Dinosaurs

Article

July 5, 2022

Dinosaurs (Dinosauria) - a diverse clade of sauropsids. They appeared in the Triassic about 237 million years ago. They constituted the dominant group of terrestrial vertebrates from the beginning of the Jurassic (about 201 million years ago) through 135 million years to the end of the Cretaceous (66 million years ago), when the Cretaceous extinctions (marking the Cretaceous-Tertiary boundary and the end of the Mesozoic) led to the disappearance of most of the lines. The fossil record indicates that birds evolved from theropod dinosaurs in the Jurassic, and are therefore considered a group of dinosaurs by the literature on the subject published in the 21st century. Surviving a catastrophe from 66 million years ago, thanks to their descendants, they have continued the dinosaur lineage to the present day. Until the last decades of the 20th century, all groups of dinosaurs were considered extinct. However, the fossil record indicates that birds, now called avian dinosaurs in English, are modern descendants of feathered dinosaurs. They evolved from their ancestral ancestors during the Jurassic period. Therefore, birds are the only line of dinosaurs that survived the extinction. Therefore, birds are also included among dinosaurs. In turn, non-bird dinosaurs are referred to as non-avian dinosaurs, translated into Polish as "non-avian dinosaurs", there is also the term "non-avian theropods". Dinosaurs are a diverse group of animals from a taxonomic, morphological and ecological point of view. The birds now include over 10,000 species, making them the most diverse group of vertebrates, except the perch. Thanks to fossil evidence, until 2006, palaeontologists distinguished over 500 genera and over a thousand species of non-avian dinosaurs, while in 2014 the number of described genera was 943. Dinosaurs inhabited all continents - all of them contain fossil remains and modern species. They include both herbivores and carnivores. They were originally bipedal, but many extinct groups included quadrupedal forms as well as both two-leg and four-legged forms. Numerous groups have developed sophisticated structures such as horns and flanges. Some extinct taxa also developed skeletal modifications such as spikes and armor. Egg laying and nests were confirmed in all groups. While today's birds are usually small, which is related to the ability to fly, prehistoric forms often reached large sizes. The largest sauropods could be as long as 58 m in length with a height of 9.25 m. The vision of non-avian dinosaurs as homogeneously gigantic, however, is not true, it results from a greater tendency to behave large bones. Many of the non-avian dinosaurs were small, such as the Xixianykus about 50 cm long. The name dinosaurs means "terrible lizards", so it can be misleading - dinosaurs were not lizards, nor were they closely related to them. However, they represent a separate group of "reptiles", apart from birds, their closest modern relatives are crocodiles. Like many extinct forms, they do not exhibit features traditionally considered "reptilian", such as cold-bloodedness or moving sideways on limbs. Moreover, many groups of prehistoric animals such as mosasaurs, ichthyosaurs, pterosaurs, plesiosaurs, and even Dimetrodon, popularly recognized as dinosaurs, are not actually dinosaurs. During the first half of the 20th century, before birds were considered dinosaurs, most of the scientific community considered dinosaurs slow and cold-blooded. The change took place in the 1960s (the rebirth of the dinosaurs). It was found that all dinosaurs, including Mesozoic ones, led an active lifestyle