Hostname: page-component-586b7cd67f-tf8b9 Total loading time: 0 Render date: 2024-11-27T11:05:47.488Z Has data issue: false hasContentIssue false

Fenestrate theoretical morphology: geometric constraints on lophophore shape and arrangement in extinct Bryozoa

Published online by Cambridge University Press:  08 February 2016

Robert W. Starcher
Affiliation:
Department of Geological Sciences, Wright/Rieman Laboratories, Rutgers University, New Brunswick, New Jersey 08903
George R. McGhee Jr.
Affiliation:
Department of Geological Sciences, Wright/Rieman Laboratories, Rutgers University, New Brunswick, New Jersey 08903

Abstract

A geometric analysis of fenestrate bryozoan lophophore shape and arrangement is conducted by creating a theoretical morphospace of apertural positioning within the colonial meshwork. Working from the assumption that fenestrate bryozoans needed to form a continuous filtering surface with contact between adjacent lophophores, we show that within the morphospace three regions exist for optimum close-packing of lophophores with circular projections; all other close-packing configurations in the morphospace require the existence of noncircular lophophores.

Examination of the actual distribution of 251 fenestrate colonies within the morphospace reveals that the morphospace regions occupied by fenestellids and polyporids are displaced and have little overlap, but that they are very similar in size and shape that the colonies scale similarly. With increasing size, fenestrate meshworks expand laterally faster than the branches widen and the proximodistal spacing of the apertures increases, apparently because the larger zooids require disproportionately more room for their lophophores.

Two of the optimum close-packing regions of the morphospace are occupied by fenestrates. The positioning of the fenestellid region within the morphospace suggests that these biserial bryozoans followed a proximodistal-row placement of the lophophores that the lophophores were generally equitentacular, with circular projections. The positioning of the polyporid region within the morphospace suggests that these polyserial bryozoans followed a diagonal-row placement of the lophophores that the lophophores were heteromorphic, with medial lophophores on the branch being more equitentacular whereas the laterally placed lophophores were obliquely truncate. The third optimum close-packing region in the morphospace, corresponding to a hypothetical lateral-row placement of the lophophores within the colony, is unoccupied. We suggest that hypothetical fenestrate morphologies in the vacant region of morphospace have branches that would be too narrow to support normally shaped zooids that the lateral-row placement of the lophophores would have required the branches of the colony to have been perfectly aligned throughout growth.

Type
Articles
Copyright
Copyright © The Paleontological Society 

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Literature Cited

Boardman, R. S. 1998. Reflections of the morphology, anatomy, evolution, and classification of the class Stenolaemata (Bryozoa). Smithsonian Contributions to Paleobiology 86:159.Google Scholar
Boardman, R. S., McKinney, F. K., and Taylor, P. D. 1992. Morphology, anatomy, and systematics of the Cinctiporidae, new family (Bryozoa: Stenolaemata). Smithsonian Contributions to Paleobiology 70:181.Google Scholar
Cook, P. L. 1977. Colony-wide water currents in living Bryozoa. Cahiers de Biologie Marine 18:3147.Google Scholar
Cowen, R., and Rider, J. 1972. Functional analysis of fenestellid bryozoan colonies. Lethaia 5:145164.Google Scholar
Hageman, S. J. 1991. Approaches to systematic and evolutionary studies of perplexing groups: an example using fenestrate Bryozoa. Journal of Paleontology 65:630647.CrossRefGoogle Scholar
Hageman, S. J., Bock, P. E., Bone, Y., and McGowran, B. 1998. Bryozoan growth habits: classification and analysis. Journal of Paleontology 72:418436.Google Scholar
Holdener, E. J. 1994. Numerical taxonomy of fenestrate bryozoans: evaluation of methodologies and recognition of intra-specific variation. Journal of Paleontology 68:12011214.Google Scholar
LaBarbera, M., and Guzik, S. 1985. Hydrodynamics of fenestellid bryozoans. Geological Society of America Abstracts with Programs 17:30.Google Scholar
McGhee, G. R. Jr. 1999. Theoretical morphology. Columbia University Press, New York.Google Scholar
McKinney, F. K. 1977. Functional interpretation of the lyre-shaped Bryozoa. Paleobiology 3:9097.Google Scholar
McKinney, F. K. 1980. The Devonian fenestrate bryozoan Utropora Pocta. Journal of Paleontology 54:241252.Google Scholar
McKinney, F. K. 1981. Planar branch systems in colonial suspension feeders. Paleobiology 7:344354.Google Scholar
McKinney, F. K. 1988. Elevation of lophophores by exposed introverts in Bryozoa: a gymnolaemate character recorded in some stenolaemate species. Bulletin of Marine Science 43:317322.Google Scholar
McKinney, F. K. 1990. Feeding and associated colonial morphology in marine bryozoans. Reviews in Aquatic Sciences 2:255280.Google Scholar
McKinney, F. K. 1991. Phylogeny limits function. National Geographic Research and Exploration 7:432441.Google Scholar
McKinney, F. K., and Jackson, J. B. C. 1989. Bryozoan evolution. Unwin Hyman, Boston.Google Scholar
McKinney, F. K., and Raup, D. M. 1982. A turn in the right direction: simulation of erect spiral growth in the bryozoans Archimedes and Bugula. Paleobiology 8:101112.Google Scholar
Taylor, P. D. 1999. Bryozoans. Pp. 623646in Savazzi, E., ed., Functional morphology of the invertebrate skeleton. Wiley, Chichester, England.Google Scholar
Winston, J. E. 1977. Feeding in marine bryozoans. Pp. 233271in Woolacott, R. M. and Zimmer, R. L., eds. Biology of bryozoans. Academic Press, New York.Google Scholar
Winston, J. E. 1978. Polypide morphology and feeding behavior in marine ectoprocts. Bulletin of Marine Science 28:131.Google Scholar
Winston, J. E. 1979. Current related morphology and behaviour in some Pacific Coast bryozoans. Pp. 247267in Larwood, G. P. and Abbot, M. B., eds. Advances in bryozoology. Academic Press, London.Google Scholar
Winston, J. E. 1981. Feeding behavior of modern bryozoans. In Broadhead, T. W., ed. Lophophorates: notes for a short course. Studies in Geology 5:121. Department of Geological Sciences, University of Tennessee, Knoxville.Google Scholar