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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. The hominoid lineage underwent a major morphological change in the Miocene, acquiring strong hind legs and a more upright posture. The prevailing hypothesis pertaining to these changes has been that they were adaptive for foraging on fruit in the terminal branches of tropical forest trees. A pair of papers now argue that, instead, such changes may have been driven by adaptation to feeding on leaves in seasonally dry and open forests. Peppe et al. used new data from fossil mammal study sites and found that the expansion of grassy biomes dominated by grasses with the C4 photosynthetic pathway in eastern Africa likely occurred more than 10 million years earlier than prior estimates. MacLatchy et al. looked at fossils of the earliest ape in this region at this time, Morotopithecus, and found isotope evidence of the consumption of water-stressed vegetation and postcranial morphology indicative of strong hind limbs similar to modern apes. Together, these papers suggest that early hominoids emerged in a dryer and more irregular environment than was previously believed. —BEL and SNV A combination of data sources from fossil mammal sites pushes back the date of C4 grassland expansion in eastern Africa by over 10 million years. - Early Miocene habitat heterogeneity, open habitats, and locally abundant C4 vegetation - Implications for Neogene ecosystems of eastern Africa

INTRODUCTIONInherent in traditional views of ape origins is the idea that, like living apes, early large-bodied apes lived in tropical forests. In response to constraints related to locomoting in forest canopies, it has been proposed that early apes evolved their quintessential upright torsos and acrobatic climbing and suspensory abilities, enhancing their locomotor versatility, to distribute their weight among small supports and thus reach ripe fruit in the terminal branches. This feeding and locomotor transition from a quadruped with a horizontal torso is thought to have occurred in the Middle Miocene due to an increasingly seasonal climate and feeding competition from evolving monkeys. Although ecological and behavioral comparisons among living apes and monkeys provide evidence for versions of terminal branch forest frugivory hypotheses, corroboration from the early ape fossil record has been lacking, as have detailed reconstructions of the habitats where the first apes evolved.RATIONALEThe Early Miocene fossil site of Moroto II in Uganda provides a unique opportunity to test the predictions of terminal branch forest frugivory hypotheses. Moroto II documents the oldest [21 million years ago (Ma)] well-established paleontological record of ape teeth and postcranial bones from a single locality and preserves paleoecological proxies to reconstruct the environment. The following lines of evidence from Moroto II were analyzed: (i) the functional anatomy of femora and a vertebra attributed to the ape Morotopithecus; (ii) dental traits, including molar shape and isotopic profiles of Morotopithecus enamel; (iii) isotopic dietary paleoecology of associated fossil mammals; (iv) biogeochemical signals from paleosols (ancient soils) that reflect local relative proportions of C3 (trees and shrubs) and C4 (tropical grasses and sedges that can endure water stress) vegetation as well as rainfall; and (v) assemblages of phytoliths, microscopic plant-derived silica bodies that reflect past plant communities.RESULTSA short, strong femur biomechanically favorable to vertical climbing and a vertebra indicating a dorsostable lower back confirm that ape fossils from Moroto II shared locomotor traits with living apes. Both Morotopithecus and a smaller ape from the site have elongated molars with well-developed crests for shearing leaves. Carbon isotopic signatures of the enamel of these apes and of other fossil mammals indicate that some mammals consistently fed on water-stressed C3 plants, and possibly also C4 vegetation, in a woodland setting. Carbon isotope values of pedogenic carbonates, paleosol organic matter, and plant waxes all point to substantial C4 grass biomass on the landscape. Analysis of paleosols also indicates subhumid, strongly seasonal rainfall, and phytolith assemblages include forms from both arid-adapted C4 grasses and forest-indicator plants.CONCLUSIONThe ancient co-occurrence of dental specializations for leaf eating, rather than ripe fruit consumption, along with ape-like locomotor abilities counters the predictions of the terminal branch forest frugivory hypotheses. The combined paleoecological evidence situates Morotopithecus in a woodland with a broken canopy and substantial grass understory including C4 species. These findings call for a new paradigm for the evolutionary origins of early apes. We propose that seasonal, wooded environments may have exerted previously unrecognized selective pressures in the evolution of arboreal apes. For example, some apes may have needed to access leaves in the higher canopy in times of low fruit availability and to be adept at ascending and descending from trees that lacked a continuous canopy. Background - Terminal branch forest frugivory hypotheses - The Moroto II locality - The hominoids of Moroto II Results - Geologic and taphonomic setting - Chronology - Hominoid and other catarrhine fossils -- Femur -- Vertebra -- Dental specimens -- Stable isotopes of ename - Paleoecology -- Stable carbon isotopes of fossil enamel -- Paleosol carbon isotopes -- Paleosol n-alkanes -- Paleosols and hydroclimate -- Phytoliths Discussion - Context of the hominoid remains from Moroto - Hominoid adaptive evolution in eastern Africa Materials and methods summary

