Scientists have unearthed a dinosaur bone dated to be 64.8 million years old, according to a study published online Jan. 26 in Geology.
The fossil is a femur bone of the sauropod species Alamosaurus sanjuanensis. The species is a herbivorous dinosaur that can reach up to 20 meters (about 67 feet) in length.
The bone was dated using uranium-lead (U-Pb) dating, “based on the decay of two different U-isotopes, 238U and 235U,” Dr. Larry Heaman of the University of Alberta in Canada told The Epoch Times. “These two isotopes decay at a known rate over time to two lead isotopes, 206Pb and 207Pb respectively.”
“What is new about our approach to dating dinosaur bone is that we use relatively new technology to measure the uranium and lead isotopic composition of bone,” said Heaman.
“This new technology is called laser ablation inductively coupled plasma mass spectrometry. We prepare a thin slice of the bone and then aim a 160-micron-diameter laser beam at selected parts. The laser pulses liberate tiny particles from the bone. These particles are transported to a plasma where they are dissociated and ionized. The ionized particles are accelerated into a mass spectrometer and the isotopic composition of lead is determined.”
This technique allows the fossil to be dated directly, as apatite, which is a major component of bone mineral, can incorporate uranium, Heaman said. This makes the dating more accurate than other methods that determine the age of fossils from substances in the surrounding area.
“The new technique we developed is more accurate than previous unsuccessful attempts at direct dating of bone because the geochemistry of bone can be complex and disturbed by interaction with fluids subsequent to fossilization,” he said.
“Our technique allows us to identify pristine parts of bone that are not disturbed. These well-preserved domains are typically very small, so the ability to specifically access the material in these undisturbed domains has been key to the success of the technique.”
This discovery of a 64.8-million-year-old sauropod fossil “confounds the long-established paradigm that the age of dinosaurs ended between 65.5 and 66 million years ago,” a University of Alberta press release said.
It was previously believed that non-avian dinosaurs became extinct during the Cretaceous-Tertiary extinction event, which happened about 65.5 million years ago, 700,000 years earlier than the bone was dated.
“The fossil-bearing layer that contains the young bone we dated is located above the K/T [Cretaceous-Tertiary] boundary, a boundary identified in many places worldwide that has an anomalous content of iridium, an element that is abundant in meteorites. This has led to the theory that a giant meteorite event occurred at this time and is the single reason why so many species went extinct,” Heaman said.
He continued: “There is some debate about the age of this boundary, but the most recent Geologic Time Scale places this boundary at 65.5 Ma [million years ago]. More recent studies have proposed the boundary is even older (66.0 Ma).
“At face value, if dinosaurs were all killed off by this event, then there should be no bones preserved in layers above the K/T boundary. Scientists have proposed that, in cases like the layer we studied, dinosaur bones located above the K/T boundary were not originally deposited there; they are older, and through erosion and re-deposition have been move to this site at a later time post-K/T event.
“The age that we obtained for the dinosaur bone is in fact younger than the K/T boundary, so this is the first direct evidence that some dinosaurs survived this event. It opens the question as to what actually caused the dinosaurs to go extinct and could destroy a 30-year-old paradigm that all dinosaurs were killed by a giant meteorite impact at 65.5 Ma.”
Read the research paper here.
