Youngest Dinosaur Bone Yet Reawakens Extinction Debate

By Valerie Ross | July 13, 2011 1:26 pm

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

CATEGORIZED UNDER: Living World
  • Joel

    I don’t understand why both points of view can’t be right. Gradual extinction could have been well under way when the mass extinction happened.

  • Pam

    Ditto. Not mutually exclusive.

  • jdmimic

    Joel, your point is exactly what most scientists who support the gradual extinction hypothesis say. Most gradualists quite readily say that dinosaurs lived right up to the end, or at least vey close to it, just that the ecosystem that supported them was changing and in terms of the dinosaurs, failing. Then along comes the asteroid, which makes things just impossible for them. Quite a few gradualists would say if you asked them, that more dinosaurs may have survived (since some did in fact surivive, aka birds) if the asteroid had not hit, the asteroid just being the final straw.
    The cataclysm supporters on the other hand, state that the entire ecosystem was doing just fine and that dinosaurs were thriving right up to the end and would have continued to dominate the landscape if the asteroid hadn’t hit. So in those terms, they ARE mutually exclusive. You can’t be thriving all the way to the end and declining at the same time.

  • amphiox

    The cataclysm supporters on the other hand, state that the entire ecosystem was doing just fine and that dinosaurs were thriving right up to the end and would have continued to dominate the landscape if the asteroid hadn’t hit. So in those terms, they ARE mutually exclusive. You can’t be thriving all the way to the end and declining at the same time.

    On the other hand, you could be going through a temporary decline in fortunes, an ecological rough patch, from which, once you make it through, you rapidly recover your former levels of diversity and success and sustain them to the present day, if it were not for the unfortunate blow that knocks you over at your weakest point.

  • http://www.askwhy.co.uk/dinosauroids/ Mike Magee

    “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”

    I do not see how Lyson et al can be so assured that their discovery proves the animal was alive so close to the KT boundary. I mean, can they exclude that the bone was near the surface because deposits above had been eroded away, the animal having been buried for several millions years? The animal could have been fossilized in river mud as mudstone which later was pushed up by seismic action and then the surface eroded back to leave the bone just below the new surface. It is geologically common, so cannot be excluded surely.

    I am not defending the thesis that the dinosaurs were long dead when the asteroid fell, just questioning the assurance of the claim that this proves they were not.

  • Geack

    Mike –

    Presumably, if the bone’s location could be so easily explained away, it wouldn’t be making such a splash. These people do this for a living – it’s generally safe to assume that issues like this are well-resolved before anyone bases any major claims on them.

  • Austin

    They’re not mutually exclusive. Some paleontologists have suggested that the dinosaurs were already on their way out (or at least very weakened), and the astroid was the coup de grace that finally did them in.

    It’s certainly possible, and I think even likely. It’s often the case that extinction events have multiple causes.

  • http://www.cba.ufl.edu Harold

    I’m just thrilled with this find for a multitude of reasons, chief among which are that my son, Stephen Chester, was the one who stumbled upon this find during a break in Montana where they were digging for pre-primate fossils, not dinosaurs. Stephen is an author on the Biology Letters article on this find. He’s a Phd student in vertebrate paleontology at Yale. Tyler
    his friend and roommate, is lead author.

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