Dinosaurs & CO₂

FLYING REPTILES

Approximately 230 million years ago, certain leaping and gliding reptiles evolved into creatures that, with time, formed their separate branch on the reptile tree. Their forelimbs gradually grew long and bladelike, developing into wings with their distinct aerodynamic structure. As cousins of the dinosaurs, the Pterosaurs were the first animals after insects to fly, and they dominated the sky. The pterosaurs spread across the world, and they evolved into a wide variety of species from sparrow size through to giant creatures displaying a 35-foot wingspan. Many animals reside in the air, but the pterosaurs, alongside the birds and bats of today, remain the only vertebrates that have evolved to fly by flapping wings.

Fossil by fossil, hollow bone by hollow bone, we have studied their lives since Cosimo Collini’s first fossil discovery in 1784 (1), and we are unearthing anatomy that really captures the human imagination yet these airborne animals, are anatomically rather ill suited for life in the air.

The pterosaurs belong to a time out of mind. Their awe inspiring anatomy carried the species through the air for over 160 million years. Yet, their anatomy stands as the very obstacle to our efforts of accurately depicting them and bringing them back into life in our bright minds. The hollow bones that served their flight well have the result that they have literally turned to dust. Sixty-six million years after their extinction, we gradually excavate layer by layer and slowly piecing it together from remnants locked in rocks, fossilized sediments at the bottom of lagoons, and skeletons entombed in limestone. It paints a breathtaking picture of winged giants, the first flying vertebrates and the largest flying animal ever.

The species — or more accurately, the approximately 130 variations on its branch (2) - took up the Mesozoic skies like today’s birds. Scientists believe that they would have resided over different habitats according to sizes and behaviors. Some insect-feeding small creatures quickly fluttered through forests, while other large variations lived off baby dinosaurs and covered huge expanses and oceans.

They stayed on the wing for days, much like today’s largest flying bird, the great albatross that is still five to six times smaller than the largest of the pterosaurs despite its grand appearance.

Illustration of pterosaurs size (3)

Despite anatomy that puzzles and endlessly fascinates today’s scientists, the Pterosaurs’ ability to fly was fundamental to their biology. It was the foundation for their dominance of the skies. The question remains, how?

Can’t bumblebees fly?

The biology and aerodynamics of the pterosaurs should make flight impossible; they are too heavy and would not be able to deliver the force required to fly — or that is, in today’s atmosphere.

If we study the physiology of the pterosaurs in the context of today’s atmospheric pressure, their ability to power flight is indeed a mystery. However, we know from tiny air bubbles trapped in amber, that the Mesozoic era’s atmospheric pressure and CO₂ levels were higher (4). We also know that a combination of increased CO₂ levels and a higher air pressure would have made the air thicker — and thicker atmosphere requires less power to generate flight (5).

Though we only know them now through their bones and lives unearthed from the ground, these once-imposing kings and queens of the sky navigated their grand bodies through the air with an ease entirely dependent on a particular atmospheric pressure. Higher atmospheric pressure would allow the pterosaurs to power flight through a neat relationship of weight between an object and the surrounding air, much resembling the flight of a hot air balloon.

We achieve flight through the gas inside the balloon — heated air, helium, or hydrogen — because it is lighter than the air it travels through, and in this way, the balloon rises. If the surrounding material around the object — the balloon, the pterosaur — is heavier, then, relatively, the thing becomes lighter, and flight is enabled or becomes easier.

Archimedes’ principle

Approximately 20 kilometers east of Jerusalem lies the dead sea in a barren area ripe with history. For millennia the water of the dead sea has been attributed with healing powers and beauty benefits. Even Cleopatra is said to have imported products from the dead sea to tend to her beauty.

Located at the lowest place on Earth, 423 meters below the sea, the water that the Jordan river pours into the dead sea has nowhere to go. A hot and dry climate makes the water evaporate at astonishing speeds. Combine this with a natural occurrence of salt. As a result, the dead sea is one of the saltiest bodies of water on our planet, with almost ten times more salt than ordinary seawater.

