Fossils from Rusinga Island, Kenya, provide an exceptional collection for understanding the evolution and diversification of Early Miocene mammals in Africa, preserving rich assemblages distributed across nearly 2 million years and a variety of habitats. Placing these mammal communities within clear ecological contexts is crucial to understanding the selection pressures that shaped individual taxa but also community composition through time. Although numerous paleoenvironmental reconstructions for these deposits have been suggested, they present conflicting interpretations, with reconstructed habitats for various lithostratigraphic units and/or fossil localities ranging from closed rainforests to open and semiarid environments. Here we present the first paleoenvironmental reconstructions based on carbon and oxygen isotope composition of fossil mammal tooth enamel from Rusinga Island's important fossil assemblages, focusing on specimens from the fossiliferous Hiwegi and Kulu Formations. Our results indicate that these Early Miocene mammals foraged on plants using the C3 photosynthetic pathway in a range of habitats, including those experiencing light and/or water stress, and that habitats were differentially exploited by various species. Although the presence of a dense closed-canopy forest has been documented from at least one Hiwegi stratum, specimens sampled for our analysis exhibit only rare isotopic evidence for foraging within that habitat. Additionally, this study documents a significant difference in the oxygen isotope composition of meteoric water available to fauna found in the Hiwegi Formation versus the younger Kulu Formation. This signals a change in moisture source and/or transport path, or a climatic shift including an increase in mean annual temperature, an increase in aridity, and/or a decrease in mean annual precipitation from the Hiwegi to the Kulu Formation. These results suggest marked differences in paleoenvironmental conditions experienced by these two Early Miocene mammalian communities and underscore the need for more detailed and rigorous analyses of their taxonomic compositions, species abundances, and ecological structures.

The placental skull has evolved into myriad forms, from longirostrine whales to globular primates, and with a diverse array of appendages from antlers to tusks. This disparity has recently been studied from the perspective of the whole skull, but the skull is composed of numerous elements that have distinct developmental origins and varied functions. Here, we assess the evolution of the skull's major skeletal elements, decomposed into 17 individual regions. Using a high-dimensional morphometric approach for a dataset of 322 living and extinct eutherians (placental mammals and their stem relatives), we quantify patterns of variation and estimate phylogenetic, allometric and ecological signal across the skull. We further compare rates of evolution across ecological categories and ordinal-level clades and reconstruct rates of evolution along lineages and through time to assess whether developmental origin or function discriminate the evolutionary trajectories of individual cranial elements. Our results demonstrate distinct macroevolutionary patterns across cranial elements that reflect the ecological adaptations of major clades. Elements derived from neural crest show the fastest rates of evolution, but ecological signal is equally pronounced in bones derived from neural crest and paraxial mesoderm, suggesting that developmental origin may influence evolutionary tempo, but not capacity for specialisation.This article is part of the theme issue 'The mammalian skull: development, structure and function'.

Living hominoids are distinguished by upright torsos and versatile locomotion. It is hypothesized that these features evolved for feeding on fruit from terminal branches in forests. To investigate the evolutionary context of hominoid adaptive origins, we analyzed multiple paleoenvironmental proxies in conjunction with hominoid fossils from the Moroto II site in Uganda. The data indicate seasonally dry woodlands with the earliest evidence of abundant C4 grasses in Africa based on a confirmed age of 21 million years ago (Ma). We demonstrate that the leaf-eating hominoid Morotopithecus consumed water-stressed vegetation, and postcrania from the site indicate ape-like locomotor adaptations. These findings suggest that the origin of hominoid locomotor versatility is associated with foraging on leaves in heterogeneous, open woodlands rather than forests.

The assembly of Africa's iconic C4 grassland ecosystems is central to evolutionary interpretations of many mammal lineages, including hominins. C4 grasses are thought to have become ecologically dominant in Africa only after 10 million years ago (Ma). However, paleobotanical records older than 10 Ma are sparse, limiting assessment of the timing and nature of C4 biomass expansion. This study uses a multiproxy design to document vegetation structure from nine Early Miocene mammal site complexes across eastern Africa. Results demonstrate that between ~21 and 16 Ma, C4 grasses were locally abundant, contributing to heterogeneous habitats ranging from forests to wooded grasslands. These data push back the oldest evidence of C4 grass-dominated habitats in Africa-and globally-by more than 10 million years, calling for revised paleoecological interpretations of mammalian evolution.

