Daspletosaurus (// das-PLEET-o-SAWR-əs; meaning "frightful lizard") was a genus of tyrannosaurid dinosaur that lived in western North America between about 77 and 74 million years ago, during the Late Cretaceous Period. The genus Daspletosaurus contains two species. Fossils of the earlier type species, D. torosus, have been found in Alberta, while fossils of the later second species, D. horneri, have been found only in Montana. A possible third species, also from Alberta, awaits formal identification. (Daspletosaurus sp.)
|Cast skeleton mount of D. torosus on display at the Science Center of Iowa.|
Daspletosaurus is closely related to the much larger and more recent tyrannosaurid Tyrannosaurus rex. Like most tyrannosaurids, Daspletosaurus was a multi-tonne bipedal predator equipped with dozens of large, sharp teeth. Daspletosaurus had the small forelimbs typical of tyrannosaurids, although they were proportionately longer than in other genera.
As an apex predator, Daspletosaurus was at the top of the food chain, probably preying on large dinosaurs like the ceratopsid Centrosaurus and the hadrosaur Hypacrosaurus. In some areas, Daspletosaurus coexisted with another tyrannosaurid, Gorgosaurus, though there is some evidence of niche differentiation between the two. While Daspletosaurus fossils are rarer than other tyrannosaurids', the available specimens allow some analysis of the biology of these animals, including social behavior, diet and life history.
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 t (2.5 long tons; 2.8 short tons), but have ranged between 1.8 and 3.8 t (1.8 and 3.7 long tons; 2.0 and 4.2 short tons).
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.
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.
A study of D. horneri skulls suggest that unlike many depictions of tyrannosaurids, this genus and likely other tyrannosaurids did not possess lips. Comparisons of the skull of this species with modern crocodiles show the same rugose (roughly wrinkled) bone structure that indicates the presence of large flat scales as opposed to lips. As the rough texture descends almost to the tooth line, it is theorized that Daspletosaurus' teeth were not covered by lips, as there would have been no room for such soft tissue.
Discovery and namingEdit
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 77 to 76 Ma (million years ago). A specimen from the younger Horseshoe Canyon Formation in Alberta has been reassigned to Albertosaurus sarcophagus. Another specimen  from the Horseshoe Canyon Formation may be referrable to Daspletosaurus, but this has not been confirmed or rejected yet.
Two or three additional species have been assigned to the genus Daspletosaurus over the years, although as of 2007 none of these species have 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. There is currently disagreement over the age of the Kirtland Formation, with some workers claiming a late Campanian age, while others suggest a younger age in the early Maastrichtian stage.
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.
Classification and systematicsEdit
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.
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.
There are indications of D. horneri possessing integumentary sensory organs, possibly used in touch, modulation of precise jaw movements, temperature reading, and prey detection. The large flat scales may have further protected the snout during prey capture and intra-specific combat.
Coexistence with GorgosaurusEdit
In the late Campanian of North America, Daspletosaurus was a contemporary of the albertosaurine tyrannosaurid Gorgosaurus. This is one of the few examples of two tyrannosaur genera coexisting. In modern predator guilds, similar-sized predators are separated into different ecological niches by anatomical, behavioral or geographical differences that limit competition. Several studies have attempted to explain niche differentiation in Daspletosaurus and Gorgosaurus.
Dale Russell hypothesized that the more lightly built and more common Gorgosaurus may have preyed on the abundant hadrosaurs of the time, while the more robust and less common Daspletosaurus may have specialized on the less prevalent but better-defended ceratopsids, which may have been more difficult to hunt. However, a specimen of Daspletosaurus (OTM 200) from the Two Medicine Formation preserves the digested remains of a juvenile hadrosaur in its gut region. The higher and broader muzzles of tyrannosaurines like Daspletosaurus are mechanically stronger than the lower snouts of albertosaurines like Gorgosaurus, although tooth strengths are similar between the two groups. This may indicate a difference in feeding mechanics or diet.
