How large are the extinct giant insular rodents? New body mass estimations from teeth and bones

Authors

  • Blanca MONCUNILL-SOLÉ,

    Corresponding author
    1. Catalan Institute of Paleontology Miquel Crusafont, Autonomous University of Barcelona, Bellaterra, Spain
    • Correspondence: Blanca Moncunill-Solé, Institut Català de Paleontologia Miquel Crusafont (ICP), Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain. Email: blanca.moncunill@icp.cat

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  • Xavier JORDANA,

    1. Catalan Institute of Paleontology Miquel Crusafont, Autonomous University of Barcelona, Bellaterra, Spain
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  • Nekane MARÍN-MORATALLA,

    1. Catalan Institute of Paleontology Miquel Crusafont, Autonomous University of Barcelona, Bellaterra, Spain
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  • Salvador MOYÀ-SOLÀ,

    1. ICREA at Catalan Institute of Paleontology Miquel Crusafont, Autonomous University of Barcelona, Bellaterra, Spain
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  • Meike KÖHLER

    1. ICREA at Catalan Institute of Paleontology Miquel Crusafont, Autonomous University of Barcelona, Bellaterra, Spain
    2. Department of Ecology, University of Barcelona, Spain
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Abstract

The island rule entails a modification of the body size of insular mammals, a character related with numerous biological and ecological variables. From the Miocene to human colonization (Holocene), Mediterranean and Canary Islands were unaltered natural ecosystems, with paleofaunas formed with endemic giant rodents among other mammals. Our aim is to create methods to estimate the body masses of fossil island rodents and address the nature of ecological pressures driving the island rule. We created regression equations based on extant rodent data and used these to estimate the body masses of the extinct species. Our results show strong correlations between teeth, cranial and postcranial measurements and body mass, except for the length of the long bones, the transversal diameter of the distal tibia and the anteroposterior diameter of the proximal tibia, where the equations were less reliable. The use of equations obtained from a more homogeneous group (suborder and family) is preferable when analyzing the area of the first molar. The new regressions were applied to estimate the body masses of some Mediterranean and Canarian fossil rodents (Canariomys, C. bravoi 1.5 kg and C. tamarani 1 kg; Hypnomys, H. morpheus 230 g and H. onicensis 200 g; and Muscardinus cyclopeus 100 g). Our results indicate that under absence of predation, resource availability (island area) is the key factor that determines the size of the Canariomys sp. However, under presence of specialized predators (birds of prey), body size evolution is less pronounced (Hypnomys sp.).

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