Experimental Perspective on Fallback Foods and Dietary Adaptations in Early Hominins

The robust jaws and large, thick-enameled molars of the Plio–Pleistocene hominins Australopithecus and Paranthropus have long been interpreted as adaptations for hard-object feeding. Recent studies of dental microwear indicate that only Paranthropus robustus regularly ate hard items, suggesting that the dentognathic anatomy of other australopiths reflects rare, seasonal exploitation of hard fallback foods. Here, we show that hard-object feeding cannot explain the extreme morphology of Paranthropus boisei. Rather, analysis of long-term dietary plasticity in an animal model suggests year-round reliance on tough foods requiring prolonged postcanine processing in P. boisei. Increased consumption of such items may have marked the earlier transition from Ardipithecus to Australopithecus, with routine hard-object feeding in P. robustus representing a novel behaviour

The Trail, 1963-12-11

https://soundideas.pugetsound.edu/thetrail_all/4030/thumbnail.jp

Relationship between foramen magnum position and locomotion in extant and extinct hominoids

International audienceFrom the Miocene Sahelanthropus tchadensis to Pleistocene Homo sapiens, hominins are characterized by a derived anterior position of the foramen magnum relative to basicranial structures. It has been previously suggested that the anterior position of the foramen magnum in hominins is related to bipedal locomotor behavior. Yet, the functional relationship between foramen magnum position and bipedal locomotion remains unclear. Recent studies, using ratios based on cranial linear measurements, have found a link between the anterior position of the foramen magnum and bipedalism in several mammalian clades: marsupials, rodents, and primates. In the present study, we compute these ratios in a sample including a more comprehensive dataset of extant hominoids and fossil hominins. First, we verify if the values of ratios can distinguish extant humans from apes. Then, we test whether extinct hominins can be distinguished from non-bipedal extant hominoids. Finally, we assess if the studied ratios are effective predictors of bipedal behavior by testing if they mainly relate to variation in foramen magnum position rather than changes in other cranial structures. Our results confirm that the ratios discriminate between extant bipeds and non-bipeds. However, the only ratio clearly discriminating between fossil hominins and other extant apes is that which only includes basicranial structures. We show that a large proportion of the interspecific variation in the other ratios relates to changes in facial, rather than basicranial, structures. In this context, we advocate the use of measurements based only on basicranial structures when assessing the relationship between foramen magnum position and bipedalism in future studies

Long-term patterns of body mass and stature evolution within the hominin lineage.

Body size is a central determinant of a species' biology and adaptive strategy, but the number of reliable estimates of hominin body mass and stature have been insufficient to determine long-term patterns and subtle interactions in these size components within our lineage. Here, we analyse 254 body mass and 204 stature estimates from a total of 311 hominin specimens dating from 4.4 Ma to the Holocene using multi-level chronological and taxonomic analytical categories. The results demonstrate complex temporal patterns of body size variation with phases of relative stasis intermitted by periods of rapid increases. The observed trajectories could result from punctuated increases at speciation events, but also differential proliferation of large-bodied taxa or the extinction of small-bodied populations. Combined taxonomic and temporal analyses show that in relation to australopithecines, early Homo is characterized by significantly larger average body mass and stature but retains considerable diversity, including small body sizes. Within later Homo, stature and body mass evolution follow different trajectories: average modern stature is maintained from ca 1.6 Ma, while consistently higher body masses are not established until the Middle Pleistocene at ca 0.5-0.4 Ma, likely caused by directional selection related to colonizing higher latitudes. Selection against small-bodied individuals (less than 40 kg; less than 140 cm) after 1.4 Ma is associated with a decrease in relative size variability in later Homo species compared with earlier Homo and australopithecines. The isolated small-bodied individuals of Homo naledi (ca 0.3 Ma) and Homo floresiensis (ca 100-60 ka) constitute important exceptions to these general patterns, adding further layers of complexity to the evolution of body size within the genus Homo. At the end of the Late Pleistocene and Holocene, body size in Homo sapiens declines on average, but also extends to lower limits not seen in comparable frequency since early Homo

Early Pleistocene large mammals from Maka’amitalu, Hadar, lower Awash Valley, Ethiopia

