Appalachia (landmass)

During most of the Late Cretaceous (100.5 to 66 million years ago) the eastern half of North America formed Appalachia (named for the Appalachian Mountains), an island land mass separated from Laramidia to the west by the Western Interior Seaway.

This seaway had split North America into two massive landmasses due to a multitude of factors such as tectonism and sea-level fluctuations for nearly 40 million years.

[1][2] The seaway eventually expanded, divided across the Dakotas, and by the end of the Cretaceous,[3] it retreated towards the Gulf of Mexico and the Hudson Bay.

[6] Due to high sea levels, subsequent erosion,[7] and the lack of orogenic input of sediment into the Western Interior Seaway unlike the east coast of Laramidia, no terrestrially formed deposits have survived, with most dinosaur remains originating from seaborne carcasses that were transported into marine environments.

[19] Some scientists have proposed the idea that an archipelago of islands had formed during the time that the Western Interior Seaway had divided Laramidia and Appalachia apart until the near end of the Cretaceous.

For instance, the southeastern assemblage (which consists of the Carolinas and the Gulf Coast sites) has some tyrannosauroids such as Appalachiosaurus, some hadrosauroids such as Eotrachodon and Lophorhothon, nodosaurs, dromaeosaurs, and new leptoceratopsian while the northern assemblage (which consists of New Jersey, Delaware, and Maryland) has some tyrannosauroids such as Dryptosaurus, hadrosauroids such as Hadrosaurus, smaller theropods, and a possible lambeosaur in the area.

[28] In Late Cretaceous North America, the dominant predators were the Tyrannosauroidea, huge predatory theropods built for ripping flesh from their prey.

Rather than developing the huge heads and massive bodies of their western relatives such as Gorgosaurus, Albertosaurus and Lythronax,[29] dryptosaurs had more in common with the basal tyrannosaurs like Dilong and Eotyrannus.

Dryptosaurs were characterized by long arms with three fingers;[30] while they were not as large as the largest tyrannosaurids, fossils from the Potomac Formation in New Jersey show that some of them did evolve some of the large-bodied features that can be found on other tyrannosaurs.

[38][39] Finds from the Campanian Tar Heel Formation in North Carolina indicate that there may have been dromaeosaurids of considerable size; intermediate between genera such as Saurornitholestes and Dakotaraptor.

[49][50] Another common group, arguably the most widespread species in the area,[51] of Appalachian dinosaurs were the hadrosaurs which were represented by three groups including Hadrosauromorpha, Hadrosauroidea, and the Hadrosauridae[52] which is now considered to be their "ancestral homeland"; eventually making their way to Laramidia, Asia,[53][54][55][56][57] Europe,[58][59] South America[60] and Antarctica[61] where they diversified into the lambeosaurine and saurolophine dinosaurs, though some of the primitive hadrosaurs[62] were still present until the end of the Mesozoic.

The genus likely took up the environmental niche occupied by large sauropods in other areas, possibly grown to colossal sizes to that of Magnapaulia[71] and Shantungosaurus.

[77][78][79] Indeterminate lambeosaurinae remains, mostly similar to Corythosaurus, have been reported from New Jersey's Navesink Formation, Bylot Island and Nova Scotia, Canada.

[81] While ornithopod fossils have been unearthed in the eastern United States in the past, including footprints in Virginia,[82] they primarily belonged to scrappy remains and couldn't be described as distinct species, with the exception being Tenontosaurus.

However, by the latest Cretaceous, nodosaurids were scarce in western North America,[88] limited to forms like Edmontonia, Denversaurus and Panoplosaurus; perhaps due to competition from the ankylosauridae; though they did thrive in isolation, most notably in Appalachia, as mentioned earlier and in the case of Struthiosaurus,[89] Europe as well.

[102] The owner of this one particular tooth was probably a chasmosaurine since by the end of the Cretaceous while the centrosaurines had completely vanished from most of North America, though they were thriving in Asia as in the case of Sinoceratops, and most likely entered Appalachia as soon as the Western Interior Seaway closed.

Just like their larger cousins, the leptoceratopsids were thought to be absent from Appalachia until the mid-2010s when a jaw bone of an indeterminate genus was unearthed in North Carolina.

This specimen bears a uniquely long, slender and downcurved upper jaw, suggesting that it was an animal with a specialized feeding strategy, yet another example of speciation on an island environment.

They appear to be completely absent from the northern part of Appalachia, states like New Jersey, Delaware, and Maryland, suggesting the idea, proposed by paleontologist David R. Schwimmer, that there was a possible providence during the Late Cretaceous[105] (although it may be a case of preservation bias).

The Appalachian leptoceratopsian that was unearthed in the Tar Heel Formation, which grew to the size of a large dog, had a more slender jaw that teeth that curved downward and outward in its beak.

Amidst lissamphibians, there is evidence for sirenids (including the large Habrosaurus), the batrachosauroidid salamander Parrisia, hylids, and possible representatives of Eopelobates and Discoglossus.

These show 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.

[118] There is also a high degree of endemism in regards to its reptilian fauna: among squamates, the teiid Prototeius is exclusive to the landmass,[119] and native representatives of iguanids, helodermatids, and necrosaurids are also known.

[144] Fossils unearthed in South Carolina and New Jersey shows that some of the crocodilians endemic to Appalachia survived the extinction of the dinosaurs and even persisted into the Cenozoic.

[156] There have been a number of specimens of pterosaurs unearthed in areas that were a part of Appalachia during the time that the Western Interior Seaway had divided North America into two landmasses.

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.

[173][174][175][176][177][178][179][180] Examples of the marine fauna that lived near Appalachia include chondrichthyes, osteichthyes, chelonioids, plesiosaurs, and mosasaurs, which were the apex predators of their environment at the time.

In the Ellisdae Fossil Site, excavations have revealed that plants like Picea, Metasequoia, Liriodendron, and possibly Rhizophora inhabited the region during the late Cretaceous period, implying that the environment during that time period was a coastal forest with a few types of marine environments as well including estuarine, lagoonal, marine, and terrestrial.

Plant fossils found in neighboring states such as Delaware and Maryland have revealed that ferns, gymnosperms, and angiosperms did indeed inhabit the area.

[191] Plant fossils of Minnesota have revealed that cycads, evergreens, Equisetum, laurels, ferns, willows, redwoods, poplars, tulip trees, and pomegranates were present in the area during the Cretaceous.