Other authors have suggested that competition was limited by geographical separation. Unlike some other groups of dinosaurs, there appears to be no correlation with distance from the sea. Neither Daspletosaurus nor Gorgosaurus was more common at higher or lower elevations than the other. However, while there is some overlap, Gorgosaurus appears to be more common at northern latitudes, with species of Daspletosaurus more abundant to the south. The same pattern is seen in other groups of dinosaurs. Chasmosaurine ceratopsians and hadrosaurine hadrosaurs (a group now generally referred to as saurolophines) are also more common in the Two Medicine Formation and in southwestern North America during the Campanian. Thomas Holtz has suggested that this pattern indicates shared ecological preferences between tyrannosaurines, chasmosaurines and hadrosaurines. Holtz notes that, at the end of the later Maastrichtian stage, tyrannosaurines like Tyrannosaurus rex, hadrosaurines and chasmosaurines like Triceratops were widespread throughout western North America, while albertosaurines and centrosaurines became extinct, and lambeosaurines were very rare.
A young specimen of the Dinosaur Park Daspletosaurus species (TMP 94.143.1) shows bite marks on the face that were inflicted by another tyrannosaur. The bite marks are healed over, indicating that the animal survived the bite. A full-grown Dinosaur Park Daspletosaurus (TMP 85.62.1) also exhibits tyrannosaur bite marks, showing that attacks to the face were not limited to younger animals. While it is possible that the bites were attributable to other species, intraspecific aggression, including facial biting, is very common among predators. Facial bites are seen in other tyrannosaurs like Gorgosaurus and Tyrannosaurus, as well as in other theropod genera like Sinraptor and Saurornitholestes. Darren Tanke and Phil Currie hypothesize that the bites are due to intraspecific competition for territory or resources, or for dominance within a social group.
Evidence that Daspletosaurus lived in social groups comes from a bonebed found in the Two Medicine Formation of Montana. The bonebed includes the remains of three Daspletosaurus, including a large adult, a small juvenile, and another individual of intermediate size. At least five hadrosaurs are preserved at the same location. Geologic evidence indicates that the remains were not brought together by river currents but that all of the animals were buried simultaneously at the same location. The hadrosaur remains are scattered and bear numerous marks from tyrannosaur teeth, indicating that the Daspletosaurus were feeding on the hadrosaurs at the time of death. The cause of death is unknown. Currie speculates that the daspletosaurs formed a pack, although this cannot be stated with certainty. Other scientists are skeptical of the evidence for social groups in Daspletosaurus and other large theropods;
Brian Roach and Daniel Brinkman have suggested that Daspletosaurus social interaction would have more closely resembled the modern Komodo dragon, where non-cooperative individuals mob carcasses, frequently attacking and even cannibalizing each other in the process. Evidence of cannibalism in Daspletosaurus was published in 2015.
Paleontologist Gregory Erickson and colleagues have studied the growth and life history of tyrannosaurids. Analysis of bone histology can determine the age of a specimen when it died. Growth rates can be examined when the age of various individuals are plotted against their size on a graph. Erickson has shown that after a long time as juveniles, tyrannosaurs underwent tremendous growth spurts for about four years midway through their lives. After the rapid growth phase ended with sexual maturity, growth slowed down considerably in adult animals. Erickson only examined Daspletosaurus from the Dinosaur Park Formation, but these specimens show the same pattern. Compared to albertosaurines, Daspletosaurus showed a faster growth rate during the rapid growth period due to its higher adult weight. The maximum growth rate in Daspletosaurus was 180 kilograms (400 lb) per year, based on a mass estimate of 1800 kilograms (2 tons) in adults. Other authors have suggested higher adult weights for Daspletosaurus; this would change the magnitude of the growth rate but not the overall pattern.
By tabulating the number of specimens of each age group, Erickson and his colleagues were able to draw conclusions about life history in a population of Albertosaurus. Their analysis showed that while juveniles were rare in the fossil record, subadults in the rapid growth phase and adults were far more common. While this could be due to preservation or collection biases, Erickson hypothesized that the difference was due to low mortality among juveniles over a certain size, which is also seen in some modern large mammals like elephants. This low mortality may have resulted from a lack of predation, since tyrannosaurs surpassed all contemporaneous predators in size by the age of two. Paleontologists have not found enough Daspletosaurus remains for a similar analysis, but Erickson notes that the same general trend seems to apply.
