July 31 (UPI) -- New X-ray images of ancient fish fossils have helped scientists solve a 160-year-old mastery about the origins of the vertebrate skeleton.
Heterostracans are a group of fossil fishes that lived 400 million years ago. The heterostracan fossil record has offered the oldest evidence of mineralized skeletons among vertebrates. But scientists have struggled to determine what type of tissue heterostracan skeleton's were made of.