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1 May 2016 Anchors and snorkels: heterochrony, development and form in functionally constrained fossil crassatellid bivalves
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Abstract
New growth rate estimates for nine species from three genera of New Zealand Crassatellidae (Mollusca: Bivalvia), combined with existing morphometric ontogenetic descriptions, allow identification of heterochronic processes in the evolution of these genera. Both paedomorphosis (progenesis and neoteny) and peramorphosis (hypermorphosis and acceleration) have occurred within the clade. Overall, morphological variability and response to environmental pressure in this nonsiphonate group is restricted by the interplay of anatomical and life habit constraints. Stability in the substrate, predator avoidance, sluggish burrowing speed, and inability to escape by deep burial are suggested as key drivers of, or constraints on, morphological change. Two groups of shell characters are identified: heavy, armored “anchors” and elongate “snorkels,” which combine juvenile and adult traits in shells of different sizes and ages, produced by heterochronic variation in developmental timing. Anchors and snorkels both represent different “solutions” to the problems of life as a nonsiphonate, infaunal bivalve.
© 2016 The Paleontological Society. All rights reserved.
Katie S. Collins, James S. Crampton, Helen L. Neil, Euan G. C. Smith, Michael F. Gazley and Michael Hannah "Anchors and snorkels: heterochrony, development and form in functionally constrained fossil crassatellid bivalves," Paleobiology 42(2), (1 May 2016). https://doi.org/10.1017/pab.2015.48
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