Daspletosaurus

*Daspletosaurus torosus*

* Timothy Bradley Artwork
* Robert F Walters Artwork

***Daspletosaurus*** (meaning "frightful lizard") is an extinct genus of tyrannosaurid theropod dinosaur that lived in North America during the Late Cretaceous period. Similar to other members of the tyrannosaurids, it had a powerful jaw and short arms. It had a huge body balanced upon two powerful back legs. The three-toed taloned feet (much like those of a modern bird) probably held the prey down while it ate. Like all tyrannosaurids, the front limbs were short and had only two fingers each. An attack from a *Daspletosaurus* or its relative *Albertosaurus* would have been a nasty way to go, due to their brute strength, robust teeth and jaws powerful enough to puncture through bone.

## Discovery and naming

The type specimen of *Daspletosaurus torosus* (CMN 8506) is a partial skeleton including the skull, the shoulder, a forelimb, the pelvis, a femur and all of the vertebrae from the neck, torso and hip, as well as the first eleven tail vertebrae. It was discovered in 1921 near Steveville, Alberta, by Charles Mortram Sternberg, who thought it was a new species of *Gorgosaurus*. It was not until 1970 that the specimen was fully described by Dale Russell, who made it the type of a new genus, *Daspletosaurus*, from the Greek δασπλής (dasplēs, stem and connective vowel resulting in dasplēto-) ("frightful") and σαυρος (sauros) ("lizard"). The type species is *Daspletosaurus torosus*, the specific name torosus being Latin for 'muscular' or 'brawny'. Aside from the type, there is only one other well-known specimen, RTMP 2001.36.1, a relatively complete skeleton discovered in 2001. Both specimens were recovered from the Oldman Formation in the Judith River Group of Alberta. The Oldman Formation was deposited during the middle Campanian stage of the Late Cretaceous, from about 79.5 to 77 Ma (million years ago).

Dale Russell also suggested that a specimen of an immature *Albertosaurus* (CMN 11315) from the younger Horseshoe Canyon Formation in Alberta actually belonged to a third specimen of *Daspletosaurus* as *D. cf. torosus*, extending the temporal range of the genus by approximately 3.5 million years into the Maastrichtian. He based this referral on features of its limb and pelvic girdle, as well as the curvature of the hand claws, which he interpreted as traits matching *Daspletosaurus*. This reassignment was not universally accepted, and thorough re-examination of the specimen favoured its initial referral to *Albertosaurus sarcophagus*, despite lacking many of the diagnostic skeletal traits used to identify mature tyrannosaurids. An additional maxilla and various teeth from an *Edmontosaurus*-dominated bonebed in the Horseshoe Canyon Formation was also mistakenly referred to *Daspletosaurus*, but all the tyrannosaurid material has all since been confirmed to belong to *Albertosaurus*.

### Assigned species

Two or three additional species have been assigned to the genus *Daspletosaurus* over the years, although as of 2007 none of these species has received a proper description or scientific name. In the meantime, all are designated as *Daspletosaurus* spp; this does not imply that they all are the same species.

Along with the holotype, Russell designated a specimen collected by Barnum Brown in 1913 as the paratype of *D. torosus*. This specimen (AMNH 5438) consists of parts of the hindleg, the pelvis and some of its associated vertebrae. It was discovered in the Dinosaur Park Formation in Alberta. The Dinosaur Park Formation was formerly known as the Upper Oldman Formation and dates back to the middle Campanian, between 76.5 and 74.8 million years ago. *Daspletosaurus* fossils are known specifically from the middle to upper section of the formation, between 75.6 and 75.0 million years ago. In 1914, Brown collected a nearly complete skeleton and skull; forty years later his American Museum of Natural History sold this specimen to the Field Museum of Natural History in Chicago. It was mounted for display in Chicago and labeled as *Albertosaurus libratus* for many years, but after several skull features were later found to be modeled in plaster, including most of the teeth, the specimen (FMNH PR308) was reassigned to *Daspletosaurus torosus* by Thomas Carr in 1999. A total of eight specimens have been collected from the Dinosaur Park Formation over the years since, most of them within the boundaries of Dinosaur Provincial Park. Phil Currie believes that the Dinosaur Park specimens represent a new species of *Daspletosaurus*, distinguished by certain features of the skull. Pictures of this new species have been published, but it still awaits a name and full description in print.

