Matching sets of dinosaur footprints from the Early Cretaceous have been discovered on what are now two different continents.
More than 260 footprints have been found in Brazil and Cameroon, showing where land dinosaurs were last able to freely cross between South America and Africa millions of years ago before the two continents split apart.
“We determined that in terms of age, these footprints were similar,” said SMU paleontologist Louis L. Jacobs, who led the research. “In their geologic and plate tectonic contexts, they were also similar. In terms of their shapes, they are nearly identical.”
The footprints, imprinted in mud and silt along ancient rivers and lakes, were found more than 6,000 kilometers (3,700 miles) apart. Dinosaurs left the tracks 120 million years ago on a single supercontinent known as Gondwana, which broke away from the larger land mass of Pangaea, Jacobs said.
“One of the youngest and tightest geological connections between Africa and South America was the northeastern Brazilian elbow, located against what is now the coast of Cameroon along the Gulf of Guinea,” Jacobs explained. “The two continents were continuous along that narrow stretch, so animals on either side of that connection could potentially move across it.”
Most of the dinosaur fossils were created by three-toed theropod dinosaurs. Some were also likely made by sauropods or ornithischians, said Diana P. Vineyard, who is a research associate at SMU and co-author of the study.
The study was published by the New Mexico Museum of Natural History and Science in tribute to the late paleontologist Martin Lockley, who spent much of his career studying dinosaur tracks and footprints.
Separated 140 million years ago
Africa and South America began to break apart about 140 million years ago, causing cracks in the Earth’s crust called rifts to open along pre-existing weaknesses.
As the tectonic plates beneath South America and Africa moved apart, magma from the Earth’s mantle rose to the surface, creating new oceanic crust as the continents moved away from each other. And eventually, the South Atlantic Ocean filled the gap between these two newly formed continents.
Signs of some of those important events were evident between the two locations where the dinosaur footprints were found: in the Borborema region in northeastern Brazil and the Koum Basin in northern Cameroon. Half-grazet basins – geological structures formed during rifting as the Earth’s crust separates and faults form – are found in both areas and contain sediments from ancient rivers and lakes.
Along with dinosaur footprints, these sediments contain fossil pollen that indicates an age of 120 million years.
Before the continental connection between Africa and South America was severed, “rivers flowed and lakes formed in the basins,” Jacobs said. “Plants fed herbivores and supported a food chain. Muddy sediments left behind by rivers and lakes contain dinosaur footprints, including those of carnivores, documenting that these river valleys could provide specific pathways for life to travel across continents 120 million years ago.”
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