When did the dinosaurs died out: what prevented them from living

“Ichthyosaurs died out millions of years before their ecological counterparts among cetaceans appeared. Pterodactyls disappeared long before bats occupied a similar or overlapping zone. Dinosaurs died out before land mammals spread so quickly in almost the same zones ”(D. Simpson).

When dinosaurs died out

Nature forever parted with marine, freshwater, land, running, flying, living in a variety of environmental conditions pangolins. And not only with lizards. The same thing happened to the Ammonites. The genus of even some mammals has come to an end. Never has death reaped such a bountiful harvest.

What prevented them from living, earthly creatures that died 65 million years ago?

There was a time in the Mesozoic when 16 orders of reptiles simultaneously existed on Earth. Now there are only four of them: turtles, crocodiles, and scaly ones; the fourth order – tuatara – is represented in the modern fauna by only one relict species with a very limited habitat (New Zealand).

Of course, extinction did not happen in an instant and not in one year, not even a hundred centuries, but about five million years before the start of the Cenozoic. But what is five million years in three billion years of life on Earth: a puddle compared to the ocean!

Almost a third of the Cretaceous fauna tried to explain this mysterious departure from life for various reasons, excluding, of course, the intervention of the “creator”. The famous Austrian paleontologist E. Tenius listed them in the following order:

  1. Climate change (with or without a pole shift), caused the death of the main plants that the herbivorous pangolins fed on.
  2. Mountain building (for example, the so-called Laram phase at the end of the Cretaceous). This led to the drying up of swamps, river deltas, and lagoons.
  3. Degeneration.
  4. Epidemics of dangerous diseases.
  5. Death from parasites.
  6. The extermination of herbivores by carnivorous reptiles, was followed by the extinction of carnivores.
  7. The appearance of mammals that ate the eggs of lizards.
  8. Pathological formations of a too thick shell, which the “children” of dinosaurs that developed in the eggs could not break through. (I’ll add on my own that lizard eggs were found with a really too thick shell, probably not pierced from the inside.)
  9. Change in atmospheric pressure as a result of the accumulation of volcanic gases in it or for other secondary reasons.
  10. A sudden increase in cosmic radiation after the explosion of a supernova close to the solar system, led to a sharp increase in deadly mutations in the heredity of newborn animals.
  11. A strong increase in high-energy cosmic radiation as a result of a violation of the Earth’s magnetic field.

The hypothesis of increased radioactivity as a factor that killed the dinosaurs attracts many supporters for the variety of its harmful effects. Indeed, even direct penetrating radiation could kill, and the harmful changes in heredity that occur after it bring death and degeneration of offspring.

In addition, the following question is being solved: why did other animals not suffer from one or another reason that destroyed the pangolins?

The fact is that studies of recent years have shown that not all creatures are equally sensitive to penetrating radiation. Spiders and scorpions, for example, carry dozens of times more radiation than would quickly kill many other animals.

And it can be assumed that dinosaurs were the least resistant to such doses of radiation, which had little effect on mammals, birds, and reptiles that survived after the Mesozoic.

“… The solar system in its orbit around the center of our Galaxy in certain areas crosses high-energy particle flows (“spiral arms”). This, according to our assumptions, should have caused an increase in radiation, an increase in the speed of the Earth’s rotation, the development of mountain-building processes and huge emissions of radioactive ash … The last such meeting with the “spiral arm” should have occurred about 70 million years ago “(V. Bogoslovsky).

Together with other Soviet scientists, V. Bogoslovsky, with the permission and participation of the head of the Paleontological Museum of the USSR Academy of Sciences, Professor K. Flerov, decided to measure the residual radioactivity of many museum exhibits from different eras of the Earth’s history.

The results he got were very convincing. The radioactivity of some late Cretaceous dinosaur bones is six times higher than the average for a span of 400 million years! Moreover, “radioactivity is increased to varying degrees in almost all areas of excavation.”

The conclusion from these studies is clear. However, not all paleontologists are satisfied with it. Hypotheses follow hypotheses…

In 1974, the English scientist T. Swain proposed a very original project to solve the riddle of the sudden extinction of dinosaurs. He reasoned as follows: the death of the lizards coincided with the massive spread throughout the Earth of the highest class of plants – angiosperms (flowering). It was they who produced, in his opinion, “a bloodless beating of dinosaurs.”

