Sometimes I feel like I'm watching scientists concerned with the end-Cretaceous extinction (the one that killed off all those nifty non-avian dinosaurs and other animals) engage in a more formal version of the Monty Python "Argument Clinic" Sketch. Some that favor the impact of a comet or meteor of being the "smoking gun" accuse their opponents of being grumpy old uniformitarian fundamentalists, while some that favor a more gradual extinction that was mostly over by time the extraterrestrial body hit the earth say that the other side is made up a bunch of catastrophists that wouldn't know a trilobite if one bit them on the nose. The topic has come up again and again in some of my recent reading material, and the argument sometimes seems more like a playground spat more than a scientific debate;
Many parts of the what happened as the Cretaceous came to a close, like the impact at Chicxulub, the activity of the Deccan Traps, and the regression of the Western Interior Seaway, are all backed up by solid evidence and could have combined (along with some other factors we may not yet recognize) to create an ecological "bad day" as the Cretaceous came to a close, and the debate seems to center around the timing of these events and how important they may have been in the extinction of various groups of animals. Making things even more difficult, geologic formations covering enough time to allow for a determination of whether the extinction of groups was gradual or abrupt are scarce, Hell Creek being the most famous, and so far there is no worldwide picture as to what happened to many groups in the late Cretaceous crossing over into the Paleogene. Some researchers, however, have preferred extinction mechanisms of a more biological nature (from diseases to egg-hungry mammals), and now George Poinar Jr. has released a new book detailing how he thinks insects were behind the extinction of non-avian dinosaurs.
In What Bugged the Dinosaurs?, George and his wife Roberta propose that flowers, disease, and insects emerged as a "triple threat" which ultimately caused the extinction of non-avian dinosaurs. While they do not doubt that major events like the eruption of the Deccan Traps and the impact that left the Chicxulub crater occurred, the authors propose that the "real" extinction started earlier, major ecological shifts caused by catastrophes sweeping up what was left. I haven't read the book yet (I will try to secure a review copy), but I am a little skeptical of the premise. It reminds me a bit of the idea that mammals suddenly got the urge to eat dinosaur eggs, thus preventing any new dinosaurs from being born, and while I'm not expert on disease or epidemics I'm a little unsure of the idea that many diseases would have suddenly come out of nowhere to wipe out the dinosaurs. Perhaps the effect of a new disease would be catastrophic, but then again their very well could be animals that posses variations that make them resistant and able to found another population (even if they had to go through a genetic bottleneck). Likewise, not all microorganisms kill; they may weaken their host organism for a time (or even permanently and eventually lead to death), creating more of an arms race between microorganisms and the animals they affect rather than wiping out entire species.
Ecological shifts resulting in new diseases, new kinds of plants, and perhaps a greater influx of biting insects would have definitely affected dinosaurs and other forms of life present in the Cretaceous, but I still don't think the hypothesis explains the larger patterns of extinction in groups other than non-avian dinosaurs. More information is needed, especially about end-Cretaceous diversity all around the world, and I think that the various events proposed as the triggers for extinction need better resolution as far as timing and effect. Perhaps the scenario in the new book is correct and global dinosaur populations were weakened, eventually killed off due to various catastrophes, but overall I think that the debate needs a somewhat wider focus and that much more information is required in order to solve one of the greatest mysteries in the history of life on earth.
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Try this theory out for fun the next time it comes up:
The T-Rex's were refusing to let Adam and Eve saddle them up and take them for Sunday rides to Church, praise Jesus, so he sent teh "Aids virus for Dinosaurs" to punish them.
But seriously, I love that Pythin sketch. Those guys was good. Just be careful you make sure not to go into the abuse room by mistake.
Maybe it was Avian flu?
Well they may be on to a slight sliver of the extinction.
There is evidence building that Hadrosaurs specialized in eating mostly non-angiosperm plants compared to ceratopsians.
In Alberta (which I applogize for harping on about, but it's where all my detailed knowledge is based) we find the trend of duck bill diversity decrease every couple million years after 75 with a gradual increase in ceratopsian diversity.
It can be inferred that this COULD be flowering plants invading the borreal ecosystems and taking over.
Though at the same time it could just be climatic shifts caused by the draining bearpaw sea in which hadrosaurs aren't as adapted for the less temporate climate.
To me, it does seem quite a stretch. After all, I suppose it would be fair to assume that many modern insect groups were already living alongside the dinosaurs since the Jurassic. To me it strikes me as very unlikely that the insects would bring about the decline of the dinosaurs only at the end of the Cretaceous, not when both groups had already been coexisting for more than 100 million years prior to that.
