With extreme lows in sea level, land masses which are now distinct would have been single islands, allowing, at 10,000 year intervals, long isolated reptiles to move freely between them. ‘Our work indicates that the other reptiles – racer snakes, land iguanas, lava lizards and leaf-toed geckos – have been affected by the oscillating sea-level mechanism we have identified.’ Note that the maps cover 92° W–89° W and 2° S–1° N as a scale guide, the north–south extent is c. 20 ka (b), which includes eustasy, subsidence and unloading (−143.8 m) – see text. Palaeogeographical reconstruction (−145 m) for the Galápagos at c. Geography, topography and bathymetry of the Galápa gos today (a) constructed using GeoMapApp ( ) and data from Ryan et al. Their models took account of thermal subsidence, eustatic sea-level change, and associated sea-floor loading, creating a detailed picture of how the islands may have looked through geological time. ![]() ‘My geology told me that sea-level falls must have regularly reconnected the islands, and that this must have profoundly shaped the land-locked biota’s distribution, and very likely its composition.’Īli and Aitchison used palaeogeographical modelling to reconstruct the volcanic island chain for the last 700 thousand years. ‘As soon as I saw that half the islands in the Galapagos archipelago were sat on a single, shallow, submarine platform, I realized that the implications for biology could be significant’ says Ali. Now, Ali has published a study with his University of Sydney colleague Professor Jonathan Aitchison in the Journal of Biogeography, which suggests changes in relative sea level across the islands hold the answer. ‘Most effort has been focused on the legendary Darwin finches and the iconic giant tortoises.’ ![]() ‘No one has given it any real thought’ he told us. Despite Darwin’s question, there has been little research into how the Galapagos’ land locked reptiles came to be scattered across the archipelago, says University of Hong Kong Earth scientist Jason Ali.
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