These Could Be the Oldest Animal Fossils Ever Found, or Just Squiggles

Critics challenged a study’s claim that a netlike structure found in rocks in a Canadian mountain range could be an 890-million-year-old sponge fossil.

A spongelike structure discovered in exposed 890-million-year-old rock in Canada’s Northwest Territories may be the oldest known fossilized animal body, according to a study whose findings will likely add another controversy to longstanding debates about the planet’s earliest animal life. In a paper published Wednesday in the journal Nature, Elizabeth Turner, a geologist at Laurentian University in Ontario, described the branching, tubular structures she observed while examining ultrathin slices — about as thick as a human hair — of what were once reefs in a prehistoric ocean. Dr. Turner suggests the meshlike structures closely resemble the fiber networks of modern keratose sponges, also known as horny sponges, found around the world today. But she concedes that what she saw under a microscope may not clarify when animal life first emerged on Earth.