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New study changes our understanding of mammal evolution

Australia is home to a vast variety of mammals, with over 350 native species, half of which are marsupials such as the kangaroos, wombats, koalas, and Tasmanian Devils. Scientists believed for nearly two centuries that placental mammals and related marsupials (a group of animals known as “Theria”) had originated in the Northern Hemisphere. 

But now, a new study led by the Australian Museum proposes that the ancestors of Theria evolved in Gondwana – a supercontinent encompassing today’s Australia, New Zealand, South America, Antarctica, Africa, Madagascar, and India – 50 million years before migrating to Asia during the early Cretaceous Period around 126 million years ago. 

“This new research has completely revised and turned on its head our understanding of early mammal evolution. It’s the most important piece of palaeontological research, from a global perspective that I’ve ever published, but it may take some time to find full acceptance among Northern Hemisphere researchers,” said study lead author Timothy Flannery, an Honorary Associate at the Australian Museum.

“Our research indicates that Theria evolved in Gondwana, thriving and diversifying there for 50 million years before migrating to Asia during the early Cretaceous. Once they arrived in Asia they diversified rapidly, filling many ecological niches,” added study senior author Kristofer Helgen, a chief scientist at the same museum.

According to Helgen, teeth are a useful tool in identifying mammals, and advances in imaging techniques have significantly helped clarifying where fossils fit in the wider evolutionary picture. “A key component to the evolutionary success of Theria lies in their teeth. With their sophisticated molars, known as tropospheric molars, they were able to crush, puncture, and cut through food simultaneously.” 

These astonishing discoveries have significantly changed our long-held theories about mammal evolution, suggesting that they evolved in the Southern Hemisphere in the Early Jurassic, about 50 million years prior to their earliest dated occurrence in the Northern Hemisphere. Unfortunately, human habituation and rapid climate change have had a major impact on Australia’s flora and fauna, leading to the extinction of many mammal species.

“If we can change the planet so profoundly, it is in our capability to rectify and stem the loss. We now know more about how our mammals evolved, and now we have to ensure that what is left pulls through the current extinction crisis we humans have triggered,” Helgen concluded.

The study is published in the journal Alcheringa: An Australasian Journal of Palaeontology

By Andrei Ionescu, Staff Writer

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