Wednesday, December 13, 2006
From the New Scientist: Fossil bones of a mouse-sized creature that died between 16 million and 19 million years ago have been discovered on the South Island of New Zealand. It is the first hard evidence that the islands once had their own indigenous land mammals.
Today the only land mammals that live in New Zealand are animals like Australian possums - which have arrived since human settlement - although the country does have its own species of bats, seals and sea lions.
The find, by Trevor Worthy* of Adelaide University, Australia, and colleagues, includes two jawbones, and one thigh bone, from at least two of the creatures, says team member Suzanne Hand. "The amazing thing is, it is unlike any other fossil mammal found anywhere else," she says.
The shape of the fossil bones suggest a very primitive mammal that would have evolved before the mammal-line split into placental mammals and marsupials, 125 million years ago, says Hand of the University of New South Wales in Sydney, Australia. As the fossil bones are only around 16 million to 19 million years old, it appears the mammal managed to survive for at least 100 million years before going extinct.
Continued at "Fossils reveal New Zealand's indigenous 'mouse'"
Based on the open access/free Proceedings of the National Academy of Sciences (PNAS) paper:
"Miocene mammal reveals a Mesozoic ghost lineage on insular New Zealand, southwest Pacific"
Abstract (Full Text available at same link)
New Zealand (NZ) has long been upheld as the archetypical example of a land where the biota evolved without nonvolant terrestrial mammals. Their absence before human arrival is mysterious, because NZ was still attached to East Antarctica in the Early Cretaceous when a variety of terrestrial mammals occupied the adjacent Australian portion of Gondwana. Here we report discovery of a nonvolant mammal from Miocene (19-16 Ma) sediments of the Manuherikia Group near St Bathans (SB) in Central Otago, South Island, NZ. A partial relatively plesiomorphic femur and two autapomorphically specialized partial mandibles represent at least one mouse-sized mammal of unknown relationships. The material implies the existence of one or more ghost lineages, at least one of which (based on the relatively plesiomorphic partial femur) spanned the Middle Miocene to at least the Early Cretaceous, probably before the time of divergence of marsupials and placentals >125 Ma. Its presence in NZ in the Middle Miocene and apparent absence from Australia and other adjacent landmasses at this time appear to reflect a Gondwanan vicariant event and imply persistence of emergent land during the Oligocene marine transgression of NZ. Nonvolant terrestrial mammals disappeared from NZ some time since the Middle Miocene, possibly because of late Neogene climatic cooling.
*Trevor Worthy was also involved in finding New Zealand's first snake fossil:
"Geologists have found a fossil bonanza in Central Otago - including the first evidence that New Zealand once had snakes.
The treasure-trove of animal and bird fossils was unearthed in the Manuherikia Valley, about 100km northwest of Dunedin.
The remains, dated at between 18 and 14 million years old, include tiny jaw and teeth of a python-like snake, fish, birds, and fragments from an ancient crocodile.
The find is the first evidence of a land snake living in New Zealand. It is particularly significant because it had long been thought that New Zealand did not have snakes," said palaeontologist Craig Jones of the GNS Science Limited (GNS).
GNS, Alan Tennyson of Te Papa, moa specialist Trevor Worthy, and James McNamara from the South Australian Museum combined forces in the project."