I kept forgetting to write this blog - for years, in fact. I came up with the basic theory in the early '80's and assumed that some paleontologist or evolutionary theorist would derive it independently, or someone would shoot it down. So far as I know, neither has happened and more evidence in its favor is accumulating, while I, in turn, have become incrementally more knowledgeable, as well. So, before I lose it to Alzheimer's or a stroke, etc., I figured I better get this in print.
So, here it is, folks, the REAL reason why the dinosaurs died out...
http://en.wikipedia.org/wiki/Cycas_revoluta
The "Sago palm" is not really a palm at all but a rogue leftover from the days of dinosaurs, a cycad. The cycads were palm-like plants that were contemporaneous with the dinosaurs and constituted a large portion of the herbivorous dinosaurs' diet. Notable among the Sago Palm's traits is an EXTREME toxicity that results in many pet deaths every year, as the flesh and seeds - especially the seed, which are the most toxic - are somehow attractive to them, in spite of being generally fatal within a day after ingestion. So, three interesting anomalies among plants: extreme toxicity, attractive seeds and pulp, extremely ancient heritage.
My theory started by examining another anomaly. How was it that NONE of the dinosaurs survived? Not one species, unless one includes the birds, the surviving species of which now are thought to have branched off from the non-flying dinosaurs fairly early on, and well before the Great Extinction. There were big dinosaurs, and tiny dinosaurs, carnivorous, herbivorous, omnivorous. They were all probably as warm-blooded as you or I. They were well adapted to their environment, which they dominated for tens of millions of years.
Also, why the huge size of many of the dinosaurs? Size by itself is inherently counterevolutionary. I.e., your size is related to how much you consume, and there is a finite limit to that, set by the incoming solar radiation being converted into edible biomass. The same energy flux that could feed a million rat-sized dinosaurs can only feed a hundred or so brontosauri. The DNA turnover is related to the numbers of animals being born and passing on their genes, irrespective of size (the amount of DNA of species of various masses is generally not related to their mass as individuals). Thus, size becomes a relative impediment to evolutionary selection. Those rat-sized dinos will evolve a ten-thousand times as fast as that bronto, because there will be ten-thousand times as many selections in the same time period.
However, enormous size DID evolve and prosper for a LONG time, so there must have been some clear evolutionary advantage.
The artists' conception of dinosaurs usually has them surrounded in a forest of cycads, which typically have long trunks and very tough palm-like leaves way up at the top. How many small dinosaurs - or mammals - could therefore eat those leaves? They would have to climb the trunks, exposing themselves to predators all the way. Not likely.
The bigger issue, however, which is at the heart of the matter, is what advantage did the cycads gain in being eaten? After all, if the only creatures that can even reach your leaves and seeds are characterized by having necks thirty feet long, just how many of your precious seeds will survive that gargantuan intestine? And, on the same note, if you ARE going to eat Cycads, with the toughest imaginable fibers and every toxic compound that could possibly be selected for, then you had better not only have long necks, but also a devil's brew of intestinal enzymes and juices and that enormous gut to handle all that mess.
Now note that the corresponding picture for our own ancestors, the mammals, is completely different. Being small and living in burrows underground, our folks could not eat the cycads anyway. So, they scavenged on dino carcasses, where other plants grew up in the underbrush, plants that improved their propagation when one of these scavenging rat-like mammals happened to carry a seed or two in their gut or fur into that burrow, nicely safe from predatory birds and perfectly positioned to germinate.
While the dinosaurs developed huge, powerful guts, which required - along with the neck length - enormous overall mass, and thus a very slow rate of evolution - the cycads developed ever more tough and toxic flesh and seeds in response. I.e., it was total war.
Simultaneously, however, the little mammals benefited from benefitting the plants at their level, and those plants, receiving that benefit, began to evolve methods for protecting and nurturing those helpful little mammals. Instead of war, there was mutuality and synergy.
The dinosaurs were doomed. As were the cycads. Both species had reached an impasse. There is a limit to how big you can be and still walk and defend yourself. There is a limit to how tall you can grow and not be blown over in the first storm. Both sides were pushing that limit and an ever larger proportion of their energy was being spent in the struggle.
Meanwhile, we mammals were getting into a cozier and cozier rapport with our plant buddies.
In the millions or so years immediately prior to their extinction, the dinosaurs had been reduced to a few hundred species, even though they still dominated in total biomass. Evolution depends upon a library of genetic information that contains the possibility of diversity, which the dinosaurs had largely lost in their lock-step battle with toxic plants.
After all, each mutation has to be selected for by giving an advantage to some individual animal. Simultaneous election for multiple new traits doesn't work out very well. Most of the room for selection was going to dealing with the evolving toxicity of the plants, leaving little adaptive diversity in the gene pool for other challenges.
Something would have happened, and it did. The great asteroid did hit and did trigger the great die-off. However, the reason that not one dino survived begs the issue. They died because they were already poised to die. Synergy defeats predation.
That's the essense. More to follow.