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Reptile fossil reignites debate over New Zealand submergence

Publication date: Jan 21, 2009 9:32:54 AM

The fossil of a lizard-like New Zealand reptile has been identified by a team of scientists from UCL (University College London), University of Adelaide, and the Museum of New Zealand Te Papa Tongarewa. The fossil, dating back 18 million years, has triggered fresh arguments over whether the continent was fully submerged some 25 million years ago.

Today, the endangered New Zealand tuatara (Sphenodon) is a lizard-like reptile that is the only survivor of a group that was globally widespread at the time of the dinosaurs. The tuatara lives on 35 islands scattered around the coast of New Zealand, mainland populations having become extinct with the arrival of humans and associated animals some 750 years ago.

The oldest known Sphenodon fossil dates to the Pleistocene era (around 34,000 years old), while the new discovery dates to the Early Miocene some 19 to 16 million years ago (Mya).The fossil, of jaws and dentition closely resembling those of the present-day tuatara, bridges a gap of nearly 70 million years in the fossil record of the group between the Late Pleistocene of New Zealand and the Late Cretaceous of Argentina.

In a paper published this week in the Proceedings of the Royal Society B, the team says that its findings offer further evidence that the ancestors of the tuatara have been on the landmass since it separated from the rest of the southern continents (Gondwana) some 82 Mya.

Lead author Dr Marc Jones, UCL Cell and Developmental Biology, says: "It has been argued that New Zealand was completely submerged during the Oligo-Miocene drowning of the continent some 25 to 22 million years ago (Mya). However, the diversity of fossils now known from the Miocene (St Bathans Fauna of the Manuherikia Group) suggests it is more likely that enough land remained above the water to ensure the survival of a number of species, such as frogs, kauri trees and several modern freshwater insects, as well as the tuatara."

“The fossil also provides the first direct evidence that the ancestors of the tuatara survived in New Zealand despite substantial climatic and environmental changes, such as a global temperature drop of some eight degrees celsius around 14 million years ago (Mid-Miocene).

“Between the Late Oligocene and earliest Miocene (35 to 22 Mya) a global sea-level rise submerged much of

New Zealand, but the question is, by how much? If the continent of Zealandia was completely submerged, the Sphenodon would have had to recolonize it by ocean rafting. If we look at the transoceanic capabilities of modern Sphenodon, it can swim, but only short distances; it is able to survive without food for several months, but dehydration would be a serious problem for a long journey because of high rates of water loss through the skin. Furthermore, there is currently no evidence of a population outside New Zealand at that time.

“It seems more likely that some local land surface persisted during the drowning of the continent and allowed the

ancestors of the tuatara along with some frogs, birds and mammals (known from the Miocene but now extinct) to survive the transgression, although the extent of the remaining land surface at the time is open to speculation. However, even if Zealandia was reduced to only one per cent of today’s surface area it would still represent over 2,500 square kilometres, well over 1,000 times the surface area of Stephen’s Island (1.5 km squared), where over 30,000 tuatara currently live.”

Notes for Editors

1. For more information or to set up an interview, please contact Dr Marc Jones on +44 (0)20 7679 7698, email marc.jones@ucl.ac.uk.

2. Alternatively, please contact Jenny Gimpel in the UCL Media Relations Office on tel: +44 (0)20 7679 9726, mobile: +44 (0)7747 565 056, out of hours +44 (0)7917 271 364, e-mail: j.gimpel@ucl.ac.uk.

3. An image to accompany the story is available from the UCL Media Relations Office.

4. ‘A sphenodontine (Rhynchocephalia) from the Miocene of New Zealand and palaeobiogeography of the tuatara (Sphenodon)’ by Marc Jones, Alan Tennyson, Jennifer Worthy, Susan Evans and Trevor Worthy, is published in the Proceedings of the Royal Society B. Journalists can obtain copies of the paper by contacting the UCL Media Relations Office.

5. The study was funded by the Public Good Science Fund of the New Zealand Foundation for Research, Discovery Grant from the Australian Research Council and The Palaeontological Association.

6. The Royal Society is an independent academy promoting the natural and applied sciences. Founded in 1660, the Society has three roles, as the UK academy of science, as a learned Society, and as a funding agency.