Paleontology and Chronology of Two Evolutionary Transitions by
Hybridization in the Bahamian Land Snail Cerion
Glenn A. Goodfriend
and
Stephen Jay Gould
The late Quaternary fossil record of the Bahamian land snail
Cerion on Great Inagua documents two transitions apparently
resulting from hybridization. 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 modern form found on the
south coast was documented by morphometry of fossils dated by amino
acid racemization and radiocarbon. Hybrid intermediates persisted for
many thousands of years.
G. A. Goodfriend, Geophysical Laboratory, Carnegie Institution of
Washington, 5251 Broad Branch Road, NW, Washington, DC 20015, USA.
S. J. Gould, Museum of Comparative Zoology, Harvard University,
Cambridge, MA 02138, USA.