 In 2008 Butterfield described a set of micro-fossils dated to between and , found in the Mahto Formation in Alberta's Jasper National Park – this fossil bed is 5 – 10 M years older than the Burgess Shale in which the only known specimens of "Odontogriphus" and "Wiwaxia" were found.Some groupings of these micro-fossils showed a consistent arrangement that he interpreted as an "articulated apparatus" with tens of closely spaced tooth rows, apparently mounted on an organic base, and with noticeable signs of wear in the rows at one end.The rows were not quite identical, but he noted that some modern aplacophoran molluscs show similar variations.