A team at Caltech (California Institute of Technology) have developed a new technique for determining the body temperatures of extinct vertebrates. The technique analyses rare isotopes in bones, teeth and egg shells, which clump in different ways dependent on temperature; higher temperatures result in less clumping. The process has an accuracy of just one or two degrees. They first tested this with living mammals, finding the temperature given came as 37 degrees, before testing it on mammoth teeth to find the same results. They then tested it on 12 million year old rhinoceros and crocodile fossils and found that it matched the results of living organisms.
This breakthrough can potentially have a big impact on palaeontology, giving more insight into palaeoclimates and investigations into both the physiology of extinct organisms and the evolution of warm blood, perhaps even illuminating what drove the change. Of course, one of the biggest questions it may finally provide an answer for (or at least strong evidence) is the classic question were dinosaurs warm or cold blooded? For the record I do not have a strong view on this and it is a while since I looked into it, so I could not formulate any sort of backing for my position without doing more research (which could potentially alter my view). At the moment I see the answer being a big mix. I believe some dinosaurs are likely to have been cold blooded, particularly the larger ones and possibly all of the ornithischians; I think many of the theropods, particularly the large ones, were possibly midway between being warm and cold blooded, but that they may have appeared to be warm blooded due to the warmer climates "turbo-charging" them; I also think that the smaller, feathered theropods were likely warm blooded and that birds inherited their warm blood from their dino ancestors.
Hopefully they will test a variety of dinosaurs when they come to answer this question. This test could potentially be misleading if not used carefully and on a wide range of specimens as it provides data only for a specific time (when the tooth grew for example).
For more information, the ScienceDaily article is here and the journal paper can be viewed here.