A fossilized dinosaur bone discovered in New Mexico contradicts previous scientific data that suggests that dinosaur extinction occurred between 65.5 and 66 million years ago, says a team of researchers from the University of Alberta. 

Larry Heaman, study leader from the Department of Earth and Atmospheric Sciences at the University of Alberta, along with a team of researchers from the university, have found a fossilized femur bone of a hadrosaur in New Mexico that is only 64.8 million years old, showing that dinosaurs lived 700,000 years beyond mass extinction in the late Cretaceous period. 

Paleontologists believe that dinosaurs became extinct between 65.5 and 66 million years ago when debris from a large meteorite impact blocked the sun, changing the climate drastically and killing vegetation. Paleontologists determined this time period as the age of extinction by using a traditional technique called relative chronology, which has been used in this field of science to estimate the age of fossils. Relative chronology is when a fossil's age is determined by the depositional age of a layer of sediment where the fossil was found, or by the depositional age of layers of sediment above and below the fossil. But the problem with this method is that environmental and geologic forces can cause fossils to shift or migrate from their original layers of sediment, leading to a potentially inaccurate estimate of age. 

For this particular study, Heaman and the University of Alberta team checked the age of the recently discovered dinosaur bone using a technique called U-Pb (uranium-lead) dating. This method uses a laser beam to "unseat" tiny particles of the fossil. These particles are then subjected to isotopic analysis, which both determines age and the type of food the dinosaur ate.  

The U-Pb dating method is accurate because living bone carries low levels of uranium, but fossilized bone is rich with uranium. These uranium atoms decay into lead over time, and determining the isotopic composition of the lead in fossilized bones leads to its absolute age.  

After using this technique on the femur bone of the hadrosaur, Heaman and his team concluded that the bone is 64.8 million years old, which means that this hadrosaur came from a line of dinosaurs that survived the great mass extinction in the late Cretaceous period, and lived 700,000 years beyond it. Researchers believe these particular plant-eaters were able to survive mass extinction because some of the vegetation may have survived the climate change allowing them to eat.  

Now the researchers are looking to figure out if dinosaur eggs could have potentially survived during the period of mass extinction, which would further explain the survival of these dinosaurs. They also plan to use the U-Pb dating method to continue measuring the absolute age of other dinosaur fossils. Heaman believes that this technique will replace relative chronology, and will be used to rewrite the history of the extinction of the dinosaurs.   

This study, titled "Direct U-Pb dating of Cretaceous and Paleocene dinosaur bones, San Juan Basin, New Mexico," was published in Geology.