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. Since the middle of the Cretaceous, North America had been divided in half by the Western Interior Seaway, with much of Montana and Alberta below the surface. However, the uplift of the Rocky Mountains in the Laramide Orogeny to the west, which began during the time of Daspletosaurus, forced the seaway to retreat eastwards and southwards. Rivers flowed down from the mountains and drained into the seaway, carrying sediment along with them that formed the Two Medicine Formation, the Judith River Group, and other sedimentary formations in the region. About 73 million years ago, the seaway began to advance westwards and northwards again, and the entire region was covered by the Bearpaw Sea, represented throughout the western United States and Canada by the massive Bearpaw Shale.
Daspletosaurus lived in a vast floodplain along the western shore of the interior seaway. Large rivers watered the land, occasionally flooding and blanketing the region with new sediment. When water was plentiful, the region could support a great deal of plant and animal life, but periodic droughts also struck the region, resulting in mass mortality as preserved in the many bonebed deposits found in Two Medicine and Judith River sediments, including the Daspletosaurus bonebed. Similar conditions exist today in East Africa. Volcanic eruptions from the west periodically blanketed the region with ash, also resulting in large-scale mortality, while simultaneously enriching the soil for future plant growth. It is these ash beds that allow precise radiometric dating as well. Fluctuating sea levels also resulted in a variety of other environments at different times and places within the Judith River Group, including offshore and nearshore marine habitats, coastal wetlands, deltas and lagoons, in addition to the inland floodplains. The Two Medicine Formation was deposited at higher elevations farther inland than the other two formations.
The excellent vertebrate fossil record of Two Medicine and Judith River rocks resulted from a combination of abundant animal life, periodic natural disasters, and the deposition of large amounts of sediment. Many types of freshwater and estuarine fish are represented, including sharks, rays, sturgeons, gars and others. The Judith River Group preserves the remains of many aquatic amphibians and reptiles, including frogs, salamanders, turtles, Champsosaurus and crocodilians. Terrestrial lizards, including whiptails, skinks, monitors and alligator lizards have also been discovered. Azhdarchid pterosaurs, and birds like Apatornis and Avisaurus flew overhead, while several varieties of mammals coexisted with Daspletosaurus and other types of dinosaurs in the various formations that make up the Judith River wedge.
In the Oldman Formation (the geological equivalent of the Judith River formation), Daspletosaurus torosus could have preyed upon the hadrosaur species Brachylophosaurus canadensis, the ceratopsians Coronosaurus brinkmani and Albertaceratops nesmoi, pachycephalosaurs, ornithomimids, therizinosaurs and possibly ankylosaurs. Other predators included troodontids, oviraptorosaurs, the dromaeosaurid Saurornitholestes and possibly an albertosaurine tyrannosaur (genus currently unknown). The younger Dinosaur Park and Two Medicine Formations had faunas similar to the Oldman, with the Dinosaur Park in particular preserving an unrivaled array of dinosaurs. The albertosaurine Gorgosaurus lived alongside unnamed species of Daspletosaurus in the Dinosaur Park and Upper Two Medicine environments. Young tyrannosaurs may have filled the niches in between adult tyrannosaurs and smaller theropods, which were separated by two orders of magnitude in mass. A Saurornitholestes dentary has been discovered in the Dinosaur Park Formation that bore tooth marks left by the bite of a young tyrannosaur, possibly Daspletosaurus.
- "City Site Was Dinosaur Dining Room". ScienceDaily. ScienceDaily. 2007-07-03. Retrieved 2008-12-07.
- Russell, Dale A. (1970). "Tyrannosaurs from the Late Cretaceous of western Canada". National Museum of Natural Sciences Publications in Paleontology. 1: 1–34.
- Paul, Gregory S. (1988). Predatory Dinosaurs of the World. New York: Simon & Schuster. pp. 464pp. ISBN 978-0-671-61946-6.
- Christiansen, Per; Fariña, Richard A. (2004). "Mass prediction in theropod dinosaurs". Historical Biology. 16 (2–4): 85–92. doi:10.1080/08912960412331284313.
- Erickson, Gregory M., GM; Makovicky, Peter J.; Currie, Philip J.; Norell, Mark A.; Yerby, Scott A.; Brochu, Christopher A. (2004). "Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs". Nature. 430 (7001): 772–775. doi:10.1038/nature02699. PMID 15306807.