Why these plants are dangerous, I will say a little later. And now some calculations. A lizard weighing five tons must eat about 200 kilograms of plants per day. And therefore the annual area of ​​​​its pasture is approximately 20 square kilometers.

And then what can be said about the appetite of fifty-ton lizards – diplodocus, brontosaurs, brachiosaurs? And about the doses of “poison” that they, knowing nothing, took with food …

What is this poison?

Tannins and alkaloids say, Dr. T. Swain. These substances were not found in lower gymnosperms, which dinosaurs fed on for more than 150 million years. The higher plants contained these new bitter and poisonous substances. Tannins, which are plentiful, such as those found in strong tea and unripe apples, are astringent in taste. In large doses, they suppress the digestion of proteins and the activity of enzymes, destroying the liver.

Alkaloids have a broader aspect of physiological action. Some of them are very poisonous. The well-known strychnine is an alkaloid. And morphine too: it has a strong effect on the psyche. Other alkaloids cause harmful effects on heredity and breeding cycles.

T. Swain believes that 40-50 grams of alkaloids are a lethal dose for a dinosaur, “and such an amount could well have accumulated in 200 kilograms of a daily diet.” So dinosaurs turned out to be defenseless against these new poisons for them, to which herbivorous mammals were able to adapt.

The mass death of vegetarian dinosaurs doomed their carnivorous counterparts to starvation.

“Thus, it can be assumed that dinosaurs died as a result of the “predatory aggression” of angiosperms” (T. Swain).

It is possible to assume that the timing of the appearance of “poisonous” plants and the disappearance of dinosaurs is completely linked. The Soviet scientist V. Eliseev quite reasonably rejects T. Swain’s hypothesis.

“From the very beginning of the Late Cretaceous, angiosperms, pushing the gymnosperms far into the background, become the mainland plants. Therefore, if alkaloids … are really deadly for a dinosaur, then the animals should have died already at the beginning of the Late Cretaceous, which, however, did not happen. Dinosaurs continued to live until the end of the Late Cretaceous, that is, they lived for another 20-25 million years after they had swallowed the “poison”. I believe that the new food was harmless to them, and they liked it.

To all sorts of hypotheses about the causes of the extinction of dinosaurs, one can add such a very real version.

Geneticists have long known an indisputable truth: all animals that do not have deadly dangerous enemies in nature are inevitably doomed. There is no natural selection. Freaks and non-viable descendants born to them, no one eliminates (does not destroy), does not eliminate from the biological cycle of procreation. Animals with life-threatening mutations (spontaneous changes in heredity) continue to multiply and breed their own kind, passing them lethal (deadly) genes.

Giant lizards – brachiosaurus, diplodocus, brontosaurus – hardly moved on land and spent almost their entire lives on the shores of the same reservoirs. They were, so to speak, residents of “micro districts” and here, therefore, they entered into marriages with each other.

Inbreeding (closely related reproduction) sharply increased the homozygosity of harmful genes, and hence their accumulation in the genotype. (Homozygosity, popularly speaking, is the reunion of the same maternal and paternal traits in the heredity of children.)

The moment finally came when they began to give birth only to non-viable descendants with many homozygous lethal genes identified in the phenotype, that is, in the physique and physiology of the animal. And then the complete extinction of the entire population of giant lizards followed, first on one of some “swamps”, and then on all.

The same was expected of tyrannosaurs and similar large predators. The sword of Damocles of negative selection, brought over them by nature, did not cut off diseased branches from a healthy trunk.

But all this applies only to animals over which natural selection did not weigh – large predators and giants, no enemies were dangerous to them. However, we see that at the end of the Cretaceous period, not only huge reptiles and two-meter ammonites died out everywhere on Earth, but also their small relatives, not immune from death in the teeth of predators and subject to sorting in the struggle for existence.

It turns out that the genetic hypothesis does not explain the whole essence of the mysterious and sudden disappearance of many thousands of species of Mesozoic animals. It remains only to shrug it off … Science has not yet found an answer to the question posed in the title of this article.

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