Dinosaurs Survived Mass Extinction Event by 700,000 Years

[n2doc]

ScienceDaily (Jan. 27, 2011) — University of Alberta researchers determined that a fossilized dinosaur bone found in New Mexico confounds the long established paradigm that the age of dinosaurs ended between 65.5 and 66 million years ago.

The U of A team, led by Larry Heaman from the Department of Earth and Atmospheric Sciences, determined the femur bone of a hadrosaur as being only 64.8 million years old. That means this particular plant eater was alive about 700,000 years after the mass extinction event many paleontologists believe wiped all non-avian dinosaurs off the face of earth, forever.

Heaman and colleagues used a new direct-dating method called U-Pb (uranium-lead) dating. A laser beam unseats minute particles of the fossil, which then undergo isotopic analysis. This new technique not only allows the age of fossil bone to be determined but potentially can distinguish the type of food a dinosaur eats. Living bone contains very low levels of uranium but during fossilization (typically less than 1000 years after death) bone is enriched in elements like uranium. The uranium atoms in bone decay spontaneously to lead over time and once fossilization is complete the uranium-lead clock starts ticking. The isotopic composition of lead determined in the hadrosaur's femur bone is therefore a measure of its absolute age.

Currently, paleontologists date dinosaur fossils using a technique called relative chronology. Where possible, a fossil's age is estimated relative to the known depositional age of a layer of sediment in which it was found or constrained by the known depositional ages of layers above and below the fossil-bearing horizon. However, obtaining accurate depositional ages for sedimentary rocks is very difficult and as a consequence the depositional age of most fossil horizons is poorly constrained. A potential weakness for the relative chronology approach is that over millions of years geologic and environmental forces may cause erosion of a fossil-bearing horizon and therefore a fossil can drift or migrate from its original layer in the strata. The researchers say their direct-dating method precludes the reworking process.

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http://www.sciencedaily.com/releases/2011/01/110127141707.htm

[mike_c]

1. um, I'm assuming that 700K years is well within the margins of error...

...for typical relative chronology dating. I wouldn't draw too many conclusions until a wider selection of existing (and strata dated) fossils is dated more accurately.

[Odin2005]

3. You can tell if it is younger than the K/T Impact quite easily.

Because of the Iridium-rich clay band.

The real issue is redeposition, fossils can be eroded out of sediment and re-deposited in younger sediment.

[jberryhill]

2. Some will run for office in 2012 /nt

[intaglio]

4. Problems, with this research

Indeed I smell a tactical announcement in the battle for funds. First look at the date they have produced and how it relates to the date of the KT boundary; the difference is 700,000 years which is pretty close to 1% of the timeline (64.8 to 65.3 millions of years). In other words - not a lot.

Second, calibration; how well is this method calibrated against others? C14 dating had to be recalibrated from finds in dendrochronology, ocean sediments, lake sediments and cave deposits. The calibration curves for C14 correct apparent date according to apparent age and location. This U to Pb method they say is new; so how well calibrated is it?

Third is the is sampling error. The method described ablates a sample from the surface of the fossil so you are dealing with pretty tiny quantities of material; so how did the researchers avoid contamination problems? The "surface" of the sample will be pretty ill defined to start with.

Fourthly, we do not know much about the diet or metabolism of dinosaurs in general, let alone individual species, and the metabolism of this species (or it's primary food source) could well have concentrated or diluted particular isotopes of Uranium or lead. Related to this is the environment locally at the time of the Dino's life. Was there something similar to Oklo in the vicinity.

And lastly from me; what was the stratigraphy, if any, round the sample? Have they been able to find a local analogue of the iridium rich KT layer and where was the sample in relation to that layer?

[sofa king]

5. On the other hand....

This post is really just to point out how cogent and organized intaglio's observation above is, by offering something far less convincing.

But the earth is a big place, with local and unique phenomenon across its surface. Even in the event of a disaster as large as the K-T event, there must exist the possibility that some tiny population of dinosaurs survived the event for a time, (like, for example, by being near a heat source like a volcano in an area where there were fungi to feed on even when photosynthesis was impossible).

If such a thing were to happen, the survivors would almost certainly be herbivores, as hadrosaurs were. And if that population were to survive through the immediate aftermath of the event, there would of course be no predators to cull the population, so they might rebound fairly well for a time.

But their eggs would also be a prime target for emerging proto-rodents, so even if they survived the event, their days might be numbered.

And wouldn't that be interesting, if two competing theories of the demise of the dinosaurs both turned out to be the case?

[intaglio]

6. I'm blushing, but you're right -about the implications of survival

The KT is convenient horizon in the strata and we know that some dinosaurs survived (birds). There is no reason why other parts of the group could not have survived for hundreds or thousands of years - as damaged populations moving jerkily towards extinction. But 700,000 years is a bit too long and I am suspicious.


I remember following (as a layman) the fights and tussles between the "Gradualists" and the "Catastrophists" of both the evolutionary and paleontological worlds. This seemingly finished with the discovery of the KT boundary and the simple "Disney" like ending to the "Reign of The Dinosaurs". Even then the scientific community knew things had to be more complicated, but it made a simple, dramatic story to stop the general public asking annoying questions.

[Ian David]

7. Obviously, this is the group that escaped to The Great Valley