South America's earliest crinoids

GUENSBURG, T.E.; WAISFELD, B.G.

JOURNAL OF PALEONTOLOGY

PALEONTOLOGICAL SOC INC

Lugar: Lawrence; Año: 2015 vol. 89 p. 622 - 630

0022-3360

Two new Floian-aged taxa from Gondwanan rocks of northwest Argentina add to the meager record and sketchy understanding of early crinoid phylogeny. Ramseyocrinus argentinus n. sp. material, among the most complete for thegenus, aids in reinterpretation of key morphology. Ramseyocrinus is unorthodox with four radials forming the entire cup, these supporting five arms above and a tetrameric stem below. Evidence is presented radials comprise A, B, D, and E ray elements (C absent) with B and D radials adjoining to form a compound facet for the C arm. Thus the cup lacks posterior cup plating entirely; the elongate anal sac projects from the CD tegmen region and curves alongside the C arm. Cup synapomorphies link Ramseyocrinus and the Middle Ordovician Tetragonocrinus as a clade apart from all other crinoids.Association of the anal sac and C arm coupled with few-plated construction supports tenuous linkage with disparids.Quechuacrinus ticsa n. gen. and sp., increases the paleogeographic range ofreteocrinid camerates, previously documented only from Laurentia. This taxon expresses synapomorphies characterizing the Late Ordovician Reteocrinus, demonstrating the antiquity of this clade.