title: Modelling the climatic niche of turtles: a deep-time perspective.
abstract: Ectotherms have close physiological ties with the thermal environment; consequently, the impact of future climate change on their biogeographic distributions is of major interest. Here, we use the modern and deep-time fossil record of testudines (turtles, tortoises, and terrapins) to provide the first test of climate on the niche limits of both extant and extinct (Late Cretaceous, Maastrichtian) taxa. Ecological niche models are used to assess niche overlap in model projections for key testudine ecotypes and families. An ordination framework is applied to quantify metrics of niche change (stability, expansion, and unfilling) between the Maastrichtian and present day. Results indicate that niche stability over evolutionary timescales varies between testudine clades. Groups that originated in the Early Cretaceous show climatic niche stability, whereas those diversifying towards the end of the Cretaceous display larger niche expansion towards the modern. Temperature is the dominant driver of modern and past distributions, whereas precipitation is important for freshwater turtle ranges. Our findings demonstrate that testudines were able to occupy warmer climates than present day in the geological record. However, the projected rate and magnitude of future environmental change, in concert with other conservation threats, presents challenges for acclimation or adaptation.
authors.affiliation: School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK School of Geographical Sciences, University of Bristol, University Road, Bristol BS8 1SS, UK aw13663@bristol.ac.uk.
authors.forename: Amy M
authors.identifier: 0000-0002-5620-0269
authors.initials: AM
authors.lastname: Waterson
authors.affiliation: School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK.
authors.forename: Daniela N
authors.initials: DN
authors.lastname: Schmidt
authors.affiliation: School of Geographical Sciences, University of Bristol, University Road, Bristol BS8 1SS, UK.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Valdes
authors.affiliation: Museum of Paleontology, University of California, 1101 Valley Life Science Building, Berkeley, CA 94720, USA.
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Holroyd
authors.affiliation: Department of Earth Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK.
authors.forename: David B
authors.identifier: 0000-0002-1296-5673
authors.initials: DB
authors.lastname: Nicholson
authors.affiliation: School of Geographical Sciences, University of Bristol, University Road, Bristol BS8 1SS, UK.
authors.forename: Alexander
authors.initials: A
authors.lastname: Farnsworth
authors.affiliation: Department of Earth Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK.
authors.forename: Paul M
authors.identifier: 0000-0003-0412-3000
authors.initials: PM
authors.lastname: Barrett
mesh_terms: D000818:Animals; D005075:Biological Evolution; D057231:Climate Change; D017753:Ecosystem; D005580:Fossils; D014426:Turtles
keywords: Late Cretaceous; ecological niche model; niche stability; testudine