For those of us who have experienced swimming in The Dead Sea, we know that this requires no physical effort — we float in the water. We float because of the high content of salt in the water, which means that the water of The Dead Sea is denser or, in other words, heavier than normal seawater. Its high salinity implies that humans float in The Dead Sea due to its high density, compared to our average mass. The Dead Sea’s high salt content has the effect of making the human body more buoyant.

Now, imagine that you are a lousy swimmer yet kept afloat by the salty water. With a change in the water composition, a dilution of its saline content occurring, your buoyancy in water equally changes, and your body suddenly becomes heavier, requiring much more physical effort to swim.

Similarly, the change in the atmosphere’s density caused the bodies of the pterosaurs to be relatively heavier and therefore they ultimately were no longer able to fly the same distances.

The Archimedes principle describes the buoyancy of a body in a liquid.

Archimedes’ principle is a physical law of buoyancy. Archimedes was an ancient Greek mathematician and inventor who lived from 287 to 212 BC. His principle states that any physical object, entirely or partially submerged in a fluid (gas or liquid) while not moving, is acted upon by an upward, or buoyant, force. The magnitude of the force exerted on the body is equal to the weight of the fluid displaced by the body.

Illustration of Archimedes principle

Extinction of the dinosaurs

The glorious era of the airborne giants ended 66 million years ago when the last of five known mass extinctions within 500 million years hit the Earth. Today, the only colossal wing spans taking up the sky are airplanes.

In Yucatan, Mexico, lies the Chicxulub crater. The crater, buried under the peninsula, bears witness to an impact with devastating consequences. It is 150 kilometers in diameter and 20 kilometers deep. Most of us know this story; the extinction of the dinosaurs after a giant asteroid hit the Earth. Wildfires, almost 1,000 kilometers from the impact center, ravaged the land. A tsunami of unimaginable size was set off from the collision impact, causing almost overnight the beginning of the collapse of the ecosystem, which had been sustaining most of the Earth’s animal forms. Initially, this affected mainly the non-avian dinosaurs. Due to their mobility, many pterosaurs could move to more food abundant areas, but as we know now, they too succumbed, unable to maintain their life form (6).

The reason for this outcome is found in the air. Alongside the enormous immediate impact that happened on the ground, the asteroid’s collision with Earth flung near unimaginable volumes of debris, dust, and sulfur into the stratosphere, disrupting the climate and bringing on severe global cooling. It was a time of minimal light, with dusk-like conditions and little animal life on the planet.

While there was undoubtedly a slowing down in growth, plants were not affected as severely by the darkness caused by the dust covering. With not much animal to plant ratio, the CO₂ dropped dramatically; the plants consumed the CO₂ and, the animals that typically would produce CO₂, did no longer do so, since 75 percent of these had become extinct. So, a drop in CO₂ occurred.

Our atmosphere consists of multiple gases: nitrogen, oxygen, argon, CO₂, and water vapor. While these gases disperse independently of each other, the atmosphere’s composition influences the atmosphere’s mass. This became the critical change to the lives of these avian lords. Due to a change in the CO₂ level, and a reduction in light, the atmosphere on the planet cooled down, the oceans cooled down — and cooler oceans can absorb more CO₂. Plants consume CO₂, and the atmosphere’s composition was changed by plants sucking CO₂ out of the air. While oxygen increased, less water evaporated due to the Earth’s cooling down, and the overall atmospheric pressure changed.

The air became thinner, meaning that the pterosaurs relatively became heavier in the air. Their unusual anatomy faced a different atmosphere which altered the course of their lives catastrophically.

Illustration of a pterosaur, struggling to fly.

These drastic changes to the atmosphere over millions of years meant that life forms equally had to change. The giant pterosaurs could no longer sustain flight, behavior, and life in their physiological form. So, one of the important evolutionary stories finally came to an end.

Compare this period to the mere five million years since our primate ancestors first rose and walked upright to this moment when we stand, homo sapiens, wise man, with our feet solidly planted on the ground.

