Equid Teeth Research Articles

Stable isotopes show Homo sapiens dispersed into cold steppes ~45,000 years ago at Ilsenhöhle in Ranis, Germany

The spread of Homo sapiens into new habitats across Eurasia ~45,000 years ago and the concurrent disappearance of Neanderthals represents a critical evolutionary turnover in our species’ history. ‘Transitional’ technocomplexes, such as the Lincombian–Ranisian–Jerzmanowician (LRJ), characterize the European record during this period but their makers and evolutionary significance have long remained unclear. New evidence from Ilsenhöhle in Ranis, Germany, now provides a secure connection of the LRJ to H. sapiens remains dated to ~45,000 years ago, making it one of the earliest forays of our species to central Europe. Using many stable isotope records of climate produced from 16 serially sampled equid teeth spanning ~12,500 years of LRJ and Upper Palaeolithic human occupation at Ranis, we review the ability of early humans to adapt to different climate and habitat conditions. Results show that cold climates prevailed across LRJ occupations, with a temperature decrease culminating in a pronounced cold excursion at ~45,000–43,000 cal bp. Directly dated H. sapiens remains confirm that humans used the site even during this very cold phase. Together with recent evidence from the Initial Upper Palaeolithic, this demonstrates that humans operated in severe cold conditions during many distinct early dispersals into Europe and suggests pronounced adaptability.

Ochre use at Olieboomspoort, South Africa: insights into specular hematite use and collection during the Middle Stone Age

Recent excavations at Olieboomspoort (OBP) in the Waterberg Mountains of South Africa confirmed previous research at the site that highlighted an abundance of ochre in the Middle Stone Age (MSA) deposits. Here, we report on the results of an analysis of the ochre from the MSA deposits excavated in 2018–2019. Fossilised equid teeth from these deposits were recently dated to approximately 150 ka, an early date for such a sizeable ochre assemblage in southern Africa. Calcium carbonate concretions were removed from ochre pieces using hydrochloric acid. Macro- and microscopic analyses were undertaken to identify raw material types and to investigate utilisation strategies. There are 438 pieces in the assemblage and only 14 of them show definite use-traces. The predominant raw material is a micaceous, hard specular hematite, which is rare at MSA sites elsewhere in southern Africa. A preliminary investigation into the geological nature of the ochreous materials in the archaeological sample and those available in the area was performed using semi-quantitative portable X-ray fluorescence (pXRF), XRF, and inductively coupled plasma mass spectrometry (ICP-MS). Together with site formation processes, we suggest possible, primarily local sources of the ochre found in the deposits. The data do not support previous suggestions that OBP was used as an ochre caching site that may have formed part of an exchange network during the MSA. Instead, the local abundance of nodules of specular hematite within the Waterberg sandstone, the limited number of used pieces in the assemblage, and the stratigraphic context indicate a more natural, less anthropogenic explanation for the abundance of ochre at the site.

Modeling periodicity in equid serial enamel isotopes as a proxy for precipitation seasonality

Seasonality shapes environments by driving vegetation patterns and faunal community composition, and identifying seasonality patterns in the past can provide unique insight into paleoenvironments and how they changed over time. Many environmental proxies operate on too large a time scale to glean data about intra-annual seasonality. However, serial enamel isotope samples from the teeth of high-crowned ungulates show promise for providing this temporal resolution of data. Interpreting these data remains a challenge due to the complexity of factors related to animal physiology and the isotopic values of environmental inputs. This study seeks to establish a method for interpreting intra-tooth isotopic change in modern equid teeth as a signal of seasonality by applying a linear mixed effect model to the isotope data to detect periodicity in serial enamel isotope values. Using a modern assemblage of zebra (Equus quagga) from Ol Pejeta Conservancy in Kenya, where long-term climate data has been collected, allows us to compare known climatic seasonality patterns to periodicity in the zebra tooth enamel isotopes. The results of the linear mixed effect modeling, in tandem with the climate data from Ol Pejeta, demonstrate the impact high precipitation variability can have on an environment. While our isotope results point towards measured precipitation seasonality patterns at Ol Pejeta, noise in our data and the variation identified by the models illustrate the challenges of working with serial enamel isotope data. Future refinement and application of this model will allow us to better characterize seasonality in both modern and fossil enamel datasets.

