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85-488: 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

170-562: A cladistic analysis of the Tyrannosauridae. He concluded that there were two subfamilies : the more primitive Aublysodontinae , characterized by unserrated premaxillary teeth ; and the Tyrannosaurinae . The Aublysodontinae included Aublysodon , the " Kirtland Aublysodon ", and Alectrosaurus . Holtz also found that Siamotyrannus exhibited some of the synapomorphies of the tyrannosauridae, but lay "outside

255-406: A crack in the tooth ending in a round void called an ampulla. Tyrannosaurid teeth were used as holdfasts for pulling meat off a body, so when a tyrannosaur would have pulled back on a piece of meat, the tension could cause a purely crack-like serration to spread through the tooth. However, the presence of the ampulla would have distributed these forces over a larger surface area , and lessened

340-493: A 1902 expedition of the American Museum of Natural History , led by Barnum Brown . Initially, Osborn considered these to be distinct species. The first, he named Dynamosaurus imperiosus ("emperor power lizard"), and the second, Tyrannosaurus rex ("king tyrant lizard"). A year later, Osborn recognized that these two specimens actually came from the same species. Despite the fact that Dynamosaurus had been found first,

425-460: 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

510-451: 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

595-443: 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

680-560: 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

765-649: A new name for them: Albertosaurus sarcophagus ("flesh-eating Alberta lizard"). Cope described more tyrannosaur material in 1892, in the form of isolated vertebrae, and gave this animal the name Manospondylus gigas . This discovery was mostly overlooked for over a century, and caused controversy in the early 2000s when it was discovered that this material actually belonged to, and had name priority over, Tyrannosaurus rex . In his 1905 paper naming Albertosaurus , Osborn described two additional tyrannosaur specimens that had been collected in Montana and Wyoming during

850-401: A plexiglass bar with incisions called "kerfs" and drilled holes was more than 25% stronger than one with only regularly placed incisions. Unlike tyrannosaurs and other theropods, ancient predators like phytosaurs and Dimetrodon had no adaptations to prevent the crack-like serrations of their teeth from spreading when subjected to the forces of feeding. The skull was perched at the end of

935-571: A prominent sagittal crest , which ran longitudinally along the sagittal suture and separated the two supratemporal fenestrae on the skull roof. Behind these fenestrae, tyrannosaurids had a characteristically tall nuchal crest, which also arose from the parietals but ran along a transverse plane rather than longitudinally. The nuchal crest was especially well-developed in Tyrannosaurus , Tarbosaurus and Alioramus . Albertosaurus , Daspletosaurus and Gorgosaurus had tall crests in front of

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1020-492: 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

1105-430: 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

1190-417: 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

1275-402: A thick, S -shaped neck, and a long, heavy tail acted as a counterweight to balance out the head and torso, with the center of mass over the hips. Tyrannosaurids are known for their proportionately very small two-fingered forelimbs, although remnants of a vestigial third digit are sometimes found. Tarbosaurus had the shortest forelimbs compared to its body size, while Daspletosaurus had

1360-543: A tyrannosaurid were found in the Horseshoe Canyon Formation of Alberta , and consisted of nearly complete skulls with partial skeletons. These remains were first studied by Edward Drinker Cope in 1876, who considered them a species of the eastern tyrannosauroid Dryptosaurus . In 1905, Henry Fairfield Osborn recognized that the Alberta remains differed considerably from Dryptosaurus , and coined

1445-509: A variety of research into their biology . Scientific studies have focused on their ontogeny , biomechanics and ecology , among other subjects. The first remains of tyrannosaurids were uncovered during expeditions led by the Geological Survey of Canada , which located numerous scattered teeth. These distinctive dinosaur teeth were given the name Deinodon ("terrible tooth") by Joseph Leidy in 1856. The first good specimens of

1530-550: Is a family in rank-based Linnaean taxonomy , within the superfamily Tyrannosauroidea and the suborder Theropoda . Tyrannosauridae is uncontroversially divided into two subfamilies. Albertosaurinae comprises the North American genera Albertosaurus and Gorgosaurus , while Tyrannosaurinae includes Daspletosaurus , Teratophoneus , Bistahieversor , Tarbosaurus , Nanuqsaurus , Zhuchengtyrannus , and Tyrannosaurus itself. Some authors include

1615-610: Is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to fifteen genera , including the eponymous Tyrannosaurus . The exact number of genera is controversial, with some experts recognizing as few as three. All of these animals lived near the end of the Cretaceous Period and their fossils have been found only in North America and Asia . Although descended from smaller ancestors , tyrannosaurids were almost always

