Albertosaurus

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Albertosaurus
Skeletal reconstruction of Albertosaurus at the Royal Tyrrell Museum in Alberta

Skeleton reconstruction of Albertosaurus in the Royal Tyrrell Museum in Alberta

Temporal occurrence
Upper Cretaceous (early Maastrichtian )
72 to 69.9 million years
Locations
Systematics
Lizard dinosaur (Saurischia)
Theropoda
Tyrannosauroidea
Tyrannosauridae
Albertosaurinae
Albertosaurus
Scientific name
Albertosaurus
Osborn , 1905
Art
  • Albertosaurus sarcophagus

Albertosaurus ("Alberta lizard", derived from Alberta and σαῦρος / sauros ) was a theropod dinosaur from the Tyrannosauridae family, who lived about 72 to 69 million years ago in the Upper Cretaceous in what is now the Canadian province of Alberta.

Usually only one species is distinguished from this genus , the type Albertosaurus sarcophagus . However, some researchers believe that the genus Gorgosaurus is identical to Albertosaurus and is therefore a second species. If Gorgosaurus were actually a species of Albertosaurus , the spatial and temporal distribution of Albertosaurus would be much greater.

Albertosaurus forms, together with the closely related Gorgosaurus , the subfamily Albertosaurinae. Like all tyrannosaurids, Albertosaurus was a bipedal carnivore with very small, two-fingered arms and a large head with dozens of large, sharp teeth. All Albertosaurus sarcophagus fossils are from the Horseshoe Canyon Formation ; in the ecosystem handed down from this rock unit , Albertosaurus stood as a top predator at the top of the food chain.

So far, the fossils of more than 30 individuals have been found, making the genus better studied than most other tyrannosaurids. The discovery of 22 individuals in a single site gives clues to a possible pack life and allows studies of developmental and population biology - such conclusions are hardly possible with less well-known dinosaurs.

features

Live reconstruction of Albertosaurus sarcophagus

Albertosaurus was smaller than the gigantic tyrannosaurids Tarbosaurus and Tyrannosaurus , but about the same size as Daspletosaurus and Gorgosaurus . Adults were usually up to nine meters long, but some fossils suggest that some specimens could have reached ten meters or more. Different independent weight estimates based on different methods give a weight between 1.3 and 1.7 tons.

Incomplete jaws of Albertosaurus in the Royal Ontario Museum

As with all tyrannosaurids, the massive skull sat on a short, "S" -shaped neck and was about one meter long in the largest individuals. The long jaws housed more than 60 banana-shaped teeth, more than those of larger members of the same family. Unlike other theropods, the teeth of the Tyrannosauridae were heterodontic , so they were structured differently depending on their position in the dentition. In Albertosaurus the teeth of the intermaxillary bone (premaxillary) in the front area of ​​the upper jaw were much smaller than the remaining teeth, were closer together and were "D" -shaped in cross-section. Short, bony combs that were possibly brightly colored for courtship sat above the eyes.

Systematics

Albertosaurus is a member of the Tyrannosauridae family and the Albertosaurinae subfamily . Its closest relative is the slightly older geological Gorgosaurus libratus who sometimes called Albertosaurus libratus the Albertosaurus is attributed (see below). These two species are the only albertosaurins described, although other as yet undescribed species may exist. Thomas Holtz (2004) thought Appalachiosaurus to be an albertosaurine, but in a later publication he placed the genus just outside the Tyrannosauridae, which other authors agreed with.

The other large subfamily of the Tyrannosauridae is the Tyrannosaurinae, which includes Daspletosaurus , Tarbosaurus, and Tyrannosaurus . Compared to the robust tyrannosaurines, alberto saurines had a slimmer structure with proportionally smaller skulls and longer lower leg, foot and toe bones.

Discovery history and naming

Albertosaurus was named by Henry Fairfield Osborn in a very brief note at the end of his description of the Tyrannosaurus rex in 1905. The generic name ("Alberta lizard") honors Alberta, while the epithet sarcophagus means "carnivore" and has the same etymology as the sarcophagus of the same name ; a combination of the ancient Greek words σάρξ / sarx ("meat") and φαγεῖν / phagein ("eat"). Today there are over 30 scientific findings known, covering all ages.