Carefully sourced, carefully managed: multi-isotopic analysis from Bronze and Iron Age equid teeth from Can Roqueta (Barcelona, Spain)

Equids played an important role in the development of communication in past societies, and were part of the exchanges between populations. The multi-isotopic study (strontium, carbon and oxygen isotopes) conducted on equid teeth from Bronze and Early Iron Age Can Roqueta suggests that animals originate from diverse locations and their diet was carefully managed. The enriched oxygen and carbon isotopic ratios in equid teeth compared with other taxa from the same site suggest that equids may have drunk from water troughs, thus creating a 13C and 18O isotopic enrichment and partial covariance, similar to a “lake” effect. This is the most comprehensive study on equid mobility in Iberia so far.

A geometric morphometric evaluation of equid tooth shape at Natural Trap Cave, Wyoming

Natural Trap Cave is an enigmatic site in Wyoming that has been accumulating fossils for tens of thousands of years from animals falling into it. One of the more common taxa present at this site are horses. North American equids have been separated into two main groups: caballine “stout legged” horses, which include the modern Equus ferus caballus; and the extinct non-caballine so-called “New World Stilt Legged” horses, which possess more gracile distal limb elements than modern horses. Genetic evidence has shown that both taxa are present at the Natural Trap Cave site. While post-cranial elements of both have been found, the most common horse specimens recovered have been isolated teeth, which have historically been difficult to identify to a specific taxon, though recent studies have been successful using geometric morphometrics on the occlusal surfaces of cheek teeth to differentiate equid taxa and populations. This study also uses geometric morphometrics to attempt to differentiate upper cheek tooth specimens between caballine and non-caballine stilt legged horses from Natural Trap Cave. Two landmark schemes were employed, one with fewer landmarks, and one with greater coverage, including sliding semi-landmarks. These schemes were used first on a dataset of only known specimens that had been taxonomically identified, and then unknown specimens from Natural Trap Cave were added. These analyses showed that the two taxa do indeed occupy statistically significant different areas of morphospace, as do premolars and molars. Surprisingly, the smaller landmark scheme produced better resolution on the Principal Components Analysis plots, possibly because the larger landmark scheme introduced ontogenetic variation due to different levels of tooth wear. While definitive identification does not seem advisable with this methodology, the unknown specimens grouped more with the known stilt legged specimens, suggesting that this taxon was more prevalent at Natural Trap Cave than the caballine Equus.

Resource partitioning among late Pleistocene herbivores of Natural Trap Cave, Wyoming

Natural Trap Cave (NTC) preserves abundant late Pleistocene herbivore remains including equids (Equus and Haringtonhippus) and the sheep Ovis. The NTC equid sample contains a minimum of two taxa, while other large herbivore genera are represented by single species. In modern communities, sympatric herbivores partition resources by feeding on different plants or different plant parts. Previous dental isotopic studies indicated that most NTC herbivores consumed C3 plants, including grasses. To test the hypothesis that resource partitioning occurred among grass-feeders at NTC, we collected mesowear data from both equids as well as Ovis, using samples collected by teams from the University of Kansas between 1974 and 1985.Assessed on upper cheek teeth, mesowear derives from either attritional (tooth on tooth) or abrasional (tooth on abrasive food) wear. The paracone and metacone were examined on each specimen to determine cusp shape (sharp, rounded, or blunt) and occlusal relief (high or low). A diet of non-abrasive material yields high and sharp cusps and one of heavily abrasive materials results in low and blunt cusps, while rounded cusps indicate intermediate levels of abrasion. A large sample (N = 143) of equid teeth included two morphs. A smaller sample (N = 10) of Ovis teeth provided comparison with the equid teeth. Data collected consisted of individual variables of cusp heights and shape, as well as stages of mesowear combining both variables. Upper adult M1/2s and P4s were used.Results from the equid sample revealed that 8% exhibited high and sharp/rounded cusps, indicating little dietary abrasion; 58% had low and rounded cusps; and 34% had low and blunt cusps. The latter grouping is evidence for a highly abrasive diet. In the sample of Ovis, the results are strikingly different: 40% had high and sharp cusps and 60% had high and rounded cusps. Even though mountain sheep are often interpreted to be grass feeders, their mesowear suggests they did not eat an abrasive diet at NTC.The distribution of mesowear scores among the equid fossils conforms with an interpretation of two equid taxa at NTC, as well as supporting our hypothesis that these taxa partitioned grass resources. The very different nature of the mesowear signature seen in Ovis, compared to the equid fossils, also supports our hypothesis that these grass-feeders either consumed a more mixed or browse-dominated diet with different overall levels of abrasion, or else ate different parts of grass plants. As observed in the Serengeti grazing succession, we propose that equids may have moved through the area first, consuming taller, older, more abrasive parts of grass plants, followed by mountain sheep eating softer, younger plants.