- Therrien, François; Henderson, Donald M. (2007). "My theropod is bigger than yours ... or not: estimating body size from skull length in theropods". Journal of Vertebrate Paleontology. 27 (1): 108–115. doi:10.1671/0272-4634(2007)27[108:MTIBTY]2.0.CO;2.
- Carr, Thomas D. (1999). "Craniofacial ontogeny in Tyrannosauridae (Dinosauria, Coelurosauria)". Journal of Vertebrate Paleontology. 19 (3): 497–520. doi:10.1080/02724634.1999.10011161.
- Currie, Philip J. (2003). "Cranial anatomy of tyrannosaurids from the Late Cretaceous of Alberta" (PDF). Acta Palaeontologica Polonica. 48 (2): 191–226.
- Holtz, Thomas R. (2004). "Tyrannosauroidea". In Weishampel, David B.; Dodson, Peter; & Osmólska, Halszka (eds.). (eds.). The Dinosauria (Second ed.). Berkeley: University of California Press. pp. 111–136. ISBN 978-0-520-24209-8.CS1 maint: Uses editors parameter (link)
- "Candeiro.vp" (PDF). geology.cz. Retrieved 11 April 2018.
- Molnar, R. E. (2001). "Theropod paleopathology: a literature survey". In Tanke, D. H.; Carpenter, K.; Skrepnick, M. W. (eds.). Mesozoic Vertebrate Life. Bloomington: Indiana University Press. pp. 337–363. ISBN 978-0-253-33907-2.
- "New Dinosaur Found in Montana Reveals Tyrannosaurs' True Face (They Didn't Have Lips)". westerndigs.org. Retrieved 11 April 2018.
- Carr, Thomas D.; Varricchio, David J.; Sedlmayr, Jayc C.; Roberts, Eric M.; Moore, Jason R. (2017). "A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system". Scientific Reports. 7: 44942. doi:10.1038/srep44942. PMC 5372470. PMID 28358353.
- Liddell, Henry G.; Scott, Robert (1980). Greek-English Lexicon (Abridged ed.). Oxford: Oxford University Press. ISBN 978-0-19-910207-5.
- Eberth, David A.; Hamblin, Anthony P. (1993). "Tectonic, stratigraphic, and sedimentologic significance of a regional discontinuity in the Upper Judith River Group (Belly River wedge) of southern Alberta, Saskatchewan, and northern Montana". Canadian Journal of Earth Sciences. 30: 174–200. doi:10.1139/e93-016.
- Eberth, D.A. (2005). "The geology." In: Currie, P.J., and Koppelhus, E.B. (eds), Dinosaur Provincial Park: A Spectacular Ancient Ecosystem Revealed. Indiana University Press: Bloomington and Indianapolis, 54–82.
- Arbour, V.M.; Burns, M. E.; Sissons, R. L. (2009). "A redescription of the ankylosaurid dinosaur Dyoplosaurus acutosquameus Parks, 1924 (Ornithischia: Ankylosauria) and a revision of the genus". Journal of Vertebrate Paleontology. 29 (4): 1117–1135. doi:10.1671/039.029.0405.
- Lehman, Thomas M.; Carpenter, Kenneth (1990). "A partial skeleton of the tyrannosaurid dinosaur Aublysodon from the Upper Cretaceous of New Mexico". Journal of Paleontology. 64 (6): 1026–1032. JSTOR 1305741.
- Carr, Thomas D.; Williamson, Thomas E. (2000). "A review of Tyrannosauridae (Dinosauria: Coelurosauria) from New Mexico". In Lucas, Spencer G.; & Heckert, Andrew B. (eds.). (eds.). Dinosaurs of New Mexico. New Mexico Museum of Natural History and Science Bulletin 17. pp. 113–146.CS1 maint: Uses editors parameter (link)
- Carr, T.D.; Williamson, T.E. (2010). "Bistahieversor sealeyi, gen. et sp. nov., a new tyrannosauroid from New Mexico and the origin of deep snouts in Tyrannosauroidea". Journal of Vertebrate Paleontology. 30 (1): 1–16. doi:10.1080/02724630903413032.
