(CN) – Millions of years ago during the Middle Jurassic Period, the Isle of Skye in Scotland was home to a large community of dinosaurs that traversed along the ancient coastline, according to a study published Wednesday in the journal PLOS One.
The second epoch of the Jurassic period lasting from about 174.1 to 163.5 million years ago, the Middle Jurassic was a time period of major evolutionary diversification with marine life flourishing and new types of dinosaurs evolving on land. Despite this spike in terrestrial life, finding dinosaur fossils from this time period is a generally rare occurrence.
However, Scotland’s Isle of Skye is a fortunate exception, yielding both body and trace fossils of diverse Middle Jurassic ecosystems. It is the largest island in the Inner Hebrides archipelago and serves as an invaluable location for paleontological science as well as tourism.
University of Edinburgh scientist and study co-author Stephen Brusatte conducted a similar study with colleagues in 2015 and discovered two types of dinosaur footprints were discovered on the island. "The more we look on the Isle of Skye, the more dinosaur footprints we find. This new site records two different types of dinosaurs – long-necked cousins of Brontosaurus and sharp-toothed cousins of Tyrannosaurus rex – hanging around a shallow lagoon, back when Scotland was much warmer and dinosaurs were beginning their march to global dominance," Brusatte said in the 2015 study.
In their current research, Brusatte, co-author Paige dePolo and their colleagues describe two recently discovered fossil sites with around 50 preserved dinosaur footprints on ancient coastal mudflats, a discovery similar to one in 2008 – also in coastal mudflats – on the Arabian Peninsula in Yemen.
The footprints detailed by Brusatte and dePolo include the first record on the Isle of Skye of a type called deltapodus, which was most likely created by a stegosaurian dinosaur. These exceptional impressions are the oldest deltapodus tracks known today, as well as the first solid evidence that stegosaurian dinosaurs were part of the island's Middle Jurassic fauna.
Stegosaurian dinosaurs were herbivores that lived in the Jurassic and early Cretaceous periods, characterized by their back plates or spikes and small heads with beak-shaped mouths, and they walked on all fours. This group of herbivores were also ornithischian, meaning they had a pelvic structure like that of birds. Once thought to have flourished toward the end of the Jurassic period, new evidence indicates they were present in the Middle Jurassic Period as well.
Additionally, three-toed footprints such as the ones discovered in the Isle of Skye mudflats represent multiple sizes of early carnivorous theropods and belong to a series of other large tracks tentatively identified as some of the oldest evidence of large-bodied herbivorous ornithopod dinosaurs. The prints discovered from Brusatte’s previous study are similar in this way, as they were stomped into the ground by a long-necked sauropod and a sharp-toothed theropod, a cousin of the Tyrannosaurus rex.
When all tracks are considered, these two sites contribute to expanding the known diversity of what was apparently a thriving ecosystem of Middle Jurassic dinosaurs in Scotland, including at least one type of stegosaur not previously known from the region. The results of this study emphasize the importance of footprints as a vital source of information supplemental to body fossils.
Furthermore, the authors note the importance of going back and revisiting previously explored dig sites. These new sites where the prints were discovered were found in an area that has long been popular for fossil prospecting, but the tracks were only recently revealed by storm activity.
"These new track sites help us get a better sense of the variety of dinosaurs that lived near the coast of Skye during the Middle Jurassic than what we can glean from the island's body fossil record. In particular, deltapodus tracks give good evidence that stegosaurs lived on Skye at this time,” dePolo said.
Brusatte said, "These new track sites give us a much clearer picture of the dinosaurs that lived in Scotland 170 million years ago. We knew there were giant long-necked sauropods and jeep-sized carnivores, but we can now add plate-backed stegosaurs to that roster, and maybe even primitive cousins of the duck-billed dinosaurs too. These discoveries are making Skye one of the best places in the world for understanding dinosaur evolution in the Middle Jurassic.”
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