Quibas-Sima: A unique 1 ma-old vertebrate succession in southern Iberian Peninsula

With the identification of the Jaramillo geomagnetic subchron, the late Early Pleistocene vertebrate succession of the Quibas-Sima section (Quibas karstic complex, southern Spain) represents a time span scarcely recorded in Europe. To complete the existing chronostratigraphic framework published earlier by Piñero et al. (2020), we provide here additional new information about the lithostratigraphy and micromammal succession along the sedimentary sequence. Seven lithostratigraphic units have been differentiated (QS-1 to QS-7) at Quibas-Sima, documenting an almost continuous small mammal record, including representatives of the families Soricidae, Erinaceidae, Rhinolophidae, Vespertilionidae, Arvicolidae, Muridae, Gliridae, Sciuridae, Leporidae and Ochotonidae. The small mammal association indicates that units QS-1 to QS-4 have an intermediate biostratigraphic position between the sites of Fuente Nueva 3 (ca. 1.2 Ma) and Cueva Victoria (ca. 0.9 Ma). New numerical age result from the combined U-series/ESR dating of one equid tooth from QS-3 consistently support the general chronostratigraphic framework based on magnetostratigraphy and biostratigraphic inferences by confirming a post-Olduvai age. Based on an estimation of the sedimentation rate during the Jaramillo subchron, these broad chronological constraints may be confidently refined to approx. 1.1–0.9 Ma for the whole sequence. While we acknowledge the existing uncertainty associated to this age range, it is nevertheless consistent with biostratigraphic evidence indicating that all stratigraphic units most likely do not significantly differ from a chronological point of view. Both independent proxies (biostratigraphy and the sedimentation rate) strongly suggest that the sedimentary sequence covers a relatively short time interval (<200 kyr). These results place the Quibas-Sima sequence as one of the longest and most complete pre-Jaramillo (QS-1) to Jaramillo (QS-2 to QS-5) continental vertebrate succession in Europe.

The place beyond the trees: renewed excavations of the Middle Stone Age deposits at Olieboomspoort in the Waterberg Mountains of the South African Savanna Biome

Olieboomspoort is one of the few rock shelters in the vast interior of southern Africa documenting pulses of occupation from the Acheulean until the end of the Later Stone Age. Revil Mason excavated the site in 1954 and attributed the large Middle Stone Age (MSA) lithic assemblage to his middle phase of the so-called Pietersburg Industry. Recent work at the site has focused on the Holocene layers, but little is known about the earlier phases of shelter use. Here, we provide some background to the shelter, give a history of past research and present initial results following renewed fieldwork at the site. The MSA deposits contain abundant lithic artefacts and ochre, and we present an initial description of these cultural remains. Palynological analysis reveals limited potential for palaeoenvironmental reconstructions, but some faunal remains indicate open grasslands. We dated two equid teeth that provided highly consistent combined U-series-ESR estimates, resulting in a mean age of 150 ± 14 ka (1σ). Even when considering potential sources of uncertainty such as variations in water-intake, these fossils can securely be dated to Marine Isotopic Stage 6. Our reappraisal of site formation processes highlights the fact that the archaeological assemblage is strongly time-averaged. We discuss these different results in the context of a recently rekindled interest in the so-called Pietersburg Industry.

