11. Dinosaurs and Dragonflies
Life Evolves and Thrives According to its Environment

(Western Australia Now and Then)
Three-and-a-half-billion-year-old fossilized microorganisms and stromatolites provide evidence of the single-celled life that evolved not long after Earth's formation. Over billions of years, these organisms developed increasing complexity until, around 541 million years ago, they reached the next major evolutionary milestone: multicellular life. This sudden emergence, known as the Cambrian Explosion, marks the beginning of the Phanerozoic Eon. These early multicellular organisms were marine plants and animals, while terrestrial animals did not appear until 100 to 200 million years later.
This chapter explores the relationship between Earth’s changing atmosphere and the evolution of species. The search for an explanation of how dinosaurs and pterosaurs grew so large led to the realization that the atmosphere has changed significantly over time. This and other paradoxes arose from the long-held assumption that Earth’s atmospheric conditions remained relatively stable. Recognizing the dramatic shifts in atmospheric thickness allows us to resolve these mysteries. While these changes influenced both marine and terrestrial life, their effects were most evident in land-dwelling species, which existed directly within the atmosphere.

Species evolve to occupy ecological niches, which are shaped by both physical and biological constraints. Fossils provide evidence of the environments in which these species lived, often revealing clear reasons for their success. However, some organisms exhibit puzzling traits that suggest deeper evolutionary and environmental influences. Nature offers endless scientific mysteries, but most can be solved by assuming a rational explanation exists.
By analyzing fossil evidence, we can infer past atmospheric conditions and, in turn, better understand the adaptations of species that lived during those periods. In addition to physical constraints, species must also compete with one another for survival, adding another layer of complexity to their evolution. Solving scientific paradoxes requires an open mind—one that embraces evidence rather than dismissing it when it challenges existing assumptions.
DinosaurTheory originated from the idea that the enormous size and unique form of dinosaurs and pterosaurs reflect their environmental conditions. Geological and fossil evidence strongly suggests that Earth had an extremely thick atmosphere during the Mesozoic Era. Furthermore, records indicate that before the Mesozoic, the atmosphere was thin during the Permian—preceded by earlier periods of extreme atmospheric density. With this understanding, we can now reassess past life through the lens of atmospheric change, shedding new light on long-standing scientific mysteries.
Gigantic Insects, Millipedes, and Spiders Oh My
Carboniferous and Permian Periods, 360 to 245 mya

Dinosaurs and flying pterosaurs are not the only giant oddities of the prehistoric world. About 400 million years ago, long before dinosaurs and other vertebrates, the first arthropods crawled out of the water and onto land. Many of these creatures soon grew to sizes far exceeding most arthropods we see today.
During the Carboniferous period, an early centipede or millipede known as Arthropleura reached lengths of up to 2.6 meters. The same period was home to Pulmonoscorpius, a 70-centimeter-long air-breathing scorpion, and Meganeura, a dragonfly-like predator with a wingspan of 70 centimeters. Of course, let’s not forget about giant cockroaches—these nasty insects were among the first to crawl on Earth, and they will likely still be here long after Homo sapiens are gone.
Why did late Paleozoic arthropods grow so much larger than those of today? It’s tempting to assume the same conditions that enabled the massive dinosaurs of the Mesozoic also drove arthropod gigantism, but the situation is more complex. The atmosphere was indeed extremely thick during the Carboniferous, just as it was in the Mesozoic, making these creatures feel lighter. However, weight was less of a limiting factor for arthropods, especially considering their multiple legs. As we will see, the thicker atmosphere played a role in their size, but it was not the only factor.

Recall from Chapter Four — The Solution to the Dinosaur Paradox — that both the physical and biological environment shape a species’ size, form, and behavior, and it is often difficult to determine which has the greater impact.
Other when terrestrial arthropods first evolved, they have always existed alongside much larger terrestrial vertebrates that often towered over them and preyed upon them. This aspect of their biological environment may have been as important—if not more so—than the physical environment shaped by atmospheric thickness. To better understand the significance of the biological environment, we need to compare terrestrial vertebrates and arthropods. What are the strengths and weaknesses of each group? Why are most terrestrial vertebrates much larger than the vast majority of arthropods? And how have terrestrial vertebrates limited the size of arthropods? Answering these questions requires a deeper understanding of terrestrial arthropods.
For aquatic animals to evolve into terrestrial animals, they must be able to stand and move on land. Arthropods and vertebrates solved this challenge in different ways: arthropods developed hardened exoskeletons to support their bodies, while vertebrates evolved bony internal skeletons. Structurally, placing the support frame on the outside makes sense—an external or hollow frame is stronger than a solid rod of the same weight in resisting bending or breaking. Additionally, unlike vertebrates, whose muscles and organs are exposed to potential injury, an arthropod’s rigid exterior acts as natural armor, protecting its internal organs from cuts and abrasions. Given these advantages, one might wonder why all animals aren’t built this way. However, for larger animals, the benefits of an exoskeleton diminish when we consider two critical factors: growth and respiration.
Bones are living tissue, meaning they continuously grow and rejuvenate throughout a vertebrate’s life, along with its other organs. In contrast, an arthropod’s exoskeleton is made of hardened chitin, calcium, and carbonate, and it cannot expand as the animal grows. To accommodate growth, an arthropod must periodically shed its old exoskeleton and wait for a new, larger one to harden—a process called molting. Most insects molt five to seven times during their lives.



