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Planet Earth

Post-Cretaceous Dinosaurs

Gene ExpressionBy Razib KhanApril 29, 2009 11:20 PM

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New Geochronologic And Stratigraphic Evidence Confirms The Paleocene Age Of the Dinosaur-Bearing Ojo Alamo Sandstone And Animas Formation In The San Juan Basin, New Mexico and Colorado:

...An assemblage of 34 skeletal elements from a single hadrosaur, found in the Ojo Alamo Sandstone in the southern San Juan Basin, provided conclusive evidence that this assemblage could not have been reworked from underlying Cretaceous strata. In addition, geochemical studies of 15 vertebrate bones from the Paleocene Ojo Alamo Sandstone and 15 bone samples from the underlying Kirtland Formation of Late Cretaceous (Campanian) age show that each sample suite contained distinctly different abundances of uranium and rare-earth elements, indicating that the bones were mineralized in place soon after burial, and that none of the Paleocene dinosaur bones analyzed had been reworked.

Here's ScienceDaily with more:

So does this provide conclusive proof that dinosaurs survived the Cretaceous extinctions? According to David Polly, one of the editors of the journal in which the research is published, "this is a controversial conclusion, and many palaeontologists will remain sceptical", but we already know that flying theropod dinosaurs (more generally referred to as birds) and crocodiles survived, so the possibility of pockets of survivors of other types of dinosaur is not quite as far fetched as it might sound. Finding conclusive evidence, however, is a difficult matter when the crime scene is 65 million years old. "One thing is certain," continues Polly, "if dinosaurs did survive, they were not as widespread as they were before the end of the Cretaceous and did not persist for long." The 'Lost World scenario' of humans and dinosaurs existing at the same time, still belongs firmly in the realms of pure fantasy.

Extraordinary claims demand extraordinary evidence. Nevertheless, from what little I know lineages tend to predate and postdate the last extant fossils at any given time. This probably explains some of the periodic discrepancies between fossils and molecular evolution clocks.

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