Topic:Fossil
Fossil remains of horses provide valuable insights into the evolutionary history and adaptation of the Equidae family. These fossils, which include bones, teeth, and occasionally soft tissues, help researchers understand the morphological changes that have occurred over millions of years. The study of horse fossils encompasses various aspects such as the identification of different species, the reconstruction of ancient ecosystems, and the examination of evolutionary trends like limb and dental adaptations. This research area also explores the geographical distribution and migration patterns of ancient horse populations. This page compiles peer-reviewed research studies and scholarly articles that investigate the evolutionary development, ecological roles, and paleobiological significance of horse fossils.
New Data on Dental Morphology of Hipparion tchicoicum Ivanjev, 1966 from Western Transbaikalia, Russia. Morphological features of the teeth were studied in the three-toed horse Hipparion tchicoicum from the Pliocene of Western Transbaikalia (Russia). Several diagnostic signs of the Chicoi hipparion were described for the first time to provide criteria for distinguishing the taxon among other fossils of three-toed horses and estimating their real diversity at the final stage of their distribution in Inner Asia.
Equid Nutritional Physiology and Behavior: An Evolutionary Perspective. Like other members of the odd-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 fa...
Investigating the reliability of metapodials as taxonomic Indicators for Beringian horses. The metapodials of extinct horses have long been regarded as one of the most useful skeletal elements to determine taxonomic identity. However, recent research on both extant and extinct horses has revealed the possibility for plasticity in metapodial morphology, leading to notable variability within taxa. This calls into question the reliability of metapodials in species identification, particularly for species identified from fragmentary remains. Here, we use ten measurements of metapodials from 203 specimens of four Pleistocene horse species from eastern Beringia to test whether there are s...
Collapse of the mammoth-steppe in central Yukon as revealed by ancient environmental DNA. The temporal and spatial coarseness of megafaunal fossil records complicates attempts to to disentangle the relative impacts of climate change, ecosystem restructuring, and human activities associated with the Late Quaternary extinctions. Advances in the extraction and identification of ancient DNA that was shed into the environment and preserved for millennia in sediment now provides a way to augment discontinuous palaeontological assemblages. Here, we present a 30,000-year sedimentary ancient DNA (sedaDNA) record derived from loessal permafrost silts in the Klondike region of Yukon, Canada. ...
Evolution of Old World Equus and origin of the zebra-ass clade. Evolution of the genus Equus has been a matter of long debate with a multitude of hypotheses. Currently, there is no consensus on either the taxonomic content nor phylogeny of Equus. Some hypotheses segregate Equus species into three genera, Plesippus, Allohippus and Equus. Also, the evolutionary role of European Pleistocene Equus stenonis in the origin of the zebra-ass clade has been debated. Studies based on skull, mandible and dental morphology suggest an evolutionary relationship between North American Pliocene E. simplicidens and European and African Pleistocene Equus. In this contributio...
A Find of Early Pliocene Fossils of Three-toed Horse (Hipparion tchicoicum Ivanjev, 1966) in Western Transbaikalia. This report analyzes a find of fossils of Pliocene three-toed horse (Hipparion tchicoicum) in western Transbaikalia. The age of the mammalian fauna from red-brown clay in the Udunga locality indicates that Chikoi hipparion lived in the south of Eastern Siberia as early as the second half of the Early Pliocene; its remains in this area were known only from the red beds of the Upper Pliocene. This find made it possible to fill the existing hiatus (Early Pliocene) in its stratigraphic distribution: Late Miocene-Late Pliocene. The range of this three-toed horse species did not go beyond the border...
Molecular identification of late and terminal Pleistocene Equus ovodovi from northeastern China. The extant diversity of horses (family Equidae) represents a small fraction of that occurring over their evolutionary history. One such lost lineage is the subgenus Sussemionus, which is thought to have become extinct during the Middle Pleistocene. However, recent molecular studies and morphological analysis have revealed that one of their representatives, E. ovodovi, did exist in Siberia during the Late Pleistocene. Fossil materials of E. ovodovi have thus far only been found in Russia. In this study, we extracted DNA from three equid fossil specimens excavated from northeastern China dated a...
