From Jerry in Los Angeles, CA
Some scientists have speculated that a few of the dinosaur species were warm-blooded and that some dinosaurs were feathered. However, these claims are not yet scientifically validated. Scientists do know that dinosaurs were not mammals. Dinosaurs, like reptiles today, laid eggs. Mammals have placentas.
Scientists also know for certain that many of the dinosaur species could not have been warm-blooded. The sheer size of the larger land-dwelling dinosaurs rules out the possibility. Additionally, many dinosaurs had small mouths, which means they could not have consumed enough food to maintain blood temperatures significantly different from the ambient temperatures of their environments. Thus, they could not have been warm-blooded.
The problem with identifying dinosaurs as feathered creatures is that land-dwelling dinosaurs overlapped birds in the fossil record by more than 70 million years. In some cases the “feather evidence” is ambiguous. In other instances, it is not possible to determine whether the fossil find is a dinosaur or a flightless bird.
For more on whether or not dinosaurs were warm-blooded, check out “Were Dinosaurs Warm-Blooded?” (podcast). For more on whether or not dinosaurs had feathers, check out “Feathered Dinosaur or Flightless Bird?” (article).