Recent study of the braincases of an ancient species of shark has shown that humans and sharks shared an ancestor known as Acanthodes bronni. Acanthodes was a 300-million-year-old sea creature that measured about a foot long, had gills and big eyes, and munched on plankton. Most interesting is this shark’s relation to us. Scientists think that A. bronni was the ancestor of all jawed vertebrates. The currently accepted tree of life shows that 420 million years ago, there was a split in the ancestral tree of vertebrates. Cartilaginous fish (like today’s sharks) diverged from the bony fishes (e.g., trout), eventually leading to the human branch of the tree. Cartilaginous fish include early sharks, rays, and ratfishes. They have a skeleton made entirely of cartilage (instead of bone) and have gills on the outside of their bodies; bony fishes, on the other hand, have bones and gills inside the body. Sharks and bony fish also differ in certain physiological aspects as well as reproductive and fertilization traits. Professor Michael Coates, a biologist at the University of Chicago, who led the study, worked with Dr. Maureen Kearney, of the National Science Foundation and other researchers who studied numerous Acanthodes fossils from Europe, North America, and Australia, and compared them to other early shark and bony fish fossils to make this exciting discovery. They hope that further study of A. bronni will answer questions about early vertebrate evolution.
Discover more at The Telegraph.
The study on Acanthodes was published in the journal Nature.
Read more about the differences between cartilaginous fish and bony fish at Preserve Articles.