Hypotheses about the extinction of dinosaurs

Hypotheses about the extinction of dinosaurs

Many hypotheses about the extinction of dinosaurs exist, since a single asteroid impact alone cannot explain the mass extinction at the Cretaceous-Paleogene boundary. The process was complex and lengthy, influenced by a significant number of different factors. There are almost as many hypotheses about the extinction of dinosaurs as there are researchers studying this topic.

Currently, there are two main hypotheses about the extinction of dinosaurs: the asteroid impact and the volcanism of the Deccan Traps, both accompanied by climate change. They compete with each other in credibility and in the accuracy of describing the events that occurred at the Cretaceous-Paleogene boundary. However, the main problem with both hypotheses is the question of the selectivity of mass extinction.

Hypotheses about the extinction of dinosaurs: volcanic activity or asteroid impact?
The extinction of the dinosaurs was a result of volcanic activity and an asteroid impact.

Looking at the problem from a different perspective, the two main current scenarios explaining the KT event (including the extinction of the dinosaurs) are the “gradualist” model of ecological succession by Van Valen1 and others and the “catastrophist” model of extraterrestrial impact by Luis Alvarez2 and others.

The fall of an asteroid and the eruptions of the Deccan Traps were, in any case, extraordinary events that significantly influenced the state of the Earth’s biosphere. However, these factors alone cannot explain many existing facts. This inevitably led to the emergence of a variety of hypotheses about the extinction of dinosaurs. Some of them were amateurish, others were merely curious, but many of them, although they do not fully explain the mass Cretaceous-Paleogene extinction, clearly contain some grains of truth.

Early hypotheses about the extinction of dinosaurs

19th century

Since the 19th century, researchers have been interested in the events that occurred at the boundary between the Cretaceous and Paleogene periods and the extinction of dinosaurs at that time. The first described dinosaur fossils attracted attention due to their unusual nature. Gradually, the understanding came that between the Mesozoic and Cenozoic eras, there had been significant changes that required explanation. And various hypotheses about the extinction of dinosaurs did not take long to emerge.

William Buckland
William Buckland © National Portrait Gallery, London

In 1823, British geologist and paleontologist William Buckland supported the catastrophic theory in geology, claiming that the Great Flood destroyed “antediluvian relics”. Buckland suggested “a change in the inclination of the earth’s axis, or the near approach of a comet, or any other cause or combination of causes purely astronomical” as possible causes of climate change after the last catastrophe (the Flood).3

Dinosaurs as aquatic or semi-aquatic animals
Some 19th-century paleontologists considered dinosaurs to be aquatic or semi-aquatic animals. E. D. Cope, “The fossil reptiles of New Jersey.”

In 1825, French naturalist and naturalist Georges Cuvier (Jean Léopold Nicolas Frédéric, Baron Cuvier) explained the mass extinction at the end of the Cretaceous with a catastrophic drop in sea level, which destroyed the habitat of aquatic and semi-aquatic reptiles. (He believed that until the end of the Mesozoic, vertebrates were essentially marine or swamp dwellers).4 Cuvier, however, did not consider catastrophic extinctions on a global scale. In 1949, Martin Wilfarth essentially repeated the claim that dinosaurs were marine animals and died out due to a drop in sea level in the late Cretaceous period, leading to the drying up of their habitat.

1826. Fleming, a critic of catastrophism, discussed mammalian extinctions and proposed that predators might have caused earlier extinctions.5

In 1836, Buckland proposed that the cooling earth had induced the major catastrophes.6

In 1842, the English zoologist and paleontologist Richard Owen asserted that the Mesozoic era was more suitable for dinosaurs due to its unique atmospheric conditions. He believed that the air during that time contained a reduced level of oxygen, which was more conducive to dinosaurs and other reptiles. When the oxygen level increased, it became more favorable for birds and mammals. As a result, the world became inhospitable for giant reptiles, and they became extinct along with the gigantic marine reptiles and flying pterosaurs.7

Rapid disappearance of ammonites
Darwin believed that the rapid disappearance of ammonites was due to gaps in the paleontological record or some other cause.

In 1854, in his work “The Origin of Species”, Charles Darwin concluded that the extinction of most taxonomic groups occurs gradually. However, he found the extinction of ammonites at the end of the Mesozoic era to be “astonishingly sudden.”

