The meteorite discovered in 1996 that was originally announced to have fossil martian microbes on it was very likely a false positive resulting from overeager researchers misidentifying shapes in rocks. Biomorphology is notoriously unreliable in the absence of other corroborating evidence, as both of these stories attest to.To be nitpicky about it (as per usual, sorry), we already knew there's (was) life on Mars since 80s when scientists found bacteria fossils in an asteroid with confirmed martian origin.
As it stands, we have no conclusive evidence of life having ever existed on Mars, but the closest bit of circumstantial evidence came from the Viking landers in the mid-70s, when one experiment tested positive for metabolism, but also negative for organic material...a contradiction that hasn't been fully resolved.
Mars did have a much thicker atmosphere in the past, but there are far more problems with the supposed existence of insects and lizards on modern Mars than an inability to fly.Why would critters on Mars have Earth-critter-like wings? Earth-wings are useless in Mars' thin atmosphere for actual flying.