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COMPUTER‐SIMULATED SHELL SIZE AND SHAPE VARIATION IN THE CARIBBEAN LAND SNAIL GENUS CERION : A TEST OF GEOMETRICAL CONSTRAINTS
Author(s) -
Stone Jonathon Richard
Publication year - 1996
Publication title -
evolution
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.84
H-Index - 199
eISSN - 1558-5646
pISSN - 0014-3820
DOI - 10.1111/j.1558-5646.1996.tb04497.x
Subject(s) - biology , disjunct , disjunct distribution , land snail , shell (structure) , genus , phylogenetic tree , constraint (computer aided design) , variation (astronomy) , evolutionary biology , paleontology , ecology , geometry , astrophysics , snail , physics , mathematics , population , biochemistry , materials science , demography , sociology , composite material , gene
A computer graphical model of gastropod shell form is used to test a hypothesis of geometric constraint proposed to explain the disjunct distribution of shell forms observed in Cerion , a species‐rich and geometrically varied genus of terrestrial gastropods. The mapping of computer‐simulated forms into a morphospace of Cerion shells produces a continuum of sizes and shapes. Therefore, the absence of particular shell forms is not explained by geometric constraints. Two proposed modes of shell morphogenesis at extreme ranges in size (“dwarfs” and “giants”) previously were thought to be exclusive routes to the construction of high‐spired (“smokestack”) forms. The present study shows that there are, in fact, multiple routes of transformation. In addition, these routes are geometrically reversible and interconnect the members of the shell‐form continuum. Thus, the possible pathways followed during the course of evolution within this genus cannot be determined until an adequate phylogenetic hypothesis has been proposed.