In 1882, American paleontologist Othniel Charles Marsh considered the extinction of dinosaurs as a gradual reduction in their population during the Cretaceous period. He simply noted that they “continued in diminishing numbers to the end of the Cretaceous period, when they became extinct.”8

And in 1898, English paleontologist Arthur Smith Woodward already asserted that dinosaurs gradually became extinct at the end of the Mesozoic era.9

20th century

In 1910, A.S. Woodward claimed that the reason for the extinction of dinosaurs was “racial senility” and that evolutionary lines have a finite lifespan, just like individual organisms.10 He believed that the appearance of strange non-adaptive traits in dinosaurs (such as the plates adorning the backs of stegosaurs, large sizes, the absence of teeth in some species) and a number of others, led to the general extinction of dinosaurs. Schuchert (1924),11 Beurlen (1933),12 and Swinton (1939)13 supported this hypothesis.

1911. Austro-Hungarian scientist Franz Nopcsa stated that the large amount of cartilage, which he believed was necessary for growth to enormous sizes, “perhaps… was one of the causes for the rapid extinction of the Sauropoda.”14

In 1917, Franz Nopcsa went on to suggest that “a reduction in their sexual functions” could have played a role in the demise of dinosaurs.15

In 1921, Canadian and American geologist and paleontologist William Diller Matthew asserted that dinosaurs gradually became extinct because geological uplift changed the wet lowland habitats of dinosaurs (Laramide orogeny). Matthew believed that the more elevated landscape was preferable for mammals.16

In 1922, Franz Nopcsa proposed that changes in the landscape were fatal for the plants on which the dinosaurs depended (a variant of Matthew’s hypothesis). Additionally, the competition between dinosaurs and mammals, which had arrived in North America from Asia, played a role.17

Hypotheses about the extinction: The cold climate froze the dinosaurs
The cold climate froze the dinosaurs. ©James McKay – Creative Commons/PA

1922. N. M. Yakovlev (Jakovlev) suggested that dinosaurs became extinct because the Earth’s climate became too cold for their existence.18

The diseases perished dinosaurs
The diseases perished dinosaurs.

1923. Dinosaurs perished due to diseases. American geologist and paleopathologist Roy Lee Moodie, based on the findings of bones in a pathological state, put this hypothesis forward in 1923. He believed that arthritis, tooth decay, fractures, and infections contributed to the extinction of dinosaurs.19

George Reber Wieland
George Reber Wieland

1925. American paleobotanist George Reber Wieland hypothesized that Tyrannosaurus rex fed on the eggs of other dinosaurs and destroyed their last generation before they could hatch. Mammals, which also fed on dinosaur eggs, aided him in this.20

In 1928, German herpetologist Lorenz Müller proposed that volcanic eruptions destroyed dinosaurs.21 Harry T. Marshall, Professor of Pathology at Virginia University, suggested that cosmic ultraviolet radiation and bombardment from space were to blame for the extinction of dinosaurs.22

1929. Alexander Audova hypothesized that the gradual decrease in temperature hindered the normal embryonic development of dinosaurs and other Mesozoic reptiles.23

1939. American paleontologist Percy Edward Raymond hypothesized that the brain size of dinosaurs gradually decreased throughout the Mesozoic era. They became too foolish to survive and went extinct.24

Lakes and swamps where dinosaurs lived
©Neave Parker

In 1939, Scottish paleontologist William Elgin Swinton argued that dinosaurs became extinct due to the drying up of lakes and swamps where they lived.25 American paleontologists Edwin Harris Colbert and Ermine Cowles Case26 in 1946 and German paleontologist Martin Wilfarth27 in 1949 supported this idea.

Heinrich Otto Wieland
Heinrich Otto Wieland

1942. German organic chemist and biochemist Heinrich Otto Wieland suggested that endothermic dinosaurs went extinct when the amount of carbon dioxide in the Earth’s atmosphere decreased to such low levels that it no longer stimulated them to breathe, and they suffocated.

1945. American herpetologist Raymond Bridgman Cowles hypothesized that dinosaurs went extinct when the Earth’s climate became so hot and dry that it affected the ability of male dinosaurs to produce sperm.28 In 1949, he added that the rise in temperature at the end of the Mesozoic era led to the death of vulnerable young dinosaurs.29

1946. American vertebrate paleontologist Edwin Harris Colbert and some other researchers supported the hypothesis that dinosaurs went extinct due to an excessively hot and dry climate.

Hypotheses about the extinction: radiation
©Joschua Knuppe

1954. Solar Flare Hypothesis. E.Stechow proposed that solar flares destroyed the ozone layer, leading to the demise of dinosaurs due to increased ultraviolet radiation.30 This is a variant of the George Marshall hypothesis.

Max Walker de Laubenfels
Max Walker de Laubenfels

1956. Meteorite Impact Hypothesis. American spongiologist Max Walker de Laubenfels from Oregon State College was the first to put forward a hypothesis that linked the death of dinosaurs to a meteorite explosion.31 The occasion for his article was the double (1937 and 1941) passage of the kilometer-long asteroid Hermes at a short distance from Earth’s orbit.

