Allosaurus fragilis
- 演化之聲
- 6 hours ago
- 3 min read
Age
Jurassic（Tithonian）
150 Ma
Taxonomy
Kingdom：Animalia
Phylum： Chordata
Class：Reptilia
Order：Saurischia
Family：Allosauridae
Genus：Allosaurus
Species：Allosaurus fragilis
Morphological description
Allosaurus fragilis is a large theropod dinosaur characterized by relatively short forelimbs and long hindlimbs. However, compared to most later large theropods, its forelimbs are proportionally more developed.
On average, Allosaurus fragilis reached a body length of approximately 8.5 meters and a body mass of around 1.7 tonnes. The largest known specimens may have reached up to 9.7 meters in length and an estimated weight of 2.5 tonnes. The skull measures about 1 meter in length and is proportionally well balanced.
Above and anterior to the orbit, the lacrimal bones extend to form a pair of prominent horns. These connect with low ridges along the dorsal margin of the nasal bones, forming a distinctive cranial feature characteristic of Allosaurus.
The vertebral column consists of 9 cervical vertebrae, 14 dorsal vertebrae, and 5 sacral vertebrae, while the number of caudal vertebrae varies and is correlated with body size. The anterior cervical and dorsal vertebrae are pneumatic, containing air-filled cavities associated with the respiratory air sac system, which helped reduce body weight. The thoracic cavity is broad, giving the torso an overall barrel-shaped appearance.
Etymology
The generic name Allosaurus is derived from the Greek allos (“different” or “strange”) and sauros (“lizard”), referring to the unusual morphology of its vertebrae compared to other dinosaurs known at the time.
name fragilis is Latin for “fragile,” referring to the lightweight, pneumatic nature of its vertebrae.
Biological interpretation
Allosaurus fragilis is the type species of the genus Allosaurus. Its fossils are primarily found in the Late Jurassic Morrison Formation of North America, although possible remains have also been reported from Europe, particularly the Iberian Peninsula.
The holotype specimen, YPM 1930, was named by Othniel Charles Marsh in 1877. However, due to its fragmentary nature, a more complete specimen (USNM 4734), also collected by Marsh’s team, was later designated as a replacement type specimen.
The discovery of Allosaurus fragilis occurred during the Bone Wars between Marsh and Edward Drinker Cope. During this period of intense competition, many fossils were hastily described and named without sufficient study, resulting in numerous synonyms. Allosaurus was significantly affected by this, and its taxonomy has required extensive revision to clarify its diversity.
Allosaurus fragilis was one of the most abundant and successful theropods of the Late Jurassic. At the Cleveland-Lloyd Dinosaur Quarry, a large number of dinosaur fossils have been discovered, including at least six theropod taxa. Among them, Allosaurus fragilis is represented by approximately 44 to 60 individuals—far exceeding the total number of other theropod fossils combined—indicating that it was a dominant predator in its ecosystem.
Phylogenetically, Allosaurus belongs to the clade Tetanurae, meaning “stiff tails.” This indicates a relatively rigid tail, which, although less flexible, likely contributed to enhanced stability during locomotion.
The ecosystem in which Allosaurus fragilis lived was highly diverse. In addition to other species within the genus, it coexisted with large theropods such as Torvosaurus and Ceratosaurus, which likely acted as competitors.
Herbivorous dinosaurs were also abundant, including ornithischians such as Stegosaurus and Dryosaurus, as well as sauropodomorphs like Diplodocus and Camarasaurus. These taxa likely formed the primary prey base for Allosaurus.
Interestingly, bite marks are commonly found on Allosaurus fossils themselves, indicating that it may also have been preyed upon or scavenged. This could have involved other large theropods or even cannibalism within the species.
（Author: Bai Leng）
Reference
1. Marsh, Othniel Charles (1877). Notice of new dinosaurian reptiles from the Jurassic formation. American Journal of Science and Arts.
2. Carpenter, Kenneth (2002). Guide to the major dinosaur sites near Cañon City, Colorado. Trilobite Tails.
3. Glut, D. F. (1997). Allosaurus. Dinosaurs: The Encyclopedia. Jefferson, North Carolina: McFarland & Co
4. Mortimer, Mickey (2003). And the largest Theropod is... The Dinosaur Mailing List.
5. Chure, D. J., Litwin, R., Hasiotis, S. T., Evanoff, E., Carpenter, K. (2006). The fauna and flora of the Morrison Formation: 2006. In Foster, John R.; Lucas, Spencer G. (eds.). Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin 36. Albuquerque, New Mexico: New Mexico Museum of Natural History and Science.
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