A Late Occurring “Hipparion” from the middle Villafranchian of Monopoly, Italy (early Pleistocene; MN16b; ca. 2.5 Ma)

We report here for the first time the occurrence in the Montopoli large mammal fossil assemblage of a small equid taxon identified as “Hipparion” sp., associated to the monodactyl large horse Equus cf. livenzovensis. This occurrence has been recognised on a specimen that the late De Giuli (1938-1988) identified as Hipparion sp. in unpublished notes available in the archives of the Vertebrate Palaeontology Laboratory of the Dipartimento di Scienze della Terra at the Università degli Studi di Firenze. Although fragmentary, the specimen documents the occurrence of “Hipparion” at the middle Villafranchian (early Pleistocene, ca. 2.5 Ma) site of Montopoli, one of the latest occurrences of an hipparionine horse in western Europe. The western Eurasian “Hipparion” evolutionary history is summarised herein

SIVALHIPPUS PTYCHODUS AND SIVALHIPPUS PLATYODUS (PERISSODACTYLA, MAMMALIA) FROM THE LATE MIOCENE OF CHINA

  Herein, the authors report on skulls, mandibles and postcranial specimens of two species of Chinese Sivalhippus, S. ptychodus and S. platyodus. We frame our description and analyses within the context of newly described characters of the cheek teeth of Hippotherium from the Pannonian C of the Vienna Basin, the oldest and most primitive Old World hipparions. Our report includes original skull, mandibular and limited postcranial material of Sivalhippus ptychodus and skulls and dentitions of Sivalhippus platyodus from the Paleontological Museum of Uppsala (PMU, Uppsala, Sweden), the American Museum of Natural History (AMNH, New York, USA) and the Licent Collection in Tianjin Natural History Museum (Tianjin, China). The skull, maxillary and mandibular material we attribute to Sivalhippus ptychodus and Sivalhippus platyodus exhibit some primitive features for Old World hipparions and synapamorphies of the face and dentition that unite it with the Sivalhippus clade. Our analysis shows that S. ptychodus and S. platyodus differ significantly from the Cormohipparion occidentale – Hippotherium primigenium clade. Species belonging to the Sivalhippus clade are found in IndoPakistan (S. nagriensis, S. theobaldi, S. perimensis and S. anwari), Libya and Kenya (S. turkanensis) and Uganda (S. macrodon). We hypothesize that the Sivalhippus clade originated in South Asia where it is earliest represented by Sivalhipus nagriensis, ca. 10.4 Ma and underwent range extension into Africa and China circa 9-7 Ma

Testing Equid Body Mass Estimate Equations on Modern Zebras-With Implications to Understanding the Relationship of Body Size, Diet, and Habitats of Equus in the Pleistocene of Europe

The monodactyl horses of the genus Equus originated in North America during the Pliocene, and from the beginning of the Pleistocene, they have been an essential part of the large ungulate communities of Europe, North America and Africa. Understanding how body size of Equus species evolved and varied in relation to changes in environments and diet thus forms an important part of understanding the dynamics of ungulate body size variation in relation to Pleistocene paleoenvironmental changes. Here we test previously published body mass estimation equations for the family Equidae by investigating how accurately different skeletal and dental measurements estimate the mean body mass (and body mass range) reported for extant Grevy's zebra (Equus grevyi) and Burchell's zebra (Equus quagga). Based on these tests and information on how frequently skeletal elements occur in the fossil record, we construct a hierarchy of best practices for the selection of body mass estimation equations in Equus. As a case study, we explore body size variation in Pleistocene European Equus paleopopulations in relation to diet and vegetation structure in their paleoenvironments. We show a relationship between diet and body size in Equus: very large-sized species tend to have more browse-dominated diets than small and medium-sized species, and paleovegetation proxies indicate on average more open and grass-rich paleoenvironments for small-sized, grazing species of Equus. When more than one species of Equus co-occur sympatrically, the larger species tend to be less abundant and have more browse-dominated diets than the smaller species. We suggest that body size variation in Pleistocene Equus was driven by a combined effect of resource quality and availability, partitioning of habitats and resources between species, and the effect of environmental openness and group size on the body size of individuals.Peer reviewe

Evolution of Early Equus in Italy, Georgia, the Indian Subcontinent, East Africa, and the Origins of African Zebras