1964. L. Ginsburg argued that the cause of the extinction of dinosaurs was marine regression.32 This was not the first hypothesis on this topic and is far from the last. For example, N.D.Newell, 1967.33

1967. John M. Cys asserted that dinosaurs went extinct because they could not survive the harsh winters resulting from Earth’s changing climate. Their inability to enter winter hibernation contributed to their demise.34

Dust killed the dinosaurs.
A dark, dusty world in which the last non-avian dinosaurs were on the verge of extinction. Mark A. Garlick. Photo: Reuters

1967.  Selenium poisoning from volcanic lava and dust (N.C. Koch, 1967).35

In 1968, American paleobotanist Daniel Isaac Axelrod and geographer Harry Paul Bailey suggested that the dinosaurs became extinct when the earth experienced a more pronounced seasonal climate rather than stable year-round conditions as a result of rock formation and volcanism.36

1968. Landscape Leveling Hypothesis. Helen Tappan, an American micropaleontologist, proposed that dinosaurs went extinct when the Earth’s topographic relief began to reduce, destroying their preferred habitats.37

Hypotheses about the extinction: supernova explosion
Supernova. ©Axel Mazzarino

1968. Supernova Radiation Hypothesis. K. D. Terry from the University of Kansas and Wallace Hampton Tucker suggested that dinosaurs possibly went extinct due to ionizing radiation caused by a supernova explosion.38 Russell and Tucker promoted the same hypothesis in 1971.39

1970. Craig B. Hatfield and Mark J. Camp proposed that dinosaurs went extinct due to the oscillations of the Earth around the galactic plane. Periodically increased doses of cosmic radiation, related to the sun’s position in the galaxy, are the cause of recorded mass extinctions at intervals of 80–90 million years and an exceptionally large mass extinction every 225–275 million years.40 David M. Raup and John J. Jr Sepkoski reported a 26-year periodicity for mass extinctions based on studies of marine fossils.41 42 Richard D. Schwartz and Philip B. James insisted on the same period.43 In turn, Alfred G. Fischer and Michael A. Arthur substantiated the 32-million-year period of major extinctions. At present, hypotheses about the periodicity of mass extinctions are not considered proven and do not have sufficient scientific support.

Volcanic eruptions killed the dinosaurs.
The death of dinosaurs was a result of volcanic eruptions. ©Zheng Qiuyang

1972. American molecular biologist Peter K. Vogt reported evidence of intense volcanic activity in India around the end of the Cretaceous period. He suggested that this volcanic activity released toxic microelements that led to mass extinctions. This was the first association of the Deccan Traps with a mass extinction event.44

Comets could cause mass extinctions

In 1973, American physicist Harold Clayton Urey argued that the effects of comets could cause mass extinctions.45

1974. Dutch paleontologist Jan Smit studied the extinction of foraminifera at the K-T boundary in Caravaca, Spain. He noted that some of these extinctions must have been rapid. Smit was one of the early proponents of the asteroid hypothesis.

1977. Analysis of rock samples from the K-T boundary in Caravaca revealed high levels of metals such as antimony, chromium, cobalt, nickel, and selenium. This led Jan Smit to suspect that the mass extinction at the end of the Cretaceous might have had an extraterrestrial cause.

1977. American paleontologist Robert Thomas Bakker essentially reiterated the hypothesis of Helen Tappan regarding the reduction in the area of preferred dinosaur habitats. He also believes that the main reason for the extinction of all non-avian dinosaurs was actually a plague, caused by invasive species invading through newly formed land bridges.46

Hypotheses about the extinction: Deccan Traps
The volcanic activity of the Deccan Traps may have caused the mass extinction.

In 1978, paleontologist Burger Wilhelm Oelofsen supported the volcanic hypothesis, claiming that kimberlite volcanoes were very common in the late Cretaceous and likely emitted large amounts of carbon dioxide into the atmosphere. Uncontrolled levels of carbon dioxide negatively affected dinosaur eggs, which did not receive enough oxygen, and the embryos suffocated.47

Hypotheses about the extinction: Volcanoes release carbon dioxide
Volcanoes release huge amounts of carbon dioxide. Stratovolcano St. Helens in Washington State / ©Lyn Topinka, Wikimedia / Author: Sycophanta Duccius

1978. Dewey McLean argued that volcanic emissions of CO2 during the Cretaceous period led to a greenhouse effect, which altered ocean currents and the entire climate of the Earth, resulting in the extinction of species at the end of the period.48

1978. Hypothesis of Dinosaurs’ Overheating. British naturalist John Cloudsley-Thompson suggested that if dinosaurs were warm-blooded, an increase in temperature could have caused their overheating and led to their extinction.49

1979. J. Fremlin proposed that the lack of consciousness and the inability to change behavior caused the extinction of dinosaurs.50

Luis Walter Alvarez
Luis Walter Alvarez

1980. Alvarez and others published a report on the high concentration of platinum group metals (including iridium) at the Cretaceous-Paleogene boundary in Italy, Denmark, and New Zealand. They interpreted this phenomenon as evidence of an asteroid impact that resulted in mass extinctions at the end of the Cretaceous period.

