A friend of mine has recently told me that dinosaurs were "killed by flowers". I was a bit surprised and so I googled. And I did find a lot of recent articles in popular media on this topic, probably based on this. To me it doesn't sound convincing at all, but I'm an outsider. Does anyone think that there's more to that than just a usual journalistic overhype?


Things in the paper that strike me as suspicious

Associating toxic plant defenses with the Cretaceous

Although there continues to be uncertainty about precisely when plants first evolved toxic defenses, this period of angiosperm proliferation would seem to be a strong candidate case. (pg 50)

Against this Gleadow and Moller (2014) discuss Cyanogenic glycosides (CNglcs), a class of organic compounds that can kill overgrazing herbivores from cyanide poisoning,

CNglcs are unusually widespread in the plant kingdom. They are found in the oldest of terrestrial plants (the ferns) and in gymnosperms and angiosperms.

Similarly, poisonous terpanoids are found in the Ginkgo; Proanthocyanidins, of which oak or wine tannins are a member, is found also in maritime pines; etc. There doesn't appear to be a strong link between angiosperms and chemical defenses against herbivory in plants.

Claiming that the angiosperm proliferations and extinction of dinosaurs are linked in time

The relative co-occurrence of angiosperm proliferation and the disappearance of the dinosaurs has not gone completely unnoticed.(pg 50)

The diversification of angiosperms occurred starting about 112 MYa for the Monocots, and 100 MYa for the Eudicots, according to De Bodt, et all (2005). From Figure 1 of that linked paper, we can see that both branches of the Angiosperms were approaching their modern diversity by 90 MYa; a time still 25 million years before the extinction of the dinosaurs. 25 million years ago, our nearest ancestor hadn't diverged from the line that would lead to Old World Monkeys, and was probably arboreal. Evolution can do a lot in such a time. Calling these two events linked in time is suspicious, at best.

Using crocodilians as a test case for taste aversion

Since crocodilians are descendent from the same creatures that gave rise to dinosaurs, this creates the opportunity to evaluate the tenability of the proposition that dinosaurs went extinct due to an inherent inability to learn to avoid eating toxic plants.

Reptilian cladistics are far from settled, but I would suggest that crocodilians diverged from dinosaurs by at least the early Triassic. They are almost certainly more divergent from all dinosaurs than birds. Here is what the authors have to say about birds.

However, in contrast to caimans, birds are in fact capable of forming learned food aversions. (pg 51)

That seems to really undermine the argument here.


Rather than talk to the specifics of this idea, which others have already done well, I'll contextualise it as one anti-consensus view among many. Many. Many.

The extinction of non-avian dinosaurs is the most publicly well-known part of a much larger systemic event at that time, one of the largest extinction events in the last 500 million years. The Cretaceous-Palaeogene extinction event killed something like 70% of Earth's species, and unless the large clade that is the dinosaurs suffered an extinction (excepting some birds) at the same time a lot of other life, both on the land and (which is arguably even better understood from the fossil record) in the oceans, suffered one coincidentally for a different reason, we need an explanation of the pattern.

This was not initially recognised. After dinosaur fossils were discovered, there was a period of about 100 years when scientists didn't think much about why it happened, because "life progresses up a ladder" was a popular idea in biology until surprisingly recently. (Bear in mind that Charles Darwin only lived to see evolution become uncontroversial among biologists, not his model of how it happens.)

Then, from c. 1920-1980, a zillion in-hindsight-stupid ideas were proposed; see here for details, including the toxic plants idea dating to 1976. It's not even the only "something went wrong with the plants they ate" idea. The consensus view (the Chicxulub impact) explains a food chain collapse, which explains why all animals over 25 kg became extinct except for ectothermic marine reptiles (crocodiles and leatherback turtles), whose different metabolism and diet explain why they could get away with being larger. Other plant ideas included "geologic uplift reduced plant supplies on the uplifted terrain" and my personal favourite (among all hypotheses, not just plant ones), "caterpillars ate the plants". Pointing out the fact that butterflies evolved 10 million years too late for that to work, making this more scientifically feasible, feels like taking a sledgehammer to a nut.

In the end, we have to look at "maybe miscellaneous heterodox idea #23 is the real answer" the same way we do when people deny contemporary anthropogenic GHG-driven climate change. The point often missed in both cases is that the consensus view explains an enormous pattern of pieces of evidence, while the rival ideas each contradict something observed, requiring a detractor from the consensus to assert inconsistent ideas to explain it all.

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    $\begingroup$ IOW, the culprit was Astrophysics, in the Caribbean. with a great big meteor :-) $\endgroup$ – jamesqf May 26 '18 at 18:24

No, it's not convincing; angiosperms evolved in the middle part of the dinosaurs' reign, not the end, and toxins evolve slowly which gives herbivores a chance to compensate, also conifers can be riddled with toxins just as easily.

Lastly, the idea that dinosaurs could not learn taste aversion is ludicrous; it is one of the simplest neurological feats, anything with even the simplest brain can accomplish it. Claiming dinosaurs would not be able to do so would require extraordinary evidence and the article provides nothing even slightly convincing.

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    $\begingroup$ The "evidence" is supposedly (I didn't check if its true or not) is crocodiles don't have taste aversion now. $\endgroup$ – Joshua May 27 '18 at 0:03
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    $\begingroup$ @Joshua Which is pretty weak evidence, considering the fact that crocodiles don't usually eat plants anyway, so they don't speak to the neurology of any herbivorous dinosaur. $\endgroup$ – J.G. May 27 '18 at 7:11
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    $\begingroup$ @Joshua its also wrong, crocodiles have and learn taste aversion, sydney.edu.au/science/biology/shine/publications/reprints_legal/… $\endgroup$ – John May 27 '18 at 16:31

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