*SPECIAL NOTE* - After being described in 1998, Eobrontosaurus has since been found to be a synonym of Brontosaurus. This page remains online for archive purposes only.


Name: Eobrontosaurus ‭(‬Dawn thunder lizard‭)‬.
Phonetic: E-owe-bron-toe-sore-us.
Named By: Robert T.‭ ‬Bakker‭ ‬-‭ ‬1998.
Synonyms: Apatosaurus yahnahpin.
Classification: Chordata,‭ ‬Reptilia,‭ ‬Dinosauria,‭ ‬Saurischia,‭ ‬Sauropodomorpha,‭ ‬Sauropoda,‭ ‬Diplodocidae,‭ ‬Apatosaurinae.
Species: E.‭ ‬yahnahpin‭ (‬type‭)‬.
Diet: Herbivore.
Size: 21‭ ‬meters long.
Known locations: USA,‭ ‬Wyoming‭ ‬-‭ ‬Morrison Formation.
Time period: Kimmeridgian to Tithonian of the Jurassic.
Fossil representation: Almost complete post cranial skeleton as well as additional fragmentary remains.

       Eobrontosaurus was initially described as a new species of Apatosaurus called A.‭ ‬yahnahpin by James Filla and Patrick Redman in‭ ‬1994.‭ ‬However when the material was re-examined by Robert Bakker in‭ ‬1998‭ ‬he found that it represented a similar but more primitive sauropod dinosaur to Apatosaurus.‭ ‬The second species of Apatosaurus,‭ ‬A.‭ ‬excelsus,‭ ‬originally went by the name of Brontosaurus excelsus until it was declared to be a synonym to the earlier Apatosaurus by Elmer S.‭ ‬Riggs in‭ ‬1903.‭ ‬This is a clearly definable species to the Apatosaurus type species of A.‭ ‬ajax,‭ ‬and in the‭ ‬1990s Bakker suggested that A.‭ ‬excelsus is different enough to resurrect Brontosaurus as its own genus,‭ ‬although this was largely refuted by other palaeontologists and to this day Brontosaurus is still a synonym to Apatosaurus.‭ ‬This is in part why Bakkar chose the‭ ‬name Eobrontosaurus instead of Eoapatosaurus,‭ ‬although it does also help prevent confusion with the Apatosaurus genus.
       Suggestions have been made that Eobrontosaurus may actually be a specimen of Camarasaurus,‭ ‬although most palaeontologists do not accept this idea.

Further reading
- Apatosaurus yahnahpin: a preliminary description of a new species of diplodocid dinosaur from the Late Jurassic Morrison Formation (Kimmeridgian-Portlandian) and Cloverly Formation (Aptian-Albian) of the western United States. - Mémoires de la Société Géologique de France (Nouvelle Série) 139 (Ecosystèmes Continentaux du Mésozoique): 87-93. - J. A. Filla & P. D. Redman - 1994.
- Dinosaur mid-life crisis: the Jurassic-Cretaceous transition in Wyoming and Colorado. - Lower and Middle Cretaceous Terrestrial Ecosystems, New Mexico Museum of Natural History and Science Bulletin 14:67-77 - R. T. Bakker - 1998.


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