Interesting paper, the focus of which is twofold: 1) demonstate the applicability of new U-Pb dating technology on fossil bone material; and 2) support the hypothesis that some non-avian dinosaurs survived into the earliest Paleocene. I'll need someone with more background on radioisotopic dating techniques to evaluate this paper for me, especially regarding aspects of Pb loss, diagenetic recrystallization, etc., but the implications are exciting if indeed this technique can be used to directly date fossil materials.
I think the idea of Paleocene dinosaurs will be debated for a long time, but really what does it matter? It is not as if non-avian dinosaurs made it into the Paleocene, that they made it very far in. Our base geologic timescales are based upon stratigraphic ranges of marine organisms, which are only now starting to be well calibrated. Correlation of these intervals between the marine and terrestrial realms is tricky at best and I would not be surprised if as we get more precision and accuracy in our dating techniques we find that there is a little slop around boundary defining events (i.e. extinctions of major terrestrial groups) and the exact dates defining the marine-defined boundaries.
But does it really matter if the last non-avian dinosaurs died out entirely by the exact last day of the Cretaceous, or if a few locally squeezed into the earliest Paleocene? These dates are so similar in relation to the overall earth timescale that they are pretty much simultaneous and really have no bearing on our ideas regarding the extinction of non-avian dinosaur. Same goes for the Triassic, if we find a phytosaur in the very earliest Jurassic strata is this really significant other than for general bean counting? I for one would not be surprised one bit if such a specimen was found; however, these data would not offer much in resolving the real question, which is why these major extinctions occurred in the first place.
Fassett, J.E., Heaman, L.M., and A. Simonetti. 2011. Direct U-Pb dating of Cretaceous and Paleocene dinosaur bones, San Juan Basin, New Mexico. Geology 39:159-162. doi: 10.1130/G31466.1
Abstract - Vertebrate fossils have been important for relative dating of terrestrial rocks for decades, but direct dating of these fossils has heretofore been unsuccessful. In this study we employ recent advances in laser ablation in situ U-Pb dating techniques to directly date two dinosaur fossils from the San Juan Basin of northwestern New Mexico and southwestern Colorado, United States. A Cretaceous dinosaur bone collected from just below the Cretaceous-Paleogene interface yielded a U-Pb date of 73.6 ± 0.9 Ma, in excellent agreement with a previously determined 40Ar/39Ar date of 73.04 ± 0.25 Ma for an ash bed near this site. The second dinosaur bone sample from Paleocene strata just above the Cretaceous-Paleogene interface yielded a Paleocene U-Pb date of 64.8 ± 0.9 Ma, consistent with palynologic, paleomagnetic, and fossil-mammal biochronologic data. This first successful direct dating of fossil vertebrate bone provides a new methodology with the potential to directly obtain accurate dates for any vertebrate fossil.
Botany 2015 - Tuesday
4 hours ago in The Phytophactor