Laura Domingo

Late Neogene and Early Quaternary Paleoenvironmental and Paleoclimatic Conditions in Southwestern Europe: Isotopic Analyses on Mammalian Taxa

Climatic and environmental shifts have had profound impacts on faunal and floral assemblages globally since the end of the Miocene. We explore the regional expression of these fluctuations in southwestern Europe by constructing long-term records (from ∼11.1 to 0.8 Ma, late Miocene–middle Pleistocene) of carbon and oxygen isotope variations in tooth enamel of different large herbivorous mammals from Spain. Isotopic differences among taxa illuminate differences in ecological niches. The δ13C values (relative to VPDB, mean −10.3±1.1‰; range −13.0 to −7.4‰) are consistent with consumption of C3 vegetation; C4 plants did not contribute significantly to the diets of the selected taxa. When averaged by time interval to examine secular trends, δ13C values increase at ∼9.5 Ma (MN9–MN10), probably related to the Middle Vallesian Crisis when there was a replacement of vegetation adapted to more humid conditions by vegetation adapted to drier and more seasonal conditions, and resulting in the disappearance of forested mammalian fauna. The mean δ13C value drops significantly at ∼4.2−3.7 Ma (MN14–MN15) during the Pliocene Warm Period, which brought more humid conditions to Europe, and returns to higher δ13C values from ∼2.6 Ma onwards (MN16), most likely reflecting more arid conditions as a consequence of the onset of the Northern Hemisphere glaciation. The most notable feature in oxygen isotope records (and mean annual temperature reconstructed from these records) is a gradual drop between MN13 and the middle Pleistocene (∼6.3−0.8 Ma) most likely due to cooling associated with Northern Hemisphere glaciation.

Resource partitioning among top predators in a Miocene food web

The exceptional fossil sites of Cerro de los Batallones (Madrid Basin, Spain) contain abundant remains of Late Miocene mammals. From these fossil assemblages, we have inferred diet, resource partitioning and habitat of three sympatric carnivorous mammals based on stable isotopes. The carnivorans include three apex predators: two sabre-toothed cats (Felidae) and a bear dog (Amphicyonidae). Herbivore and carnivore carbon isotope (δ13C) values from tooth enamel imply the presence of a woodland ecosystem dominated by C3 plants. δ13C values and mixing-model analyses suggest that the two sabre-toothed cats, one the size of a leopard and the other the size of a tiger, consumed herbivores with similar δ13C values from a more wooded portion of the ecosystem. The two sabre-toothed cats probably hunted prey of different body sizes, and the smaller species could have used tree cover to avoid encounters with the larger felid. For the bear dog, δ13C values are higher and differ significantly from those of the sabre-toothed cats, suggesting a diet that includes prey from more open woodland. Coexistence of the sabre-toothed cats and the bear dog was likely facilitated by prey capture in different portions of the habitat. This study demonstrates the utility of stable isotope analysis for investigating the behaviour and ecology of members of past carnivoran guilds.

New insights on the taphonomy of the exceptional mammalian fossil sites of Cerro de los Batallones (late Miocene, Spain) based on rare earth element geochemistry

Abstract Cerro de los Batallones fossil sites are distinguished by large and diverse accumulations of Miocene vertebrate fauna. Little taphonomic research has been conducted on these assemblages so far, however. Results of Rare Earth Element (REE) analyses constrain diverse aspects of the taphonomic history undergone by the bones and constitute a starting point for subsequent taphonomic studies. Cerro de los Batallones localities were formed as cavities and seem to be composed of two types of assemblages that differ in their stratigraphic position, internal stratigraphic architecture, taxonomic composition and several taphonomic features. Despite these differences, chemically analyzed bones from the Batallones-1 upper and lower level assemblages exhibit undistinguishable REE patterns both within and between them. This, together with other taphonomic features, indicates that bones are autochthonous and that the depositional context remained constant during the sedimentation of the cavity filling. In addition, REE analyses are a key tool in unveiling the provenance of those fossil bones that could be regarded as allochthonous considering their peculiar macroscopic modifications. Negative Ce anomalies exhibited by isolated fossil bones lead to the proposal that the ponds that existed in the lower level of Batallones-1 were oxic. This inference clarifies the mode of accumulation of individuals in this assemblage: the carcasses did not accumulate massively over a brief period of time but rather they concentrated and, therefore, decayed over a relatively prolonged time span.