Contemporary methods used to predict isotopic variation at regional scales have yet to include underlying distributions of the abundance of isotopic substrates. Additionally, traditional kriging methods fail to account for the potential influences of environmental grouping factors (i.e., random effects) that may reduce prediction error. We aim to improve upon traditional isoscape modeling techniques by accounting for variation in the abundances of isotopic substrates and evaluating the efficacy of a mixed-effects, regression kriging approach. We analyzed common moose forage from northeast Minnesota for δ 13 C and δ 15 N and estimated the isotopic landscape using regression kriging, both with and without random effects. We then compared these predictions to isoscape estimates informed by spatial variation in above-ground biomass. Finally, we kriged the regression residuals of our best-fitting models, added them to our isoscape predictions, and compared model performance using spatial hold-one-out cross validation. Isoscape predictions driven by uninformed and biomass-informed models varied by as much as 10‰. Compared to traditional methods, incorporating biomass estimates improved RMSE values by as much as 0.12 and 1.00% for δ 13 C and δ 15 N, respectively, while random effects improved r 2 values by as much as 0.15 for δ 13 C and 0.87 for δ 15 N. Our findings illustrate how field-collected data, ancillary geospatial data, and novel spatial interpolation techniques can be used to more accurately estimate the isotopic landscape. Regression kriging using mixed-effects models and the refinement of model predictions using measures of abundance, provides a flexible, yet mechanistically driven approach to modeling isotopic variation across space.

North American mammals follow a well-established latitudinal diversity gradient in species richness. However, the degree to which species in different mammal clades follow the same latitudinal gradient-and to which each clade contributes to the pattern observed for all mammals remains unknown. Here, we separate the overall mammalian latitudinal diversity gradient by mammal orders and investigate the impact of climate and topography on the distribution of each major mammal clade. We joined an equal-area grid (100 x 100 km cells) of continental North America embedded with environmental variables (n = 10) with mammalian species ranges (n = 753). We used spatial regression models to quantify the relationship between species richness and latitude for all mammals, all mammals excluding select clades, and for each individual subordinate clade (n = 9). We used multiple linear regression and simultaneous autoregressive regression models to determine which environmental variables best explained patterns of species richness for each mammal order. Whereas North American mammals altogether exhibit a strong latitudinal diversity gradient in species richness, most orders deviate from the species richness pattern observed for all mammals and their gradients are weak or entirely absent. Bats (Chiroptera) exhibit the strongest latitudinal gradient-their removal from the pattern for all mammals substantially weakens the total mammalian gradient, more so than when rodents are removed. Environmental variables explain patterns of species richness well for some clades, but poorly for others. The gradient we observe for North American mammals today is likely a combined product of multiple diversification events, dispersals, and climatic and tectonic histories.

AbstractNOW (New and Old Worlds) is a global database of fossil mammal occurrences, currently containing around 68,000 locality-species entries. The database spans the last 66 million years, with its primary focus on the last 23 million years. Whereas the database contains records from all continents, the main focus and coverage of the database historically has been on Eurasia. The database includes primarily, but not exclusively, terrestrial mammals. It covers a large part of the currently known mammalian fossil record, focusing on classical and actively researched fossil localities. The database is managed in collaboration with an international advisory board of experts. Rather than a static archive, it emphasizes the continuous integration of new knowledge of the community, data curation, and consistency of scientific interpretations. The database records species occurrences at localities worldwide, as well as ecological characteristics of fossil species, geological contexts of localities and more. The NOW database is primarily used for two purposes: (1) queries about occurrences of particular taxa, their characteristics and properties of localities in the spirit of an encyclopedia; and (2) large scale research and quantitative analyses of evolutionary processes, patterns, reconstructing past environments, as well as interpreting evolutionary contexts. The data are fully open, no logging in or community membership is necessary for using the data for any purpose.

The Cenozoic diversification of placental mammals is the archetypal adaptive radiation. Yet, discrepancies between molecular divergence estimates and the fossil record fuel ongoing debate around the timing, tempo, and drivers of this radiation. Analysis of a three-dimensional skull dataset for living and extinct placental mammals demonstrates that evolutionary rates peak early and attenuate quickly. This long-term decline in tempo is punctuated by bursts of innovation that decreased in amplitude over the past 66 million years. Social, precocial, aquatic, and herbivorous species evolve fastest, especially whales, elephants, sirenians, and extinct ungulates. Slow rates in rodents and bats indicate dissociation of taxonomic and morphological diversification. Frustratingly, highly similar ancestral shape estimates for placental mammal superorders suggest that their earliest representatives may continue to elude unequivocal identification.

