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> > The question here is that you can use cladistics to link > different genera using only the mineral parts?Or it would make more > sense first study bio-mineralisation processes in similar modern > cases and apply them to fossil analyses? Any cladistic analysis will depend on the quality of the characters and data. Some biomineralization seems almost accidental-an organism affects the chemistry of surrounding water, which causes precipitation of some mineral. Such mineralization is not a good guide to phylogenetic relationships, except insofar as the precipitated minerals show distinctive morphological features of the organism. On the other hand, some organisms have detailed biological control over the details of biomineralization-microstructure, sculpture, mineralogy, etc. Close similarity in detail of biomineralization in such a case is strongly suggestive of close relationship. However, there are some cautions. For example, in mollusks there are some frequent parallel trends in microstructure evolution, so that you need to consider not only what the structure is like but also how it fits in chronologically. It also depends on how strongly you are excluding knowledge of modern forms from the strictly mineral study. The fragmentary nature of most fossil vertebrate skeletons would make it difficult to be confident about the form of the organism, but from knowledge of modern forms we can be quite confident that an entire skeleton ought to have 0, 2, or 4 limbs, bilateral symmetry, a head, backbone, ribs, etc. Thus, you can be fairly confident that three adult femurs with radically different morphology and no evidence of abnormalities come from three different types of organism, not a three-legged creature, even if you don't know what class the specimens belong to. Study of modern relatives will help recognize what mineral differences correlate to other significant differences. E.g., does one species make skeletons of significantly different type (as in some microfossils)? Does one egg have different microstructure near the ends than in the middle? How much do species differ, and where are the greatest differences in their skeleton? A classic example comes from Cuvier's discovery of a fossil marsupial skeleton. From the visible bones and from his knowledge of modern osteology, he was confident that he had a marsupial skeleton. For proof, he removed part of the skeleton and found the marsupial bones underneath. Another aspect helped by knowledge of modern forms is understanding likely diagenetic changes. For example, a superfluous genus name was created for fossil Spondylus in which the aragonitic layer was dissolved away, leaving only calcite. Familiarity with the structure of modern shells and well-preserved fossils, combined with knowledge of aragonite diagenesis, would have prevented this mistake. (The ignorance was understandable, given when it occurred.) -- Dr. David Campbell 425 Scientific Collections Building Department of Biological Sciences Biodiversity and Systematics University of Alabama, Box 870345 Tuscaloosa AL 35487-0345 USA
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