Scientists discover first known aquatic dinosaur in Morocco

Paleontologists have discovered the first dinosaur known to have lived much of its life in the water.

The find of a variety of bones from an animal called Spinosaurus aegyptiacus vastly improves scientists’ understanding of the role played by the huge predatory dinosaur in the Cretaceous period ecosystem of modern-day North Africa.

“Today we are resurrecting a giant from deep time,” Dr. Nizar Ibrahim, a paleontologist at the University of Chicago and the lead author of a paper published in the Sept. 11, 2014 edition of Science Express, said. “The animal we are resurrecting is so bizarre, it is going to force dinosaur experts to re-think many things they thought they knew about dinosaurs.”

Spinosaurus aegyptiacus was first identified in 1915 by the German anatomist, geologist, and paleontologist Ernst Stromer von Reichenbach. He identified an animal unlike any other theropod dinosaur then known.

Spinosaur fossils mounted on the wall of a German museum before a Royal Air Force bombing in 1944. Courtesy Washington University.

“The size of the bones suggested to Stromer that the animal rivaled Tyrannosaurus rex in size, but it clearly differed from the North American predator in many ways,” Ibrahim said. “The skull was more elongate and the tall spines formed a large sail on the back of Spinosaurus.”

Stromer stored the holotype in the Paläontologische Staassammlung in Munich, Germany. Unfortunately, an April 1944 bombing raid by Britain’s Royal Air Force destroyed Stromer’s fossils.

The German scientist’s drawings survived.

Stromer’s drawings of Spinosaurus aegyptiacus were detailed and survived the World War Ii bombing. Courtesy Wikimedia.

During the ensuing decades paleontologists used those drawings, along with a few fragmentary finds of additional Spinosaurus remains, to develop a rudimentary idea of the animal’s appearance. They conceived Spinosaurus as a land animal, the largest predatory dinosaur known.

The findings published Thursday cast no doubt on Spinosaurus’ size, but revealed a number of body features that are unique among dinosaurs and that indicate the animal likely searched for food in the rivers that were ubiquitous in the region now known as North Africa during the Mesozoic era. Those features include a nasal opening high on the skull, long teeth shaped like cones, and wide and flat feet that may have been webbed.

“Other more subtle, but equally startling, finds were made,” Dr. Paul C. Sereno, a vertebrate paleontologist at the University of Chicago and a principal author of the paper published online in Science Express, said. “The thigh bone was robust and shorter than the shin bone, a very unusual proportion for a large dinosaur. And all of the long bones were solid without a marrow cavity, something never before observed in a predatory dinosaur.”

The highly dense bones are similar to those found in modern-day penguins.

“This adaptation is useful to facilitate buoyancy control,” Dr. Simone Maganuco, a vertebrate paleontologist at Italy’s Museo di Storia Naturale di Milano and another co-author on the paper, said.

Spinosaurus’ skull also exhibited small pits at the end of its snout called foramina. The authors of the study used computer tomography to examine them and found that they served to regulate pressure.

The foramina closely resemble those found in modern-day crocodiles and that have been confirmed in at least one species of extinct marine reptile.

“The pressure receptors of crocs play a key role in capturing prey based on water movements, and permit to hunt even in darkness or in muddy water, without relying on sight,” Dr. Cristiano Dal Sasso, curator of vertebrate paleontology at the Museo di Storia Naturale di Milano and a co-author of the paper, said.

She explained that their presence in Spinosaurus’ skull is an indication that the dinosaur may have used its long snout to find prey, with no need to see it.

Sereno noted that the new Spinosaurus specimen also exhibited a tail with characteristics similar to those found in some modern fish.

“These facts strongly supported a semi-aquatic existence for Spinosaurus, the first water-adapted non-avian dinosaur on record,” Sereno said.

The spines on the animal’s back and the sail-like structure they formed were a means of communication.

“Even the big sail on the back of Spinosaurus may, in part, be an adaptation to a life often spent in water,” Ibrahim said. “It would have been a great display structure, and would remain visible even when the animal is partially submerged.”

Spinosaurus would not have been an agile creature, at least on land, and would have had most of its weight at its front.

“It’s quite short, but surprisingly, solid,” Dr. Thomas Holtz, a vertebrate paleontologist at the University of Maryland who was not a part of the research team, said. “These adaptations don’t make sense for a terrestrial strider but they are very reasonable for an animal that’s spending its time in the water and shuffling on land occasionally.”

“How it walked on land and swam are of much interest, its center of gravity far forward compared to other land-based predators,” Sereno said. “Foot-propelled paddling with webbed feet seems likely, to explain the anatomical findings at the rear of the beast. At the other end, its neck and trunk are particularly long, which give the skeletal model and mount its record-shattering 50-foot length. The bones at the base of the neck are also adapted for bending downward, perhaps for fishing while swimming.”

Nevertheless, Sereno explained, the animal would have been a formidable opponent of any land predator of its time, including the nearly T-rex-sized Carcharodontasaurus.

“Spinosaurus had a large head,” Sereno said. “It was nothing to sneer at. You would not want to encounter this animal.”

Despite its odd adaptations, Spinosaurus probably reproduced in a conventional way for its order: Like all other dinosaurs, it was almost certainly oviparous.

“As far as we know, no member of the dinosaur group was ever able to make that switch away from laying eggs,” Holtz explained. “It seems, until we have evidence to the contrary, that Spinosaurus probably did shuffle up onto land to lay its eggs there.”

Spinosaurus aegyptiacus, the largest known predator ever to walk the Earth, lived in Cretaceous period Africa. The dinosaur’s unique aquatic adaptations would have allowed it to hunt fish and other prey in the region’s then-ubiquitous rivers. Illustration by Davide Bonadonna, courtesy University of Chicago.

Most of the fossils that serve as the basis for the new paper are of one individual, which also help scientists to understand the proportions of Spinosaurus aegyptiacus. The recently discovered remains were found in the Kem-Kem fossil beds of southeastern Morocco.

On Friday the National Geographic Society will premiere an exhibition in Washington, D.C. focused on Spinosaurus aegyptiacus.