The debate whether dinosaurs went extinct due to a large space rock that
struck the Earth \(65.5\) million years ago (MYA) may have been answered with
the discovery of a distinctive brow horn from a Ceratopsian dinosaur just 13
centimeters (5.1 inches) below the K-T boundary-the distinct layer of
geological sediments separating the Cretaceous and Tertiary periods.
Rocks laid down \(65.5\) MYA show a thin layer abundant in rare elements like
Iridium, spherules and shocked Quartz that could only have come from a
meteorite impact. Since no fossils have ever been found in sediments above the
\(\mathrm{K}-\mathrm{T}\) boundary, conventional wisdom has it that the end of
dinosaurs came with an asteroid impact that caused firestorms, acid rain and a
nuclear winter that blotted out the Sun.
But that theory had a hole in it. The fossil record showed an apparent lack of
dinosaur fossils in the last few million years leading up to the impact,
suggesting that the "three meter gap" proves that dinosaurs went extinct long
before the catastrophic impact.
Scientists working in the Hell's Creek formation in the Montana badlands say
they have resolved that dispute.
Writing in the Royal Society journal Biology Letters, the paleontologists
report on the new discovery of the closest dinosaur fossil ever found to the
\(\mathrm{K}\)-T boundary.
The ancient remains uncovered in Montana belong to the last known dinosaur to
ever walk the planet and gives weight to the theory that dinosaurs were in
fact wiped out by an asteroid impact. All other dinosaur fossils found are
either much older, or were unearthed after being washed from their original
graves into much younger sediments, long after they died.
The fossil is most likely of an adult triceratops, a dinosaur growing up to 30
feet long and weighing up to 13 tons. The nearly 18 -inch fossilized brow horn
was found just 5 inches below the \(\mathrm{K}-\mathrm{T}\) boundary.
"This is the youngest dinosaur that has been discovered in situ. Others can be
found in younger deposits, but those have been put there by geological
processes and are actually much older" said Tyler Lyson, a paleontologist at
Yale University.
The discovery undermines the theory that gained ground in the \(1980
\mathrm{~s}\), that dinosaurs died out due to climate change or rising sea
levels long before the planet was struck by a space rock. The theory carried
some weight due to a lack of fossils found within the "three meter gap" of the
\(\mathrm{K}-\mathrm{T}\) boundary.
The finding "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," Lyson told the Guardian.
Gaps in the fossil record-which is patchy at best-are nothing new. Another,
covering tens of millions of years, is clearly evident in the Hell's Creek
formations some 60 meters ( 200 feet) below the K-T boundary.
But because similar dinosaur fossils are found both above and below this gap
it is assumed the absence of fossils has more to do with geological processes,
or simply blind prospecting luck, than any extinction event and subsequent
miraculous reintroduction.
The "three meter gap" prior to the \(\mathrm{K}-\mathrm{T}\) boundary is unique
because dinosaur fossils never reappear in the geological record.
Dr. Paul Barrett of the Natural History Museum said the discovery was strong
evidence that dinosaurs were killed off in North America by a catastrophic
event, but the evidence is not conclusive globally.
"It shows that in this part of the world dinosaurs were still viable and still
roaming around at the time the meteorite hit. But what it doesn't tell us is
what was going on in the rest of the world, and it could be that in other
parts of the world dinosaurs were dying out at different rates and for
different reasons because of other things going on at the time," he told BBC
News.
He argues that just one brow horn discovery doesn't resolve the dispute over
dinosaur extinction.
Source: Scientists Find Fossil Below K-T Boundary" by Lawrence LeBlond.
RedOrbit.com, July 13, 2011. Reprinted by permission.
http://www.redorbit.com/news/science/2078377/
scientists_find_fossil_below_kt_boundary/
1\. What are the key observations mentioned in this article (select all that
apply)?
a) Dinosaurs were wiped out by a meteor impact
b) A dinosaur fossil was found within a few centimeters of the KT boundary
c) No in-situ, non-bird dinosaur fossils are found above the KT boundary
d) Climate change played a major role in the extinction of dinosaurs
2\. What hypothesis is best supported from the observations?
a) Dinosaurs across the planet were killed off by a meteor impact.
b) Dinosaurs in North America were killed off by a meteor impact.
c) Dinosaurs across the planet were not killed off by a meteor impact.
d) Dinosaurs in North America were not killed off by a meteor impact.
