Herbivorous dinosaurs may have reached the Northern Hemisphere millions of years after the arrival of their carnivorous cousins, a difference that could be due to the climatic conditions of the time. This hypothesis derives from a study, published in the journal Proceedings of the National Academy of Sciences, conducted by scientists at Columbia University, who used a more specific way of calculating the age of dinosaur fossils discovered in Greenland, which shows a difference of millions of years from previous considerations.
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“The remains of herbivores known as sauropodomorphs – he explains Dennis Kent of Columbia University – they were about 215 million years old, up from 228 previously assumed. This leads us to rethink dinosaur migrations. ”The team worked out a more accurate way to get the age of the fossils, based on analyzing changes in Earth’s magnetism in the soil, which highlighted differences in migration timing. “The first dinosaurs could have developed in South America about 230 million years ago – says the author – and then migrate to all parts of the world“.
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Scientists believed that the migration occurred indiscriminately for carnivores and non-carnivores, but this work suggests that the former may have reached the northern hemisphere millions of years before the sauropodomorphs. “There are no documented skeletons of herbivores over 215 million years old in Greenland – observes Randy Irmis, of the University of Utah, who did not participate in the study – while carnivores have been present in most of the globe for at least 220 million years. does”. According to the authors, the difference in migration times could be due to climate change. “About 230 million years ago, during the Triassic period – explains Kent – the levels of carbon dioxide were about 10 times higher than the current situation. In the regions north and south of the equator, the climate was very dry and there were no present plants suitable for feeding sauropodomorphs, while carnivores may have fed on other animals during the journey across the hemispheres “. The researcher then points out that after 15 million years, however, the levels of CO2 they have dropped considerably, up to halving, which has allowed the sauropodomorphs to travel the journey and migrate, encountering vegetation suited to their nutritional needs.
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Elena Dusi
“This theory also fits many existing species – he comments Hans-Otto Portner of the Alfred Wegener Institute in Germany, biologist and climate scientist, not involved in the research – who stay away from specific climates “.” This is a very interesting hypothesis, but it has a potential flaw – concludes Paul Sereno of the University of Chicago – just because no herbivore fossils older than 215 million years have been discovered in the Northern Hemisphere does not necessarily imply that no sauropodomorphs were present in the region in earlier times. The fossils may simply not have survived. “
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