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Phylogeny of Equidae used in this study (after MacFadden [25]). North American Land Mammal Ages indicated on the bottom. The size of the colored regions represents relative diversity among the groups. Horizontal lines represent time ranges of each genus or clade. This study begins with the Barstovian to capture the most advanced Equinae with derived enamel prismatic structure. doi:10.1371/journal.pone.0090184.g002
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Four groups of equids, "Anchitheriinae," Merychippine-grade Equinae, Hipparionini, and Equini, coexisted in the middle Miocene, but only the Equini remains after 16 Myr of evolution and extinction. Each group is distinct in its occlusal enamel pattern. These patterns have been compared qualitatively but rarely quantitatively. The processes influenc...
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... originally created in a pre- Darwinian context to describe similarity amongst organisms. Like most natural systems, phylogenetic relationships are more complicated than the initial set of categories defined by man. The current consensus on equid phylogeny includes three subfamilies, ''Hyracotheriinae,'' ''Anchitheriinae,'' and Equinae [5,24,25] (Fig. 2). Within Equinae, there are two sub-clades, the tribes Hipparionini and Equini, and a basal grade mostly assigned to ''Merychippus.'' This genus has long been considered a paraphyletic taxon, maintained through convenience to include all basal equines that do not possess apomorphies of either Equini or Hipparionini. Typical ...
Context 2
... terms of species richness, Hipparionini were the most successful tribe during the Clarendonian in the Great Plains, but were eventually replaced by Equini at the end of the Blancan. ''Anchitheriini'' and ''Merychippini'' go extinct by the Hemphil- lian, leaving Equini and Hipparionini (Fig. 2). The two tribes are significantly different in the Hemphillian and Blancan. Hippar- ionini are constrained to the southern latitudes during the Blancan and are extinct by the end of the Blancan [59]. Hipparionini remain in regions closer to the equator where the effects of climate change would not have been as strong [53,60]. In those ...
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The masticatory apparatus has been the focus of many studies in comparative anatomy—especially analyses of skulls and teeth, but also of the mandibular adductor muscles which are responsible for the production of bite force and the movements of the mandible during food processing and transport. The fiber architecture of these muscles has been corre...
Citations
... Protocone small and isolated; complex plications on the pre-and post-fossettes; well-developed pli caballins. More specific identification is difficult with isolated teeth because they lack a majority of diagnostic characters (Famoso and Davis, 2014 Shotwell (1955aShotwell ( , 1956Shotwell ( , 1958 are Cormohipparion, because he never identified the specific specimens that he assigned to Hipparion. Additionally, Skinner and MacFadden (1977) named Cormohipparion from material previously identified as Hipparion in North America well after Shotwell's original work. ...
... Protocone large, elliptical, and isolated in early wear stages but appears to connect in later wear stages (estimated from observance on the exterior of the tooth); simple plications on both fossettes; prominent hypoconal lake. More specific identification is difficult with isolated teeth because they lack a majority of diagnostic characters (Famoso and Davis, 2014). Remarks.-UOMNH ...
Encompassing global cooling, the spread of grasslands, and biogeographic interchanges, the Hemphillian North American Land Mammal Age is an important interval for understanding the factors driving ecological and evolutionary change through time. McKay Reservoir near Pendleton, Oregon is a natural laboratory for analyses of these factors. It is remarkable for its small vertebrate fauna including rodents, bats, turtles, and lagomorphs, but also for its larger mammal fossils like camelids, rhinocerotids, canids, and felids. Despite the importance of the site, few revisions to its faunal list have been published since its original description. We expand on this description by identifying taxa not previously known from McKay Reservoir based on specimens collected during fieldwork and through reidentification of previously collected fossils. Newly identified taxa include the borophagine canid Borophagus secundus (Matthew and Cook, 1909), the camelids Megatylopus Matthew and Cook, 1909 and Pleiolama Webb and Meachen, 2004, a dromomerycid, and the equids Cormohipparion Skinner and MacFadden, 1977 and Pseudhipparion Ameghino, 1904. Specimens previously assigned to Neohipparion Gidley, 1903 and Hipparion de Christol, 1832 lack the features necessary to diagnose these genera, which are therefore removed from the site's faunal list. The presence of Borophagus secundus , Cormohipparion , and Pseudhipparion is especially important, because each occurrence represents a major geographic range extension. This refined understanding of the fauna lays the foundation for future studies of taphonomy, taxonomy, functional morphology, and paleoecology—potentially at the population, community, or ecosystem levels—at this paleobiologically significant Miocene locality.
