PALEOBIOGEOGRAPHY OF SOUTH AMERICAN CRETACEOUS ECHINOIDS

In a census of South American literature, 58 genera with over 120 species of Cretaceous fossil echinoids have been identified. This census accounts for the most recent synonomies and generic reclassifications in the literature. Trends in distribution and preservation show distinct patterns. The highest species diversity is found in Brazil, followed by Peru, Argentina, and Colombia. Some countries with low diversity in the Cretaceous have higher diversity prior to or following the Cretaceous (e.g. Chile and Venezuela, respectively). Some countries, such as Guyana, Suriname, and French Guyana, do not have any record of fossil echinoids in the Cretaceous. Regular echinoids are infrequently encountered outside Brazil and Peru, and are generally poorly preserved. The majority of preserved species are irregular echinoids. More spatangoid species are preserved than species in any other echinoid group. Though they have lifestyle and preservation potential similar to spatangoids, fewer cassiduloid species are found than spatangoid species; however, this study does not include any specimen counts so no conclusion on the preservability or populations of either group can be inferred. Overall a temporal trend toward higher diversity shows up in the mid-Cretaceous record – especially in the Albian. This high diversity corresponds with the presence of shallow seas along the eastern coast of South America as the separation from the rest of Gondwana neared completion. Within South America, generic affinities are common between Brazil and Peru, as well as Brazil and Argentina, but less frequently between Argentina and Peru. Affinities to Africa, North America and Europe are common, even at the species level. Species found in Colombia and Venezuela are often found in Texas and Mexico, while species found in Brazil are frequently found in Angola or parts of North Africa. Some species, such as Mecaster batnensis and Mecaster fourneli are more cosmopolitan. Many species are endemic to South America, but all have generic affinities outside of South America.