Cosmic, exogenous, extraterrestrial hypotheses about the extinction

For at least 250 years, European and American scientists periodically proposed hypotheses about the extinction of dinosaurs caused by extraterrestrial reasons. These hypotheses suggest that cosmic events or forces caused the mass extinctions on Earth. Let’s list some of these hypotheses.

Comet Dust: The cause of dinosaur extinction was dust from comet tails, which affected the climate. In reality, the density of matter in a comet’s tail is negligible compared to the density of the atmosphere, so it cannot reach Earth in any significant quantities.

Gamma radiation
Gamma radiation caused a mass extinction.

Cosmic Rays: The mechanism of their supposed impact is not very clear, and there is no evidence of such events yet. This also includes short bursts of gamma radiation, which are supposed to be more dangerous than long gamma bursts. They allegedly destroyed the planet’s ozone layer or affected living organisms through radiation. There is no evidence of any extraterrestrial events with dangerous radiation capable of significantly affecting life on Earth. And, again, how is the selectivity of their effects explained?

The Sun changes its magnetic field.
The Sun’s magnetic field.

The Sun is to blame: changes in its magnetic field from toroidal (along meridians) to poloidal (along parallels); fluctuations in its size; changes in its gravitational field; sunspots, etc. There is no data on this topic yet, so it is not worth drawing conclusions from the absent evidence.

Dark companion star of the Sun
The Sun’s presumed invisible satellite, Nemesis, is a red, white, or brown dwarf.

Another of the variants of the development of hypotheses of catastrophic extinction. It is assumed that a hypothetical dark companion star of the Sun (or the Ninth Planet) periodically causes perturbations in the asteroid belt or the Oort cloud. This leads to regular meteorite bombardments of Earth, responsible for all extinctions in its history. The hypothesis paints colorful apocalyptic pictures of the end of the world, scaring the average person with the possibility of its repetition in our time. Therefore, it has become very popular among journalists and the general public, but it does not inspire confidence in serious paleontologists. To date, researchers have not yet discovered neither the star Nemesis nor the Ninth Planet.

American-Canadian geologist and paleontologist Dale Alan Russell and physicist Wallace Tucker proposed the flash of a nearby supernova, whose electromagnetic radiation and cosmic rays destroyed the dinosaurs, in 1971.51 No traces of such a flash have been found. In addition, it should have indiscriminately affected all life on Earth.

Hypotheses about the extinction: Interstellar dust
Interstellar dust.

Clouds of gas and interstellar dust could theoretically block solar radiation, leading to global cooling. (Renard and Rocchia, 1984).52 However, when this material falls onto the Sun, due to the release of gravitational energy, its luminosity and, consequently, the temperature on the surface of the Earth, on the contrary, increase.

Hypotheses about the extinction: Dark matter
Dark matter, a cosmic, ghostly-white web, in a cosmological computer simulation. Visualization by Ralf Kähler (Kipac/Slac/Stanford), simulation by Oliver Hahn & Tom Abel

The effects of a high concentration of dark matter when passing through the plane of the Milky Way. Supposedly, this can heat up the Earth’s core and lead to an increase in the intensity of tectonic and volcanic processes, which in turn leads to mass extinction. Dark matter itself has not yet been detected, but it has already killed the dinosaurs…

Entropy: increasing chaos in the universe and, consequently, the extinction of large organized life forms.

Exobiological influences

There are two main groups of disagreements among scientists about the causes of mass extinctions. Biologists, paleontologists, and ecologists adhere to endogenous (biotic) theories, while physicists, astronomers, and geologists defend exobiological hypotheses about extinction.

Acid rain
The sulfur trioxide released upon impact could have caused acid rain on a global scale.

The fallout of sulfate acid rains, which is comparable in impact to battery acid. Ffrogs and other amphibians with permeable skin should have disappeared first and forever. Moreover, scientists have not identified any fluctuations in the values of sulfur isotope ratios in the interval of the boundary between Cretaceous and Tertiary sediments in the Atlantic.

Archaeopteryx
Archaeopteryx
Struthiomimus
Struthiomimus

The peculiar pose of many fossilized dinosaurs, with wide-open mouth, head thrown back and recurved tail, likely resulted from the agonized death throes typical of brain damage and asphyxiation.