Limb bone histology records birth in mammals. The annual cyclicality of cortical bone growth marks (BGMs) allows reconstruction of some important life history traits, such as longevity, growth rate or age at maturity. Little attention has been paid, however, to non-cyclical BGMs, though some record key life history events such as hatching (egg-laying vertebrates), metamorphosis (amphibians), or weaning (suggested for Microcebus and the hedgehog). Here, we investigate the relationship between non-cyclical BGMs and a stressful biological event in mammals: the moment of birth. In the present study, we histologically examine ontogenetic serie...
First Radiological Study of a Complete Dental Ontogeny Sequence of an Extinct Equid: Implications for Equidae Life History and Taphonomy. The sequence of cheek teeth mineralization, eruption, and replacement of an extinct horse species is here documented with radiological techniques for the first time thanks to the exceptional preservation of Hipparion sp. mandibles from Cerro de los Batallones (Madrid Basin, Spain). The sequence of dental ontogeny in mammals provides valuable insights about life history traits, such as the pace of growth, and about the mode of formation of fossiliferous assemblages. We have determined that the order of permanent cheek teeth mineralization and eruption of hipparionine horses is m1, m2, (p2, p3),...
Mechanics of evolutionary digit reduction in fossil horses (Equidae). Digit reduction is a major trend that characterizes horse evolution, but its causes and consequences have rarely been quantitatively tested. Using beam analysis on fossilized centre metapodials, we tested how locomotor bone stresses changed with digit reduction and increasing body size across the horse lineage. Internal bone geometry was captured from 13 fossil horse genera that covered the breadth of the equid phylogeny and the spectrum of digit reduction and body sizes, from to To account for the load-bearing role of side digits, a novel, continuous measure of digit reduction was also esta...
Decoupled ecomorphological evolution and diversification in Neogene-Quaternary horses. Evolutionary theory has long proposed a connection between trait evolution and diversification rates. In this work, we used phylogenetic methods to evaluate the relationship of lineage-specific speciation rates and the mode of evolution of body size and tooth morphology in the Neogene and Quaternary radiation of horses (7 living and 131 extinct species). We show that diversification pulses are a recurrent feature of equid evolution but that these pulses are not correlated with rapid bursts in phenotypic evolution. Instead, rapid cladogenesis seems repeatedly associated with extrinsic factors t...
New insights on equid locomotor evolution from the lumbar region of fossil horses. The specialization of equid limbs for cursoriality is a classic case of adaptive evolution, but the role of the axial skeleton in this famous transition is not well understood. Extant horses are extremely fast and efficient runners, which use a stiff-backed gallop with reduced bending of the lumbar region relative to other mammals. This study tests the hypothesis that stiff-backed running in horses evolved in response to evolutionary increases in body size by examining lumbar joint shape from a broad sample of fossil equids in a phylogenetic context. Lumbar joint shape scaling suggests that st...
Early Eocene fossils suggest that the mammalian order Perissodactyla originated in India. Cambaytheres (Cambaytherium, Nakusia and Kalitherium) are recently discovered early Eocene placental mammals from the Indo-Pakistan region. They have been assigned to either Perissodactyla (the clade including horses, tapirs and rhinos, which is a member of the superorder Laurasiatheria) or Anthracobunidae, an obscure family that has been variously considered artiodactyls or perissodactyls, but most recently placed at the base of Proboscidea or of Tethytheria (Proboscidea+Sirenia, superorder Afrotheria). Here we report new dental, cranial and postcranial fossils of Cambaytherium, from the Camb...
Global evolution of Equidae and Gomphotheriidae from South America. The contemporary South American mammalian communities were determined by the emergence of the Isthmus of Panama and by the profound climatic oscillations during the Pleistocene. Horses and gomphotheres were 2 very conspicuous groups of immigrant mammals from North America that arrived in South America during the Pleistocene. The present study compiles updated data on the phylogeny, systematics and ecology of both groups in South America. The horses in South America are represented by 2 genera, Hippidion and Equus, as are the gomphotheres, represented by Cuvieronius and Stegomastodon. Both gene...