A Geometric Morphometric Evaluation of Equid Tooth Shape at Natural Trap Cave, Wyoming

Natural Trap Cave is a sinkhole cave located in Big Horn County in northern Wyoming. The cave preserves many Quaternary taxa, including pollen and large carnivorous and herbivorous mammals such as various felids and ungulates. Many of these taxa went extinct in North America following the late Pleistocene megafaunal extinction. The cave was first excavated in the 1970s and 80s by teams from the University of Kansas and the University of Missouri, and more recently by teams from Des Moines University, The University of Adelaide, and The University of Rochester, along with a wide variety of volunteers. Specimens from this cave have been used to elucidate floral change in the area, disentangle ancient food webs, and extend the hypothesized range for Beringian wolves.Horses are the most common megafaunal group from this site, encompassing two genera: Equus and Haringtonhippus, the “New World stilt‐legged” horse, based on post‐cranial elements and mitochondrial DNA. Some recent studies have shown that horse taxa can be identified by tooth occlusal surface morphology. This study aims to test if isolated equid cheek teeth from Natural Trap Cave can be identified to the genus level, between Equus and Haringtonhippus using geometric morphometrics. 2D landmarks and sliding semi‐landmarks were taken around the periphery of a set of upper cheek teeth, including the areas of greatest curvature at the metastyle, mesostyle, parastyle, and around the protocone and post protoconal valley. Principal component analyses on known specimens do in fact separate Equus and Haringtonhippus, and this difference is statistically sigificant, with the primary difference being the width of the protocone. Additionally, molars and premolars also occupied significantly different areas of morphospace, opening up the possibility of identifying tooth position on unknown specimens as well. With the abundance of isolated horse teeth (either Equus or Haringtonhippus) from Natural Trap Cave, having a reliable means to distinguish between genera will allow us to better study the ecological differences between them and better understand the environment and faunal interactions in late Pleistocene Wyoming.Support or Funding InformationNSF EAR/SGP 1425059 (Natural Trap Cave Revisited: Ancient DNA, Climate and the Megafaunal Extinction) Julie Meachen, PI

Isotopic records of climate seasonality in equid teeth

We investigate how oxygen isotopes in equid teeth can be used as a record of seasonality. First, we use in situ laser ablation and conventional microsampling techniques to understand time-averaging of environmental signals in intra-tooth isotope profiles in modern feral horse teeth (n = 5) from Mongolia, where there is a large seasonal gradient in the oxygen isotopic composition of precipitation. We demonstrate that laser ablation can be used to sample inner, middle, and outer enamel layers in large mammalian herbivore teeth. The inner enamel layer records less attenuated isotopic signals than other layers, as predicted by the mineralization patterns, but intra-tooth signal amplitude is similar for laser and conventional sampling methods. Second, we use modern zebra teeth (n = 21) collected in eastern Africa to evaluate how intra-tooth oxygen isotope variation relates to rainfall patterns in the tropics. We show that the intra-tooth isotopic range increases with intra-annual precipitation isotopic range, which in turn relates to aridity in the equatorial bimodal rainfall region but is influenced by other hydroclimate processes in the region as a whole. Finally, we address isotopic seasonality during the Early Pleistocene in eastern Africa using oxygen isotopes in fossil equid teeth from southwestern Kenya (n = 11) and northern Tanzania (n = 5). We find variable isotopic seasonality in the past, similar to present-day eastern Africa, consistent with the notion that hominins and other mammals were able to accommodate environmental variability on intra-annual scales in addition to well-documented orbital cycles.

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), p4, m3. Cheek teeth mineralization timing of hipparionine horses coincides with the one observed in modern equids. In turn, there are differences in the eruption timing of the p4 and m3 between horses belonging to the Anchitheriinae and Hipparionini compared to equids of the Equus genus that might be related to the shorter durability of the deciduous tooth dp4 in anchitheriine and hipparionine horses and, more broadly, to an increased durability of equid teeth through their evolutionary history. Based on the dental eruption sequence, hipparionine horses are slow-growing, long-living mammals. The Hipparion sp. assemblage from Batallones-10 conforms to an attritional model, as individuals more vulnerable to natural mortality predominate.