... Hipparions and equins are distinguished from one another by details of molar morphology (including an isolated protocone vs. a connected protocone on the upper molars, respectively), the possession and disposition of facial fossae (depressions on the skull in front of the orbits that may have housed glands or musclescomplex and extensive in hipparions, usually reduced or absent in equins [except for Pliohippus]), and additionally hipparions tend to have cheek teeth occlusal surfaces that have a greater relief than those of equins, with a higher density of enamel plications (Famoso & Davis, 2014). ...
Recent studies have demonstrated dramatic changes in North American rodent and lagomorph faunas through the Cenozoic, with open-habitat specialists (characterized by increased tooth crown height and adaptations for burrowing, jumping, or running) becoming common as open and arid habitats spread. These studies have primarily focused on continental scale analyses, but comparisons of regional and local scale changes are key to understanding how individual faunas changed over time and the roles exerted by topography and local climatic conditions on these faunal changes. Here, we use a database of all fossil rodents and lagomorphs in North America modified from NOW, MIOMAP, and FAUNMAP to compare faunas through time across nine distinct regions. Our analyses reveal asynchronous changes across the continent, with specialized dietary and locomotor adaptations in rodents and lagomorphs occurring earlier in relatively cool, arid regions at higher latitudes. Findings suggest topographic complexity and volcanic activity potentially drove aspects of ecomorphological evolution in rodents and lagomorphs. The attributes of open and arid-adapted taxa likely facilitated their spread from tectonically and volcanically active regions across the continent, as environmental conditions changed through the Cenozoic.KeywordsClimate changeHypsodontyMammal FaunasNorth AmericaRodentiaLagomorpha
... Hipparions and equins are distinguished from one another by details of molar morphology (including an isolated protocone vs. a connected protocone on the upper molars, respectively), the possession and disposition of facial fossae (depressions on the skull in front of the orbits that may have housed glands or musclescomplex and extensive in hipparions, usually reduced or absent in equins [except for Pliohippus]), and additionally hipparions tend to have cheek teeth occlusal surfaces that have a greater relief than those of equins, with a higher density of enamel plications (Famoso & Davis, 2014). ...
This volume presents an array of different case studies which take as primary material data sourced from the NOW (‘New and Old Worlds’) database of fossil mammals. The NOW database was one of the very first large paleobiological databases, and since 1996 it has been expanded from including mainly Neogene European land mammals to cover the entire Cenozoic at a global scale. In the last two decades the number of works that are based in the use of huge databases to explore ecological and evolutionary questions has increased exponentially, and even though the importance of big data in paleobiological research has been outlined in selected chapters of general works, no volume has appeared before this one which solely focuses on the databases as a primary source in reconstructing the past. The purpose of this book is to provide an illustrative volume showing the importance of big data in paleobiological research, and presenting a broad array of unpublished examples and case studies. The book is mainly aimed to professional palaeobiologists working with Cenozoic land mammals, but the scope of the book is broad enough to fit the interest for evolutionary biologists, paleoclimatologists and paleoecologists.
The volume is divided in four parts. The first part includes two chapters on the development of large paleobiological databases, providing a first-hand account on the logic and the functioning of these databases. This is a much-needed perspective which is ignored by most researchers and users of such databases and, even if centered in the NOW database, the lessons that can be learned from this part can be extended to other examples. After this introductory part, the body of the book follows and is divided into three parts: patterns in regional faunas; large scale patterns and processes; and ecological, biogeographical and evolutionary patterns of key taxa. Each chapter is written by well-known specialists in the field, with some participation of members of the NOW advisory board. The array of selected mammal taxa ranges from carnivores, equids, ruminants and rodents to the genus Homo. The topics studied also include the diversification and radiation of major clades, large-scale paleobiogeographical patterns, the evolution of ecomorphological patterns and paleobiological problems such as evolution of body size or species longevity. In most cases the results are discussed in relation to protracted environmental or paleogeographic changes.
... Hipparions and equins are distinguished from one another by details of molar morphology (including an isolated protocone vs. a connected protocone on the upper molars, respectively), the possession and disposition of facial fossae (depressions on the skull in front of the orbits that may have housed glands or musclescomplex and extensive in hipparions, usually reduced or absent in equins [except for Pliohippus]), and additionally hipparions tend to have cheek teeth occlusal surfaces that have a greater relief than those of equins, with a higher density of enamel plications (Famoso & Davis, 2014). ...
