Functional Morphology and Biomechanics of Articulate Brachiopod Shells

Abstract

In the first Paleontological Society short course dealing with functional morphology of extinct brachiopod taxa, Grant (1981, p. 127) emphasized analogy with living species in reconstruction of life habits, but then cited many pitfalls of taxonomic uniformitarianism. The present is hardly the key as to how brachiopod shells functioned in the past, given the plethora of morphologic structures that have vanished since the Paleozoic diversity climax of articulates. Although direct observations (Table 1), such as clasping spines encircling a blastoid columnal (Grant, 1963), or biomechanical tests (e.g., Thayer, 1975a) and flume experiments (e.g., LaBarbera, 1978) on living articulate brachiopods, enable convincing assertion of a morphologic structure's function, indirect methodologies (Savazzi, 1999)(Table 1) have supplanted mere analogies with living brachiopods. Indirect methodologies (Savazzi, 1999, p. 6) reconstruct and infer the function of skeletal structures from theoretical (morphospace) and actual scaled models of extinct taxa, hydrodynamic and biomechanical tests on empty shells, commensal associations with fossilized epibionts, clinal variations in structures over paleogeographic and paleobathymetric gradients, and post-mortem, post-burial orientational evidence. The common denominator of indirect methodologies is that inferences are made on dead shells usually, but not always, from extinct taxa. Although such inferences of skeletal function of extinct taxa vary in the rigor by which they are deduced, indirect methodologies have been increasingly refined over the last 20 years (Table 1).