We report here ecological and morphological characterization of the main Old World Equus in North America, Asia, Europe, and Africa, by comparing the studied fossil forms with the living Equus grevyi zebra. Equus simplicidens from North America, Equus livenzovenzis, Equus stenonis, and Equus stehlini from Italy, Equus sivalensis from India, Equus cf. stenonis and a small Equus from Georgia (Caucasus), Equus oldowayensis, Equus koobiforensis, and Equus cf. tabeti from Kenya and the extant Equus grevyi are described in their cranial and dental features and are compared in morphological postcranial dimensions by means of log10 ratio analysis. The occurrence of the two horses at the Dmanisi Homo site in Georgia is reported here for the first time. Our comparative analyses allow to confirm the primitive lineage of the ancient zebras as derived from Equus simplicidens, and the successive evolution of the stenonine horses in Asia, South Asia, and Europe during the Plio—Pleistocene. The morphological analysis has reveals a clear trend in third metacarpals and third metatarsals of E. simpicidens, the small Equus from Dmanisi and E. grevyi, suggesting a close relationship between these species. The trend of the stenonine Equus from Europe and Asia confirms the possible derivation from the North America Equus simplicidens. The description of all the Old World Equus is integrated with an overview of their paleoecological context, with a referred section for each locality where these fossils were found. This contribution represents a comprehensive review of the present knowledge of the Old World Equus evolutionary history, with some new important data in deciphering the deep origin and evolution of ancient and living zebras

Eurygnathohippus feibeli (Perissodactyla: Mammalia) from the Late Miocene of As Sahabi (Libya) and its Evolutionary and Biogeographic Significance

ABSTRACT -The discovery of a new hipparionine metacarpal III in 2010 has led to the recognition of the occurrence of the Eas

SAHABI EURYGNATHOHIPPUS FEIBELI: ITS SYSTEMATIC, STRATIGRAPHIC, CHRONOLOGIC AND BIOGEOGRAPHIC CONTEXTS

Sahabi, Libya is an important latest Miocene locality having yielded an extensive paleobotanical and vertebrate fauna. Amongst the fossil mammals there occurs an extensive, species diverse record of hipparionine horses. We develop here a complete record of Sahabi Eurygnathohippus feibeli now based on dental and postcranial material, in comparison to other equids from late Miocene equids from Europe, West Asia and Africa. We find that E. feibeli is the earliest recognized species of the predominantly African clade Eurygnathohippus, that its biogeographic range was Kenya, Ethiopia, Libya and Morocco, it ranged between 7.0 and 5.7 Ma and that it had deep-time evolutionary roots extending back to first occurring Old World hipparions. We further find that Eurygnathohippus was restricted to Africa until a more advanced member of the clade extended its range into the Indian Subcontinent during the late Pliocene, ca. 3.6-2.6 Ma

The Evolution of Equid Monodactyly: A Review Including a New Hypothesis

The traditional story of horse evolution is well-known: over time, horses became larger, they attained higher-crowned teeth, and they changed from having three toes (tridactyly) to a single toe (monodactyly). Evolution is often perceived as a progression toward some optimum outcome, in this case the “Noble Steed.” However, the evolutionary advantages of monodactyly are not entirely clear, other than the notion that it must somehow be “more efficient,” especially at the larger body size of the genus Equus. It is not commonly appreciated that the reduction of the digits to the monodactyl condition was not the main anatomical foot transition in equid history. Rather, the most important change was the transformation of the original “pad foot” into the more derived “spring foot,” with the acquisition of an unguligrade limb posture, characteristic of the family Equinae. Species within the Equinae tribes—Hipparionini, Protohippini, and Equini—evolved hypsodont teeth and diverged into both small and large body sizes, but monodactyly evolved only within the Equini. Despite the Plio-Pleistocene success of Equus, Hipparionini was by far the richest tribe for most of the Neogene, in terms of taxonomic diversity, numbers of individuals, and biogeographic distribution; but hipparionins remained persistently tridactyl over their duration (17–1 Ma). We propose that the adaptive reasons for monodactyly must be considered in the context of reasons why this morphology never evolved in the Hipparionini. Additionally, Equus inherited monodactyly from smaller species of Equini, and consideration of Miocene taxa such as Pliohippus is critical for any evolutionary hypothesis about the origins of monodactyly. We review the literature on equid locomotor biomechanics and evolution, and propose two novel hypotheses. (1) The foot morphology of derived Equini is primarily an adaptation for increasing locomotor efficiency via elastic energy storage, and the accompanying digit reduction may be circumstantial rather than adaptive. (2) Differences in foraging behavior and locomotor gait selection in Equini during late Miocene climatic change may have been a prime reason for the evolution of monodactyl horses from tridactyl ones