Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 257 Functional Morphology of Gastropods and Bivalves JENNY SÄLGEBACK ACTA UNIVERSITATIS UPSALIENSIS ISSN 1651-6214 UPPSALA ISBN 91-554-6764-4 2006 urn:nbn:se:uu:diva-7424 ! " #$ %%& #%'%% ( ( ( ) * + ) , - ") %%.) ! / ( 0 1 ) 2 ) 3&) 4# ) ) 5,1 $#63376.&.767) ! 8 * ( ( ) 9 * ( : ) ! * * ( ( ) ( ( ; * ( * 6 ) ( (( 8 ( ) / ( ( ( ) < ( ) ( ) 1 - ( * ) - ( * - ) ( ( ) = ( ( * - * ) ) / ( (( * ) , * ( ( ' ( ( 6 * ( ( 8 ( ) / ( * 6 * ) 5 ) 2 * ( ( ) + * > * ) 9 * * ( * 74? ( ) ) ! " 0 1 ( # $ %&' ( ' ) ' % **' ' (+,-*./ ' ! @ " , - %%. 5,, #.3#6. #7 5,1 $#63376.&.767 ' ''' 6&7 7 A 'BB )-)B C D ' ''' 6&7 7E Till mina föräldrar List of papers I Savazzi, E. and Sälgeback, J. 2004. A comparison of morphological adaptations in the cardiid bivalves Cardium and Budmania. Paleontological Research 8, 221-239. II Sälgeback, J. and Savazzi, E. 2006. Constructional morphology of cerithiform gastropods. Paleontological Research 10, 233- 259. III Sälgeback, J. (In progress). Shell strength and breakage patterns in the intertidal snail Nucella lamellosa. Biological Bulletin. Reproduction of papers I and II was made with permission of the copyright holder. Paper I © 2004 The Palaeontological Society of Japan Paper II © 2006 The Palaeontological Society of Japan Paper III © by the author Statement of authorship Paper I: Jenny Sälgeback was deeply involved in the studies of the cardiid material and performed the measurements and analyses for the weight versus volume in vivo comparison. Enrico Savazzi studied the lymnocardiid material. Shared writing. Paper II: Jenny Sälgeback participated in the fieldwork in Japan in 2003 and 2004 and was involved in all experiments performed between 2001-2006. Enrico Savazzi studied the repository material in London, Paris and Italy. Shared writing. Paper III: Michael LaBarbera wrote the methodology section about the tensometer and performed the permutation analyses and part of the ANCOVA analyses. Contents Introduction.....................................................................................................9 Aims of this study ....................................................................................10 Living with a shell ........................................................................................12 Function of the shell.................................................................................12 Shell sculpture..........................................................................................12 Shell strength .......................................................................................13 Adaptations to habitat..........................................................................15 The papers in this study ................................................................................21 Paper I ......................................................................................................21 Paper II .....................................................................................................22 Paper III....................................................................................................23 Svensk sammanfattning ................................................................................24 Acknowledgements.......................................................................................27 References.....................................................................................................29 Introduction The general definition of functional morphology is “The study of the relationship between form and function of organisms and/or their parts”, (Savazzi, 1999). The general definition however, breaks down between palaeontologists and biologists who have differing opinions concerning which methods are valid to use. Biologists often regard direct observation of the organism as the only valid method to evaluate adaptive significance; the function has to be seen in action. This is not possible in the study of fossils where inferential methods have to be used. Confining studies to direct observations excludes some important aspects whereas the fossil record offers a possibility to study a broad range of morphologies through time to observe evolutionary trends. It is in the fossil record that morphological adaptation is especially evident. Inferential methods can also be used with available extant specimens. Direct observations can then be used to verify the results and methods can be refined. Biologists often study the soft parts of molluscs, while palaeontologists are confined to the shell for interpretations. To make a comprehensive analysis of the causal origins of any organic structure an integration of different types of studies is needed, (see references in Thomas, 1988). Constructional morphology was developed by Seilacher (1970) for this purpose, as a broader attempt to explain morphology than provided by studies restricted to a single species. Constructional morphology is probably the working method followed by most palaeobiologists dealing with questions on form and function. Its aim is to place functional morphology in an evolutionary context, (Savazzi, 1999). The form of an organism is explained as the interplay between three factors/aspects; (1), the phylogenetic or evolutionary heritage, (2), its constructional (developmental and morphogenetic) mechanisms, and (3), its functional morphology, (Fig. 1A). This method provides a conceptual framework for the analysis of form, (Savazzi, 1999). It has been expanded by Seilacher, (1991, 1993), and developed into biomorphodynamics, by adding the aspect of the effective environment involving all effects on morphology, growth and evolution caused by the environment that immediately surrounds the organism, (Fig. 1B). One of the advantages with constructional morphology is that it can be applied simultaneously to whole lineages. When using functional analysis by itself, it is usually only possible to study adaptive strategies at the species 9 level. In constructional morphology, however, it is often unsatisfactory to study a single species, and the best results are accomplished by analyzing several species simultaneously, as this facilitates the understanding of their phylogenetic heritage and Bauplan (“The basic set of characters and adaptations that constitute the common background of a group, but that need not be expressed in all its members.” Savazzi, 1999). Figure 1. The working methods of constructional morphology (A) and biomorphodynamics (B). Each corner represents one aspect that affects the form of an organism. (After Savazzi, 1999 and Seilacher, 1991) Aims of this study In this project the principles of constructional morphology (sensu Seilacher 1970) have been used to study morphological adaptations of the shell in some post-Paleozoic gastropods and bivalves. Special attention has been given to relationships between morphology and mode of life. The adaptive features of gastropods have not been widely studied even though they are among the most common shell-bearing invertebrates in shallow-water environments. Bivalves have been much more thoroughly studied in functional terms. However, bivalves do not exhibit the behavioral complexity observed in gastropods. Shell geometry, sculptures and pigmentation are much more varied in gastropods, and as a consequence, are more difficult to interpret in adaptive terms (Signor, 1982b). Life habits in marine bivalves appear to be consistently predictable from shell form, (Stanley, 1970, 1972, 1975, 1977). For this study field observations on recent organisms were performed when possible, allowing the possibility to see how different shell characteristics are used in the animal’s natural habitat, thus facilitating the 10 interpretation of similar characters in fossil forms. Further it includes studies of fossil and recent material in museum collections and some laboratory experimentation. Evaluation of the taxonomic position of gastropods and bivalves studied herein has not been part of this project. All discussions are based on existing taxonomy. 11 Living with a shell Function of the shell In both gastropods and bivalves, the shell provides protection for the vulnerable soft parts. Kohn (1999) stated that “A snail’s shell is its castle” and with this in mind it is easy to understand that the shell is of major importance to the survival of a gastropod. The primary function, and reason for the evolution of the gastropod shell, is thought to be protection from predators (Vermeij, 1977a, 1993; Bengtsson, 1994). Most gastropods are helically coiled and consist of several whorls. In the large majority of species, each whorl is cemented onto and partly overlaps the preceding whorl, (e.g. Savazzi and Sasaki, 2004). The bivalve shell is the simplest possible lever skeleton, consisting of two valves, rigid enough