A sudden drop in the oxygen content in the atmosphere, leading to suffocation. The oxygen content supposedly fell to 16%, and then to a minimum—12%. Evidence of this may arise from the unnatural postures commonly observed in ancient animal skeletons. The idea was proposed by by Cynthia Marshall Faux, a paleontologist from Yale University, and Kevin Padian, a professor of integrative biology from the University of California, Berkeley. Studies of the composition of the air in ancient deposits and rocks show that during the Cretaceous period, there were no significant changes in the composition of the air. And what did the surviving mammals, birds, and crocodiles breathe?

There is an excess of oxygen in the atmosphere. For example, excessive oxygen results from increased photosynthesis (Schatz, 1957).53 Since there was no decrease in oxygen levels, it means the dinosaurs were killed by the increase. It’s logical, isn’t it?

Does oxygen not fit? Take CO2. An increase in the level of carbon dioxide in the Earth’s atmosphere caused the oceans to stagnate, leading to the extinction of the dinosaurs (suggested by M. L. Keith, 1983).54

Another very common theory is that the Earth’s climate gradually changed over a long period of time, and the dinosaurs could not adapt to the cooler and drier climate.

The inversion of the Earth’s magnetic field
Earth’s magnetic field.

The inversion of the Earth’s magnetic field (there are no traces that it affects the Earth’s biosphere in any way, as such inversions occur regularly).

It was not the impact of the asteroid itself that killed the dinosaurs, but the fine silicate dust in the atmosphere, resulting from the ejection of a giant cloud of small fragments of silicate rocks and sulfates. This caused the cessation of plant photosynthesis and global cooling. This is just a version of the “asteroid winter,” which has not yet been proven. Geophysicist Sean Gulick from the University of Texas at Austin does not consider this assumption convincing.

Hypotheses about the extinction: regression
A regression is a decrease in sea level. Changes in sea level have occurred on Earth throughout its geological history.

The sudden drop in sea level. For example, the Interior Seaway in North America gradually became shallow and disappeared. There is no compelling evidence that the Maastrichtian regression of the global ocean level was abrupt and could have caused mass extinction on a significant scale or contributed to the demise of dinosaurs. On the contrary, amidst the overall regression, individual extensive transgressions of epicontinental seas were well documented during the late Maastrichtian, spreading across continental plains. However, a direct cause-and-effect relationship between ocean level fluctuations and dinosaur extinction remains strictly unproven.

As usual, if sea regression is not suitable, then transgression is to blame. Hallam in 1984 argued that benthic anoxia at the beginning of the transgression started the extinction chain.55

The sharp decline in ocean temperature. There is no evidence of significant temperature fluctuations during this period.

The overflow of fresh Arctic water from the previously enclosed northern basin into the oceans led to a worldwide drop in temperature, less precipitation, and a 10-year drought. All of this combined to kill the dinosaurs. (Gartner and Keany, 1978;56 Gartner and McGuirk, 197957).

Continental drift
Continental drift.

The drift of continents at the end of the Cretaceous period altered the system of atmospheric and oceanic currents, negatively affecting the biosphere. Dinosaurs, being a specialized group, were particularly vulnerable to such changes and eventually went extinct. Continental drift is an extremely slow phenomenon, and its consequences manifest even more gradually. These natural changes occur over extended periods (spanning millions of years). Where certain species and entire genera faced extinction, others, closely related, took their place. Although mass extinction did not occur suddenly, it was still a faster process than the centuries-long movement of continental plates.

Endogenous (ecological, biotic) hypotheses about the extinction

Many facts suggest that biological (ecological) factors could have been the cause of mass extinctions. This has spawned a whole series of hypotheses about the extinction of dinosaurs based on the endogenous causes of this phenomenon.

Hypotheses about the extinction: plants with toxic alkaloids

The change in vegetation type and poisoning by plants with toxic alkaloids is not suitable—they could not spread across the entire planet so quickly as to kill all dinosaurs simultaneously. Also, this could not have affected piscivorous and marine reptiles. If we are talking about flowering plants, then dinosaurs fed on them for tens of millions of years without harm to their health, as flowering plants appeared in the early Cretaceous. By the middle of the Cretaceous, they had already predominated on Earth. At the same time, entire groups of individual herbivorous dinosaurs achieved evolutionary success by adapting to the new ecological niche of grassy steppes. Biochemist Tony Swain first proposed the idea of the demise of dinosaurs from alkaloids and tannins from flowering plants in 1976.58

Hypotheses about the extinction: Hay fever killed the dinosaurs
Hypotheses about the extinction: Hay fever killed the dinosaurs. ©UniquePaleoart.