1700-474: Is considered by some experts to be a juvenile. Albertosaurus , Gorgosaurus and Daspletosaurus all measured between 8 and 9 metres (26 and 30 ft) long, while Tarbosaurus reached lengths of 11 metres (36 ft) from snout to tail. The massive Tyrannosaurus reached 13 metres (43 ft) in the largest specimen, RSM P2523.8 . Tyrannosaurid skull anatomy is well understood, as complete skulls are known for all genera but Alioramus , which

1785-479: 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

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1870-628: Is known only from partial skull remains. Tyrannosaurus , Tarbosaurus , and Daspletosaurus had skulls that exceeded 1 m (3.3 ft) in length. Adult tyrannosaurids had tall, massive skulls, with many bones fused and reinforced for strength. At the same time, hollow chambers within many skull bones and large openings ( fenestrae ) between those bones helped to reduce skull weight. Many features of tyrannosaurid skulls were also found in their immediate ancestors, including tall premaxillae and fused nasal bones . Tyrannosaurid skulls had many unique characteristics, including fused parietal bones with

1955-543: 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 ,

2040-531: 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

2125-601: 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

2210-537: 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

2295-442: Is unclear when the arctometatarsus first evolved; it was not present in the earliest tyrannosauroids like Dilong , but was found in the later Appalachiosaurus . This structure also characterized troodontids , ornithomimids and caenagnathids , but its absence in the earliest tyrannosauroids indicates that it was acquired by convergent evolution . A comparative analysis of the teeth suggests that tyrannosaurids, as well as

2380-570: 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 . Tyrannosauridae Tyrannosauridae (or tyrannosaurids , meaning " tyrant lizards")

2465-515: The Soviet Union began expeditions into Mongolia , and uncovered the first tyrannosaur remains from Asia. Evgeny Maleev described new Mongolian species of Tyrannosaurus and Gorgosaurus in 1955, and one new genus: Tarbosaurus ("terrifying lizard"). Subsequent studies, however, showed that all of Maleev's tyrannosaur species were actually one species of Tarbosaurus at different stages of growth. A second species of Mongolian tyrannosaurid

2550-590: 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

2635-859: 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 ,

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2720-467: The Deinodontidae is Deinodon , which was named after isolated teeth from Montana . However, in a 1970 review of North American tyrannosaurs, Dale Russell concluded that Deinodon was not a valid taxon, and used the name Tyrannosauridae in place of Deinodontidae, stating that this was in accordance with ICZN rules. Therefore, Tyrannosauridae is preferred by modern experts. Tyrannosaurus

2805-850: 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

2890-554: 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

2975-707: 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

3060-462: The [ family ] proper." Later in the same paper, he proposed that Tyrannosauridae be defined as "all descendants of the most recent common ancestor of Tyrannosaurus and Aublysodon ". He also criticized definitions previously proposed by other workers, like one proposed by Paul Sereno , that the Tyrannosauridae was "all taxa closer to "Tyrannosaurus" than to Alectrosaurus , Aublysodon , and Nanotyrannus ". Holtz observed that since Nanotyrannus

3145-438: The absence of a bony prong connecting the nasal and lacrimal bones. Alioramus was found to be the closest relative of Tarbosaurus in this study, based on a similar pattern of stress distribution in the skull. A related study also noted a locking mechanism in the lower jaw shared between the two genera. In a separate paper, Currie noted the possibility that Alioramus might represent a juvenile Tarbosaurus , but stated that

3230-688: 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

3315-524: 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

3400-440: The definition. Holtz redefined the clade in 2004 to use all of the above as specifiers except for Alioramus and Alectrosaurus , which his analysis could not place with certainty. However, in the same paper, Holtz also provided a completely different definition, including all theropods more closely related to Tyrannosaurus than to Eotyrannus . The most recent definition is that of Sereno in 2005, which defined Tyrannosauridae as

3485-789: 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

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3570-401: 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

3655-504: 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

3740-827: 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

3825-429: The extent seen in other large theropods like abelisaurids or carnosaurs . The third metatarsals of tyrannosaurids were pinched between the second and fourth metatarsals, forming a structure known as the arctometatarsus . Tyrannosaurids also had large preserved leg muscle attachments and low rotational inertia relative to their body mass, indicating that they could turn more quickly than other large theropods. It