The Early Pleistocene was a critical time period in the evolution of eastern African mammal faunas, but fossil assemblages sampling this interval are poorly known from Ethiopia's Afar Depression. Field work by the Hadar Research Project in the Busidima Formation exposures (similar to 2.7-0.8 Ma) of Hadar in the lower Awash Valley, resulted in the recovery of an early Homo maxilla (A.L. 666-1) with associated stone tools and fauna from the Maka'amitalu basin in the 1990s. These assemblages are dated to similar to 2.35 Ma by the Bouroukie Tuff 3 (BKT-3). Continued work by the Hadar Research Project over the last two decades has greatly expanded the faunal collection. Here, we provide a comprehensive account of the Maka'amitalu large mammals (Artiodactyla, Carnivora, Perissodactyla, Primates, and Proboscidea) and discuss their paleoecological and biochronological significance. The size of the Maka'amitalu assemblage is small compared to those from the Hadar Formation (3.45-2.95 Ma) and Ledi-Geraru (2.8-2.6 Ma) but includes at least 20 taxa. Bovids, suids, and Theropithecus are common in terms of both species richness and abundance, whereas carnivorans, equids, and megaherbivores are rare. While the taxonomic composition of the Maka'amitalu fauna indicates significant species turnover from the Hadar Formation and Ledi-Geraru deposits, turnover seems to have occurred at a constant rate through time as taxonomic dissimilarity between adjacent fossil assemblages is strongly predicted by their age difference. A similar pattern characterizes functional ecological turnover, with only subtle changes in dietary proportions, body size proportions, and bovid abundances across the composite lower Awash sequence. Biochronological comparisons with other sites in eastern Africa suggest that the taxa recovered from the Maka'amitalu are broadly consistent with the reported age of the BKT-3 tuff. Considering the age of BKT-3 and biochronology, a range of 2.4-1.9 Ma is most likely for the faunal assemblage.info:eu-repo/semantics/publishedVersio

Fossils from Mille-Logya, Afar, Ethiopia, elucidate the link between Pliocene environmental changes and Homo origins

Several hypotheses posit a link between the origin of Homo and climatic and environmental shifts between 3 and 2.5 Ma. Here we report on new results that shed light on the interplay between tectonics, basin migration and faunal change on the one hand and the fate of Australopithecus afarensis and the evolution of Homo on the other. Fieldwork at the new Mille-Logya site in the Afar, Ethiopia, dated to between 2.914 and 2.443 Ma, provides geological evidence for the northeast migration of the Hadar Basin, extending the record of this lacustrine basin to Mille-Logya. We have identified three new fossiliferous units, suggesting in situ faunal change within this interval. While the fauna in the older unit is comparable to that at Hadar and Dikika, the younger units contain species that indicate more open conditions along with remains of Homo. This suggests that Homo either emerged from Australopithecus during this interval or dispersed into the region as part of a fauna adapted to more open habitats.info:eu-repo/semantics/publishedVersio

Early Pleistocene large mammals from Maka’amitalu, Hadar, lower Awash Valley, Ethiopia

The Early Pleistocene was a critical time period in the evolution of eastern African mammal faunas, but fossil assemblages sampling this interval are poorly known from Ethiopia ’ s Afar Depression. Field work by the Hadar Research Project in the Busidima Formation exposures (~2.7 – 0.8 Ma) of Hadar in the lower Awash Valley, resulted in the recovery of an early Homo maxilla (A.L. 666-1) with associated stone tools and fauna from the Maka ’ amitalu basin in the 1990s. These assemblages are dated to ~2.35 Ma by the Bouroukie Tuff 3 (BKT-3). Continued work by the Hadar Research Project over the last two decades has greatly expanded the faunal collection. Here, we provide a comprehensive account of the Maka ’ amitalu large mammals (Artiodactyla, Carnivora, Perissodactyla, Primates, and Proboscidea) and discuss their paleoecological and biochronological signi fi cance. The size of the Maka ’ amitalu assemblage is small compared to those from the Hadar Formation (3.45 – 2.95 Ma) and Ledi-Geraru (2.8 – 2.6 Ma) but includes at least 20 taxa. Bovids, suids, and Theropithecus are common in terms of both species richness and abundance, whereas carnivorans, equids, and megaherbivores are rare. While the taxonomic composition of the Maka ’ amitalu fauna indicates signi fi cant species turnover from the Hadar Formation and Ledi-Geraru deposits, turnover seems to have occurred at a constant rate through time as taxonomic dissimilarity between adjacent fossil assemblages is strongly predicted by their age difference. A similar pattern characterizes functional ecological turnover, with only subtle changes in dietary proportions, body size proportions, and bovid abundances across the composite lower Awash sequence. Biochronological comparisons with other sites in eastern Africa suggest that the taxa recovered from the Maka ’ amitalu are broadly consistent with the reported age of the BKT-3 tuff. Considering the age of BKT-3 and biochronology, a range of 2.4 – 1.9 Ma is most likely for the faunal assemblag

