Monday, April 19, 2021

Astrodon: Beast of the Week

 Today we will be checking out a dinosaur with historical significance, Astrodon johnstoni!

Astrodon was a plant-eating sauropod dinosaur roamed what is now eastern half of United States, during the early Cretaceous period, about 112 million years ago.  Adults would have measured between 50 to 60 feet (15 to 18 meters) long from snout to tail.  The genus name translates to "star tooth" and the species name honors Christopher Johnson, the dentist and professor who studied the first known fossils of this dinosaur back in the 1800s.  

Watercolor life reconstruction of Astrodon johnstoni by Christopher DiPiazza

Astrodon was one of the first fossil dinosaurs to be discovered and named in North America.  It was initially known from a few teeth discovered and studied in Maryland, where Professor Christopher Johnson, at the Baltimore Dental College, noticed they had a star-shaped pattern in the cross section, and thus Astrodon earned its genus name.  Over the years more fossils from Astrodon would be discovered in the eastern half of the United States, including many bones from juvenile individuals.  

Original Astrodon tooth currently at the Yale Peabody Museum.  Photo courtesy of Kenneth Carpenter.

By comparing its bones to other sauropods, it is currently thought Astrodon was a kind of macronarian, which is a clade of sauropod dinosaurs that had boxy skulls with large nasal cavities. In fact, the term, macronarian, translates to "big nose" based on this common feature.  Another example of a macronarian sauropod is the larger and very famous, Brachiosaurus.  

Juvenile Astrodon bones on display at the Maryland Science Center.

Astrodon had somewhat shorter vertebra in its neck when compared to some of its relatives, like Brachiosaurus.  Based on the fact that most sauropod dinosaurs had about the same number of neck vertebrae, it could be assumed that Astrodon's neck would have been proportionally shorter.  

Astrodon's teeth were spoon-shaped and therefore ideal for scraping leaves off of branches and clipping softer foliage.  Like all sauropods, Astrodon wouldn't have had any teeth in the back of its mouth for chewing.  Rather it would have swallowed plant material whole and possibly ingested small rocks, called gastroliths, to aid in mechanical digestion within the stomach.  

When alive, Astrodon would have shared its environment with other plant-eating dinosaurs, like Tenontosaurus and its larger sauropod relative, Sauroposeidon.  Meat-eating dinosaurs from the same area include Deinonychus, which may have hunted young Astrodon, and the giant Acrocanthosaurus, which very likely would have been able to hunt adults.

References

Carpenter, Kenneth; Tidwell, Virginia (2005). "Reassessment of the Early Cretaceous sauropod Astrodon johnstoni Leidy 1865 (Titanosauriformes)". In Kenneth Carpenter; Virginia Tidswell (eds.). Thunder Lizards: The Sauropodomorph Dinosaurs Indiana University Press. 

d'Emic, Michael D. (2013). "Revision of the sauropod dinosaurs of the Lower Cretaceous Trinity Group, southern USA, with the description of a new genus". Journal of Systematic Palaeontology11 (6): 707–726.

P. Larkin. 1910. The occurrence of a sauropod dinosaur in the Trinity Cretaceous of Oklahoma. Journal of Geology 17:93–98

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