Palaeontology

Scientists report first semiaquatic dinosaur, Spinosaurus

Enormous predator was over 9 feet longer than largest Tyrannosaurus Rex.

On Thursday scientists unveiled what appears to be the first truly semiaquatic dinosaur, Spinosaurus aegyptiacus. New fossils of the massive Cretaceous-era predator expose that it adapted to life in the water some 95 million years ago, providing the most compelling evidence to date of a dinosaur able to live and hunt in an aquatic environment. The fossils also indicate that Spinosaurus was the largest known predatory dinosaur to walk the Earth, measuring up to an impressive 9 feet longer than the world’s largest Tyrannosaurus rex specimen. These findings, published yesterday in the journal Science, are also featured in the October issue of National Geographic magazine as the cover story, which will be available online from September 11th. In addition, Spinosaurus will be the subject of a new exhibition at the National Geographic Museum, opening September 12th, as well as National Geographic/NOVA special airing on PBS November 5th at 9 p.m.

An international research team‒ including palaeontologists Nizar Ibrahim and Paul Sereno from the University of Chicago; Cristiano Dal Sasso and Simone Maganuco from the National History Museum in Milan, Italy; and Samir Zouhri from the Université Hassan II Casablanca in Morocco‒ discovered that Spinosaurus developed a variety of previously unknown aquatic adaptations. The researchers made conclusions after analysing new fossils uncovered in the Moroccan Sahara and a partial Spinosaurus skull and other remains housed in museum collections around the world as well as historical records and images from the first reported Spinosaurus discovery in Egypt over a century ago. According to lead author Ibrahim, a 2014 National Geographic Emerging Explorer, “Working on this animal was like studying an alien from outer space; it’s unlike any other dinosaur I have ever seen.”

The aquatic adaptations of Spinosaurus vary considerably from earlier members of the spinosaurid family that resided on land but were known to consume fish. These adaptations include:

  • Small nostrils located in the middle of the skull. The small size and placement of the nostrils farther back in the skull enabled Spinosaurus to breathe when part of its head was submerged in water.
  • Neurovascular openings at the end of the snout. Similar openings on the crocodile and alligator snouts contain pressure receptors that allow them to sense movement in water. It’s likely that these openings served a comparable function in Spinosaurus.
  • Giant, slanted teeth that interlocked at the front of the snout. The conical shape and location of the teeth were well-suited for catching fish.
  • A long neck and trunk that shifted the dinosaur’s centre of mass forward. This meant walking on two legs on land was nearly impossible, but facilitated movement in water.
  • Powerful forelimbs with curved, blade-like claws. These claws were perfect for hooking or slicing slippery prey.
  • A small pelvis and short hind legs with muscular thighs. Similar to the earliest whales, these adaptations were for paddling in water and differ markedly from other predatory dinosaurs that used two legs to move on land.
  • Particularly dense bones lacking the marrow cavities typical to predatory dinosaurs. Similar adaptations, which enable buoyancy control, are seen in modern aquatic animals like king penguins.
  • Strong, long-boned feet and long, flat claws. Unlike other predators, Spinosaurus had feet resembling some shore birds that stand on or move across on soft surfaces rather than perch. In fact, Spinosaurus possibly had webbed feet for walking on soft mud or paddling.
  • Loosely connected bones in the dinosaur’s tail. These bones allowed its tail to bend in a wave-like fashion, similar to tails that helped propel some bony fish.
  • Enormous dorsal spines covered the skin that created a huge “sail” of the dinosaur’s back. The tall, thin, blade-shaped spines were anchored by muscles and composed of dense bone with few blood vessels. This suggests the sail was meant for display and not to trap heat or store fat. The sail would have been visible even when the animal entered water.
Spinosaurus: Wikimedia
Spinosaurus: Wikimedia

More than 100 years ago, German palaeontologist Ernest Freiherr Stromer von Reichenbach first discovered evidence of Spinosaurus in the Egyptian Sahara. Unfortunately, all of Stromer’s fossils were destroyed during the April 1944 allied bombing in Munich, Germany. Ibrahim, however, was able to track down Stromer’s surviving notes, sketches and photos in archives and at the Stromer family castle in Bavaria to supplement Stromer’s surviving publications.

     

The new Spinosaurus fossils were discovered in the Moroccan Sahara along desert cliffs known as the Kem Kem beds. This area was once a large river system, stretching from present-day Morocco to Egypt. At the time, a variety of aquatic life populated the system, including large sharks, coelacanths, lungfish and crocodile-like creatures, along with giant flying reptiles and predatory dinosaurs.

The most important of the new fossils, a partial skeleton unveiled by a local fossil hunter, was spirited out of the country. As a result, critical information about the context of the disovery was seemingly lost, and locating the local fossil hunter in Morocco was almost impossible. Ibrahim remarked, “It was like searching for a needle in a desert.” After an exhaustive search, Ibrahim finally found the man and confirmed the site of the original discovery.

To uncover some of the mysteries of Spinosaurus, the team created a digital model of the skeleton with funding provided by the National Geographic Society. The researchers Conducted CT scans on all of the new fossils, which will be repatriated to Morocco, complementing them with digital recreations of Stromer’s specimens. Missing bones were modelled based on known elements of related dinosaurs. According to Maganuco, “We relied upon cutting-edge technology to examine, analyse and piece together a variety of fossils. For a project of this complexity, traditional methods wouldn’t have been nearly as accurate.”

The researchers then used the digital model to create an anatomically precise, life-size 3-D replica of the Spinosaurusskeleton. After it was mounted, the researchers measured Spinosaurus from head to tail, confirming their calculation that the new skeleton was longer than the largest documented Tyrannosaurus by more than 9 feet. According to Sereno, head of the University of Chicago’s Fossil Lab, “What surprised us even more than the dinosaur’s size were its unusual proportions. We see limb proportions like this in early whales, not predatory dinosaurs.”

Dal Sasso added, “In the last two decades, several finds demonstrated that certain dinosaurs gave origins to birds. Spinosaurus represents an equally bizarre evolutionary process, revealing that predatory dinosaurs adapted to a semiaquatic life and invaded river systems in Cretaceous North Africa.”

 

Contributing Source: National Geographic Society

Header Image Source: WikiPedia

     

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