Washington D.C. - Curved claws like giant meathooks and a long, narrow, crocodile-like skull were among the fossil remains of a new genus and species of dinosaur recently excavated in the Ténéré Desert of central Niger. The findings by a group of scientists from the U.S., France, the U.K, and Niger, are reported in the 13 November issue of Science.
The new species is a member of a peculiar group of fish-eating dinosaurs, the spinosaurids, who have long, narrow jaws studded with cone-shaped teeth, a fin-like sail varying in height along their backs, and large, sickle-shaped thumb claws. Spinosaurids themselves are theropods, two-legged carnivores whose ranks include Tyrannosaurus and Velociraptor. The new dinosaur, estimated to be about 100 million years old, is named Suchomimus tenerensis. ("Souchos" is Greek for crocodile, and "tener" refers to the desert where the skeleton was found.)
According to reconstructions, Suchomimus was about 11 meters, or 36 feet, long. An average-sized adult human would have stood at eye-level with the thigh of the dinosaur's hind leg. Although the researchers had learned of a couple of spinosaurid fragments found near their site, their discovery of the most complete spinosaurid skeleton yet was somewhat of a surprise.
"We had been looking for really excellent fossils, not just of dinosaurs but of other organisms as well," said Paul Sereno, of the University of Chicago, who led the excavation. But the researchers knew immediately that their find had significant implications for understanding spinosaurids. While they were still in the field, Sereno and his colleagues suspected from the age and characteristics of the fossils that the dinosaur belonged to a new genus (Suchomimus), as well as a new species (tenerensis).
By analyzing Suchomimus and other spinosaurids, Sereno and his colleagues have determined that the spinosaurid skull is even more elongate and crocodile-like than previously thought. In a Perspective that accompanies Sereno and his colleagues' report, Thomas Holtz of the University of Maryland considers that several of the features of the skull, which parallel those of the ancient crocodilians, may have arisen as adaptations towards a diet that included fish as well as meat. A narrow snout, for example, might allow a smoother passage through water, and pointy, cone-shaped teeth function better to pierce and grasp rather than to slice. (Other theropods have serrated, blade-like teeth.)
The first spinosaurid, Spinosaurus, was discovered in Egypt in 1912 but destroyed during the bombing of Munich in World War II. Additional bones of Spinosaurus-like predators have since been found in Niger, Brazil, and Europe. Before the discovery of Suchomimus, it seemed that the evolutionary relationships between the three known spinosaurid genera were a simple matter of geography, because the two genera in the Southern hemisphere were more closely related to each other than to the European genus, Baryonyx.
According to this scenario, spinosaurids were initially distributed across the enormous landmass of Pangaea. As Pangaea rifted apart and the Tethys Seaway formed between the northern and southern halves (which would later form the continents in the Northern and Southern hemispheres), Baryonyx evolved separately on the northern continent and the two more closely related spinosaurids evolved to the south.
However, the discovery of Suchomimus in Africa complicates the picture, because Suchomimus appears to be more closely related to the European Baryonyx than to the southern spinosaurids found in Egypt and Brazil. The similarities between the two dinosaurs suggest that Suchomimus' ancestor evolved in the north. Spinosaurids from the north then colonized the Southern continent via a land bridge across the seaway.
"This finding will add significant information to the idea that there was traffic across the Tethys seaway during the Cretaceous Period," said Sereno. "We are trying to understand evolution in a fragmenting world."
Materials provided by American Association For The Advancement Of Science. Note: Content may be edited for style and length.
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