Early in the 20th century, Tyrannosaurus itself was discovered by Barnum Brown and named by Henry Fairfield Osborn, who would recognize it as a representative of a distinct family of dinosaurs he called the Tyrannosauridae. Tyrannosaur taxonomy would be controversial for many decades afterward. One controversy centered around the use of the name Tyrannosauridae for this family, as the name "Deinodontidae" had already been proposed. The name Tyrannosauridae came out victorious following arguments put forth by Dale Russell in 1970. The other major controversy regarding tyrannosaur taxonomy was the family's evolutionary relationships. Early in the history of paleontology, it was assumed that the large carnivorous dinosaurs were all part of one evolutionary lineage ("carnosaurs"), while the small carnivorous dinosaurs were part of a separate lineage (coelurosaurs). Tyrannosaurid anatomy led some early researchers like Matthew, Brown, and Huene, to cast doubt on the validity of this division. However, the traditional carnosaur-coelurosaur division persisted until the early 1990s, when the application of cladistics to tyrannosaur systematics confirmed the doubts of early workers and found tyrannosaurs to be large-bodied coelurosaurs.
Another debate about tyrannosaurs would not be settled until the early 21st century: their diet. Early researchers were so overwhelmed by the massive bulk of Tyrannosaurus rex that some, like Lawrence Lambe, were skeptical that it was even capable of hunting down live prey and assumed that it lived as a scavenger. This view continued to be advocated into the 1990s by Jack Horner but was shown false by Kenneth Carpenter, who reported the discovery of a partially healed tyrannosaur bite wound on an Edmontosaurus annectens tail vertebra, proving that T. rex at least sometimes pursued living victims.
The Delaware people of what is now New Jersey or Pennsylvania had a tradition regarding a hunting party that returned with a piece of an ancient bone supposedly belonging to a monster that killed humans. One of the village's wise men instructed people to burn bits of the bone in clay spoons with tobacco and make a wish while the concoction was still smoking. This ritual could bestow such favors as success in hunting, long life, and health for one's children. This tale might be inspired by local fossils, which include Dryptosaurus, ankylosaurs, Coelosaurus, and Hadrosaurus.
The Cheyenne believed that a mythical creature called an Ahke once lived in the prairies of the western United States. These creatures were thought to resemble giant buffalo, whose bones turned to stone. Ahke bones were found both on land as well as buried in the banks of streams. Tyrannosaurus rex fossils preserved in Hell Creek Formation strata may have been influences on this old legend. Its contemporary Triceratops is another possible influence, as well as the more recent Cenozoic fossils of Titanotherium and mastodons.
Edward Drinker Cope described the new genus and species Laelaps aquilunguis. This discovery proved that theropod dinosaurs walked on their hind limbs rather than on all fours like in earlier reconstructions. He also erected the family Deinodontidae.
Matthew and Brown named the Tyrannosaurinae. Despite still classifying tyrannosaurs as members of the family Deinodontidae, they proposed that, contrary to researchers who regarded tyrannosaurs as carnosaurs related to other large carnivorous dinosaurs like Allosaurus and Megalosaurus, the tyrannosaurs were actually more closely related to the small carnivores known as coelurosaurs.
Matthew and Brown described the new species Gorgosaurus sternbergi. They still regarded tyrannosaurs as members of the family Deinodontidae.
Friedrich von Huene regarded tyrannosaurs as members of the family Deinodontidae. Like Brown and Matthew, Huene thought tyrannosaurs were more closely related to the small carnivores called coelurosaurs than to other large carnivorous dinosaurs like Allosaurus and Megalosaurus.
Huene still regarded tyrannosaurs as members of the family Deinodontidae and continued to advocate for the hypothesis that tyrannosaurs were more closely related to the small carnivores called coelurosaurs than to other large carnivorous dinosaurs like Allosaurus and Megalosaurus.
