"By looking at a host of animals with different physiologies, we were better able to pin down warm- and cold-month temperatures," she said. "Many aspects of biodiversity and species richness are related more to seasonal temperatures and ranges such as cold-month means rather than to mean annual temperature."
Bowfins -- which have a long dorsal fin and powerful jaws -- inhabit a variety of waters today from the Saint Lawrence River drainage in Quebec south to Florida and Texas. The team also compared the ranges of bowfins, aquatic turtles and giant tortoises of today with their ranges in the Eocene to help them estimate temperatures, according to co-author Newbrey, an expert in both contemporary and extinct fishes.
Eberle said the new study implies Eocene alligators could withstand slightly cooler winters than their present-day counterparts, although data from captive alligators show they are heartier than other members of the crocodilian family and can survive short intervals of subfreezing temperatures by submerging themselves in the water.
In contrast, the existence of large land tortoises in the Eocene High Arctic is still somewhat puzzling, said Eberle, since today's large tortoises inhabit places like the Galapagos Islands where the cold-month average temperature is about 50 degrees F (10 degrees C.)
But during the late Pleistocene period some 10,000 to 50,000 years ago -- when air temperatures were comparable to those today -- large land tortoises were found as far north as present-day Pennsylvania and Illinois, Eberle said. This suggests their present range in the Americas does not represent their fullest geographic range as allowed by climate. Facto
|Contact: Jaelyn Eberle|
University of Colorado at Boulder