Early discoveries

The Red Deer River near Drumheller , Alberta . Almost three quarters of all Albertosaurus remains have been discovered along this river.

The type material is a partial skull discovered in 1884 in an outcrop of the Horseshoe Canyon Formation along the Red Deer River in Alberta. This and another find, a smaller skull with a few other bones from the skeleton, were discovered by expeditions of the Geological Survey of Canada , led by the famous geologist Joseph Tyrrell . Edward Drinker Cope attributed the two skulls to the already existing species Laelaps incrassatus in 1892 , although the name Laelaps was already given to a mite and therefore had to be changed ( priority rule ). So Othniel named Charles Marsh Laelaps in 1877 in Dryptosaurus ; However, Cope did not recognize this new name given by his arch-rival. Lawrence Lambe attributed Laelaps incrassatus to Dryptosaurus incrassatus when he detailed the findings in 1904. A little later, Osborn noticed that the type of Dryptosaurus incrassatus was based on a typical tyrannosaurid tooth that could not be further assigned, which is why he could not reliably attribute both skulls from Alberta to this genus. The skulls also differ considerably from the remains of Dryptosaurus aquilunguis , the type species of Dryptosaurus , which is why Osborn established the new name Albertosaurus sarcophagus in 1905. He only roughly described the remains, referring to Lambe's full description from the previous year. Both finds ( CMN 5600 and 5601) are now in the Canadian Museum of Nature in Ottawa .

Dry Island Bonebed

In 1910, the famous paleontologist Barnum Brown discovered a bonebed in a quarry along the Red Deer River that housed the remains of a large group of Albertosaurus . Because of the large number of bones and the limited time available to Brown's team, they did not collect every bone, they simply tried to retrieve at least one bone from each identifiable individual. Among these bones, now in the American Museum of Natural History in New York, are seven sets of right metatarsals and two isolated toe bones that are not sized to match any of the metatarsals. This suggests the presence of at least nine individuals. The Royal Tyrrell Museum of Palaeontology rediscovered the bone store in 1997 and continued fieldwork at the site, which is now within Dry Island Buffalo Jump Provincial Park. Excavations from 1997 to 2005 uncovered the remains of 13 other individuals of various ages, including a tiny two-year-old animal and a very old animal estimated to be over ten meters long. None of these individuals is known of complete skeletons, most are represented by remains in both museums.

Gorgosaurus libratus

In 1913, the paleontologist Charles Hazelius Sternberg discovered another tyrannosaurid from the somewhat older Dinosaur Park Formation in Alberta. Lawrence Lambe named this dinosaur as Gorgosaurus libratus in 1914 . Other finds were later discovered in Alberta and Montana . Dale Russell examined the two genera in a publication in 1970 but found few differences and re-described Gorgosaurus as a juvenile synonym with Albertosaurus . Since Albertosaurus was the first name given ( priority rule ), Russell renamed Gorgosaurus libratus to Albertosaurus libratus . This new species extends the temporal occurrence of Albertosaurus several million years back and the spatial occurrence hundreds of kilometers south.

In a study published in 2003, Philip Currie compared different tyrannosaurid skulls and concluded that both species are more different than previously thought. The decision to have one or two genera is quite arbitrary, as both species are sister taxa and are thus more closely related than any other species. Nevertheless, Currie recommends viewing Albertosaurus and Gorgosaurus as separate genera, as they are no more similar than Daspletosaurus and Tyrannosaurus , which are almost always separated. Various albertosaurine finds have been discovered from Alaska and New Mexico , and Currie notes that the Albertosaurus - Gorgosaurus situation may be cleared up once these finds are fully described. Most authors follow Currie's recommendation, but some do not.

More discoveries

William Parks described a new species, Albertosaurus arctunguis , in 1928 based on a partial skeleton excavated near the Red Deer River - but this species has been believed to be identical to Albertosaurus sarcophagus since 1970 . Parks' find (ROM 807) is now in the Royal Ontario Museum in Toronto . Six other skulls and skeletons have since been discovered in Alberta and are on display in various Canadian museums. In addition, finds from Montana, New Mexico and Wyoming have also been reported - these fossils may not belong to Albertosaurus sarcophagus and may not even belong to the genus Albertosaurus .