The bulk elemental composition of soil subsurface (B) horizons is influenced by environmental, biological, geological, and climatic factors. Because fossil soils (paleosols) are common in the geologic record, quantitative models that link climate to paleosol geochemistry are highly desirable in the paleoclimate community. Error associated with these models is typically reported as the root mean square error (RMSE) of a regression analysis and reflects the variability imparted by non-climatic influences on soil formation and the uncertainty associated with model fitting. However, for prediction purposes, the RMSE is well known to underestimate model uncertainty. In this work we re-evaluate a widely used transfer function for mean annual precipitation (MAP) based on the chemical index of alteration minus potassium (CIA-K) using data science best practices on two continental-scale soil data sets. Data set inter-comparisons and cross-validation of exponential regression models indicate that the root mean square prediction error (RMSPE) between CIA-K and MAP for soils representative of climates across the continental United States is around 299 mm, significantly higher than the currently accepted 182 mm RMSE. Further, CIA-K is unable to predict perhumid (>2000 mm MAP) climate zones. We show that transitioning from a simple regression framework to one of recursive partitioning via random forests can significantly increase prediction accuracy while automating variable selection. We introduce two new, widely applicable random forest models for MAP (RF-MAP) that use 10 elemental oxides as input variables and were calibrated on the Baylor University Soil Informatics (BU-SI) data set. RF-MAP version 1.0 (RF-MAP1.0) was generated using the entire BU-SI data set (n = 685) and can predict MAP values up to 6865 mm with a RMSPE of 395 mm. RF-MAP version 2.0 (RF-MAP2.0) was generated using a modification of the BU-SI data set (n = 642) and can predict MAP values up to ∼1600 mm with a RMSPE of 209 mm. Pruned regression trees provide insight into the mechanisms driving the random forest models and demonstrate the first empirical confirmation of the sensitivity of soil elemental responses to global climate zones. The RF-MAP1.0 and RF-MAP2.0 models predict MAP values comparable to independent proxy estimates for a range of deep-time paleosols. We advocate for application of RF-MAP1.0 in settings where no a priori information on paleoclimate is available, and encourage the use of either RF-MAP1.0 or RF-MAP2.0 if users have independent constraints that paleo-MAP was below 1600 mm.

