Enamel microwear in caviomorph rodents

Rodents are important components of most modern ecosystems. Understanding their roles in paleocommunities requires robust methods for inferring diet and other autecological characteristics. This pilot study tests whether a relationship between incisor morphology and diet exists among extant rodents that might be used to infer diets of extinct species. We focused on 11 genera of caviomorph rodents classified in 3 dietary categories: fruit–leaf, fruit–seed, and grass–leaf. For each genus 6 variables describing morphology of the upper incisor were measured on 5 specimens. Data were analyzed using a series of stepwise discriminant analyses. Discriminant analyses correctly predicted diets of nearly all training cases (,95%) using 4 incisor characteristics. Five additional species (1 caviomorph and 4 noncaviomorph), treated as unknowns, also were classified correctly. Jackknife analyses correctly predicted diets of approximately two-thirds of training cases. Our study indicates that incisor morphology is related to diet in extant caviomorph rodents. Incisor data therefore might be useful for inferring diets of extinct species.

The diversity of terrestrial mammals in South America is the result of both isolation and continental interchanges, preceded and followed by extinction and speciation (Simpson 1980; Marshall 1988). Mammalian biodiversity in South America can be partitioned into three major phases, beginning in the Paleocene (65.5–55.8 million years ago – Ma) with xenarthrans, notoungulates, marsupials, and ending with the “Great American Interchange” that occurred with the influx of North American mammals upon formation of the Panamanian land bridge approximately 3 Ma (Simpson 1980; Marshall 1988; Flynn and Wyss 1998). South America’s first rodents, the New World Hystricognathi (Caviomorpha), termed “old native rodents” by Simpson (1980) appear in the fossil record around 37.5–31 Ma in the Eocene/Oligocene transition (Wyss et al. 1993; Vucetich et al. 1999; Flynn et al. 2003). The origin of South American caviomorph rodents is apparently a consequence of over-water dispersal from Africa during the Late Paleocene (c.58 Ma) to Middle Eocene (c.40 Ma; Lavocat 1969, 1980; Huchon and Douzery 2001; Rowe 2002; Rowe et al. 2010). The Late Eocene to Early Oligocene of South America represents a period of transition in terms of climatic and environmental changes (Flynn and Wyss 1998). According to both Mares and Ojeda (1982) and Simpson (1980), caviomorph rodents during this time period experienced an adaptive radiation that resulted in these “hypsodont herbivores” (herbivores with high-crowned cheek teeth) filling niches previously occupied by archaic ungulates from the first phase of mammalian history in South America (Flynn and Wyss 1998). One particular Pliocene/Pleistocene (4–2 Ma) form, Josephoartigasia monesi, was the size of a rhinoceros and adapted for a semiaquatic life style (Rinderknecht and Blanco 2008). By the Late Oligocene (24 Ma), representatives of all four superfamilies and 8 of the 14 recent families of caviomorph rodents were present in the fossil record (Simpson 1980; Vucetich et al. 1999).

Attempts to establish relationships between mandibular morphology and either traditional dietary categories or geometric and material properties of primate diets have not been particularly successful. Using our conceptual framework of the feeding factors impacting mandibular morphology, we argue that this is because dietary categories and food geometric and material properties affect mandibular morphology only through intervening variables that are currently poorly understood, i.e., feeding behavior, mandibular loading, and stress and strain regimes. Our studies of 3-dimensional jaw kinematics in macaques and capuchins show that, although jaw movement profiles during chewing are affected by food material properties and species-level effects, patterns of jaw movements in these two species are broadly similar. However, because mandibular loading, stress, and strain regimes are determined by interactions between feeding behavior (such as jaw kinematics) and mandibular morphology, it is difficult to say whether these similarities in chewing kinematics also mean similarities in loading, stress, and strain. Comparative analyses of the scaling of daily feeding time and chew cycle duration reveal only weak support for the hypothesis that larger primates chew more than smaller primates. Consideration of these results suggests that better data are needed on the relationship between dietary categories, food material and geometric properties, the amount of time/cycles associated with different feeding behaviors (ingestion, premolar biting, mastication), and mandible stress and strain patterns if we are to understand fully relationships between mandibular morphology and diet in primates.

