No doubt about it, the dinosaurs that roamed the Earth millions of years ago were big, powerful, and likely very fierce. But like the stereotypical "jocks" in your high school, who at the time seemed equally big, powerful, and fierce, maybe those dinosaurs weren't very smart.
At least they weren't smart enough to realize that the food they were eating was slowly killing them.
It's what has been termed "the biotic revenge hypothesis". In recent years we've pretty much all concluded that the dinosaurs were killed off by a giant meteor that struck the Earth 66 million years ago. A recently published study by Michael Frederick of the University of Baltimore and Gordon Gallup of the State University of New York at Albany proposes that the dinosaurs began declining BEFORE the Chicxlub meteor impact. It isn't that the meteor was unimportant, just that it can't explain everything that happened. Let's take a look at the argument.
Needless to say, be very happy that you weren't around when the meteor hit the Yucatan Peninsula. Scientists who've studied the resultant crater estimate that the meteor itself was about 6 to 9 miles in diameter. They've hypothesized that when it hit the Yucatan, it released energy equivalent to a billion times what was released in the Hiroshima and Nagasaki atomic bombs combined!
We humans have had some experience with the result of massive volcanic explosions. Anyone more than a few years old in May, 1980 probably recalls the eruption of Mt. St. Helens in Washington State. Of far greater consequence, however, was the eruption of Mount Tambora in Indonesia in 1815. The Tambora eruption was so big that it had huge climactic impacts for years thereafter.
But even Tambora was a trivial event compared to the Yucatan meteor explosion. The dust cloud created by the Yucatan meteor likely lasted for ten years, doubtless causing widespread destruction, as well as extinctions of many plants and animals.
While large animals died, a number of smaller creatures survived the disaster, likely because the latter were able to get by living off detritus. I like to joke that this phenomenon will ensure that cockroaches - which apparently have been with us for 320 million years - will be the last creature standing when the world ends!
No doubt, the meteor killed a lot of dinosaurs! But did it cause them to go extinct? The evidence suggests that dinosaurs actually went extinct over a seven million year period. While the meteor explosion caused an awful lot of premature deaths, its effects probably didn't stretch out over seven million years. That suggests there had to have been something else.
One theory of the "something else" is what's called the Deccan Traps, located in what is now India. Geologists believe that the traps began forming 66.25 million years ago, at the end of the Cretaceous Period. The timing coincides perfectly with the demise of the dinosaurs.
Those studying the Deccan Traps believe there were a series of large volcanic eruptions over a 30,000 year period. Imagine, not one Tambora sized eruption but nearly continuous ones over 30,000 years! The eruptions released a very large amount of sulphur dioxide, leading to an average temperature drop of two degrees Celsius. You probably know that scientists today fear the effects of an increase of global temperatures of two degrees Celsius on Earth's climate. The Deccan Traps may have caused a climatic disaster in reverse.
But the Deccan Trap theory suffers the same problem as the meteor one: it can't really explain why it took about seven million years for the dinosaurs to disappear. You know those stereotypically drawn out operatic death scenes in operas such as "Carmen" or "Don Giovanni"? Trivial, if the meteor strike and Deccan Traps took seven million years to kill off the dinosaurs.
Enter the new theory of Professors Frederick and Gallup. Their thesis is that the dinosaurs started going extinct before either the meteor strike or the Deccan Traps. The cause, they believe, was toxic plants eaten by dinosaurs that were herbivores.
Evolution has caused some plants to develop shells as a defense against predators. Likewise, others have developed toxins to discourage others from eating them. Conversely, many animals have developed the ability to avoid toxic plants. It's called "learned, or conditioned taste aversion". Rats apparently are especially good at this. They lack the ability to regurgitate bad things, so they have to be especially careful what they eat. Rats have exquisitely learned how to avoid eating bad things.
Not the dinosaurs. Thus, the "dumb jock" hypothesis: the dinosaurs died because they were too dumb to realize what they were eating was killing them! Professors Frederick and Gallup are more charitable to the hapless dinosaurs, calling their theory "the Biotic Revenge Hypothesis".
That could explain why herbivorous dinosaurs went extinct, but what about the carnivores? They weren't eating these toxic plants. But they were eating the dinosaurs who were eating them. Thus, if toxic plants were killing off the herbivorous dinosaurs, the food supply for the carnivores would have slowly disappeared … to be followed by the carnivorous dinosaurs themselves.
The idea of plant toxins killing dinosaurs actually isn't new. In fact, Tony Swain, a biologist working at the Royal Botanic Gardens, advanced the idea about forty years ago, before anyone had discovered the Yucatan meteor site. But Swain's theory didn't gain much traction because the available evidence suggested that herbivorous dinosaurs were thriving right up to the time of the meteor impact.
So what evidence do Professors Frederick and Gallup provide in their new paper? They focused on crocodilians, including modern day crocodiles, alligators and caimans, each a descendant from precursors to dinosaurs. They then constructed an experiment that showed caimans do not develop specific learned taste aversions.
The fact that the caimans didn't develop specific learned taste aversions, then in contrast to animals such as rats, they wouldn't avoid food that turned toxic. So with respect to food, they're today's "dumb jocks", incapable of realizing something they're eating is killing them!
But what about birds? After all, there is evidence that birds are descendants of the dinosaurs. If dinosaurs were killed off because they were indiscriminate eaters, why haven't robins gone the way of T-Rex? The authors cite the work done in the 1970's showing that birds can form food aversions. They do it, however, not by taste but by sight. So if a bird has a bad experience with a particular type of food, they develop a visual association and avoid it in the future.
The experimenters provided some jays an opportunity to eat monarch butterflies for the first time. The butterflies have a milkweed toxin that makes life miserable for any jay that eats it. The jays survived the, to them, bad experience that results from eating monarch butterflies, but the jays developed a visual cue and avoided the misery in the future.
So are Frederick and Gallup suggesting that the dinosaurs died off because of indiscriminate eating? No, they haven't gone that far. Instead, they see the "biotic revenge hypothesis" as merely one contributing factor. So a lot of indiscriminate eating on the part of dinosaurs probably helped weaken them. Inhaling an excess of sulphur dioxide from the Deccan Traps made it even worse. All to be followed by the mother of meteor explosions.
Death and destruction on a scale never before seen … and all witnessed by those pesky cockroaches, who survived! I guess size does matter, but in the case of dinosaurs and cockroaches, not the outcome you might have expected.
