Remember when scientists announced three years ago that they had found the soft tissue of a Tyrannosaurus Rex in a 70-million-year-old fossil? Never mind. New evidence suggests those findings, which startled the public and the scientific community alike, might be bogus.

Researchers led by Thomas Kaye, a paleontologist at the University of Washington in Seattle, report in PLoS ONE that slimy bacterial colonies called biofilms mimic the fleshy residues allegedly recovered from a fossilized bone unearthed in Montana in 2005. These bacterial films may have faked out researchers by growing into the channels and spaces where the T. Rex's blood vessels and bone cells (osteocytes) had once been, mirroring both the shape and elasticity of this vanished soft tissue. The new study argues that the suspected dinosaur flesh is more similar to biofilms than to present-day collagen, the connective tissue protein supposedly harvested from the ancient dinosaur thigh bone.

Kaye and other researchers first used a scanning electron microscope to probe the inner, cave-like chambers in dinosaur bone samples and noted striking similarities to the biofilms they reared and reaped from a bucket of pond water. The original dinosaur flesh-finders relied on a different approach, namely bone-dissolving acids that left behind bits of pliable material later characterized as soft tissue remnants. Kaye's team duplicated this technique as well, and found that iron deposits, thought to be from prehistoric blood cells, were instead natural mineral formations called framboids.

Mary Schweitzer, the North Carolina State University paleontologist who announced the 2005 discovery, stands by her claims in an email statement. She says that all of her team's data cannot simply be chalked up to biofilm-building bacteria infiltrating old bones. Schweitzer also points to genetic analyses completed last year of the extracted pulpy material that indicated T. Rex's closest known, modern-day kin is a chicken. That work fell in line with the emerging theory that birds are descended from dinosaurs, and the new PLoS ONE study does not directly address the validity of these later experimental results.

The bottom line: the jury is still out on whether the flesh was the real McCoy, according to various media reports.