Terrestrial paleoenvironmental reconstructions from the Pliocene Epoch (5.3-2.6 Ma) of the Neogene Period are rare from the North American continental interior, but are important because they provide insight into the evolutionary context of modern landscapes and ecological systems. Pliocene marine records indicate that global climate was warmer and atmospheric pCO2 was higher than pre-industrial conditions, spurring efforts to understand regional climate and environmental variability under conditions potentially analogous to future warming scenarios. In this study, we investigate sedimentary environments and paleoclimate conditions from the Meade Basin of southwest Kansas, a moderately sized basin formed from dissolution and withdrawal of deep evaporites. Pliocene intervals of the Meade Basin have yielded classic faunal assemblages representing the early to middle Blancan North American Land Mammal Age (∼ 4.5-3.2Ma).We reconstruct the paleoenvironments using a multidisciplinary approach of lithofacies analysis, paleopedology, and ichnology. The stratigraphic interval we examined is bounded by large-scale, fluvial trunk channels that show paleocurrent trends to the south-southwest-tangential to modern drainages-likely due to local halotectonic subsidence during the Neogene. The stratigraphic interval between these fluvially dominated phases consists of palustrine landscapes with temporally and laterally variable subaqueous and subaerial facies. Paleosols are abundant; however, most pedotypes are poorly to variably drained, and so their elemental compositions do not reflect local climate state. The few mature, oxidized, and relatively well-drained paleosols observed contain elemental signatures consistent with subhumid climate conditions. Frequent and recursive ponding events are discerned through the tiering of burrows (Camborygma ISP.) similar to those produced by modern freshwater decapod crustaceans (i.e., crayfish). The drivers of these flooding events are most likely episodic halotectonic subsidence and groundwater discharge, though influence from intervals of relatively wetter climate cannot be ruled out. By the late middle Pliocene, landscapes returned to fluvially dominated environments as sedimentation began to outpace accommodation. Our results collectively indicate that climate was likely wetter than modern conditions in the early to middle Pliocene in the western Great Plains, contrary to forecasts for the region under current pCO2-driven warming.

The wet summers and dry winters of monsoon systems in East Asia are a first-order control on food and water security for a significant portion of the global population today. The onset, characteris...

Modern physical and chemical soil properties can favor or exclude C3 and C4 plants, yet little is known regarding these relationships from deep-time records that track the evolution and expansion of C4 vegetation. In this study, we used a multi-proxy approach to reconstruct vegetation (C3 vs. C4 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 C4 herbivory in the Great Plains of North America. Local proportion of C4 biomass was assessed using stable carbon isotope ratios of calcium carbonates (δ13Ccc) and organic matter (δ13Com) analyzed on four different paleosol types, freshwater tufa, and reworked carbonate nodules in fluvial channel lags. Using a Monte Carlo uncertainty analysis, we interpret δ13Ccc (range = −8.5 to −5.2‰ VPDB) and δ13Com values (range = −25.9 to −24.2‰ VPDB) to be consistent with C4 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 δ13C values, contrary to some modern mixed C3-C4 biomes. Using late Miocene CO2 and paleoclimate model reconstructions, we argue that conditions were at or near crossover thresholds favoring C4 over C3 photosynthesis in the Great Plains despite the low abundance of C4 vegetation across the paleolandscapes. This study presents evidence that abiotic factors that select for C4 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 C4 plants prior to their increase in abundance in the Great Plains in the Pliocene.

Soil pH is essential for understanding weathering, nutrient availability, and biological-edaphic relationships. However, standard pH measurement on soils requires friable material, thereby ...

The late Miocene Coffee Ranch fossil assemblage contains some of the earliest evidence of C4 herbivory in North America. However, little is known regarding the environmental setting associated with the fauna, and a general lack of detailed paleoclimate data exists for the late Miocene from the North American continental interior. In this study, the sedimentary environments, stratigraphy, geochronology, and paleoclimate are interpreted for a series of outcrops of the late Miocene Ogallala Formation in the Texas Panhandle that includes the Coffee Ranch locality. Updated magnetostratigraphy coupled with previously published geochronology indicates that all exposed strata were deposited over a ~ 277 kyr interval within chron C3An.2n from ~ 6.42–6.70 Ma. Depositional environments include fluvial channels, floodplain ponds, floodplain paleosols, eolian paleosols, riverine tufa, and reworked volcanic ash. Trunk and tributary fluvial channels are differentiated using channel dimensions, sedimentary structures, and bounding surface architecture, and indicate seasonally-variable discharge. Paleosols from nine pedofacies are described and preserve a spectrum of weakly developed Entisols and weakly to moderately mature Inceptisols and Vertisols. Constitutive mass-balance calculations reveal that mature paleosols formed along distinct pedogenic pathways. Calcic Vertisols accumulated pedogenic carbonate and exhibited either net volumetric dilation or collapse as a result of mineral weathering. In contrast, non-calcic Vertisols show patterns of decalcification and variable degrees of volumetric dilation and collapse. The presence of the paleosols described in this study requires paleoprecipitation between of 900–1150 mm/yr—approximately double modern values—and a westward shift of the continental udic-ustic soil moisture boundary by ~ 400 km during the late Miocene. This finding suggests that climates in the southern midcontinent were not sufficiently arid to select for C4 photosynthetic pathways over C3 photosynthesis in the late Miocene.

