An international team of researchers, led by Southern Methodist University (SMU) paleontologist Louis L. Jacobs, has discovered matching sets of Early Cretaceous dinosaur footprints on what are now two different continents. Over 260 footprints were found in Brazil and Cameroon, providing evidence of the last time terrestrial dinosaurs could freely cross between South America and Africa millions of years ago before the continents drifted apart.

We determined that, in terms of age, these footprints were similar, Jacobs said. In their geological and tectonic plate contexts, they were also similar. In terms of their shapes, they are almost identical.

The footprints, left in ancient mud and silt along rivers and lakes, were found more than 6,000 kilometers apart. The dinosaurs made the tracks 120 million years ago on a supercontinent known as Gondwana, which had split from the larger landmass of Pangaea, Jacobs explained. The discovery provides compelling evidence of a critical land bridge that connected Africa and South America during the Early Cretaceous period, allowing the free movement of dinosaurs between these two landmasses.

Two representative theropod footprints of the Koum basin, in northern Cameroon
Two representative theropod footprints of the Koum basin, in northern Cameroon. Credit: SMU

One of the youngest and closest geological connections between Africa and South America was the northeastern corner of Brazil, which fit snugly against what is now the coast of Cameroon along the Gulf of Guinea, according to Jacobs. The two continents were continuous along that narrow stretch, so animals on both sides of that connection could potentially cross it, he explained.

The majority of the dinosaur footprints were created by three-toed theropod dinosaurs. Some may also have been made by sauropods or ornithischians, according to Diana P. Vineyard, a research associate at SMU and co-author of the study. The study was published in print by the New Mexico Museum of Natural History and Science in honor of the late paleontologist Martin Lockley, who dedicated much of his career to studying dinosaur footprints.

Africa and South America began to separate around 140 million years ago, leading to the formation of rifts in the Earth’s crust called fissures along pre-existing weaknesses. As the tectonic plates beneath South America and Africa pulled apart, magma from the Earth’s mantle rose to the surface, creating new oceanic crust as the continents drifted away from each other. Eventually, the South Atlantic Ocean filled the gap between these two newly formed continents.

Theropod footprint of the Sousa Basin, Lower Cretaceous of northeastern Brazil.
Theropod footprint of the Sousa Basin, Lower Cretaceous of northeastern Brazil. Credit: Ismar de Souza Carvalho

Evidence of some of these significant events is visible at both locations where the dinosaur footprints were found: the Borborema region in northeastern Brazil and the Koum Basin in northern Cameroon.

Crescent-shaped basins, geological structures formed during the rifting when the Earth’s crust split and faults formed, are present in both areas and contain ancient river and lake sediments. Alongside the dinosaur footprints, these sediments contain fossil pollen indicating 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, said Jacobs. Plants fed herbivores and supported a food chain. The muddy sediments left by the 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.

SOURCES

Southern Methodist University

Louis L. Jacobs, Lawrence J. Flynn, et al., The Early Cretaceous Borborema-Cameroon Dinosaur Dispersal Corridor. En Vertebrate Paleoichnology: A Tribute to Martin Lockley. New Mexico Museum of Natural History and Science Bulletin 95

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