East Coast Vs West Coast Cretaceous Dinosaurs of North America - Why the Fossil Preservation Difference?
When one thinks about dinosaur fossils, Western North America usually comes to mind, and it's no wonder. The Western United States is world famous for its dinosaur fossils in quantity, quality, and diversity in all three dinosaur ages. Here, nearly complete specimens of Coelophysis from the Late Triassic are found. The Jurassic Morrison Formation preserves numerous Stegosaurs, a wide range of Sauropods, and the famous theropod, Allosaurus.
It gets even better in the Cretaceous, where layers such as the Dinosaur Park and Hell Creek Formations contain over 30 genera of dinosaurs! Ceratopsids and Hadrosaurs are more diverse here than anywhere else in the world. A plethora of theropods have been found, from the smaller dromaeosaurids (the feathered raptors) to the larger Tyrannosaurs. There are numerous nearly complete specimens and even "mummified" specimens that have swaths of skin impressions. The list goes on and on!
The Eastern United States is a bit different. From elusive Triassic footprints in the Mid-Atlantic to fragmented Early Jurassic bones and prints Nova Scotia and New England, Eastern North America has never cooperated in giving up its dinosaur secrets. In fact, the Eastern dinosaur record of the late Jurassic does not exist. Also, the only Early Cretaceous dinosaur fossils come from one single formation, the Arundel Clay in Maryland and D.C.
This frustrating and fragmented record of Dinosaurs in the East continues until the bitter end; the late Cretaceous. One publication describes it best; "Eastern North America is a 'dark continent' of Late Cretaceous dinosaur paleontology" (Carr et al, 2005). Late Cretaceous fossils overwhelmingly consist of isolated and fragmented bones and teeth… Usually of poor preservation. Why are dinosaur fossils, particularly, Late Cretaceous fossils, so different in the East than the West?
in the Cretaceous
To understand why the East and West are very different, we must look at the Paleogeography and preservation of fossils during the late Cretaceous. By the Late Cretaceous the Western Interior Seaway had split North America into two "island continents" that we call Laramidia and Appalachia. At this point in time, the dinosaurs were trapped on their respective mini continents, isolated and free to evolve differently.
Laramidia - the Western Island Continent
In Laramidia, the Rocky Mountains were uplifting, creating lots of sediment that washed into HUGE alluvial plains along the Western Interior Seaway. In the Late Cretaceous, this was an area with high rates of sediment deposition, which was ideal for fossil formation. Dead land animals (Dinosaurs) would wash downstream and become buried in sediments. Also, the Western Interior Seaway coast was not as rough as the Atlantic Ocean coast. As a result, many of the formations that contain dinosaurs are either alluvial freshwater deposits or near shore deposits, but not open marine deposits. Today, Laramidia, is an area of erosion, like the "badlands." Fossil bearing layers are naturally eroding from the ground. It's a paleontologists dream.
Badlands in Montana - Cretaceous Dinosaur Formations are Exposed.
Appalachia - The Eastern Continent
On the other side of the Western Interior Seaway was the island continent of Appalachia. It was very different than Laramidia. By the late Cretaceous, the now ancient Appalachian Mountains were eroding away (and would re-uplift at a later date). Areas of erosion are places that lose sediments, not build them up. This makes fossil formation almost impossible. The only areas in the Cretaceous that were building up sediments were narrow flood plains very close to the Atlantic Ocean. Here, carcasses could sometimes float down estuaries and out to sea, being battered by the Ocean and nibbled on by sharks. Little pieces of the animals would fall to the ocean bottom in what are called lag deposits. These lag deposits of bits and pieces of animals that accumulate offshore would eventually be buried by sediments. As a result, almost all formations that contain dinosaurs are lag deposits in marine environments. These deposits are great for fish fossils, but not ideal for dinosaur fossils.
To make things worse, these tiny lag deposits, that might contain bits of dinosaurs, are hard to get to because, today, much of Appalachia is a place of deposition. Vegetation and soil layers are building up, so fossil bearing rock units are not eroding. The main areas where fossil bearing units turn up are road cuts, mines, and riverbanks. These areas are tiny compared to the 1000's of miles of badlands out west. It's a paleontologists nightmare.
