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Astrodon is a genus of large herbivorous sauropod
/ref> It lived in what is now the eastern United States during the Early Cretaceous period, and fossils have been found in the Arundel Formation, which has been dated through to the Albian about 112 to 110 million years ago.
In 1888, O. C. Marsh named some bones from the Arundel found near Muirkirk, Maryland Pleurocoelus nanus and P. altus. However, in 1903 John Bell Hatcher, taking into account the similarity of the teeth of Astrodon johnstoni and the teeth from the Arundel Formation referred to Pleurocoelus nanus, argued that the latter represents the same species as the former and that the name Astrodon therefore had priority. In 1921 Charles W. Gilmore agreed that the genus Pleurocoelus is a junior synonym of Astrodon, but at the same time kept P. nanus and P. altus as separate species of Astrodon. Other species at one time assigned to the genus include Astrodon valdensisW.E. Swinton, 1936, "The dinosaurs of the Isle of Wight", Proceedings of the Geologists' Association 47(3): 204–220 and Astrodon pussilus.Lapparent, A. F. de, & Zbyszewski, G., 1957, Les Dinosauriens du Portugal, Mémoires des Services Geologiques du Portugal. Nouvelle série, numéro 2, 63 pp In 1962 R. F. Kingham assigned Brachiosaurus, including all its species, to Astrodon as a subgenus.Kingham, R. F., 1962, "Studies of the sauropod dinosaur Astrodon Leidy", Proceedings of the Washington Junior Academy of Sciences, 1: 38–44 Carpenter and Tidwell (2005) accepted Hatcher's argument that there is only one species of sauropod dinosaur known from the Arundel Formation and that Astrodon johnstoni is the senior synonym of Pleurocoelus nanus (as well as P. altus) in the first in-depth description of this dinosaur. The majority of the bones of Astrodon are of juveniles, and Carpenter and Tidwell considered the two species named by Marsh, P. nanus and P. altus, as different growth stages of Astrodon johnstoni.
However, other authors did not find the argument in favor of the synonymization of Astrodon and Pleurocoelus so convincing. According to Peter Rose (2007) it has not been demonstrated that either the teeth of Astrodon johnstoni or those attributed to Pleurocoelus are "morphologically diagnostic among titanosauriforms", which limits their utility when it comes to distinguishing them from the teeth of other taxa. The type series of Pleurocoelus nanus and P. altus (four vertebrae and two hindlimbs bones, respectively) cannot be directly compared to the teeth from the type series of Astrodon, so any comparison has to be conducted based on the referred specimens of Pleurocoelus. These, however, are all isolated bones from the Arundel Formation, which themselves were referred to Pleurocoelus only based "on proximity of the localities and the size of the bones". Rose concludes that, as Astrodon is not based on the diagnostic material, "new discoveries should not be aligned with that genus" and that "the argument to synonymize the two taxa, Astrodon and Pleurocoelus, seems unfounded". The type material of Pleurocoelus may not be diagnostic as well, according to the author. A similar argument was made by Michael D. d'Emic (2013). The author did not find any diagnostic features of the type material of Astrodon johnstoni, Pleurocoelus nanus and P. altus and considered the three taxa to be Nomen dubium; according to the author there is no direct evidence that any sauropod bones from the Arundel Formation other than their type series can be referred to these taxa. D'Emic also stated that the exact provenance of the bones from the type series of Pleurocoelus nanus is uncertain and thus "these bones could represent a chimera of individuals or taxa". The author also commented on the diagnosis of Astrodon johnstoni proposed by Carpenter and Tidwell (which was based on all of the sauropod material from the Arundel Formation, not only on the teeth from the type series); he claimed that most of the supposed Autapomorphy of this taxon "are indistinguishable compared to other sauropods such as Camarasaurus (...) and/or are related to the juvenile nature of the material".
Fossil material assigned to Astrodon has also been found in two Oklahoma localities of the Antlers Formation, which stretches from southwest Arkansas through southeastern Oklahoma and into northeastern Texas.P. Larkin. 1910. The occurrence of a sauropod dinosaur in the Trinity Cretaceous of Oklahoma. Journal of Geology 17:93–98R. L. Cifelli. 1997. Oklahoma Geology Notes 57(1):4–17 This geological formation has not been dated radiometrically. Scientists have used biostratigraphic data and the fact that it shares several of the same genera as the Trinity Group of Texas, to surmise that this formation was laid down during the Albian stage of the Early Cretaceous Period, approximately 110 mya.Wedel, M. J., and Cifelli, R. L. 2005. Sauroposeidon: Oklahoma’s native giant. Oklahoma Geology Notes 65 (2):40–57. The Papo Seco Formation of the Lusitanian Basin in Portugal also provided fossils referred to Astrodon.
In prehistoric Oklahoma, Astrodon lived alongside other dinosaurs, such as the sauropod Sauroposeidon proteles, the dromaeosaurid Deinonychus antirrhopus and the carnosaur Acrocanthosaurus atokensis.Weishampel, David B.; Barrett, Paul M.; Coria, Rodolfo A.; Le Loeuff, Jean; Xu Xing; Zhao Xijin; Sahni, Ashok; Gomani, Elizabeth, M.P.; and Noto, Christopher R. (2004). "Dinosaur Distribution", in The Dinosauria (2nd), p. 264.Brinkman, Daniel L.; Cifelli, Richard L.; & Czaplewski, Nicholas J. (1998). "First occurrence of Deinonychus antirrhopus (Dinosauria: Theropoda) from the Antlers Formation (Lower Cretaceous: Aptian – Albian) of Oklahoma". Oklahoma Geological Survey Bulletin 146: 1–27. The most common dinosaur in the paleoenvironment preserved in the Antlers Formation is the ornithopod Tenontosaurus. Other vertebrates present at the time of Astrodon included the amphibian Albanerpeton arthridion, the reptiles Atokasaurus metarsiodon and Ptilotodon wilsoni, the crurotarsan reptile Bernissartia, the chondrichthyans fish Hybodus buderi and Lissodus anitae, the actinopterygians fish Gyronchus dumblei, the crocodilian Goniopholis, and the turtles Glyptops and Naomichelys.Nydam, R. L. and R. L. Cifelli. 2002a. Lizards from the Lower Cretaceous (Aptian–Albian) Antlers and Cloverly formations. Journal of Vertebrate Paleontology. 22:286–298.Cifelli, R. Gardner, J. D., Nydam, R. L., and Brinkman, D. L. 1999. Additions to the vertebrate fauna of the Antlers Formation (Lower Cretaceous), southeastern Oklahoma. Oklahoma Geology Notes 57:124–131. Possible indeterminate bird remains are also known from this formation. The fossil evidence suggests that the gar Lepisosteus was the most common vertebrate in this region. The early mammals known from this region include Atokatherium boreni and Paracimexomys crossi.Kielan-Jarorowska, Z., and Cifelli, R. L. 2001. Primitive boreosphenidan mammal (?Deltatheroida) from the Early Cretaceous of Oklahoma. Acta Palaeontologica Polonica 46: 377–391.
A life-sized Astrodon model (featuring a wound on its left rear leg) is displayed in the Terror of the South exhibit on the third floor of the North Carolina Museum of Natural Sciences. Another Astrodon model is also on display at the Maryland Science Center in Baltimore, Maryland.
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