PALEO

In Homestead Cave near Utah’s Great Salt Lake, owls have been regurgitating pellets containing the undigested bones and hair of prey — typically small mammals like rodents — at a relatively constant rate since the end of the Pleistocene glaciations about 13,000 years ago. Those pellets have stacked up and fossilized in the cave to present a near-continuous glimpse into how mammal communities in this part of the Great Basin region have changed over time. Now, paleontologists examining bones in the pellets have found that, although small mammals in the region have generally been able to adapt to shifting ecosystems in the past, today, in the face of landscape-altering human activity, the mammal population is changing in unprecedented ways.

Dinosaurs dominated the continents during the Mesozoic, and for a long time, paleontologists assumed our mammalian ancestors kept a low-profile in that era, existing only as small, ground-dwelling, nocturnal insect-eaters. But in the last decade, discoveries of an ever-increasing diversity of mammal fossils have forced a rethink: Mesozoic mammals were also gliders, climbers, diggers and swimmers. Now, scientists looking at mammalian rates of evolution during the time of the dinosaurs have found that this diversity peaked in the Mid-Jurassic, leading to new physical characteristics that would remain for millions of years.

 

While moving across the country from California to Michigan two years ago, I stopped at Dinosaur National Monument, or “Dinosaur,” which today covers 85,000 hectares and straddles the northern portion of the border between Colorado and Utah. I camped at the Green River Campground on the Utah side, and from there, Split Mountain, on the western margin of the east-west-trending Uinta Mountains, glowed violet-pink in the sunset light. 

 

Fossil dinosaur eggs and nests offer clues about dinosaur development and behavior: Based on past work, for example, scientists have thought that some dinosaurs, like oviraptors, brooded, or sat on their eggs, much like modern birds do. Now, the results of a new study describing two fossil egg nests suggest that some dinosaurs used the same nesting sites again and again.