Fossil footprints reveal both carnivores and herbivores strolled by an ancient lagoon
A theropod dinosaur and a sauropod dinosaur strolling through soft sediments on what’s now the Isle of Skye in this artist’s reconstruction.
Tone Blakesley and Scott Reid, CC-BY 4.0
Scotland’s remote Isle of Skye was once a bustling dinosaur thoroughfare. A newly discovered set of at least 131 fossilized footprints dating to between 170 million and 166 million years ago reveals that both long-necked sauropods and carnivorous theropods splashed through the shallow waters of what was then a balmy, subtropical lagoon, imprinting their tracks onto the soft sands.
These fossil trackways reveal that two main groups of dinosaurs casually strolled across what’s now Prince Charles’s Point on the Trotternish Peninsula of the island, paleontologist Tone Blakesley of the University of Edinburgh and colleagues report April 2 in PLOS One. Sets of three-toed tracks point to bipedal carnivorous theropods, which were probably species of megalosaurs, based on previous fossil data from the region, the researchers say. A second group of footprints, round and huge, were probably left by a species of sauropod.
Based on the spacing of the footprints, the dinosaurs that left these tracks weren’t in any hurry or heading anywhere in particular. The tracks don’t have a consistent direction, and the spacing indicates that the dinosaurs were moving at a walking speed — in other words, they were casually milling about, the team suggests.
Fossils of dinosaurs dating to the Middle Jurassic Period, between about 175 million and 161 million years ago, are relatively rare. It was a harrowing time environmentally, marked by widespread volcanism and tectonic activity linked to the breakup of the supercontinent Pangaea, the opening of the central Atlantic Ocean, elevated carbon dioxide in the atmosphere, high temperatures and swelling seas that rose and engulfed much of the land surface.
Those aren’t great conditions for preserving fossils.
But the fossil evidence that did survive from this time hints that the Middle Jurassic was also an era of dramatic diversification among dinosaur clades. Many major groups of dinosaurs emerged during this period, including massive sauropods like cetiosaurs and brachiosaurs, sharp-toothed theropods like megalosaurs, and some early ornithopods, the herbivorous group including duck-billed dinos that flourished during the Cretaceous.
The Isle of Skye, once a landscape of warm shallow seas and freshwater lagoons at the southern edge of Pangaea, harbored an abundance of Middle Jurassic life — and is one of the few places on Earth with abundant fossil evidence dating to that time, the researchers note. The site’s shallow seas and gentle freshwater lagoons, underlain by soft sediment, were excellent for fossil preservation.
Previous evidence has indicated that sauropods in particular were fond of the area — but the plethora of theropod tracks in the new find suggests that this setting was even more cosmopolitan than once thought.
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