Infaunal or semi‐infaunal bellerophont gastropods: analysis of Euphemites and functionally related taxa

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Abstract
Burrowing and plowing gastropods may have existed prior to the Mesozoic, contrary to the conservative tendency of categorizing Paleozoic archaeogastropods as herbivorous hardground dwellers. Euphemites and other bellerophontiform mollusks, such as Praematuratropis and Beyrichidiscus, make functional and paleoecological sense only if reconstructed with an internal shell adapted to an infaunal mode of life. Attributes diagnostic of a probable infaunal mode of life in fossil bellerophontiform mollusks are as follows: lack of apertural flare; restricted aperture; low rate of whorl expansion; semi-radial aperture; extensive secondary shell deposits; absence of extensive collabral ornament; dorsolateral or umbilical furrows; color patterns indicative of mantle extension and retraction capabilities; absence of shell breakage and repair; and associated lithologies indicative of penetrable substrates such as mudstones. Niche diversity in the bellerophontacean mollusks was probably much greater than previously suspected. This is entirely consistent with their long geologic range. Most bellerophontaceans, particularly the Late Paleozoic forms, were probably either nestling or semi-infaunal, with the apertural margins enwrapped by mantle or mantle and foot. They may have been particularly susceptible to predation during the postulated Mesozoic increase in number of infaunal predators, a factor which may have been contributory to the bellerophontacean demise.