On 01/29/2011 06:33 AM, Thomas R. Holtz, Jr. wrote:
On Sat, January 29, 2011 2:57 am, Roberto Takata wrote:How reliable are those results?Not terribly.
The range on their data is pretty broad, too. The date for the "Paleocene" dinosaur bone was 64.8 ±0.9 million years (and the "test" Cretaceous bone has similarly broad ranges)! So, anywhere from 63.9 to 65.7 is tenable. Compare this with the 65.5 ± 0.3 Ma K-Pg boundary that David mentions (65.2 - 65.8), and a Paleocene date is hardly convincing. Let's not forget that even if the date for the bone is accurate, it only reflects the date when the uranium was emplaced in the bone (highly dependent on groundwater conditions - may have been 3 years after the bone was buried, may have been 300,000). As Tom mentions, the recent comment in PE points out many concerns for a Paleocene date on certain fossils from the San Juan Basin.
AndyP.S.: For another great (and oft-neglected) paper on the issue of Paleocene dinos in the Western Interior, check out:
Lofgren, D.L., Hotton, C.L., and Runkel, A.C. 1990. Reworking of Cretaceous dinosaurs into Paleocene channel deposits, upper Hell Creek Formation, Montana. Geology, 18:874-877.