Palaeoecological interpretation of the late Miocene landscapes and vegetation of northern Greece: A comment to Merceron et al., 2016 (Geobios 49, 135–146)

Recent works on feeding habits of ungulates, isotopic composition of equid tooth enamel, and phytoliths from late Miocene localities of northern Greece suggested the presence of savannah and excluded dense forests. Furthermore, Mediterranean-like climates were advocated for the late Miocene of Greece. Here, I compare palaeoenvironments inferred for two mammal localities from Chalkidiki and the Axios Valley (Nikiti, upper Vallesian and lower Turolian; Dytiko, upper Turolian) with evidence from contemporaneous plant assemblages from adjacent areas in Greece and Bulgaria. I use vegetation units inferred from pollen and spore, fruit and seed, and leaf assemblages and compare them with the vegetation inferred from mammal and phytolith data. Open vegetation as inferred from mammal and phytolith data is also part of the range of vegetation units discovered from the pollen and spore, seed and fruit, and leaf record (here called the palaeobotanical record). Poaceae are consistently present in late Vallesian to late Turolian pollen records of northern Greece. Further, a number of vegetation units are indicative of forest vegetation ranging from lowland to upland forests dominated by woody angiosperms and mixed coniferous-angiosperm forests. The presence of such forests is not in conflict with the results from mammal and phytolith studies, but it broadens the view on landscapes present in the late Miocene of northern Greece. In addition to a generalized vegetation type commonly inferred by mammal studies, the palaeobotanical record demonstrates the presence of various complementary vegetation types. A comprehensive view on late Miocene landscapes in northern Greece shows that there is no conflict in inferring open herb dominated landscapes and light to dense forests and provides new opportunities for the ecological interpretation of late Miocene ungulates.

On the relationship between enamel band complexity and occlusal surface area in Equids (Mammalia, Perissodactyla).

Enamel patterns on the occlusal surfaces of equid teeth are asserted to have tribal-level differences. The most notable example compares the Equini and Hipparionini, where Equini have higher crowned teeth with less enamel-band complexity and less total occlusal enamel than Hipparionini. Whereas previous work has successfully quantified differences in enamel band shape by dividing the length of enamel band by the square root of the occlusal surface area (Occlusal Enamel Index, OEI), it was clear that OEI only partially removes the effect of body size. Because enamel band length scales allometrically, body size still has an influence on OEI, with larger individuals having relatively longer enamel bands than smaller individuals. Fractal dimensionality (D) can be scaled to any level, so we have used it to quantify occlusal enamel complexity in a way that allows us to get at an accurate representation of the relationship between complexity and body size. To test the hypothesis of tribal-level complexity differences between Equini and Hipparionini, we digitally traced a sample of 98 teeth, one tooth per individual; 31 Hipparionini and 67 Equini. We restricted our sampling to the P3-M2 to reduce the effect of tooth position. After calculating the D of these teeth with the fractal box method which uses the number of boxes of various sizes to calculate the D of a line, we performed a t-test on the individual values of D for each specimen, comparing the means between the two tribes, and a phylogenetically informed generalized least squares regression (PGLS) for each tribe with occlusal surface area as the independent variable and D as the dependent variable. The slopes of both PGLS analyses were compared using a t-test to determine if the same linear relationship existed between the two tribes. The t-test between tribes was significant (p < 0.0001), suggesting different D populations for each lineage. The PGLS for Hipparionini was a positive but not significant (p = 0.4912) relationship between D and occlusal surface area, but the relationship for Equini was significantly negative (p = 0.0177). λ was 0 for both tests, indicating no important phylogenetic signal is present in the relationship between these two characters, thus the PGLS collapses down to a non-phylogenetic generalized least squares (GLS) model. The t-test comparing the slopes of the regressions was not significant, indicating that the two lineages could have the same relationship between D and occlusal surface area. Our results suggest that the two tribes have the same negative relationship between D and occlusal surface area but the Hipparionini are offset to higher values than the Equini. This offset reflects the divergence between the two lineages since their last common ancestor and may have constrained their ability to respond to environmental change over the Neogene, leading to the differential survival of the Equini.

Exponentially decreasing tooth growth rate in horse teeth: implications for isotopic analyses

A range of archaeological and palaeoclimatic studies use isotopic analyses of ungulate hypsodont tooth enamel. Such studies commonly assume a constant growth rate, though this has not been fully tested. Here, we use stable isotope analyses of sequential enamel samples to study horse tooth growth. We fit the data using models corresponding to constant and exponentially decreasing rates of growth, and compare the results to metrical data showing the geometry and timing of apposition. The results indicate enamel apposition and maturation advances at an exponentially decreasing rate. An understanding of this variable growth rate is crucial for interpreting isotopic data from equid teeth.

