Allosaurus ( Saurophaganax ) maximus skeletal By Franoys Watch

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Allosaurus maximus is one of the larger theropods of the Morrison formation, potentially tied with Allosaurus fragilis and Torvosaurus tanneri (=Edmarka rex). Of the at least 4 individuals present in the quarry as stated by Chure (2000),two are of very large and similar size, with the third being sligthly smaller and the fourth substantially smaller. The larger individuals were used for the composite, the smaller ones consist of cervical and dorsal centra and pedal phalanges.



The size of the humerus catalogued as OMNH 1935 has gotten some attention, due to the scalebar in Chure 1995 yielding a maximum length of 545 mm. However the photograph with the scalebar in Chure 2000 yields only 450 mm as the maximum length of the bone. In an attempt to avoid the scalebar conflict, Smith 1998 provies an humerus length of 480 mm which is highly coherent with the size that the rest of the larger elements yield and was used for this reconstruction.



In Chure 1995 the potential body length attainable by the taxon was stated to be 14 m, taking from granted that a 825 mm femur belongs to a 12 m Allosaurus. However, complete skeletons of the genus show that this is implausible, as said femur length correlates with a body length between 7.5 and 8 m. USNM 4734 is 7.4 m long with a 75-85 cm femur(varies depending on the source), and DINO 2560 is 8 m long with a 88 cm femur. Therefore the large femur of Saurophaganax (113.5 cm) yields between 10.3 and 11.2 m, coherent with the size of this composite. The size of the composite is therefore most coherent with the estimate by Gregory S.Paul (10.5 m, Priceton field guide to dinosaurs second edition, 2016).



Of the autapomorphies suggested for Saurophaganax, only two vertebral characters are considered valid (Carrano 2012). The apendicular skeleton is indistinguishable from Allosaurus fragilis (Smith 1998). Therefore at least the generic separation is not guaranteed.



A.maximus is more recent than most of the allosaurid specimens from the Morrison formation, having been found only 12 m below the top of the formation. Remains of Camarasaurus, Apatosaurus, Camptosaurus, Stegosaurus and Ceratosaurus were found in the same quarry.



References:



Chure, D. J. (1995). A reassessment of the gigantic theropod Saurophagus maximus from the Morrison Formation (Upper Jurassic) of Oklahoma, USA. In 6th Symposium on Mesozoic terrestrial ecosystems and biotas, short papers. Edited by A.-L. Sun and Y.-Q. Wang. China Ocean Press, Beijing, China (pp. 103-106).



Chure, D. J. (2000). A new species of Allosaurus from the Morrison Formation of Dinosaur National Monument (UT-CO) and a revision of the theropod family Allosauridae. Ph. D. dissertation, Columbia University.



Madsen Jr, J. H. (1976). Allosaurus fragilis: a revised osteology. Utah Geological and Mining Survey Bulletin, 109, 1-163.



Gilmore, Charles W. (1920). "Osteology of the carnivorous dinosauria in the United States National Museum, with special reference to the genera Antrodemus (Allosaurus) and Ceratosaurus". Bulletin of the United States National Museum. 110: 1–159. doi:10.5479/si.03629236.110.i.

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Published : Dec 29, 2018