Horodyskia williamsii new species, a Mesoproterozoic macrofossil from Western Australia

A new species of abundant macrofossil, previously described informally as a ‘string of beads’, is here assigned to the genus Horodyskia Yochelson and Fedonkin, 2000, and formally named Horodyskia williamsii. It is known from Mesoproterozoic siliciclastic rocks that are older than 1070 Ma and younger than 1465 Ma; the Backdoor Formation of the Collier Group, and the poorly time-constrained, but probably correlative, Stag Arrow Formation of the Manganese Group, both part of the Bangemall Supergroup of the Ashburton region of Western Australia. The fossils are most commonly found as impressions on the sole of thin, frequently ripple-marked, sandstones. Very rarely, they are present as traces on the tops of sandstone beds. At some localities, there are thin, silty partings separating the sandstone beds. Some strings are current oriented, but commonly most strings crosscut current directions. Much of the observed variation appears to be taphonomic.