Sharks' long-held status as primeval "living fossils" unchanged since before the time of dinosaurs has been challenged by a new fossil discovery which suggests the creatures have modernised far more than previously thought.
Findings by US researchers, published in Nature, describe the discovery of 325m-year-old fossils found in the Ozark mountains in Arkansas in the US.
The fossils are of an ancient shark ancestor which was just a metre long with tiny teeth, although its bite would give you a painful nip, researchers said. The fossils are the earliest known remnants of chondrichthyans, a group which includes sharks and rays.
The ancient shark had an anatomy very different to its modern-day counterpart, looking much like an average fish.
This overturns previous assumptions that sharks developed gill systems before modern fish. The findings suggest fish are the ones with ancient gill structures, with sharks evolving over time.
Scien! tists have previously theorised that the structure of sharks gills had remained unchanged since the emergence of the creatures 400m years ago, long before the arrival of dinosaurs.
The discovery has implications beyond sharks, with the paper claiming it could "profoundly affect our understanding of evolutionary history".
The support structure for gills are thought to have evolved into jaws in fish, allowing them to hunt, before developing later into land-based animals.
The paper states: "The arrangement of the visceral branchial arches, which are part of this support structure, is very similar to that of bony fishes, signifying that the most recent common ancestor of jawed vertebrates possessed some elements that were more bony fish-like than shark-like.
"This challenges the longstanding view that modern sharks have preserved an unchanged ancestral condition, and indicates that modern sharks have acquired features stemming from evolutionar! y innovation.
"The findings suggest that bony fishes m! ay provide more clues about our first jawed ancestors than modern sharks."
Source : http://www.theguardian.com/environment/2014/apr/17/sharks-more-evolved-than-thought-fossil-discovery
