Fish fossil yields jaw-dropping switch in animals’ evolutionary
path   The ancestor of all creatures with jaws and a backbone
was not a sleek sharklike beast but a toothless armored fish,
according to a study that rewrites man’s evolutionary history.
Scientists said they have found a 419-million-year-old fish
fossil in China that disproves the long-held theory that modern
animals with bony skeletons — collectively known as
osteichthyans — evolved from a sharklike creature with a frame
made of cartilage. The osteichthyan group includes most living
fish plus land animals with limbs, including humans.  It had
long been thought that cartilaginous fish such as sharks and
rays, which form a sister group to osteichthyans, most closely
represent the original jawed ancestor that gave rise to the two
types.  This meant that we osteichthyans evolved our bony frames
while the group that includes sharks, rays and ratfish retained
their ancestral cartilage skeletons.  But the new find of a
primordial fish with a complex a