Albertosaurus megagracilis is based on a small tyrannosaurid skeleton from the Hell Creek Formation of Montana. The find was renamed Dinotyrannus in 1995 ; but today it is assumed that it is a juvenile Tyrannosaurus rex .

Paleobiology

Developmental and Population Biology

A graph showing the putative growth curves (body mass versus age) for four tyrannosaurids. Albertosaurus is shown in red. According to Erickson et al. a., 2004.

Researchers led by Gregory Erickson used bone histology to determine the age of different individuals and determined growth curves by relating the age of an individual to his or her height. The youngest animal that could be identified was a two-year-old cub from the Dry Island Bonebed, weighing about 50 kilograms and a little over two meters long. The ten-meter-tall individual from the same quarry is the oldest and largest known animal - Erickson gives an age of 28 years. If you compare age and size, the same pattern emerges as with other tyrannosaurids: In the middle of their lives, the animals lived through a rapid four-year growth period, which followed a long period as young. Albertosaurus grew 122 kilograms per year during this growing season, assuming an adult weight of 1.3 tons. This makes Albertosaurus similar to other tyrannosaurids of about the same size, although the much larger Tyrannosaurus rex grew almost five times faster at 601 kilograms per year. Like other tyrannosaurids, Albertosaurus reached sexual maturity at the end of the growth phase, although growth continued - albeit more slowly.

Albertosaurus skeleton in the Redpath Museum , Montreal

Most known Albertosaurus individuals were 14 years of age or older at the time of death. Juveniles are generally rarely found, since the smaller bones of young animals fossil less often than the larger bones of adult animals; in addition, smaller fossils are more difficult to find by collectors. Juvenile Albertosaurus are relatively large compared to juveniles of other animals, but their remains are nonetheless rare compared to adults. Some researchers suspect the cause is that the death rate in juvenile Albertosaurus may have been generally lower.

One hypothesis suggests that although there was a high mortality among very young Albertosaurus , they have not been passed down as fossils due to their small size and fragile bone structure. After two years, juvenile Albertosaurus were larger than any other predator in the region, save for adult Albertosaurus . This, so the hypothesis, results in a very low death rate, as the fossil record shows. The death rate doubled by the age of 12, perhaps due to the physiological demands of the rapid growth phase. With sexual maturity at 14 or 16 years of age, the death rate doubled again. This increased death rate continued into adulthood, perhaps due to high physiological demands, stress, and injury from peer competition for females or resources, and perhaps due to the increasing effects of aging. The higher death rate of adult animals could explain their more frequent occurrence in the fossil record. Very large individuals are rare, as only a few survived long enough to reach such sizes. High death rates in very young animals, followed by reduced mortality among older pups and a sudden increase in mortality after sexual maturity, with very few individuals reaching maximum size - this pattern is also seen in many large recent animals, including elephants, and bison Rhinos as well as other tyrannosaurids. Nevertheless, deficiencies in the fossil record could have significantly influenced this picture, as more than two thirds of all Albertosaurus finds come from just one location.

Pack behavior

Albertosaurus models in the Royal Tyrrell Museum

The Dry Island Bonebed, discovered by Barnum Brown, contains the remains of 22 Albertosaurus - the largest number of individuals in the same place ever discovered by a Cretaceous theropod, and the second largest of any major theropod; only the Allosaurus mass grave at Cleveland Lloyd Dinosaur Quarry in Utah is even larger. The group found in the quarry consists of one very old individual, eight adult, 17 to 23 year old individuals, seven almost adult, 12 to 16 year old individuals in the growing season and six juvenile, 2 to 11 year old individuals who have not yet reached the growth phase.