Change drives evolution

The air itself brought an end to its giants, and their story points us towards the relationship between life on Earth and CO₂. While the pterosaurs could not sustain themselves in the form they had and did die out, an adaptation also took place, bringing the birds to the sky.

The extinction of the giant pterosaurs is the well-known story of evolution — the changes required over generations to adapt to the living conditions of a species. It is essential to state that the CO₂ levels in the atmosphere have constantly been changing.

Through well-documented ice core drillings (7) we can, for instance, measure a fluctuation in CO₂ levels between 180 and 280 ppm over the last million years. CO₂ itself is not the enemy as evolution and adaptation will take place accordingly, but the timespan of this change is critical. A transition takes time and works in cycles of approximately 100,000 years so that generations can adapt to the changing environment. The change we are witnessing today is, however, accelerated.

Our current CO₂ level of above 400ppm is estimated to rise to 600ppm, some even predicting 1200ppm, by the year 2100. How such a potentially high CO₂ level might impact our species, our development, and our ability to function cognitively and physically is examined in detail in Part 2 of this book.

Pause a moment to reflect on the link between CO₂ and the survival of a species. The pterosaurs’ story, a once-dominant species on our Earth, just like us. Speculate about how falling CO₂ levels from 2.000ppm to 400 ppm over millions of years impacted the flying dinosaurs’ lives.

Directly translated, Homo Sapiens means wise man. We differentiate ourselves from our Earth cohabitants with our larger and more complex brains. It is what has allowed us to dominate our planet, despite our somewhat inferior physiology.

Homo Sapiens have invented the wheel, built pyramids, and traveled to the moon. All these achievements are thanks to the sophistication of our brains. The brain is also the most oxygen consuming part of our body, burning 25–30% percent of our energy.

Not surprisingly, the composition of the atmosphere has a direct impact on our ability to function. Our current atmosphere has a recorded CO₂ level of approximately 400ppm.

When we get exposed to increased CO₂ levels, studies show that we witness a decrease in our ability to function — from tiredness, inability to concentrate, through to headaches. We experience increased levels of CO₂ in poorly ventilated offices or meeting rooms. More pronounced levels of CO₂, such as conditions experienced in submarines, cause symptoms such as restrictive lung behavior, increased heart rate, and significantly impaired cognitive function.

Contrary to us humans, the pterosaurs were a dominant force due to their physiology. However, we share with them that our common dominance on Earth is dependent on the same element, the air. What made the pterosaurs dominant was their ability to fly, while the sophistication of our brain places us at the top of the food chain. Though we consider intellectual and physical superiority in opposition to one another, for both of these dominant species, the pterosaurs, and homo sapiens, it seems that their dominance is directly dependent on the composition of the atmosphere.

One generation after the other, an adaptation brought the birds to our current skies, and we humans have a special relationship with them. They feature heavily in cultural and religious texts worldwide and are even attributed a messenger role by some. While we won’t reflect on this symbolism, we may still benefit from the lesson they bring to us: That these winged messengers derive from imposing and seemingly invincible creatures who, after 160 million years of dominance, were felled by the very element they mastered, the air.

Book

This is the first chapter of my book “Atmosphere, CO₂ on my mind”. You can find more information and references on my website.

Next chapter

You can continue by reading the next chapter here.

References

1. Wellnhofer, Peter (2008). “A short history of pterosaur research”.Zitteliana B. 28: 7–19
2. Witton, Mark (2013). Pterosaurs: Natural History, Evolution, Anatomy. Princeton University Press.
3. Matt Martyniuk, Mark Witton and Darren Naish
4. Robert A. Berner (1987), Yale University, Gary P. Landis, U.S. Geological Survey, Gas Bubbles in Fossil Amber as Possible Indicators of the Major Gas Composition of Ancient Air
5. Dinosaur Theory
6. Nicholas R. Longrich, David M. Martill, Brian Andres (2018), Late Maastrichtian pterosaurs from North Africa and mass extinction of Pterosauria at the Cretaceous-Paleogene boundary
7. Wikipedia on Ice Cores