Evolutionary Past

The evolutionary past of the Turbo lineage is surprisingly well studied, with the story beginning approximately 68 Mya, which is the point in time when all Indo-West Pacific (IWP) Turbo species are thought to have stemmed from their last common ancestor. In terms of significant evolutionary events, this diversification predates the closure of the Tethys Sea, suggesting that a physical separation of the IWP species from its more distant relatives was not the evolutionary driver (Williams 2007).

Around this time, a large increase in biodiversity was observed globally during a period known as the Cenozoic. This increase in diversity began around 65 Mya, continuing right through and particularly noticeable during the Noegene period which began just 23 Mya (Williams 2007). The diversification of species was observed not just in marine lineages, but in terrestrial animals alike, and it was suggested by Williams (2007) that a single factor or group of associated factors may be responsible for the observed trend. Movement of tectonic plates throughout this extreme period of global diversification has been suggested as the likely causal agent, with the collision of plates thought to have a significant effect on global oceanic circulation and global climate change in particular (Williams 2007).

Williams (2007) aimed to investigate the effect of tectonic movement and the corresponding altered weather regime (focussing specifically on changes in temperature) on the diversification experienced by Turban Snail (Turbo) species in the IWP. It has been established through fossil evidence that some Turbo lineages that are currently found only in the IWP were once distributed throughout much more distant ocean regions. By combining this fossil evidence with phylogenetic studies, Williams (2007) suggested that the present diversity of Turbo species in the IWP is a direct result of the persistence of numerous, morphologically distinct lineages that were once far more widespread during the period of diversification mentioned earlier. Persistence has been attributed to increased availability of shallow water habitats as a result of tectonic movement, along with an increase in carbonate habitat structures as a result of the parallel evolution of many corals (Williams 2007).

Despite temperate habitats being considered an ancestral requirement of Turbininae species, the IWP is also considered to be a source of ‘many evolutionary novelties’ (Williams 2007), and is considered to be the source from which many temperate regions are now populated. This has been attributed to the temperatures experienced in the tropics, which has resulted in tropical Turbininae species with a much greater evolution rate and a corresponding slower extinction rate than their temperate relatives.

The IWP is therefore considered a museum as well as a cradle of diversity, as it is home to both ancestral lineages that predate the separation of the IWP from other oceans along with modern lineages that have evolved within the IWP itself (Williams 2007).