Philip Currie sees this location as an indication of pack behavior and considers the possibility that the bonebed could have come about through a predator trap to be unlikely. For example, a famous predator trap is the La Brea tar pits in California , where animals sank into a tar pit and attracted a multitude of predators who also perished. Currie argues that in the Albertosaurus mass grave, unlike in La Brea, almost no remains of herbivores are known. In addition, the degree to which the bones have loosened from their original anatomical bond is similar for all fossils, from which he concludes that all animals died at the same time and had the same taphonomic history. Other scientists are skeptical and note that the animals could also have been brought together by a drought, a flood, or other reasons.

Although there is ample evidence of herd life in herbivorous dinosaurs such as ceratopsians and hadrosaurs , theropods are rarely found in large numbers in a single site. Groups of several individuals are known from small theropods such as Deinonychus , Coelophysis and Megapnosaurus (Syntarsus) rhodesiensis as well as from larger theropods such as Allosaurus and Mapusaurus . There are also indications of group life in other tyrannosauroids: fragmentary remains of smaller individuals were discovered alongside the tyrannosaurus skeleton "Sue" and a bonebed in the Two Medicine Formation of Montana contains the remains of at least three Daspletosaurus individuals, which have been preserved alongside some hadrosaurids. However, some researchers suspect that at least some of these sites came about through aggressive fighting between solitary individuals, in which some animals were killed - similar to today's Komodo dragons .

Currie also speculated about possible hunting strategies for an Albertosaurus group. In juvenile specimens, the lower legs were longer than the thighs - a characteristic that distinguishes fast runners such as ornithomimids . Currie hypothesized that the quick-footed juvenile group members might have driven the prey in the direction of the adults, which were larger and more powerful but slower at the same time. Young animals may also have had different habits than adults and, as medium-sized predators, may fill in niches that existed between the very large adult tyrannosaurids and the contemporary small theropod species.

Paleoecology

The Horseshoe Canyon Formation is open-minded at its type locality in Horseshoe Canyon , Alberta

All identifiable Albertosaurus sarcophagus fossils are from the Horseshoe Canyon Formation in Alberta. This geological formation dates to the late Campanian and early Maastrichtian (Upper Cretaceous) approximately 76 to 69 million years ago. Just below this formation lie the marine deposits of the Bearpaw Formation, which show that this area was covered by the Western Interior Seaway a few million years earlier ; an arm of the sea that divided North America in half during the Late Cretaceous. The retreat of the sea was not a straightforward process, however, and parts of the land continued to flood during the deposition of the Horseshoe Canyon Formation, until the sea finally disappeared. These changing sea levels resulted in a variety of different habitats within the Horseshoe Canyon Formation, including marine habitats near the coast, deltas, lagoons, estuaries and mud flats. Coal layers indicate peat-rich swamps.

Like most of the formation's other vertebrate fossils, the Albertosaurus remains were found in debris formed on the floodplains of large rivers during the latter half of the formation's deposition period.

The fauna of the Horseshoe Canyon Formation is well known and includes a wide variety of vertebrate fossils. Almost half of the dinosaurs found were herbivorous hadrosaurids such as Edmontosaurus , Saurolophus, and Hypacrosaurus ; other common dinosaur groups were ceratopsians and ornithomimosaurids . Ankylosaurs and pachycephalosaurs are found much less frequently . All of these herbivores could have been the prey of various theropods, including troodontids , dromaeosaurids, and caenagnathids . Adult Albertosaurus were probably the top predators of this fauna.