And the idea of insect-borne diseases helping to bring about the doom of the dinosaurs, well, it just reminds me of the whole hyperdisease hypothesis to explain the Late Pleistocene extinctions. Sure, diseases can be pretty important, and wreak great havoc on isolated populations, but I doubt that the Dinosauria as a whole were ever threatened with extinction simply due to disease. =/
And of course, proposing insects as a contributing factor towards the dinosaurs' extinction doesn't really explain the disappearance of all the other creatures that snuffed it at or close to the K-T. What about the ammonites, mosasaurs, plesiosaurs, pterosaurs, inoceramids, rudists, protostegids etc.? If their extinction can already be explained away by the ecological disruption caused by volcanic eruption/meteorite impact/sea level change, then why should the dinosaurs warrant special treatment?
Hey it makes perfect sense! Have you ever seen a dinosaur try to swat a mosquito? Like T-rex with those little bitty forelimbs? Or Brachiosaurus smashing his own brain by trying to swat a fly on his head with his tail?
Mammals, it turns out, are exquisitely adapted to the task of swatting bugs.
Clearly, the evolution of bug-swatting behavior saved the mammals from extinction.
That also explains why insects got smaller - because big, slow-moving insects are easier targets (and make a better meal for rodents too).
Look for my new book Swattin' at the KT.
As Hai ~ Ren has mentioned above, this theory - like all theories that deal only with the extinction of non-avian dinosaurs, without caring about the broader context - fails to explain why marine ecosystems suffered extinctions on a similar or perhaps even greater scale than terrestrial ones. Clearly, insects had hardly an influence on mosasaurs, rudists or ammonites.
BTW, the last time I heard about the connection between insects and the K/Pg extinction, it was the other way around: It was supposed that there were not too many insects, but too few of them. The idea was that parasitic mites had killed most insects, thus drastically disturbing the ecosystem. Needless to say, the "too few bugs" theory doesn't work any better than its "too many bugs" opposite.
For all my best knowledge (wich might be limited - I have to admit that I'm not an expert on insect palaeontology), there was neither a massive insect radiation nor a massive insect extinction at the K/Pg-boundary.
Like most other debunked dinosaur extinction theories, this one doesn't take into account what happened to all of the non-dinosaurid taxa that went extinct, especially the marine taxa (which probably weren't being bitten by insects).
I think the mammals did it. Anywhere you find flightless birds (basically dinosaurs) and add mammals, especially rats, the flightless birds decline in a big way. Another way to look at it is that the only dinosaurs to survive the big extinction were the ones that could fly (birds). Birds that fly can put their nests in places that are very difficult if not impossible for mammals to get at. Mammals reproduce much quicker than birds, have sharp teeth for getting into eggs, and are very fast at snatching chicks and getting away quickly. If you introduced polar bears to Antarctica, there wouldn't be a single penguin left after awhile.
This is because
Michael,
the mammal theory fails to explain the extinctions of marine taxa at about the same time. Nor does it explain the extinction of metatherians - who gave live birth - in North America and their survival in South America. Nor does it explain the extinction of enantiornithine birds, who were probably better flyers than contemporary neoornithines. BTW, those birds who are probably most similar to Cretaceous neoornithines, chickens and tinamous, are ground-breeders.
> Anywhere you find flightless birds (basically dinosaurs)
> and add mammals, especially rats, the flightless birds
> decline in a big way.
But these are naive island species. Flightless birds on large continental masses, like ratites or phorusrhacids, did well enough among mammals, the latter even becoming top predators in South America.
Mammals - if not crown group mammals - had been around since the Triassic. Non-avian dinosaurs had co-existed with them for hundreds of millions of years. There is no evidence that Maastrichtian mammals were better egg predators than Jurassic or Aptian-Albian ones. A large eutriconodont would have been as good an egg-thief than a stagodontid or nanocurid, perhaps a better one, having a lower silhouette and poisonous spurs for self defence.
If there was a new threat for ground-nesters in the late Cretaceous, it came from monitors. But remember crocodiles have survived egg-predation by monitors just fine.
> Mammals reproduce much quicker than birds,
Those ground-nesting birds that are adapted for survival among mammals, like chickens or ratites, reproduce fast enough. Most, if not all non- avian dinosaurs bred like rabbits.
You've pretty much said everything that needed to be said johannes (thanks!). Mammals lived alongside dinosaurs for most of their history, so it would be strange if all of a sudden they got a craving for omelettes and relentlessly ate all the dinosaur eggs. Like johannes noted, while cats and rats and other mammal invasive/introduced species can be a problem for birds today, the extinction of the dinosaurs by mammals would have required world-wide coordination that would involve the consumption of a wide diversity of eggs. I wouldn't doubt that some animals may have eaten the eggs of some dinosaurs if given the chance, but it just doesn't make sense as an extinction hypothesis and does not explain the other extinctions that took place.
johannes, you asked about insect extinctions across the K-T. I remember a paper in a GSA Special Publication that looked at leaf damage types (caused by different insect groups) across the K-T. They found that about half of the types of insect damage did not occur after the K-T.
Here you can read most of the article on Google Books
http://books.google.com/books?id=dVX3X7-1-SUC&pg=PA301&lpg=PA301&dq=lea…