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Saurophaganax

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"Saurophagus maximus" redirects here. For the bird, see Saurophagus.

Saurophaganax
Temporal range: Late Jurassic
Kimmeridgian
Holotype specimen, a dorsal neural arch
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: incertae sedis
Genus: †Saurophaganax
Chure, 1995
Species:
†S. maximus
Binomial name
†Saurophaganax maximus
Chure, 1995
Synonyms

Saurophaganax ("lord of lizard-eaters") is a dubious, chimeric genus of large saurischian dinosaur, possibly a sauropod, from the Late Jurassic (Kimmeridgian) Morrison Formation of Oklahoma, United States. This taxon was historically considered to represent a species of Allosaurus or very large allosaurid. However, re-examinations of the attributed specimens suggested that it is a chimera of multiple dinosaur genera, since some specimens most likely belong to a diplodocid sauropod, while the other referred specimens could be reassigned to a novel species of Allosaurus.

Discovery and naming

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A drawer of vertebrae historically assigned to Saurophaganax, Oklahoma Museum of Natural History

In 1931 and 1932, John Willis Stovall uncovered remains of a large theropod near Kenton in Cimarron County, Oklahoma in layers of the late Kimmeridgian. In 1941, these were named Saurophagus maximus by Stovall in an article by journalist Grace Ernestine Ray.[1] The generic name is derived from Greek σαυρος, sauros, "lizard", φάγειν, phagein, "to eat", with the compound meaning of "lizard eater". The specific epithet maximus means "the largest" in Latin. Because the naming article did not contain a description, the name remained a nomen nudum. In 1987, Spencer George Lucas erroneously made OMNH 4666, a tibia, the lectotype, unaware that Saurophagus was a nomen nudum.[2]

Later, it was discovered that the name Saurophagus was preoccupied: in 1831, it had already been given by William Swainson to a tyrant-flycatcher, an extant eater of taxonomically true lizards.[3] In 1995, Daniel Chure named a new genus Saurophaganax, adding Greek suffix -άναξ, anax which means "ruler", replacing the earlier informal name "Saurophagus"; he also found OMNH 4666 undiagnostic in relation to Allosaurus, so he chose OMNH 1123, a neural arch, as the holotype for Saurophaganax.[4][5] Much of the material informally named "Saurophagus maximus", namely those diagnostic elements that could be distinguished from Allosaurus, were referred to Saurophaganax maximus by Chure; they contain disarticulated bones of at least four individuals.[4]

In 2024, Danison and colleagues revised the referral of various specimens assigned to Saurophaganax maximus including the fragmentary holotype neural arch (OMNH 1123) based on their comparative analysis. They suggested that the holotype could not confidently be regarded as a theropod or sauropod, although the complex accessory laminae are more comparable to those of sauropods, especially some juvenile specimens of Apatosaurus. Some referred specimens more likely belong to diplodocids than the large Kenton 1 Quarry allosaurid. Since the holotype neural arch is so fragmentary, the researchers couldn't confidently refer it to a theropod or sauropod, so they considered Saurophaganax maximus to be a nomen dubium.[6]

Previously assigned allosaurid specimens

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Mounted skeletons showing Saurophaganax as an Allosaurus-like taxon attacking Apatosaurus sp., in Oklahoma Museum of Natural History. The latter dinosaur may be closer to the actual identity of Saurophaganax

The identification of the allosaurid elements referred to Saurophaganax was a matter of dispute. It has been described as its own genus,[4] or as a species of Allosaurus: Allosaurus maximus.[7] A review of basal tetanurans in 2004 and Carrano et al.'s comprehensive 2012 analysis of Tetanurae accepted Saurophaganax as a distinct genus.[8][9] Possible Saurophaganax material from New Mexico may clear up the status of the genus.[10] In 2019, Rauhut and colleagues noted that the definitive taxonomic placement of Saurophaganax within Allosauroidea is unstable, being recovered as a sister taxon of Metriacanthosauridae or Allosauria, or even as a basalmost carcharodontosaurian.[11] Re-evaluation of the assigned specimens in a 2024 reassessment suggested that the referred allosaurid specimens belong to a novel species of Allosaurus, named as Allosaurus anax.[6]