PALEOENVIRONMENTAL RECONSTRUCTION OF THE ''LO HUECO'' FOSSIL SITE (UPPER CRETACEOUS, CUENCA, SPAIN): PRELIMINARY STABLE ISOTOPE ANALYSES ON CROCODILIANS AND DINOSAURS

ABSTRACT Stable isotope analyses (&dgr;18OPO4, &dgr;18OCO3, and &dgr;13C) are reported for the first time on crocodilian, theropod, and sauropod teeth from two stratigraphic levels (G1 and G2) from the late Campanian–early Maastrichtian “Lo Hueco” fossil site (Cuenca, Spain) in order to better understand paleoclimatic and paleoenvironmental conditions existing in the Iberian Peninsula during the Late Cretaceous. Diagenetic alteration was evaluated using three tests: (1) consistent differences in enamel and dentine &dgr;18OPO4 values, (2) crocodilian &dgr;18OPO4 values consistently lower than dinosaur &dgr;18OPO4 values in agreement with the proposed latitudinal distribution between ectotherms and endotherms, and (3) a &Dgr;&dgr;18OCO3-PO4 value of 9.1 ± 1.7‰ for dinosaurs in accordance with the expected equilibrium fractionation between carbonate and phosphate in unaltered modern mammalian bioapatite. Calculated &dgr;18OH2O values are slightly higher in crocodilians compared to dinosaurs since semiaquatic ectothermic taxa &dgr;18OH2O represents local meteoric waters in a brief window of time when the conditions are favorable for apatite synthesis, whereas terrestrial endothermic taxa &dgr;18OH2O records ingested water year-round. Mean air temperature calculated using crocodilian and dinosaur &dgr;18OH2O values shows an increase between G1 and G2, which may be related to differences in the sedimentological setting and/or to a shift toward warmer conditions over time. Finally, the sauropod mean &dgr;13C value (−11.1 ± 0.2‰, VPDB) is in the predicted range for C3 vegetation.

Trace element analyses indicative of paleodiets in Middle Miocene mammals from the Somosaguas site (Madrid, Spain)

Trace element analysis of fossil bone and enamel constitutes a useful tool to characterize the paleoecological behavior of mammals. Up to now, most trace element studies have focused on Plio-Pleistocene fossils. Here, we show that paleodietary inferences based on trace element analyses can be also obtained from ~14Ma old Miocene mammals, in a period of time when important paleoclimatic changes took place due to the development of the East Antarctic ice sheet. Trace element ratio (Ba/Ca, Sr/Ca) analyses have been performed on herbivore tooth enamel (gomphothere Gomphotherium angustidens, equid Anchitherium cf. A. cursor, suid Conohyus simorrensis and ruminants) across three stratigraphic levels from the Somosaguas site (Middle Miocene, Madrid Basin, Spain). Previous scanning electron microscope, rare earth element and stable isotope analyses suggested minimal diagenetic alteration of the tooth enamel samples. Trace element analyses reported here show different paleoecological behavior among the studied fossil taxa. Anchitherium cf. A. cursor shows higher Ba/Ca and Sr/Ca ratios than Gomphotherium angustidens, indicating the equid was a mixed-feeder, while the gomphothere was a browser. The enrichment in Ba/Ca and Sr/Ca ratios in the ruminants is attributed to differences in their gastrointestinal tracts and to a more grazing diet. A high variability in trace element values characterizes the suid Conohyus simorrensis, which is believed to be connected to some degree of omnivory.

