title: Dietary specializations and diversity in feeding ecology of the earliest stem mammals.
abstract: The origin and radiation of mammals are key events in the history of life, with fossils placing the origin at 220 million years ago, in the Late Triassic period. The earliest mammals, representing the first 50 million years of their evolution and including the most basal taxa, are widely considered to be generalized insectivores. This implies that the first phase of the mammalian radiation--associated with the appearance in the fossil record of important innovations such as heterodont dentition, diphyodonty and the dentary-squamosal jaw joint--was decoupled from ecomorphological diversification. Finds of exceptionally complete specimens of later Mesozoic mammals have revealed greater ecomorphological diversity than previously suspected, including adaptations for swimming, burrowing, digging and even gliding, but such well-preserved fossils of earlier mammals do not exist, and robust analysis of their ecomorphological diversity has previously been lacking. Here we present the results of an integrated analysis, using synchrotron X-ray tomography and analyses of biomechanics, finite element models and tooth microwear textures. We find significant differences in function and dietary ecology between two of the earliest mammaliaform taxa, Morganucodon and Kuehneotherium--taxa that are central to the debate on mammalian evolution. Morganucodon possessed comparatively more forceful and robust jaws and consumed 'harder' prey, comparable to extant small-bodied mammals that eat considerable amounts of coleopterans. Kuehneotherium ingested a diet comparable to extant mixed feeders and specialists on 'soft' prey such as lepidopterans. Our results reveal previously hidden trophic specialization at the base of the mammalian radiation; hence even the earliest mammaliaforms were beginning to diversify--morphologically, functionally and ecologically. In contrast to the prevailing view, this pattern suggests that lineage splitting during the earliest stages of mammalian evolution was associated with ecomorphological specialization and niche partitioning.
authors.affiliation: School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK.
authors.forename: Pamela G
authors.initials: PG
authors.lastname: Gill
authors.affiliation: Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, UK.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Purnell
authors.affiliation: 1] School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK [2] Natural History Museum, Cromwell Road, London SW7 5BD, UK (N.C.); Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton SO14 3ZH, UK (N.J.G.).
authors.forename: Nick
authors.initials: N
authors.lastname: Crumpton
authors.affiliation: Department of Archaeology and Anthropology, University of Bristol, Woodland Road, Bristol BS8 1UU, UK.
authors.forename: Kate Robson
authors.initials: KR
authors.lastname: Brown
authors.affiliation: 1] School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK [2] Natural History Museum, Cromwell Road, London SW7 5BD, UK (N.C.); Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton SO14 3ZH, UK (N.J.G.).
authors.forename: Neil J
authors.initials: NJ
authors.lastname: Gostling
authors.affiliation: 1] Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen, Switzerland [2] Institute for Biomedical Engineering, University and ETH Zürich, Gloriastrasse 35, CH-8092 Zürich, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Stampanoni
authors.affiliation: School of Earth Sciences, University of Bristol, Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.
authors.forename: Emily J
authors.initials: EJ
authors.lastname: Rayfield
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D002685:Chiroptera / Q000033:anatomy & histology / Q000502:physiology; D004032:Diet / Q000266:history* / Q000662:veterinary; D005247:Feeding Behavior; D005580:Fossils; D049690:History, Ancient; D007568:Jaw / Q000033:anatomy & histology* / Q000502:physiology; D008322:Mammals / Q000033:anatomy & histology* / Q000502:physiology*; D014056:Tomography, X-Ray; D014070:Tooth / Q000033:anatomy & histology* / Q000502:physiology