FIGURE 12. Changes in ecospace utilization in upper-offshore deposits through the early Paleozoic in northwest Argentina in connection with the establishment of the Trichophycus ichnofabrics. Furongian to early Tremadocian ichnofaunas are dominated by shallow-tier trace fossils, such as various ichnospecies of Cruziana (Cr), Rusophycus (Ru) and Palaeophycus (Pa), and the ichnospecies Arthrophycus minimus (Ar). Late Tremadocian to Caradocian ichnofaunas are characterized by the appearance of the mid-tier Trichophycus (Tr).