Juan A. Pérez-Claros

A RE-EVALUATION OF THE DIVERSITY OF MEGANTEREON (MAMMALIA, CARNIVORA, MACHAIRODONTINAE) AND THE PROBLEM OF SPECIES IDENTIFICATION IN EXTINCT CARNIVORES

Abstract In this article, hypotheses about the origin, evolution and dispersal of Megantereon are reviewed using the fossil specimens included in previous comparative studies as well as the remains identified in the late Pliocene site of Fonelas (Spain) and the early Pleistocene localities of Lantian, Lingyi, Longdan, Renzidong (China), and Untermassfeld (Germany). The validity of the two species proposed by Martínez-Navarro and Palmqvist (1995), Megantereon cultridens and M. whitei, is evaluated using tooth measurements and multivariate statistical methods. The hypothesis of sexual dimorphism as an explanation for the morphological variability of Megantereon is tested with a large sample of sexed individuals of Panthera pardus and Panthera leo. Results obtained indicate similar or even smaller differences in tooth dimensions between M. cultridens and M. whitei than between sexes in both leopards and lions, except in the case of the lower fourth premolar. However, in spite of a substantial overlap between both Megantereon species in the size of the upper canine, this tooth reverses the differences found for other tooth measurements, because M. cultridens shows larger cheek teeth on average than M. whitei but smaller sabers. This is confirmed by principal components and discriminant analyses, which reveal that sexual dimorphism in leopards and lions is a matter of tooth size and not of relative proportions and argues against the interpretation of M. cultridens and M. whitei as the sexes (males and females, respectively) of a single species. These results indicate that M. cultridens and M. whitei are valid species, because the differences in tooth measurements exceed those expected from sexual dimorphism and do not reveal the effects of biased sampling. Finally, an analysis of jaw anatomy reveals biomechanical differences between both Megantereon species, related to the relative efficiency of the biting muscles at the level of the lower carnassial.

Cenozoic climate change influences mammalian evolutionary dynamics

Global climate change is having profound impacts on the natural world. However, climate influence on faunal dynamics at macroevolutionary scales remains poorly understood. In this paper we investigate the influence of climate over deep time on the diversity patterns of Cenozoic North American mammals. We use factor analysis to identify temporally correlated assemblages of taxa, or major evolutionary faunas that we can then study in relation to climatic change over the past 65 million years. These taxa can be grouped into six consecutive faunal associations that show some correspondence with the qualitative mammalian chronofaunas of previous workers. We also show that the diversity pattern of most of these chronofaunas can be correlated with the stacked deep-sea benthic foraminiferal oxygen isotope (δ18O) curve, which strongly suggests climatic forcing of faunal dynamics over a large macroevolutionary timescale. This study demonstrates the profound influence of climate on the diversity patterns of North American terrestrial mammals over the Cenozoic.

Constraint and adaptation in the evolution of carnivoran skull shape

Abstract The evolutionary history of the Order Carnivora is marked by episodes of iterative evolution. Although this pattern is widely reported in different carnivoran families, the mechanisms driving the evolution of carnivoran skull morphology remain largely unexplored. In this study we use coordinate-point extended eigenshape analysis (CP-EES) to summarize aspects of skull shape in large fissiped carnivores. Results of these comparisons enable the evaluation of the role of different factors constraining the evolution of carnivoran skull design. Empirical morphospaces derived from mandible anatomy show that all hypercarnivores (i.e., those species with a diet that consists almost entirely of vertebrate flesh) share a set of traits involved in a functional compromise between bite force and gape angle, which is reflected in a strong pattern of morphological convergence. Although the paths followed by different taxa to reach this “hypercarnivore shape-space” differ because of phylogenetic constraints, the morphological signature of hypercarnivory in the mandible is remarkably narrow and well constrained. In contrast, CP-EES of cranial morphology does not reveal a similar pattern of shape convergence among hypercarnivores. This suggests a lesser degree of morphological plasticity in the cranium compared to the mandible, which probably results from a compromise between different functional demands in the cranium (e.g., feeding, vision, olfactory sense, and brain processing) whereas the mandible is only involved in food acquisition and processing. Combined analysis of theoretical and empirical morphospaces for these skull data also show the lower anatomical disparity of felids and hyaenids compared to canids and ursids. This indicates that increasing specialization within the hypercarnivorous niche may constrain subsequent morphological and ecological flexibility. During the Cenozoic, similar skull traits appeared in different carnivoran lineages, generated by similar selection pressures (e.g., toward hypercarnivory) and shared developmental pathways. These pathways were likely the proximate source of constraints on the degree of variation associated with carnivoran skull evolution and on its direction.