A variant of this extinction hypothesis: hay fever killed the dinosaurs. Flowering plants (angiosperms) spread, and dinosaurs died from allergic reactions to these new toxic invaders. Flowering plants existed millions of years before the disappearance of dinosaurs. We have no evidence that their pollen or other products killed the dinosaurs. It is unlikely that we would find evidence if it existed. And this still would not explain the mass extinction of the marine environment; marine angiosperms never existed. (Dott, 1983)59

Since the middle of the Cretaceous period, there has been a shift in the dominant vegetation from gymnosperms and ferns to angiosperms. The new flora was richer in proteins and had fewer poorly digestible fibers. This led to large herbivorous dinosaurs receiving far more calories than necessary for their massive body size. The dinosaurs’ bodies could not handle the excess energy, which was converted into heat. For this reason, the giant dinosaurs were doomed to extinction. (Russian paleontologist Andrey Zhuravlev)

Mammals outcompeted and defeated dinosaurs. It is impossible to fully reconstruct the ecosystem of the late Cretaceous and see whether mammals outperformed dinosaurs in the struggle for food, habitats, or other resources. But we know that dinosaurs and mammals evolved together for most of the Mesozoic era. They could not occupy similar ecological niches. Mammals had their own food resources, and larger dinosaurs could not survive by eating the same as mammals, and vice versa. And, almost as always, this does not explain the extinction in the ocean.

Mammals ate dinosaur eggs.
Mammals ate dinosaur eggs.

Some people explain the extinction of dinosaurs by claiming that mammals ate dinosaur eggs. Then why didn’t they eat the eggs of toothless birds, crocodiles, turtles, lizards, etc.? How could this have affected the marine community? Moreover, mammals and dinosaurs have coexisted since the late Triassic! Why didn’t they eat them right away instead of waiting for the entire Mesozoic era?

No species that ate eggs could have eaten all the dinosaur eggs; they would have only driven themselves to complete extinction (they would have run out of food). And the expansion of mammals did not begin only after the extinction of dinosaurs. Although Mesozoic mammals were small in size, their species diversity at the end of the Mesozoic era was quite comparable to the number of species and genera of dinosaurs. In the latest Mesozoic deposits of North America, for example, 29 genera of mammals and 34 genera of dinosaurs were found. And Mesozoic mammals had no fundamental evolutionary advantages compared to their contemporary reptiles.

Also, some sources claim that large marine reptiles could not withstand competition with modern-type sharks that appeared at that time. However, as early as the Devonian period, sharks (cartilaginous fish) proved to be non-competitive in relation to more advanced vertebrates. Bony fish pushed them into the background. New, very large, and relatively progressive sharks began to appear in the late Cretaceous period after the extinction of ichthyosaurs and the decline of plesiosaurs, and they indeed competed with mosasaurs.

The abundant feed received by chewing dinosaurs led to an increase in the volume of dung. This is when dung beetles appeared, as confirmed by both paleontological and molecular data. Since soil biogenic substances ultimately end up in lakes and oceans, the aquatic biota changes as well. In stagnant freshwater bodies, previous groups of insects, crustaceans, and fish almost disappeared. The ocean could not cope with the excessive runoff of biogens. The “blooming” of cyanobacterial and algal plankton began, leading to mass mortality events known as “oceanic anoxic events,” which led to the extinction of some groups of organisms and the spread of others…

The increase in the temperature of surface waters, also facilitated by the “blooming” and death of temperature-lowering groups of planktonic algae, likely led to the extinction of marine reptiles and large sharks, which found it harder to cope with body overheating. One way or another, all marine inhabitants were affected, including pterosaurs on a marine diet.

Flushing of nutrients into the sea
Flushing of nutrients into the sea. A view of the Betsiboka River estuary in Madagascar was taken by the STS-104 crew from the space shuttle Atlantis. NASA

Another variant. In the above phenomena, trees were to blame, which loosened the soil with their roots and intensified the washout of biogenic elements into the sea, leading to eutrophication, anoxia, and mass mortality events.

The direct opposite hypothesis. Flowering plants, primarily herbaceous plants and grasses, bound the soil with their roots, reducing the washout of biogenic elements into the sea; phytoplankton withered, and everyone died of hunger. In fact, the reduction in the influx of biogenic substances into the sea could have played a certain role in mass extinction, but as a very slow and gradual factor.

Genetic disorders destroyed the dinosaurs. Excessive mutation rates due to cosmic rays and ultraviolet radiation reduced the size of the population, burdened by a high genetic load. This has led to vulnerability to environmental changes. (Tsakas and David, 1987)60

Dinosaurs simply went extinct?

