How body plans of those ancient species transmuted over time from jawless to jawed fishes, and eventually to humans, is a puzzle yet to be solved.
New research has suggested that, amazingly, the common ancestor of all vertebrates on Earth that have jaws, – including humans of course, was a primitive fish dubbed Acanthodes bronni – Acanthodes is a Greek word for spiny, and these creatures existed long before the evolutionary split that would separate earliest sharks from first bony fishes.
That lineage eventually came to include humanity, and new research, on
fossil findings in Australia, Europeand North America has thrown up some fascinating facts. When compared with other spiny sharks of the time, Acanthodes was relatively large at a foot in length.
It had not teeth but gills, large eyes and lived on plankton, and according to research team head – University of Chicago biologist professor Michael Coates, unexpectedly turned out to be the best window so far on the last common ancestor of bony fishes and sharks.
The research is revealing in fact that the earliest bony fishes looked pretty much like sharks, and what might be thought of as sharkterritory, in evolutionary terms, in fact represents general modern jawed vertebrate territory.
So-called cartilaginous fish – sharks, rays, and ratfish – split in evolutionary history from bony fish over 420 million years ago, though what that last common ancestor of humans, manta rays and great white sharks might have looked like is shrouded in mystery. These creatures died out about 250 million years ago, Leaving only tiny scales and elaborate fin spines behind.
The best-preserved species available is in the form of fossils of Acanthodes bronni, which the the researchers re-examined, the braincases – 290 million years old – showing the fish to have been a member of gnathostomes –jaw-mouths, as in many thousands of living modern including human beings.
Looking inside the head of Acanthodes enabled the team to describe it within the whole new context of similarities found with sharks, acanthodians as a whole appearing to cluster with ancient sharks, though how body plans of those ancient species transmuted over time from jawless to jawed fishes, and eventually to humans, is a puzzle yet to be solved.
The research does help to get a better handle on primitive conditions for jawed vertebrates, the study showing researchers more about important, history of life evolutionary transitions, as well as providing a new window into evolutionary change sequences.