The very first dinosaurs probably evolved in South America – New Scientist

Dezembro de 2018

Dinosaurs may have come from the south

Hemis / Alamy

By Colin Barras

Os dinossauros eram sulistas. O famoso grupo dominou o mundo por dezenas de milhões de anos e deixou para trás fósseis em todas as principais massas de terra, o que levou a alguma confusão sobre onde os primeiros dinossauros nasceram. Dois novos estudos se acumulam na evidência de que os primeiros dinossauros viviam na América do Sul ou em um dos outros continentes do sul.

Quando os primeiros dinossauros apareceram, cerca de 240 ou 250 milhões de anos atrás, os continentes da Terra estavam unidos no supercontinente Pangea. Em princípio, os dinossauros poderiam ter surgido em qualquer canto do Pangea. No entanto, dado que muitos dos primeiros fósseis de dinossauros foram desenterrados na América do Sul, África e outras regiões que formaram o sul da Pangea, os paleontologistas começaram a suspeitar que esta região era o berço da evolução dos dinossauros.

Last year, though, a high-profile study suggested an alternative. A team of British palaeontologists led by Matthew Baron at the University of Cambridge argued for the most radical overhaul of the dinosaur evolutionary tree in 130 years. In their new tree, some of the fossils that lie closest to the base of the dinosaur group come from Europe – such as one called Saltopus that was found in Scotland. The team said this might suggest the dinosaur cradle was in northern Pangaea.

Advertisement

Now, a team led by Júlio Marsola at the University of Sao Paulo, Brazil, has looked at the subject in more detail. They examined six dinosaur evolutionary trees published over the last 20 years – including the radically different one published last year. Then they looked at the geographical distribution of the species near the base of the dinosaur family in each tree. Almost without exception, the evolutionary trees suggest dinosaurs came from southern Pangaea.

Surprisingly, even last year’s radically different dinosaur tree favours a southern birthplace. Although Baron and his colleagues emphasised that northern fossils like Saltopus plot out near the base of the dinosaurs, their evolutionary tree actually shows that these northerners were the exception rather than the rule: most of the fossils that fall near the base of their modified dinosaur group are southerners.

“Our results greatly support the Southern hypothesis as the most plausible, given our current understanding,” says Marsola. “Not only that, our result didn’t yield any indication of a possible [northern] origin for the group.”

One of Marsola’s co-authors is Richard Butler at the University of Birmingham, UK. He points out that Baron’s team independently published their own analysis of dinosaur origins this week – and also overturned their northern dinosaur idea. Baron and his colleagues concluded there is a 99 per cent chance dinosaurs came from South America, and an 83 per cent chance they came from the very southernmost part of that continent.

Neither team knew about the work that the other team was doing, says Butler. “In any case, even [Baron’s team] accept that a southern origin is by far the most likely.”

Journal reference: Palaeontology, DOI: 10.1111/pala.12411

Journal reference: Earth and Environmental Science Transactions of The Royal Society of Edinburgh, DOI: 10.1017/S1755691018000920