I'm an amateur paleontologist, and rocks that happen to resemble fossils
are called pseudofossils (I've got a rock that looks like a giant
toothy grin because a whitish mineral got into a crescent-shaped crack
in it, and then it was ground down smooth be glacial effects.- this is
my "Fossil Cheshire Cat".) but using the rover's microscopic viewer on
any Martian fossils should be able to identify them with some degree of
certainty true fossils show detail and symmetry under magnification;
pseudofossils don't.

Pseudo fossils can fool reasonable people. They can also fool Ed "Man as old
as coal" Conrad and his Concretions (from talk.origins) into thinking that
he's found the pancreases, brains, livers, and assorted other viscera of
nine-foot tall 300 million year old humanoids.