Mammals in NZ

Hi all, in a change from movie and music reviews...I present the third M, mammals. A really important paper has just been published in the Proceedings of the Nat Academy by Trevor Worthy et al concerning the first mammalian fossils to be found in New Zealand. The NewScientist summary can be found here, and the online version of the paper (if you have access to PNAS) here. Actually that takes you to the abstract which everyone can get to.

So why is this interesting? The general version of the history of NZ biota has been that NZ didn't have many mammals - the exceptions being bats (three species). The absence of mammals led to the development of our unique flora and fauna, in particular the diverse reptilian and avian fauna using niches that mammals would normally occupy. And lets not even start on the weta as a mouse :-)
This has always seemed a bit suspect when you think about all the lands NZ was joined to as part of Gondwanaland, all of which have mammals. The problem stems from a poor fossil record in NZ. Geologically NZ has been a bit like Divine Brown, up and down rather quickly...so old hills and lakeshores where fossils may have been are now buried deep underground, or in the middle of mountains.

This paper details further exploration in the St Bathans, Central Otago region which has previously produced a sphenodontid, a crocodile, lizards, bats and birds dating around 19-16 million years ago (MYA). Phylogenetic analysis of the mammal sample suggested a basal mammal that isn't a monotreme (baby monotremes are called puggles, how cool is that?!). Dating of the fossil post Oligocene drowning (OD) is important. NZ was reduced to a small archipelago around 30-25 MYA (Oligocene) which would have caused extinction of some, and a severe bottleneck to other flora and fauna. Finding this fossil, which is significantly different to other mammals alive at the same time (Worthy et al compared it to Australian fossils) demonstrates that NZ had its own endemic mammalian fauna that survived the OD. Therefore our unique reptile and avian fauna evolved in the presence of mammals.

The fossil, and its absence from Australia, causes more problems for the recent suggestion that NZ was entirely under water during the OD period and that all of our unique biota was post-Oligocene. Worthy et al acknowledge that it is possible the mammal dispersed to NZ post-OD, but absence of any major adaptations for swimming (and no evidence for flight) argue against that. This means that there are at least four major high levels groups of animals that lived only in NZ and haven't been found anywhere else since the Mesozoic era - tuatara, NZ frogs, wrens and now the mammal.

George Gibbs has just published a really interesting book on how the NZ flora and fauna evolved called Ghosts of Gondwana. Apparently UnityBooks are the cheapest place to buy it.

Me.