Evidence Shows Some Large Dinosaurs Survived Mass Extinction

[sparkchaser]

Saw this on Slashdot and had to share.

http://www.examiner.com/examiner/x-1242-Sc...mass-extinction

Original paper here: http://www.palaeo-electronica.org/2009_1/149/index.html

What do you think?

[Auspex]

The K-T "boundary" was established to mark a point of large-scale changes in the fossil record. I don't think of it as a hard line-in-the-sands-of-time, so I guess my attitude about the "controversy" is "Meh".

[Shamalama]

I agree, The article says half a million years beyond the end of the Cretaceous. Ok.... so a small pocket survived, maybe we need to move the K-T boundary date up by a million years. It doesn't change much of anything and is not too suprising. I find it hard to believe that every single dinosaur died at exactly the same time when the meteor hit. There will always be survivors, the real question is why didn't they prosper and diversify?

[Boesse]

Well, here's the breakdown, and afterward, I'm sure your attitude will be even more dismal than just 'meh'.

It is a partial skeleton that happens to occur within a Paleocene formation. The Paleocene age is constrained by palynology, paleobotany, and paleomagnetism. The fossil is said to be in-situ and not reworked because of the REE signature (Rare Earth Elements).

The REE signature of the bones and associated sediment were identical/similar. REE's (e.g. Uranium, Thorium atoms) get 'locked' into the bone matrix and accompanying sediment during early diagenesis due to migration of porewater (which has REE atoms in solution). When bones get eroded and transported, they will end up having a different REE signature (because during early diagenesis, there is extreme 'local' variability) from the associated sediment.

However, REE analysis ignores Le Chatelier's Principle - that chemical reactions can go both ways. It has been documented that migrating 'fronts' of other elements/minerals (i.e. iron) change through time, and literally migrate as an expanding boundary that cross-cuts sediment layers, sometimes vertically. Iron oxide banding in those beautiful Eolian deposits in the Southwest are a prime example of this exact phenomenon, which applies just the same to REE's.

So - the REE's don't really tell us anything. It is certainly possible to rework and transport a skeleton and keep it associated (and in at least one case, articulated). This is the same as the 'Bug Creek' Triceratops, which occurs in the formation overlying the Hell Creek Fm. in Montana.

My two cents - really inconclusive, no definitive evidence that this thing has not been reworked, and most importantly - even if it did, a single data point is only a single data point. The big-picture shows only one other example (Bug Creek Trike); both of which are more parsimoniously explained as being reworked.

I.e., much ado about nothing.

Bobby

[jpbowden]

I yawn in their general direction!

[ashcraft]

However, REE analysis ignores Le Chatelier's Principle - that chemical reactions can go both ways. It has been documented that migrating 'fronts' of other elements/minerals (i.e. iron) change through time, and literally migrate as an expanding boundary that cross-cuts sediment layers, sometimes vertically. Iron oxide banding in those beautiful Eolian deposits in the Southwest are a prime example of this exact phenomenon, which applies just the same to REE's.

Dude! Quoteing chemistry! I'll get you in an honorary labcoat yet!

Seriously though, I am glad you read the report and were able to synthesize, not an easy task. I haven't read the whole thing, but it threw up a flag when the submitted/accepted dates are measured in years and the acknowledgments mention "stimulating" debate.

Currently kneee deep in professional papers on ants,

Brent Ashcraft

[Boesse]

Haha, thanks. I don't think I deserve one - most of that was formulated by my fellow grad student Bryan, who knows a bit more about chemistry than myself. He brought that up during one of our regular socratic debates. I haven't read the entire paper, and I don't intend to (it is 120 pages about a subject of little relation to my research). However, these are salient points that the study does not address.

Bobby

[2ynpigo]

Not all of the evidence was mentioned. Jim Fassett also has found an articulated partial skeleton, strongly suggesting that the bones were not reworked.

[Boesse]

Yes, I know - that's the specimen in the paper. And it is possible to rework an articulated skeleton - hard to believe, but it is documented.

This would actually hold water if there were more than a couple of these things worldwide.

Bobby

[Boesse]

Actually, the skeleton is not articulated. It is a disarticulated (but associated) skeleton. Two points about this:

1) We do not know enough about fluvial processes to say that this (reworking and transporting a partial skeletal assemblage) cannot happen.

2) We know enough to infer that it has happened in many cases, and that it definitely happened in non-fluvial environments.

Fasset spends 95% of the article establishing the age of the formation - fine - its Paleocene, I get that. BUT, he fails to address that skeletons such as this may not be in-situ. And in this case, the odds are stacked highly, highly against it that it is in fact ex-situ.

Bobby

[siteseer]

Actually, the skeleton is not articulated. It is a disarticulated (but associated) skeleton. Two points about this:

1) We do not know enough about fluvial processes to say that this (reworking and transporting a partial skeletal assemblage) cannot happen.

2) We know enough to infer that it has happened in many cases, and that it definitely happened in non-fluvial environments.

Fasset spends 95% of the article establishing the age of the formation - fine - its Paleocene, I get that. BUT, he fails to address that skeletons such as this may not be in-situ. And in this case, the odds are stacked highly, highly against it that it is in fact ex-situ.

Bobby

I remember when Rigby (1987) found teeth of a subset of the Hell Creek dinosaurs in an overlying Paleocene formation and his results were roundly dismissed though many of the teeth were pristine with features that almost certainly would have been worn off with minimal to moderate transport. A paleo grad student told me that the teeth were still most likely reworked. If they are Cretaceous teeth, wouldn't they find a sample of just about everything from the Hell Creek. I know that can be explained too but it's quite a coincidence that only some of the dinosaurs are represented, which is in line with the observed decline in dinosaur diversity in the last 5-6 million years of the Cretaceous.

