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The mammalian adult dentition is a non-renewable resource. Tooth attrition and disease must be accommodated by individuals using behavioral, physiological, and/or musculoskeletal shifts to minimize impact on masticatory performance. From a biomechanical perspective, the musculoskeletal system becomes less efficient at producing bite force for a given amount of muscle input force over an individual's life, because tooth-food contact area increases as cusps wear. In this study we ask the question: does mandibular biomechanical performance show evidence of compensation with increasing tooth wear? We use representative taxa of three carnivoran ecomorphologies (meat specialist, scavenger, bone cracker) as a study system to compare morphofunctional data on tooth macrowear, jaw depth, bite mechanical efficiency, and jaw stress during biting. No significant shifts in adult mandibular corpus dimensions occurs in the sampled taxa as canine and carnassial teeth wear. In bone cracking spotted hyenas carnassial biting mechanical efficiency increases significantly with increasing tooth wear, with no significant change in mandibular stress. Analyses of the fossil carnivore Hyaenodon suggests an increase in canine biting efficiency with increased tooth wear, but this may reflect interspecific variation or phylogenetic contingency rather than a life history shift. Overall, these findings indicate that scavenging hyaenids and felid meat specialists do not exhibit morphofunctional compensation for the decreased mechanical capability of worn and dull teeth. Behavioral modifications, rather than musculoskeletal adjustments, may instead play a major role in maintaining food acquisition and processing capabilities for individuals surviving into advanced ontogenetic age and tooth wear. These observations highlight the mammalian masticatory system as having a dynamic performance profile through its useful lifespan, and encourage a more nuanced understanding of past and present carnivore guilds by considering wear-dependent performance changes as a possible source of selection. [ABSTRACT FROM AUTHOR]

Antibiotic resistance, genetically modified produce, avian flu, and invasive species persistence are just a few scientific issues pulled from the headlines that affect society on a daily basis. Understanding these issues requires knowledge of evolutionary processes. Educating students about evolution may never have been as necessary as it is today; however, public battles between science and religion provide hurdles to teaching evolution. The need to produce students equipped to understand current and future scientific issues of societal relevance is rarely disputed. Therefore, it is important to find creative ways to accomplish this goal. Improving a student's ability to understand evolution may be achieved through an inquiry-based module that focuses on relevant and uncontroversial geological, physical, and life sciences. This article describes a module which engages students in determining the age of their fossil, its relationship to living organisms, and observing natural selection through inquiry-based and collaborative learning. By first understanding the scientific methods used by paleontologists to document evolutionary processes, later lessons specific to evolution are effective and well-received. The module described in this article consists of three lessons that address "National Science Education Standards" and have the potential to improve science process skills through interdisciplinary content. All lessons utilize group collaborations and provide inquiry-based activities that model the science done by university professors and scientists. Additionally, each lesson focuses on understanding uncontroversial scientific material including the law of superposition (i.e., the idea that younger sediments are laid down on top of older sediments), relative vs. absolute dating (i.e., methods for determining the age of fossils and surrounding rocks), classification methods, and the process of natural selection. (Contains 3 tables and 5 figures.)

The gomphotheres were a diverse and widespread group of proboscideans occupying Eurasia, North America, and South America throughout the Neogene. Their decline was temporally and spatially heterogeneous, and the gomphotheres ultimately became extinct during the late Pleistocene; however, the genus Cuvieronius is rarely represented in late Pleistocene assemblages in North America. Two alternative hypotheses have been invoked to explain this phenomenon: (1) competitive exclusion by sympatric mammoths and mastodons or (2) ecologic displacement due to an environmental transition from closed forests to open grasslands. To test whether competition for resources contributed to the demise of North American Cuvieronius , we present herein a large collection of stable isotope and dental microwear data from populations occupying their Pleistocene refugium in the Atlantic Coastal Plain. Results suggest that Cuvieronius consumed a wide range of resources with variable textural and photosynthetic properties and was not specialized on either grasses or browse. Further, we document evidence for the consumption of similar foods between contemporaneous gomphotheres, mammoths, and mastodons. The generalist feeding strategy of the gomphotheres likely facilitated their high Miocene abundance and diversity. However, this "jack of all trades and master of none" feeding strategy may have proved challenging following the arrival of mammoths and likely contributed to the extirpation of Cuvieronius in North America. [ABSTRACT FROM AUTHOR]

The diet of the extinct European cave bear, Ursus spelaeus, has widely been debated. Diverging from the extant brown bear (Ursus arctos) approximately 1.2 million years ago, the cave bear is one of the most ubiquitous fossil bears occurring in Europe during the Middle and Late Pleistocene. Early morphological studies suggested that the cave bear was likely specialized on processing tough and/or abrasive foods, while later two-dimensional low-magnification microwear studies suggested that they were omnivorous and may have consumed more bone than U. arctos. Here, we used dental microwear texture analysis (DMTA) to further interpret the diet of the cave bear. Microscopic wear features were assessed and compared to modern ursids, including the cave bears' closest living relative, U. arctos. Results suggest that U. spelaeus consumed a diet with a diversity of textural properties, similar to most other bears and only distinguishable from the hyper-carnivorous polar bear (Ursus maritimus). Further, only U. maritimus can be distinguished from all bear species here examined (i.e., the giant panda bear, Ailuropoda melanoleuca; sun-bear, Ursus malayanus; spectacled bear, Tremarctos ornatus; American black bear, Ursus americanus; and U. arctos), with significantly greater area-scale fractal complexity (Asfc) of microwear surfaces. The DMTA of A. melanoleuca also has significantly lower Asfc than T. ornatus and U. americanus, consistent with observed dietary behavior. As modern bears vary their diets seasonally and across their range, it may be difficult to characterize the dietary ecology of extinct bears using dental microwear alone. Nevertheless, DMTA here demonstrates that U. spelaeus had a diet distinct from the hyper-carnivorous U. maritimus and instead likely consumed food with textural properties most similar to other herbivorous/omnivorous bears. Lastly, the European cave bear and North American giant short-faced bear (Arctodus simus) may have had similar diets as evident from DMTA, with U. spelaeus potentially eating tougher food items. [ABSTRACT FROM AUTHOR]

