March 15, 2012
Mammals Flourished During Last 20 Million Years Of Dinosaur Era
New research suggests that some mammals flourished during the last 20 million years of the dinosaurs' reign.
University of Washington paleontologist Gregory P. Wilson suggests the multituberculates, a rodent-like creature, did so well during this time because they developed numerous tubercles on their back teeth that allowed them to feed on flowering plants back then.
“These mammals were able to radiate in terms of numbers of species, body size and shapes of their teeth, which influenced what they ate,” Wilson, a UW assistant professor of biology, said in a press release.
Multituberculates were roughly the size of a mouse about 170 million years ago. When angiosperms, a flowering plant, started to appear about 140 million years ago, the mammals' body size increased, ranging from mouse-sized to the size of a beaver.
The mammal continued to flourish after the dinosaur's extinction, until other mammals like ungulates and rodents began to gain a competitive advantage. Multituberculates eventually became extinct about 34 million years ago.
Scientists used laser and computed tomography scanning to create 3D images of the teeth in very high resolution, less than 30 microns.
Wilson said they analyzed the tooth shape much as a geographer might in examining a mountain range when charting topography.
He said carnivores had relatively simple teeth, with about 110 patches per tooth row, because their food is easily broken down. However, animals that depend on vegetation for sustenance have teeth with substantially more patches because the food is harder to break down.
The new analysis shows multituberculates' teeth became less prominent over time and the teeth in the back became very complex, with as many as 348 patches per row.
“If you look at the complexity of teeth, it will tell you information about the diet,” Wilson said. “Multituberculates seem to be developing more cusps on their back teeth, and the bladelike tooth at the front is becoming less important as they develop these bumps to break down plant material.”
The researchers determined that some angiosperms suffered little effect from the dinosaur extinction event because the multituberculates that ate the plants continued to prosper.
Wilson said that as the plants spread, the population of insect pollinators likely grew too, and species feeding on insects would have also benefited.
The research was published in the March 14 online edition of the journal Nature.
Image Caption: An artist's conception depicts a multituberculate in its natural habitat at the time of the dinosaurs. Credit: Jude Swales/Burke Museum of Natural History and Culture