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87-481: Albertosaurines , or dinosaurs of the subfamily Albertosaurinae , lived in the Late Cretaceous of United States and Canada. The subfamily was first used by Philip J. Currie , Jørn H. Hurum , and Karol Sabath as a group of tyrannosaurid dinosaurs. It was originally defined as "( Albertosaurus + Gorgosaurus )", including only the two genera . The group is the sister clade to Tyrannosaurinae . In 2007 , it

174-499: 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

261-454: A different species. Most known Albertosaurus individuals were aged 14 years or more at the time of death. However, the youngest individual known is a juvenile two-year-old and the oldest is an adult 28-year-old. The two-year-old was discovered in the Dry Island bonebed, weighed an estimated 50 kg (110 lb), and was about 2 m (6.6 ft) in length. The 28-year-old specimen from

348-464: A distinct species yet to be named, referred to as D. sp. In the lower portion of the 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" (RMDRC 2002.MT-001), shows some characteristics of Daspletosaurus suggesting

435-451: A drought, flood, or for other reasons. There is plentiful evidence for gregarious behaviour among herbivorous dinosaurs, including ceratopsians and hadrosaurs . However, only rarely are so many dinosaurian predators found at the same site. Small theropods like Deinonychus , Coelophysis , and Megapnosaurus ( Syntarsus rhodesiensis ) have been found in aggregations, as have larger predators like Allosaurus and Mapusaurus . There

522-466: A junior synonym of D. torosus . In the same year, however, Warshaw and colleagues supported the validity of this species and referred other specimens to it. While very large by the standard of modern predators, Daspletosaurus was not the largest tyrannosaurid. Adults could reach a length of 8.5–9 metres (28–30 ft) from snout to tail, a hip height of 2.2 metres (7.2 ft), and a body mass of 2–3 metric tons (2.2–3.3 short tons). However there

609-443: A large role, especially since more than two-thirds of all Albertosaurus specimens are known from one locality. Albertosaurus and Gorgosaurus individuals both grow the most rapidly during a four-year period until they are approximately 16. The Dry Island bonebed discovered by Barnum Brown and his crew contains the remains of 26 Albertosaurus , which is the most individuals found in one locality of any large Cretaceous theropod and

696-560: A maximum growth rate of about 50 kg (110 lb) per year during the rapid growth phase, slower than in tyrannosaurines like Daspletosaurus and Tyrannosaurus , but comparable to Albertosaurus . Gorgosaurus spent as much as half its life in the juvenile phase before ballooning up to near-maximum size in only a few years. This, along with the complete lack of predators intermediate in size between huge adult tyrannosaurids and other small theropods, suggests these niches may have been filled by juvenile tyrannosaurids. This pattern

783-424: 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. In 2017, John Wilson discovered the bones of a tyrannosaurid, including a partial disarticulated skull, cervical, sacral, and caudal vertebrae, and a rib, chevron, and first metatarsal, from

870-485: A rarer species of tyrannosaurine, Daspletosaurus . This is one of the few examples of two tyrannosaurid genera coexisting. Similar-sized predators in modern predator guilds are separated into different ecological niches by anatomical, behavioral, or geographical differences that limit competition. Niche differentiation between the Dinosaur Park tyrannosaurids is not well understood. In 1970, Dale Russell hypothesized

957-416: 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

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1044-430: A similar body appearance. Typical for theropods, tyrannosaurids were bipedal and balanced their heavy head and torso with a long tail. However, tyrannosaurid arms were extremely small for their body size and retained only two digits. The legs were long and ended in a four-toed foot. The first digit, called the hallux , was short and only the other three contacted the ground, with the third (middle) digit being longer than

1131-534: A species of Daspletosaurus , D. degrootorum , but this has not been widely supported. Daspletosaurus is closely related to the much larger and more recent tyrannosaurid Tyrannosaurus rex . Like most tyrannosaurids, Daspletosaurus was a large bipedal predator , with the average adult measuring 8.5–9 m (28–30 ft) and weighing 3 metric tons (3.3 short tons). However, the largest potential specimen measures around 11 metres (36 ft) long and weighs up to 5 metric tons (5.5 short tons). Daspletosaurus had

