MODELLING THE PALEOENVIRONMENTAL NICHES OF TESTUDINES: A DEEP-TIME PERSPECTIVE

Recent global climate change is exerting a profound influence on the ecology and evolution of many organisms including changes in densities, abundance and geographical range, as well as phenological and evolutionary shifts. Most ecological observations represent short time-series (decadal), undermining the ability of such studies to predict possible long-term consequences of environmental change. Similar biotic responses are represented in the fossil record, which provides the only direct evidence for the long-term ecological and evolutionary effects of major climate perturbations. Recent studies on extant Testudines (turtles, terrapins and tortoises) indicate that this clade is vulnerable to climate change. As globally distributed ectotherms with an extensive fossil record, Testudines are an excellent target for using the past ecological impacts of environmental change to inform our understanding of the future. Here, we apply ecological niche models (MaxEnt and BIOCLIM) to estimate the potential environmental niches of key testudine families (Testudinoidea, Trionychidae, Compsemydidae & Chelydridae) and ecotypes (freshwater and terrestrial) during the Turonian, Coniacian, Santonian, Maastrichtian and Eocene. We explore the impact of biases in the fossil record and the presence of non-analogous climates in the quantification of our niche estimates. In addition we use an ordination framework to quantify metrics of niche change (unfilling, stability and expansion).

Fossil occurrence records are derived from the Paleobiology Database; outputs from the Hadley Centre general circulation model are used to assess the importance of temperature, precipitation and vegetation on the potential distributions of Testudines at global and regional scales. We assess environmental limits on testudine biogeography and the retention of niche-related traits over time. These findings allow us to provide baseline information for assessing current threats to future testudine diversity.