Fossil record, evolutionary history, and paleobiology of Plio-Pleistocene Conus from the southeastern United States.

摘要

Conus is the most species-rich extant genus of marine animal and is also among the most thoroughly studied. Despite this, the Eocene to Pleistocene fossil record of cone snails remains underutilized for exploring the evolutionary history of the genus. Cone shells are common in Plio-Pleistocene fossil deposits from the southeastern United States, but significant taxonomic problems have prevented analyses of the evolutionary history of this Conus fauna, including study of the paleobiology of individual species, patterns of evolution and extinction within the genus across time and space, and the relationships of fossil to modern species. This dissertation revises the systematics of this fauna and addresses some of these issues.; Nearly eighty species names have been applied to Plio-Pleistocene Conus shells from the southeastern United States. Examination of over 20,000 museum specimens (including all available type specimens) utilizing a morphological species concept resulted in the recognition of 20 distinctive Conus morphospecies, only one of which is new. Under this revised classification scheme, this fauna shows a pattern of decreasing species diversity through time, with extinction rates outpacing origination rates, and peak diversity occurring in the Pliocene Tamiami Formation of Florida.; One species, Conus adversarius Conrad, is unusual in that, unlike all other living and fossil cone species, its shell coils sinistrally (to the left). The larval shell morphology of Conus adversarius suggests that it had lecithotrophic development. This developmental mode likely contributed to the origin of this species through instantaneous sympatric speciation, and poor larval dispersal may explain the high amount of shell variation observed within this species.; Cladistic analyses combining previously published molecular sequence data from 131 living Conus species with a new matrix including 16 shell characters were used to investigate hypotheses of Conus phylogeny. Inclusion of shell characters resulted in far fewer most parsimonious trees and a better resolved strict consensus tree than molecular sequence data alone. Four of six fossil Conus species added individually to the combined matrix were successfully placed within subclades of extant Conus when analyzed, the first time that the relationships of fossil Conus shells have successfully been resolved using cladistic methods.