Appalachia (Mesozoic)

For other uses of Appalachia, see Appalachia (disambiguation).

Appalachia, circa 100 mya

In the Mesozoic Era (252 to 66 million years ago) Appalachia, named for the Appalachian Mountains, was an island land mass separated from Laramidia to the west by the Western Interior Seaway. The seaway eventually shrank, divided across the Dakotas, and retreated towards the Gulf of Mexico and the Hudson Bay. This left the island masses joined in the continent of North America as the Rocky Mountains rose.

From the Turonian age of the Late Cretaceous to the very beginning of the Paleocene, Appalachia was separated from the rest of North America. Because of this, its fauna was isolated, and developed very differently from the tyrannosaur, ceratopsian and ankylosaur dominated fauna of the western part of North America, the geologist's "Laramidia". Due to numerous undiscovered fossiliferous deposits and due the fact that half of Appalachia's fossil formations being destroyed by the Pleistocene ice age, little is known about Appalachia, with exception of plant life. In addition, due to a lack of interest in Appalachia, many fossils that have been found in Appalachia lie unstudied and remain in the inaccurate genera to which they were assigned in the days of E.D. Cope and O.C. Marsh. Many of the various fossil formations not destroyed by the Pleistocene ice age still remain elusive to the field of paleontological study. However, some fossil sites, such as the Navesink Formation, Ellisdale Fossil Site, Mooreville Chalk Formation, Demopolis Chalk Formation, Black Creek Group and the Niobrara Formation have given us a glimpse into this forgotten world of paleontology.

Fauna

Dinosaurs

In Late Cretaceous North America, the dominant predators were the tyrannosaurs, huge predatory theropods with proportionately massive heads built for ripping flesh from their prey. Tyrannosaurs were the dominant predators in Appalachia too, but rather than the massive Tyrannosaurinae, like Gorgosaurus and Albertosaurus, the smaller dryptosaurs were the top predators of Appalachia. Rather than developing the huge heads and massive bodies of their kin, dryptosaurs had more in common with the basal tyrannosaurs like Dilong and Eotyrannus, having long arms with three fingers, a more lithe skull and body, and were not as large as the largest tyrannosaurids. Three genera of Appalachian tyrannosaurs are known, Dryptosaurus, Diplotomodon and Appalachiosaurus while other indeterminate fossils lie scattered throughout most of the southern United States like Georgia, North Carolina, and South Carolina. These fossiled teeth possibly belong to a species of Appalachiosaurs or an undescribed species of a new tyrannosaur. Various ornithomimid bones, such as Coelosaurus, have also been reported from Appalachia from Mississippi, Alabama, Georgia and as far north in states like Maryland, New Jersey and Delaware, but it is now believed that some of these are the bones of juvenile dryptosaurs while others belong to various undescribed species of ornithomimids. The case of Arkansaurus is such an example of indeterminate fossils being discovered to be dating back to the Early Cretaceous. Indeterminate dromeaosaurine fossils and teeth, mostly matching those of Velociraptor and Saurornitholestes, have also been unearthed in Appalachia as well; mostly in the southern states like North Carolina, South Carolina, Alabama, Mississippi and Georgia.

Another common group of Appalachian dinosaurs were the Hadrosauroidea. While the fossil record shows a staggering variety of hadrosaur forms in Laramidia, hadrosaur remains for Appalachia show less diversity due to the relative uncommon number of fossil beds. However, many hadrosaurs are known from Appalachia, such as Claosaurus, Eotrachodon, Lophorhothon, Hypsibema, its subspecies Hypsibema missouriensis, and Hadrosaurus. These hadrosaurs from Appalachia seem to be closely related to the crestless hadrosaurs of Laramidia like Gryposaurus and Edmontosaurus, despite the fact that they are not considered to be saurolophines. Claosaurus is known from a specimen which floated into the Interior Seaway and was found in Kansas, might also be from Appalachia, since it was found closer to the Appalachia side of the seaway and is unknown from Western North America. Hypsibema, over fifty feet long, was one of the largest eastern hadrosaurs, outgrowing some of the more larger and more derived western hadrosaurs like Lambeosaurus and Saurolophus. The genus likely took the environmental niche occupied by large sauropods in other areas, possibly grown to colossal sizes to that of Shantungosaurus. Indeterminate lambeosaurinae remains, mostly similar to Corythosaurus, have been reported from New Jersey's Navesink Formation and Nova Scotia, Canada. It cannot yet be explained how lambeosaurines might have reached Appalachia though some have theorized that a land bridge must have formed some time during the Campanian.

