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Macroecology strives to identify ecological patterns on broad spatial and temporal scales. One such pattern, Rapoport's rule, describes the tendency of species' latitudinal ranges to increase with increasing latitude. Several mechanisms have been proposed to explain this rule. Some invoke climate, either through glaciation driving differential extinction of northern species or through increased seasonal variability at higher latitudes causing higher thermal tolerances and subsequently larger ranges. Alternatively, continental tapering or higher interspecific competition at lower latitudes may be responsible. Assessing the incidence of Rapoport's rule through deep time can help to distinguish between competing explanations. Using fossil occurrence data from the Palaeobiology Database, we test these hypotheses by evaluating mammalian compliance with the rule throughout the Caenozoic of North America. Adherence to Rapoport's rule primarily coincides with periods of intense cooling and increased seasonality, suggesting that extinctions caused by changing climate may have played an important role in erecting the latitudinal gradients in range sizes seen today.

Dental microwear texture analysis (DMTA) is commonly used to assess the dietary ecology of modern and fossil taxa. In carnivorans, teeth with different functions record dietary behavior differently. Here, we assess DMTA variability along the tooth row of an extant carnivorous marsupial—the Tasmanian devil, Sarcophilus harrisii —which has multiple carnassial-like molars that may function and record diet similarly. We compared the complexity (Asfc), anisotropy (epLsar), and textural fill volume (Tfv) of the lower second, third, and fourth molars of Tasmanian devils to test the hypothesis that teeth with similar forms yield similar functions. Although third molars do have significantly higher epLsar values than fourth molars, all other DMTA attributes are indistinguishable from one another. These data suggest that teeth with comparable morphologies in the same taxon have similar functions and largely record diet similarly. In addition, we compared fossil and modern specimens of S. harrisii from Tasmania to assess dietary behavior over time. These analyses indicate that foods with similar textures have been consumed since the late Quaternary. [ABSTRACT FROM AUTHOR]

Palaeoecological interpretations are based on our understanding of dietary and habitat preferences of fossil taxa. While morphology provides approximations of diets, stable isotope proxies provide insights into the realized diets of animals. We present a synthesis of the isotopic ecologies (δ13C from tooth enamel) of North American mammalian herbivores since approximately 7 Ma. We ask: (i) do morphological interpretations of dietary behaviour agree with stable isotope proxy data? (ii) are grazing taxa specialists, or is grazing a means to broaden the dietary niche? and (iii) how is dietary niche breadth attained in taxa at the local level? We demonstrate that while brachydont taxa are specialized as browsers, hypsodont taxa often have broader diets that included more browse consumption than previously anticipated. It has long been accepted that morphology imposes limits on the diet; this synthesis supports prior work that herbivores with 'grazing' adaptions, such as hypsodont teeth, have the ability to consume grass but are also able to eat other foods. Notably, localized dietary breadth of even generalist taxa can be narrow (approx. 30 to 60% of a taxon's overall breadth). This synthesis demonstrates that 'grazing-adapted' taxa are varied in their diets across space and time, and this flexibility may reduce competition among ancient herbivores. [ABSTRACT FROM AUTHOR]

Most dental microwear texture studies to date have focused on enamel surfaces. However, for xenarthran microwear we must, in effect, "reinvent the wheel," because adult xenarthrans lack enamel. Dentin is softer than enamel and may record microwear differently. Thus, we aim to determine if dental microwear texture analysis (DMTA, which quantifies microwear in 3 dimensions) of dentin can yield biologically meaningful results by asking: do dentin and enamel in other eutherians record microwear texture the same way; and can DMTA differentiate between extant xenarthrans with different diets? We analyzed the carnassials of Florida panthers (Puma concolor coryi, n = 14), which have functional dentin and enamel, and found differences in texture fill volume and heterogeneity, suggesting that enamel and dentin DMTA cannot be directly compared. Next, we analyzed the teeth of sloths (Bradypus variegatus, n = 12; Choloepus hoffmanni, n = 9) and the 9-banded armadillo (Dasypus novemcinctus, n = 12), which differ in 2 attributes (surface complexity and fill volume) associated with food or abrasive properties. Other DMTA attributes show no differences between trophic groups, suggesting that dentin and enamel may differ in types of texture attributes that separate taxa by diet. [ABSTRACT FROM AUTHOR]