The equid subfamily Equinae radiated 17.5 Ma in the New World and reached the Old World at around 11 Ma. The New World radiation comprised three tribes (Hipparionini, Protohippini, and Equini), with a maximum diversity of 31 equine species in the early Late Miocene, while the Old World radiation comprised only Hipparionini until the arrival of Equus in Eurasia at 2.58 Ma. All New World tribes increased average levels of hypsodonty over time; the Equini maintained the highest average tribal body mass but were the least diverse tribe (in terms of species numbers and morphology) until the Pliocene. Old and New World equids differed in their pattern of Miocene locality occupancy: New World localities commonly contained three to five equids while Old World ones contained one to two. Numbers of equids per locality declined in both areas in the latest Miocene along with decline in species diversity, likely related to climatic cooling and drying.KeywordsEquidaeEquiniHipparioniniProtohippiniHypsodontyBody massLocality occupancy
... Rather, this happens because, from the variety of life forms evolution offers as solutions to the challenges of life, some prevail and survive longer, as species or taxa, in evolutionary time, whereas others go extinct. For example, there was a fossil equid lineage that had occlusal surfaces of even much higher complexity than extant equids-the three-toed Hipparionini [8] . If one would put them 'in sequence', it would appear as if extant equids had lost some of the occlusal surface complexity (which is not the case-they are just not part of the equid branch with the most complex surfaces). ...
Like other members of the even-toed ungulates (the perissodactyls), equids once had a higher species diversity in the fossil record than they have today. This is generally explained in comparison to the enormous diversity of bovid ruminants. Theories on putative competitive disadvantages of equids include the use of a single toe as opposed to two toes per leg, the lack of a specific brain cooling (and hence water-saving) mechanism, longer gestation periods that delay reproductive output, and in particular digestive physiology. To date, there is no empirical support for the theory that equids fare better on low-quality forage than ruminants. In contrast to the traditional juxtaposition of hindgut and foregut fermenters, we suggest that it is more insightful to sketch the evolution of equid and ruminant digestive physiology as a case of convergence: both evolved a particularly high chewing efficacy in their respective groups, which facilitates comparatively high feed and hence energy intakes. But because the ruminant system, less based on tooth anatomy but more on a forestomach sorting mechanism, is more effective, equids depend more on high feed intakes than ruminants and may well be more susceptible to feed shortages. Arguably, the most under-emphasized characteristic of equids may be that in contrast to many other herbivores including ruminants and coprophageous hindgut fermenters, equids do not use the microbial biomass growing in their gastrointestinal tract. Equids display behavioral and morphophysiological adaptations to high feed intakes, and their cranial anatomy that facilitates the cropping of forage while performing grinding chewing at the same time might be unique. Rather than looking for explanations how equids are better adapted to their present niches than other organisms, considering them remnants of a different morphophysiological solution may be more appropriate.
... Occlusal features of molars capture several aspects of the mechanics and durability of dental pieces during mastication (Famoso & Davis, 2014;Kaiser et al., 2009;von Koenigswald et al., 2014). Thus, these occlusal traits are good candidates to serve as proxies for the diet and the environment of extinct species, having attracted a lot of interest in evolutionary and paleoecological studies. ...
Dental morphology is a major aspect of ecological and evolutionary studies of both extant and fossil mammalian species. Mammalian dentitions are diverse feeding systems that can be defined through continuous numerical descriptors of the enamel pattern.
We developed a comprehensive toolkit to quantify complex occlusal enamel patterns from two‐dimensional images of herbivore mammals, widespread in the scientific literature, in form of three novel enamel complexity descriptors: two‐dimensional orientation patch count (2D OPC), enamel folding (EF), and enamel thickness (ET). Previously proposed parameters such as occlusal enamel index or indentation index are implemented as well.
The current method is devised for extracting continuous variables of enamel complexity from macro and microherbivore mammalian species with conspicuous wear facets. A general case study is proposed using two clades within the Family Rhinocerotidae containing species regarded as hypsodonts. The results show that antagonist dental adaptations were achieved through disparate evolutionary strategies in both groups. To test the robustness of this tool under different practical scenarios, other mammalian groups have been evaluated as well. Additional sensitivity analyses include the impact of image size, rotation, or differences in dental wear.