Paleoenvironment

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The Morrison Formation is a sequence of shallow marine and alluvial sediments which, according to radiometric dating, ranges between 156.3 million years old (Ma) at its base,[12] to 146.8 million years old at the top,[13] which places it in the late Oxfordian, Kimmeridgian, and early Tithonian stages of the Late Jurassic period. This formation is interpreted as a semiarid environment with distinct wet and dry seasons. The Morrison Basin where dinosaurs lived, stretched from New Mexico to Alberta and Saskatchewan, and was formed when the precursors to the Front Range of the Rocky Mountains started pushing up to the west. The deposits from their east-facing drainage basins were carried by streams and rivers and deposited in swampy lowlands, lakes, river channels and floodplains.[14] This formation is similar in age to the Solnhofen Limestone Formation in Germany and the Tendaguru Formation in Tanzania. The fossils known of Saurophaganax (both the possible material from New Mexico and the Oklahoma material) are known from the Brushy Basin Member, which is the latest part of the Morrison Formation, suggesting that this genus was either always uncommon or that it first appeared rather late in the Jurassic. Because of the rarity of discovered remains, not much about its behavior is known.[15]

The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs such as Barosaurus, Apatosaurus, Brontosaurus, Camarasaurus, Diplodocus, and Brachiosaurus. Dinosaurs that lived alongside Saurophaganax included the herbivorous ornithischians Camptosaurus, Dryosaurus, Stegosaurus, and Nanosaurus. Predators in this paleoenvironment included the theropods Torvosaurus, Ceratosaurus, Marshosaurus, Stokesosaurus, Ornitholestes, and[16] Allosaurus, which accounted for 70 to 75% of theropod specimens and was at the top trophic level of the Morrison food web.[17] Other vertebrates that shared this paleoenvironment included ray-finned fishes, frogs such as Eobatrachus, salamanders, turtles, sphenodonts, lizards, terrestrial and aquatic crocodylomorphs like Goniopholis, and several species of pterosaur like Kepodactylus. Early mammals were present in this region, such as Fruitafossor, docodonts, multituberculates, symmetrodonts, and triconodonts. The flora of the period has been revealed by fossils of green algae, fungi, mosses, horsetails, cycads, ginkgoes, and several families of conifers. Vegetation varied from river-lining forests of tree ferns, and ferns (gallery forests), to fern savannas with occasional trees such as the Araucaria-like conifer Brachyphyllum.[18]

