Post by Barry the Baryonyx on Jun 26, 2007 0:07:14 GMT -5
Albertosaurus sarcophagus
Albertosaurus meaning "Alberta lizard") is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, more than 70 million years ago. The type species, A. sarcophagus, was restricted in range to the modern-day Canadian province of Alberta, after which the genus is named. Scientists disagree on the number of species represented in the genus, recognizing either one or two species. As a tyrannosaurid, Albertosaurus was a bipedal predator with a massive head, jaws lined with dozens of large teeth and tiny, two-fingered 'hands'. It may have been at the top of the food chain in its local ecosystem. Although relatively large for a theropod, Albertosaurus was much smaller than its more famous relative Tyrannosaurus, probably weighing only as much as a modern black rhinoceros. Fossils of more than twenty individuals have been recovered, providing scientists with a more detailed knowledge of Albertosaurus anatomy than is available for other tyrannosaurids. The discovery of ten individuals at one site provides evidence of pack behavior and allows studies of developmental biology which are impossible with lesser-known animals.
Description
Albertosaurus was smaller than the truly gigantic tyrannosaurids like Tarbosaurus and Tyrannosaurus. Adults measured approximately 9 m (30 ft) long. Several independent mass estimates, obtained by different methods, suggest that a full-grown Albertosaurus weighed between 1.282 tonnes (1.4 short tons) and 1.685 tonnes (1.85 short tons). The massive skull of Albertosaurus, perched on a short, S-shaped neck, was approximately 1
m (3.3 ft) long in the largest adults. Wide openings in the skull (fenestrae) reduced the potential weight of the head, and provided areas for muscle attachment and sensory organs. Its long jaws contained more than 60 banana-shaped teeth; larger tyrannosaurids possessed fewer teeth. Unlike most other theropods, tyrannosaurids were heterodont; the teeth took different forms depending on their position in the mouth. The premaxillary teeth at the tip of the upper jaw were much smaller than the rest, more closely packed, and D-shaped in cross section.
All tyrannosaurids, including Albertosaurus, shared a similar body appearance. Typically for a theropod, Albertosaurus was bipedal and balanced the heavy head and torso with a long tail. However, tyrannosaurid forelimbs were extremely small for their body size and
retained only two digits. The hindlimbs were long and ended in a four-toed foot. The first of these digits, called the hallux, was very short and only the other three contacted the ground, with the middle digit longer than the rest.
Classification
Albertosaurus is a member of the theropod family Tyrannosauridae. Within this family, Albertosaurus sarcophagus is usually classified with Gorgosaurus libratus (sometimes called Albertosaurus libratus; see below) in the subfamily Albertosaurinae. Albertosaurines were more slender than the robust tyrannosaurines, the other major subfamily of tyrannosaurids. Appalachiosaurus has been called an albertosaurine in at least one study, although this is disputed.
Albertosaurus sarcophagus
The type species of Albertosaurus is A. sarcophagus, also named by Osborn in 1905. The name means "flesh-eater" and has the same etymology as the funeral container with which it shares its name: a combination of the Ancient Greek words (sarx, meaning "flesh") and (phagein, meaning "to eat"). More than twenty specimens of all ages are known to science.
Taxonomy
Albertosaurus was named in 1905 by Henry Fairfield Osborn of the American Museum of Natural History in a very brief note at the end of his description of Tyrannosaurus rex. The name honors Alberta, the Canadian province in which the first remains were found. The generic name also incorporates the Greek term (sauros, meaning "lizard"), the most common suffix in dinosaur names.