Molting leaves arthropods temporarily without structural support, making them highly vulnerable. Predators may take advantage of this weakness, or unforeseen complications may arise, preventing the arthropod from successfully transitioning to its new exoskeleton. Unlike the steady, continuous growth of vertebrates, the dangers associated with molting cause many, if not most, arthropods to die before reaching adulthood.
This need to periodically molt imposes limitations on the size and shape of terrestrial arthropods. While weight is negligible for the smallest insects, it becomes a major limiting factor for larger species. Without structural support during molting, the bodies of the largest terrestrial arthropods tend to flatten out, much like a water balloon laid on a table, before hardening into their final shape. This explains the noticeably flattened form of the coconut crab—the world's largest terrestrial arthropod.

However, the greatest difficulty that arthropods face when growing large is their breathing system—or more precisely, the fact that they cannot breathe in the same way vertebrates do. While vertebrates expand and contract their chest to draw fresh air into their lungs and expel old air, arthropods cannot perform this expansion and contraction because their body is enclosed in a rigid exoskeleton. Instead, insects and other arthropods rely on a passive system to exchange oxygen and carbon dioxide with the atmosphere. This system consists of several openings, called spiracles, spread along the body, which allow air to enter. The oxygen then travels down air ducts called tracheae before diffusing into the cells. The cells take in oxygen while releasing carbon dioxide. As the oxygen travels through the tracheae, the carbon dioxide travels in the opposite direction to exit the arthropod’s body.
This passive system works well for small insects but becomes inefficient for larger arthropods. It is another example of the Square-Cube Law. As an arthropod grows larger, the volume of its body increases at a faster rate than the surface area of the spiracle openings that supply oxygen from the atmosphere. To make matters worse, the larger the arthropod, the farther oxygen must travel through the tracheae to reach the cells. As a result, the exchange of oxygen and carbon dioxide slows down significantly in larger terrestrial arthropods. This slower rate of oxygen intake leads to reduced cellular metabolism, causing the animal to move more slowly. Hence, larger terrestrial arthropods are much slower than smaller ones.

Speed can be crucial for survival. In a race between a carnivore and its prey, the winner often determines who will survive. Additionally, in a confrontation between two predators, the victor is usually the one who can deliver faster, fatal blows. Generally, as vertebrates grow larger, their increase in overall speed and strength more than compensates for any slight decrease in reflexes, making them more likely to win a conflict. However, for large terrestrial arthropods, the inefficiency of their respiration system means they are typically too slow to win a confrontation with a vertebrate of equal or greater size. In environments where both terrestrial arthropods and vertebrates coexist, evolution favors smaller arthropods that are more capable of surviving, rather than larger, slower ones that cannot defend themselves, escape quickly, or hide from vertebrates.
To better understand how terrestrial arthropods grow to such large sizes, we can look at the largest arthropods of today and compare them to those of the past. While most terrestrial arthropods are small, there are some regions of the world where insects and other arthropods grow to impressive sizes. However, even the largest modern arthropods are dwarfed by those from the Carboniferous period. The reasons behind the large size of both modern and ancient arthropods are largely similar: changes in atmospheric conditions or the absence of vertebrate predators.

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Many of today’s largest arthropods—such as insects, millipedes, and spiders—are found in isolated environments like islands, caves, deserts, and tropical rainforests. In these regions, the environment provides conditions that support larger sizes. In particular, the humid environments of places like the Amazon, Southeast Asian rainforests, and the Congo basin play a significant role. The high humidity in these areas enhances the efficiency of the arthropods' respiratory systems. Although their atmosphere is not denser than usual, the humidity helps by creating a thin layer of water over the tracheae, aiding the diffusion of gas molecules. This boosts the effectiveness of their passive respiratory system, allowing for better oxygen absorption and enabling these arthropods to grow larger than those in less humid environments.
Thus, there are three key factors that support the growth of large terrestrial arthropods: a dense atmosphere that makes them feel lighter, high humidity that facilitates gas exchange, and the absence of vertebrate predators, which typically limit the size of arthropods. The giants of the Carboniferous period were likely able to grow so large because they enjoyed all three of these advantages: a dense atmosphere, high humidity, and the absence of large vertebrate predators. In fact, the atmosphere during the Carboniferous period was not only thick but likely humid as well, thanks to the swampy vegetation responsible for creating coal. This would have created an environment highly conducive to large arthropod growth. Furthermore, vertebrates did not evolve onto land until the Permian period, meaning the Carboniferous arthropods faced little threat from predators.

