A team of scientists has discovered in the rocks of the Hanna Formation in south-central Wyoming, in the United States -which 58 million years ago was on the edge of the ocean-, the oldest known evidence of mammals gathered near the sea: a collection of thousands of footprints on the shore in what is now southern Wyoming.
The tracks left by two species of mammals, one identified as Coryphodon and the other unknown, were made 58 million years ago, according to an analysis by US experts. The Coryphodon was a primitive creature with hooves and four legs the size of a brown bear, one of the largest known mammals of its time. It was a heavy, slow-moving animal with a strong constitution.
“Tracking fossils, like footprints, record interactions between organisms and their environments, providing information that body fossils alone cannot,” says Anton Wroblewski, associate associate professor in the Department of Geology and Geophysics and co-author. of the work published in the journal Scientific Reports. “In this case, fossil tracks show that large mammals regularly used marine environments only eight million years after non-avian dinosaurs became extinct.”
Among the examined and fossilized samples are footprints, impressions in soft sediments made when heavy animals walk on overlying layers of sediment, as well as footprints pressed into the surfaces of ancient tidal flats. Preserved today in sandstone, they are 1,032 meters long and were made by a minimum of two species of mammals: an animal with four fingers and another with five (the Coryphodon).
This finding suggests that mammals would have used marine habitats for the first time at least 9.4 million years earlier than previously thought, in the late Paleocene era (66-56 million years ago), rather than the Eocene era (56-33.9 million years ago).