Geological Magazine

Original Articles

First discovery of Early Palaeozoic Bathysiphon (Foraminifera) – test structure and habitat of a ‘living fossil’

ED LANDINGa1 c1, SANDRA PATRUCCO REYESa2, AMANDA L. ANDREASa2 and SAMUEL S. BOWSERa2

a1 New York State Museum, 222 Madison Avenue, Albany, NY 12230 USA

a2 Wadsworth Center, New York State Department of Health, P. O. Box 509, Albany, NY 12201–0509 USA

Abstract

The giant, agglutinated foraminiferan Bathysiphon Sars, previously Triassic–Recent, occurs in much older sedimentary rock (Early Ordovician, late early Tremadocian) of Avalonia. The genus extends back to c. 485 Ma based on its discovery in platform mudstone of the Chesley Drive Group in Cape Breton Island, Nova Scotia. Elongate (up to 60 mm), epibenthic Bathysiphon tubes occur in wave-rippled, green-grey mudstone with a low diversity, probably dysoxic fauna. The mudstone is coeval with and lithologically similar to the Shineton Formation in Shropshire and the Welsh Borderlands. Scanning microscopy of the Bathysiphon walls shows imbricated mica grains that parallel the long axis of the tests. The lumen has a mélange of packed sediment grains, some of which are spherical structures of siliciclastic mud studded with tetrahedral pyrite crystals. A felt-like, agglutinated test, a lumen packed with spherical structures (probable stercomata) and the domal ends of some specimens are consistent with modern Bathysiphon. This report is the first time that cytoplasmic activity and stercomata formation have been used to refer fossil protists to a modern group. Bathysiphon differs from the Cambrian foraminiferan Platysolenites Pander, which has an open lumen without stercomata, but support a comparable, sediment deposit-feeding niche. Bathysiphon is truly a ‘living fossil’, with a mode of test construction, cytoplasmic activity that formed stercomata and a niche unchanged for almost 500 million years. Foraminiferans have not been found prior to the Cambrian Period, and the Early Cambrian appearance of agglutinated foraminiferans is part of the radiation of Phanerozoic communities.

(Received July 21 2011)

(Accepted February 13 2012)

(Online publication April 12 2012)

Keywords:

  • Bathysiphon ;
  • Foraminifera;
  • stercomata;
  • Lower Ordovician;
  • Tremadocian;
  • Avalon;
  • Nova Scotia;
  • Cape Breton Island

Correspondence:

c1 Author for correspondence: elanding@mail.nysed.gov

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