1218-417: A sudden increase in mortality after sexual maturity, with very few animals reaching maximum size, is a pattern observed in many modern large mammals, including elephants, African buffalo , and rhinoceros . The same pattern is also seen in other tyrannosaurids. The comparison with modern animals and other tyrannosaurids lends support to this life history hypothesis , but bias in the fossil record may still play

1305-1005: Is a genus of tyrannosaurid dinosaur that lived in Laramidia between about 78 and 74.4 million years ago, during the Late Cretaceous Period . The genus Daspletosaurus contains three named species . Fossils of the earlier type species , D. torosus , have been found in Alberta , while fossils of a later species, D. horneri , have been found only in Montana . D. wilsoni has been suggested as an intermediate species between D. torosus and D. horneri that evolved through anagenesis , but this theory has been disputed by other researchers. There are also multiple specimens which may represent new species of Daspletosaurus from Alberta and Montana, but these have not been formally described. The taxon Thanatotheristes has been suggested to represent

1392-844: Is a cladogram of Tyrannosaurinae based on the phylogenetic analysis conducted by Warshaw & Fowler (2022). Here, it is proposed that the three Daspletosaurus species evolved through anagenesis in the Tyrannosaurinae in a line leading to Zhuchengtyrannus , Tarbosaurus , and Tyrannosaurus . Due to their more fragmentary nature, Thanatotheristes and Nanuqsaurus were excluded from this analysis. Alioramus remotus [REDACTED] Alioramus altai [REDACTED] Qianzhousaurus [REDACTED] Dynamoterror Teratophoneus [REDACTED] Lythronax [REDACTED] Daspletosaurus wilsoni Daspletosaurus horneri Zhuchengtyrannus Tarbosaurus [REDACTED] In 2024, Scherer and Voiculescu-Holvad argued that

1479-474: Is it particularly evident that a true systematic decline was ever in place, especially with the discovery of smaller pterosaur species. Several old mammal groups began to disappear, with the last eutriconodonts occurring in the Campanian of North America . In the northern hemisphere, cimolodont , multituberculates , metatherians and eutherians were the dominant mammals, with the former two groups being

1566-536: Is no evidence of group behavior in the close relative Gorgosaurus . [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Late Cretaceous During the Late Cretaceous, the climate was warmer than present, although throughout the period a cooling trend is evident. The tropics became restricted to equatorial regions and northern latitudes experienced markedly more seasonal climatic conditions. Due to plate tectonics ,

1653-671: Is no stratigraphic overlap between D. torosus and D. wilsoni , since a large specimen (CMC VP 15826) previously referred to as D. torosus is from a strata recently dated to be later than D. wilsoni , and since this specimen likely belongs to a distinct species of Daspletosaurus yet to be named. They also recovered the paraphyletic Daspletosaurus at the base of Tyrannosaurini, making the genus ancestral to Tyrannosaurus . 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

1740-418: Is one potential specimen of D. torosus or a new unnamed species, CMC VP 15826 (nicknamed "Pete III"), that suggests the genus could reach lengths of nearly 11 metres (36 ft) and weigh 5 metric tons (5.5 short tons). Daspletosaurus had a massive skull that could reach more than 1 metre (3 ft 3 in) in length. The bones were heavily constructed and some, including the nasal bones on top of

1827-525: Is seen in modern Komodo dragons , whose hatchlings start off as tree-dwelling insectivores and slowly mature into massive apex predators capable of taking down large vertebrates. During growth, thickening of the tooth morphology changed so much that, had the association of young and adult skeletons on the Dry Island bonebed not proven they belonged to the same taxon, the teeth of juveniles would likely have been identified by statistical analysis as those of

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1914-635: Is some evidence of gregarious behaviour in other tyrannosaurids as well. Fragmentary remains of smaller individuals were found alongside "Sue," the Tyrannosaurus mounted in the Field Museum of Natural History in Chicago , and a bonebed in the Two Medicine Formation of Montana contains at least three specimens of Daspletosaurus preserved alongside several hadrosaurs. These findings may corroborate