- Sullivan, Robert M.; Lucas, Spencer G. (2006). "The Kirtlandian land-vertebrate "age" – faunal composition, temporal position and biostratigraphic correlation in the nonmarine Upper Cretaceous of North America". In Lucas, Spencer G.; & Sullivan, Robert M. (eds.). (eds.). Late Cretaceous vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 35. pp. 7–29.CS1 maint: Uses editors parameter (link)
- Ryan, Michael J. (1997). "Kirtland Formation". In Currie, Philip J. & Padian, Kevin (eds.). (eds.). Encyclopedia of Dinosaurs. San Diego: Academic Press. pp. 390–391. ISBN 978-0-12-226810-6.CS1 maint: Uses editors parameter (link)
- Horner, John R.; Varricchio, David J.; Goodwin, Mark B. (1992). "Marine transgressions and the evolution of Cretaceous dinosaurs". Nature. 358 (6381): 59–61. doi:10.1038/358059a0.
- Varricchio, David J. (2001). "Gut contents from a Cretaceous tyrannosaurid: implications for theropod dinosaur digestive tracts". Journal of Paleontology. 75 (2): 401–406. doi:10.1666/0022-3360(2001)075<0401:GCFACT>2.0.CO;2. DOI: 10.1666/0022-3360(2001)075<0401:GCFACT>2.0.CO;2
- Currie, Philip J.; Trexler, David; Koppelhus, Eva B.; Wicks, Kelly; Murphy, Nate (2005). "An unusual multi-individual tyrannosaurid bonebed in the Two Medicine Formation (Late Cretaceous, Campanian) of Montana (USA)". In Carpenter, Kenneth (ed.) (eds.). The Carnivorous Dinosaurs. Bloomington: Indiana University Press. pp. 313–324. ISBN 978-0-253-34539-4.CS1 maint: Uses editors parameter (link)
- Stein, Walter W.; Triebold, Michael (2013). "Preliminary Analysis of a Sub-adult Tyrannosaurid Skeleton from the Judith River Formation of Petroleum County, Montana". In J. Michael Parrish, Ralph E. Molnar, Philip J. Currie, Eva B. Koppelhus (eds.) (eds.). Tyrannosaurid Paleobiology. Bloomington: Indiana University Press. pp. 55–77.CS1 maint: Uses editors parameter (link)
- Currie, Philip J.; Hurum, Jørn H; Sabath, Karol. (2003). "Skull structure and evolution in tyrannosaurid phylogeny" (PDF). Acta Palaeontologica Polonica. 48 (2): 227–234. Archived from the original (PDF) on 2007-10-25.
- Carr, Thomas D.; Williamson, Thomas E.; Schwimmer, David R. (2005). "A new genus and species of tyrannosauroid from the Late Cretaceous (middle Campanian) Demopolis Formation of Alabama". Journal of Vertebrate Paleontology. 25 (1): 119–143. doi:10.1671/0272-4634(2005)025[0119:ANGASO]2.0.CO;2.
- Loewen, M.A.; Irmis, R.B.; Sertich, J.J.W.; Currie, P. J.; Sampson, S. D. (2013). Evans, David C (ed.). "Tyrant Dinosaur Evolution Tracks the Rise and Fall of Late Cretaceous Oceans". PLoS ONE. 8 (11): e79420. doi:10.1371/journal.pone.0079420. PMC 3819173. PMID 24223179.
- "This Is Our Best Look Yet at a Tyrannosaur's Face". nationalgeographic.com. 30 March 2017. Retrieved 11 April 2018.
- "Tyrannosaurus Rex fossil reveals that fearsome beast looked like a crocodile and had incredible sixth sense". thesun.co.uk. 30 March 2017. Retrieved 11 April 2018.
- "Scientists discover new dinosaur evolved by anagenesis". upi.com. Retrieved 11 April 2018.
- Farlow, James O.; Pianka, Eric R. (2002). "Body size overlap, habitat partitioning and living space requirements of terrestrial vertebrate predators: implications for the paleoecology of large theropod dinosaurs". Historical Biology. 16 (1): 21–40. doi:10.1080/0891296031000154687.