If you can’t fly, the next best thing is to evolve a long, sticky tongue. During the Permian period, there were no flying vertebrates to prey on insects, so the swamps must have been buzzing with swarms of flying invertebrates.
The age of giant terrestrial arthropods lasted for many millions of years, but significant changes began during the Permian period. Vertebrates were evolving onto land. The first amphibians, which evolved from fish, must have seen the abundant, slow-moving terrestrial arthropods as a ready source of food. Many of the giant arthropods were wiped out by these amphibians, but some still survived, as amphibians were limited to the marshes and swamps. This situation changed, however, when reptiles evolved from the amphibians. By the end of the Permian period, amphibians and reptiles had effectively wiped out the giant crawling arthropods. The only giant arthropod to survive was Meganeura, a massive ancestor of today's dragonflies, which continued to fly overhead.
So, why did Meganeura remain giant while all other giant arthropods shrank? The answer lies in the absence of flying vertebrates during the Permian. Flying vertebrates, such as pterosaurs and birds, did not evolve until the late Triassic and late Jurassic periods, respectively. As a large carnivorous insect, Meganeura filled the ecological role of present-day birds, preying on smaller insects. Without vertebrate predators in the air, Meganeura could continue to grow large and thrive.
Flying vertebrates evolved in stages: pterosaurs appeared in the Triassic period, birds evolved in the late Jurassic, and bats, the flying mammals, evolved in the early Cenozoic era. Today, birds and bats play a critical role in controlling insect populations. Birds are particularly effective during the day, and at night, bats take over, eating many of the insects that are active in the dark. If vertebrates had never developed the ability to fly, our world would be very different, with far fewer checks on insect populations.
As a closing thought, let us consider why arthropods were so far ahead of vertebrates in conquering new environments.
Ironically, the primary reason that the terrestrial arthropods of the Carboniferous period were able to grow so large is because they started out so small. Unlike vertebrates, there is virtually no limit to how small arthropods can be. In fact, there are countless invertebrate species that are microscopic. From an evolutionary standpoint, smaller individuals have shorter generation cycles, which allows species to evolve more quickly into new forms. This ability to evolve rapidly gave arthropods a significant advantage over vertebrates as they adapted to terrestrial life.
Once arthropods successfully evolved to live on land, the terrestrial environment was essentially theirs alone. Without competition from vertebrates, they were free to grow larger and fill all the ecological niches available. Whether evolving to live on land or to fly, arthropods were tens of millions of years ahead of vertebrates in these key evolutionary steps.
The Evolution of Flight: How Evolution Works
There is no mystery in how insects evolved the ability to fly. A slight breeze is enough to lift most small, lightweight insects into the air. In fact, from the perspective of a tiny insect, the greater challenge is staying grounded. What we consider a gentle breeze or a slightly windy day must feel like a hurricane to them. While many insects seek shelter from the wind, others may have benefited from using it to expand their range. From there, only a series of small evolutionary steps was needed to develop controlled flight.
For small animals, evolving flight is relatively easy, and insects demonstrate this with the remarkable variety of ways they have achieved powered flight. In contrast, the evolution of flight in vertebrates has long been a scientific puzzle. The key to understanding this puzzle lies in two factors: (1) smaller organisms, such as arthropods, evolve much faster than larger ones, and (2) the Earth's atmosphere during the Permian period was thinner than it later became, making the evolution of vertebrate flight significantly more difficult.

Before exploring these factors, it is important to clarify what it means to fly. Today, many vertebrates have "flying" in their name—such as flying dragons, flying snakes, flying fish, flying squirrels, flying lemurs, and flying geckos—yet none of these animals are true flyers; they are gliders. To fly, an animal needs more than just wings or a flat surface to slow its fall—it must generate enough power to propel itself forward and maintain level flight. Airplanes make this distinction clear: they require both wings for lift and a propulsion system, such as a jet engine or a propeller, for forward motion. Birds and other flying animals achieve both through the flapping of their wings, which requires considerable muscular power output.
Evolution does not follow a predetermined plan. A species cannot "aim" toward flight simply because flying offers many advantages. Instead, evolution is driven by immediate benefits. A species will only evolve new traits if each small step along the way provides an advantage in survival or reproduction. Furthermore, evolutionary change occurs gradually, with each new generation offering another opportunity to take a small step toward developing a new feature. If a partial feature—such as rudimentary wings—does not provide any benefit, it will not be selected for, and the evolutionary process will stall.

