Abstract

The late Miocene Gatun Formation of northern Panama contains a highly diverse and well sampled fossil marine assemblage that occupied a shallow-water embayment close to a purported connection between the Pacific and Atlantic (Caribbean) oceans. However, the diverse chondrichthyan fauna has been poorly documented. Based on recent field discoveries and further analysis of existing collections, the chondrichthyan fauna from this unit comprises at least 26 taxa, of which four species are extinct today. The remaining portion of the total chondrichthyan biodiversity has affinities with modern taxa and is therefore comprised of long-lived species. Based on known records of the modern geographic distribution range of the Gatun chondrichthyans, the fauna has mixed biogeographic affinities suggesting that around 10 million yr ago, a connection likely occurred between the Pacific Ocean and the Caribbean Sea. Given the known habitat preferences for modern chondrichthyans, the Gatun fauna was primarily adapted to shallow waters within the neritic zone. Finally, comparisons of Gatun dental measurements with other faunas suggest that many of the taxa have an abundance of small individuals, in agreement with previous studies that proposed this area as a paleonursery habitat for the species Carcharocles megalodon.

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