3910-442: The eyes on the lacrimal bones , while Tarbosaurus and Tyrannosaurus had extremely thickened postorbital bones forming crescent-shaped crests behind the eyes. Alioramus had a row of six bony crests on top of its snout, arising from the nasal bones; lower crests have been reported on some specimens of Daspletosaurus and Tarbosaurus , as well as the more basal tyrannosauroid Appalachiosaurus . The snout and other parts of

3995-515: 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

4080-546: The frontals. In 2014, Lü Junchang et al. described the Alioramini as a tribe within the Tyrannosauridae containing the genera Alioramus and Qianzhousaurus . Their phylogenetic analysis indicated that the tribe was located at the base of the Tyrannosaurinae. Some authors, such as George Olshevsky and Tracy Ford, have created other subdivisions or tribes for various combinations of tyrannosaurids within

4165-459: 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

4250-726: The largest predators in their respective ecosystems , putting them at the apex of the food chain . The largest species was Tyrannosaurus rex , the most massive known terrestrial predator, which measured over 13 metres (43 ft) in length and according to most modern estimates up to 8.87 metric tons (9.78 short tons) in weight. Tyrannosaurids were bipedal carnivores with massive skulls filled with large teeth. Despite their large size, their legs were long and proportioned for fast movement. In contrast, their arms were very small, bearing only two functional digits . Unlike most other groups of dinosaurs, very complete remains have been discovered for most known tyrannosaurids. This has allowed

4335-415: The least inclusive clade containing Albertosaurus , Gorgosaurus and Tyrannosaurus . Cladistic analyses of tyrannosaurid phylogeny often find Tarbosaurus and Tyrannosaurus to be sister taxa , with Daspletosaurus more basal than either. A close relationship between Tarbosaurus and Tyrannosaurus is supported by numerous skull features, including the pattern of sutures between certain bones,

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4420-485: The longest. Tyrannosaurids walked exclusively on their hindlimbs, so their leg bones were massive. In contrast to the forelimbs, the hindlimbs were longer compared to body size than almost any other theropods. Juveniles and even some smaller adults, like more basal tyrannosauroids, had longer tibiae than femora , a characteristic of cursorial (fast-running) dinosaurs like ornithomimids . Larger adults had leg proportions characteristic of slower-moving animals, but not to

4505-460: 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

4590-636: 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

4675-492: The much higher tooth count and more prominent nasal crests in Alioramus suggest it is a distinct genus. Similarly, Currie uses the high tooth count of Nanotyrannus to suggest that it may be a distinct genus, rather than a juvenile Tyrannosaurus as most other experts believe. However, the discovery and description of Qianzhousaurus reveals that Alioramus is not a close relation to Tarbosaurus , instead belonging to

4760-621: The name Tyrannosaurus had appeared one page earlier in his original article describing both specimens. Therefore, according to the International Code of Zoological Nomenclature (ICZN), the name Tyrannosaurus was used. Barnum Brown went on to collect several more tyrannosaurid specimens from Alberta, including the first to preserve the shortened, two-fingered forelimbs characteristic of the group (which Lawrence Lambe named Gorgosaurus libratus , "balanced fierce lizard", in 1914). A second significant find attributed to Gorgosaurus

4845-540: 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

4930-407: 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

5015-402: The other large theropods, had lips that protected their teeth from external damage. This anatomical feature gave these animals more visual resemblance to lepidosaurs than to closely related crocodilians. The name Deinodontidae was coined by Edward Drinker Cope in 1866 for this family, and continued to be used in place of the newer name Tyrannosauridae through the 1960s. The type genus of

5100-411: The presence of a crescent-shaped crest on the postorbital bone behind each eye, and a very deep maxilla with a noticeable downward curve on the lower edge, among others. An alternative hypothesis was presented in a 2003 study by Phil Currie and colleagues, which found weak support for Daspletosaurus as a basal member of a clade also including Tarbosaurus and Alioramus , both from Asia, based on

5185-495: 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

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5270-488: 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

5355-419: 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

5440-564: The rest. Unlike earlier tyrannosauroids and most other theropods, the maxillary and mandibular teeth of mature tyrannosaurids are not blade-like but extremely thickened and often circular in cross-section, with some species having reduced serrations. Tooth counts tend to be consistent within species, and larger species tend to have lower tooth counts than smaller ones. For example, Alioramus had 76 to 78 teeth in its jaws, while Tyrannosaurus had between 54 and 60. William Abler observed in 2001 that Albertosaurus tooth serrations resemble

