Synopsis: What really ended the giant dinosaurs is a threat to us.
The fact is, even many dinosaur species survived the meteorite, and we now just call their descendants “birds”. It is not really that dinosaurs all died out, it is that those giant dinosaurs that attracted all the attention all died out.
Blaming the meteor for the death of the giant dinosaurs without noting they were already dying is misleading, and avoiding the question as to why theses giant dinosaurs were the most vulnerable, and why evolution did not result in new species of giant dinosaurs once the earth recovered.
The Earth also once supported giant insects with wingspans of over 70cm (over 2 feet) too, but they also died out even long before that meteor.
It turns out that as this planet progresses from peak life over 500 million years ago towards the extinction of all complex life in around 100 million years, the largest species will become the most vulnerable and then die out. One day, that would include us.
Moving past the Myths
The image here has dinosaurs watching as the meteorite hurtles towards collision and their imminent demise, and this commonly repeated image is central to many myths. Most realise this is not reality, but bear with me for the myths.
Myths vs Reality:
- the meteorite was tiny compared to the huge earth and most of the planet (and most of the dinosaurs) would not have been killed instantly but died as a result of the change in conditions following the impact.
- not all dinosaurs actually died out, as some lived to evolve and prosper as what we now call ‘birds’ and many already had feathers and other bird features. Amazing what over 60 million years of evolution can achieve.
- the peak time for the dinosaurs, the Jurassic, as referenced in ‘Jurassic Park’, ended 145 million years ago, over twice as long ago as the meteorite impact.
- the earth had been changing for over a hundred million years before the meteorite impact, and dinosaurs had becoming extinct the entire time. The meteorite appears to have accelerated climate change been the ‘final straw’ for all ‘non-avian’ dinosaurs, but it still took millions of years for these extinctions.
- the proportion of dinosaurs close enough to observe the meteorite would have been similar to the proportion of humans who could observe the recent meteorite explode over Russia.
- Reality is the meteor accelerated the demise of the largest and most famous dinosaurs, but they were already dying out.
But if those dinosaurs that were so huge were so successful before the meteor, why didn’t evolution see them return afterwards?
Land of the Giants?
The dinosaurs are not the only ‘giants’ to have lived on earth. The blue whale, which still lives in the oceans, is larger than any dinosaurs ever were, but it is only recently found that 30 million years ago it seems there were even larger whales.
While there are some animal classifications where examples still surviving are the largest ever or close to the largest ever, these are unusual, as for almost every animal, the largest examples to ever to have lived are now extinct.
We humans are fascinated by ‘big’.
It was easy to find web pages dedicated to the biggest animals ever. Trying to find a list of the most ‘yellow’ animals… not so easy, because to us being the biggest is not only significant, in some ways it is the ‘best’. The biggest mountain, the biggest river, all attract our attention. The biggest mountain is the ultimate mountain to climb, the biggest river is the ultimate river, the largest carnivorous dinosaur the ultimate predator.
Evolution: Survival of the fittest.
If two animals fight, all else being equal, we would normally expect the larger animal to win. This should make the largest be the “fittest” in any battle, and best equipped to survive. If the biggest was always the fittest, evolution would lead to all animals continually increasing in size, and what we observe is that there is always some upper limit for every species before being too big becomes a disadvantage. Evolution should allow a range of sizes with the limits in order for species to adapt to different niches.
The upper size limit keeps changing.
The giant moa, one of the largest ever modern birds became extinct just over 300 years ago, and the even larger Vorombe titan became extinct just 1,000 years ago, but of course were nowhere near as large as their dinosaur ancestors. Almost all of the “the largest ever” were from long ago, and well before eth appearance of humans.
The largest ever marsupials became extinct over 110,000 years ago, the largest whales, over 30 million years ago. Insects with wingspans of 3/4 of a metre (over 2 feet) existed 300 million years ago. With almost any animal, the largest to ever live, is now extinct, despite thriving at some earlier time. Clearly, being the biggest can turn from an asset to a liability. Looking at the history of animal life, over an over we find that a species thrived as that species grew larger and larger, but eventually died out with no new species at that time emerging of a similar size.
So, what happened to the giant dinosaurs?
In reality, it was that the giant ones all died out.
Remember, only ‘non-avian’ dinosaurs actually died out. Also remember that the very biggest dinosaurs ever became extinct around 30 million years before the meteorite arrived as did most of the other largest dinosaurs. When things changed, all that survived were smaller animals. The lesson seems to be, that at any given time there is a maximum size for survival. The large dinosaurs all died out, and it was smaller avian dinosaurs that lived on to flourish today and become birds, one of the most successful animal groups.
The biggest dinosaurs, the ones that capture our imagination, were all simply too big for the changed world. What made the dinosaurs that became extinct and was different from other animals and even other dinosaurs that survived, was their size.
Why didn’t giant dinosaurs and other giant species return?
Sometime after the meteor impact, the Earth should have returned to “normal”. If the largest dinosaurs evolved during “normal;” times, it would seem logical that new species of a similar size would evolve again. If these dinosaurs were the “fittest”, then evolution should result in a return to “the fittest”.
However, just as old people don’t actually die of “old age”, but rather die because they are vulnerable to a variety of conditions because they are old, it seems these largest dinosaurs were, as a group of species, old and thus vulnerable. When any major catastrophe occurs, death rates are highest among the old and vulnerable, and again, those biggest dinosaurs even died out long before the meteor.
When dinosaurs first evolved, the Sun was producing less radiation, and the Earth stayed warm courtesy of much higher levels of CO2, and as a result the main engine of life on Earth, photosynthesis, could happen much faster. Back near “peak life“, the Earth supported around twice the total amount of life it supports today, and food could grow much faster, providing support for larger species than the planet does today.
As the total biomass of all life continues to decline in response to the evolution of the Sun, the largest species of most types of life will continue to disappear. Without some human intervention, we would become the largest and most vulnerable mammal before, we too, would find our time has passed.
It is clear that growing to be the largest possible can make you the strongest, at least until the rules change and you suddenly being so large makes you vulnerable.
We current live in a world where the largest tech companies now have GDP at the level of entire nations, they are getting larger and larger at amazing speed. Lesson: beware of changing conditions!
At a human level, there is another lesson. Nature does not provide for things to exist forever.