Stable isotope patterns found in early Eocene equid tooth rows of North America: Implications for reproductive behavior and paleoclimate

Reproductive behaviors of early Eocene equids were likely different from their modern-day counterparts as a result of their small body size and warmer global temperatures. To better understand the paleoenvironment and ecology of these early horses, teeth of Protorohippus montanum jaws from a single stratigraphic locality in early Eocene sedimentary deposits of Wyoming were sampled for oxygen and carbon isotope analysis. These enamel data along with an inferred body mass of ~7.5kg suggests that adult teeth formed over a matter of months, with the final tooth erupting at ~1.3years of age. Thus, average isotopic values from each tooth likely represent environmental conditions from a single season. Results indicate two isotopic patterns. In the case of isotopic “pattern A,” the second forming molars (m/2s) have significantly lower isotopic ratios compared to other teeth within the jaw. This suggests the first forming molars (m/1s) formed during a cooling fall season, followed by formation of the m/2s during the cooler winter. In the case of isotopic “pattern B,” results suggest that m/1s formed during a warming spring season, while the m/2s formed during the following warmer summer season. Isotopic ratios of m/1s may represent an individual's birth season (or in utero season, depending on timing of initial formation), implying that early equids experienced at least two birth seasons per year. These results suggest that temperatures and reduced seasonality of the early Eocene played a strong role in early equid birth cycles. Lastly, the mean and variance in carbon and oxygen isotope ratios was not significantly different across tooth positions of all jaws when all individuals were grouped together, regardless of their pattern assignment. Such results indicate that isotopic data from fourth premolars, first molars, second molars, and third molars can be combined for purposes of temporal reconstructions of paleoclimate, thus increasing the potential sample sizes for these types of studies.

Occlusal Enamel Complexity in Middle Miocene to Holocene Equids (Equidae: Perissodactyla) of North America

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 influencing the evolution of these occlusal patterns have not been thoroughly investigated with respect to phylogeny, tooth position, and climate through geologic time. We investigated Occlusal Enamel Index, a quantitative method for the analysis of the complexity of occlusal patterns. We used analyses of variance and an analysis of co-variance to test whether equid teeth increase resistive cutting area for food processing during mastication, as expressed in occlusal enamel complexity, in response to increased abrasion in their diet. Results suggest that occlusal enamel complexity was influenced by climate, phylogeny, and tooth position through time. Occlusal enamel complexity in middle Miocene to Modern horses increased as the animals experienced increased tooth abrasion and a cooling climate.

Late Miocene climatic and environmental variations in northern Greece inferred from stable isotope compositions (δ18O, δ13C) of equid teeth apatite

During the late Miocene Vallesian–Turolian transition, an important faunal turnover affected continental vertebrate faunas, and particularly primates with the replacement of hominids by cercopithecid monkeys in Europe. In order to better understand this turnover from a climatic perspective, stable oxygen and carbon isotope compositions of fossil equid tooth enamel contemporaneous with either hominids or cercopithecids have been analyzed. Hipparion teeth recovered from seven Greek localities spanning from the late Vallesian to the end of Turolian have δ18Op values of apatite phosphate suggesting an increase in mean air temperatures from 13±3°C at the beginning of the Vallesian to 17±2°C during the late Turolian. δ13C values of local plants have been estimated using the carbon isotope compositions of apatite carbonate. By applying to our data the relationship established between the δ13C value of modern C3 plants and mean annual precipitations, estimated average precipitations slightly decreased from 890 (+109−100) mma−1 to 471 (+58−54) mma−1 during this time span. According to Köppen's classification of climates, northern Greece was submitted to modern-like Mediterranean climates during the late Miocene. The change in climatic conditions, which took place during the late Vallesian–early Turolian transition, remained within the range of Mediterranean climate modes, thus being unlikely at the origin of a dramatic modification in local vegetation. This study strongly suggests that climate might not be the key factor of the Vallesian–Turolian major faunal turnover at least in the Eastern Mediterranean Basin.

