Paul Sereno shapes a clay model of Suchomimus in his University lab

Expedition unearths dinosaur fossil

It is not easy for a dinosaur skeleton to hide from a Paul Sereno expedition. Not even when what is left of said dinosaur is mostly buried in sand deep within central Africa’s vast, inhospitable Tènèrè Desert.

On Dec. 4, 1997, it was only a claw that gave away a then-unknown species of dinosaur to expedition member David Varricchio. But it was a big, sickle-shaped claw measuring a foot long. With Sereno’s mounting list of discoveries, the creature might as well have been thumbing a ride on Lake Shore Drive.

“The thumb claw was on the ground, ridiculously well-exposed,” said Sereno, Professor in Organismal Biology & Anatomy at Chicago. “We think that the sand and wind had uncovered it perhaps as much as two or three centuries ago, and that it’s been sitting at the surface ever since, waiting for someone to walk by.”

The claw belongs to a new species of spinosaur, a large predator that Sereno and his team have named Suchomimus tenerensis, which means “crocodile mimic from Tènèrè.” Sereno and his co-authors announced the discovery in the Nov. 13 issue of the journal Science. Among the co-authors were Chicago graduate students Allison Beck, Hans Larsson, Jonathan Marcot, Christian Sidor and Jeffrey Wilson.

Suchomimus belongs to a peculiar group of predators called spinosaurs that lived in Europe and South America as well as in Africa. In a perspective article that accompanies the Suchomimus announcement, Thomas Holtz of the University of Maryland, College Park, said the discovery provides important new insights on spinosaur evolution and adaptation.

At 36 feet in length and 12 feet in height at the hip, Suchomimus was as large as Tyrannosaurus rex but had a longer, more flexible neck and a skull like a crocodile’s.

“The forelimbs were particularly powerful,” Sereno said. Approximately four feet long, the forelimbs had enormous, grasping hands that came equipped with those meat-hook thumb claws for subduing prey.

But the skull of Suchomimus makes it even more strikingly different from other dinosaurs, said Sereno. It had a long, narrow snout. And instead of having blade-shaped teeth for slicing, Suchomimus had nearly round, fluted teeth that served as little hooks–the better with which to snare wiggling fish.

“We find this kind of fluting in marine reptiles. We find them in crocodiles. We don’t find them anywhere else in dinosaurs,” Sereno said. “I wouldn’t doubt that the snout, developed for fishing, meant that Suchomimus spent a good deal of its time in the shallows, waiting for something to pop by.”

Suchomimus also sported a thin, two-foot bony sail over its hips. Sails characterize most spinosaurs and were probably used for display. In fact, the skeletons of two plant-eating dinosaurs found in the same rock formation also grew sails along their backs.

Sereno’s international team of excavators pulled the remains of Suchomimus from 100-million-year-old sediment in the Niger Republic. The excavators, who had to bring all their water with them, were hampered at times by blowing sand and temperatures that soared to 120 degrees Fahrenheit.

“This is an area that is remote by anybody’s standards,” Sereno said. “It definitely gives you the feeling: Am I going to be coming out?”

But the deposits reveal that 100 million years ago, this region boasted a lush river environment. Trees resembling evergreens grew alongside broad rivers somewhat narrower than the Mississippi, which teemed with turtles and 50-foot crocodiles. Overhead soared pterosaurs, reptiles with 15-foot wingspans, looking for carrion.

Large, plant-eating land animals of the day included two types of duck-billed dinosaurs and two kinds of sauropods, the dinosaur family that includes the popularly known Brontosaurus.

“It was pleasant times 100 million years ago, with forests and rivers and a lot of wildlife,” Sereno said.

The Suchomimus discovery came as a surprise because then, as now, large plant-eating animals far outnumbered large predators. And yet, North African sites of a similar age already had produced two, and possibly three, other large predators. These included Carcharodontosaurus, discovered by Sereno during his 1995 expedition to Morocco.

Nevertheless, Sereno said, “We can say that Suchomimus dominated a large-bodied predator niche 100 million years ago in Africa.”

The fish-eating adaptations of spinosaur anatomy could help explain the success of Suchomimus, wrote Holtz in his Science perspective article. “Perhaps these different enormous carnivores were capable of coexisting by exploiting different parts of the potential food supply, and in particular because spinosaurs had more immediate access to the freshwater part of the food web,” Holtz wrote.

But there was still another surprise. Suchomimus more closely resembled its older, and probably somewhat smaller, spinosaur relative in England, Baryonyx, than its younger, larger cousin from Egypt, Spinosaurus.

Given the geography of the dinosaur era, scientists would have expected Suchomimus to have a closer relationship with Spinosaurus.

The earliest spinosaurs all would have lived on the huge continent of Pangea. But as geological forces slowly tore apart the continent into northern and southern halves, it seems more likely that Baryonyx would have evolved separately from Suchomimus and Spinosaurus.

Now it appears Suchomimus had ancestors that were able to get across the Tethys seaway that separated Europe and Africa, possibly via a land bridge, Sereno said.

“This finding will add significant information to the idea that there was traffic across the Tethys seaway during the Cretaceous Period,” he said. “We are trying to understand evolution in a fragmenting world.”

An even better understanding of evolution during the Cretaceous could be in the offing. The Suchomimus remains represent only a small percentage of the fossils Sereno and his team recovered in Niger. Further analysis of the remains is underway.

Expedition and laboratory work on Suchomimus was funded by the National Geographic Society, the David and Lucile Packard Foundation, the Pritzker Foundation and the Women’s Board of the University of Chicago.