TULANE STUDIES IN GEOLOGY AND PALEONTOLOGY is devoted primarily to the geology and paleontology of the coasts and adjacent land areas of the Gulf of Mexico and the Caribbean Sea Each number is issued separately and contains an individual monographic study, or several minor studies As volumes are completed, title pages and tables of contents will be distributed to institutions exchanging the entire series

Tulane Studies in Geology and Paleontology

Geographical heterochrony: Comtemporaneous coexistence of neogene and recent molluscan faunas in the Americas

The modern structure of marine benthic ecosystems was largely established during the Jurassic and Early Cretaceous (200-100 Ma), a transition that has been termed the Mesozoic Marine Revolution (MMR). Although it has been suggested that the MMR marks an increase in the average energy consumption of marine animal ecosystems, this hypothesis has not been evaluated quantitatively. In this study, we integrate body size and abundance data from the fossil record with physiological data from living representatives to estimate mean per capita metabolic rates of tropical to subtropical assemblages of shallow-marine gastropods—a major component of marine ecosystems throughout the Meso-Cenozoic—both before and after the MMR. We find that mean per capita metabolic rate rose by ,150% between the Late Triassic and Late Cretaceous and remained relatively stable thereafter. The most important factor governing the increase in metabolic rate was an increase in mean body size. In principle, this size increase could result from secular changes in sampling and taphonomic biases, but these biases are suggested to yield decreases rather than increases in mean size. Considering that post-MMR gastropod diversity is dominated by predators, the net primary production required to supply the energetic needs of the average individual increased by substantially more than 150%. These data support the hypothesis that benthic energy budgets increased during the MMR, possibly in response to rising primary productivity.

/pdf/escargots-through-time-an-energetic-comparison-of-marine-3aiws58cdc.pdf

Escargots through time : an energetic comparison of marine gastropod assemblages before and after the Mesozoic Marine Revolution

The Cocinetas Basin of Colombia provides a valuable window into the geological and paleontological history of northern South America during the Neogene. 
Two major findings provide new insights into the Neogene history of this Cocinetas Basin: (1) a formal re-description of the Jimol and Castilletes formations, including a revised contact; and (2) the description of a new lithostratigraphic unit, the Ware Formation (Late Pliocene). We conducted extensive fieldwork to develop a basin-scale stratigraphy, made exhaustive paleontological collections, and performed 87Sr/86Sr geochronology to document the transition from the fully marine environment of the Jimol Formation (ca. 17.9–16.7 Ma) to the fluvio-deltaic environment of the Castilletes (ca. 16.7–14.2 Ma) and Ware (ca. 3.5–2.8 Ma) formations. We also describe evidence for short-term periodic changes in depositional environments in the Jimol and Castilletes formations. The marine invertebrate fauna of the Jimol and Castilletes formations are among the richest yet recorded from Colombia during the Neogene. The Castilletes and Ware formations have also yielded diverse and biogeographically significant fossil vertebrate assemblages. The revised lithostratigraphy and chronostratigraphy presented here provides the necessary background information to explore the complete evolutionary and biogeographic significance of the excellent fossil record of the Cocinetas Basin.

/pdf/revised-stratigraphy-of-neogene-strata-in-the-cocinetas-3s1ftedw02.pdf

Revised stratigraphy of Neogene strata in the Cocinetas Basin, La Guajira, Colombia

Throughout the vast majority of Tertiary time (almost 65 million years) there was no Panama land bridge, and North and South America were detached from one another. This condition can be traced back to the initial separation of the North American and South American (still attached to Africa) plates in the Jurassic, about 165 million years ago (Pindell and Dewey, 1982). Following the onset of rifting and continental break-up in the early Mesozoic, it is uncertain as to the amount of time during which North and South America were actually isolated. The reconstructions of Pindell and Dewey (1982) and Donnelly (Chapter 4, this volume) suggest an early isolation, shortly after 165 m.y.a. Anderson and Schmidt (1983), however, propose a different scenario for the evolution of middle America, which would have juxtaposed blocks preserving land contact between North and South America much longer, perhaps into the late Cretaceous. Regardless of the preferred reconstruction, most authors agree that no land bridge existed for at least 70 m.y., from the late Cretaceous up until contact was reestablished in the Plio-Pleistocene. The establishment of the Panama land bridge has been well documented from considerations of the interchange between terrestrial faunas arising on both continents (e.g., Simpson, 1940, 1953; Webb, 1976; Marshall et al., 1979, 1982; and others in this volume), although the precise timing of this event is more poorly known. The migration route is also uncertain as some have argued for migration via the Nicaraguan Rise rather than through present-day Guatemala (Durham, 1985).

History and Development of the Marine Invertebrate Faunas Separated by the Central American Isthmus

Miocene Mollusca from the Paraguana peninsula, Venezuela

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Miocene Mollusca from the Paraguana peninsula, Venezuela