2001-405: Is some evidence of niche differentiation between the two. While Daspletosaurus fossils are not as common as other tyrannosaurid fossils, the available specimens allow some analysis of the biology of these animals, including social behavior , diet, and life history. The type specimen of Daspletosaurus torosus ( CMN 8506) is a partial skeleton including the skull, the shoulder, a forelimb,

2088-530: Is the Tyrannosauridae , including genera such as Daspletosaurus , Tarbosaurus , and Tyrannosaurus . The close similarities between Gorgosaurus libratus and Albertosaurus sarcophagus have led many experts to combine them into one genus over the years. Albertosaurus was named first, so by convention it is given priority over the name Gorgosaurus , which is sometimes considered its junior synonym . William Diller Matthew and Barnum Brown doubted

2175-623: The Deccan Traps , both of which have been firmly dated to the time of the extinction event. In theory, these events reduced sunlight and hindered photosynthesis , leading to a massive disruption in Earth's ecology . A much smaller number of researchers believe the extinction was more gradual, resulting from slower changes in sea level or climate . Daspletosaurus Daspletosaurus ( / d æ s ˌ p l iː t ə ˈ s ɔːr ə s / das- PLEET -ə- SOR -əs ; meaning "frightful lizard")

2262-673: 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

2349-450: 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

2436-486: 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

2523-565: 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

2610-400: 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

2697-420: The "Jack’s B2" site of the Judith River Formation. Elías A. Warshaw and Denver W. Fowler described these remains ( BDM 107) in 2022 as belonging to a new species of Daspletosaurus , D. wilsoni . It represents a transitional species between D. torosus and D. horneri , as it existed between them in time. It has been suggested that the three species may have evolved directly through anagenesis , but this theory

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2784-569: The Americas were gradually moving westward, causing the Atlantic Ocean to expand. The Western Interior Seaway divided North America into eastern and western halves; Appalachia and Laramidia . India maintained a northward course towards Asia. In the Southern Hemisphere, Australia and Antarctica seem to have remained connected and began to drift away from Africa and South America. Europe

2871-813: The Cretaceous Period derived from the German name Kreidezeit , and T is the abbreviation for the Tertiary Period (a historical term for the period of time now covered by the Paleogene and Neogene periods). The event marks the end of the Mesozoic Era and the beginning of the Cenozoic Era. "Tertiary" being no longer recognized as a formal time or rock unit by the International Commission on Stratigraphy ,

2958-484: 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. In 2024, Warshaw and colleagues suggested that

3045-471: The Dinosaur Park specimens likely belong to D. wilsoni . 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

3132-648: 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

3219-847: The K-T event is now called the Cretaceous—Paleogene (or K-Pg) extinction event by many researchers. Non- avian dinosaur fossils are found only below the Cretaceous–Paleogene boundary and became extinct immediately before or during the event. A very small number of dinosaur fossils have been found above the Cretaceous–Paleogene boundary, but they have been explained as reworked fossils , that is, fossils that have been eroded from their original locations then preserved in later sedimentary layers. Mosasaurs , plesiosaurs , pterosaurs and many species of plants and invertebrates also became extinct. Mammalian and bird clades passed through

3306-604: The North American varieties. Pachycephalosaurs were also present in both North America and Asia. Dromaeosaurids shared the same geographical distribution, and are well documented in both Mongolia and Western North America. Additionally therizinosaurs (known previously as segnosaurs) appear to have been in North America and Asia. Gondwana held a very different dinosaurian fauna, with most predators being abelisaurids and carcharodontosaurids ; and titanosaurs being among

3393-627: The Two Medicine Formation of Montana and in southwestern North America during the Campanian, while centrosaurine and lambeosaurines dominate in northern latitudes. Holtz has suggested this pattern indicates shared ecological preferences between tyrannosaurines , chasmosaurines , and hadrosaurines . At the end of the later Maastrichtian stage, tyrannosaurines like Tyrannosaurus rex , hadrosaurines like Edmontosaurus annectens , and chasmosaurines like Triceratops were widespread throughout western North America, while lambeosaurines were rare and