A new tyrannosaurid specimen (OMNH 10131), including skull fragments, ribs and parts of the hindlimb, was reported from New Mexico in 1990 and assigned to the now-defunct genus *Aublysodon*. Many later authors have reassigned this specimen, along with a few others from New Mexico, to yet another unnamed species of *Daspletosaurus*. However, research published in 2010 showed that this species, from the Hunter Wash Member of the Kirtland Formation, is actually a more primitive tyrannosauroid, and was classified in the genus *Bistahieversor*.

In 1992, Jack Horner and colleagues published an extremely preliminary report of a tyrannosaurid from the upper parts of the Campanian Two Medicine Formation in Montana, which was interpreted as a transitional species between *Daspletosaurus* and the later *Tyrannosaurus*. Currie (2003) stated that the tyrannosaurid from the Two Medicine Formation mentioned by Horner et al. (1992) may be an unnamed third species of *Daspletosaurus*. Another partial skeleton was reported from the Upper Two Medicine in 2001, preserving the remains of a juvenile hadrosaur in its abdominal cavity. This specimen was assigned to *Daspletosaurus* but not to any particular species. The remains of at least three more *Daspletosaurus* have also been described in a Two Medicine bonebed by Currie et al. (2005); the authors stated that this fossil material likely represents then-unnamed species mentioned by Horner et al. (1992), but cautioned that further study and description of *Daspletosaurus* would be necessary before the species can be determined with certainty. In 2017, the Two Medicine Formation taxon was named as the new species *D. horneri*.

Isolated tyrannosaurid teeth in the upper portions of the Judith River Formation are likely from *Gorgosaurus* as well as some species of *Daspletosaurus*, probably *D. torosus*. However, in the lower portion Judith River formation, around 78 million years ago, there is some evidence for a new undescribed tyrannosaurid taxon. A specimen in the collections of Triebold Paleontology excavated between 2002 and 2004, known as "Sir William", shows some characteristics of *Daspletosaurus* suggesting a new earlier species to the genus. However the specimen shows many characteristics typical of early tyrannosaurines such as *Teratophoneus* and even some of the later *Tyrannosaurus*, which may suggest an entirely new genus.

## Description

While very large by the standard of modern predators, *Daspletosaurus* was not the largest tyrannosaurid. Adults could reach a length of 8–9 meters (26–30 ft) from snout to tail. Mass estimates have centered on 2.5 metric tons (2.8 short tons), but have ranged between 1.8 and 3.8 metric tons (2.0 and 4.2 short tons).

### Skull

*Daspletosaurus* had a massive skull that could reach more than 1 meter (3 ft 3 in) in length. The bones were heavily constructed and some, including the nasal bones on top of the snout, were fused for strength. Large fenestrae (openings) in the skull reduced its weight. An adult *Daspletosaurus* was armed with about six dozen teeth that were very long but oval in cross section rather than blade-like. Unlike its other teeth, those in the premaxilla at the end of the upper jaw had a D-shaped cross section, an example of heterodonty always seen in tyrannosaurids. Unique skull features included the rough outer surface of the maxilla (upper jaw bone) and the pronounced crests around the eyes on the lacrimal, postorbital, and jugal bones. The orbit (eye socket) was a tall oval, somewhere in between the circular shape seen in *Gorgosaurus* and the 'keyhole' shape of *Tyrannosaurus*. Split carinae (edges) have been found on *Daspletosaurus* teeth.