Feeding ecology and habitat preferences of top predators from two Miocene carnivore-rich assemblages

Abstract. Carnivore-rich fossil sites are uncommon in the fossil record and, accordingly, provide valuable opportunities to study predators from vantages that are rarely applied to ancient faunas. Through stable isotopes of carbon and a Bayesian mixing model, we analyze time-successive (nearly contemporaneous), late Miocene carnivoran populations from two fossil sites (Batallones-1 and Batallones-3) from central Spain. Stable isotopes of carbon in tooth enamel provide a reliable and direct methodology to track ancient diets. These two carnivoran-dominated fossil sites display differences in the composition and abundance of the carnivoran species, with some species present at both sites and some present only at one site. This disparity has been interpreted as the consequence of habitat differences between Batallones-1, the older site, and Batallones-3, the younger site. However, carbon isotope values of carnivore and herbivore tooth enamel suggest a common habitat of C3 woodland originally present at both sites. The differences in the carnivoran faunas rather may be the consequence of the dynamics of species entrance and exit from the Madrid Basin during the time elapsed between Batallones-1 and Batallones-3 and changes in population densities due to biotic factors. We infer higher levels of interspecific competition in Batallones-3 than in Batallones-1 because of the larger number of similar-sized, sympatric predators; the clear overlap in their δ13C values (except for the amphicyonid Magericyon anceps); and similarity of their preferred prey: the hipparionine horses. Finally, carbon stable isotopic composition of Indarctos arctoides teeth implies that this ursid was a carnivorous omnivore rather than a herbivorous omnivore. This work demonstrates the insights that stable isotopes can provide in characterizing the feeding ecology and trophic interactions of ancient carnivoran taxa.

Multiproxy evidence for leaf-browsing and closed habitats in extinct proboscideans (Mammalia, Proboscidea) from Central Chile

Significance The multiproxy approach represents a novel methodology and a unique opportunity to obtain a more detailed view of ancient resource use. Our multiproxy study, carried out on gomphotheres from Chile, widens potential occupied habitats to closed-canopy forests. This habitat variability supports the hypothesis that the diet of gomphotheres appears to be more constrained by resource availability than by the potential dietary range. We strongly recommend the use of a multiproxy approach, where morphology analyses are complemented by other sources of information. This approach prevents misleading conclusions about the origin of the proxy’s signal from arising, such as a leaf-browsing diet inferred from the dental calculus and microwear not necessarily being indicative of humidity. Proboscideans are so-called ecosystem engineers and are considered key players in hypotheses about Late Pleistocene megafaunal extinctions. However, knowledge about the autoecology and chronology of the proboscideans in South America is still open to debate and raises controversial views. Here, we used a range of multiproxy approaches and new radiocarbon datings to study the autoecology of Chilean gomphotheres, the only group of proboscideans to reach South America during the Great American Biotic Interchange (∼3.1 to 2.7 million years before present). As part of this study, we analyzed stable isotopes, dental microwear, and dental calculus microfossils on gomphothere molars from 30 Late Pleistocene sites (31° to 42°S). These proxies provided different scales of temporal resolution, which were then combined to assess the dietary and habitat patterns of these proboscideans. The multiproxy study suggests that most foraging took place in relatively closed environments. In Central Chile, there is a positive correlation between lower δ13C values and an increasing consumption of arboreal/scrub elements. Analyses of dental microwear and calculus microfossils have verified these leaf-browsing feeding habits. From a comparative perspective, the dietary pattern of South American gomphotheres appears to be constrained more by resource availability than by the potential dietary range of the individual taxa. This multiproxy study is aimed at increasing knowledge of the life history of gomphotheres and thus follows an issue considered one of the greatest challenges for paleontology in South America, recently pointed out by the need to thoroughly understand the role of ecological engineers before making predictions about the consequences of ecosystem defaunation.