3480-688: The albertosaurines and centrosaurines had gone extinct . Gregory Erickson and colleagues have studied the growth and life history of tyrannosaurids using bone histology , which can determine the age of a specimen when it died. A growth curve can be developed when the ages of various individuals are plotted against their sizes on a graph. Tyrannosaurids grew throughout their lives, but underwent tremendous growth spurts for about four years, after an extended juvenile phase. Sexual maturity may have ended this rapid growth phase, after which growth slowed down considerably in adult animals. Examining five Gorgosaurus specimens of various sizes, Erickson calculated

3567-399: The animal survived the bite. 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

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3654-683: The basis of morphological and stratigraphical data, and that anagenesis will not be supported unequivocally due to the limited sample and nature of the fossil record, which does not show a great degree of variation in morphology. The cladogram presented for their phylogenetic analysis is shown below. Alioramus remotus [REDACTED] Alioramus altai Qianzhousaurus [REDACTED] Lythronax [REDACTED] Teratophoneus Dynamoterror Thanatotheristes Daspletosaurus horneri Daspletosaurus wilsoni Dinosaur Park and Oldman formations taxon ( TMP 2001.36.1) Zhuchengtyrannus Tarbosaurus [REDACTED] In

3741-484: The bites are due to intraspecific competition for territory or resources, or for dominance within a social group. A young specimen of the tyrannosaurid (TMP 1994.143.1), initially identified as the Dinosaur Park Daspletosaurus but subsequently referred to Gorgosaurus libratus , also shows bite marks on the face that were inflicted by another tyrannosaur. The bite marks are healed over, indicating that

3828-519: The boundary with few extinctions, and evolutionary radiation from those Maastrichtian clades occurred well past the boundary. Rates of extinction and radiation varied across different clades of organisms. Many scientists hypothesize that the Cretaceous–Paleogene extinctions were caused by catastrophic events such as the massive asteroid impact that caused the Chicxulub crater , in combination with increased volcanic activity , such as that recorded in

3915-471: 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 . Over the years, various additional species have been assigned to

4002-785: The distinction of the two genera as early as 1922. Gorgosaurus libratus was formally reassigned to Albertosaurus (as Albertosaurus libratus ) by Dale Russell in 1970, with many subsequent authors following his lead. Combining the two greatly expands the geographical and chronological range of the genus Albertosaurus . Other experts maintain the two genera as separate. Canadian paleontologist Phil Currie claims there are as many anatomical differences between Albertosaurus and Gorgosaurus as there are between Daspletosaurus and Tyrannosaurus , which are almost always kept separate. He also notes that undescribed tyrannosaurids discovered in Alaska , New Mexico , and elsewhere in North America may help clarify

4089-401: The dominant herbivores. Spinosaurids were also present during this time. Birds became increasingly common, diversifying in a variety of enantiornithe and ornithurine forms. Early Neornithes such as Vegavis co-existed with forms as bizarre as Yungavolucris and Avisaurus . Though mostly small, marine Hesperornithes became relatively large and flightless, adapted to life in

4176-497: The evidence for social behaviour in Albertosaurus , although some or all of the above localities may represent temporary or unnatural aggregations. Others have speculated that, instead of social groups, at least some of these finds represent Komodo dragon -like mobbing of carcasses, where aggressive competition leads to some of the predators being killed and cannibalized . Even though Albertosaurus are commonly found in packs, there

4263-602: 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. Fossils of other tyrannosaurids like Teratophoneus and Albertosaurus among other genera suggest that gregarious behavior may have been widespread in tyrannosaurs and thus may vindicate

4350-827: The exception of Tarbosaurus , which had short arms for its size. Albertosaurus was smaller than some other tyrannosaurids, such as Tarbosaurus and Tyrannosaurus . Typical adults of Albertosaurus and Gorgosaurus measured up to 8 to 9 m (26 to 30 ft) long, while rare individuals of Albertosaurus could grow to over 10 m (33 ft) in length. Several independent mass estimates, obtained by different methods, suggest that an adult Albertosaurus weighed between 1.3 tonnes (1.4 short tons; 1.3 long tons) and 2 tonnes (2.2 short tons; 2.0 long tons). Gorgosaurus estimates are higher, around 2.5 tonnes (2.8 short tons; 2.5 long tons), although greater estimates exist of about 2.8–2.9 tonnes (3.1–3.2 short tons; 2.8–2.9 long tons). All tyrannosaurids, including albertosaurines, shared

