PRINCETON, N.J., Aug. 18 (UPI) -- U.S. researchers say they found what may be the oldest fossils of fully developed animal bodies, pushing evidence of animal life into an earlier geologic time.
The newly discovered fossils, resembling sponges, are in rocks between 635 million and 659 million years old from a time when most of the Earth was covered by ice, a geologic period known as the Cryogenian, ScienceNews.org reported Wednesday.
Princeton University scientists found fossils in south Australia of what might be ancient marine sponges in the rocks between mounds of fossilized bacterial mats, or stromatolites.
The fossils "have all the hallmarks" of being something more than just fragments of microbial mats, biogeochemist Roger Summons of MIT, who was not involved in the study, says.
The fossil samples were irregular lumps shot through with a network of fine channels that opened to the outside.
"The absence of symmetry and the internal canal system strongly suggests that they are fragments of sponges," Summons said.
Before settling on sponges, Adam Maloof of Princeton University and his colleagues rejected various notions of what else the fossils could be. Possibilities included the goblet-shaped animal Namacalathus (shaped nothing like it), animals burrows (too tangled, among other things) and some giant one-celled creature (the fossil had too much internal network and no symmetry).
"The one hypothesis we could not reject was the sponges," Maloof said.