Gorgosaurus libratus
In 1913, paleontologist Charles Hazelius Sternberg recovered another tyrannosaurid skeleton from slightly older sediments in Alberta. This dinosaur was named Gorgosaurus libratus in 1914 by Lawrence Lambe. Finding few differences to separate the two genera, Dale Russell declared Gorgosaurus a junior synonym of Albertosaurus in 1970, creating the new combination Albertosaurus libratus. This extended the temporal range of the genus backwards by several million years and its geographic range southwards by hundreds of kilometers. More recent examination of Albertosaurus and Gorgosaurus has cast doubt on Russell's proposed synonymy. In 2003, Phil Currie and colleagues examined skulls of the two species and came to the conclusion that the two distinct genera should be retained, although they acknowledged that the two genera are sister taxa and that the distinction is therefore rather arbitrary. However, according to Currie, Albertosaurus and Gorgosaurus are no more similar than Daspletosaurus and Tyrannosaurus, which are almost always retained as separate genera. In addition, several undescribed albertosaurine specimens have been recovered from other parts of North America, including Alaska and New Mexico, so Currie has recommended leaving the two genera separate until more of this diversity is clarified. Most authors have since followed Currie's recommendation, but some have not.
Invalid species
Other species of Albertosaurus have been named but later invalidated. William Parks described a partial skeleton from Alberta as Albertosaurus arctunguis in 1928, but this is universally considered a junior synonym of A. sarcophagus.Albertosaurus megagracilis (later renamed Dinotyrannus) was based on a small tyrannosaurid skeleton from the Hell Creek Formation of Montana in the United States. However, it is now thought to be a juvenile Tyrannosaurus.
History of discovery
The type specimen is a partial skull, collected in 1884 from an outcrop alongside the Red Deer River in Alberta. This specimen, along with an additional smaller skull and some skeletal material, was recovered by an expedition of the Geological Survey of Canada, led by the famous Canadian geologist Joseph B. Tyrrell. The specimen is now stored in the Canadian Museum of Nature. The two skulls were assigned to the existing species Laelaps incrassatus by Edward Drinker Cope in 1892. However, as early as 1877 the name Laelaps had been found to be preoccupied by a genus of mite, and it was changed to Dryptosaurus by Cope's rival, Othniel Charles Marsh. (Cope refused to recognize the new name.) Lawrence Lambe moved Laelaps incrassatus to the genus Dryptosaurus in 1904. Finally, because D. incrassatus was only based on generic tyrannosaurid teeth that could not be said to belong to any particular species, and because the Alberta skull material differed markedly from that of Dryptosaurus, Osborn named it Albertosaurus sarcophagus in 1905.
In 1910, American paleontologist Barnum Brown uncovered the remains of a large group of Albertosaurus at another quarry alongside the Red Deer River. Because of the large number of bones and the limited time available, Brown's party did not collect every specimen, but made sure to collect bones from all of the individuals present. Among many other bones deposited in the American Museum of Natural History collections in New York City, seven sets of right metatarsals were collected, along with two isolated toe bones that did not match any of the metatarsals in size. This indicates the presence of at least nine individuals in the quarry. The Royal Tyrrell Museum of Palaeontology rediscovered the site in 1997 and resumed fieldwork there. This further excavation turned up a tenth, very young individual in 2002. The specimen originally named A. arctunguis was also excavated near the Red Deer River and is housed in the Royal Ontario Museum in Toronto, Canada. Six more skulls and skeletons have since been discovered in Alberta and are housed in other Canadian museums. All identifiable fossils of Albertosaurus sarcophagus are known from the Horseshoe Canyon Formation in Alberta. This formation dates to the early Maastrichtian stage of the Late Cretaceous period, 70 to 73 million years ago. Many other dinosaurs have been found there, including smaller theropods like Ornithomimus, Chirostenotes and several dromaeosaurids, and a wide variety of herbivores like ankylosaurians, ceratopsians, pachycephalosaurs and hadrosaurids. Fossils of Albertosaurus have also been reported from the American states of Montana, New Mexico, and Wyoming, but these probably do not represent A. sarcophagus and may not even belong to the Albertosaurus genus.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Superorder: Dinosauria
Order: Saurischia
Suborder: Theropoda
Family: Tyrannosauridae
Subfamily: Albertosaurinae
Genus: Albertosaurus
Species: A. sarcophagus
Albertosaurus meaning "Alberta lizard") is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, more than 70 million years ago. The type species, A. sarcophagus, was restricted in range to the modern-day Canadian province of Alberta, after which the genus is named. Scientists disagree on the number of species represented in the genus, recognizing either one or two species. As a tyrannosaurid, Albertosaurus was a bipedal predator with a massive head, jaws lined with dozens of large teeth and tiny, two-fingered 'hands'. It may have been at the top of the food chain in its local ecosystem. Although relatively large for a theropod, Albertosaurus was much smaller than its more famous relative Tyrannosaurus, probably weighing only as much as a modern black rhinoceros. Fossils of more than twenty individuals have been recovered, providing scientists with a more detailed knowledge of Albertosaurus anatomy than is available for other tyrannosaurids. The discovery of ten individuals at one site provides evidence of pack behavior and allows studies of developmental biology which are impossible with lesser-known animals.
