Gradual Miocene to Pleistocene uplift of the Central American isthmus: Evidence from tropical American tonnoidean gastropods

Tonnoidean gastropods have planktotrophic larval lives of up to a year and are widely dispersed in ocean currents; the larvae maintain genetic exchang e between adult populations. They therefore are expected to respond rapidly to new geographic barriers by either extinction or speciation. Fossil tonn oideans on the opposite coast of the Americas from their present-day range demonstrate that larval transport still was possible through Central Americ a at the time of deposition of the fossils. Early Miocene occurrences of Cy praecassis tenuis (now eastern Pacific) in the Caribbean probably indicate that constriction of the Central American seaway had commenced by Middle Mi ocene lime. Pliocene larval transport through the seaway is demonstrated by Bursa rugosa (now eastern Pacific) in Caribbean Miocene-latest Pliocene/Ea rly Pleistocene rocks; Crossata ventricosa (eastern Pacific) in late Plioce ne rocks of Atlantic Panama; Distorsio clathrata (western Atlantic) in midd le Pliocene rocks of Ecuador; Cymatium wiegmanni (eastern Pacific) in middl e Pliocene rocks of Atlantic Costa Pica, Sconsia sublaevigata (western Atla ntic) in Pliocene rocks of Darien, Pacific Panama; and Distorsio constricta (eastern Pacific) in latest Pliocene-Early Pleistocene rocks of Atlantic C osta Pica. Continued Early or middle Pleistocene connections are demonstrat ed by Cymatium cingulatum (now Atlantic) in the Armuelles Formation of Paci fic Panama. Tonnoideans indicate that the Central American seaway began to be constricted after early Miocene time, and some larval transport through the seaway was possible throughout Pliocene time. Intermittent marine conne ctions were maintained at least during late Pliocene to early Pleistocene i nterglacial periods of high sea-level, and alternated with a land bridge du ring glacial periods of low sea-level.