Our approach differs from previous 2D techniques in its affordability, versatility, and control over individual regions within each tooth while delivering continuous numerical data. Additionally, the 2D reference images required as input are widespread in the literature and easier to process in comparison to 3D data alternatives.
... Such conditions could be related to a variety of environmental factors such as ecotope differentiation, temperature dynamics, taxon migration, etc. (MACFADDEN et al. 1994;WANG et al. 2006b;ZHANG et al. 2012;PÉREZ-CRESPO et al. 2016;PÉREZ-CRESPO et al. 2017;MACFADDEN 2008). Equid ancestors evolved from biocenoses with large, occasionally rare, nutrientrich herbs, to drier biocenoses (VOLLMERHAUS et al. 2002;FAMOSO & DAVIS 2014). ...
... The complexity of the occlusal surface of teeth and enamel in horses was fixed at the time of the Middle Miocene to the Holocene, the evidence for this being drawn from current knowledge of long-term climate changes, the steady direction of climate aridization, and periods of climate cooling. These changes to dental structure were accompanied by a process of increased rate of tooth abrasion and the establishment of the evolution of hypsodont and rootless teeth (FAMOSO & DAVIS 2014). In this process, phytoliths played a significant role in the overall evolution of both grasses and horses (STRÖMBERG et al. 2007;ERICKSON 2014;DE WINTER et al. 2016). ...
... Problems of tooth hardness and features of tooth abrasion as the most functionally active structures are always relevant (FORTELIUS & SOLOUNIAS 2000;FAMOSO et al. 2013;TÜTKEN et al. 2013;FAMOSO & DAVIS 2014;VIRANTA & MANNERMAA 2017). This issue relates specifically to the incisors (SCHROCK et al. 2013) and to the molars (RAMZAN & PALMER 2010;SAHARA 2014). ...
This review searches for and analyzes existing knowledge on horse tooth anatomy in terms of evolutionary and morphological changes, feeding habits, breeding practices, and welfare. More than 150 articles from relevant databases were analyzed, taking into account the issues of our experimental research on the ultrastructure of Equidae tooth enamel. After our analysis, the knowledge on this subject accumulated up in the past, almost 50 years has been logically arranged into three basic directions: evolutionary-palaeontological, morpho-functional, and dentistic, which is also demonstrated by the latest trends in the study of enamel morphology and in the practice of equine dentistry. The obtained data show that in recent years we have observed a rapid increase in publications and a thematic expansion of the scope of research. It is caused by the need to deepen knowledge in theory and in the practice of feeding species in nature and in captivity as well as the possibility of using new technical resources to improve the excellence of such research. It is a summary of the knowledge of a certain stage of equine tooth enamel studies for this period of time, which serves as the basis for our experimental research (the materials are prepared for publication) and at the same time, defines research perspectives for the next stage of development.
... Paleoecological studies of extinct mammals, especially regarding their feeding habits, support paleobiological and ecological niche inferences, and even assumptions on the putative extinction causes of Quaternary mammals (Domingo et al., 2012;Bocherens et al., 2016Bocherens et al., , 2017de Oliveira et al., 2020a). Several methodologies are used to recover paleodiet data, including analyses of stable isotopes (δ 13 C e δ 16 O) from mineralized tissues, meso and microwear of dental enamel, occlusal enamel complexity, and the examination of content from dental calculus (or tartar) and coprolites (see Sánchez et al., 2004;Croft and Weinstein, 2008;Asevedo et al., 2012;Domingo et al., 2012;Marcolino et al., 2012;Famoso et al., 2013;Famoso and Davis, 2014;Bocherens et al., 2016Bocherens et al., , 2017Rotti et al., 2018;de Oliveira et al., 2020b). Dental calculus is an oral pathology caused by the accumulation of mineralized bacterial plaque on the teeth surface, mainly along the gum line (Akcali and Lang, 2017;Mothé et al., 2021). ...
