Allosaurus

*Allosaurus* is an extinct genus of theropod dinosaur that lived in North America during Late Jurassic.

## Description

*Allosaurus* was first discovered in 1877 during the bone wars. Because of the competitive nature of the bone wars, many species that where described were re evaluated as *Allosaurus* fossils. Three species of *Allosaurus* have been discovered.

*Allosaurus* has a large skull, filled with teeth for butchering Sauropods and other medium sized dinosaurs. The jaw of *Allosaurus* was built for slicing movements. An *Allosaurus* would theoretically used an axe like action to slice down and kill their prey. The arms of *Allosaurus* have two medium size claws and one larger sickle claw for grabbing onto larger animals. *Allosaurus* is estimated to be about 4 meters tall, 3.5 tons heavy and 36 feet long. These estimates are based upon the largest *Allosaurus* fossils discovered.

Fossil teeth of an indeterminate theropod in the Arundel Formation were once attributed to *Allosaurus*, but is now considered discredited.

## Paleoecology

*Allosaurus* was the apex predator in the Morrison Formation ecosystem. *Allosaurus* was an apex predator that hunted medium sized sauropod like *Diplodocus* in the Late Jurassic Morrison Formation. *Allosaurus* coexisted with *Ceratosaurus*, and more indeterminate theropods like *Epanterias* and *Saurophaganax*.

Allosaurus is thought to have hunted *Diplodocus*, *Barosaurus*, *Apatosaurus*, *Brontosaurus*, *Supersaurus*, *Amphicoelias* and *Maraapunisaurus*, among other sauropods.

## Paleobiology

*Allosaurus* may have hunted in small packs, but is unknown if they were cooperative or aggressive among their own. Several individuals may have bit other *Allosaurus* on the head, which may have been a dominance display. *Allosaurus* may have hunted together to take down large sauropods that roamed the Morrison ecosystem.

## Species

### Reassigned Species

* *A. medius* (=indet. theropod)
* *"A." valens*
* *A. lucaris* (=*Labrosaurus*, =*A. fragillis*)
* *A. sibiricus* (=*Chilantaisaurus*, =indet. theropod)
* *A. meriani* (=*Megalosaurus meriani*, =*Ceratosaurus* sp.)
* *A. amplexus/maximus*?
* *A. tendagurensis* (=carcharodontosaurian/megalosaurid indet.)
* *A. sp*. 1 (=indet. theropod, =*Torvosaurus*)
* *A.* "robustus" (=Polar Allosaur, =*Australovenator*)
* *"A." antunesi*
* "A. whitei" (=*A. atrox*)
* *A. atrox*
* *A. amplus*
* *A. lucasi*

## Synonyms

* *Antrodemus*?
* *Creosaurus*?
* *Epanterias*?
* *Labrosaurus*?
* "Madsenius"
* *Saurophaganax*?
* "Wyomingraptor"
* *Metricanthosaurus* "huxleyi" (=*Megalosaurus*)

## Notable Specimens

* + *Allosaurus jimmadseni* (**Credit: @Harry20059 on Twitter.**)
	+ *Allosaurus jimmadseni* (**Credit: @Harry20059 on Twitter.**)1/2MOR 693 "Big Al": The Big Al specimen, being the most famous *Allosaurus* specimens, was discovered in 1991. Upon discovery, it was found to be ~8 meters (26 feet) long, found near Shell, Wyoming and excavated by a Museum of the Rockies and University of Wyoming Geological Museum joint team. It was found by a Swiss team, however, lead by Kirby Siver. Chure and Loewen (2020) identified Big Al as *A. jimmadseni*. It gained its common name due to completion, preservation and importance, but was below the average size for *A. fragilis* and was a subadult (~87% grown at death). Breithaupt (1996) described Big Al. Of the skeleton, 19 bones showed paleopathology. 5 ribs, 5 vertebrae and 4 feet bones show evidence of this; damaged bones show osteomyelitis with an infection of the first phalanx of the third toe, inflicted by an involucrum that was long-lived (up to ~6 months?) and infection and trauma of the right foot which likely affected movement and may have predisposed other injury due to a gait change.
* SMA 0005 "Big Al II" or "Big Al 2": Discovered by the same team, Al II (0r 2) was discovered by the same team as Al I. It is the best-preserved specimen, assigned to *A. jimmadseni*. Like it's counterpart, it is known to have sustained many injuries.
* USNM 4734: A partial tail missing the very end, appearing to articulate with the sacrum in situ and being mostly or quite complete. Before it was realized the remains were so complete, they were put into a dump pile at the quarry and lost, save for some caudals being mutilated and others completely lost, creating indentations in the nearby sandstone. Thus, most of the specimens value was lost, but the 33 recovered vertebrae were helpful for comparisons with contemporaneous theropods like *Ceratosaurus*.
* USNM 8367: 8 caudals from Quarry Number(s) 10, 9, 8, 7, 6, 5, 4 (for the first 7 in the series) and 15 (for a caudal from the middle of the tail). They are heavy and stout, with the first 4 with centra that are higher than long. As the move back, they form a cylindrical shape, they reduce in height and they reduce at slower intervals.
* M200000 "Arkhane": A mounted Allosaurus skeleton that is advertised as a new species, according to paleontologists who briefly studied it. It is mounted at the Royal Belgium Institute of Natural Sciences in a gallery that lasted until Spring 2021. It is 8.7 meters long, "authentic" and 70% complete. The braincase seems to be missing from the mount, with much histological information retrieved from the specimen. Diet was inferred from stable isotopic analysis of the teeth, with strontium isotopic structures suggesting that the teeth are not of the same individual. A cortical core sample from the femur finds clear growth marks, with femoral length and these marks suggesting that this individual was a subadult or adult. The specimen was discovered in 1992 by Museon, a popular museum in the Netherlands from fluvial sandstones of the Morrison. However, field notes were lost, making much of the discovery data unknown.

## Gallery

### Reconstructions

**Credit: XStreamChaosOfficial on DeviantArt.****Credit: Gabriel Ugueto.****Credit: Sphenaphinae on DeviantArt.**
### Mounts

*Allosaurus* and *Camptosaurus* at the Royal Tyrrell.*Allosaurus* mount at the Royal Ontario Museum.
**Credit: Clumsystiggy on DeviantArt.**
## References

1. ↑ https://twitter.com/Fossilcrates/status/1676967686943932418
2. ↑ "3.25 Maryland, United States; 1. Arundel Clay," in Weishampel, et al. (2004). Page 556.
3. ↑ "Table 4.1," in Weishampel, et al. (2004). Page 78.
4. ↑ https://archive.org/details/g.s.paul2016theprincetonfieldguidetodinosaurs/page/n87/mode/2up
5. ↑ http://theropoddatabase.blogspot.com/2010/04/pickerings-taxa-3-metriacanthosaurus.htm
6. ↑ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4435507/
7. ↑ 7.0 7.1 https://repository.si.edu/handle/10088/10107
8. ↑ https://www.naturalsciences.be/en/museum/exhibitions-view/251/428/391
9. ↑ https://pbs.twimg.com/media/FJPAUVcXMAEn4yj?format=jpg&name=large

https://en.wikipedia.org/wiki/Allosaurus