The Last Dinosaurs of Brazil

[ZoPteryx]

An open-access review of the Bauru Group and its dinosaurian fauna from latest Cretaceous Brazil:

http://www.scielo.br/pdf/aabc/v89n3/0001-3765-aabc-89-03-01465.pdf

This study challenges the view that dinosaurs were already in decline before the meteor impact, as some hold to be true.  At the very least, it demonstrates that dinosaur diversity had not changed in this part of the world significantly from earlier in the Cretaceous.  Titanosaurs were still numerous and diverse, abelisaurs and carcharodontosaurs were still the top predators, and megaraptorans were still present as were a number of maniraptorans.  If any decline in diversity is present in the few known Maastrichtian Northern Hemisphere localities, such as Hell Creek, it may be something specific to those regions and not reflective of the world as a whole.

[Simon]

An open-access review of the Bauru Group and its dinosaurian fauna from latest Cretaceous Brazil:

http://www.scielo.br/pdf/aabc/v89n3/0001-3765-aabc-89-03-01465.pdf

This study challenges the view that dinosaurs were already in decline before the meteor impact, as some hold to be true.  At the very least, it demonstrates that dinosaur diversity had not changed in this part of the world significantly from earlier in the Cretaceous.  Titanosaurs were still numerous and diverse, abelisaurs and carcharodontosaurs were still the top predators, and megaraptorans were still present as were a number of maniraptorans.  If any decline in diversity is present in the few known Maastrichtian Northern Hemisphere localities, such as Hell Creek, it may be something specific to those regions and not reflective of the world as a whole.

in other news (with apologies to "Saturday Night Live") - "Generalissimo Francisco Franco is still dead!" 

Why so many people have clung for so long, so stubbornly, to the old, worn, transparently shaky and illogical, pre-Alvarez, meme about how "the dinosaurs were in decline at the end of the Cretaceous", based solely on the fragmentary discoveries at ONE site in the entire world (ie. "Hell Creek") has always mystified me.

Animals that dominated, adapted and evolved, over and over and over again for 160 MY would not "dwindle away" suddenly.  They would (and did, many many times over eons and eons) adapt to change, evolve, adapt to change, evolve, etc. etc.

The only thing that could - and DID - end their reign - was a catastrophe so sudden, so complete, and so world-wide, that it did not give them the time or the chance to adapt to it.

I will now sit back, kick back, open a beverage, and listen for the few dying echoes, slowly growing more and more quiet, from the Hell Creek canyons and Badlands, about the (non-existent) 'dinosaur decline at the end of the Cretaceous' ....

... (Well anyway, I was in a poetic mood tonight) 

[Gwangi]

[Neosodon]

Your solely basing the end cretaceous decline on the fossil record. Excuse my assumption but I thought the theory was based off of geological evidence of an increase in volcanic activity.

[ZoPteryx]

Your solely basing the end cretaceous decline on the fossil record. Excuse my assumption but I thought the theory was based off of geological evidence of an increase in volcanic activity.

In part, yes.  The Deccan Traps in India were increasing in activity right around the K/Pg boundary, but even there, dinosaur diversity seems unaffected based on the continued survival of top-of-the-food-chain species, titanosaurs and abelisaurs.  These are the species we would expect to disappear first if something was wrong.  Volcanic activity seems to have suddenly increased 66 mya, occurring either at or just after the Chicxulub impact in Mexico.  This has led to some speculation that the impact sent shock waves through Earth's core, igniting the volcano.  I'm not sure how likely that scenario is though, differing densities in Earth's core would complicate things.  Either way, while the Deccan Traps may have locally worsened the effects of the extinction, it does not appear that they proceeded it in any meaningful way.

North America, where most studies have been conducted, had its own issues.  Sea level drop had connected Laramidia and Appalachia, causing the faunas to homogenize to a degree.  This means that diversity was lower than previously, but this is to be expected.  Microfossil studies have not found a drop in diversity among small animals, or small dinosaurs for that matter.  As for the "three meter gap", my personal guess is that it does not represent several hundreds of thousands of years like we would traditionally think.  Instead, I suggest it represents a much shorter time interval and represents excessive amounts of erosion during the extinction event, caused by the effects of the impact.  In this scenario, the scarcity of fossils would be expected.  I believe there were a few lines of evidence that support this, such as the uneven distribution of the gap and the reports of shocked quartz being preset in the layer.

[WarrenJB]

I have to say I'm fairly amused by the way some 'facts' about dinosaur diversity are being overturned, just by dragging the gaze away from Laramidia. I love post-jurassic sauropods...

[amargasaurus cazaui]

A few things being stated perhaps in an incorrect light...the Deccan traps eruptions did precede the impact events by at least 2 million years if not more, depending what dating you accept. This means the world was already in the grip of a rather massive volcanic event prior to the suggested extinction event. There is also evidence that a massive marine regression was occurring prior to the extinction event. Either of these was quite serious in scope and possibly helped to undermine, and certainly at least did not help the dinosaurs chances for survival. Further there is also evidence for an impact of massive scale in Russia preceding the supposed extinction event, which itself times favorable to several impacts, at Sillvertip in the North Sea for instance. How did that all shape the outcome and final result? we may never know......but there are some potential clues in the record aside from measuring supposed dinosaur diversity.

[DC]

Good thread

thanks