The cause, or causes, of the Pleistocene megafaunal extinctions have been difficult to establish, in part because poor spatiotemporal resolution in the fossil record hinders alignment of species disappearances with archeological and environmental data. We obtained 172 new radiocarbon dates on megafauna from Rancho La Brea in California spanning 15.6 to 10.0 thousand calendar years before present (ka). Seven species of extinct megafauna disappeared by 12.9 ka, before the onset of the Younger Dryas. Comparison with high-resolution regional datasets revealed that these disappearances coincided with an ecological state shift that followed aridification and vegetation changes during the Bølling-Allerød (14.69 to 12.89 ka). Time-series modeling implicates large-scale fires as the primary cause of the extirpations, and the catalyst of this state shift may have been mounting human impacts in a drying, warming, and increasingly fire-prone ecosystem.

Dietary variation within species has important ecological and evolutionary implications. While theoreticians have debated the consequences of trait variance (including dietary specialization), empirical studies have yet to examine intraspecific dietary variability across the globe and through time. Here, we use new and published serial sampled δ 13 C enamel values of herbivorous mammals from the Miocene to the present (318 individuals summarized, 4134 samples) to examine how dietary strategy (i.e. browser, mixed-feeder, grazer) affects individual isotopic variation. We find that almost all herbivores, regardless of dietary strategy, are composed of individual specialists. For example, Cormohipparion emsliei (Equidae) from the Pliocene of Florida (approx. 5 Ma) exhibits a δ 13 C enamel range of 13.4‰, but all individuals sampled have δ 13 C enamel ranges of less than or equal to 2‰ (mean = 1.1‰). Most notably, this pattern holds globally and through time, with almost all herbivorous mammal individuals exhibiting narrow δ 13 C enamel ranges (less than or equal to 3‰), demonstrating that individuals are specialized and less representative of their overall species' dietary breadth. Individual specialization probably reduces intraspecific competition, increases carrying capacities, and may have stabilizing effects on species and communities over time. Individual specialization among species with both narrow and broad dietary niches is common over space and time-a phenomenon not previously well recognized or documented empirically.

The scimitar-toothed cat Homotherium was one of the most cosmopolitan cats of the Pleistocene, present throughout Eurasia, Africa, and the Americas until at least ~28 thousand years ago. 1-3 Friesenhahn Cave (Bexar County, Texas) contains some of the best-preserved specimens of Homotherium serum alongside an abundance of juvenile mammoths, leading some to argue that H. serum preferentially hunted juvenile mammoths. 1 , 4 Dietary data of Homotherium are rare, with their ecology inferred from morphological, taphonomic, and genetic data. 1 , 3-10 Here, we use a multi-proxy approach to clarify the dietary ecology of H. serum as compared to extinct and extant cats and their relatives. Dental microwear texture analysis (DMTA) reveals that H. serum consumed soft and tough foods, similar to the extant cheetah, which actively avoids bone, 11 , 12 but in stark contrast to extant lions and hyenas, which are observed to engage in durophagy (i.e., bone processing). 11-14 DMTA data are consistent with taphonomic evidence of bone defleshing and the absence of bone-crunching behavior in H. serum. Stable carbon isotope values of H. serum indicate a clear preference for C 4 grazers including juvenile mammoths, in agreement with taphonomic evidence suggestive of a "Homotherium den" 1 , 4 and morphological data indicative of a relatively cursorial lifestyle. 6-8 Notably, the inferred diet of H. serum contrasts with the extinct dirk-tooth sabertooth cat Smilodon fatalis, which preferred forest/woodland prey and engaged in bone processing. 15-19 Homotherium serum exhibited a novel combination of morphological adaptations for acquiring open-country prey, consuming their soft and tough flesh-including the tough flesh of juvenile mammoths. VIDEO ABSTRACT., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021. Published by Elsevier Inc.)

The fossils preserved in the Rancho La Brea "tar" seeps in southern California span the past ∼50,000 years and provide a rare opportunity to assess the ecology of predators (e.g., the American lion, sabertooth cats, cougars, dire wolves, gray wolves, and coyotes), including clarifying the causes and consequences of the terminal Pleistocene extinction event. Here, a multi-proxy approach elucidates dietary responses of carnivorans to changing climates and megafaunal extinctions. Using sample sizes that are unavailable anywhere else in the world, including hundreds of carnivoran and herbivore specimens, we clarify the paleobiology of the extinct sabertooth cats and dire wolves-overturning the idea that they heavily competed for similar prey. Canids (especially the dire wolf) consumed prey from more open environments than felids, demonstrating minimal competition for prey throughout the latest Pleistocene and largely irrespective of changing climates, including just prior to their extinction. Coyotes experienced a dramatic shift in dietary behavior toward increased carcass utilization and the consumption of forest resources (prey and/or plant resources) after the terminal Pleistocene megafaunal extinction. Extant predators' ability to effectively hunt smaller prey and/or utilize carcasses may have been a key to their survival, especially after a significant reduction in megafaunal prey resources. Collectively, these data suggest that dietary niches of carnivorans are not always static and can instead be substantially affected by the removal of top predators and abundant prey resources., (Copyright © 2019 Elsevier Ltd. All rights reserved.)