References

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  1. ^ Ray, G.E., 1941, "Big for his day", Natural History 48: 36–39
  2. ^ Lucas, S.G., Mateer, N.J., Hunt, A.P., and O'Neill, F.M., 1987, "Dinosaurs, the age of the Fruitland and Kirtland Formations, and the Cretaceous-Tertiary boundary in the San Juan Basin, New Mexico", p. 35-50. In: Fassett, J.E. and Rigby, J.K., Jr. (eds.), The Cretaceous-Tertiary boundary in the San Juan and Raton Basins, New Mexico and Colorado. GSA Special Paper 209
  3. ^ W. Swainson and J. Richardson, 1831, Fauna boreali-americana, or, The zoology of the northern parts of British America: containing descriptions of the objects of natural history collected on the late northern land expeditions under command of Captain Sir John Franklin, R.N. Part 2, Birds, London, J. Murray
  4. ^ a b c Chure, Daniel J. (1995). "A reassessment of the gigantic theropod Saurophagus maximus from the Morrison Formation (Upper Jurassic) of Oklahoma, USA". In A. Sun; Y. Wang (eds.). Sixth Symposium on Mesozoic Terrestrial Ecosystems and Biota, Short Papers. Beijing: China Ocean Press. pp. 103–106.
  5. ^ Chure, D., 2000, A new species of Allosaurus from the Morrison Formation of Dinosaur National Monument (Utah-Colorado) and a revision of the theropod family Allosauridae. Ph.D. dissertation, Columbia University, pp. 1–964
  6. ^ a b Danison, Andrew; Wedel, Mathew; Barta, Daniel; Woodward, Holly; Flora, Holley; Lee, Andrew; Snively, Eric (December 21, 2024). "Chimerism in specimens referred to Saurophaganax maximus reveals a new species of Allosaurus (Dinosauria, Theropoda)". Vertebrate Anatomy Morphology Palaeontology. 12. doi:10.18435/vamp29404. ISSN 2292-1389.
  7. ^ Smith, David K. (1998). "A morphometric analysis of Allosaurus". Journal of Vertebrate Paleontology. 18 (1): 126–142. Bibcode:1998JVPal..18..126S. doi:10.1080/02724634.1998.10011039.
  8. ^ Holtz, Thomas R. Jr.; Molnar, Ralph E.; Currie, Philip J. (2004). Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (eds.). The Dinosauria (2nd ed.). Berkeley: University of California Press. pp. 71–110. ISBN 978-0-520-24209-8.
  9. ^ Carrano, Matthew T.; Benson, Roger B. J.; Sampson, Scott D. (June 1, 2012). "The phylogeny of Tetanurae (Dinosauria: Theropoda)". Journal of Systematic Palaeontology. 10 (2): 211–300. Bibcode:2012JSPal..10..211C. doi:10.1080/14772019.2011.630927. ISSN 1477-2019. S2CID 85354215.
  10. ^ Foster, John (2007). Jurassic West: the Dinosaurs of the Morrison Formation and Their World. Bloomington, Indiana:Indiana University Press. p. 117.
  11. ^ Rauhut, Oliver W. M.; Pol, Diego (December 11, 2019). "Probable basal allosauroid from the early Middle Jurassic Cañadón Asfalto Formation of Argentina highlights phylogenetic uncertainty in tetanuran theropod dinosaurs". Scientific Reports. 9 (1): 18826. doi:10.1038/s41598-019-53672-7. ISSN 2045-2322. PMC 6906444. PMID 31827108. Supplementary information
  12. ^ Trujillo, K.C.; Chamberlain, K.R.; Strickland, A. (2006). "Oxfordian U/Pb ages from SHRIMP analysis for the Upper Jurassic Morrison Formation of southeastern Wyoming with implications for biostratigraphic correlations". Geological Society of America Abstracts with Programs. 38 (6): 7.
  13. ^ Bilbey, S.A. (1998). "Cleveland-Lloyd Dinosaur Quarry – age, stratigraphy and depositional environments". In Carpenter, K.; Chure, D.; Kirkland, J.I. (eds.). The Morrison Formation: An Interdisciplinary Study. Modern Geology 22. Taylor and Francis Group. pp. 87–120. ISSN 0026-7775.
  14. ^ Russell, Dale A. (1989). An Odyssey in Time: Dinosaurs of North America. Minocqua, Wisconsin: NorthWord Press. pp. 64–70. ISBN 978-1-55971-038-1.
  15. ^ Foster, J. (2020). Jurassic West, Second Edition: The Dinosaurs of the Morrison Formation and Their World (Life of the Past). Indiana University Press. ISBN 9780253051578.
  16. ^ Foster, J. (2007). "Appendix." Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. pp. 327–329.
  17. ^ Foster, John R. (2003). Paleoecological Analysis of the Vertebrate Fauna of the Morrison Formation (Upper Jurassic), Rocky Mountain Region, U.S.A. New Mexico Museum of Natural History and Science Bulletin, 23. Albuquerque, New Mexico: New Mexico Museum of Natural History and Science. p. 29.
  18. ^ Carpenter, Kenneth (2006). "Biggest of the big: a critical re-evaluation of the mega-sauropod Amphicoelias fragillimus". 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. pp. 131–138.

Sources

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Wikimedia Commons has media related to Saurophaganax.
Wikispecies has information related to Saurophaganax.
  • Dixon, Dougal. The World Encyclopedia of Dinosaurs and Prehistoric Creatures.
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