Article: The first Tertiary sclerosponge from the Americas
Edward C. Wilson
Promissum pulchrum Kovacs-Endrody, 1986, originally described as the earliest vascular land plant or an ancestor of the same, is shown to be a conodont. The species is represented by several spectacular bedding plane assemblages which occur in the Soom Shale Member of the Cedarberg Formation, Table Mountain Group, near Clanwilliam, South Africa. Invertebrate fossils from the Soom Shale indicate a late Ashgill (late Rawtheyan to Hirnantian) age. The conodont assemblages are the largest known, reaching 17 mm in length, with individual ramiform elements as long as 14 mm. The apparatuses are octomembrate with 2Pa, 2Pb, 2Pc, 2M, ISa, 4Sb, 2Sc and 2Sd elements. The possession of three pairs of P elements and a fully developed Sa-Sd symmetry transition series distinguishes Promissum from any other known conodont genus. The arrangement of the elements is unlike that shown by Carboniferous polygnathacean assemblages and implies a significantly different apparatus architecture. Promissum probably represents a cold-water Gondwanan lineage that survived the late Ordovician extinction event, and may well have given rise to the radiation of the Pterospathodontidae in the warmer Llandovery seas.