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Shifting the thinking on tetrapod evolution: Ancient four-limbed animals lived near the poles

June 07, 2018

It has long been presumed that the ancestors of all vertebrates - the amphibious, aquatic tetrapods that first colonized the land - evolved in warm tropical environments. Now, however, the unexpected unearthing of two ancient tetrapod fossils in South Africa, near polar latitudes, hints that four-limbed animals were more widespread in their early stages of evolution. To date, fossils of early tetrapods have only been uncovered in tropical regions, at latitudes that lie within 30° of the palaeoequator. The newly uncovered fossils suggest that scientists will have to broaden the range of environments in which they consider ancient tetrapods to have existed, which holds implications for understanding the evolution of these creatures. Here, Robert Gess and Per Erik Ahlberg described Tutusius umlambo and Umzantsia amazana, which were recovered from Waterloo Farm, near Grahamstown, South Africa. Accounting for how continents have shifted over time, this means that the two animals lived at a latitude of about 70°S about 350 million years ago, close to what today is the Antarctic. The authors note that the abundance and type of plants present at the site rule out the possibilities that the two tetrapods lived in a truly polar climate; however, the animals' proximity to the pole implies that they endured several months of complete winter darkness. Gess and Ahlberg say that the presence of tetrapods in such an environment raises the question of whether high-latitude environments played a distinctive role in the evolutionary transition between fish and four-limbed animals -- for example, these environments could have been drivers of evolutionary innovation or served as refuges for archaic taxa.
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American Association for the Advancement of Science

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