Neurocranium versus Face: A Morphometric Approach with Classical Anthropometric Variables for Characterizing Patterns of Cranial Integration in Extant Hominoids and Extinct Hominins

The relative importance of the two main cranial complexes, the neurocranium and the splanchnocranium, has been examined in the five species of extant hominoids and in a huge sample of extinct hominins using six standard craniometric variables that measure the length, width and height of each cranial module. Factor analysis and two-block partial least squares were used for establishing the major patterns of developmental and evolutionary integration between both cranial modules. The results obtained show that all extant hominoids (including the anatomically modern humans) share a conserved pattern of developmental integration, a result that agrees with previous studies. The pattern of evolutionary integration between both cranial modules in australopiths runs in parallel to developmental integration. In contrast, the pattern of evolutionary and developmental integration of the species of the genus Homo is the opposite, which is probably the consequence of distinctive selective regimes for both hominin groups.JAPC, JMJA and PP received fundings from Ministerio de Ciencia e Innovación, Gobierno de España (http://www.idi.mineco.gob.es), project CGL2011-30334, and Consejería de Economía, Innovación, Ciencia y Empleo, Junta de Andalucía, España (http://www.juntadeandalucia.es/organismo​s/economiainnovacioncienciayempleo.html), project P11-HUM-7248 and Research Groups RNM-146 and HUM-607

A volumetric technique for fossil body mass estimation applied to Australopithecus afarensis

Fossil body mass estimation is a well established practice within the field of physical anthropology. Previous studies have relied upon traditional allometric approaches, in which the relationship between one/several skeletal dimensions and body mass in a range of modern taxa is used in a predictive capacity. The lack of relatively complete skeletons has thus far limited the potential application of alternative mass estimation techniques, such as volumetric reconstruction, to fossil hominins. Yet across vertebrate paleontology more broadly, novel volumetric approaches are resulting in predicted values for fossil body mass very different to those estimated by traditional allometry. Here we present a new digital reconstruction of Australopithecus afarensis (A.L. 288-1; ‘Lucy’) and a convex hull-based volumetric estimate of body mass. The technique relies upon identifying a predictable relationship between the ‘shrink-wrapped’ volume of the skeleton and known body mass in a range of modern taxa, and subsequent application to an articulated model of the fossil taxa of interest. Our calibration dataset comprises whole body computed tomography (CT) scans of 15 species of modern primate. The resulting predictive model is characterized by a high correlation coefficient (r2 = 0.988) and a percentage standard error of 20%, and performs well when applied to modern individuals of known body mass. Application of the convex hull technique to A. afarensis results in a relatively low body mass estimate of 20.4 kg (95% prediction interval 13.5–30.9 kg). A sensitivity analysis on the articulation of the chest region highlights the sensitivity of our approach to the reconstruction of the trunk, and the incomplete nature of the preserved ribcage may explain the low values for predicted body mass here. We suggest that the heaviest of previous estimates would require the thorax to be expanded to an unlikely extent, yet this can only be properly tested when more complete fossils are available

Extraordinary Biomass-Burning Episode and Impact Winter Triggered by the Younger Dryas Cosmic Impact ∼12,800 Years Ago. 2. Lake, Marine, and Terrestrial Sediments

Part 1 of this study investigated evidence of biomass burning in global ice records, and here we continue to test the hypothesis that an impact event at the Younger Dryas boundary (YDB) caused an anomalously intense episode of biomass burning at ∼12.8 ka on a multicontinental scale (North and South America, Europe, and Asia). Quantitative analyses of charcoal and soot records from 152 lakes, marine cores, and terrestrial sequences reveal a major peak in biomass burning at the Younger Dryas (YD) onset that appears to be the highest during the latest Quaternary. For the Cretaceous-Tertiary boundary (K-Pg) impact event, concentrations of soot were previously utilized to estimate the global amount of biomass burned, and similar measurements suggest that wildfires at the YD onset rapidly consumed ∼10 million km2 of Earth’s surface, or ∼9% of Earth’s biomass, considerably more than for the K-Pg impact. Bayesian analyses and age regressions demonstrate that ages for YDB peaks in charcoal and soot across four continents are synchronous with the ages of an abundance peak in platinum in the Greenland Ice Sheet Project 2 (GISP2) ice core and of the YDB impact event (12,835–12,735 cal BP). Thus, existing evidence indicates that the YDB impact event caused an anomalously large episode of biomass burning, resulting in extensive atmospheric soot/dust loading that triggered an “impact winter.” This, in turn, triggered abrupt YD cooling and other climate changes, reinforced by climatic feedback mechanisms, including Arctic sea ice expansion, rerouting of North American continental runoff, and subsequent ocean circulation changes