Dinosaur - Daspletosaurus torosus

Introduction

Pronounced das-PLEE-toe-SORE-us tore-ROH-sus

Daspletosaurus means 'frightful lizard' in Greek. The species name torosus is Latin for 'muscular'.

Daspletosaurus torosus was a theropod, as are all carnivorous dinosaurs. Theropod means 'beast foot', inspired by the very sharply clawed, three-toed feet of these animals.

Stocky and powerful, Daspletosaurus was the king predator of its time, approximately 10 million years older than its close relative T. rex. Up to nine metres long, Daspletosaurus was a formidable beast with heavy bones, a muscular tail and crests above its eyes. It grew by about 180 kilograms a year – 10 per cent of its final adult weight.

Identification

Daspletosaurus torosus was an enormous animal, almost nine metres in length.

This stocky and powerful meat-eater had the largest teeth of any of the tyrannosaurids, larger even than those of Tyrannosaurus rex. Each tooth was dagger-sharp, curved and saw-edged. Like other tyrannosaurids (those in the family Tyrannosauridae), this species also had a pair of small, two-fingered hands.

Daspletosaurus torosus was built much like T. rex but smaller, with a large skull and a long muscular tail. It had pronounced crests in front of and behind the eyes, giving it a distinctive appearance.

This tyrannosaur was one of the first for which clavicles were described. It was previously thought that tyrannosaurs lacked these bony struts in the shoulder girdle.

Habitat

Daspletosaurus torosus lived near a coastal plain with meandering rivers and streams during the Late Cretaceous period, 77-74 million years ago, in what is now western North America. Lowland areas were swampy and upland areas were forested. The climate was seasonal, warm and temperate. Other animals from the area included fish and crocodiles (found near the ancient coastline), amphibians, turtles, carnivorous dinosaurs like dromaeosaurs and troodontids, and plant-eating ceratopsians, hadrosaurs and ankylosaurs.

Distribution

Currently, there are at least seven known specimens of Daspletosaurus torosus and remains of possible others in this genus. Identified remains all come from what is now Alberta, Canada, but yet-to-be-identified fossils have been found in Montana, USA.

Feeding and diet

With its formidable teeth and jaws, clawed feet, and sheer bulk, Daspletosaurus torosus was easily capable of killing even the largest of its herbivorous prey. Daspletosaurus torosus was the first tyrannosaurid for which gut contents were identified - dinner included a duck-billed hadrosaur.

Daspletosaurus is known to have co-existed with another tyrannosaurid, Gorgosaurus. Scientists believe they probably adopted different feeding strategies, or hunted different prey, in order to 'share' available resources.

Other behaviours and adaptations

There is fossil evidence that Daspletosaurus was either prey, or a scavenged dinner, to others of its own species, or to other large predators. One individual was found with a tooth (its owner is yet to be identified) embedded in the right hip and a part of the hip appears to have been removed during the attack. Teeth marks were also found along the tail and on the foot, suggesting the feeding animal tried to pull its meal around or remove the leg.

Some specimens of Daspletosaurus torosus also have facial injuries from fights with other tyrannosaurs. The injuries had healed, so the animal survived the bite. These bites may have come from another species, but such fighting over food or mating rights is more common within predatory species.

Fossils description

The first Daspletosaurus remains were discovered by prolific fossil-hunter Charles M Sternberg in Canada in 1921, but he thought it was a new species of Gorgosaurus. It wasn’t until 1970 that fellow Canadian Dale Russell gave Daspletosaurus its current name.

There are a number of known specimens of Daspletosaurus torosus, although some are yet to be described and may represent new species. The type specimen is the partial skeleton recovered by Charles M Sternberg from the Oldman Formation of Alberta, Canada. Many of the fossil remains, including juveniles, were discovered during the Golden Age of dinosaur collecting in North America from 1895 to 1925. During that time, the badlands of Alberta spurred what has been called the 'Canadian Dinosaur Rush'. In order not to be outdone by the US scientists, who were collecting dinosaur fossils for the American Museum of Natural History, the Canadian Geological Survey appointed Charles H Sternberg as their Head Collector and Preparator of Vertebrate Fossils, and sent him to Alberta. Sternberg, who became one of the best-known collectors in the world, and his three sons (including Charles M Sternberg) would spend much of their lives digging for dinosaurs.

There may well be other species of Daspletosaurus in addition to D. torosus, as scientists are busy reassessing the fossil evidence.

Evolutionary relationships

Daspletosaurus torosus belongs in the family Tyrannosauridae and subfamily Tyrannosaurinae. The subfamily also includes Tarbosaurus, Tyrannosaurus, Teratophoneus, Zhuchengtyrannus and Alioramus.

Further reading

http://paleodb.org/cgi-bin/bridge.pl?a=checkTaxonInfo&taxon_no=57258&is_real_user=1