Individual evidence

  1. ^ Gregory S. Paul : The Princeton Field Guide To Dinosaurs. Princeton University Press, Princeton NJ et al. 2010, ISBN 978-0-691-13720-9 , p. 105, online .
  2. ^ A b c Dale A. Russell : Tyrannosaurs from the late cretaceous of Western Canada (= Publications in Palaeontology. Vol. 1, ISSN  0068-8029 ). National Museum of Natural Sciences (Canada), Ottawa 1970, digitized .
  3. ↑ a b c d e f Thomas R. Holtz Jr .: Tyrannosauroidea. In: David B. Weishampel , Peter Dodson , Halszka Osmólska (eds.): The Dinosauria . 2nd edition. University of California Press, Berkeley CA et al. 2004, ISBN 0-520-24209-2 , pp. 111-136.
  4. ↑ a b c d e f g h i Gregory M. Erickson, Philip J. Currie , Brian D. Inouye, Alice A. Winn: Tyrannosaur Life Tables: An Example of Nonavian Dinosaur Population Biology. In: Science . Vol. 313, No. 5784, 2006, pp. 213-217, doi : 10.1126 / science.1125721 , PMID 16840697 .
  5. ↑ a b c d Gregory M. Erickson, Peter J. Makovicky , Philip J. Currie, Mark A. Norell , Scott A. Yerby, Christopher A. Brochu: Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs. In: Nature . Vol. 430, No. 7001, 2004, pp. 772-775, doi : 10.1038 / nature02699 .
  6. ^ Per Christiansen, Richard A. Fariña: Mass prediction in theropod dinosaurs. In: Historical Biology. Vol. 16, No. 2/4, 2004, ISSN  0891-2963 , pp. 85-92, doi : 10.1080 / 08912960412331284313 .
  7. ^ A b c Philip J. Currie: Allometric growth in tyrannosaurids (Dinosauria: Theropoda) from the Upper Cretaceous of North America and Asia. In: Canadian Journal of Earth Sciences. Vol. 4, No. 4, 2003, ISSN  0008-4077 , pp. 651-665, doi : 10.1139 / e02-083 .
  8. ↑ Peter Dodson, Britt Brooks, Kenneth Carpenter , Catherine A. Forster, David D. Gillette, Mark A. Norell, George Olshevsky, J. Michael Parrish, David B. Weishampel: Albertosaurus. In: Peter Dodson: The Age of Dinosaurs. Publications International, Lincolnwood IL 2003, ISBN 0-7853-0443-6 , pp. 106-107.
  9. ^ A b Philip J. Currie, Jørn H. Hurum, Karol Sabath: Skull structure and evolution in tyrannosaurid dinosaurs . In: Acta Palaeontologica Polonica. Vol. 48, No. 2, 2003, pp. 227-234, (PDF; 137 kB).
  10. ^ A b c d Philip J. Currie: Cranial anatomy of tyrannosaurids from the Late Cretaceous of Alberta . In: Acta Palaeontologica Polonica. Vol. 48, No. 2, 2003, ISSN  0567-7920 , pp. 191-226, (PDF; 1.8 MB).
  11. ^ Thomas R. Holtz: RE: Burpee Conference (LONG). September 20, 2005, accessed July 28, 2014 .
  12. ↑ a b Thomas D. Carr, Thomas E. Williamson, David R. Schwimmer: A new genus and species of tyrannosauroid from the Late Cretaceous (middle Campanian) Demopolis Formation of Alabama. In: Journal of Vertebrate Paleontology. Vol. 25, No. 1, 2005, ISSN  0272-4634 , pp. 119-143, doi : 10.1671 / 0272-4634 (2005) 025 [0119: ANGASO] 2.0.CO; 2 .
  13. ^ A b Henry Fairfield Osborn : Tyrannosaurus and other Cretaceous carnivorous dinosaurs. In: Bulletin of the American Museum of Natural History. Vol. 21, Article 14, 1905, ISSN  0003-0090 , pp. 259-265, digitized .
  14. ^ Edward D. Cope : On the Skull of the Dinosaurian Lælaps incrassatus Cope. In: Proceedings of the American Philosophical Society held at Philadelphia for promoting useful knowledge. Vol. 30, No. 138, 1892, ISSN  0003-049X , pp. 240-245, digitized .
  15. ↑ Lawrence M. Lambe : On Dryptosaurus incrassatus (Cope), from the Edmonton series of the north west territory (= Contributions to Canadian Palaeontology. Vol. 3 (Quarto), Part 3, ZDB -ID 979678-2 ). Government Printing Bureau, Ottawa 1904.
