Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news about fascinating discoveries, scientific advances and more.
Matching footprints discovered in Africa and South America reveal that dinosaurs traveled on a kind of highway 120 million years before the two continents separated, according to a new study.
Paleontologists have found more than 260 dinosaur footprints from the Early Cretaceous Period in Brazil and Cameroon, on opposite shores of the Atlantic Ocean. These two footprints are now more than 6,000 kilometers apart.
The footprints are similar in age, shape and geological context, said Louis L. Jacobs, a paleontologist at Southern Methodist University in Texas and lead author of the study describing the tracks released Monday by the New Mexico Museum of Natural History and Science.
Most of the fossilized footprints belong to three-toed theropod dinosaurs, while a few belong to sauropods, which were bulky quadrupeds with long necks and tails, or ornithischians, whose pelvic structures resembled those of birds, said study co-author Diana P.
Vineyard is a research associate at SMU.
The tracks tell a story of how the movements of massive landmasses created ideal conditions for dinosaurs before supercontinents split into the seven continents we know today.
Lifelong green basins
The footprints were preserved in mud and silt along ancient rivers and lakes that once existed on the supercontinent Gondwana, which broke away from the larger land mass of Pangea, Jacobs said.
“One of the youngest and narrowest geological connections between Africa and South America was the northeastern Brazilian elbow along the Gulf of Guinea, which juts into the coast of Cameroon,” Jacobs said. “The two continents were continuous along that narrow strip, so animals on both sides of that connection could potentially move across it.”
Africa and South America began to separate from each other about 140 million years ago. The separation created cracks in the Earth’s crust, and as the tectonic plates beneath South America and Africa moved apart, magma from the Earth’s mantle formed new oceanic crust. Over time, the South Atlantic Ocean filled the gap between the two continents.
But before this gradual change happened, the Earth’s surface began to separate into different types of basins, with rivers feeding the basins to form lakes, Jacobs said.
The study authors found evidence of a basin known as a half-graben basin in the Borborema region of northeastern Brazil and a similar basin in the Koum Basin in northern Cameroon.
“A half graben is an elongated basin where a fault forms on one side of the Earth’s surface, with the valley floor dipping toward the fault where movement is occurring,” Jacobs said in an email. “Hold your hand in front of you. Curve your fingers down, which represents movement along the fault. Rivers will flow through the valley and deposit sediment, and the sediment will erode from the high side of the valley.”
In both basins, researchers found dinosaur tracks, ancient river and lake sediments, and fossilized pollen.
“Plants fed herbivores and supported a food chain,” he said. “Muddy sediments left by rivers and lakes contain dinosaur footprints, including those of meat-eaters, documenting that these river valleys may have provided specific routes for life to travel between continents 120 million years ago.”
While dinosaur fossils can provide unique insights into the animal species that roamed our planet millions of years ago, footprints also offer other windows into the past.
“Dinosaur tracks are not uncommon, but unlike bones that are usually found, footprints are evidence of dinosaur behavior, how they walked, ran or otherwise behaved, who they walked with, what environment they walked in, what direction they went and where they were when they did it,” Jacobs said.
It’s hard to say exactly what types of dinosaurs traveled across the basins, but they provide a broader portrait of the ancient climate and how different types of animals thrived in the environment created by the continental rifting.
“If your dog and a coyote walk across the same mudflat, you might know that there are two canine creatures walking there, that they look very similar, but you might not know if they are different species. The same goes for dinosaur tracks,” Jacobs says. “All animals have home ranges. All animals expand their home ranges. All animals use resources as needed, usually seasonally, depending on availability. Herbivores follow nutritious plants; carnivores follow herbivorous food.”
At that time, rainfall levels helped create a tropical rainforest-type environment with abundant vegetation. Animals arrived in the basins from both present-day Africa and South America, causing their populations to mix.
“Imagine a lush, open basin with vegetation for herbivores and carnivores,” says study co-author Lawrence Flynn, associate director of the American Prehistoric Research School and laboratory safety coordinator in the department of human evolutionary biology at Harvard University. “If there’s no one in the ‘new’ area, the animals will disperse in the absence of competition.”
Later, when the continents drifted apart, this disruption likely led to a disruption of genetic continuity, which is the primary driver of evolution, Jacobs said.
Dinosaur tracks in Cameroon were first discovered in the late 1980s, and Jacobs described them at the First International Symposium on Dinosaur Tracks and Traces, organized by paleontologist Martin Lockley in 1986.
Jacobs later befriended the study’s author, Ismar de Souza Carvalho, now a professor in the geology department of the Federal University of Rio de Janeiro. While Jacobs was studying dinosaur movements from the African side, Carvalho was studying them from the Brazilian side.
As research into basins in Africa and South America continued in subsequent decades, Jacobs and Carvalho and their colleagues reviewed existing and new fieldwork and research to analyze the patterns. The new study is a tribute to Lockley, who devoted his career to studying dinosaur footprints.
“We wanted to bring together new and evolving geological and paleontological evidence to tell a more specific story of where, why and when dispersals across continents occurred,” Jacobs said.
“One of the beauties of this Earth is that we can all see Africa and South America once fitting together like puzzle pieces. In an interconnected world, it’s easy to think that animals, including dinosaurs, could and would move from place to place.”
For more CNN news and bulletins, create an account at CNN.com