- Snively, Eric; Henderson, Donald M.; Phillips, Doug S. (2006). "Fused and vaulted nasals of tyrannosaurid dinosaurs: implications for cranial strength and feeding mechanics" (PDF). Acta Palaeontologica Polonica. 51 (3): 435–454. Archived from the original (PDF) on 2007-07-04.
- Tanke, Darren H.; Currie, Philip J. (1998). "Head-biting behavior in theropod dinosaurs: paleopathological evidence" (PDF). Gaia. 15: 167–184. Archived from the original (PDF) on 2008-02-27. [not printed until 2000]
- Eberth, David A.; McCrea, Richard T. (2001). "Were large theropods gregarious?". Journal of Vertebrate Paleontology. 21 (Supplement to Number 3): 46A. doi:10.1080/02724634.2001.10010852.
- Roach, Brian T.; Brinkman, Daniel L. (2007). "A reevaluation of cooperative pack hunting and gregariousness in Deinonychus antirrhopus and other nonavian theropod dinosaurs". Bulletin of the Peabody Museum of Natural History. 48 (1): 103–138. doi:10.3374/0079-032X(2007)48[103:AROCPH]2.0.CO;2. Archived from the original on 2007-08-10.
- Hone, D. W. E.; Tanke, D. H. (2015). "Pre- and postmortem tyrannosaurid bite marks on the remains of Daspletosaurus (Tyrannosaurinae: Theropoda) from Dinosaur Provincial Park, Alberta, Canada". PeerJ. 3: e885. doi:10.7717/peerj.885. PMC 4393819. PMID 25870775.
- Erickson, Gregory M.; Currie, Philip. J.; Inouye, Brian D.; Wynn, Alice A. (2006). "Tyrannosaur life tables: an example of nonavian dinosaur population biology". Science. 313 (5784): 213–217. doi:10.1126/science.1125721. PMID 16840697.
- Wolff, E. D. S.; Salisbury, S. W.; Horner, J. R.; Varricchio, D. J. (2009). "Common Avian Infection Plagued the Tyrant Dinosaurs". PLoS ONE. 4 (9): e7288. doi:10.1371/journal.pone.0007288. PMC 2748709. PMID 19789646.
- English, Joseph M.; Johnston, Stephen T. (2004). "The Laramide Orogeny: what were the driving forces?" (PDF). International Geology Review. 46 (9): 833–838. doi:10.2747/0020-68126.96.36.1993.
- Eberth, David A. (1997). "Judith River Wedge". In Currie, Philip J. & Padian, Kevin (eds.). (eds.). Encyclopedia of Dinosaurs. San Diego: Academic Press. pp. 199–204. ISBN 978-0-12-226810-6.CS1 maint: Uses editors parameter (link)
- Rogers, Raymond R. (1997). "Two Medicine Formation". In Currie, Philip J. & Padian, Kevin (eds.). (eds.). Encyclopedia of Dinosaurs. San Diego: Academic Press. pp. 199–204. ISBN 978-0-12-226810-6.CS1 maint: Uses editors parameter (link)
- Rogers, Raymond R. (1990). "Taphonomy of three dinosaur bonebeds in the Upper Cretaceous Two Medicine Formation of northwestern Montana: evidence for drought-induced mortality". PALAIOS. 5 (5): 394–413. doi:10.2307/3514834. JSTOR 3514834.
- Falcon-Lang, Howard J. (2003). "Growth interruptions in silicified conifer woods from the Upper Cretaceous Two Medicine Formation, Montana, USA: implications for palaeoclimate and dinosaur palaeoecology". Palaeogeography, Palaeoclimatology, Palaeoecology. 199 (3–4): 299–314. doi:10.1016/S0031-0182(03)00539-X.
- Farlow, James O. (1976). "Speculations about the diet and foraging behavior of large carnivorous dinosaurs". American Midland Naturalist. 95 (1): 186–191. doi:10.2307/2424244. JSTOR 2424244.
- Jacobsen, A. R. (2001). "Tooth-marked small theropod bone: An extremely rare trace". In Tanke, D. H.; Carpenter, K.; Skrepnick, M. W. (eds.). Mesozoic Vertebrate Life. Bloomington: Indiana University Press. pp. 58–63. ISBN 978-0-253-33907-2.