March 2003

From Geological Society of America

GSA cordilleran section meets this week in Puerto Vallarta

Geoscientists from around the globe are gathering this week in Puerto Vallarta, Mexico, for the 99th annual meeting of the Geological Society of America Cordilleran Section. Topics of interest include new data on when South American mammals crossed the Panamanian land bridge into central America, and what Earth's oceans were like after the Permian-Triassic mass extinction.


The Great American Biotic Interchange: Earlier Than We Thought?

Scientists generally hold that the first South American animals crossed the Panamanian land bridge into Central America anywhere from 2.5-3.1 million years ago. This view is now being called into question based on recent discoveries in central Mexico. Oscar Carranza-Castaneda of the Center for Geosciences at UNAM and his colleagues Wade Miller and Bart Kowallis at Brigham Young University have identified several South American immigrants who may have arrived more than a million years earlier. Carranza-Castaneda will describe mammals whose remains were found in several different areas of central Mexico. They include ground sloths (Megalonyx and Glossotherium), giant armadillo-like animals (Glyptodont and Pampathere), and very large rodents (two species of Capybaras). He will also discuss the radiometric dating processes used to estimate their time of arrival. These discoveries may be considered evidence that the Isthmus of Panama was formed earlier than previously thought.

Oscar Carranza-Castaneda
Universidad Nacional Autonoma de Mexico
[email protected] 45 234 112 ext. 110

Thursday, April 3, Hotel NH Krystal, Mismaloya, 9:55 a.m.
View abstract at

Oceans Hostile to Life: Biotic Recovery from the Permian-Triassic Mass Extinction
The Permian-Triassic mass extinction, one of five major mass extinctions in Earth's history, took place approximately 250 million years ago. At that time, the supercontinent Pangea was surrounded by a mega-ocean known as the Panthalassic. Deep waters had lost much of their life-supporting oxygen and it would be 7-10 million years before life would begin to flourish again. Adam Woods of Santa Ana College will present research that suggests low levels of oxygen weren't the only reason waters were detrimental to life. Woods examined rocks and the environmental conditions under which they formed in east-central California, Nevada, and portions of Wyoming, Idaho, Montana and western Alberta. Rocks from California's Union Wash Formation reveal evidence of elevated levels of carbon dioxide. Ocean chemistry may thus have been a throwback to that of the Paleozoic 2.5 billion years ago. A combination of too little oxygen and too much carbon dioxide may have played a role in delaying biotic recovery.

Adam D. Woods
Santa Ana College
Santa Ana, CA
[email protected]

Thursday, April 3, Hotel NH Krystal, Mismaloya, 8:55 a.m.
View abstract at

** View the entire scientific program at

This article comes from Science Blog. Copyright 2004

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