18 December 2006

Once were mammals

Cosmos Online
Remarkable fossils found in New Zealand show for the first time that the so-called 'land of birds' was also once home to mammals.
Once were mammals

The discovery of mammal fossils in New Zealand turns on its head the long-held theory that the islands' unique bird community evolved in the absence of mammal competitors. Credit: University of New South Wales

SYDNEY: Remarkable fossils found in New Zealand show for the first time that the so-called ‘land of birds’ was also once home to mammals.

The tiny fossilised bones – part of a jaw and hip – belonged to a unique, mouse-sized land animal unlike any other mammal known. The fossils were unearthed from the rich St Bathans fossil bed, in the Otago region of South Island.

But the real shock to scientists was that they was there at all: until now, decades of searching had shown no hint that mammals, which which thrived and prospered so widely in other lands, had ever trodden on New Zealand soil.

The fact that even one land mammal had lived there, albeit at least 16 million years ago, has put paid to the theory that New Zealand’s rich bird fauna had evolved because they had no competition from land mammals.

“Scientists have long held the view that New Zealand has this weird and wonderful avian biota that lived on the ground because there were no mammals to impede or compete with birds. It appears that this little mouselike animal was part of the fauna on the ancient Gondwana supercontinent and it got stuck on New Zealand when the latter separated more than 80 million years ago,” said co-author Trevor Worthy, of the University of Adelaide, in Australia.

The international team, led by Worthy, included researchers from the Museum of New Zealand Te Papa Tongarewa, and the University of New South Wales, in Sydney.

The research has been published in the U.S. journal Proceedings of the National Academy of Sciences.

“This amazing find suggests that other mammals are waiting to be found there, and that New Zealand belonged to the birds only in more recent times,” said Worthy. “It also suggests that New Zealand was not completely submerged, as some scientists thought, when sea levels were high about 25 to 30 million years ago.”

The team believes that more mammal specimens may emerge, perhaps even other species that predate the split between pouched marsupials such as koalas, and live-bearing placental mammals like humans and dogs.

The St Bathans fossil field – which has also produced many other species of animals, including fish and birds – also promises to shed new light on climate change in the Australasian region.

The rock and fossils contained in the bed record a massive shift from a warm, wet phase to a much cooler and drier period.

“This promises to be a richly rewarding fossil field and the heraldic discovery of New Zealand’s first non-flying mammal represents just the first page of a fascinating new chapter in the history of the world’s mammals,” said co-author Mike Archer of the University of New South Wales.

with the Universities of Adelaide and New South Wales

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