Ancient feeding ecology inferred from stable isotopic evidence from fossil horses in South America over the past 3 Ma. Stable isotope ratios (13C/12C and 18O/16O) in fossil teeth and bone provide key archives for understanding the ecology of extinct horses during the Plio-Pleistocene in South America; however, what happened in areas of sympatry between Equus (Amerhippus) and Hippidion is less understood. Results: Here, we use stable carbon and oxygen isotopes preserved in 67 fossil tooth and bone samples for seven species of horses from 25 different localities to document the magnitude of the dietary shifts of horses and ancient floral change during the Plio-Pleistocene. Dietary reconstructions inferred from s...
Dietary change and evolution of horses in North America. The evolution of high-crowned molars among horses (Family Equidae) is thought to be an adaptation for abrasive diets associated with the spread of grasslands. The sharpness and relief of the worn cusp apices of teeth (mesowear) are a measure of dietary abrasion. We collected mesowear data for North American Equidae for the past 55.5 million years to test the association of molar height and dietary abrasion. Mesowear trends in horses are reflective of global cooling and associated vegetation changes. There is a strong correlation between mesowear and crown height in horses; however, most horse ...
The impact of regional climate on the evolution of mammals: a case study using fossil horses. One of the classic examples of faunal turnover in the fossil record is the Miocene transition from faunas dominated by anchitheriine horses with low-crowned molar teeth to faunas with hipparionine horses characterized by high-crowned teeth. The spread of hipparionine horses is associated with increased seasonality and the expansion of open habitats. It is generally accepted that anchitheriine horses did not display an evolutionary increase in tooth crown height prior to their extinction. Nevertheless, to test whether anchitheriines showed any changes interpretable as adaptation to local condit...
What fossils can tell us about the evolution of viviparity and placentation. Recently a fossil of one of the earliest jawed fishes was found with a fetal skeleton and the remains of a cord. It was from the Devonian period and takes the history of vertebrate placentation back to 380 million years ago. This and later fossil evidence for viviparity in marine reptiles and early mammals is reviewed. Of particular interest are the fossils of horses as they document that a reproductive strategy with a single precocial newborn was evolved early on. In one instance there is sufficient representation of soft tissue to imply that early horses had a diffuse placenta, much as had b...
Ancient DNA clarifies the evolutionary history of American Late Pleistocene equids. Hippidions are past members of the equid lineage which appeared in the South American fossil record around 2.5 Ma but then became extinct during the great late Pleistocene megafaunal extinction. According to fossil records and numerous dental, cranial, and postcranial characters, Hippidion and Equus lineages were expected to cluster in two distinct phylogenetic groups that diverged at least 10 MY, long before the emergence of the first Equus. However, the first DNA sequence information retrieved from Hippidion fossils supported a striking different phylogeny, with hippidions nesting inside a p...
On the Pleistocene extinctions of Alaskan mammoths and horses. The fossil record has been used to shed light on the late Pleistocene megafaunal extinctions in North America and elsewhere. It is therefore important to account for variability due to the incompleteness of the fossil record and error in dating fossil remains. Here, a joint confidence region for the extinction times of horses and mammoths in Alaska is constructed. The results suggest that a prior claim that the extinction of horses preceded the arrival of humans cannot be made with confidence.
Evolution, systematics, and phylogeography of pleistocene horses in the new world: a molecular perspective. The rich fossil record of horses has made them a classic example of evolutionary processes. However, while the overall picture of equid evolution is well known, the details are surprisingly poorly understood, especially for the later Pliocene and Pleistocene, c. 3 million to 0.01 million years (Ma) ago, and nowhere more so than in the Americas. There is no consensus on the number of equid species or even the number of lineages that existed in these continents. Likewise, the origin of the endemic South American genus Hippidion is unresolved, as is the phylogenetic position of the "stilt-legged"...