Biogeochemical and Ecomorphological Inferences On Prey Selection and Resource Partitioning Among Mammalian Carnivores In An Early Pleistocene Community

Abstract Biogeochemical (δ13C, δ15N, and δ18O values) and ecomorphological analyses of the early Pleistocene fauna of Venta Micena (Orce, Guadix-Baza basin, SE Spain) provide interesting clues on the physiology, dietary regimes, habitat preferences, and ecological interactions of large mammals. Such inferences are useful in deciphering aspects of paleocommunity structure and predator-prey relationships. Specifically, the hypsodonty index combined with δ13C values allows classifying the ungulates among grazers from open habitat (Equus altidens, Bison sp., Praeovibos sp., Hemitragus albus, Hippopotamus antiquus, and Mammuthus meridionalis), mixed feeders (Soergelia minor and Pseudodama sp.), and browsers from canopy areas (Stephanorhinus sp. and Praemegaceros cf. verticornis). Given that δ13C values indicate that all these herbivores fed exclusively on C3 plants, significant differences in isotopic values between perissodactyls (monogastric, hindgut fermenters) and ruminants (foregut fermenters) reflect differences in digestive efficiency. Values of δ18O indicate the dietary water source of ungulates, revealing that Pseudodama sp., Hemitragus albus, and Soergelia minor obtained a significant fraction of their metabolic water from vegetation. Carnivores show higher δ15N values than herbivores, which records the isotopic enrichment expected with an increase in trophic level. Hippopotamus antiquus and Praeovibos sp. have unexpectedly high δ15N values, suggesting that they predominantly consumed aquatic plants and lichens, respectively. Inferences on predator-prey relationships, derived from the use of linear mixing models, indicate resource partitioning among sympatric predators; saber-tooth Megantereon whitei and jaguar Panthera cf. gombaszoegensis were ambushers in closed habitat while saber-tooth Homotherium latidens and wild dog Lycaon lycaonoides were coursing predators in open plains. The giant hyena Pachycrocuta brevirostris scavenged the prey of these hypercarnivores.

Mitochondrially encoded methionine is inversely related to longevity in mammals

Methionine residues in proteins react readily with reactive oxygen species making them particularly sensitive to oxidation. However, because oxidized methionine can be reduced back in a catalyzed reaction, it has been suggested that methionine residues act as oxidant scavengers, protecting not only the proteins where they are located but also the surrounding macromolecules. To investigate whether methionine residues may be selected for or against animal longevity, we carried out a meta‐examination of mitochondrial genomes from mammalian species. Our analyses unveiled a hitherto unnoticed observation: mitochondrially encoded polypeptides from short‐lived species are enriched in methionine when compared with their long‐lived counterparts. We show evidence suggesting that methionine addition to proteins in short‐lived species, rather than methionine loss from proteins in long‐lived species, is behind the reported difference in methionine usage. The inverse association between longevity and methionine, which persisted after correction for body mass and phylogenetic interdependence, was paralleled by the methionine codon AUA, but not by the codon AUG. Although nuclear encoded mitochondrial polypeptides exhibited higher methionine usage than nonmitochondrial proteins, correlation with longevity was only found within the group of those polypeptides located in the inner mitochondrial membrane. Based on these results, we propose that short‐lived animals subjected to higher oxidative stress selectively accumulate methionine in their mitochondrially encoded proteins, which supports the role of oxidative damage in aging.

Demythologizing Arctodus simus, the ‘Short-Faced’ Long-Legged and Predaceous Bear that Never Was

ABSTRACT In this study, we review the previous evidence on the paleobiology of the giant, ‘short-faced’ bear Arctodus simus (Mammalia: Carnivora: Ursidae) and contribute new ecomorphological inferences on the paleobiology of this enigmatic species. Craniodental variables are used in a comparative morphometric study across the families Felidae, Hyaenidae, Canidae, and Ursidae. Principal components analyses (PCAs) do not show an ecomorphological adaptation towards bonecracking or hypercarnivory in the ‘short-faced’ bear. In contrast, PCAs and discriminant analyses restricted to the craniodental data set of ursids suggest close morphological resemblance between A. simus and the extant omnivorous bears. In addition, the scaling of snout length on neurocranial length in bears indicates that the face of A. simus was not particularly short. Body mass estimates obtained from major limb bone measurements reveal that A. simus specimens of around 1000 kilograms were more common than previously suspected. Scaling relationships in extant bears of limb lengths on the least width of the femoral shaft (the variable best correlated with body mass) indicate that A. simus was not as relatively long-legged as previously thought. For these reasons, although the isotopic signature of A. simus has been interpreted as evidencing that it consumed large amounts of flesh relative to some contemporary populations of Ursus arctos, our results do not support the previous views of A. simus as a fast-running super-predator or as a specialized scavenger. In contrast, the picture that emerges from this study is one of a colossal omnivorous bear whose diet probably varied according to resource availability.