  16. ^ A b c Philip J. Currie: Possible evidence of gregarious behavior in tyrannosaurids. In: Gaia. Revista de Geociências. Vol. 15, 2000, ISSN  0871-5424 , pp. 271-277.
  17. ↑ Lawrence M. Lambe: On a new Genus and Species of Carnivorous Dinosaur from the Belly River Formation of Alberta, with a Description of the Skull of Stephanosaurus Marginatus from the same Horizon. In: The Ottawa Naturalist. Vol. 28, No. 1, 1914, ISSN  0316-4411 , pp. 13-20, digitized .
  18. ↑ a b Robert E. Ricklefs : Tyrannosaur aging. In: Biology Letters. Vol. 3, No. 2, 2007, ISSN  1744-9561 , pp. 214-217, doi : 10.1098 / rsbl.2006.0597 .
  19. ^ William A. Parks : Albertosaurus arctunguis. A new species of Therapodous dinosaur from the Edmonton formation of Alberta (= University of Toronto Studies. Geological Series. Vol. 25, ISSN  0372-4913 ). University Library, Toronto 1928.
  20. ^ Gregory S. Paul: Predatory Dinosaurs of the World. A complete and illustrated guide. Simon & Schuster, New York NY et al. 1988, ISBN 0-671-61946-2 .
  21. ↑ George Olshevsky, Tracy L. Ford: The origin and evolution of the tyrannosaurids, part 1. In: Kyoryugaku Saizensen. = Dinosaur Frontline. Vol. 9, 1995, pp. 92-119 (Japanese).
  22. ^ A b c Brian T. Roach, Daniel T. Brinkman: A reevaluation of cooperative pack hunting and gregariousness in Deinonychus antirrhopus and other nonavian theropod dinosaurs. In: Bulletin of the Peabody Museum of Natural History. Vol. 48, No. 1, 2007, ISSN  0079-032X , pp. 103-138, doi : 10.3374 / 0079-032X (2007) 48 [103: AROCPH] 2.0.CO; 2 .
  23. ^ David A. Eberth, Richard T. McCrea: Were large theropods gregarious? In: Journal of Vertebrate Paleontology. Vol. 21, Supplement to No. 3 = Abstracts of Papers, 61st Annual Meeting of the Society of Vertebrate Paleontology , 2001, p. 46A.
  24. ^ John R. Horner : Behavior. In: Philip J. Currie, Kevin Padian (Eds.): Encyclopedia of dinosaurs. Academic Press, San Diego CA et al. 1997, ISBN 0-12-226810-5 , pp. 45-50.
  25. ^ W. Desmond Maxwell, John H. Ostrom : Taphonomy and paleobiological implications of Tenontosaurus-Deinonychus associations. In: Journal of Vertebrate Paleontology. Vol. 15, No. 4, 1995, pp. 707-712, doi : 10.1080 / 02724634.1995.10011256 .
  26. ^ Michael A. Raath: Morphological variation in small theropods and its meaning in systematics: evidence from Syntarsus rhodesiensis. In: Kenneth Carpenter, Philip J. Currie (Eds.): Dinosaur Systematics. Approaches and Perspectives. Cambridge University Press, Cambridge et al. 1990, ISBN 0-521-36672-0 , pp. 91-105.
  27. ↑ Rodolfo A. Coria , Philip J. Currie: A new carcharodontosaurid (Dinosauria, Theropoda) from the Upper Cretaceous of Argentina. In: Geodiversitas. Vol. 28, No. 1, 2006, ISSN  1280-9659 , pp. 71-118, (PDF; 2.92 MB).
  28. ↑ Philip J. Currie, David Trexler, Eva B. Koppelhus, Kelly Wicks, Nate Murphy: An unusual multi-individual tyrannosaurid bonebed in the Two Medicine Formation (Late Cretaceous, Campanian) of Montana (USA). In: Kenneth Carpenter (Ed.): The Carnivorous Dinosaurs. Indiana University Press, Bloomington IN et al. 2005, ISBN 0-253-34539-1 , pp. 313-324.
  29. ^ A b David A. Eberth: Edmonton Group. In: Philip J. Currie, Kevin Padian (Eds.): Encyclopedia of dinosaurs. Academic Press, San Diego CA et al. 1997, ISBN 0-12-226810-5 , pp. 199-204.

Web links

Commons : Albertosaurus  - collection of images, videos and audio files