An isolated Hadrosaurus tooth sits in the upper left of the screen mixed with other fossil fragments.
Progress on East Coast Dinosaurs
Despite the uphill battle paleontologists have studying dinosaurs of Appalachia, progress has been made. From the Late Cretaceous, at least two Tyrannosaurids have been identified, Dryptosaurus, and Appalachiosaurus. There have been at least three Hadrosaurids identified, Hadrosaurus foulkii, Lophorhonthon, and the newly discovered Eotrachodon orientalis from Alabama (discovered by amateur fossil hunters). The first Ceratopsid from Appalachia has also recently been discovered; it's a Leptoceratopsid from North Carolina. Also fragments of an Ornithomomus (Bird Mimmic) and various Nodosaurid (Armored Dinosaurs) fragments have been found.
Although the diversity is clearly lower than Laramidia, these dinosaurs have been found to be uniquely adapted to the Appalachian environment. I'm sure in the future, many more dinosaurs will be discovered from these fragmentary deposits of bones and teeth on the East Coast
Small worn Dinosaur tail vertebra from the Eastern United States Cretaceous.
Prieto-Márquez, A., G. M. Erickson, and J. A. Ebersole., (2016) A primitive hadrosaurid from southeastern North America and the origin and early evolution of 'duck-billed' dinosaurs. Journal of Vertebrate Paleontology. 01/2016.
King, D.T., Jr., and Jones E.D., (1997) Late Cretaceous dinosaurs of the southeastern United States. Gulf Coast Association of Geological Societies Transactions, v. 47, p. 263-269.
Longrich. N. R., (2016) A ceratopsian dinosaur from the Late Cretaceous of eastern North America, and implications for dinosaur biogeography. Cretaceous Research, vol. 57, pp. 199-207; doi: 10.1016/j.cretres.2015.08.004
Schwimmer, D.R., (1997) Late Cretaceous dinosaurs in eastern USA: A taphonomic and biogeographic model of occurences. In: Wolberg, D.L., Stump, E., and Rosenberg, G.D. (eds). Dinofest International. Academy of Natural Sciences, Philadelphia. Pp. 203-211.
Weishampel, D.B., (2006) Another look at the dinosaurs of the East Coast of North America. III Jornadas Internacionales sobre Paleontología de Dinosaurios y su Entorno, Salas de los Infantes, Burgos, Spain. Colectivo Arqueológico-Paleontológico Salense Actas, pp 129-168.
Hadrosaurus foulkii, the first "nearly complete" dinosaur ever found. From Haddenfield, New Jersey (Appalachia).
A Hadrosaur tooth found in a lag deposit on the East Coast.
Tyrannosaurid dinosaur fossil tooth found in a lag deposit on the East Coast. Notice the shark tooth to the lower left.
Dinosaur Tooth from the Eastern United States Cretaceous.
Dinosaur Teeth from the Eastern United States Cretaceous.
Recommended Books on East Coast Dinosaurs:
Dinosaurs of the East Coast
by David B. Weishampel and Luther Young
This is an easy read about the Dinosaurs of Appalachia (Eastern North America). It goes through all the Dinosaur time periods from the Triassic to the late Cretaceous. It also describes the various dinosaurs found along Eastern North America. I highly recommend this book for anyone who likes Dinosaurs and lives in the Eastern United States.
When Dinosaurs Roamed New Jersey
by William B. Gallagher, 1997
This is a great book to learn about New Jersey Paleontology and the geologic history of New Jersey. It is very accurate, as the author is a scholar in the field of paleontology. There is even a section that describes fossil hunting sites in New Jersey.
Dinosaurs: A Concise Natural History
by David E. Fastovsky and David B. Weishampel
The reason why I love this book is that it is not overly simplified, yet not overly technical. It's hard to find a medium between a college level book and a simple 8th grade reading level dinosaur book. This one is it. It discusses many aspects of the dinosaurs from a biological perspective and includes numerous pictures and diagrams. Fastovsky and Weishampel are two leading dinosaur paleontologists, and they have done a wonderful job creating this book! Follow the link and you can browse through many sample pages of the book.