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Exquisitely preserved fossil of Jurassic sea turtle includes near-complete skull and limbs


By Mindy Weisberger, CNN

(CNN) — About 150 million years ago, a marine turtle with a massive head dived through a shallow, tropical sea covering what is now Europe. Few complete fossils of this Jurassic sea turtle, named Solnhofia parsonsi, have been discovered. However, scientists recently described a remarkable fossil that has all its limbs with nearly all the bones of the feet in place — revealing the shape and structure of the turtle’s extremities for the first time.

Today’s marine turtle species all have elongated, rigid flippers to propel them through the ocean depths. But the newly described fossil’s limbs were stumpier than those of modern sea turtles relative to its body size. These shorter limbs suggest that S. parsonsi swam in coastal waters rather than in the open ocean, scientists reported July 26 in the journal PLOS One.

Fossils of this marine turtle were first discovered in the 1970s, but the new specimen “is the best preserved individual of this species,” said lead study author Felix Augustin, a doctoral candidate in the department of geosciences at the University of Tübingen in Germany. “It is the first that preserves the complete skull, the complete shell, and also all four complete limbs.”

In life, S. parsonsi measured about 12 inches (30 centimeters) long from nose to tail, and its head was “relatively large” — the skull measured about 4 inches (10 centimeters) long, Augustin told CNN.

Such a large skull may have been useful for crunching through the hard shells of bottom-dwelling crustaceans and mollusks, but such conclusions are “highly speculative at this point” as paleontologists have yet to find direct evidence of the extinct turtle’s diet, said study coauthor Dr. Márton Rabi, a postdoctoral researcher in the University of Tübingen’s department of geosciences.

The fossil was excavated in 2014 from a limestone quarry in southeastern Germany at a site rich in fossils from the latter part of the Jurassic Period (199.6 million to 145.5 million years ago). Plenty of turtles are preserved there, along with fishes, crocodilians and even marine reptile giants such as plesiosaurs and ichthyosaurs, according to the study. The site has been an actively mined quarry since the 1950s, but fossil excavations only began there about 20 years ago.

S. parsonsi was described as a species in 1975 based on two near-complete skulls: one from Bavaria and one from Switzerland. Over the decades, discoveries of partial skeletons — all found in Jurassic marine deposits — provided more clues about the turtle’s anatomy and aquatic lifestyle. In 2000, scientists discovered a skeleton with a more complete shell than had ever been seen before. The specimen also included some bones from the reptile’s paddling limbs.

The newly described fossil presents a far more complete view of those limbs, showing that they differed dramatically from the extremities of sea turtles alive today.

“In modern-day sea turtles, the limbs are really elongated — especially the digits and the phalanges of the digits — to serve as flippers in this marine environment,” Augustin said. By comparison, the limbs and feet of the S. parsonsi fossil from Bavaria were less elongated, so the species was probably better adapted to swim closer to the shore, rather than hundreds of miles away in the open ocean.

That hypothesis makes sense considering the locale where the fossil was excavated, Rabi told CNN. During the Jurassic, what is now southern Germany was an archipelago of small islands. S. parsonsi’s habitat was likely a network of coastal reefs and lagoons. The turtles “were always more or less close to the shore,” Rabi said.

Numerous fossils from these rich and diverse coastal ecosystems are found in fine-grained limestone deposits known as “plattenkalk” across southern Germany. Such rock is known for preserving fossils in exquisite detail, and the quarry where the turtle was unearthed has already yielded many examples of marine animals and plants as well as fossils of terrestrial dinosaurs and pterosaurs.

But because the site is relatively new, many of those fossils have yet to be studied and scientifically described, and there is much to be learned about the individual species and the coastal habitat where they coexisted millions of years ago, Augustin said.

“We are particularly interested in reconstructing the ecosystem as a whole to show the diversity — how it functioned, and what different constituents of the ecosystems were present during the Late Jurassic,” he said.

Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American and How It Works magazine.

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