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Ontogenetic development of Pa element cup microsculpture in Lochriea commutata (Branson and Mehl, 1941) (Conodonta, Carboniferous): taxonomic implications

Published online by Cambridge University Press:  14 July 2015

Peter H. von Bitter  and
Rodney D. Norby
Peter H. von Bitter
Affiliation:
Department of Invertebrate Palaeontology, Royal Ontario Museum, and Department of Geology, University of Toronto, Toronto, Canada M5S 2C6
Rodney D. Norby
Affiliation:
lllinois State Geological Survey, Champaign, 61820
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Abstract

Cup nodes on Lochriea commutata Pa elements bear microsculpture fields composed of polygonal microsculpture. As Pa elements grow larger, the cup nodes and their microsculpture fields increase in size during early to middle growth. With subsequent growth, cup nodes may broaden transversely, split, fuse, or cease to broaden; similarly, their microsculpture fields may increase in size, split, or disappear as the element gets larger. The loss of microsculpture fields results in the loss of polygonal microsculpture.

The presence of polygonal microsculpture on the cup nodes of Pa elements of the holotype of Lochriea montanaensis Scott, 1942, on topotype Pa elements of L. commutata (Branson and Mehl, 1941), as well as on L. commutata Pa elements from diverse localities, suggests that this micromorphological feature cannot be used to distinguish them. Instead, these similarities support the practice of treating L. montanaensis as a junior synonym of L. commutata. The fact that cup node, microsculpture field, and polygonal microsculpture development are closely related to growth and ontogeny and are variable in the larger growth stages suggests that these morphological features should be used with caution in taxonomy. This lack of reliability contrasts with the taxonomic utility of pustulose micrornamentation on the homeomorphic Pa elements of the Permian genus Sweetognathus.

Type
Research Article
Information
Journal of Paleontology , Volume 68 , Issue 4 , July 1994 , pp. 861 - 869
Copyright
Copyright © The Paleontological Society 

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