Ecological conditions and isotopic diet (13C and 15N) of Holocene caviomorph rodents in Northern Patagonia

Carbon isoscapes of rodent diets in the Great Plains USA deviate from regional gradients in C4 grass abundance due to a preference for C3 plant resources

Previous articleNext article No AccessNotes and CommentsMore Thoughts on Vertebrate Predator Regulation of PreySam Erlinge, Gorgen Goransson, Goran Hogstedt, Goran Jansson, Olof Liberg, Jon Loman, Ingvar N. Nilsson, Torbjorn von Schantz, and Magnus SylvenSam Erlinge Search for more articles by this author , Gorgen Goransson Search for more articles by this author , Goran Hogstedt Search for more articles by this author , Goran Jansson Search for more articles by this author , Olof Liberg Search for more articles by this author , Jon Loman Search for more articles by this author , Ingvar N. Nilsson Search for more articles by this author , Torbjorn von Schantz Search for more articles by this author , and Magnus Sylven Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 132, Number 1Jul., 1988 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/284842 Views: 3Total views on this site Citations: 21Citations are reported from Crossref Copyright 1988 The University of ChicagoPDF download Crossref reports the following articles citing this article:Anders Pape Møller, Timothy A. 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Researchers studying molar topography have traditionally categorized primate taxa based on their purported primary dietary guild, typically as insectivores, folivores, frugivores, or omnivores. Categorizing primates by diet can be subjective and reductionist as different researchers may define a given dietary category differently and primate diet tends to be quite complex, varying seasonally, for example. As the earliest members of the order Primates were said to experience a shift from insectivory to frugivory, it is important to develop methods to study that dietary shift. The following work treats diet as a continuous variable as the percentage of foraging time spent feeding on insects (%insects) instead of categorizing primates by broad dietary categories. Extant taxa were chosen for this analysis where both relevant dietary data were available in the literature, as well as previously published dental topographic data; in this case Dirichlet normal energy (DNE), which is a measure of surface curvature or sharpness. This study considered 16 non-folivorous primate taxa that vary in %insects, including tarsiers, lorises, galagos, lemurs, platyrrhines, and a cercopithecoid. Results suggest that as taxa spend more of their foraging time feeding on insects, their molar curvature increases. Aphylogenetic generalized least squares regression suggests that %insects is significantly correlated ( P < 0.001) and a moderate predictor ( R 2 = 0.579) of molar curvature. This method of treating diet as a continuous variable served as a more nuanced approach to characterize variation in molar topography compared to previous methods of categorizing taxa by diet. Overall, these results provide further evidence that DNE is a useful method for capturing molar shape relevant to important dietary transitions throughout primate evolution, and that treating an aspect of diet as a continuous variable rather than a categorical variable provides insight into important differences in molar form among primates and mammals more generally.

Establishing a link between mandibular morphology and diet in extant primates has long been a goal in biological anthropology because it should provide important insight into the diets of extinct primates, including fossil hominins. To date, efforts to explore this question have produced mixed results, largely perhaps due to a reliance on the use of 2D morphological data. Here, we report a study where we investigated whether 3D shape data would provide a clearer picture. We used geometric morphometrics to analyse 3D mandibular shape variation in a sample of > 200 primate specimens, representing individuals from 27 species and five families. Two sets of analyses investigated i) whether there was a relationship between mandibular shape and four standard dietary categories and ii) whether there was a relationship between mandibular shape and a well-known index of diet quality. We found an association between mandibular shape and the dietary categories when we employed raw Procrustes coordinates and allometry-free residuals, but the relationship was weak to non-existent when the effects of phylogeny were taken into account. We found no relationship between shape and the diet quality index, no matter whether the data were raw, corrected for the effects of allometry, corrected for the effects of phylogeny, or corrected for the effects of both allometry and phylogeny. Taken together, the results of the two sets of analyses suggest that there is a weak relationship between 3D mandibular shape and diet in extant primates. Allometry and phylogeny appear to be more important influences on the 3D shape of extant primate mandibles than is diet. We conclude from this that 3D analysis of mandibular shape is unlikely to further illuminate the diets of extinct primates, and research efforts should, therefore, be directed elsewhere.

Past attempts to establish a relationship between mandibular morphology and different dietary categories (e.g., frugivore, folivore, insectivore) have had mixed results, possibly because descriptive dietary categories are too broad and obscure variation within primate diets. Another potential reason is that not all aspects of skeletal architecture, especially trabecular anisotropy, have factored into functional assessments of dietary inputs into jaw form. Recent emphasis on quantifying food mechanical properties (FMPs) has provided an alternative to reliance on dietary categories. We used data on FMPs to test for correlations among dietary toughness and Young's modulus and the trabecular structure of the mandibular condyle, which is loaded during feeding and should reflect differences in masticatory stresses associated with different dietary FMPs. Adult primate mandibles from 11 species were imaged using high-resolution X-ray computed tomography, and trabecular structure was analyzed with BoneJ and Quant3D to assess common three-dimensional trabecular parameters. Results of phylogenetic generalized least squares analysis suggested a positive correlation between the degree of anisotropy (DA) and toughness, and weaker correlations between FMPs and various other trabecular variables. Because the DA contributes to the mechanical properties of bone, these results suggest a functional relationship between dietary toughness and trabecular anisotropy in the mandibular condyle. Such a perspective underscores the need to consider all aspects of skeletal morphology in evaluating the links between diet and jaw biomechanics. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc.