Hey, geology grad students know more about how remains can preserve than I but what I've noticed is that all the "Paleocene dinosaurs" I've heard of in Early Paleocene deposits where you might would expect to find the stragglers if any. I've never heard of anyone seriously report Middle or Late Paleocene dinosaur survivors. You'd think their remains would have been nudged, washed, rolled into those deposits as well.

Also, when Rigby found those teeth, other paleontologists said, "Yeah, whatever, find a skeleton and we'll talk." Now, someone has a skeleton and it's still being questioned. Obviously, science is all about the questioning and the testing and retesting until something is still sitting in the crucible, but is a "Paleocene dinosaur" some kind of taboo concept? Paleontologists seem to dislike that idea intensely. As Auspex noted, the K/T boundary is an imaginary line humans have designated. They can move it over a little if they want.

The odds are bad for any skeleton to fossilize but what are the odds of it getting removed from its resting place later in time and still staying at least partly together. I realize that can happen and has happened but wouldn't that be less likely than the idea of an Early Paleocene dinosaur? Occam's razor does apply to everything.

[trilo-biker]

I agree, The article says half a million years beyond the end of the Cretaceous. Ok.... so a small pocket survived, maybe we need to move the K-T boundary date up by a million years. It doesn't change much of anything and is not too suprising. I find it hard to believe that every single dinosaur died at exactly the same time when the meteor hit. There will always be survivors, the real question is why didn't they prosper and diversify?

thats is a good question because during the time that these bones are apperently dated mammals still werent that divesified yet meaning that there were still some niches that had not been filled yet

[ashcraft]

There are also studies that show dinosaur diversity was not declining at the end-Cretaceous, can't quote the source, but I have read them. Survivorship in North America would be unlikely, impact was too close. Survivorship would have been more likely in Aisa/Africa/Australia/Antartica. Studies of surviving species, particularly birds, show that most of the new species arose from species that existed in these areas that were more protected.

Brent Ashcraft

[Guest Inyo]

Well, here's the breakdown, and afterward, I'm sure your attitude will be even more dismal than just 'meh'.

It is a partial skeleton that happens to occur within a Paleocene formation. The Paleocene age is constrained by palynology, paleobotany, and paleomagnetism. The fossil is said to be in-situ and not reworked because of the REE signature (Rare Earth Elements).

The REE signature of the bones and associated sediment were identical/similar. REE's (e.g. Uranium, Thorium atoms) get 'locked' into the bone matrix and accompanying sediment during early diagenesis due to migration of porewater (which has REE atoms in solution). When bones get eroded and transported, they will end up having a different REE signature (because during early diagenesis, there is extreme 'local' variability) from the associated sediment.

However, REE analysis ignores Le Chatelier's Principle - that chemical reactions can go both ways. It has been documented that migrating 'fronts' of other elements/minerals (i.e. iron) change through time, and literally migrate as an expanding boundary that cross-cuts sediment layers, sometimes vertically. Iron oxide banding in those beautiful Eolian deposits in the Southwest are a prime example of this exact phenomenon, which applies just the same to REE's.

So - the REE's don't really tell us anything. It is certainly possible to rework and transport a skeleton and keep it associated (and in at least one case, articulated). This is the same as the 'Bug Creek' Triceratops, which occurs in the formation overlying the Hell Creek Fm. in Montana.

My two cents - really inconclusive, no definitive evidence that this thing has not been reworked, and most importantly - even if it did, a single data point is only a single data point. The big-picture shows only one other example (Bug Creek Trike); both of which are more parsimoniously explained as being reworked.

I.e., much ado about nothing.

Bobby

Actually, there's more to the story than the Rare Earth Elements signatures, a geochemical analysis which in itself is quite important; your easy dismissal of REE technology is perplexing, to say the least. The comparison to iron oxide migrations in "fossil" sand dunes throughout the US Southwest might hold water if one could prove that REE signatures found within the examined dinosaur bones and their Paleocene matrix matched REEs in both overlying and underlying geologic rock formations.

One of the other major telling points is that some 34 Hadrosaur bones from a single individual were found situated near one another in the Paleocene deposit, above the K-T boundary. Redeposition due to exhumation of remains and scattering of bones would certainly not concentrate that many vertebrate remains from the same creature in such a close proximity. Ergo, we're talking about in-situ dinosaur preservations here.

Perhaps additionally illuminating to this discussion would be to produce what evidence was used to determine that that partially articulated "Bug Creek Triceratops" had been reworked. One cannot instantly invoke parsimony without having considered other options; perhaps the Triceratops had not been reworked, after all, a conclusion that could be reached when investigators considered additional, complicated lines of evidence. But, if one were to lay claim to the "law of most parsimonious explanations"--what could be a simpler explanation, upon finding a partially articulated dinosaur skeleton, than to say that the specimen had been not been reworked?

At any rate, many years ago Rigby came to essentially the same conclusions while studying dinosaur material from a Paleocene formation--Rigby easily dismissed detractors who claimed that his specimens had been reworked and concluded, undoubtedly with great accuracy, that many dinosaurs had indeed survived the K-T boundary.

Fossil Leaves And Seeds In West-Central Nevada

http://inyo1.110mb.com/middlegate/middlegate.html