Terrestrial biodiversity is higher in topographically complex regions than in low relief ones, and this diversity evolved over millions of years along elevation gradients with disequilibrium of climatic conditions and biological interactions. Also, the mountainous complex is heterogeneous, consisting of orogenic and volcanic mountains with different geological and climatic features. However, there has not been an investigation in regard how a volcanic environment may have influenced ecosystem changes or faunal evolution to. Rodents are an excellent model to explore these questions because they are the most speciose clade of mammals and many species live in montane regions. Hypotheses of the ecological evolution in different volcanic provinces in America were discussed during the Workshop on Volcanism and Rodent Evolution organized by the Research Group “Mammal diversification about dynamic landscapes of the North American Rodents Landscapes, Evolution & Ecology”. Workshop consisted of two modules: 1) origin and development of volcanic provinces in North America during the late Cenozoic with an emphasis on the geological process crucial to the ecosystem; 2) some examples of ecosystems in volcanic regions and evolutive patterns related to sky-island process. In both modules, we discuss the evolution of different lineages of rodents, fossil and extant species, and how we can distinguish the volcanic influence on their biodiversity. The topics were: speciation, endemism, genetic drift, geographic-range shifts, environmental sorting, and sky-island processes.

The Pliocene Epoch is a high priority for understanding climatic and geomorphic responses to rising CO2 levels, yet the majority of paleoclimate records from this interval are from marine basins. Paleosols (fossil soils) preserve in situ archives of terrestrial paleoclimate, paleovegetation, and surface processes. This presentation showcases ongoing efforts to leverage paleosols from Pliocene deposits in North America and eastern Africa to develop quantitative estimates of mean annual precipitation (MAP), temperature (MAT) and paleovegetation (C3 vs. C4 biomass). We use a previously published random-forest recursive partitioning model (RF-MAP) that reconstructs MAP values using 10 major and minor elemental oxides from paleosol B horizons as input variables and is applicable on most soil types in most climate regimes. Our work in the Meade Basin of Kansas, USA, shows evidence of expanding and contracting wetlands during the Pliocene, with paleosols consisting of Vertisols to Aridisols depending on geomorphic position. Average paleoprecipitation totals appear to be near the semi-arid to subhumid boundary (~500 mm, similar to modern values) and remain steady across the Pliocene through early Pleistocene. Pliocene deposits of the Baringo Basin of central Kenya consists of orbitally-controlled lacustrine-alluvial cycles. Paleosols tend to be Vertisols in lowland marsh to alluvial plain settings, however localized Andisols and Inceptisols are also present. Our continuing efforts include analyses of pedogenic carbonate formation temperatures from clumped isotopes (Δ47) development of paleovegetation records from δ13C analyses on pedogenic carbonates and organic matter, and application of the RF-MAP model on Baringo Basin paleosols.

Modern physical and chemical soil properties can favor or exclude C-3 and C-4 plants, yet little is known regarding these relationships from deep-time records that track the evolution and expansion of C-4 vegetation. In this study, we used a multi- proxy approach to reconstruct vegetation (C-3 vs. C-4 biomass) and pedogenic properties (soil alkalinity, salinity, sodicity, and texture) from paleolandscapes at Coffee Ranch, Texas, a site from which fossil horses provide the earliest evidence for C-4 herbivory in the Great Plains of North America. Local proportion of C-4 biomass was assessed using stable carbon isotope ratios of calcium carbonates (delta C-13(cc)) and organic matter (delta(13)(Com)) analyzed on four different paleosol types, freshwater tufa, and reworked carbonate nodules in fluvial channel lags. Using a Monte Carlo uncertainty analysis, we interpret delta C-13(cc) (range = 8.5 to 5.2% VPDB) and delta(13)(Com) values (range = 25.9 to 24.2% VPDB) to be consistent with C-4 biomass low in abundance and variability at the study site, but with large uncertainties that would be overlooked using simple linear mixing model approaches. Paleo-pedogenic properties were reconstructed using pedotransfer functions and provide evidence of possible salinity and sodicity in two of five paleosol profiles. However, saline-sodic conditions and soil texture were not correlated with delta C-13 values, contrary to some modern mixed C-3-C-4 biomes. Using late Miocene CO2 and paleoclimate model reconstructions, we argue that conditions were at or near crossover thresholds favoring C-4 over C-3 photosynthesis in the Great Plains despite the low abundance of C-4 vegetation across the paleolandscapes. This study presents evidence that abiotic factors that select for C-4 plants in modern systems-high growing season temperature, low atmospheric CO2, salinity-sodicity, and soil texture-were less influential in the late Miocene than biotic factors (i.e., ecological feedbacks) that suppressed C-4 plants prior to their increase in abundance in the Great Plains in the Pliocene.