The hypothesis that dinosaurs simply went extinct? Now that is a truly testable hypothesis. It has some basis—there is evidence that indeed suggests a gradual reduction in dinosaur diversity during the late Cretaceous period. Sauropods and many others went extinct even before the end of the Cretaceous period. Many well-known paleontologists, such as Charles Darwin, Othniel Marsh, Arthur Woodward, and others, adhered to this hypothesis. However, this hypothesis faces challenges related to temporal resolution and the scarcity of fossils. So at present, it is not considered absolutely conclusive. Moreover, it does not specify any cause—the hypothesis merely asserts that dinosaurs gradually went extinct.

Exotic hypotheses about the extinction of dinosaurs

There is also a whole range of more exotic hypotheses about the extinction, attempting to explain the demise of dinosaurs through various catastrophic causes. Everyone who could hasten to speak out on the topic of the extinction of dinosaurs. Both people are far from science and non-paleontologists, experts in their fields, but know little about the fossils of Late Cretaceous dinosaurs. Paleontologists can confidently say that some of the proposed explanations for the extinction of non-avian dinosaurs simply do not align with reality.

One such hypothesis suggests that an asteroid impact hit a large reservoir of oil, causing it to explode when released into the air. This would explain the presence of tiny carbon spheres approximately 50 micrometers in diameter in Earth’s rocks from that period.

Caterpillars of butterflies ate all the plants
Butterfly caterpillars led to the death of dinosaurs.

Another exotic hypothesis proposes that dinosaurs starved to death because caterpillars of butterflies ate all the plants that were the primary food source for herbivorous dinosaurs. After the herbivores died out, the predators also went extinct (while the plants themselves somehow survived). Entomologist Stanley E. Flanders put forth this idea in 1962.61

Pandemics or epizootics killed the dinosaurs
Pandemics or epizootics killed the dinosaurs.

Pandemic or epizootic. The drift of continents at the end of the Cretaceous period opened up new pathways for dinosaurs to migrate to other areas previously inaccessible to them. Thus, the mixed dinosaurs spread diseases and destroyed each other. Robert Thomas Bakker suggested that it could have been the plague. Another idea proposes that dinosaurs died out due to diseases caused by superpathogens that their immune systems could not cope with. A pandemic erupted, which eventually wiped them off the face of the earth. In reality, dinosaurs were very diverse animals and could not have perished from one type of virus or bacteria.

Dinosaurs became too big, could not control their bodies, or simply crushed themselves, and therefore died out. There is no general trend towards increasing size for all dinosaurs in the Mesozoic era. Certain lines, for example, some theropods and ceratopsians, indeed show noticeable trends towards increasing size, but none of them became so large that they could not move; this is evolutionarily impossible. Most of the largest dinosaurs lived millions of years before the mass extinction.

Some researchers have even suggested that dinosaurs were stupid (compared to mammals) because they had to spend too much internal energy to grow huge and fierce. This idea does not explain why some of the largest and strangest specimens, such as stegosaurs and sauropods, thrived for most of the Mesozoic (respectively, 70 and 140 million years).

Dinosaurs destroyed themselves when predatory species began to eat the eggs of herbivorous species, thus exterminating all. In nature, a balance is always maintained between the number of predators and their prey, as was the case with dinosaurs, since they existed for over 180 million years.

The eggshells became too thick
From “Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction” by Kenneth Carpenter.

The eggshells of some species became too thick, while others became too thin, and they perished. German paleontologist Heinrich Karl Erben and others62 proposed this idea based on the paleopathologies of Hypselosaurus eggs in the late Cretaceous deposits in the Pyrenees Mountains in southern France. Researchers suggested that toxic substances released into the atmosphere from volcanoes or some climate change triggered hormonal changes in dinosaur mothers. Philip Kerourio refuted this idea in 1981. In reality, changes in shell thickness do not occur in one season; genetic changes must accumulate, which would be selected out in the course of evolution if they led to the death of offspring. Moreover, many surviving taxa, including birds (living dinosaurs), crocodiles, and turtles, have thin eggshells.

An excessively favorable climate could lead to an extreme level of birth rates. The dinosaur population growth led to overcrowding. In turn, overpopulation caused stress that prevented the dinosaurs from laying healthy eggs, leading to their extinction.

Dinosaurs perished due to improper functioning of the pituitary gland, which made them pathologically large, causing their extinction. But giant dinosaurs existed for hundreds of millions of years, and somehow their pituitary glands did not kill them. There is no evidence of malfunctioning pituitary glands; moreover, why then did small-sized class dinosaurs go extinct?. Baron Franz Nopcsa proposed this idea in 1917.63

Hypotheses about the extinction: Dinosaurs went blind
Dinosaurs went blind from too bright a sun.