Dale Russell described the new genus and species Daspletosaurus torosus. He classified it in the family Tyrannosauridae rather than the historical home of tyrannosaurs, the Deinodontidae, setting a trend among paleontologists that would see the latter familial name fall into disuse in favor of the former. He observed that Daspletosaurus and Gorgosaurus lived at the same time and place, while Daspletosaurus was less common. He also noticed that hadrosaurs and ceratopsians were both present in the same deposits, with ceratopsians being less common. He speculated that this parallel may have been due to niche partitioning between the tyrannosaurs as each specialized in prey, with the lighter built and more common Gorgosaurus feeding on hadrosaurs and the more rugged and less common Daspletosaurus specializing in the rarer and more dangerous ceratopsians. He noted that while adult tyrannosaurs may have fed on such large prey, very young individuals would be limited to quarry like birds, frogs, mammals, and small reptiles.
Farlow and others studied tyrannosaur tooth biomechanics, finding them to be more resistant to forces in both the front-to-back and side-to-side planes than the more blade-like teeth of other carnivorous dinosaurs.
William Abler studied tyrannosaur tooth biomechanics. He concluded that the serrations on tyrannosaur teeth did not function like the serrations on a saw blade. Instead he thought the serrations may have caught pieces of rotting meat inside them, sustaining bacterial colonies that make its bite likely to transmit deadly infections to potential prey items. Similar use of decaying meat trapped in tooth serrations as a vector for infected prey had been reported in monitor lizards.
Fernando Emilio Novas performed a phylogenetic analysis of the tyrannosauridae, finding tyrannosaurs to actually be coelurosaurs, as advocated by a few contrarian workers during the 1920s, rather than carnosaurs as had been generally supposed for decades. Novas found them equally related to the ornithomimosaurs and maniraptorans.
Bernardino Pérez Pérez-Moreno and others performed another phylogenetic analysis of the Tyrannosauridae and found additional support for reclassifying the family as coelurosaurs. They found that within the coelurosaurs, tyrannosaurs were arctometatarsalians. In other words, they were more closely related to the ostrich dinosaurs than to birds.
Farlow found that the ancient ecology of tyrannosaur habitats were inconsistent with the idea that they were scavengers.
Lockley and Hunt reported a possible T. rex footprint in 1994.
Pérez-Moreno and others performed another phylogenetic analysis of the Tyrannosauridae and found additional support for reclassifying the family as coelurosaurs. They found tyrannosaurids to lie outside of the maniraptoriformes. In other words, they are less closely related to birds than the ostrich dinosaurs are.
Thomas Holtz performed another phylogenetic analysis of the Tyrannosauridae and found additional support for reclassifying the family as coelurosaurs. He found that within the coelurosaurs, tyrannosaurs were arctometatarsalians. In other words, they were more closely related to the ostrich dinosaurs than to birds.
Horner interpreted tyrannosaurids as scavengers.
Emily B. Giffin observed that the brachial plexus of the tyrannosaurid neural canal was smaller than those of other theropods, suggesting that tyrannosaurids really did have reduced forlimb function.
Farlow and others calculated that an adult T. rex running at 20 m/s or faster would sustain fatal injuries if it tripped, suggesting that they didn't actually run that fast.
Holtz observed that tyrannosaurids had the longest limbs relative to their body size of any theropod dinosaurs apart from the ostrich dinosaurs and a small, slender ceratosaur called Elaphrosaurus. Although the ostrich dinosaur on average had relatively longer limbs overall, the ratios of femur length to the length of the tibia and fibula were actually very close between the smaller tyrannosaurs and the largest ostrich dinosaurs. Holtz found ostrich dinosaurs and tyrannosaurs to have other traits of the hindlimb in common as well. Both groups had a pinched third metatarsal, called an arctometatarsus, that strengthened the foot. Holtz concluded that these traits indicated that tyrannosaurids were among the best adapted for running of all carnivorous dinosaurs.
