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 recognising they were already dying is misleading and avoids the question as to why these giant dinosaurs were the most vulnerable, and why evolution did not produce new species of giant dinosaurs once the earth recovered.
Evolution is survival of the species “fittest”. The reality is the giant dinosaurs that died were vulnerable and least fit to deal with the change of environment. Even when the environment stabilised, they did not return because just has the total amount of all complex life has been declining since the most recent “garden of Eden event” around 500 million years ago, how large a species should grow follows the same trend. The real lesson is that the largest of each animal type usually become vulnerable long before smaller species, which means as quite large mammals, our natural extinction event is not that far in the future.
The Earth also once supported giant insects like Arthropleura that were bigger than a modern human and dragonflies 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 from now, at any given time the largest species of any animal type will be among the most vulnerable, as large species require more food. As the total life on Earth declines, so does the amount of food, 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 instead 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, with the total amount of complex life already down to around half of that at ‘peak life’, and large dinosaurs had been becoming extinct for quite some time before the impact. The meteorite appears to have accelerated climate change been the ‘final straw’ for all giant and ‘non-avian’ dinosaurs, but it still may have taken millions of years for many of 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 giant dinosaurs that were so huge were so successful before the meteor, why didn’t evolution see them return afterwards? Clearly, things were changing which meant that at the time of the meteor, the giant dinosaurs were already vulnerable. If fact, the meteor was just a blip on the continuing decline in the total amount of life in the biosphere.
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.
So far, the food mass to support large whales has not suffered the same decline as the amount of life overall.
While there are some animal classifications where examples still surviving are the largest ever or close to the largest ever, these are rare, as for almost every animal, the largest examples to ever to have lived are now extinct.
Dinosaurs, even the large ones did not completely die out with the asteroid.
What we definitely know is that the number of the largest dinosaurs plummeted with a very short time span at the time of the asteroid impact, but it only led to the extinction of the “non-avian” dinosaurs, and birds the descendants that prove how many species survived.
However, science now has a more nuanced understanding of the diversity of dinosaur physiology. Many dinosaurs sported brightly colored feathers like birds. Dinos lived in many different ecosystems, including the Arctic, where they would have encountered snow (if not the ice caps of today) and winters devoid of light.
The evolutionary twist that could have helped dinosaurs rule Earth
The more we learn about dinosaurs, the more we discover how bird like they were.
Evolution: Survival of the fittest is not just the largest.
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 for “fittest” keeps getting smaller.
We still keep finding evidence of ancient huge bird species from well after the age of the dinosaurs, but the fossil record is far less complete than people imagine, and only a small fraction of the dinosaur species that were bird ancestor species from 50 million years ago have been discovered through fossil remains. Our record of the largest birds tends to only include recent ones, but even with those, the further back we go, the larger the species we discover.
The largest ever flying birds (Argentavis or even more ancient Pelagornis sandersi) became extinct over 5 million (5,000,000) years ago.
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.
G. newtoni was about 7 feet (2 meters) tall and weighed up to 529 pounds (240 kilograms). It belonged to the family Dromornithidae, a group of flightless birds known from fossils found in Australia.
Rare skull of an extinct, massive ‘thunder bird’ discovered in Australia
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.
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.
So, what happened to the giant dinosaurs?
In reality, it was only the giant ones that 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 more suddenly with the Chicxulub event, 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, then being so large was part of being the fittest. It would seem logical that new species of a similar size would evolve again. If these largest 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. Being so large had already become old. 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.
The lessons.
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.
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