Benthic aquatic ecosystems across the Permian-Triassic transition: record from biogenic structures in fluvial sandstones, central Transantarctic Mountains

The effect of the Permian extinction in communities inhabiting sandy stream bottoms can be evaluated using trace fossils as proxies for body fossils. Permian and Triassic sandstones exposed in the Beardmore and Shackleton Gla cier areas (central Transantarctic Mountains) were deposited in sandy braid ed streams and contain four types of trace fossils (vertical shafts and hor izontal, bilobed and chevron traces). These traces were produced by a singl e type of animal that moved in the top 30 cm of sediment and dominated the benthic community. Evidence for a single producer includes similar size (di ameter) of all traces and change within single specimens from one trace typ e to another. The animal was not affected by the Permian extinction event, as evidenced by its equal abundance within the Permian (Buckley formation) and Triassic (Fremouw Formation) fluvial sandstones in the Beardmore Glacie r area. Based on trace morphology and on domination of modern sandy river e cosystems by insects, the producer most likely was an insect, although its more precise identity is problematic. Although families of insects with mod ern aquatic burrowers are not known before the Jurassic, these trace fossil s may show that these burrowers were present earlier than the insect body-f ossil record suggests. Alternatively, archaic insect groups, many of which became extinct at the end-Permian and are known to have been aquatic but no t infaunal, may have included some active burrowers that were unscathed by the Permian extinction. (C) 2000 Elsevier Science Limited. All rights reser ved.