First evidence of Equus asinus L. in the Chalcolithic disputes the Phoenicians as the first to introduce donkeys into the Iberian Peninsula

Two equid species have been documented in the Pleistocene of the Iberian Peninsula, the horse Equus caballus, and the Eurasian hemione Equus hydruntinus. While the former survived the Holocene–Pleistocene until now, the timing for the extinction of the latter is unclear. Scarce, fragmented archaeological remains assess the presence of small equids living in the Holocene of Iberia. Those could possibly correspond to the Eurasian hemione although unambiguous morphological identification is often not possible. With the find of an equid tooth from Leceia, a Chalcolithic fortified site in Portugal, and using both morphological and mitochondrial genome analyses, we demonstrate for the first time the presence of a new equid species in Holocene Iberia, namely a donkey (Equus asinus). Radiocarbon dating of the tooth to Cal 2340–2130, and 2080–2060 BC with 95% probability, demonstrates that donkeys were present in Iberia well before the arrival of Phoenicians in the first quarter of the first millennium BC (900–750 years BC), which were considered so far as the first who introduced donkeys in the region.

High resolution LA-ICP-MS mapping of U and Th isotopes in an early Pleistocene equid tooth from Fuente Nueva-3 (Orce, Andalusia, Spain)

We have produced detailed maps of U and Th isotopes for three cross-sections of an Early Pleistocene equid tooth from the archaeological site of Fuente Nueva-3 (Orce, Andalusia, Spain). This permits us to visualise, for the first time, U migration processes in 3 dimensions. The tooth shows a concentration gradient from the top to the base, indicating the U profile had not equilibrated after >1 Ma. The spatial pattern of 230Th/ 234U and 234U/ 238U indicates complex U-mobilisation processes over the last 100 ka, dominated by small-scale redistribution of U. Leaching from the tooth through the pulp cavity started at least 93 ka ago with several later phases in various domains of the dentine and cement. This leaching event could have been triggered by changes in the local hydrological regime associated with periods of increased erosion in the Guadix-Baza basin. The results illustrate the difficulty of dating faunal material from Early Pleistocene sites. They also demonstrate that dental tissues can neither be considered as homogeneous media for U-diffusion, nor behave as closed systems for U-series isotopes because diagenetic alterations seem to trigger U-migration. The results do not support the notion that U-uptake into dental tissues is necessarily of short duration. Nevertheless, rapid laser ablation scanning can be used to identify suitable samples for dating as well as domains within the teeth that may have preserved original isotopic signatures, i.e. domains that have not been affected by recent U-mobilisation process.

Geographic variation in diets of ancient populations of 5-million-year-old (early Pliocene) horses from southern North America

Using tooth morphology and carbon isotopes, geographic differences in diets are presented for four species of early Pliocene horses (late Hemphillian, Hh 4, between 5.8 and 4.8 Ma) from four localities in Florida, Texas, and Mexico. These four species include three-toed Nannippus aztecus, Neohipparion eurystyle, and one-toed Astrohippus stockii, and Dinohippus mexicanus. The amount of dental variation represented in local populations of these extinct species is similar to that seen in extant equid populations (coefficients of variation, Vs, between ~ 4 and 10). As such, the fossil accumulations of individual species from single localities can be treated as paleopopulations. All four of these horses have high-crowned teeth (hypsodonty indices between 2.6 and 3.1) and the question is addressed how these closely-related species partitioned their available resources to minimize competition. Comparisons of tooth morphology indicate negligible geographic differences between paleopopulations of the same species. Therefore local differences in diets evolved within a context of stasis in tooth morphology. Carbon isotopes of fossil equid tooth enamel indicate that most of the populations and species studied here were primarily C4 grazers, although with some exceptions: Nannippus aztecus tends to be more negative, indicating a higher proportion (~ 20%, or sometimes greater) of C3 plants in its diet. A few individuals within the paleopopulations demonstrate relatively negative tooth enamel carbon isotope values (between ~ − 3 and − 10‰), indicating a diet with some, to predominantly, C3 plants. The sources of isotopic variation result from a variety of factors including latitudinal and seasonal differences in C4 and C3 grass availability, local microhabitat differences, and possibly migration patterns. For the most part these four species of early Pliocene horses have similar diets consisting of predominantly C4 grasses. They therefore differentiated their niches through other evolutionary and ecological strategies, possibly including body size and local habitat differences.