4437-515: The fossil record compared with adults. It has been suggested that this phenomenon is a consequence of life history , rather than bias, and that fossils of juvenile Albertosaurus are rare because they simply did not die as often as adults did. A hypothesis of Albertosaurus life history postulates that hatchlings died in large numbers, but have not been preserved in the fossil record due to their small size and fragile construction. After just two years, juveniles were larger than any other predator in

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4524-412: The genus Daspletosaurus . Though some have been designated as Daspletosaurus spp, this does not imply that they all represent 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

4611-577: The head and torso, with the center of gravity over the hips. From a comparison of the degree of wear of teeth of Daspletosaurus with other extinct and extant animals, it is concluded that Daspletosaurus , as well as other non-avian theropods, had lips that protected the teeth from external influences. Due to this feature, the snout of Daspletosaurus more closely resembled lizards than crocodiles, which lack lips. A skin impression from Daspletosaurus torosus has been described, showing small polygonal scales measuring 3 mm in diameter. The placement of

4698-459: The high physiological demands of procreation, including stress and injuries received during intraspecific competition for mates and resources, and eventually, the ever-increasing effects of senescence . The higher mortality rate in adults may explain their more common preservation. Very large animals were rare because few individuals survived long enough to attain such sizes. High infant mortality rates, followed by reduced mortality among juveniles and

4785-566: 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

4872-460: The more common Gorgosaurus actively hunted fleet-footed hadrosaurs , while the rarer and more troublesome ceratopsians and ankylosaurians (horned and heavily armoured dinosaurs) were left to the more heavy built Daspletosaurus . However, a specimen of Daspletosaurus ( OTM 200) from the contemporaneous Two Medicine Formation of Montana preserves the digested remains of a juvenile hadrosaur in its gut region, with another bonebed containing

4959-539: The most basal species, in spite of being the youngest species stratigraphically. While the authors did not completely refute the possibility that anagenesis was the main driver of Daspletosaurus evolution based on the intermediate morphological features, they also suggested that D. wilsoni may be a junior synonym of D. torosus , since there is a near lack of autapomorphic characters that can differentiate this species. They also claimed that Daspletosaurus did not evolve from Thanatotheristes , since they found no support on

5046-636: The most common mammals in North America. In the southern hemisphere there was instead a more complex fauna of dryolestoids , gondwanatheres and other multituberculates and basal eutherians ; monotremes were presumably present, as was the last of the haramiyidans , Avashishta . Mammals, though generally small, ranged into a variety of ecological niches, from carnivores ( Deltatheroida ), to mollusc-eater ( Stagodontidae ), to herbivores (multituberculates, Schowalteria , Zhelestidae and Mesungulatidae ) to highly atypical cursorial forms ( Zalambdalestidae , Brandoniidae ). True placentals evolved only at

5133-531: The numerous teleost fishes, which in turn evolved into new advanced and modern forms ( Neoteleostei ). Ichthyosaurs and pliosaurs , on the other hand, became extinct during the Cenomanian-Turonian anoxic event . Near the end of the Cretaceous Period, flowering plants diversified. In temperate regions, familiar plants like magnolias , sassafras , roses , redwoods , and willows could be found in abundance. The Cretaceous–Paleogene extinction event

5220-407: The open sea. Though primarily represented by azhdarchids , other forms like pteranodontids , tapejarids ( Caiuajara and Bakonydraco ), nyctosaurids and uncertain forms ( Piksi , Navajodactylus ) are also present. Historically, it has been assumed that pterosaurs were in decline due to competition with birds, but it appears that neither group overlapped significantly ecologically, nor

