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Planet Earth

Youngest Dinosaur Bone Yet Reawakens Extinction Debate

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What's the News: Researchers have uncovered the youngest known dinosaur bone, dating from shortly before an asteroid slammed into Mexico's Yucatan peninsula around 65 million years ago. The find, published today in Biology Letters, has revived debate among paleontologists over what, exactly, killed the dinosaurs. What's the Context:

  • Scientists generally agree that the asteroid's impact triggered some sort of mass extinction, a time called the Cretaceous-Tertiary, or K-T, boundary.

  • Some researchers say the asteroid, which may have led to a thermal pulse or something like a nuclear winter, is what did the dinosaurs in.

  • Others say dinosaurs were dying out before the asteroid hit, as a result of volcanic eruptions, climate change, or shrinking inland seas.

  • The K-T boundary is a clearly demarcated layer in the sedimentary rock of the Earth's crust. Below it is a zone about 10 feet thick often called the "three-meter gap" because of the lack of fossils found there. Scientists who believe the dinosaurs were in gradual decline pointed to this gap as support for their theory: If the dinosaurs lived right up until the asteroid hit, where were the fossils?

How the Heck:

  • Digging in the Hell Creek formation in Montana, the researchers found an 18-inch-long horn belonging to a ceratopsian dinosaur (the group that includes Triceratops).

  • The horn was only about 5 inches below the K-T boundary, suggesting the dinosaur---and, likely, other dinosaurs---may have been alive shortly before the asteroid hit. (The three-meter gap, in total, is thought to correspond to 100,000 years.)

What Does It Mean:

  • Take 1: The Asteroid Did It. "This demonstrates that dinosaurs did not go extinct prior to the impact and that at least some dinosaurs were doing very well right up until we had the impact," paleontology grad student Tyler Lyson, the study's lead author, told the Guardian. Finding a fossil so close to the K-T boundary lends weight to the idea that the asteroid triggered the dinosaurs' extinction. Several finds in recent years uncovered fossils and even T. rex footprints in the gap, some less than a foot below the K-T boundary, but none have narrowed the gap as much as this discovery has. Some researchers suspect more such fossils are waiting to be found.

  • Take 2: This Changes Nothing. Since this is only one bone, other researchers aren't convinced it proves anything. Scientists who favor gradual extinction say that their theories suggest there will be fewer fossils close to the K-T boundary, not that there won't be any; a single find doesn't disprove that. As paleontologist J. David Archibald, a proponent of the idea that shrinking seas led to the dinosaurs' extinction, told ScienceNOW, "finding one fragment of dinosaur [does not] suddenly make this gap go away."

Reference: Tyler R. Lyson, Antoine Bercovici, Stephen G. B. Chester, Eric J. Sargis, Dean Pearson, & Walter G. Joyce. "Dinosaur extinction: closing the ‘3 m gap’." Biology Letters online before print, July 13, 2011. DOI: 10.1098/rsbl.2011.0470

Image: Wikimedia Commons / ArthurWeasley

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