5525-458: The risk of damage to the tooth under strain. The presence of incisions ending in voids has parallels in human engineering. Guitar makers use incisions ending in voids to, as Abler describes, "impart alternating regions of flexibility and rigidity" to the wood they work with. The use of a drill to create an "ampulla" of sorts and prevent the propagation of cracks through material is also used to protect airplane surfaces. Abler demonstrated that

5610-477: 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

5695-652: 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

5780-538: 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

5865-503: 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

5950-405: The skull also sported numerous foramina . According to the 2017 study which described D. horneri , scaly integument as well as tactile sensitivity was correlated with the multiple rows of neurovascular foramina seen in crocodilians and tyrannosaurids. Tyrannosaurids, like their tyrannosauroid ancestors, were heterodonts , with premaxillary teeth D -shaped in cross section and smaller than

6035-474: The species Gorgosaurus libratus in the genus Albertosaurus and Tarbosaurus bataar in the genus Tyrannosaurus , while others prefer to retain Gorgosaurus and Tarbosaurus as separate genera. Albertosaurines are characterized by more slender builds, lower skulls, and proportionately longer tibiae than tyrannosaurines. In tyrannosaurines, the sagittal crest on the parietals continues forward onto

6120-522: The subfamilies. However, these have not been phylogenetically defined, and usually consisted of genera that are now considered synonymous with other genera or species. Additional subfamilies have been named for more fragmentary genera, including Aublysodontinae and Deinodontinae . However, the genera Aublysodon and Deinodon are usually considered nomina dubia , so they and their eponymous subfamilies are usually excluded from taxonomies of tyrannosaurids. An additional tyrannosaurid, Raptorex ,

6205-481: 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

6290-437: 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

6375-433: 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

6460-537: 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

6545-514: 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

6630-483: 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

6715-482: Was found later, described by Sergei Kurzanov in 1976, and given the name Alioramus remotus ("remote different branch"), though its status as a true tyrannosaurid and not a more primitive tyrannosaur is still controversial. The tyrannosaurids were all large animals, with all species capable of weighing at least 1 metric ton. A single specimen of Alioramus of an individual estimated at between 5 and 6 metres (16 and 20 ft) long has been discovered, although it

6800-517: 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

6885-478: Was initially described as a more primitive tyrannosauroid, but likely represents a juvenile tyrannosaurine similar to Tarbosaurus . However, as it is known only from a juvenile specimen, it is also currently considered a nomen dubium . However, Thomas Carr maintains its validity and finds it to be similar to tyrannosaurines. With the advent of phylogenetic taxonomy in vertebrate paleontology, Tyrannosauridae has been given several explicit definitions. The original

6970-415: Was made in 1942, in the form of a well-preserved, though unusually small, complete skull. The specimen waited until after the end of World War II to be studied by Charles W. Gilmore , who named it Gorgosaurus lancesnis . This skull was re-studied by Robert T. Bakker , Phil Currie , and Michael Williams in 1988, and assigned to the new genus Nanotyrannus . It was also in 1946 that paleontologists from

7055-525: Was named by Henry Fairfield Osborn in 1905, along with the family Tyrannosauridae. The name is derived from the Ancient Greek words τυραννος ( tyrannos ) ('tyrant') and σαυρος ( sauros ) ('lizard'). The very common suffix -idae is normally appended to zoological family names and is derived from the Greek suffix -ιδαι - idai , which indicates a plural noun. Tyrannosauridae

7140-447: Was probably a misidentified T. rex juvenile, Sereno's proposed definition would have the family Tyrannosauridae as a subtaxon of the genus Tyrannosaurus . Further, his proposed definition of the subfamily Tyrannosaurinae would also be limited to Tyrannosaurus . A 2003 attempt by Christopher Brochu included Albertosaurus , Alectrosaurus , Alioramus , Daspletosaurus , Gorgosaurus , Tarbosaurus and Tyrannosaurus in

7225-476: Was produced by Paul Sereno in 1998, and included all tyrannosauroids closer to Tyrannosaurus than to either Alectrosaurus , Aublysodon or Nanotyrannus . However, Nanotyrannus is often considered to be a juvenile Tyrannosaurus rex , while Aublysodon is usually regarded as a nomen dubium unsuitable for use in the definition of a clade . Definitions since then have been based on more well-established genera. In 2001, Thomas R. Holtz Jr. published

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