If the birds descend from dinosaurs and have shown an evolutionary trend towards large dimensions, because none of them have ever become as big as a T-Rex? Among the factors that have limited the growth of birds, despite their dinosaurian inheritance and the evolutionary push towards larger dimensions, there are biological limits tied to the fly, evolutionary pressures and the ecological niches post-extinction.
Biological and environmental limits
Several factors have probably prevented birds from reaching the size of non -aviar dinosaurs. For flying birdsthe flight represents a obstacle significant, the more a body becomes great, the greater theenergy request and the muscle power necessary to get up and keep in the air. There is a limit point beyond which a flying creature cannot increase by mass without losing the ability to fly.
But the question is more complex for Birds unable to fly. Although they inherited from the dinosaurs ancestors crucial characteristics for gigantism, such as the air bags that surrounded and invaded their bones, making the skeletons lighter without sacrificing their resistance, and the deposition of eggthese Biological peculiarities they removed barriers, but they did not require that i bodies they became more big. Worldwide post-cretaceous, Birds have never experienced sufficient evolutionary pressure to be high or massive as much as a T-Rex.
Evolutionary pressures and ecological niches
Perhaps, unlike dinosaurs, birds did not find themselves in situations where large dimensions represented an advantage. Take for example the birds of terror, they were formidable predators in South America prehistoricand perhaps even larger dimensions would have helped them to hunt larger prey. A study of 2023 suggests that they actually preferred prey more smallwhich could have curbed their growth. In addition, the competition with i mammalswho quickly diversified after the extinction of the dinosaurs, may have prevented birds from occupying those ecological niches essential to evolve towards giant dimensions.
The role of ecological opportunities
The ornithologist Hanneke Meijer of the University of Bergen underlines how large birds tend to evolve into environments that offer numerous “ecological opportunities“. These opportunities can manifest themselves in various ways: the absence of adults predators on an island, or the presence of abundant resource on a continent. Meijer It points out that although we consider the islands as evolutionary workshops in which rapid experiments take place, large evolution can also occur on the mainland, although more slowly and less frequently. Meijer adds that large birds can evolve even in the presence of other aviatory predators, as in the case of Moa from the New Zealand and of theHaast eagle. The important thing is that there are sufficient resources and ecological opportunities that allow these birds to thrive.