Differential mesowear in occluding upper and lower molars: opening mesowear analysis for lower molars and premolars in hypsodont horses. A new approach of reconstructing ungulate diet, the mesowear method, was recently introduced by Fortelius and Solounias ([2000] Am Mus Novitat 3301:1-36). Mesowear is based on facet development on the occlusal surfaces of the teeth. Restricting mesowear investigation to maxillary cheek teeth would allow mesowear investigation only in assemblages of large numbers of individuals and therefore would generally restrict this method to relatively few assemblages of recent and fossil ungulates. Most of the fossil, subfossil, and recent ungulate osteological assemblages that may be assigned to a singl...
Valsequillo biostratigraphy. III: Equid ecospecies in Paleoindian sites. Greater precision in North American Pleistocene equid taxonomy makes it now possible to exploit the ubiquitous horse remains in Paleoindian sites as ecological index-fossils. The horses of Central Mexico and the Southern Plains can be sorted by tooth size alone, except for two rare large horses of the Southern Plains. The species endemic to these grasslands and south to Central Mexico are Equus pacificus (large), E. conversidens (small), E. francisci (smallest). The Southern Plains were also occupied by a specialized grazer E. excelsus (Burnet and Sandia caves) and E. occidentalis (Dry and San...
Ancient diets, ecology, and extinction of 5-million-year-Old horses from florida. Six sympatric species of 5-million-year-old (late Hemphillian) horses from Florida existed during a time of major global change and extinction in terrestrial ecosystems. Traditionally, these horses were interpreted to have fed on abrasive grasses because of their high-crowned teeth. However, carbon isotopic and tooth microwear data indicate that these horses were not all C4 grazers but also included mixed feeders and C3 browsers. The late Hemphillian Florida sister species of the modern genus Equus was principally a browser, unlike the grazing diet of modern equids. Late Hemphillian horse exti...
Stabilizing Selection and the Comparative Analysis of Adaptation. Comparative studies tend to differ from optimality and functionality studies in how they treat adaptation. While the comparative approach focuses on the origin and change of traits, optimality studies assume that adaptations are maintained at an optimum by stabilizing selection. This paper presents a model of adaptive evolution on a macroevolutionary time scale that includes the maintenance of traits at adaptive optima by stabilizing selection as the dominant evolutionary force. Interspecific variation is treated as variation in the position of adaptive optima. The model illustrates how phylog...
Mitochondrial DNA of the extinct quagga: relatedness and extent of postmortem change. Sequences are reported for portions of two mitochondrial genes from a domestic horse and a plains zebra and compared to those published for a quagga and a mountain zebra. The extinct quagga and plains zebra sequences are identical at all silent sites, whereas the horse sequence differs from both of them by 11 silent substitutions. Postmortem changes in quagga DNA may account for the two coding substitutions between the quagga and plains zebra sequences. The hypothesis that the closest relative of the quagga is the domestic horse receives no support from these data. From the extent of sequence ...
DNA sequences from the quagga, an extinct member of the horse family. To determine whether DNA survives and can be recovered from the remains of extinct creatures, we have examined dried muscle from a museum specimen of the quagga, a zebra-like species (Equus quagga) that became extinct in 1883 (ref. 1). We report that DNA was extracted from this tissue in amounts approaching 1% of that expected from fresh muscle, and that the DNA was of relatively low molecular weight. Among the many clones obtained from the quagga DNA, two containing pieces of mitochondrial DNA (mtDNA) were sequenced. These sequences, comprising 229 nucleotide pairs, differ by 12 base substitu...
Oldest horse brains: more advanced than previously realized. Previous interpretations of early horse brains were based on an incorrectly identified fossil endocast, now believed to be from a condylarth. Newly prepared endocasts of Hyracotherium, the oldest horse and one of the earliest perissodactyls, reveal a relatively larger brain, with a more expanded neocortex, than existed in the condylarth ancestors of perissodactyls. Fifty million years ago, horse brains had suprasylvian, ectolateral, and lateral sulci, but the frontal lobe was undeveloped.