Northern carnivorous dinosaur was a vegetarian

February 1, 2016 - 06:25

An overlooked clue preserved in 123 million-year-old sandstone deposits debunks the belief that meat-eating dinosaurs roamed the island archipelago of Svalbard

The Norwegian island archipelago of Svalbard was much warmer and wetter 123 million years ago, during the time of the dinosaurs. The illustration shows plant-eating ornithopods on Svalbard and their tracks in the sand. Until now, scientists believed that the tracks came from a carnivorous dinosaur called a theropod, but these dinosaurs always walk on two legs. Researchers have now found the imprint of front feet in the Svalbard tracks, meaning that the dinosaur that left them walked on all fours and had to be a vegetarian. (Illustration: Esther van Hulsen)

The largest collection of dinosaur tracks on the Norwegian arctic island archipelago of Svalbard is found on the southeastern coast of the main island of Spitsbergen, in a place called Boltodden.

Although Svalbard now lies at roughly 70 degrees N latitude, 123 million years ago, when dinosaurs roamed the Earth, Svalbard was farther south, more at the latitude of Fairbanks, Alaska. That might not sound very hospitable to dinosaurs, but the climate was so much warmer and wetter then that forests of ginko trees and conifers covered Svalbard – and dinosaurs wandered its reaches.

In 1976, an American petroleum geologist named Rosalind Edwards found some of the dinosaur tracks left at Boltodden and described them as characteristic of a medium-sized carnivorous dinosaur called a theropod – the first and only carnivorous dinosaur ever found on the island. 

Boltodden is located on the southeast coast of Spitsbergen, about 100 km south-southeast of Longyearbyen, the island’s largest town. Other places where dinosaur tracks have been found are indicated with TS (track sites) on the map on the left. Festningen, just west of Longyearbyen, was the first location where dinosaur tracks were found in 1960. At the time it was a world sensation, because it was interpreted as evidence that dinosaurs could live in much colder regions. Now we know that continental plates move across the Earth's crust and that Spitsbergen was farther south and much warmer and wetter than it is today. (Figure: Journal of the Geological Society, London, doi: 10.1144, Creative Commons BY 3.0 license)

The tracks as she described them were unmistakably from a carnivore, 30 centimetres long and with the clear imprint of a claw.  And most tellingly, they were in sets of two, meaning that the dinosaurs that left them walked on two legs.  Vegetarian dinosaurs characteristically walk on all fours.

From two to four

Thirty-eight years later, in the summer of 2014, the Norwegian palaeontologist Jørn Hurum from the University of Oslo’s Natural History Museum and his colleagues returned to Boltodden to re-examine Edwards’s find.

The first thing they noticed was that there were many more dinosaur tracks here than Edwards first reported. In fact, they realized, the area held the largest collection of dinosaur tracks in the entire archipelago.

Scientists from the Natural History Museum at the University of Oslo, the University Centre in Svalbard and the University of Alaska Fairbanks map dinosaur tracks in Boltodden in 2014. (Photo: Hans Arne Nakrem, Natural History Museum, University of Oslo)

And secondly—the tracks from the carnivorous theropod that Edwards had reported in 1976 had not been left by a creature walking on two legs after all. The dinosaur that left these tracks walked on all fours. And that meant it had to be a herbivore.

“No carnivorous dinosaur has ever been found to walk on all fours, except possibly Spinosaurus,” says Hurum.

Spinosaurus was a giant among carnivorous dinosaurs. Its great weight may have forced it down on all fours from time to time, some researchers believe.

Some of the dinosaur tracks at Boltodden as photographed in 2014. The track left of centre was found in 1976. Note the small round tracks in front of the larger tracks. The ruler at the side of the photo is one metre long. (Photo: Hans Arne Nakrem, Natural History Museum, University of Oslo)

But the tracks on Svalbard were too small, and were older than Spinosaurus. The tracks left by this four-legged dinosaur led Hurum and his colleagues to a new conclusion: The tracks had to have come from an ornithopod, a vegetarian dinosaur.

Tricked by the sand

Although the tracks were clearly left by an ornithopod, Hurum and his colleagues still had a mystery to solve. The tracks from the hind feet seemed to show an imprint from a claw. But herbivores don’t have claws.

The answer, the researchers realized, was that there were no claws. The toes were round, but the condition of the sand when the dinosaurs walked there made it look like the toes were actually sharp, like claws.

The tracks were photographed and converted into three-dimensional models (right). Here is the track from a forefoot that shows that this was not a carnivorous dinosaur. (Photo: Hans Arne Nakrem, Natural History Museum, University of Oslo)

“Imagine that you are walking on a sandy beach. The imprints left by your toes are round. But then the wet sand collapses a bit and runs into the track from the sides and towards the bottom. That causes the imprint to look almost like claws,” says Hurum.

“Water-saturated sand partially collapsed at the tracking surface, resulting in distortion at the distal end of the digits and producing an artificially narrow toe outline, including a sharp claw-like morphology,” the researchers wrote in their scientific paper on the find. “The high moisture content of the sediment is inferred
from the depositional setting, which was probably a beach.”

Right dinosaur, wrong place

The tracks still pose a huge puzzle for the scientists, because the Svalbard of the Cretaceous period, or 123 million years ago, was close to Greenland and North America, but was effectively isolated from Europe.

However, the tracks of a four-footed ornithopod like this were much more typical of Europe of the period. And these dinosaurs did not fly, they could only walk. So how did they get to Svalbard?

“One possibility is that quadrupedal ornithopods were more widespread across Greenland/North America at this time than recognized but (are) poorly represented by body or trace fossils, which seems likely to be at least partly true,” the researchers wrote. “Alternatively, a potential route of terrestrial connectivity that is not currently recognized... permitted dispersal between Svalbard and Europe.”

In other words, researchers may have lost the only carnivorous dinosaur ever found on Svalbard, but they have a new mystery to solve: how did this dinosaur, only known from Europe, find its way to the Svalbard of that time?

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