Differential responses of Miocene rodent metacommunities to global climatic changes were mediated by environmental context

The study of how long-term changes affect metacommunities is a relevant topic, that involves the evaluation of connections among biological assemblages across different spatio-temporal scales, in order to fully understand links between global changes and macroevolutionary patterns. We applied multivariate statistical analyses and diversity tests using a large data matrix of rodent fossil sites in order to analyse long-term faunal changes. Late Miocene rodent faunas from southwestern Europe were classified into metacommunities, presumably sharing ecological affinities, which followed temporal and environmental non-random assembly and disassembly patterns. Metacommunity dynamics of these faunas were driven by environmental changes associated with temperature variability, but there was also some influence from the aridity shifts described for this region during the late Miocene. Additionally, while variations in the structure of rodent assemblages were directly influenced by global climatic changes in the southern province, the northern sites showed a pattern of climatic influence mediated by diversity-dependent processes.

Multi-scale interplays of biotic and abiotic drivers shape mammalian sub-continental diversity over millions of years

The reconstruction of deep-time diversity trends is key to understanding current and future species richness. Studies that statistically evaluate potential factors affecting paleodiversity have focused on continental and global, clade-wide datasets, and thus we ignore how community species richness build-up to generate large-scale patterns over geological timescales. If community diversity is shaped by biotic interactions and continental and global diversities are governed by abiotic events, which are the modulators of diversity in subcontinental regions? To address this question, we model Iberian mammalian species richness over 13 million years (15 to 2 Ma) using exhaustive fossil evidence for subcontinental species’ ecomorphology, environmental context, and biogeographic affinities, and quantitatively evaluate their impact on species richness. We find that the diversity of large Iberian mammals has been limited over time, with species richness showing marked fluctuations, undergoing substantial depletions as diversity surpasses a critical limit where a significant part of the niches is unviable. The strength of such diversity-dependence has also shifted. Large faunal dispersals and environmental heterogeneity increased the system’s critical diversity limit. Diversity growth rate (net migration and diversification) also oscillated, mainly modulated by functional saturation, patchiness of canopy cover, and local temperature and aridity. Our study provides quantitative support for subcontinental species pools being complex and dynamic systems where diversity is perpetually imbalanced over geological timescales. Subcontinental diversity-dependence dynamics are mainly modulated by a multi-scale interplay of biotic and abiotic factors, with abiotic factors playing a more relevant role.

Body-size structure of Central Iberian mammal fauna reveals semidesertic conditions during the middle Miocene Global Cooling Event.

We developed new quantitative palaeoclimatic inference models based on the body-size structure of mammal faunas from the Old World tropics and applied them to the Somosaguas fossil site (middle Miocene, central Iberian Peninsula). Twenty-six mammal species have been described at this site, including proboscideans, ungulates, carnivores, insectivores, lagomorphs and rodents. Our analyses were based on multivariate and bivariate regression models correlating climatic data and body-size structure of 63 modern mammal assemblages from Sub-Saharan Africa and the Indian subcontinent. The results showed an average temperature of the coldest month higher than 26°C for the Somosaguas fossil site, a mean annual thermal amplitude around 10°C, a drought length of 10 months, and an annual total precipitation greater than 200 mm per year, which are climate conditions typical of an ecotonal zone between the savanna and desert biomes. These results are congruent with the aridity peaks described over the middle Aragonian of Spain and particularly in the local biozone E, which includes Somosaguas. The aridity increase detected in this biozone is associated with the Middle Miocene Global Cooling Event. The environment of Somosaguas around 14 Ma was similar to the current environment in the Sahel region of North Africa, the Horn of Africa, the boundary area between the Kalahari and the Namib in Southern Africa, south-central Arabia, or eastern Pakistan and northwestern India. The distribution of modern vegetation in these regions follows a complex mosaic of plant communities, dominated by scattered xerophilous shrublands, semidesert grasslands, and vegetation linked to seasonal watercourses and ponds.