Morphometric characterization of fossil noncalcified macroalgae

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Geography and Geology


Morphometric data from noncalcified macroalgae ("seaweeds") preserved in the fossil record can provide key insights about the evolutionary and ecological history of marine macrophytes. Obtaining basic dimensional information from specimens is fairly straightforward using digital images in conjunction with freeware programs such as ImageJ. The same applies to canopy height, which can be closely approximated for a specimen as the maximum distance between the holdfast and the distal end. However, determining total surface area (SA), a measure of thallus size very different from but equally important to canopy height, is hampered because specimens are preserved as carbonized compressions and, therefore, provide only limited or, in many cases, no direct information about original three-dimensional form. To address this issue, two approaches can be employed to obtain reasonable estimates of SA. First, for specimens that can be reliably assigned to an extant group, three-dimensional form can be inferred from that of living representatives. Second, for specimens that preclude such an approach, it is possible to constrain the range of possibilities for SA by modeling the thallus in terms of minimum and maximum morphologies, such as by treating the three-dimensional form of a particular thallus element first as a flat ribbon and then as a cylinder. Preliminary results of applying morphometric characterization to noncalcified macroalgae from Cambrian to Silurian strata hint at some interesting morphological trends for macroalgae across this important timeframe in the history of life.

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