Thursday, February 23, 2006
Re-evaluation of 'Spirorbis'
A paper in the March 2006 edition of the Journal of the Geological Society reinterprets pre-Cretaceous 'Spirorbis' worm tubes as those of microconchids. Whereas modern Spirorbis is a stenohaline polychaete annelid, microconchids are possibly lophophorates and are known from freshwater, brackish and hypersaline environments. This has palaeoenvironmental implications, as well as impacting upon a creationist argument for the marine deposition of coal - as the authors point out: "Creationist literature (e.g. Coffin 1975) has argued for the rapid formation of coal in the sea during the Biblical Flood on the basis of finding marine 'Spirorbis' attached to trees and other terrestrial plants in Carboniferous Coal Measures. This argument becomes untenable with the knowledge that the tube-worms concerned were not stenohaline spirorbid polychaetes." (p.227)
Taylor P.D., Vinn O., 'Convergent morphology in small spiral worm tubes ('Spirorbis') and its palaeoenvironmental implications', Journal of the Geological Society 2006;163:225-228.
Abstract: Calcareous tube-worms generally identified as Spirorbis range from Ordovician to Recent, often profusely encrusting shells and other substrates. Whereas Recent Spirorbis is a polychaete annelid, details of tube structure in pre-Cretaceous 'Spirorbis' suggest affinities with the Microconchida, an extinct order of possible lophophorates. Although characteristically Palaeozoic, microconchid tube-worms survived the Permian mass extinction before being replaced in late Mesozoic ecosystems by true Spirorbis. Recent Spirorbis is stenohaline but spirorbiform microconchids also colonized freshwater, brackish and hypersaline environments during the Devonian-Triassic. Anomalies in the palaeoenvironmental distributions of fossil 'Spirorbis' are explained with the recognition of this striking convergence between microconchids and true Spirorbis.
Taylor P.D., Vinn O., 'Convergent morphology in small spiral worm tubes ('Spirorbis') and its palaeoenvironmental implications', Journal of the Geological Society 2006;163:225-228.
Abstract: Calcareous tube-worms generally identified as Spirorbis range from Ordovician to Recent, often profusely encrusting shells and other substrates. Whereas Recent Spirorbis is a polychaete annelid, details of tube structure in pre-Cretaceous 'Spirorbis' suggest affinities with the Microconchida, an extinct order of possible lophophorates. Although characteristically Palaeozoic, microconchid tube-worms survived the Permian mass extinction before being replaced in late Mesozoic ecosystems by true Spirorbis. Recent Spirorbis is stenohaline but spirorbiform microconchids also colonized freshwater, brackish and hypersaline environments during the Devonian-Triassic. Anomalies in the palaeoenvironmental distributions of fossil 'Spirorbis' are explained with the recognition of this striking convergence between microconchids and true Spirorbis.
# posted by Nemagraptus @ 1:51 PM 