5307-601: 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

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5394-495: The region aside from adult Albertosaurus and more fleet of foot than most of their prey animals. This resulted in a dramatic decrease in their mortality rate and a corresponding rarity of fossil remains. Mortality rates doubled at age twelve, perhaps the result of the physiological demands of the rapid growth phase, and then doubled again with the onset of sexual maturity between the ages of fourteen and sixteen. This elevated mortality rate continued throughout adulthood, perhaps due to

5481-488: The remains of three Daspletosaurus alongside the remains of at least five hadrosaurs. Unlike some other groups of dinosaurs, neither genus was more common at higher or lower elevations than the other. However, Gorgosaurus appears more common in northern formations like Dinosaur Park, with species of Daspletosaurus more abundant to the south. The same pattern is seen in other groups of dinosaurs. Chasmosaurine ceratopsians and hadrosaurine hadrosaurs are also more common in

5568-477: 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

5655-419: The rest. Albertosaurus may have been able to reach walking speeds of 14−21 kilometres per hour (8−13 miles per hour). At least for the younger individuals, a high running speed is plausible. The subfamily was first used by Philip J. Currie , Jørn H. Hurum , and Karol Sabath as a group of tyrannosaurid dinosaurs. It was originally defined as "( Albertosaurus + Gorgosaurus )", including only

5742-498: 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

5829-477: 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 have become clearer as new species have been described. Below

5916-477: The same quarry measured 10 m (33 ft) long. Juvenile animals are rarely found as fossils for several reasons, mainly preservation bias , where the smaller bones of younger animals were less likely to be preserved by fossilization than the larger bones of adults, and collection bias, where smaller fossils are less likely to be noticed by collectors in the field. Young Albertosaurus are relatively large for juvenile animals, but their remains are still rare in

6003-461: The same year, Warshaw and colleagues supported the anagenesis theory by referring other specimens to D. wilsoni (including the Dinosaur Park specimen) which they considered as a valid taxon, and by reanalysing the previous study of Scherer and Voiculescu-Holvad (2024). They claimed that the known species of Daspletosaurus show a gradient of morphologies consistent with them representing a series of ancestors and descendants. They also argued that there

6090-442: The scales on the body is not known. Daspletosaurus belongs in the subfamily Tyrannosaurinae within the family Tyrannosauridae , along with Tarbosaurus , Tyrannosaurus , and Alioramini . 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

6177-629: The second-most of any large theropod dinosaur behind the Allosaurus assemblage at the Cleveland-Lloyd Dinosaur Quarry in Utah . The group seems to be composed of one very old adult, eight adults between 17 and 23 years old, seven sub-adults undergoing their rapid growth phases at between 12 and 16 years old, and six juveniles between the ages of 2 and 11 years that had not yet reached the growth phase. The near-absence of herbivore remains and

6264-524: The similar state of preservation common to the many individuals at the Albertosaurus bonebed quarry led Currie to conclude that the locality was not a predator trap like the La Brea Tar Pits in California and that all of the preserved animals died at the same time. Currie claims this as evidence of pack behaviour. Other scientists are skeptical, observing that the animals may have been driven together by

6351-503: The situation. Gregory S. Paul has suggested that Gorgosaurus libratus is ancestral to Albertosaurus sarcophagus . Albertosaurinae is a basal subfamily of tyrannosaurids . They were recognized in the 2014 analysis of the new genus Nanuqsaurus , a derived tyrannosaurine . Albertosaurinae was recovered as including only Albertosaurus and Gorgosaurus . Albertosaurus and Gorgosaurus are kept separate by most classifications, as should be according to Currie. The cladogram below

6438-445: The small forelimbs typical of tyrannosaurids, although they were proportionately longer than in other genera. As an apex predator equipped with dozens of large, sharp teeth, 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

6525-532: The snout during prey capture and intra-specific combat. A full-grown Dinosaur Park Daspletosaurus ( TMP 85.62.1) exhibits tyrannosaur bite marks on its skull. While it is possible that the bites were attributable to other species, intraspecific aggression such as 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

