Bizarre fossil mammal in the land of birds

[Mayabird]

New Zealand, that is. Up until now, it was thought that there were no land mammals on New Zealand before humans showed up.

Mouse-like creature saves New Zealand and rewrites history


Fossil bones of a little creature that died between 16 million and 19 million years ago have a number of fascinating implications, reports Roger Highfield

The remains of a small, long headed mammal that scurried around 16 million years ago have been uncovered in New Zealand, prompting a major rewrite of evolution textbooks.

The little creature reveals for the first time that the so-called "land of birds" was once home to mammals as well and that New Zealand was not under water some 30 million years ago, as some thought. The unusual specimen could even mark an example of a third class of mammal, alongside the so called placental mammals - such as humans - and the marsupials, pouched mammals such as kangaroos.

New Zealand has long been thought to be a rare example of a land mass that evolved without land mammals after it separated from the ancient "supercontinent" of Gondwana about 82 million years ago.

Until now, decades of searching had shown no hint that furry, warm-blooded animals had ever trodden on Kiwi soil, despite them having thrived so widely in other lands. That picture is changed by the tiny fossilised bones - part of two jaws and a leg - that belonged to a unique land animal unlike any other mammal known. The bones of the creature, between the size of a mouse and a rat, were unearthed from the rich St Bathans fossil bed, in the Central Otago region of South Island and the findings are published in the journal Proceedings of the National Academy of Sciences.

The fact that even one land mammal lived there, at least 16 million years ago, has put paid to the theory that New Zealand's diverse prehistoric bird fauna had evolved there because they had no competition from land mammals, according to an international team led by Trevor Worthy, of the University of Adelaide, Alan Tennyson, of the Museum of New Zealand Te Papa Tongarewa, and Prof Mike Archer, of the University of New South Wales, note that New Zealand separated from the ancient supercontinent of Gondwana more than 80 million years ago.

Gondwana is thought to be the source of its modern plants and animals, though some have suggested that New Zealand was completely submerged 25 to 30 million years ago, a time when New Guinea saw a significant loss of land mass, and all its modern species arrived in the wake of the flood.

"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," says Mr 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."

"These new discoveries actually restore the existence of New Zealand," Prof Archer told The Daily Telegraph, adding that it seems that this creature and its ancestors evolved on New Zealand for the 80 million years since the split from Gondwana.

The team believes that more mammal specimens may emerge, perhaps even species that pre-date the split between pouched marsupials and live-bearing placental mammals. "What we are seeing here is a very ancient lineage of mammals that became isolated on New Zealand and then just went loopy, did their strange little thing, in the absence of other more conventional mammals, which is what makes this so tantalising. New Zealand may well have run its own mammal experiment.

A group that has been separated for at least 80 million years, doing its own thing on the sweet little island of New Zealand, being trampled by a million ducks, may well have evolved some very strange adaptations and become a very distinctive group of mammals that did not survive into the modern world," he said.

The newly-found creature had a longish head, a long and narrow tongue, and would have walked awkwardly, said Prof Archer. "The structure of the bones immediately tells us that this is a group we have never seen anywhere else in the world before. The femur suggests a very primitive mammal."

"The dentition is one we have not seen before," he added. "The shape of the jaw and the way the jaws are fused are extraordinarily distinctive," he said. "The fusion of the jaw suggests it may have been eating something that required rigidity of the lower jaw," he said, listing humans, wombats and koalas as other creatures with fused jaws.

"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," he concluded, adding that the team is keen to visit the region again to find more mammals.

Biologists examining the rock near the township of St Bathans over the past few years have found that it's full of unexpected plant and animal fossils. Around 17 million years ago Central Otago was a very different place. Its big lake was fringed with deltas, peaty bogs, subtropical forests full of kauri-like trees and feather palms, with grasses, eucalypts, proteas and casuarinas growing in more open places.

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