The idea that cataracts led to the extinction of dinosaurs suggests that these ancient reptiles suffered from eye problems due to prolonged exposure to a warm climate. Dinosaurs with horns or crests on their heads used these “decorations” to shield their eyes from the relentless Mesozoic sun, but they still went blind and perished. Ophthalmologist L.R. Croft proposed this hypothesis in 1982.64

However, there are several issues with this theory. The Earth has experienced epochs with warmer climates than during the Mesozoic era. For example, during the Permian period, temperatures were even higher. Other organisms, such as marine ammonites and ichthyosaurs, also went extinct during these warm periods. Why did they suffer from cataracts too? The Mesozoic era lasted 186 million years. If cataracts were the cause, why did dinosaurs only go blind toward the end of this long era? Why not earlier? The hypothesis doesn’t explain why other animals didn’t suffer from cataracts despite similar external temperature influences.

Rapid temperature changes disrupted the balanced sex ratio. This leads to the emergence of exclusively males or exclusively females from the eggs of reptiles. Ultimately, this provoked the extinction of species. A group of researchers from the University of Leeds in the UK, led by David Miller, proposed this idea. Ferguson and Joanen in 198265, Paladino in 1989, and later Sherman Silber supported them. However, this does not explain why other animals, whose sex is also affected by external temperature (such as alligators and crocodiles), survived. Furthermore, it remains unclear whether temperature or genetics alone determined the sex of dinosaurs.

Among the many exotic hypotheses about extinction, there is even this one: the extraction of the Moon from the Pacific Basin. These are the ideas that fantastic hypotheses about the collision of the Earth with the hypothetical planet Theia lead to.

Fluctuations of gravitational constants. Obviously, such fluctuations did not like dinosaurs, while mammals were quite satisfied with them. It is impossible to verify this statement.

Aliens exterminated the dinosaurs
Aliens vs. dinosaurs. ©drawasaurus04

Aliens, who landed on Earth in the Mesozoic era, exterminated the dinosaurs. Why did they leave the crocodiles, and where are the traces of these extraterrestrials? Perhaps they wanted to clear space for humanity, which was supposed to emerge 60 million years later? There is no scientific basis for this theory.

The expansion of angiosperms and the reduced availability of gymnosperms, ferns, etc. This led to a reduction in fern oils in the dinosaur diet and a prolonged death from incurable constipation (Baldwin, 1964).66

If dinosaurs could not poison themselves with alkaloids and tannin, oxygen and carbon dioxide, silicate dust, and selenium, they would have to poison themselves with uranium sucked from the soil (Neruchev, 1984).67 So what to do? They had to be killed somehow anyway, right?

Dinosaurs farted themselves to extinction.

Due to the abundant release of intestinal gases by sauropods, dinosaurs poisoned themselves, could not breathe, and doomed themselves to extinction. Sauropods existed for 125 million years and somehow endured; how did birds survive this genocide? By the way, modern birds are the evolutionary descendants of dinosaurs, and they do not fart at all.

Dinosaurs fart affected on the global climate
©Karl Tate, LiveScience Contributor

Paleontologist David Wilkinson from John Moores University in Liverpool proposed a modified version of the intestinal gas hypothesis in the journal Current Biology (2012). He stated that the cause of the extinction of giant lizards could have been the gases they emitted during their own life processes. Sauropods allegedly produced about 570 million tons of methane annually. This greenhouse gas absorbed the sun’s infrared radiation and contributed to an increase in temperature, leading to global warming, which ultimately led to the extinction of dinosaurs. To be fair, Wilkinson himself only considered the impact on the global climate, not the extinction of dinosaurs.

Conclusion

Most of the hypotheses about the extinction are unscientific speculations and do not withstand even elementary criticism. However, there are meaningful assumptions about processes that undoubtedly played a certain role.

Many people want to find a single “main” cause, preferably one that applies universally to all extinctions. It would be convenient (we like things simple and elegant), but the world doesn’t work that way.

The extinction of dinosaurs
The extinction of dinosaurs

All the evidence suggests that the asteroid impact did not immediately lead to the demise of dinosaurs or any other organisms. This makes the asteroid hypothesis as the sole catastrophic cause of mass extinction unreliable. The impact (possibly multiple, sequential, or simultaneous) was just one component of this process. Of course, the spectacular idea of terrifying reptiles perishing in a single global catastrophe captures the imagination and attracts the attention of non-specialists. This hypothesis is visually appealing and straightforward, but it does not align with reality.

It’s essential to note that the extinction of dinosaurs was likely a complex event influenced by multiple factors acting together over geological time scales. Ongoing research and new discoveries continue to enhance our understanding of the causes and mechanisms of the mass extinction at the end of the Cretaceous period.

An informative article discusses the issues of dinosaur extinction hypotheses in detail: Scientific Methodologies in Collision. The History of the Study of the Extinction of the Dinosaurs, 1990, Michael J. Benton. Recommended to those who want to study the history of views on extinction in more depth.

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