Maternal separation and social isolation modulate the postnatal development of synaptic composition in the infralimbic cortex of Octodon degus.

Small mammals taphonomy and environmental evolution during Late Pleistocene-Holocene in Monte Desert: The evidence of Gruta del Indio (central west Argentina)

The relationship between primate mandibular form and diet has been previously analysed by applying a wide array of techniques and approaches. Nonetheless, most of these studies compared few species and/or infrequently aimed to elucidate function based on an explicit biomechanical framework. In this study, we generated and analysed 31 Finite Element planar models of different primate jaws under different loading scenarios (incisive, canine, premolar and molar bites) to test the hypothesis that there are significant differences in mandibular biomechanical performance due to food categories and/or food hardness. The obtained stress values show that in primates, hard food eaters have stiffer mandibles when compared to those that rely on softer diets. In addition, we find that folivores species have the weakest jaws, whilst omnivores have the strongest mandibles within the order Primates. These results are highly relevant because they show that there is a strong association between mandibular biomechanical performance, mandibular form, food hardness and diet categories and that these associations can be studied using biomechanical techniques rather than focusing solely on morphology.

Optimal diet and functional response models are used to understand the evolution of primate foraging strategies. The predictions of these models can be tested by examining the geographic and seasonal variation in dietary diversity. Dietary diversity is a useful tool that allows dietary comparisons across differing sampling locations and time periods. Bonobos (Pan paniscus) are considered primarily frugivorous and consume fruits, leaves, insects, vertebrates, terrestrial herbaceous vegetation, and flowers. Frugivores, like bonobos, are valuable for examining dietary diversity and testing foraging models because they eat a variety of species and are subject to seasonal shifts in fruit availability. Frugivorous primate species thus allow for tests of how variation in dietary diversity is correlated with variation in ecological factors. We investigated measures of dietary diversity in bonobos at two research camps across field seasons within the same protected area (N’dele and Iyema) in Lomako Forest, Democratic Republic of the Congo. We compared the results of behavioral observation (1984/1985, 1991, 1995, 2014, and 2017) and fecal washing analysis (2007 and 2009) between seasons and study period using three diversity indices (Shannon’s, Simpson’s, and SW evenness). The average yearly dietary diversity indices at N’dele were Shannon’s Hʹ = 2.04, Simpson’s D = 0.82, and SW evenness = 0.88 while at Iyema, the indices were Shannon’s Hʹ = 2.02, Simpson’s D = 0.82, and SW evenness = 0.88. Behavioral observation data sets yielded significantly higher dietary diversity indices than fecal washing data sets. We found that food item (fruit, leaf, and flower) consumption was not associated with seasonal food availability for the 2017 behavioral observation data set. Shannon’s index was lower during periods when fewer bonobo dietary items were available to consume and higher when fruit was abundant. Finally, we found that optimal diet models best-explained patterns of seasonal food availability and dietary diversity. Dietary diversity is an essential factor to consider when understanding primate diets and can be a tool in understanding variation in primate diets, particularly among frugivores. Dietary diversity varies across populations of the same species and across time, and it is critical in establishing a complete understanding of how primate diets change over time.

North American mammals experienced a major mass extinction at the Cretaceous/Tertiary (K/T) boundary that is tied unambiguously to the Chicxulub impact event. Immediately afterwards, there was an immense adaptive radiation that greatly expanded taxonomic diversity and the range of body sizes and ecological strategies. However, ties between later, Cenozoic impact events and specific episodes in mammalian evolution cannot be demonstrated. A time series of maximum known crater sizes within 1.0-million-year-long temporal bins is shown not to cross-correlate with five separate measures of taxonomic turnover rate, one measure of change in relative taxonomic composition, and four measures of change in body mass distributions. The lack of correlation persists even after excluding the volatile Paleocene mammalian data, adding dummy data to represent intervals without known craters, or lagging the time series against each other for up to 5 million years. Furthermore, the data fail to support broad-brush correspondences between ages of major (>20 km in diameter) craters and the timing of five key, post-K/T biotic transitions, including medium-sized extinction episodes during the late Paleocene and latest Miocene. The results challenge the idea that extraterrestrial impacts drive all, most, or even many extinction and radiation episodes in terrestrial organisms, and add to other evidence that natural, long-term biotic changes are often independent of changes in the physical environment.

Distribution and correlation analysis of typical features of electricity use profiles in non-residential buildings