Fossil mice and rats show isotopic evidence of niche partitioning and change in dental ecomorphology related to dietary shift in Late Miocene of Pakistan.

Yuri Kimura,Lawrence J Flynn,Rajeev Patnaik,Kurt M Ferguson,Thure E Cerling,Kevin T Uno,Louis L Jacobs,Laurent Viriot

doi:10.1371/journal.pone.0069308

Abstract

Stable carbon isotope analysis in tooth enamel is a well-established approach to infer C3 and C4 dietary composition in fossil mammals. The bulk of past work has been conducted on large herbivorous mammals. One important finding is that their dietary habits of fossil large mammals track the late Miocene ecological shift from C3 forest and woodland to C4 savannah. However, few studies on carbon isotopes of fossil small mammals exist due to limitations imposed by the size of rodent teeth, and the isotopic ecological and dietary behaviors of small mammals to climate change remain unknown. Here we evaluate the impact of ecological change on small mammals by fine-scale comparisons of carbon isotope ratios (δ13C) with dental morphology of murine rodents, spanning 13.8 to ∼2.0 Ma, across the C3 to C4 vegetation shift in the Miocene Siwalik sequence of Pakistan. We applied in-situ laser ablation GC-IRMS to lower first molars and measured two grazing indices on upper first molars. Murine rodents yield a distinct, but related, record of past ecological conditions from large herbivorous mammals, reflecting available foods in their much smaller home ranges. In general, larger murine species show more positive δ13C values and have higher grazing indices than smaller species inhabiting the same area at any given age. Two clades of murine rodents experienced different rates of morphological change. In the faster-evolving clade, the timing and trend of morphological innovations are closely tied to consumption of C4 diet during the vegetation shift. This study provides quantitative evidence of linkages among diet, niche partitioning, and dental morphology at a more detailed level than previously possible.

Highlights

Stable carbon isotope ratios (d13C) in bioapatite reflect carbon isotope compositions of diets through physiological processes in animals [1,2] and have been widely used to reconstruct dietary preferences between C3 and C4 plants, resource partitioning among coexisting species, and vegetation types in their habitats ([3,4] and references therein)
Stable carbon isotope data combined for all murine species are shown in Figure 1, and summarized in Table 1 and Table S2 (Dataset S1)
Comparisons at different systematic levels may contribute to the fact that large mammals have wider variation of d13C values than murine rodents

Summary

Introduction

Stable carbon isotope ratios (d13C) in bioapatite reflect carbon isotope compositions of diets through physiological processes in animals [1,2] and have been widely used to reconstruct dietary preferences between C3 and C4 plants, resource partitioning among coexisting species, and vegetation types in their habitats ([3,4] and references therein). Stable carbon isotope analysis along with tooth crown height can characterize feeding strategies of fossil mammals [5,6,7]. Stable isotope ratios in small mammals would reflect more local vegetation and environment in their habitats because of their small home ranges without seasonal migration. Stable isotope studies of small mammals have lagged behind those of large herbivores because obtaining an adequate amount of CO2 sample from bioapatite in tiny teeth of small mammals is more difficult. Few studies have been conducted using carbon isotope analysis of rodent teeth. Fossil rodents are usually preserved as isolated teeth in sedimentary deposits and are identified almost exclusively based on molar morphology. Paleoecological studies of rodents can be done only in those special cases in which incisors are identifiable, for instance, because they are recovered with complete skulls and jaws from a fossil locality with a limited diversity of rodents

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Results

Conclusion