A tuatara may look like an iguana, but it's a reptile in a category all its own. Tuataras are most closely related to lizards and snakes, but in some ways they are oddballs among reptiles, with unique characteristics among reptiles, like their affinity for cool weather, their nocturnal lifestyle, a third eye on top of the skull, and vertebrae that more closely resemble those of fish and amphibians than reptiles. Male tuataras also have another odd feature - they lack a certain member, which means their reproductive behavior differs from other lizards.
Image courtesy of the Wikipedia Commons
Evolutionary biologists find these critters interesting because they are the last surviving members of a major group of reptiles, the Rhynchocephalia, which branched off from the lizard and snake lineage some 250 million years ago. Rhynchocephalia once were spread all over the world, and in many different environmental niches, including the ocean, but the last remnants of this group are two tuatara species living on islands surrounding New Zealand. A fossil find recently published in the Proceedings of the Royal Society fills in part of a 70 million year gap in Rhynchocephalia evolution.
The researchers, based in the UK, New Zealand, and Australia, describe a set of fossil jaws that closely resemble the unique jaws of modern tuataras. What makes this fossil find interesting is that is proves the ancestors of tuataras were living in New Zealand around 19 million years ago. What's so special about 19 million years ago? It's only a few million years after New Zealand was, perhaps, completely covered by water. If New Zealand was completely sunk for a few million years, it's unique set of animals and plants must have colonized the area only in the last 20 million years. On the other hand, if New Zealand wasn't totally wet during that time, some of its present-day inhabitants evolved from long-term residents. Since tuatara-like creatures were around on New Zealand 19 million years ago, it is very likely that New Zealand retained some dry area. The alternate scenario is that tuatara ancestors colonized the place very, very rapidly after the deluge, but this fossil find narrows that window of opportunity substantially.
This paper illustrates how fossils don't just help us understand how animals changed. Fossils help us piece together the Earth's geological history.
For more 30 Days of Evolution Blogging, check out Hank's idea for an evolutionary biologist conspiracy movie a la DaVinci Code, and this Fine Scientist's piece on the Galapagos in bloom.
Join me tomorrow, here at Adaptive Complexity, for day 9 of Show Me the Science Month: 30 Days of Evolution Blogging Evolution as a science is alive and well. Each day I will blog about a paper related to evolution published in 2009.