Erickson and Olson others calculated the bite force of T. rex, finding it to have some of the strongest jaws of any carnivorous vertebrate. By contrast, other carnivorous dinosaurs like Allosaurus had relatively weak jaws.
Richard Cifelli and others reported teeth from Utah that exhibited the distinctive thickening characterizing tyrannosaurid teeth that date back to the Albian-Cenomanian boundary. As such, they were the oldest known tyrannosaurid teeth.
Kirkland and others reported teeth from Utah that exhibited the distinctive thickening characterizing tyrannosaurid teeth that date back to the Albian-Cenomanian boundary. As such, they were the oldest known tyrannosaurid teeth.
Sereno concluded that the evolutionary history of tyrannosaurids suggested a relatively complex history of biogeographic dispersal between Asia and North America.
Horner and Dobb interpreted tyrannosaurids as scavengers.
Sereno performed another phylogenetic analysis of the Tyrannosauridae and found additional support for reclassifying the family as coelurosaurs. He defined the tyrannosauridae as all tyrannosauroids closer to Tyrannosaurus than to Alectrosaurus, Aublysodon, or Nanotyrannus.
Catherine Forster and others performed another phylogenetic analysis which provided further support for the idea that tyrannosaurs are coelurosaurs, but less closely related to birds than ornithomimosaurs.
Peter Makovicky and Hans-Dieter Sues performed another phylogenetic analysis which provided further support for the idea that tyrannosaurs are coelurosaurs, but less closely related to birds than ornithomimosaurs.
Karen Chin and others reported a coprolite preserved in the Frenchman Formation of Saskatchewan that may have been left behind by Tyrannosaurus. The coprolite contained the partially digested bone fragments of the ornithischian dinosaurs it fed upon. These bones composed 30–50% of its total volume.
Holtz found that within the coelurosaurs, tyrannosaurs were arctometatarsalians. In other words, they were more closely related to the ornithomimosaurs than to birds.
Thomas Carr argued that Nanotyrannus was actually just a young Tyrannosaurus. He noticed that adult T. rex had fewer and more widely spaced teeth in the front tip of their jaws than juvenile T. rex or tyrannosaurs of other species, suggesting differences in feeding within and between tyrannosaur species.
Sereno performed another phylogenetic analysis of the Tyrannosauridae. He found that tyrannosaurs were maniraptorans.
Günter P. Wagner and Gauthier performed a phylogenetic analysis of the tyrannosaurs but found them equally related to the ornithomimosaurs and maniraptorans.
Carpenter reported a partially healed bite wound on a tail vertebra of an Edmontosaurus annectens, the size and shape of which suggested that it had been inflicted by Tyrannosaurus rex.
Carr and Williamson observed that tyrannosaurines were the most common type of tyrannosaurid in the southwestern US during the Campanian and Maastrichtian.
Phil Currie reported the discovery of at least nine Albertosaurus of different age groups preserved together in the same deposit. He speculated that if these animals were part of a social group, that members of different ages might perform different tasks in the course of a hunt. This interpretation derives by analogy from the behavior of modern pack hunting carnivorous mammals.
Darren Tanke and Currie reported that many specimens of Gorgosaurus and Daspletosaurus preserve evidence of bite wounds inflicted by members of the same tyrannosaur species. This is suggestive of face biting behavior of the sort seen in many kinds of modern predator like crocodilians, monitor lizards, and wolves.
Kenneth Carpenter and Matt Smith published a detailed description of the osteology and biomechanics of T. rex forelimbs. They concluded that T. rex arms were actually rather strong, but with a much smaller range of motion than other carnivorous dinosaurs like Allosaurus and Deinonychus. They concluded that while the arms of Tyrannosaurus would have been useless for actually killing prey, they may have been used to hold on to prey while the tyrannosaur killed it with bites. They dismissed notions that the forelimbs were useless or that Tyrannosaurus rex was an obligate scavenger. This study was the complete description of Tyrannosaurusforelimbs in the scientific literature.
