Two Ordovician asterozoans (Echinodermata) of problematic affinities
- 1 November 2014
- journal article
- Published by Cambridge University Press (CUP) in Journal of Paleontology
- Vol. 88 (6), 1163-1173
- https://doi.org/10.1666/13-114
Abstract
Phragmactis grayae Spencer and Swataria derstleri new genus new species are early (Ordovician) asterozoans (Echinodermata) that comprise the Phragmactinidae. Asterozoans are complexly varied, but as is true for other echinoderms, ambulacral construction is critical to interpretation. Phragmactinids share plesiomorphic aspects of ambulacral form and articulation with basal somasteroids and stenuroids whereas the apomorphic ambulacral expressions of asteroids and ophiuroids are lacking. Phragmactinids, like asteroids and ophiuroids, have only one virgal-series ossicle associated with each ambulacral, unlike the multiple ossicles of somasteroids and stenuroids. Virgal morphology of phragmactinids is reminiscent of expressions in somasteroids and stenuroids. Aspects of phragmactinid mouth frame construction are apomorphic. Morphologies of other ossicular series are similarly varied, and as a result, the family cannot be easily fitted into a recently proposed class-level taxonomy of early asterozoans; it is left in open nomenclature. Phragmactinid morphology does not indicate behavior significantly different from that of other early asterozaons. Asterozoan diversity suggests an early period of rapid evolutionary radiation.Keywords
This publication has 18 references indexed in Scilit:
- Early Asterozoan (Echinodermata) Diversification: A Paleontologic QuandaryJournal of Paleontology, 2013
- The new chronostratigraphic classification of the Ordovician System and its relations to major regional series and stages and to δ 13 C chemostratigraphyLethaia, 2009
- Skeletal homologies, phylogeny and classification of the earliest asterozoan echinodermsJournal of Systematic Palaeontology, 2005
- New Lower and Middle Ordovician stelleroids (Echinodermata) and their bearing on the origins and early history of the stelleroid echinodermsJournal of Paleontology, 1993
- The Ancestry of VertebratesIchthyology & Herpetology, 1987
- OphiuroidOphiocanops(Echinodermata) not a living fossilJournal of Natural History, 1977
- The phylogeny of sea-starsPhilosophical Transactions of the Royal Society of London. B, Biological Sciences, 1963
- Early Paleozoic starfishPhilosophical Transactions of the Royal Society of London. B, Biological Sciences, 1951
- Zur Morphogenie der AsterozoaPalZ, 1923
- Revision of Paleozoic Stelleroidea with special reference to North American AsteroideaBulletin of the United States National Museum, 1915