The nodosaurids, a group of large, herbivorous armored dinosaurs resembling armadillos, are another testament to Appalachia's difference from Laramidia. By the latest Cretaceous, nodosaurids were scarce in western North America, limited to forms like Edmontonia, Denversaurus and Panoplosaurus; perhaps due to competition from the ankylosauridae. Nodosaurid scutes have been commonly found in eastern North America. Often the findings are not diagnostic enough to identify the species, but the remains attest to a greater number of these armored dinosaurs in Appalachia. Multiple specimens have been earthed in Alabama, Mississippi, Delaware, Maryland and New Jersey, possibly belonging to a multitude of different species. Five possible and best known examples of Appalachian nodosaurids, from both the early and late Cretaceous period, include Priconodon, Propanoplosaurus, Niobrarasaurus, Silvisaurus and possibly Hierosaurus, though it should be noted that its validity is disputed. Just like the Claosaurus specimen, it is possible that the specimens of Niobrarasaurus, Silvisaurus and Hierosaurus floated into the Interior Seaway from the east, since these two species of nodosaurids were discovered in the famous chalk formations of Kansas and are not known from any location from Western North America. Kansas was also apart of Appalachia when the other parts were covered by oceans. It should be noted that indeterminate nodosaur remains have also been unearthed in the Ripley Formation.

A Campanian-era leptoceratopsid ceratopsian has been found in the Tar Heel Formation, marking the first discovery of a ceratopsian dinosaur in the Appalachian zone. This specimen bears a uniquely long, slender and downcurved upper jaw, suggesting that it was an animal with a specialised feeding strategy, yet another example of speciation on an island environment.

Several bird remains are known from appalachian sites, most of them sea birds like Hesperornithes, Ichthyornis, and Enantiornithes like Halimornis. Of particular interest are possible lithornithid remains in New Jersey, which would represent a clear example of palaeognath Neornithes in the Late Cretaceous.

Non-dinosaurs

Through the Ellisdale Fossil Site, a good picture of Appalachia's non-dinosaurian fauna is present. Amidst lissamphibians, there is evidence for sirenids (including the large Habrosaurus), the batrachosauroidid salamander Parrisia, hylids, possible representatives of Eopelobates and Discoglossus, showing close similarities to European faunas, but aside from Habrosaurus (which is also found on Laramidia) there is a high degree of endemism, suggesting no interchanges with other landmasses throughout the Late Cretaceous. There is also a high degree of endemism in regards for its reptilian fauna: among squamates, the teiid Prototeius is exclusive to the landmass, and native representatives of Iguanidae, Helodermatidae, and Necrosauridae. Amidst turtles, Adocus, Apalone, and Bothremys are well represented, the latter in particular more common in appalachian sites than laramidian ones. The three local crocodilian genera, Deinosuchus, Leidyosuchus, Borealosuchus, are well established in Laramidia as well, probably indicative of their ocean crossing capacities. It should be noted that no fossilized remains of snakes have been discovered in Appalachia.

Several mammals are also present on Ellisdale. The most common are ptilodontoidean multituberculates, such as Mesodma, Cimolodon and a massively sized species. The sheer diversity of species on the landmass, as well as the earlier appearance compared to other Late Cretaceous locales, suggests that ptilodontoideans evolved in Appalachia. Metatherian are also known, including an alphadontid, a stagodontid, and an herpetotheriid. Unlike ptilodontoideans, metatherians show a lesser degree of endemism, implying a degree of interchange with Laramidia and Europe.

See also

• List of Appalachian dinosaurs