American paleontologists have found the bones of dinosaurs that lived for another 700 thousand years after the Great Cretaceous extinction of these reptiles. This discovery is the first serious counterargument against the hypothesis that these lizards were killed by a giant asteroid falling to Earth. It turns out that some dinosaurs simply did not notice it …
Despite the fact that most paleontologists have always been skeptical about the version that dinosaurs became extinct as a result of the consequences of an asteroid falling to Earth (the so-called "asteroid winter"), it was she who became the most popular among the masses for many years. For some reason, despite all its absurdity, it is this assumption that is still accepted by many nonspecialists who are interested in the giant reptiles of antiquity. Perhaps because what is taken for its proof (Chkhiksulub crater, that is, the place where the asteroid fell and the discovered iridium anomalies) is very graphic. But scientists, until recently, could not find such indicative counterarguments.
A similar counterargument would be the discovery of the remains of dinosaurs that lived after the disaster. If it was established that at least one group of these reptiles managed to survive this catastrophe, then it was not so terrible for dinosaurs. And although the remains of the Mosasaurus, which lived about 60 million years ago, have long been found (recall that the asteroid fell 65 million years ago), few people were convinced. Because, firstly, the mosasaurs were not dinosaurs (they were giant relatives of modern monitor lizards, that is, lizards), and secondly, they were not terrestrial, but exclusively aquatic animals. Well, in water, as you know, any cataclysm is easier to survive.
And recently, thanks to the discovery of the American paleontologist James Fassett, the "asteroid" hypothesis of the extinction of dinosaurs was dealt a crushing blow. Back in 2009, while studying sediments in the Animas Formation on the border of the states of New Mexico and Colorado (USA), he managed to find dinosaur bones in two layers dating back to the Paleogene (that is, the first period of the Cenozoic era). Preliminary dating showed that the age of the finds is 64.5 million years.
On what basis were such conclusions drawn? The performed palynological analysis (study of pollen, spores and other plant remains) showed the presence of Paleogene flora with an insignificant admixture of Cretaceous samples. Fussette suggested that particles from the Cretaceous flora may have entered the overlying layers from older sediments. But could dinosaur bones have also been redeposited? The scientist thought no, and here's why.
First, among the bones found there are 34 bones that clearly belonged to a single dinosaur from the family of Hadrosauridae. It was not a whole skeleton, but it was not scattered, washed bones either. If we assume that the river washed the bones from the chalk deposits and reburied them, it is unlikely that 34 bones of one individual would have been nearby. Second, the content of uranium and rare earth metals in the bones of Paleogene dinosaurs and Cretaceous dinosaurs from the same region differs markedly. Geochemical conditions changed, and the underground solutions that impregnated bones in the Paleogene differed in composition from those solutions that caused fossilization of bones in the Cretaceous period.
Nevertheless, this dating still needed additional verification. It took the scientist and his colleagues over a year to complete it. To do this, Fassett and his colleagues, Larry Himan of the University of Alberta in Canada and Antonio Simonetti of the University of Notre Dame in the United States, resorted to an analysis based on the use of uranium-lead dating.
This method is based on the fact that after fossilization (about a thousand years after death), some heavy metals accumulate in the bones, in particular, the isotope uranium-238. Over time, uranium decays with the formation of the isotope lead-206 (remember that isotopes are the nuclei of the same element containing a different number of neutrons). By assessing the various isotopes of lead and uranium in a sample, scientists can determine the age of a bone. This method is considered one of the most accurate among paleontologists, and it is used quite often.
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In the process of dating, scientists for comparison took two bones - a sauropod and a hadrosaur, found nearby, but in deposits of different ages. The first bone was found in layers that scientists attributed to the Maastrichtian age of the Cretaceous period, and the second to the Danish Paleogene age. As a result, the authors obtained the following results - the age of the first bone was equal to 73.6 million years, and the second, in fact, one of the very bones of a hadrosaur from the Paleogene, was 64.5 million years old.
As a result, the validity of Fassett's assumption that this dinosaur lived at the beginning of the Paleogene was fully confirmed. It turns out that hadrosaurs calmly continued to exist after the fall of the asteroid for another 700 thousand years and no "asteroid winter" had any effect on them. But, in theory, it had to act, and first of all it was on them.
As you know, hadrosaurs are a family of duck-billed dinosaurs that lived in North America during the Cretaceous period. They were characterized by a crest of various shapes and outlines, inside which there were nasal cavities, which probably served to make loud sounds. The muzzle of these lizards ended in a flat beak resembling a duck's, although in the back of the jaw there were still a number of flat teeth.
These funny two-legged "platypuses" moved on both two and four limbs. Like most of their relatives, peaceful and, apparently, shy hadrosaurs had short front legs and long hind legs, with which they quickly ran away from their enemies. A long, flat tail served them to maintain balance. Apparently, these cute "noses" did not have any other ways to protect themselves from predators.
It is believed that these reptiles led a herd lifestyle, built nests, guarded the clutch and together took care of the offspring. That is, they were distinguished by a high degree of sociality, which is not so common among reptiles, even ancient ones. Previously, paleontologists, due to the structure of the forelimbs, with membranes between the fourth and fifth fingers, and a flat tail, considered hadrosaurs to be semi-aquatic algae animals. This is how they are shown in the famous French cartoon "The Land Before Time" (remember the charming Ducky?). Now this family of "duck-billed dinosaurs" is referred to as terrestrial inhabitants, since needles and leaves of clearly terrestrial plants were found in the stomachs of many representatives of this group. But algae have never been found there. It turns out that they occupied the ecological niche of terrestrial leaf-eating ungulates, like giraffes.
It was also found that hadrosaurs had hooves on the forelimbs and that they had a fleshy growth under the tail, which made swimming simply impossible. So, before us are typical herbivorous land dwellers, whom the fall of the meteorite and the onset of the "asteroid winter" should have deprived of food in the first place (due to the fact that the dust raised by the fall of the asteroid impeded photosynthesis, the plants had to stand for quite a long time without leaves). However, as Fasset's find proves, this did not happen.
It is also noteworthy that the remains of this dinosaur were found not far from the alleged place of the asteroid's fall (Chkhiksulubsky crater is located on the Yucatan Peninsula, it is quite close to New Mexico). But it was in this place that the effect of the notorious "asteroid winter" should have been the strongest (it weakens with distance from the crash site). But it turns out that the hadrosaurs, living dangerously close to the place where the meteorite fell, which supposedly destroyed all the dinosaurs, did not notice at all that something had happened. That is, this very "asteroid winter" did not have any impact even on neighboring ecosystems. Why, then, do many believe that it had to somehow affect the communities of living organisms around the planet?
So, apparently, the version is confirmed that in fact the mass extinction of dinosaurs at the end of the Cretaceous period was not one-time and, accordingly, was not caused by a common cause for all species. Perhaps someone was killed by the locally changed climatic conditions, someone survived mammals, which began to attack the defenseless cubs of giants, someone could not adapt to the change of plant communities. However, all of these were absolutely natural earthly reasons that were not associated with the visit of a space guest.