The muricid gastropod subfamily Rapaninae: phylogeny and ecological history

Abstract

Members of the neogastropod muricid subfamily Rapaninae are abundant, shallow-water predators whose phylogeny was previously investigated by Kool (1993b), who used mainly anatomical characters. In order to deepen understanding of the evolution of this important clade and to incorporate functional, ecological fossil evidence, we performed a phylogenetic analysis based on 34 shell characters in 45 genus-level taxa, including five muricid outgroups. Cladograms based on shell characters alone differed from those founded on anatomical features these analyses differed from the phylogenetic reconstruction combining all available morphological evidence. The preferred cladogram incorporates all evidence and reveals a “Thais group” and an “Ergalatax clade” that both emerge from the derived portion of a more primitive, paraphyletic group of other rapanines. The Ocenebrinae, the other four outgroup taxa three ergalataxine taxa all lie outside the rapanine clade that includes the remaining ergalataxines as a derived subclade.We used the phylogenetic results to probe aspects of the ecological history of the Rapaninae. Our data imply that antipredatory shell defenses (elongated aperture, denticles on the inner side of the outer lip robust external spines and tubercles) evolved multiple times, mainly in post–early Miocene clades in the Indo–West Pacific region. These results support earlier nonphylogenetic inferences.We compared known prey types and methods of predation of living rapanines with their distribution on our phylogenetic tree. The plesiomorphic mode of feeding in the Rapaninae is drilling of hard-shelled prey. Feeding by other means and on such soft-bodied prey as sipunculan and polychaete worms evolved several times independently among post–early Miocene rapanines in the Indo–West Pacific. Methods of predation on hard-shelled prey that involve edge-drilling or attack by way of the aperture also evolved independently several times, but did so throughout the geographical range of the subfamily.Specialization for life on the upper shore occurred in at least eight lineages, all but two of which are confined to the Indo–West Pacific. Ecological diversification of the Rapaninae was therefore most common in the tropical Indo–West Pacific during and after early Miocene time. This diversification occurred in a setting of already high biological diversity and intense competition and predation.

The varix: evolution, distribution, and phylogenetic clumping of a repeated gastropod innovation

“…The origin of the Ergalataxinae is difficult to determine, but appears to have been in the Eocene (Vermeij & Carlson, 2000;Claremont et al, 2013), with multiple varicate taxa from that time (Daphnellopsis, Odontopolys, Morula purulansis Martin, 1914, and Lyropupura). Ergalataxine varices are generally low and rounded, while they are flared in Lyndapterys and are mostly synchronized with two per whorl, even in the earliest L. vokesae Petuch, 1987 (E. Miocene) (Lozouet et al, 1994).…”

The utility of morphological characters in gastropod phylogenetics: an example from the Calyptraeidae

“…This preference for hard‐parts in molluscan taxonomy and systematics has two causes: (1) material from which anatomical observations can be made is or has not been available to molluscan workers; or (2) detailed examination of molluscan anatomy has not led to the discovery of characters that are useful in taxonomic or phylogenetic analyses. This second point receives some support from phylogenetic analyses of muricid gastropods by Kool (1993) and Vermeij & Carlson (2000), who find that anatomical characters can resolve nodes deep in rapanine phylogeny but that they cannot be used to resolve the relationships of closely related species. In contrast shell characters can confidently be used to identify muricid species and can be useful in resolving the tips of trees.…”

Crucibles of creativity: the geographic origins of tropical molluscan innovations

“…Large, productive systems in which competition and predation are intense are therefore expected to serve as fountains of extralimital traits (Vermeij 2003). Vermeij and Carlson (2000), for example, showed that novel shell traits and new modes of life in the muricid gastropod clades Rapaninae and Ergalataxinae evolved most frequently during the Neogene epoch in the species-rich Indo-West Pacific region, stretching from the Red Sea and East Africa to eastern Polynesia. Subsequent work on other innovations has revealed many additional examples of adaptive phenotypic departures from the ancestral norm in ecosystems where selection due to enemies is intense.…”