A useful analogy is to think of evolution like water flowing downhill toward the ocean. Water does not plan its path or have the ocean as an objective - it simply follows the route of least resistance, always moving downward. If it encounters a depression with no lower outlet, it pools to form a lake. Likewise, evolution is always "flowing" toward greater survival advantage, but it can only proceed where each incremental step provides an immediate benefit. If no advantage exists at a given stage, evolution cannot progress in that direction.
For decades, paleontologists have proposed questionable hypotheses on how vertebrates—such as pterosaurs, birds, and bats—evolved flight. Currently their favored idea is that some vertebrates hopped while flapping their partially formed wings until their wings eventually became large enough for true flight. However, this contradicts the principles of evolution—without an advantage gained at every step of the way, a species will not undergo the many generations of development needed to achieve functional wings or any other complex feature.
By understanding the evolutionary constraints imposed by size, generation time, and atmospheric conditions, we can see why insects achieved flight so much earlier than vertebrates.
Evolution of Pterosaurs
Today, in Southeast Asia, there are gliding reptiles known as Draco lizards, or Flying Dragons. These small reptiles glide from tree to tree by extending their elongated, skin-covered ribs to create a flat, aerodynamic surface. This ability allows them to save considerable time while foraging and helps them evade predators, both on the ground and in the trees. In addition to covering horizontal distances as they descend, these lizards can control their glide, enabling them to land precisely on their intended target — the trunk of a nearby tree. If the atmosphere were substantially denser, these gliding lizards would be well-positioned to evolve into true flying reptiles.

The earliest known gliding reptiles, Weigeltisaurus jaekeli, lived approximately 255 million years ago, near the end of the Permian period. These creatures were remarkably similar to modern Flying Dragons, spending their lives gliding from tree to tree. Like their present-day counterparts, they could not achieve powered flight. Similar to today, the atmosphere during the Permian was relatively thin, making it impossible for cold-blooded reptiles to generate enough power for sustained flight.
The Permian-Triassic Extinction, which marked the end of the Permian period, set the stage for vertebrate flight to evolve. This "mother of all extinctions" wiped out 96% of marine species, including those that had been removing carbon dioxide from the oceans and atmosphere. Meanwhile, volcanic activity continued to release CO₂, leading to a dramatic increase in atmospheric thickness over the next several million years. By the end of the Triassic period, life had recovered, and once again, reptiles were gliding between trees. However, this time, the much denser atmosphere significantly reduced the power requirements for flight, allowing some of these gliding reptiles to evolve into true flyers.

The gliding arboreal reptiles of the late Triassic period evolved around 230 million years ago, and just two million years later, Earth saw its first flying vertebrates. These early pterosaurs closely resembled their gliding ancestors, with the key difference being their significantly larger size and the development of wings attached to their forelimbs, enabling powered flight. These first pterosaurs, known as Rhamphorhynchoids, lived between approximately 215 and 145 million years ago.
Over time, pterosaurs generally increased in size from their initial evolution to their eventual extinction. The earliest group, the Rhamphorhynchoids, appeared during the late Triassic, around 215 million years ago. These were among the smallest pterosaurs and were characterized by their long tails and teeth. By the late Jurassic period, a new group of pterosaurs, the Pterodactyloids, had evolved. Unlike the Rhamphorhynchoids, Pterodactyloids had shorter tails and tended to be much larger, with most species having wingspans of about one meter (three feet).
Before the extinction of the Pterodactyloids in the early Cretaceous period, an even larger group of pterosaurs emerged: the Pteranodons. Many Pteranodons had wingspans ranging from five to seven meters. They differed from Pterodactyloids in several ways, including their long, robust necks, prominent cranial crests, and toothless beaks. Pteranodons first appeared in the late Jurassic and thrived throughout the later Cretaceous period.
Heads or Tails?
Why did early pterosaurs have long tails, while later pterosaurs lost most of their tails and instead developed long, robust necks?
Any self-propelled object moving through a fluid, whether animal or machine, needs a way to guide its direction. Typically, this control is at the rear, like a ship’s rudder or a bird’s stiff tail feathers, which act like a wind vane, naturally orienting the object into the wind. However, guidance can also be at the front, as seen in Pteranodons. Though this setup is dynamically unstable, it allowed them to turn simply by looking in a new direction. When a Pteranodon turned its head, the airflow shifted accordingly, causing its body to follow: look right, turn right; look left, turn left.
However, using the head as a rudder has a drawback. Turning at high speeds, especially during a dive, could generate forces strong enough to potentially break the Pteranodon’s neck. This may explain why Pteranodons evolved exceptionally large neck bones.
One of the largest pterosaurs of all time was Quetzalcoatlus, which lived during the late Cretaceous. Similar in structure to Pteranodons but substantially larger, Quetzalcoatlus stood as tall as a giraffe and had a wingspan comparable to that of a small recreational airplane.
Ptroubling Pterosaurs
*Paleontologists are still refining the classification of pterosaurs, so some reference sources may differ from the classifications presented here. However, one point of consensus among paleontologists is that pterosaurs were not dinosaurs. Despite this, the distinction remains unclear to the public, as many non-academic sources continue to refer to pterosaurs as flying dinosaurs.
Pterosaur* | Time Period | Wingspan (m) | Notes |
---|---|---|---|
Rhamphorhynchoids | Late Triassic and Jurassic |
0.25 to 1.0 | smallest pterosaurs long tail, teeth |
Pterodactyloids | Late Jurassic | 1.0 to 1.5 | medium size short tail, teeth |
Pteranodons | Cretaceous | 3 to 7 | large, toothless, robust neck, prominent crest |
Quetzalcoatlus | Late Cretaceous | 11 | one of the largest flying animals of all time |
It was only a few million years after Pteranodons appeared that the smaller Pterodactyloids went extinct. However, it would be incorrect to assume that one type of pterosaur outcompeted the other. More likely, the recently evolved birds displaced the smaller pterosaurs. Sharing the same size range and environment, Pterodactyloids could not compete with the superior flying abilities of warm-blooded birds. Meanwhile, the larger Pteranodons survived and even thrived by avoiding direct competition with birds. While agile birds flew through trees or just above them in search of prey or seeds, Pteranodons soared high above, possibly circling like vultures as they waited for carrion. Soaring requires minimal energy, making the slower, cold-blooded metabolism of pterosaurs an advantage for this type of flight.
Pterosaurs, dinosaurs, and birds coexisted throughout the Jurassic and Cretaceous periods. However, at the end of the Cretaceous—the close of the Mesozoic era—pterosaurs went extinct along with the dinosaurs.
Theories on How Pterosaurs Were Capable of Flying
Paleontologists incorrectly assume that Earth’s atmosphere has remained unchanged over time, leading them to struggle in explaining how pterosaurs flew. Their lack of training in physics and aerodynamics further hinders their understanding. Instead of focusing on whether the pterosaurs’ wings could generate enough lift, paleontologists make dubious claims about pterosaurs’ ability to launch themselves into the air with powerful leaps. But suggesting that pterosaurs flew by jumping skyward is no more scientific than telling a child that Superman flies by leaping into the sky. Not only is it easy to disprove the idea that large pterosaurs could leap as claimed, but even if they could, the discussion is irrelevant to determining whether a pterosaur could fly.
Achieving flight requires several factors, but the most fundamental is that an animal or airplane must generate enough power or forward thrust for its wings to produce lift equal to its weight.
Paleontologists have struggled in their efforts to explain how the pterosaurs flew.