6612-430: 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

6699-408: The stratigraphic ranges of D. torosus , D. wilsoni and an unnamed species from the Dinosaur Park Formation and Oldman Formation show a clear overlap, indicating that anagenesis may not be the predominant factor of speciation within the genus, since all species of Daspletosaurus were contemporaneous with each other at some point during its evolution. Phylogenetic analyzes resolved D. horneri as

6786-481: The subfamily Albertosaurinae. Its closest relative is the slightly older Gorgosaurus libratus (sometimes called Albertosaurus libratus ; see below). These two species are the only described albertosaurines, but other undescribed species may exist. Thomas Holtz found Appalachiosaurus to be an albertosaurine in 2004, but his more recent unpublished work locates it just outside Tyrannosauridae, in agreement with other authors. The other major subfamily of tyrannosaurids

6873-492: 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 favored its initial referral to Albertosaurus sarcophagus , despite lacking many of

6960-437: The two genera . This group is the sister clade to Tyrannosaurinae . In 2007 , it was found that the group also contained Maleevosaurus , often synonymized with Tarbosaurus . However, this classification has not been accepted and Maleevosaurus is still considered a juvenile Tarbosaurus or Tyrannosaurus . This classification has not been accepted. Albertosaurus is a member of the theropod family Tyrannosauridae, in

7047-546: The upper portions of the Judith River Formation are likely from Gorgosaurus as well as some species of Daspletosaurus , probably D. torosus . In 2009, preliminary preparation of a Daspletosaurus specimen from the Coal Ridge Member of the Judith River Formation measuring about 11 metres (36 ft) long was reported. Some researchers assigned this specimen to D. torosus , while others considered it to be

7134-433: The very end of the epoch; the same can be said for true marsupials . Instead, nearly all known eutherian and metatherian fossils belong to other groups. In the seas, mosasaurs suddenly appeared and underwent a spectacular evolutionary radiation. Modern sharks also appeared and penguin-like polycotylid plesiosaurs (3 meters long) and huge long-necked elasmosaurs (13 meters long) also diversified. These predators fed on

7221-537: Was a large-scale mass extinction of animal and plant species in a geologically short period of time, approximately 66  million years ago (Ma). It is widely known as the K–T extinction event and is associated with a geological signature, usually a thin band dated to that time and found in various parts of the world, known as the Cretaceous–Paleogene boundary (K–T boundary). K is the traditional abbreviation for

7308-504: Was an island chain. Populating some of these islands were endemic dwarf dinosaur species. In the Late Cretaceous, the hadrosaurs , ankylosaurs , and ceratopsians experienced success in Asiamerica (Western North America and eastern Asia). Tyrannosaurs dominated the large predator niche in North America. They were also present in Asia, although were usually smaller and more primitive than

7395-634: Was disputed by Scherer and Voiculescu-Holvad in 2024. However, at the 2023 meeting of the Society of Vertebrate Paleontology , Thomas Carr and Stephen Brusatte presented evidence questioning the validity of D. wilsoni. They said the autapomorphy (unique feature) of D. wilsoni was incorrectly determined, rendering the species a nomen dubium , but they found BDM 107 actually shared traits with D. torosus but not with D. horneri, prompting them to synonymize D. wilsoni with D. torosus . In 2024, Scherer and Voiculescu-Holvad also suggested that D. wilsoni may be

7482-407: Was found during the analysis of Nanuqsaurus by Anthony Fiorillo and Ronald Tykoski . Albertosaurus Gorgosaurus Daspletosaurus torosus Daspletosaurus horneri Teratophoneus Bistahieversor Lythronax Nanuqsaurus Tarbosaurus Zhuchengtyrannus Tyrannosaurus In the middle stages of the Dinosaur Park Formation, Gorgosaurus lived alongside

7569-517: Was found that the group also contained Maleevosaurus , often synonymized with Tarbosaurus . However, this classification has not been accepted and Maleevosaurus is still considered a juvenile Tarbosaurus or Tyrannosaurus . Albertosaurines are large, lightly built tyrannosaurids . Compared to tyrannosaurines , they are more slender and have shorter, flatter skulls, shorter ilia , and proportionally longer tibiae . Albertosaurines and tyrannosaurines share arms of about equal length, with

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