A new type of dinosaur is described every ten days on average. This year, 31 new species have already been described, but it is not yet finished. Of course, figuring out what counts as a separate species isn't easy. Paleontologists love to argue, so getting the two of them to agree on the final list of species is almost impossible. But whoever believed, we know that there were many dinosaurs - 700-800 species have already been described, perhaps more than a thousand. Why are there so many species?
First, we need an idea of how many species of dinosaurs existed in general. One study tried to estimate the overall diversity of dinosaurs through the species zone effect - the idea that if we know how many species one small part of the Earth can support, we can extrapolate how many there should have been in the entire world. These calculations show that at the end of the Mesozoic, 66 million years ago, the diversity of dinosaurs - of all species living at the same time - was between 600 and 1000 species.
This seems like a reasonable estimate, because if you count all living land mammals weighing more than 1 kg (the size of the smallest dinosaur) and then add the extinct species from the last 50,000 years, such as woolly mammoths, terrestrial sloths and giant kangaroos (adjusted for loss from human activity), you will get a similar rating.
However, this is only the number of species that exist at one point in time, and dinosaurs have existed for a very, very long time. Throughout the Mesozoic, dinosaurs constantly evolved and became extinct. After doing some quick and rough calculations and assuming that 1000 species of dinosaurs could live at the same time, and these species were replaced every million years, we get 160,000 species. Lots of dinosaurs.
This is, of course, a very rough estimate. It depends on many assumptions, such as how many different species the planet can support and how quickly they evolve and die out. If we assume a minimum of 500 species and their slow change every 2 million years, for example, we get 50,000 species. On the other hand, in the warm period of the Mesozoic type, the existence of 2000 species can also be assumed, which changed after half a million years. It turns out 500,000 species. It seems reasonable to assume that between 50,000 and 500,000 dinosaur species existed, not counting the Mesozoic birds, which could double their diversity.
Why are there so many species? It boils down to three points. Dinosaurs were quite good at specialization, localization, and speciation.
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Specialization
Dinosaurs were adept at using different niches, where different species could coexist without competing. In western North America, the giant T. rex carnivore coexisted with the small meat-eating dromaeosaurs. Giant, long-necked sauropods roamed side by side with horned ceratopsians, amiably eating flowers and herbs. There were also small herbivores - pachycephalosaurs and ornithomimids, fish-eating dinosaurs like herons and even anteater-like insectivores.
And in these niches there were further specializations. T. rex was massive and had powerful jaws, but rather stocky and clumsy limbs, and was good at hunting the slow but reinforced Triceraptops. T. rex sibling, Nanotyrannus, was smaller, but had marathon legs, so it easily caught up with its prey. This specialization means that at least 25 dinosaurs, according to research, could live side by side in the same habitat.
Localization
Localization refers to how different species are placed in different places. Mongolia had one set of animals - tyrannosaurs, platypuses, and ostrich dinosaurs - living in a lush river delta that flows through the center of the desert. Just a few kilometers away, small horned dinosaurs and parrot-headed oviraptors inhabited the dune fields. Dinosaurs also varied from continent to continent, with different species inhabiting different parts of North America, for example. The differences between continents were even more pronounced. During the Late Cretaceous Period, North America and Asia were predominantly inhabited by tyrannosaurs, duck-billed dinosaurs and horned dinosaurs. But Africa and South America, cut off by oceans for many millions of years, were inhabited by completely different species. Instead of tyrannosaurs, the horned abelisaurs were the best predators. Instead of platypus dinosaurs, the long-necked titanosaurs were the leading herbivores.
Speciation
Dinosaurs developed new species at an astonishing rate. Radioactive dating has made it possible to date rocks containing dinosaur fossils and determine how long they existed. The rocks of the Hell Creek Formation in Montana, for example, have been taking shape over 2 million years. In the lower part of these layers we have one species - Triceratops horridus - and in the upper part we have the second species, which evolved from the first, Triceratops prorsus.
This means that the species lived for a million years - a relatively short time in geological terms. Studies of other formations and other horned dinosaurs show that other species were also short-lived. In the badlands of Dinosaur Park in Canada, fossils can be found that show three different types of dinosaurs - the first is replaced by the second, the second is replaced by the third - evolved over 2 million years. Dinosaurs evolved and changed rapidly, driven by shifts in Earth's seas, climate, continents, and the evolution of other dinosaurs. If this had not happened, they would have died out.
We will never know exactly how many dinosaurs existed. These animals were so rarely preserved and became fossils that many tens of thousands of species were lost to us forever. And yet it's great that we find such interesting things as, for example, a whole dinosaur tail in amber. We've lost sight of many views, but we'll find thousands more.
ILYA KHEL