While the Mesozoic era presents several paradoxes, the most well-known to the public are how dinosaurs grew so large and how gigantic pterosaurs managed to fly. Despite efforts by paleontologists to downplay these issues, a basic understanding of Galileo’s Square-Cube Law reveals that the immense size of these terrestrial animals presents a significant scientific paradox. When examining large dinosaurs, many inquisitive individuals can logically identify key inconsistencies, such as excessive skeletal stress, inadequate muscle strength, and the need for implausibly high blood pressure. However, giving a scientific explanation for why gigantic reptiles should not be flying is problematic. While the sheer size of flying pterosaurs is highly anomalous compared to modern flyers, there was no simple theoretical framework or mathematical model that definitively explains why a bird, an airplane, or a massive winged reptile should — or should not — be capable of flight
For centuries — long before the Wright brothers' first flight and continuing to the present — debates have persisted about how birds and airplanes generate lift. Despite major advancements in wind tunnel testing, aviation design software, and aerodynamics, even experienced engineers often struggle to provide a clear yet accurate explanation of flight. Exploiting this widespread knowledge gap, many paleontologists — lacking any real background in physics or aerodynamics — have presented dubious claims, implying a full understanding of how pterosaurs flew. In doing so, they misrepresent the extent of their scientific knowledge, using unverified assertions to dismiss legitimate questions about the feasibility of pterosaur flight.

Between 2007 and 2008, the author researched aerodynamic theories and successfully derived the Science of Flight Equations, which address the fundamental question: What are the minimum requirements for achieving flight? These equations allow for the calculation of the minimum power required and the necessary takeoff speed for any flying animal or aircraft, based on key factors such as weight, wingspan, aerodynamic form, and air density. Beyond assessing whether pterosaurs could have flown in an atmosphere similar to today's, these equations also provide valuable insights into the flight capabilities of birds, bats, and airplanes. A detailed explanation of flight and the derivation of the Science of Flight Equations are presented in Chapter Three.
To meet the requirements for flight an animal needs to have wings, a means of guiding their flight, and enough power to create the lift needed to overcome the downward force of gravity. Animals that glide between trees are usually capable of fulfilling the first two requirements. However while they are airborne they typically cannot generating power or at least enough power so as to achieve true flight. How much power is needed so that an arboreal glider can evolve into a flyer mostly depends on the density of the atmosphere.
Now, let’s examine the flight equations that demonstrate how the dense atmosphere of the Mesozoic era facilitated the evolution of flying pterosaurs.
The much thicker atmosphere of the Mesozoic era made flight easier for pterosaurs in two distinct ways. First, as with dinosaurs, the dense atmosphere created a buoyant force that reduced the effective weight of the pterosaurs. Second, because lift is generated by accelerating air downward, a denser atmosphere required less power to achieve the necessary lift. We begin by calculating the effective weight.
By summing the forces acting on a pterosaur submerged in the thick atmospheric fluid and applying basic algebra, we derive the following equation for effective weight:

