Full text of paleontologist Emma Schachner’s talk: Think You Know Why Dinosaurs Dominated? Think Again at TEDxLSU conference.
Listen to the MP3 Audio here: The secret weapon that let dinosaurs take over the planet
We’ve all heard about how the dinosaurs died.
The story I’m going to tell you happened over 200 million years before the dinosaurs went extinct. This story starts at the very beginning, when dinosaurs were just getting their start.
One of the biggest mysteries in evolutionary biology is why dinosaurs were so successful.
WHAT LED TO THEIR GLOBAL DOMINANCE FOR SO MANY YEARS?
When people think about why dinosaurs were so amazing, they usually think about the biggest or the smallest dinosaur, or who was the fastest, or who had the most feathers, the most ridiculous armor, spikes or teeth.
But perhaps the answer had to do with their internal anatomy — a secret weapon, so to speak. My colleagues and I, we think it was their lungs.
I am both a paleontologist and a comparative anatomist, and I am interested in understanding how the specialized dinosaur lung helped them take over the planet.
So we are going to jump back over 200 million years to the Triassic period. The environment was extremely harsh, there were no flowering plants, so this means that there was no grass. So imagine a landscape filled with all pine trees and ferns.
At the same time, there were small lizards, mammals, insects, and there were also carnivorous and herbivorous reptiles — all competing for the same resources.
Critical to this story is that oxygen levels have been estimated to have been as low as 15%, compared to today’s 21%. So it would have been crucial for dinosaurs to be able to breathe in this low-oxygen environment, not only to survive but to thrive and to diversify.
So, how do we know what dinosaur lungs were even like, since all that remains of a dinosaur generally is its fossilized skeleton? The method that we use is called “extant phylogenetic bracketing.” This is a fancy way of saying that we study the anatomy — specifically in this case, the lungs and skeleton — of the living descendants of dinosaurs on the evolutionary tree.
So we would look at the anatomy of birds, who are the direct descendants of dinosaurs, and we’d look at the anatomy of crocodilians, who are their closest living relatives. And then we would look at the anatomy of lizards and turtles, who we can think of like their cousins.
And then we apply these anatomical data to the fossil record, and then we can use that to reconstruct the lungs of dinosaurs. And in this specific instance, the skeleton of dinosaurs most closely resembles that of modern birds.
So, because dinosaurs were competing with early mammals during this time period, it’s important to understand the basic blueprint of the mammalian lung. Also, to reintroduce you to lungs in general, we will use my dog Mila of Troy, the face that launched a thousand treats, as our model.
This story takes place inside of a chest cavity. So I want you to visualize the ribcage of a dog. Think about how the spinal vertebral column is completely horizontal to the ground. This is how the spinal vertebral column is going to be in all of the animals that we’ll be talking about, whether they walked on two legs or four legs.
Now I want you to climb inside of the imaginary ribcage and look up. This is our thoracic ceiling. This is where the top surface of the lungs comes into direct contact with the ribs and vertebrae. This interface is where our story takes place.
Now I want you to visualize the lungs of a dog. On the outside, it’s like a giant inflatable bag where all parts of the bag expand during inhalation and contract during exhalation.
Inside of the bag, there’s a series of branching tubes, and these tubes are called the bronchial tree. These tubes deliver the inhaled oxygen to, ultimately, the alveolus. They cross over a thin membrane into the bloodstream by diffusion.
Now, this part is critical. The entire mammalian lung is mobile. That means it’s moving during the entire respiratory process, so that thin membrane, the blood-gas barrier, cannot be too thin or it will break.
Now, remember the blood-gas barrier, because we will be returning to this.
So, you’re still with me? Because we’re going to start birds and it gets crazy, so hold on to your butts.
The bird is completely different from the mammal. And we are going to be using birds as our model to reconstruct the lungs of dinosaurs.
So in the bird, air passes through the lung, but the lung does not expand or contract. The lung is immobilized, it has the texture of a dense sponge and it’s inflexible and locked into place on the top and sides by the ribcage and on the bottom by a horizontal membrane.
It is then unidirectionally ventilated by a series of flexible, bag-like structures that branch off of the bronchial tree, beyond the lung itself, and these are called air sacs.