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MEGASCOPIC ALGAE 1300 MILLION YEARS OLD FROM THE BELT SUPERGROUP, MONTANA: A REINTERPRETATION OF WALCOTT'S HELMINTHOIDICHNITES

1976; Cambridge University Press; Volume: 50; Issue: 5 Linguagem: Inglês

1937-2337

M. R. Walter, John H. Oehler, D. Z. Oehler,

Paleontology and Stratigraphy of Fossils

In 1899, C. D. Walcott described carbonaceous films on bedding surfaces of dark grey shale from the 1300 m.y. old Greyson Shale of the Belt Supergroup in Montana as trace fossils, assigning them to the genus Helminthoidichnites Fitch. We have re- examined Walcott's collection and have concluded that the fossils represent megascopic and probably eukaryotic algae. They are redescribed here under the names Proterotainia mon- tana, n. gen., n. sp., P. neihartensis (Walcott) n. comb., Lanceoforma striata, n. gen., n. sp., and Grypania spiralis (Walcott), n. gen., n. comb. These are the oldest megascopic body fossils now known, and they extend the known record of megascopic algae by at least 400 m.y. The relatively high diversity and quality of preservation of these fossils demon- strate that fine-grained, clastic sediments are potential repositories of well-preserved Pre- cambrian plants.