where:
- N is the effective weight (i.e., the required lift),
- Fg is the actual weight,
- ρF is the density of the surrounding fluid (the thick atmosphere), and
- ρS is the density of the pterosaur.
Although the exact density of pterosaurs is unknown, it was likely similar to that of most vertebrates, approximately the density of water: 1000 kg/m3. Using estimated values for Quetzalcoatlus, which had a weight of 7000 N and lived during the Cretaceous period when air density was around 660 kg/m3, we calculate its effective weight to be approximately 2380 N.
The greatest potential source of error in these calculations comes from estimating the pterosaur’s metabolism. While it is well established that reptiles generally have lower metabolic rates than mammals, the fundamental differences between exothermic reptiles and endothermic mammals make precise comparisons difficult. For now, we estimate that the metabolism of reptiles is typically about five times lower than that of mammals of equivalent size. Using this assumption, the available power for Quetzalcoatlus is calculated to be approximately 0.36 kW.
With these corrected values, we can now insert them into the flight equations to determine the Quetzalcoatlus’ take-off speed, minimum power, and power ratio showing how these values are different depending on whether the atmosphere is thick or thin.
![v_min = [(2 W^2) / (3 A C b^2 ρ^2)]^1/4](flight_eq21.gif)
![P_T-min = 4/3 [ W^2 / (b^2 ρ v_min)]](flight_eq22.gif)
Flyer | Weight (N) |
Front Area Estimate (m2) |
Drag Coefficient Estimate (Front Area) |
Wingspan (m) |
Speed for least Power (m/s) |
Minimum Power for Flight (kW) |
Available Power (kW) |
Power Ratio |
---|---|---|---|---|---|---|---|---|
Quetzalcoatlus Thin Atm |
7000 | 2.5 | 0.50 | 12 | 18 | 20 | 1.8 | 0.09 |
Quetzalcoatlus Thick Atm |
2380 | 2.5 | 0.50 | 12 | 0.47 | 0.17 | 0.36 | 2.2 |
As explained in the flight chapter, the minimum required power ratio for flight is 1.0 and to maneuver and maintain altitude in real-world conditions, airplanes and flying animals must exceed this threshold. With a power ratio of 2.2, Quetzalcoatlus was a capable flyer in the dense Mesozoic atmosphere.
While this analysis primarily focuses on how large pterosaurs generated enough power for flight, it also addresses another challenge: how Quetzalcoatlus physically managed to run fast enough to takeoff and then later slow down enough to safely land.

In general, the larger a flying vertebrate or airplane, the faster it must travel to take off or land safely. While small birds or bats can simply hop into the air before flapping their wings, at the other extreme the largest jet airplanes must reach speeds over 100 mph to lift off. The same principle applies to landings, where increasing weight typically requires higher approach speeds. While airplane wheels are well-suited for high-speed travel, the short legs of some large vertebrates limit how fast they can run. Some heavy birds - especially those with narrow wings — struggle to reach takeoff speed or must use special techniques to slow down when landing. To give an example: although the albatross is revered as a graceful flyer, it sometimes fails to gain enough speed for takeoff, and its rough landings can be comically clumsy.
The thick Mesozoic atmosphere not only reduced the power required for Quetzalcoatlus to fly but also made takeoff and landing far easier. If Quetzalcoatlus had to fly in today’s atmosphere, imagine the impossibility of it running at 18 m/s (40 mph) or the number of bones it would break upon landing at such a speed. Fortunately, in the extremely thick atmosphere of the late Cretaceous, Quetzalcoatlus had no such difficulties. It needed to move at only about half a meter per second to take off or land
From their evolution 215 million years ago to their extinction 66 million years ago, pterosaurs grew from small flying reptiles to the largest creatures ever to take to the skies. This remarkable evolutionary achievement was only possible because Earth’s atmosphere was significantly thicker during the Mesozoic era.
Details about Dinosaurs
Were dinosaurs warm or cold blooded?
The analysis of the spacing of dinosaur tracks strongly suggests that many of these large animals were trotting rather than walking along at a slow lumbering pace. Based on this evidence of a higher metabolism, some paleontologists have suggested that dinosaurs may have been warm-blooded (endothermic) animals. However, while a vertebrate needs to be endothermic to achieve a high metabolism in a cold environment, the elevated temperature of an endothermic metabolism is unnecessary and can even be undesirable in climate that is consistently warm. For example, the cold-blooded (ectothermic) fish that swim in warm ocean water show high activity because the water that surrounds them keeps their bodies at a consistent warm temperature. Likewise, it is logical that dinosaurs would also be highly active if they were submersed in an extremely thick and consistently warm atmosphere.
Not only is the endothermic dinosaur hypothesis solving a problem that may not exist, the warm-blooded dinosaur hypothesis is possibly creating its own set of problems. Extremely large endothermic animals need to have some way to dissipate their thermal energy so that they do not overheat. Among the large modern mammals, elephants flap their big ears and spend much of their time soaking in water to stay cool, while the even larger whales have a strong preference to swimming in cooler ocean waters. If dinosaurs were actually warm-blooded, then the larger dinosaurs should have a stronger preference for the cooler higher latitudes than the smaller dinosaurs. If such a distinction exists, paleontologists have yet to recognize it.
Generally, an ectothermic metabolism works best in climates that are consistently warm while an endothermic metabolism is superior in climates that lean towards being cooler and have wide fluctuations in daily or seasonal temperatures. The global Mesozoic climate consisted of steady warm temperatures, a climate that favors the belief that the dinosaurs were ectothermic vertebrates.
One of the scientific paradoxes discussed in Chapter 2 is how the tallest dinosaurs, such as Brachiosaurus and Sauroposeidon, were able to manage the extreme blood pressure required to pump blood from their hearts to their elevated heads. The hydrostatic pressure due to height is calculated using the equation P = ρ g h, where P is the required pressure difference, ρ is the density of the fluid (in this case, blood, at about 1060 kg/m³), g is gravitational acceleration (9.81 m/s²), and h is the height difference between the heart and the head. For a dinosaur like Brachiosaurus, whose head may have been 9 meters above its heart, this calculation suggests a minimum required systolic blood pressure of approximately 600–700 mmHg, far higher than that of any known living animal today.
As noted in Chapter 2, the tallest land animals today — giraffes — have evolved numerous adaptations to meet the challenge of pumping blood to their heads. Weighing about 25 pounds (11 kg), a giraffe’s heart is much larger and more muscular than what would typically be expected for an animal of its size. Additionally, giraffes have a heart rate of 40 to 90 beats per minute, roughly twice the heart rate of horses (28–40 bpm) and other animals of comparable weight.

