Allosaurus anax
- 演化之聲
- 6 days ago
- 2 min read
Age
Jurassic（Tithonian）
150 Ma
Taxonomy
Kingdom：Animalia
Phylum：Chordata
Class：Reptilia
Order：Saurischia
Family：Allosauridae
Genus：Allosaurus
Species：Allosaurus anax
Morphological description
Allosaurus anax was a gigantic species of allosaur that may have exceeded 10 meters in length and weighed approximately 3 to 4 metric tons. Its postorbital bone lacks rough ornamentation, while the lateral ridge is absent or reduced. The dorsal vertebrae are hourglass-shaped and possess pneumatic openings. The proximal medial side of the fibula bears three shallow depressions, and some cervical vertebrae possess nearly vertical postzygapophyses.
Etymology
The genus name Allosaurus is derived from the Greek words allos (“strange” or “different”) and sauros (“lizard”), referring to the unusual vertebral morphology that differed from other dinosaurs known at the time of its discovery.
The species name anax comes from the Ancient Greek word ἄναξ, meaning “king” or “lord,” alluding to the fact that its fossils were originally assigned to Saurophaganax.
Biological interpretation
Allosaurus anax is the fourth recognized species within the genus Allosaurus. The holotype specimen, OMNH 1771, consists of a postorbital bone. The specimen was originally referred to Saurophaganax, which had traditionally been regarded as a distinct genus within Allosauridae. However, a later study determined that the holotype material of Saurophaganax actually belonged to a sauropod dinosaur. As a result, the remaining specimens previously referred to Saurophaganax were redescribed and reassigned to the new species Allosaurus anax. The species epithet anax was retained from the suffix of Saurophaganax, reflecting the original assignment of these fossils.
Its fossils were discovered from the Morrison Formation of the United States, and it lived during the Late Jurassic. Its temporal and geographic distribution overlapped with two other members of the genus, Allosaurus fragilis and Allosaurus jimmadseni. However, most fossils of A. anax have been recovered from younger strata within the Morrison Formation, suggesting that it may have lived somewhat later than the other species, although this pattern could also result from sampling bias caused by the rarity of its fossils.
Allosaurus anax was exceptionally large, exceeding the size of other apex predators from the same formation. Estimates based on femoral measurements suggest that it outweighed Allosaurus fragilis by more than one metric ton and may even have been larger than the Cretaceous giant theropod Acrocanthosaurus. Furthermore, these estimates were calculated using the most conservative minimum femoral circumference values, meaning that the actual body size of A. anax may have been even greater.
The substantial body-size differences among species of Allosaurus may represent an ecological evolutionary strategy, in which different species occupied separate ecological niches based on body size and fulfilled different roles within the ecosystem. However, this hypothesis still requires further analytical and comparative research for verification.
Due to the rarity and fragmentary nature of its fossils, its behavior and feeding ecology remain poorly understood. Additional fossil discoveries will be necessary to reveal more information about this species.
（Author: Bai Leng）
Reference
Danison, A., Wedel, M., Barta, D., Woodward, H., Flora, H., Lee, A., Snively, E. (2024). Chimerism in specimens referred to Saurophaganax maximus reveals a new species of Allosaurus (Dinosauria, Theropoda). Vertebrate Anatomy Morphology Palaeontology.
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