A beaked relative of the triceratops has shed light on how geographical division affected dinosaurs enjoying their last years of world domination.
During the Late Cretaceous period 100 to 66 million years ago, eastern North America was an island, divided by a large waterway, known as the Western Interior Seaway, from the western part of the continent and the Hudson Seaway from northern Canada. Such a barrier would be expected to cause isolated species to diverge. However, while the western United States and Canada have given us some of the world's richest dinosaur deposits, the eastern region remains largely mysterious.
Many of Eastern America's fossil formations were destroyed in the Ice Ages, and thick vegetation interferes with finding those that survived. The eastern island, known as Appalachia after the mountains that were already ancient when the first dinosaurs evolved, has been dubbed a “lost continent” because we know so little about its wildlife.
The publication of the jaw of a horned Appalachian dinosaur in Cretaceous Research gives us some idea of what we've been missing.
The rarity of Appalachian dinosaur bones meant that Dr. Nick Longrich of the University of Bath regarded even a fragment of a jaw bone from the Campanian Tar Heel Formation, North Carolina, as worthy of detailed study. He recognized the bone as coming from a leptoceratopsid, a smaller relative of the famous Triceratops. The discovery marks not only the first late Cretaceous leptoceratop known from Appalachia, but the first ceratopsian, the sub-order of horned dinosaurs common at the time in Asia and western North America.
Vegetarian and about the size of a large dog, leptoceratopsids were the dinosaurs you really want as a pet. The jawbone's shape indicates that, like other leptoceratopsids, its owner had a beak-like shape to its mouth. However, the jaw is more slender than that of similar species from west of the Interior Seaway, suggesting that not only had the species diverged once the Seaway opened up, but that diets differed on each side of the water.
“Just as many animals and plants found in Australia today are quite different to those found in other parts of the world, it seems that animals in the eastern part of North America in the Late Cretaceous period evolved in a completely different way to those found in the western part of what is now North America due to a long period of isolation,” Longrich said in a statement.
The existence of the Western Interior Seaway has been proposed based on both geological evidence and differences among tyrannosaurs and hadrosaurs on each side. Nevertheless, the evidence has been too patchy to remove all doubts.
Longrich said the discovery “adds to the theory that these two land masses were separated by a stretch of water, stopping animals from moving between them, causing the animals in Appalachia to evolve in a completely different direction, resulting in some pretty weird looking dinosaurs.” He describes studying the era's fragmented landmasses as “like looking at several independent experiments in dinosaur evolution.”
Image in text: North America in the late Cretaceous. Credit: USGS/ Public Domain.