The way deep-ocean sperm whales sleep offers insight into how dinosaurs could have reached such great heights. Sperm whales get their name from spermaceti, a low-density, waxy substance that fills most of their massive heads, which make up about one-third of their bodies. As they sleep, the buoyancy of this substance causes them to rotate into a vertical position, with their heads pointing toward the surface. Whales are similar in size and mass to the largest dinosaurs, and if they were on land, this upright posture would create extreme strain on the heart due to their blood’s hydrostatic pressure. However, because they are submerged in water, the surrounding fluid counteracts the effects of gravity, preventing any increase in hydrostatic pressure. As a result, despite their vertical position, their hearts can still function at a reduced pace, allowing these sperm whales to achieve restful sleep.
While the extremely thick Mesozoic-era atmosphere did not eliminate hydrostatic blood pressure in dinosaurs, it greatly reduced it, allowing them to grow to towering heights. In a medium with a density closer to 660 kg/m³, the effective weight of blood in the circulatory system would be significantly reduced due to buoyant forces. The hydrostatic equation is then modified to account for this effect:
This adjustment reflects that the effective pressure difference the heart must generate is no longer determined solely by the density of blood, but by the difference between blood density and the surrounding atmospheric density. If the surrounding medium had a substantial density, it would offset much of the gravitational force acting on the blood column. Applying this equation to Brachiosaurus, the predicted required systolic blood pressure would drop to only 250–300 mmHg — similar to that of modern giraffes and well within the plausible physiological range for large terrestrial animals.
T-Rex Awkward Pubis Bone / Lean Mean Eating Machine
The Diminishing Atmosphere's Effect On Terrestrial Vertebrates
Cenozoic Era 65 mya to Present Time
Sixty five million years ago the K-T mass extinction marked the end of the Mesozoic era and the beginning of the Cenozoic era. When this event occurred, the atmosphere was extremely thick and after the extinction and throughout all of the Cenozoic era the atmosphere transition from being extremely thick to being the relatively thin atmosphere that we have today. Mostly it was just the smaller terrestrial animals that survived the extinction: the dinosaurs were dead. Similar to other mass extinctions, several million years when by before the land was once again suitable for the evolution of larger terrestrial life.
The geological evidence gives us an idea of how the Earth transitioned from a thick to thin atmosphere throughout the Cenozoic era. For the first 25 million years, between 65 and 40 million years ago, there was no ice at the poles, the same as what it was during the Mesozoic era. Then, starting at 40 million years ago, ice at the poles came and went as the atmosphere's thickness made its unsteady decline. This went on until just over two million years ago when the Earth began a new ice age.
The dinosaurs did not make it through the K-T mass extinction and this left some big open slots that the mammals filled. Many of these mammals grew large in comparison to today’s mammals but they were still far short of being dinosaur size. This is because by the time terrestrial life had fully recovered the atmosphere had already diminished considerably and so this atmosphere was not nearly as effective in reducing the effective weight of these large mammals. In addition, these large terrestrial mammals of the Cenozoic era were not shaped like the dinosaurs because exceptionally large rear legs and a strong tail were no longer useful in the thinner atmosphere. Along with the diminishing atmosphere, from the middle of the Cenozoic era to the present time we see this general trend of these terrestrial animals shrinking in size until we reach the size of the present day animals.

