"This is arguably the most comprehensive data set for the early Eocene High Arctic, and certainly explains how alligators and giant tortoises could live on Ellesmere Island some 52 to 53 million years ago," said Eberle, who also is the curator of fossil vertebrates at the University of Colorado Museum of Natural History.
During the Eocene, Ellesmere Island -- which is adjacent to Greenland -- probably was similar to swampy cypress forests in the southeastern United States today, said Eberle. Eocene fossil evidence collected there in recent decades by various teams indicate the lush landscape hosted giant tortoises, aquatic turtles, large snakes, alligators, flying lemurs, tapirs, and hippo-like and rhino-like mammals.
The bone and tooth enamel of vertebrate fossils contains biogenic apatite -- a mineral that is fossilized after the death of living organisms and which can be used as a "flight recorder" to infer paleoclimate conditions. Since all of the fossil materials were from the same stratigraphic layer and locality, the oxygen isotope ratios from the animals are linked to the temperatures of both ingested river water and precipitation at the time, allowing them to better estimate temperatures in the Eocene both annually and seasonally, she said.
"We use the water that the animals were drinking as a proxy for paleotemperature," said Eberle. "In mammal fossils, for example, we can analyze the oxygen isotope ratios in a sequence along the length of a large fossil tooth and estimate the warm-month and cold-month averages during the Eocene because teeth grow year round. When it comes to oxygen isotope values in tooth enamel, what we found for these creatures is that you are what you drink," she said.
The team looked at teeth from a large, hippo-like mammal known as Coryphodon, as well as bones from bowfin fish and shells and bones from aquatic turtles fro
|Contact: Jaelyn Eberle|
University of Colorado at Boulder