A size comparison of the theropod dinosaur genus Allosaurus. Showing four described species and some of the specimens that have been referred to each of these species; the type species A. fragilis, A. jimmadseni, A. europaeus, and a specimen possibly referable to A. anax.

• The holotype of Allosaurus fragilis YPM 1930 is known from partial remains and has been considered undiagnostic. A more complete specimen from the same quarry, AMNH 4734, was eventually proposed as a neotype for the species.^[1][2]

DINO 2560 is a very complete specimen, consisting of most of the front half of the individual, that is usually referred to Allosaurus fragilis. However, some researchers have suggested two Allosaurus morphs exist, one shorter snouted with pointer lacrimal horns and another with a longer snout and more rounded horns. The later morph has been considered its own species as A. atrox by some researchers, with DINO 2560 as a member. Other researchers have put down the differences as individual variation. The average size of adult Allosaurus fragilis specimens are estimated at ~8.5 m ^[3].

A large Allosaurus specimen, AMNH 680, known from partial remains, has been referred to A. fragilis. This specimen preserves a femur just over 1 m long, suggesting a very large individual, possibly ~9.7 m or so in length.

• In 2020, Allosaurus jimmadseni was described with DINO 11541 designated the holotype, SMA 0005 and MOR 693 were referred to the species. A notable difference in this species is a straighter jugal bone compared to the more downward and rounded jugals in other Allosaurus species.^[4]

• Allosaurus europaeus was described based on an incomplete specimen from Portugal, ML 415, consisting of a partial skull, ribs and a few cervical vertebrae;^[5] Excepting known parts of the skull, the silhouette above is partially hypothetical and should be considered approximate.

• The genus Saurophaganax was described based on fossils from the Kenton Member of the Morrison Formation. The holotype was a large dorsal neural arch with other material assigned as paratypes, and additional material was referred to the genus. This material suggested a very large allosaurid and probably represented a few individuals. Saurophaganax maximus was considered a species of Allosaurus by some researchers (Allosaurus maximus).^[6][7] However, Danison et al. (2024) argued that the type specimen of Saurophaganax was potentially a sauropod, suggesting the genus was chimeric. They created the species Allosaurus anax and referred allosaurid material initially included in Saurophaganax. In this image, the silhouette represents the possible size of OMNH 1708, a large 1.135 m femur from the quarry. This femur might belong to the same individual as another femur from the quarry, OMNH 2114. Danison et al. (2024) referred these femora to A. sp. but also suggested that they probably are A. anax. The remains of this species are fragmentary so the silhouette should be considered approximate.

Artist Notes

• The holotype of A. anax is a postorbital, OMNH 1771. It is difficult to accurately scale up from small skull bones, so it has not been included in the image above.

• Other fragmentary material suggests very large allosaurs existed. A fragmentary genus Epanterias has been estimated 12 to 13 m.^[8][9][10] Epanterias is sometimes considered a specimen of 'Allosaurus.

• Historically, AMNH 680 has been suggested to belong to A. fragilis, such as in Chure's (2000) PHD thesis.[2] However, the specimen comes from Bone Cabin Quarry, Salt Wash Member, where Chure & Loewen (2020) referred specimens to A. jimmadseni. Unfortunately, they do not specifically mention this specimen's referral in the paper. Danison et al. (2024) mention this specimen as being 'referred to A. fragilis, so for the time being it is included there. It might be possible that future research might question this specimen's referral to A. fragilis.

• Silhouettes are based on Allosaurus skeletal reconstructions by Scott Hartman [3] and Henrique Paes [4], used with permission. The author requires that Scott Hartman, Henrique Paes and steveoc 86 at Wikimedia Commons get attribution.

• AMNH 4734, DINO 2560 (UUVP 6000), and MOR 693 are scaled using the scale bars in their respective reconstructions. AMNH 680 is not particularly complete and has been scaled to femur length using DINO 2560 as a guide. DINO 11541 is based on figures 3 and 4 in Chure et al. (2020). Allosaurus europaeus, ML 415, is scaled to ~7 m based on an estimate by Greg Paul,^[7] the skull is based on figure 16 in Chure et al. (2020). SMA 0005 silhouette based on Fig 1 in Foth et al. (2013) with some details from images of the mount online, scaled to a skull length of 79 cm.^[11][12] Allosaurus anax? OMNH 1708 is scaled up primarily from A. fragilis DINO 2560 using the femur length as a guide.

• Humans are scaled to 170 cm (5 ft 7 in) and 160 cm (5 ft 3 in).

NOTE: I often update my images. If you want to post any of my images on a website, please (if possible) don’t host/save it to the website server. I’d prefer it if the image's Wikimedia URL is used or a link to the original provided. Thanks.