text: Less ambiguous than the above ichnogenera, are the traces left behind by invertebrates such as Hibbertopterus, a giant "sea scorpion" or eurypterid of the early Paleozoic era. This marine arthropod produced a spectacular track preserved in Scotland.
  Bioerosion through time has produced a magnificent record of borings, gnawings, scratchings and scrapings on hard substrates. These trace fossils are usually divided into macroborings and microborings. Bioerosion intensity and diversity is punctuated by two events. One is called the Ordovician Bioerosion Revolution (see Wilson & Palmer, 2006) and the other was in the Jurassic. For a comprehensive bibliography of the bioerosion literature, please see the External links below.
  The oldest types of tetrapod tail-and-footprints date back to the latter Devonian period. These vertebrate impressions have been found in Ireland, Scotland, Pennsylvania, and Australia. A sandstone slab containing the track of tetrapod, dated to 400 million years, is amongst the oldest evidence of a vertebrate walking on land.
  Important human trace fossils are the Laetoli (Tanzania) footprints, imprinted in volcanic ash 3.7 Ma (million years ago) – probably by an early Australopithecus.