From Science News Blog:
Paleontologists Discover Oldest Mammalian Tooth Marks
Paleontologists discovered the oldest mammalian tooth marks on the bones of ancient animals, including several large dinosaurs. The findings were reported in a paper published online in the journal Paleontology on June 16. The image above is a close-up of the tooth marks gouged into the rib bone of a large dinosaur by a small mammal that lived 75 million years ago.
Nicholas Longrich of Yale University and Michael J. Ryan of the Cleveland Museum of Natural History came across several of the bones while studying the collections of the University of Alberta Laboratory for Vertebrate Palaeontology and the Royal Tyrrell Museum of Palaeontology. They also found additional bones displaying tooth marks during fieldwork in Alberta, Canada. The bones are all from the Late Cretaceous epoch and date back about 75 million years.
Longrich said, “The marks stood out for me because I remember seeing the gnaw marks on the antlers of a deer my father brought home when I was young. So when I saw it in the fossils, it was something I paid attention to.”
The researchers believe the marks were made by mammals because they were created by opposing pairs of teeth. This is a trait seen only in mammals from that time period. They think they were most likely made by multituberculates, an extinct branch of mammals that resemble rodents and had paired upper and lower incisors. The paleontologists discovered tooth marks on a femur bone from a Champsosaurus, an aquatic reptile that grew up to five feet long; the rib of a dinosaur, most likely a hadrosaurid or ceratopsid; the femur of another large dinosaur that was likely an ornithischian; and a lower jaw bone from a small marsupial.
The animals that made the marks were about the size of a squirrel. Longrich says, “The bones were kind of a nutritional supplement for these animals.”
See also here.
Global historical biogeography of hadrosaurid dinosaurs: here.
Double strike ‘killed dinosaurs’: here.
Researchers demonstrate that the extinction of dinosaurs 65 million years ago made way for mammals to get bigger – about a thousand times bigger than they had been. The study, which is published in the prestigious journal Science, is the first to show this new pattern of increased body size of mammals after the exit of the dinosaurs: here. And here.
ScienceDaily (Mar. 14, 2012) — Conventional wisdom holds that during the Mesozoic Era, mammals were small creatures that held on at life’s edges. But at least one mammal group, rodent-like creatures called multituberculates, actually flourished during the last 20 million years of the dinosaurs’ reign and survived their extinction 66 million years ago: here.
Mammals Grew 1,000 Times Larger After the Demise of the Dinosaurs: here.
Dinosaurs on Road to Extinction Before Asteroid Strike. Plant-eating dinosaurs like hadrosaurs were already in decline before the big asteroid struck: here.