The late Oligocene is an important deep-time analog for understanding future changes in the strength of the East Asian monsoon: it represents a climate warmer than today, yet follows the nascent uplift of the Tibetan–Himalayan orogeny during the Eocene Epoch. Here we quantify monsoon strength based on new oxygen isotope measurements on cellulose (δ18Ocell) extracted from modern and fossil wood from southern China. Tree-ring δ18Ocell values have previously been used to track Holocene climate variations in East Asia, as δ18Ocell values are primarily controlled by meteoric water δ18O (δ18OMW) and relative humidity. We find the δ18Ocell values measured on the modern samples (25.7 to 29.1‰ VSMOW) are consistent with other δ18Ocell records from trees growing in southern China under the present-day monsoon climate. However, fossil wood δ18Ocell values (21.0 to 24.1‰ VSMOW) are significantly lower than those from living trees in the region, and instead overlap with values from modern high latitudes and high elevations. We show that these low δ18Ocell values are best explained by much higher rainfall amounts in southern China during the late Oligocene, with monthly wet-season rainfall that may have been ~60% greater than today based on modern relationships. These data represent the first seasonal rainfall estimates for southern China during the late Oligocene and signify an intensification of the region's current monsoonal rainfall patterns. We speculate that significantly greater monsoon rainfall is therefore possible in the region under a warmer climate.

Paleosols (fossil soils) are abundant in the sedimentary record and reflect, at least in part, regional paleoclimate. Paleopedology thus offers a great potential for elucidating high resolution, deep-time paleoclimate records. However, many fossil soils did not equilibrate with climate prior to burial and instead dominantly express physical and chemical features reflective of other soil forming factors. Current models that use elemental oxides for climate reconstruction bypass the issue of soil-climate equilibration by restricting datasets to narrow ranges of soil properties, soil-forming environments and mean annual precipitation (MAP) and mean annual temperature (MAT). Here we evaluate a data-driven paleosol-paleoclimate model (PPM1.0) that uses subsoil geochemistry to test the ability of soils from wide-ranging environments to predict MAP and MAT as a joint response with few initial assumptions. The PPM1.0 was developed using a combined partial least squares regression (PLSR) and a nonlinear spline on 685 mineral soil B horizons currently forming under MAP ranging from 130 to 6900 mm and MAT ranging from 0 to 27 °C. The PLSR results on 11 major and minor oxides show that four linear combinations of these oxides (Regressors 1-4), akin to classic oxide ratios, have potential for predicting climate. Regressor 1 correlates with increasing MAP and MAT through Fe oxidation, desilication, base loss and residual enrichment. Regressor 2 correlates with MAT through temperature-dependent dissolution of Na- and K-bearing minerals. Regressor 3 correlates with increasing MAP through decalcification and retention of Si. Regressor 4 correlates with increasing MAP through Mg retention in mafic-rich parent material. The nonlinear spline model fit on Regressors 1 to 4 results in a Root Mean Squared Error (RMSEMAP) of 228 mm and RMSEMAT of 2.46 °C. PPM1.0 model simulations result in Root Mean Squared Predictive Error (RMSPEMAP) of 512 mm and RMSPEMAT of 3.98 °C. The RMSE values are lower than some preexisting MAT models and show that subsoil weathering processes operating under a wide range of soil forming factors possess climate prediction potential, which agrees with the state-factor model of soil formation. The nonlinear, multivariate model space of PPM1.0 more accurately reflects the complex and nonlinear nature of many weathering processes as climate varies. This approach is still limited as it was built using data primarily from the conterminous USA and does not account for effects of diagenesis. Yet, because it is calibrated over a broader range of climatic variable space than previous work, it should have the widest array of potential applications. Furthermore, because it is not dependent on properties that may be poorly preserved in buried paleosols, the PPM1.0 model is preferable for reconstructing deep time climate transitions. In fact, previous studies may have grossly underestimated paleo-MAP for some paleosols.