### Postcranial skeleton

*Daspletosaurus* shared the same body form as other tyrannosaurids, with a short, S-shaped neck supporting the massive skull. It walked on its two thick hindlimbs, which ended in four-toed feet, although the first digit (the hallux) did not contact the ground. In contrast, the forelimbs were extremely small and bore only two digits, although *Daspletosaurus* had the longest forelimbs in proportion to body size of any tyrannosaurid. A long, heavy tail served as a counterweight to the head and torso, with the center of gravity over the hips.

## Discovery and naming

*Daspletosaurus* which means "frightful lizard" from the Greek ***dasples/δασπλής*** (***dasples*** connective vowel resulting in ***daspleto***) meaning "frightful" and ***sauros/σαῦρος*** was discovered and fully described in 1970 by Dale Russell in what we know as Alberta, Canada today, the type specimen *"Daspletosaurus torosus"* comes from the Latin ***torosus*** meaning "brawny" or "muscular".

## Classification and systematics

*Daspletosaurus* belongs in the subfamily Tyrannosaurinae within the family Tyrannosauridae, along with *Tarbosaurus*, *Tyrannosaurus* and *Alioramus*. Animals in this subfamily are more closely related to *Tyrannosaurus* than to *Albertosaurus* and are known – with the exception of *Alioramus* – for their robust build with proportionally larger skulls and longer femora than in the other subfamily, the Albertosaurinae. It further belongs to the tribe Daspletosaurini, consisting of it and the taxon *Thanatotheristes*.

*Daspletosaurus* is usually considered to be closely related to *Tyrannosaurus rex*, or even a direct ancestor through anagenesis. Gregory Paul reassigned *D. torosus* to the genus *Tyrannosaurus*, creating the new combination *Tyrannosaurus torosus*, but this has not been generally accepted. Many researchers believe *Tarbosaurus* and *Tyrannosaurus* to be sister taxa or even to be the same genus, with *Daspletosaurus* a more basal relative. On the other hand, Phil Currie and colleagues find *Daspletosaurus* to be more closely related to *Tarbosaurus* and other Asian tyrannosaurids like *Alioramus* than to the North American *Tyrannosaurus*. The systematics (evolutionary relationships) of *Daspletosaurus* may become clearer once all the species have been described.

## Paleobiology

### Senses

There are indications of D. horneri possessing integumentary sensory organs, possibly used in touch, modulation of precise jaw movements, temperature reading, and prey detection.

## Paleoecology

All known Daspletosaurus fossils have been found in formations dating to the middle to late Campanian stage of the Late Cretaceous period, between 77 and 74 million years ago.

## JPInstitute.com Description

Daspletosaurus is a good example of the research methods used by scientists over many years whereby they build on each other's discoveries to form a conclusion about a dinosaur. Daspletosaurus was first discovered in 1921 by Charles Sternberg. These partial remains were thought by Sternberg to be a dinosaur he called Gorgosaurus. Later discoveries, however, added more pieces to the puzzle, and almost 50 years after the first discovery, Dr. Dale Russel was able to determine that this dinosaur was both a new species and genus, which he called Daspletosaurus. This dinosaur is an early member of the tyrannosaur family and looks a great deal like a smaller version of T. rex.

At first, some scientists argued that Daspletosaurus was a larger more adult version of Albertosaurus. Subsequent study, however, has proved otherwise. It was a typical tyrannosaur, with shorter, two-fingered front limbs. It was more robust than Albertosaurus, its contemporary cousin, and it is speculated that it was better suited to hunting the slower horned dinosaurs, thus leaving the faster hadrosaurs to the lighter and speedier Albertosaurus.

## Appearance in other media

### *The Land Before Time*

*Daspletosaurus* is represented in *The Land Before Time Animated Moviebook*, in the Mountains That Burn stage of 'The Great Fossil Hunting Grounds' minigame.

## Links

http://web.archive.org/web/20040214161308fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_daspl.html#

## References

* 1=http://animals.howstuffworks.com/dinosaurs/daspletosaurus.htm