Macrauchenia patachonica Oiwen, 1838 is a native and extinct Quaternary megamammal from South America. Although studies on macraucheniids started two centuries ago, when Darwin found their first fossils, M. patachonica paleobiology is still poorly understood. Dental calculus is an oral pathology that fossilizes and the analysis of its contents is a useful, simple, and low-cost method to access paleobiological information of fossil mammals. Here, the paleodiet of an adult M. patachonica from Buenos Aires province, Argentina, was assessed using quantitative and qualitative analyses of dental calculus content. The sample was chemically processed and many phytoliths, palynomorphs, sponge spike fragments, and diatom frustules were recovered. Both herbaceous phytoliths (49%) and eudicotyledons (35.4%) were well represented. These results support, for this individual, a mixed feeding habit, including consumption of C3 and C4 plants composed of tree/shrub plants and C3/C4 grasses, although C3 could have been more significant. Dental calculus provided direct evidence of paleodiet elements of an extinct South American native mammal for the first time, and such data might support broader paleoecological, paleoenvironmental, and evolutionary studies.
... Famoso et al. (2013) show that there is a strong phylogenetic effect when OEI and feeding strategy data were statistically analyzed within each family. Famoso and Davis (2014) argue that the relative enamel complexity between the Equini and Hipparionini clades is also influenced by phylogenetic relationships, which is later reinforced by . Yet, in Figure 5, Oliveira et al. (2020) seem to only compare the OEI values of each species with general values of the Artiodactyla and Perissodactyla orders. ...
... In fact, when we look at the cladograms of , we see species such as Alces alces and Giraffa camelopardalis which are well-known browsers that not quite consume monocots (Schwartz, 1992;Conor et al., 2015). Famoso et al. (2013) and Famoso and Davis (2014) also comment how dental wear and tooth position influence occlusal enamel analysis in ungulates. Oliveira et al. (2020) do not mention their criteria for selecting specimens for the OEI analysis, but on Table 3 we see that they used upper molars (M1-M3). ...
In this reply we present several methods mistakes in the interpretation of the diet of late Pleistocene Macrauchenids from South America, showing the correct interpretation for the studied taxa." as abstract section.
... The enhanced development of the stay-apparatus, which allows the individual to conserve energy while standing, is also potentially an adaptation to living in open habitats MacFadden, 1992, 1996). Potential adaptations of the digestive system, particularly the dentition, to feeding on low-quality, high-fiber vegetation in open environments include increased crown-height of cheek teeth and incisors (Janis, 1976(Janis, , 1988Damuth and Janis, 2011;Mihlbachler et al., 2011;Schoenecker et al., 2016), increased enamel complexity (Famoso and Davis, 2014; including increased implications of the occlusal enamel [ (Gromova, 1949;Simpson, 1951;Rensberger et al., 1984;Eisenmann and David, 1990;Kaiser, 2002)]), elongation of the protocones of the upper molars and premolars (Eisenmann, 1982;Guadelli and Prat, 1995), increased separation of the metastylid and metaconid, and enlargement of the metastylid to the point of being equal or subequal in size to the metaconid in the lower molars (MacFadden and Carranza-Castañeda, 2002). ...
Interest in the origin and evolution of Equus dates back to over a century, but there is still no consensus on the definition of the genus or its phylogenetic position. We review the placement of Equus within several phylogenetic frameworks and present a phylogenetic analysis of derived Equini, including taxa referred to Equus, Haringtonhippus, Dinohippus, Astrohippus, Hippidion, and Boreohippidion. A new, morphology-based phylogenetic tree was used as an initial hypothesis for discussing what taxa Equus encompasses, using four criteria previously used to define the genus category in mammals: phylogenetic gaps, uniqueness of adaptive zone, crown group definition, and divergence time. According to the phylogenetic gaps criterion, Equus encompasses clade 6 (Ha. francisci = E. francisci, E. conversidens, E. quagga, E. hemionus, E. mexicanus, E. ferus, E. occidentalis, and E. neogeus) based on morphological synapomorphies. Equus is assigned to clade 6, or possibly clade 7, according to the uniqueness of adaptive zone criterion. The crown group criterion places Equus at clade 6. Based on the time-calibrated phylogeny of Equini, the divergence time criterion suggests that Equus encompasses clade 9. This clade comprises all taxa traditionally assigned to Equus analyzed in our study, including the eight taxa listed above as well as E. stenonis, E. idahoensis, and E. simplicidens; the latter two are sometimes referred to the subgenus Plesippus and the former to the subgenus Allohippus. With the exception of the divergence time criterion, the results of our evaluation are congruent in identifying clade 6 as the most suitable position for Equus. The taxonomic implications of delimiting Equus to clade 6 in our phylogenetic tree include elevation of Allohippus and Plesippus to generic rank, assignment of a new genus to “Dinohippus” mexicanus, and synonymy of Haringtonhippus with Equus.
