Bali-like temperatures in Wyoming? Fossils reveal tropically hot North America 95 million years ago

Cretaceous oysters of the genus Pycnodonte investigated in the new study. These specimens were collected in San Miguel County, Colorado ( top left ), Kane County, Utah ( top right ), Big Horn County, Wyoming ( bottom left ), and Natrona County, Wyoming ( bottom right ), with a penny for scale. Image credit: Matt Jones A new University of Michigan study that used fossil oyster shells as paleothermometers found the shallow sea that covered much of western North America 95 million years ago was as warm as today's tropics. The study provides the first direct temperature data from that vast mid-latitude sea during the height of the Cretaceous Thermal Maximum, one of the planet's hottest climate intervals of the past several hundred million years. The findings, published online May 9 in the journal Geology, also hint at what may be in store for future generations unless emissions of heat-trapping greenhouse gases are reined in. "These data indicate that the North American interior during the peak of the Cretaceous greenhouse was as warm as the hottest conditions in the modern-day tropics-imagine the climate of Bali, Indonesia, in places like Utah or Wyoming,” said study lead author Matt Jones, a former University of Michigan postdoctoral researcher now at the Smithsonian Institution's National Museum of Natural History. The study found that average water temperatures in the Western Interior Seaway during the mid-Cretaceous ranged from 28 to 34 degrees Celsius (82 F to 93 F), as warm as modern tropical extremes like the Indo-Pacific Warm Pool, which consistently exhibits the highest water temperatures over the largest expanse on the Earth's surface.