Description
Albertosaurus was smaller than the truly gigantic tyrannosaurids like Tarbosaurus and Tyrannosaurus. Adults measured approximately 9 m (30 ft) long. Several independent mass estimates, obtained by different methods, suggest that a full-grown Albertosaurus weighed between 1.282 tonnes (1.4 short tons) and 1.685 tonnes (1.85 short tons). The massive skull of Albertosaurus, perched on a short, S-shaped neck, was approximately 1
m (3.3 ft) long in the largest adults. Wide openings in the skull (fenestrae) reduced the potential weight of the head, and provided areas for muscle attachment and sensory organs. Its long jaws contained more than 60 banana-shaped teeth; larger tyrannosaurids possessed fewer teeth. Unlike most other theropods, tyrannosaurids were heterodont; the teeth took different forms depending on their position in the mouth. The premaxillary teeth at the tip of the upper jaw were much smaller than the rest, more closely packed, and D-shaped in cross section.
All tyrannosaurids, including Albertosaurus, shared a similar body appearance. Typically for a theropod, Albertosaurus was bipedal and balanced the heavy head and torso with a long tail. However, tyrannosaurid forelimbs were extremely small for their body size and
retained only two digits. The hindlimbs were long and ended in a four-toed foot. The first of these digits, called the hallux, was very short and only the other three contacted the ground, with the middle digit longer than the rest.
Classification
Albertosaurus is a member of the theropod family Tyrannosauridae. Within this family, Albertosaurus sarcophagus is usually classified with Gorgosaurus libratus (sometimes called Albertosaurus libratus; see below) in the subfamily Albertosaurinae. Albertosaurines were more slender than the robust tyrannosaurines, the other major subfamily of tyrannosaurids. Appalachiosaurus has been called an albertosaurine in at least one study, although this is disputed.
Albertosaurus sarcophagus
The type species of Albertosaurus is A. sarcophagus, also named by Osborn in 1905. The name means "flesh-eater" and has the same etymology as the funeral container with which it shares its name: a combination of the Ancient Greek words (sarx, meaning "flesh") and (phagein, meaning "to eat"). More than twenty specimens of all ages are known to science.
Taxonomy
Albertosaurus was named in 1905 by Henry Fairfield Osborn of the American Museum of Natural History in a very brief note at the end of his description of Tyrannosaurus rex. The name honors Alberta, the Canadian province in which the first remains were found. The generic name also incorporates the Greek term (sauros, meaning "lizard"), the most common suffix in dinosaur names.