Detection of mineral system footprints in regions under thick cover is challenging. The difficulties are enhanced in regions with low-relief landscapes that are deeply weathered. This research examines how information from a single drill hole in an underexplored region can deliver a significant amount of information to assist in greenfields exploration. This study describes the geochemical dispersion processes through >500 m of cover based on observations from drill hole CDP008, and explores the possibility of recognising landscape features that link basement features with the surface.Our study revealed that: (1) the lower fluvial sandstone package contains a geochemical footprint of the underlying basement rocks, produced by vertical and lateral geochemical dispersion; whereas (2) the overlying sediments do not record any footprint of the basement rocks; and (3) the top limestone units are a chemical barrier for vertical geochemical dispersion due to their lack of permeability.Basement features identified from magnetic data are mimicked by linear surface landscape features that lie above them, which may potentially be associated with vertical geochemical dispersion processes, linking the basement with the surface. Hence from the point of view of mineral exploration, surface geochemical sampling should target these particular neotectonic/reactivation-associated features of the landscape.We suggest that in areas of deep cover, neotectonics/reactivation surface landscape features have the highest prospectivity to detect deep basement geochemical signatures at surface. The findings from this study may therefore impact approaches to mineral exploration under cover in similar landscape contexts around the world, such as regions in West Africa, India, China and Brazil.

Equations estimating body mass were used to depict a near 5-million-year history of size change in pocket gophers and cotton rats from the Meade Basin of southwestern Kansas. Although phyletic size decrease was noted in Sigmodon minor and Geomys minor and size increase in Geomys quinni, no long-term intra-basin size trends were observed. Immediately following the Huckleberry Ridge ash-fall at 2.11 Ma, the small Pliocene cotton rat S. minor became extinct, a large cotton rat entered the basin, two gophers became extinct, and two new ones entered the basin. Assuming the same rodent contingent at the Short Haul locality as at the Aries A site, between deposition of the Borchers and Short Haul assemblages, minimally about 0.12 million years, 40% of the Meade Basin rodent fauna turned over and Microtus dispersed into North America across Beringia. Geochemical environmental proxy data did not identify significant climatic events in the Borchers Badlands Pleistocene sequence; consequently it is possible that a super-eruption from the Yellowstone caldera was at least partly responsible for size shifts in cotton rats and pocket gophers and significant modifications to the Meade Basin rodent community.

The Early Pleistocene is recognized as a time of major global climatic and environmental change, including increasing aridity, significant spread of grasslands, and substantial faunal turnovers and dispersals. Importantly, this is the first time hominins are found in Eurasia. Reconstructing the types of environments that existed during this time is imperative for understanding mammalian, including hominin, dispersal patterns relative to climatic change. One proposed dispersal corridor across Europe is the Danube River. Here we characterize the 2.2 to similar to 1.1 million years ago (Ma) paleoenvironments surrounding one of the tributaries to the Danube, the Oltet River, in southern Romania using a multiproxy approach, including taxonomic uniformitarianism, dental mesowear, dental microwear, enamel stable isotope (carbon and oxygen), and coprolite/palynology analyses, and compare our results to other penecontemporaneous Eurasian sites. Older sites from this region, Graunceanu and La Pietris, both dating to 2.2 1.9 Ma, are reconstructed as being primarily open, though with some nearby woodlands and significant water resources. Fantana lui Mitilan, which is younger (1.8-1.1 Ma), is reconstructed as slightly more closed, though still relatively open in nature. These results are similar to reconstructions for other Early Pleistocene Eurasian sites, including ones with and without hominins, suggesting that hominins were likely not inhibited from dispersing across Eurasia due to environmental constraints at this time.