The largest of these terrestrial animals was a tall giant rhinoceros like mammal named Paraceratherium (besides Paraceratherium this species has had numerous other names that have come and gone in popularity: Indricotherium, Baluchitherium, Dzungariotherium, and Aralotherium). While it is taller than a giraffe and about three times heavier than an African Elephant, its exact size is unclear because of the incompleteness of the fossil bones. The Paraceratherium went extinct about twenty three million years ago.
Besides the Paraceratherium there were numerous other large terrestrial species that existed during the middle and even late Cenozoic era. These include the giant ground sloth, the saber tooth tiger, giant otters, giant beavers, giant armadillos, and many others. While generally terrestrial animals shrunk in size during the Cenozoic era this is not always the case for every species. The reason for this is because biological competition within an environment can be every bit as important as physical constraints in determining how large an animal can be, and so we need to carefully consider what is actually limiting the size of an animal. For example, what is there that limits the size of beavers? If there are no bears in a wooded environment what is there to keep beavers from evolving to the size of bears or even larger? Hence the reason that beavers are much smaller today appears to be due to differences in the biological competition rather than having anything to do with the thinning of the atmosphere.
External Links / References
Species Interactions With Each Other and the Environment: Ecology
- Species Interactions - Libre Text
- Keystone Species in an Ecosystem - National Geographic
- Understanding Global Change - Berkeley
- Evolutionary Adaptations of Species Impact Their Environment - Sci Teck Daily
- Intro to Ecology - Libre Texts
- What Is Ecology? - Ecological Society of America
Monster Terrestrial Arthropods of the Carboniferous and Permian Periods
- Pulmonoscorpius - Dinopedia
- Car-Size Millipede - Live Science
- Arthropleura - Furman University
- Largest Fossil Cockroach - Ohio State University
- Cockroaches are not 300 million years old - Entomology Today
- Meganeura - Furman University
- 10 Astounding Things You Should Know About the Dragonfly - Tara Wildlife
Largest Insects and Spiders
- Ten Largest Insects on Earth - Our Planet
- Ten of the Worlds Largest Spiders - Conservation Institute
- Understanding Evolution: Small Size - University of California Museum of Paleontology
Difference between Terrestrial Arthropods and Terrestrial Vertebrates
- Basic Bug Design: Exoskeletons - University of Wisconsin
- A Vertebrate Looks at Arthropods - Barbara Terkanian
- How Lungs Work - American Lung Association
- What Are the Functions of the Spiracles? - Sciencing
- 13 Advantages and Disadvantages of Exoskeletons - Brandon Miller
- The Arthropod Story - Berkeley University of California
- Are bones living or dead? - Discovery Place
Evolution of Flying Vertebrates
- The Evolution of Flight - Berkeley
- Evolution of Flight - Fullerton
- Evolution of Flight - Science World
- The Physics of Flight - Berkeley
Leaping Lizards
- Gliders of the Prehistoric World - Darrwin's Door
- Flying dragon lizard - Australian Geographic
- Flight of Dragons - Lazy Lizard Tales
- Flying Lizard - Ten Random Facts
Pterosaurs
- Flying Lizard - Ten Random Facts
- Flight of Dragons - Lazy Lizard Tales
- Rhamphoryncoids and Pterodactyloids - Hooper Museum
- Pterosaurs Taxonomy - The Pterosaur Database
- Vertebrate Flight - University of California at Berkeley
- Quetzalcoatlus - New Dinosaurs
- ‘Rhamphorhynchoids’ and Pterodactyloids - Dave Hone
- Pterodactyl Vs Pteranodon What is the difference? - Fun Biology
- Facts about pteranodon and other pterosaurs - Live Science
- Meet the Pterosaur Flock - Chicago Field Museum
- Difference Between a Pteranodon and a Pterodactyl - Reference
- pteranodon and other pterosaurs - Live Science
- The flying reptiles - Berkeley
- Pterosaur - Britannica
Endothermic and Ectothermic (Warm and Cold Blooded) Vertebrates
- How Does Temperature Affect Metabolism? - Sciencing
- Endotherms & Ectotherms - Khan Academy
- Phylum Chordata Characteristics - Online Biology Notes
- Mongoose vs. Cobra - Animal Facts Encyclogedia
- Cold-blooded and Warm-blooded Animals - The Biology Notes
- Metabolism and Enzymes - libretexts
- Factors Affecting Enzyme Action - BBC
- How Cells Obtain Energy from Food - National Library of Medicine
- Evidence for Endothermy in Dinosaurs - DinoBuzz Berkeley
Geological Ages
- Ice Ages and Glacial Epochs - Arizona Independent
- Interactive Map Showing Dinosaurs Over Time - Mental Floss
- Interactive Globe and Dinosaurs - DinosaursPictures