measurements of mosasaur pectoral girdles published in other studies.

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Fossil from oldest ancestor of modern sea turtles

Date: October 3, 2016

Source: University of Alabama at Birmingham

Several 80-million-year-old fossils found in Alabama are from a species of sea turtle that is the oldest known member of the lineage that gave rise to all modern species of sea turtle, according to new research from the University of Alabama at Birmingham.

Researchers from the College of Arts and Sciences' Department of Biology worked with two relatively complete turtle skeletons, along with several smaller pieces, that are housed at Birmingham's McWane Science Center, to unearth the evolutionary clues tying the ancient turtles to modern sea turtles, and confirm the existence of that ancient species, previously known only from a few isolated fragments.

The McWane fossils help solve a long-standing debate as to whether this animal was a unique species. They also provide insights into the evolutionary history of living species of sea turtles, including the Kemp's Ridley, Loggerhead and the endangered Green sea turtle.

According to research published in the Journal of Systematic Palaeontology, the fossils belong to Ctenochelys (tee-no-key-lees) acris, a marine-adapted turtle that lived in the shallow, subtropical sea that once covered most of Alabama. By dating the rock formation from which these fossils were recovered, C. acris is presumed to have lived more than 80 million years ago, during the Late Cretaceous, a period of time when sea turtle diversity was at an all-time high.

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76-million-year-old, pig-snouted turtle is ‘one of the weirdest turtles that ever lived’

OCTOBER 22, 2015

by Savanna Walker

A new species of turtle that lived 76 million years ago has been described as “one of the weirdest turtles that ever lived” by Joshua Lively, who studied the fossil and has recently published his analysis in the Journal of Vertebrate Paleontology.

Found in Grand Staircase-Escalante National Monument by a team from the Natural History Museum of Utah, the turtle was about two feet long, with a streamlined shell evolved for a life spent in rivers. But unlike any other turtle in history, the snout of this specimen had two openings, making it look like a turtle with a transplanted pig’s nose.

All other turtles have just one nasal opening, according to Time magazine. It’s been named Arvinachelys goldeni as a result of this strange feature, with the first part being derived from arvina, the Latin word for pig fat or bacon.

Where'd this ugly guy come from?

In the Late Cretaceous period when A. goldeni lived, western North America was an island continent named Laramidia and was separated from eastern North American by a large sea. It's already known that the dinosaurs of southern Laramidia diversified while isolated from their relatives in the northern parts of the continent, and did not seem to interbreed with the populations from the north.

With this new discovery, it would seem that the turtles of that period fit the same pattern. It's still unknown exactly why the southern populations were isolated from the north, but researchers have suggested rising sea levels and persistent climate changes prevented animals from ranging over wide sections of territory.

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