First and Second Orders of Suture Complexity in Ammonites: A New Methodological Approach Using Fractal Analysis

The study of septal patterns in ammonoids has been centered on functional and/or constructional issues. Complexly fluted septa have been considered as complementary structures that reinforce the ammonite shell, their frilled sutures possibly manifesting the demand for strength. Ammonitic sutures display features that denote typical fractal behavior, since they can present very long perimeters relative to the contiguous shell areas, and most provide evidence of statistical self-similarity when observed at varying scales of magnification. However, there is a lower limit of scale measurements below which the fractal behavior of the curve no longer holds, and the perimeter length/step size relationship approaches an Euclidean geometry. This paper describes a new methodology that allows the accurate characterization of suture complexity in ammonoids using the technique of fractal analysis (step-line procedure). The proposed methodology helps to fix the position of this “cut-off point,” allowing for independent estimates of the fractal dimensions of the curve for both large and small measurement scales (i.e., first and second orders of suture complexity). This approach improves the resolution of fractals in the analysis of suture complexity, thus facilitating the potential interpretation of suture patterns in functional/constructional, evolutionary and paleoecological terms.

Patterns of morphological integration in the appendicular skeleton of mammalian carnivores

We investigated patterns of evolutionary integration in the appendicular skeleton of mammalian carnivores. The findings are discussed in relation to performance selection in terms of organismal function as a potential mechanism underlying integration. Interspecific shape covariation was quantified by two‐block partial least‐squares (2B‐PLS) analysis of 3D landmark data within a phylogenetic context. Specifically, we compared pairs of anatomically connected bones (within‐limbs) and pairs of both serially homologous and functional equivalent bones (between‐limbs). The statistical results of all the comparisons suggest that the carnivoran appendicular skeleton is highly integrated. Strikingly, the main shape covariation relates to bone robustness in all cases. A bootstrap test was used to compare the degree of integration between specialized cursorial taxa (i.e., those whose forelimbs are primarily involved in locomotion) and noncursorial species (i.e., those whose forelimbs are involved in more functions than their hindlimb) showed that cursors have a more integrated appendicular skeleton than noncursors. The findings demonstrate that natural selection can influence the pattern and degree of morphological integration by increasing the degree of bone shape covariation in parallel to ecological specialization.

Body Mass Estimation in Amphicyonid Carnivoran Mammals: A Multiple Regression Approach from the Skull and Skeleton

The body masses of sixteen species of amphicyonids (Mammalia, Carnivora, Amphicyonidae) from the New and Old World were estimated on the basis of 86 osteological variables measured from the craniodental (N = 44) and postcranial (N = 42) skeleton of living species of Canidae and Ursidae. Given the absence of complete and well preserved skeletons of amphicyonids in the fossil record, multiple regression functions were derived separately from measurements taken from the mandible, the cranium and the major limb bones. The accuracy of the regression functions was evaluated using the percentage prediction error and the percentage standard error of the estimates. Mass values were calculated with these equations using measurements taken in adult individuals from a number of daphoenine and amphicyonine species. Results obtained show that three distinct size classes of amphicyonids emerged through the evolutionary history of the “beardog” family and that these size classes correlate with presumably different ecomorphs. Quantitative estimates of body size of amphicyonids are critical for deciphering the paleobiology of this poorly understood family of large fissiped carnivorans and can be used for placing it within a broader ecological context.

Recent Advances in Morphometric Approaches to Covariation of Shell Features and the Complexity of Suture Lines in Late Jurassic Ammonites, With Reference to the Major Environments Colonized

We report recent advances concerning a research programme focused on the characterization of suture complexity in ammonoids using the method of fractal analysis (stepline procedure), as well as the covariation between suture complexity, shell geometry and sculpture, paying attention to assumed major environments colonized by Late Jurassic ammonites. The application of the logarithmic spiral model and Fourier descriptors of whorl section have improved our previous characterization of shell morphology. In 507 specimens analysed, significant differences in fractal dimension (D f ) mean values were observed according to shell coiling, the shape of whorl section and flanks, the sculpture, and the ratio of outer surface to inner volume (S: V) of the chambers being especially determinant. Factor analysis shows a complex covariation between shell features and suture complexity, which determines a heterogeneous distribution of D f values within the ammonite morphospace. In addition, the results obtained indicate that suture complexity was not directly related to bathymetry, and/or that there were no major differences in habitat depths between epicontinental and epioceanic ammonites. Finally, we envisage the potential resolution of fractals in the analysis of suture complexity in ammonoids, as well as the potential interpretation of suture complexity in ecological terms, facing the future research in this field.