Gorgosaurus libratus
In 1913, paleontologist Charles Hazelius Sternberg recovered another tyrannosaurid skeleton from slightly older sediments in Alberta. This dinosaur was named Gorgosaurus libratus in 1914 by Lawrence Lambe. Finding few differences to separate the two genera, Dale Russell declared Gorgosaurus a junior synonym of Albertosaurus in 1970, creating the new combination Albertosaurus libratus. This extended the temporal range of the genus backwards by several million years and its geographic range southwards by hundreds of kilometers. More recent examination of Albertosaurus and Gorgosaurus has cast doubt on Russell's proposed synonymy. In 2003, Phil Currie and colleagues examined skulls of the two species and came to the conclusion that the two distinct genera should be retained, although they acknowledged that the two genera are sister taxa and that the distinction is therefore rather arbitrary. However, according to Currie, Albertosaurus and Gorgosaurus are no more similar than Daspletosaurus and Tyrannosaurus, which are almost always retained as separate genera. In addition, several undescribed albertosaurine specimens have been recovered from other parts of North America, including Alaska and New Mexico, so Currie has recommended leaving the two genera separate until more of this diversity is clarified. Most authors have since followed Currie's recommendation, but some have not.
Invalid species
Other species of Albertosaurus have been named but later invalidated. William Parks described a partial skeleton from Alberta as Albertosaurus arctunguis in 1928, but this is universally considered a junior synonym of A. sarcophagus.Albertosaurus megagracilis (later renamed Dinotyrannus) was based on a small tyrannosaurid skeleton from the Hell Creek Formation of Montana in the United States. However, it is now thought to be a juvenile Tyrannosaurus.
History of discovery
The type specimen is a partial skull, collected in 1884 from an outcrop alongside the Red Deer River in Alberta. This specimen, along with an additional smaller skull and some skeletal material, was recovered by an expedition of the Geological Survey of Canada, led by the famous Canadian geologist Joseph B. Tyrrell. The specimen is now stored in the Canadian Museum of Nature. The two skulls were assigned to the existing species Laelaps incrassatus by Edward Drinker Cope in 1892. However, as early as 1877 the name Laelaps had been found to be preoccupied by a genus of mite, and it was changed to Dryptosaurus by Cope's rival, Othniel Charles Marsh. (Cope refused to recognize the new name.) Lawrence Lambe moved Laelaps incrassatus to the genus Dryptosaurus in 1904. Finally, because D. incrassatus was only based on generic tyrannosaurid teeth that could not be said to belong to any particular species, and because the Alberta skull material differed markedly from that of Dryptosaurus, Osborn named it Albertosaurus sarcophagus in 1905.
In 1910, American paleontologist Barnum Brown uncovered the remains of a large group of Albertosaurus at another quarry alongside the Red Deer River. Because of the large number of bones and the limited time available, Brown's party did not collect every specimen, but made sure to collect bones from all of the individuals present. Among many other bones deposited in the American Museum of Natural History collections in New York City, seven sets of right metatarsals were collected, along with two isolated toe bones that did not match any of the metatarsals in size. This indicates the presence of at least nine individuals in the quarry. The Royal Tyrrell Museum of Palaeontology rediscovered the site in 1997 and resumed fieldwork there. This further excavation turned up a tenth, very young individual in 2002. The specimen originally named A. arctunguis was also excavated near the Red Deer River and is housed in the Royal Ontario Museum in Toronto, Canada. Six more skulls and skeletons have since been discovered in Alberta and are housed in other Canadian museums. All identifiable fossils of Albertosaurus sarcophagus are known from the Horseshoe Canyon Formation in Alberta. This formation dates to the early Maastrichtian stage of the Late Cretaceous period, 70 to 73 million years ago. Many other dinosaurs have been found there, including smaller theropods like Ornithomimus, Chirostenotes and several dromaeosaurids, and a wide variety of herbivores like ankylosaurians, ceratopsians, pachycephalosaurs and hadrosaurids. Fossils of Albertosaurus have also been reported from the American states of Montana, New Mexico, and Wyoming, but these probably do not represent A. sarcophagus and may not even belong to the Albertosaurus genus.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Superorder: Dinosauria
Order: Saurischia
Suborder: Theropoda
Family: Tyrannosauridae
Subfamily: Albertosaurinae
Genus: Albertosaurus
Species: A. sarcophagus
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