The Hell Creek Formation and overlying Fort Union Formation record a geologically rapid base-level rise that was approximately contemporaneous with the K/Pg extinction and deposition of Chicxulub-impact indicators. An outstanding question that remains is whether this base-level rise is attributable to: 1) a multi-thousand-year transgression adjacent to a relatively low-relief coastal plain, causing a rise in the water table; or 2) catastrophic flooding due to upland denudation, rapid channel accretion, and hydrologic reorganization resulting from wildfires/deforestation consequential of the impact. Herein we aim to address which of these hypotheses is most consistent with a paleolandscape reconstruction at Mud Buttes, a locality where the boundary clay (BC) is coincident with the Hell Creek-Fort Union contact. One hundred twenty-seven trenches were examined laterally across ∼2 km transect of K/Pg boundary. The uppermost Hell Creek is comprised of three pedotypes: Pale-Silt Inceptisol (PSI), Olive-Clay Vertisol (OCV), and Chocolate-Clay Vertisol (CCV), which range from moderately well-drained, to variable to poorly drained, to very poorly drained, respectively. All of the BC occurs superjacent to the CCV, despite this pedotype accounting for only ∼50% of the pre-event landscape. The edaphic features preserved in the CCV pedotype are not attributable to Paleogene overprinting, which indicates that hydromorphic conditions began prior to the impact. Furthermore, 46% of BC is overlain by lignite, despite lignite occurrence on 17% of the earliest Paleogene landscape. This reveals that the poorest-drained landscape positions of the latest Cretaceous persisted across the boundary. These relationships are most consistent with a non-catastrophic base-level rise.

Soil organic carbon (SOC) storage in alluvial depositional zones is important as it serves as a centennial to millennial timescale sink of C. This study examines SOC variability in alluvial bars, floodplains and terraces in a forested, humid-subtropical setting along the Clarks River in the Mississippi River basin (MRB) using replicated soil sampling, characterization and modeling. Soil and depositional profiles range in age from a minimum of 8000 years ago to modern. Normalized (by depth) mean SOC stocks (kg m−2) of the surface soil and buried layers, i.e., buried soils and layers underlying lithologic discontinuities, are highest in the terraces. Normalized mean surface SOC stocks decrease from terraces to floodplains and then to bars; whereas normalized mean buried layer SOC stocks decrease from terraces to bars, and then floodplains. The depth distribution of stocks showed that buried layers accounted for >50% of the total SOC pool, regardless of landform type. A regression tree analysis shows that soil horizon, pH, landform, and magnetic susceptibility were significant predictors of mean SOC content. Notably, the regression tree shows that alkaline pH (>7.9), observed only in buried layers in the terrace, is an important predictor in higher mean SOC. These alkaline soil pH values were associated with paleosol calcite, where the δ13C and 14C from the calcite suggests it formed under C3 vegetation during the drier than modern mid-Holocene hypsithermal, ~8000 years ago. Buried soil and sediment contain the majority of the SOC in this humid-subtropical valley bottom, while landform position and past buried soil-forming environments (paleosols) played an important role in the storage of that SOC. This work reconfirms that there is a long record of a passive, buried SOC pool found deep in our river valley bottoms that holds clues to the past biogeochemical cycling of C on land prior to intensive agriculture and industrialization. The legacy of past Holocene climates and paleosols are directly linked to our current understanding of long-term storage of SOC.

Soils form as a product of physical, chemical, and biological activity at the outermost veneer of Earth’s surface. Once buried and incorporated into the sedimentary record, these soils, now paleosols, preserve archives of ancient climates, ecosystems, and sedimentary systems. Paleopedology, the study of paleosols, includes qualitative interpretation of physical characteristics and quantitative analysis of geochemical and mineralogical assays. In this chapter, the paleosol macroscopic, micromorphological, mineralogical, and geochemical indicators of paleoecology are discussed with emphasis on basic analytical and interpretative techniques. These data can reveal a breadth of site-specific interpretations of vegetation, sedimentary processes, climatic variables, and durations of landscape stability. The well-known soil-forming factors are presented as a theoretical framework for understanding landscape-scale soil evolution through time. Vertical and lateral patterns of stacked paleosols that appear in the rock record are discussed in order to address practical approaches to identifying and describing paleosols in the field. This chapter emphasizes a robust multi-proxy approach to paleopedology that combines soil stratigraphy, morphology, mineralogy, biology, and chemistry to provide an in-depth understanding of paleoecology.

