PALEONTOLOGY AND CHRONOLOGY OF 2 EVOLUTIONARY TRANSITIONS BY HYBRIDIZATION IN THE BAHAMIAN LAND SNAIL CERION

The late Quaternary fossil record of the Bahamian land snail Cerion on Great Inagua documents two transitions apparently resulting from hybr idization. In the first, a localized modern population represents the hybrid descendants of a 13,000-year-old fossil form from the same area , introgressed with the modern form now characteristic of the adjacent regions. In the second case, a chronocline spanning 15,000 to 20,000 years and expressing the transition of an extinct fossil form to the m odern form found on the south coast was documented by morphometry of f ossils dated by amino acid racemization and radiocarbon. Hybrid interm ediates persisted for many thousands of years.