Uncovering hidden diversity in New Zealand’s large geckos
As part of his University of Otago Master of Science (supervised by Dr Nic Rawlence), Lachlan Scarsbrook used micro-CT scanning and gecko bones to offer insight into whether Aotearoa has undiscovered species of extinct large geckos.
While we often hear about our birds, Aotearoa New Zealand is also home to the most diverse group of lizards of temperate regions in the world, comprising over 104 species of geckos and skinks. These two groups have radiated into almost every available role in the New Zealand ecosystem; from the intertidal foraging Suter’s skink to the alpine-adapted orange-spotted geckos, our lizards have evolved some very interesting quirks indeed. Duvaucel’s gecko is no exception, being both viviparous (gives birth to live young) and living to over 50 years old. This giant among geckos is most famous for being New Zealand’s largest living lizard, reaching up to 30cm in length!
Paleontologists have previously used the large size of Duvaucel’s gecko bones to identify prehistoric subfossil gecko bones, most of which have been found across the country in rockshelter roosts of the extinct laughing owl, which loved to eat lizards. While this use of size can be informative, Aotearoa’s lizard fauna has been poorly studied, so there has likely been cryptic extinctions; where the loss of species that are morphologically near-identical is invisible in the fossil and archaeological record. To further add to the problem, the modern distribution of Duvaucel’s gecko is restricted to a small number of offshore islands, where they have survived the ravages of introduced predators that wiped out their kin on the mainland. This means that scientists may have oversimplified the diversity of large, Duvaucel-sized, geckos in New Zealand prior to human arrival by lumping multiple distinct species together. To discover whether we’ve missed anything, I’m tackling this problem with the 21st Century science of micro-CT scanning (a scaled down version of a common hospital CT scanner, but for small things) and ancient DNA.
Gecko skulls are made up of a number of small, unfused bones, which unsurprisingly fall apart and become fragmented after passing through a laughing owl’s digestive system, making complete prehistoric skulls almost rare as hens’ teeth. As a result, my micro-CT scanning focused on one, common cranial element found in museum collections around Aotearoa: the maxilla or upper jaw bone. I also used representatives from most living New Zealand geckos to determine whether the prehistoric subfossils most closely resembled surviving species or were in fact something different, something new.
Each maxilla was micro-CT scanned to generate a 3-dimensional model for comparing how their shape differed across different gecko species. Using statistical models, I was then able to decipher what these miniature Rosetta Stones were trying to tell me. Some prehistoric subfossil maxilla grouped with living species like Duvaucel’s gecko (as we expected some of them would); Amazingly, other maxilla showed no strong association to any living New Zealand gecko. These morphologically unique jaw bones, previously thought to belong to Duvaucel’s gecko, likely represent an undiscovered species of extinct large geckos that once called Aotearoa home.
However, before we can seal the deal on a new species of gecko, we need to do some genetic time travel and extract ancient DNA from these precious prehistoric subfossils to reconstruct their whakapapa. Good things take time, so stay tuned.
Background image: Micro-CT scanned surface model of Duvaucel’s gecko skull showing a range of views and locations of measurements for taxonomic characteristics. Image supplied by Lachlan Scarsbrook.