Thomas Lehman observed that during the Campanian and Maastrichtian the distribution of albertosaurines and tyrannosaurines was strongly correlated with the distributions of their respective ornithischian prey.
Diagaram of T. rex forelimb anatomy.
David Varrichio and others reported a Daspletosaurus specimen from the Two Medicine Formation of Montana. This specimen notably preserved the contents of the animal's gut when it died, including fragments of bone from young ornithischian dinosaurs.
Foster and others observed that no other theropod inhabiting Asia or North America during the Campanian or Maastrichtian achieved a body size within "two orders of magnitude" of contemporary tyrannosaurs.~paleobio133-134~ They further speculated that this gap in body size may be attributable to juvenile tyrannosaurs occupying the ecological niches once exploited by other medium-to-large sized theropods.
Holtz found that within the coelurosaurs, tyrannosaurs were arctometatarsalians; meaning they were closer to ornithomimosaurs than to birds.
Holtz considered these definitions only tentative due to the scant remains representing most taxa in the Aublysodontinae. Holtz also noted that the lack of serrations on aublyodontines' premaxillary teeth could have been caused by tooth wear in life, postmortemabrasion, or digestion. Alternatively "Aublysodontine"-type teeth could be from an ontogenetic stage or sexual morph of another kind of tyrannosaur. Holtz also expressed the taxonomic opinion that Nanotyrannus lancensis was a juvenile T. rex. The results of his phylogenetic analysis of the Tyrannosauridae are reproduced below:
William L. Abler studied tyrannosaur tooth serration biomechanics. He observed that Albertosaurustooth serrations are so thin that they are practically a shallow crack in the tooth. However, at the base of each serration is round void called an ampulla which would have functioned to distribute force over a larger surface area, hindering the ability of the "crack" formed by the serration to propagate through the tooth.
This form resembles techniques used by guitar makers to "impart alternating regions of flexibility and ridgidity" to wood. As a proof of concept demonstrated that a plexiglass bar bearing regular incisions ending in drilled holes was more than 25% stronger than one with only regularly placed incisions. Abler interpreted tyrannosaurid teeth as holdfasts for pulling meat off a body, rather than knife-like cutting implements.
Brochu observed that the only distinguishing character of Aublysodon was the lack of serrations on its teeth, and that this condition might actually be due to damage sustained after the death of the animal. As such, he deemed that Aublysodon made a poor choice of anchor taxon for the Tyrannosauridae.
Farlow and Holtz published a study concluding that the ancient ecology of tyrannosaur habitats and morphology of tyrannosaur bodies were inconsistent with the idea that they were scavengers.
Holtz published a study concluding that the ancient ecology of tyrannosaur habitats and morphology of tyrannosaur bodies were inconsistent with the idea that they were scavengers. He also suggested that the tyrannosaur skull was subjected to greater torsional forces hunting and/or feeding than the skulls of other large carnivorous dinosaurs like allosaurs and ceratosaurs. He interpretd the breadth of the tyrannosaur skull and high development of its secondary palate as adaptations for enduring these forces. He theorized that tyrannosaurids exploited a similar hunting tactic to modern wolves and hyenas by running after prey and attacking it with their jaws. This tactic would distinguish tyrannosaurid hunting behavior from that of modern big cats, who depend more heavily on their forelimbs to take down prey.
Carrano and Hutchinson tried to reconstruct the life musculature of T. rex.
Hutchinson and Garcia used the reconstruction of T. rex musculature produced by Carrano and Hutchinson to ascertain its running abilities. They found that T. rex was not muscular enough for its body size to run quickly.
Currie interpreted Nanotyrannus lancensis as a juvenile T. rex. Currie argued that the type specimen of Alectrosaurus olseni was too incomplete to ascertain its position in the tyrannosaur family tree.
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