Recent research has demonstrated that the Lilliput effect (reduction of body size in response to a mass extinction) affected all trophic levels in the marine realm following the Cretaceous-Paleogene (K-Pg) event. However, it is unclear if this size change was strictly a marine signal, or a global phenomenon that also affected continental ecosystems. Herein we present the results of an ichnological proxy for body size of soil-dwelling insects across the K-Pg boundary in Big Bend National Park, Texas, U.S.A. Quantitative efforts focused on Naktodemasis isp., which are characterized as unbranching burrows composed of ellipsoidal packets of backfill menisci. These traces were likely produced by beetle larvae or cicada nymphs based on previous comparison with structures generated in modern soils and laboratory experiments. As an approximation for the body size of the subterranean insects, this dataset indicates that a smaller Naktodemasis diameter (DN) is statistically correlated (α < 0.05) with several edaphic factors including poor drainage and weak development (Entisols). Additionally, the DN in strata immediately superjacent to the highest Cretaceous-specific taxa is smaller by 23% (5.6 ± 1.8 mm) in comparison to DN within the subjacent Cretaceous interval (7.3 ± 2.7 mm). This abrupt shift occurs in a well-drained Inceptisol, and cannot be attributed to facies changes, drainage, or paleosol maturity. Furthermore, a reduced DN (6.6 ± 2.3 mm) persists above this anomalous shift for at least 20 stratigraphic meters within chron 29r. The cause for this negative response in body size within soil-dwelling biota may be attributed to plant-community shifts in taxonomic composition and ecological strategies, which would have caused fundamental alterations to the diet of the herbivorous, subterranean insects. This study provides empirical evidence that the Lilliput effect was not restricted to marine environments during the aftermath of the K-Pg event.

Early Miocene outcrops near Karungu, Western Kenya, preserve a range of fluvio-lacustrine, lowland landscapes that contain abundant fossils of terrestrial and aquatic vertebrates. Primates are notably rare among these remains, although nearby early Miocene strata on Rusinga Island contain a rich assemblage of fossilized catarrhines and strepsirrhines. To explore possible environmental controls on the occurrence of early Miocene primates, we performed a deep-time Critical Zone (DTCZ) reconstruction focused on floodplain paleosols at the Ngira locality in Karungu. We specifically focused on a single stratigraphic unit (NG15), which preserves moderately developed paleosols that contain a microvertebrate fossil assemblage. Although similarities between deposits at Karungu and Rusinga Island are commonly assumed, physical sedimentary processes, vegetative cover, soil hydrology, and some aspects of climate state are notably different between the two areas. Estimates of paleoclimate parameters using paleosol B horizon elemental chemistry and morphologic properties are consistent with seasonal, dry subhumid conditions, occasional waterlogging, and herbaceous vegetation. The reconstructed small mammal community indicates periodic waterlogging and open-canopy conditions. Based on the presence of herbaceous root traces, abundant microcharcoal, and pedogenic carbonates with high stable carbon isotope ratios, we interpret NG15 to have formed under a warm, seasonally dry, open riparian woodland to wooded grassland, in which at least a subset of the vegetation was likely C4 biomass. Our results, coupled with previous paleoenvironmental interpretations for deposits on Rusinga Island, demonstrate that there was considerable environmental heterogeneity ranging from open to closed habitats in the early Miocene. We hypothesize that the relative paucity of primates at Karungu was driven by their environmental preference for locally abundant closed canopy vegetation, which was likely absent at Karungu, at least during the NG15 interval if not also earlier and later intervals that have not yet been studied in as much detail.