Plio-Pleistocene Fossil Record Research Articles

Upper Pleistocene deposits from the Cauca Valley

The rise of the Isthmus of Panama is one of the major biogeographical events of the Cenozoic. It is a massive natural experiment in biological migrations, as lands formerly separated—South America and Central/North America—became connected. There is, however, a difference in timing between the final closure of the Isthmus (4.2-3.5 Ma) and the onset of the massive mammal migrations (i.e., Great American Biotic Interchange, GABI, 2.7 Ma). This time lag has been brought up to suggest that other factors rather than a land connection were major drivers of the GABI. A large biome change from forest to savanna in Central America and Northwestern South America could have provided the conduit for accelerating the biotic interchange between both continents. This hypothesis has been rarely tested as the Plio-Pleistocene fossil record of those regions has not been sufficiently studied. Gheny K. Shuster discovered a brand new Upper Pleistocene fossil deposit in and under the Cauca River (Southwestern Colombia), one of such possible migration corridors. We conducted a field geophysical and sedimentological study to understand the geometry of the fossil-rich deposits, dated them using carbon isotopes (C14), and assessed the type of biome (savanna versus forest) that dominated the region by looking at pollen samples. We found that the conglomerates accumulated in lenticular bodies, perpendicular to the modern course of the Cauca River during the Late Pleistocene in alluvial fan settings. The vegetation corresponds to a tropical dry forest and there is no evidence of extensive savannas. The Cauca River deposits could become a relevant site for the Neotropical Pleistocene.

Intrataxonomic trends in herbivore enamel δ13C are decoupled from ecosystem woody cover.

Analysis of enamel stable carbon isotopes (δ13Cenamel) of fossil herbivores is an important tool for making inferences about Plio-Pleistocene vegetation structure in Africa and the environmental context of hominin evolution. Many palaeoecological studies implicitly or explicitly assume that individual variation in C3-C4 plant consumption among fossil herbivores directly reflects the abundance of C3 (trees, shrubs) or C4 (low-altitude tropical grasses) vegetation. However, a strong link between δ13Cenamel of herbivores and ecosystem vegetation structure has not been rigorously established. Here we combine δ13Cenamel data from a large dataset (n = 1,643) with multidecadal Landsat estimates of C3 woody cover across 30 African ecosystems to show that there is little relationship between intrataxonomic variation in δ13Cenamel and vegetation structure. This is especially true when removing forested ecosystems (>80% woody cover)-which numerous lines of evidence suggest are rare in the Plio-Pleistocene fossil record of eastern Africa-from our analyses. Our findings stand in contrast with the common assumption that variation in herbivore δ13Cenamel values reflects changes in the relative abundance of C3-C4 vegetation. We conclude that analyses using herbivore δ13Cenamel data to shed light on the environmental context of hominin evolution should look to explicitly community-level approaches for making vegetation inferences.

Carbon and strontium isotope ratios shed new light on the paleobiology and collapse of Theropithecus, a primate experiment in graminivory

The rise and spread of tropical grasslands was a signal event in the Cenozoic, causing many ungulates to evolve adaptations to a diet of graminoid tissues, or graminivory. In parallel, a lineage of monkeys (Theropithecus) is distinguished among primates for its large size and commitment to graminivory, a trait expressed by species throughout the Plio-Pleistocene fossil record and T. gelada, the sole surviving species today. An open question concerns the mechanics of how fossil species of Theropithecus handled graminoid tissues. They might have exhibited preference, selecting tissues within a given tuft, or they might have practiced indiscriminate bulk-feeding in a manner similar to large grazing ungulates. To differentiate between these handling behaviors, we used time- and graminivore-calibrated carbon stable isotope values to show progressive reliance on high-throughput bulk-feeding graminivory. Variation in this behavior explains a significant amount of variation in body mass through time, and we describe these covarying traits, which peaked during the Pleistocene, as evolutionary traps. To support this characterization, we report evidence of temporal increases in strontium isotope variability among North African theropiths, a result that suggests greater lifetime travel and energetic costs in response to diminishing food resources, a probable factor in the extinction of T. oswaldi, the largest monkey that ever lived.

New Pliocene remains of Camelus grattardi (Mammalia, Camelidae) from the Shungura Formation, Lower Omo Valley, Ethiopia, and the evolution of African camels

Camels are exceptionally rare in the Plio-Pleistocene fossil record of Africa, hindering attempts to understand the evolution of this family on the continent. Here we describe recently collected camel specimens from the Shungura Formation, Lower Omo Valley, Ethiopia, and attribute these remains to Camelus grattardi. The new specimens date to the late Pliocene (~3 to 2.6 Ma) and consist of three upper molars, one upper premolar, and two proximal metatarsals. The dental specimens confirm this species’ small P4 relative to its molars, a trait that differs significantly from all extant and fossil Old World camels. The metatarsals indicate that C. grattardi was similar in size to the living Bactrian camel, C. bactrianus. Phylogenetically, we find no suitable ancestor, sister, or descendant of the eastern African fossil camel, which suggests greater lineage diversity in Plio-Pleistocene Camelus than previously recognised. Microwear analyses suggest that C. grattardi was likely a mixed-feeder preferring browse, which is consistent with carbon isotopes of enamel from the Turkana Basin. A review of the fossil record of African camels suggests no clear paleoenvironmental association, as fossil camels occur in a range of environments from dry savannas with no permanent water bodies to closed woodlands along the paleo-Omo River.

Cercopithecoid humeri from Taung support the distinction of major papionin clades in the South African fossil record

Associated cercopithecoid postcrania are rare in the Plio-Pleistocene fossil record, particularly in the case of South African karst cave sites. However, as clear postcranial differences between major papionin clades have been documented, it should be possible to assign isolated papionin postcrania to the Cercocebus/Mandrillus and Papio/Lophocebus/Theropithecus groups wherever sufficient anatomy is preserved. Here, we demonstrate that two partial humeri preserved at Taung, UCMP 56693 and UCMP 125898, are most likely attributable to the Cercocebus/Mandrillus and Papio/Lophocebus/Theropithecus clades, respectively. Univariate analyses (ANOVAs and t-tests) and multivariate analyses (discriminant function analyses) of humeral features, combined with a phylogenetic analysis of 24 humeral characters, all support our assessment. Given that the overwhelming number of craniodental specimens at Taung are attributable to two papionin taxa, Procercocebus antiquus (a member of the Cercocebus/Mandrillus clade) and Papio izodi (a purported fossil species of the modern genus Papio), we assign UCMP 56693 to Pr. antiquus and UCMP 125868 to P. izodi with a high degree of confidence. Implications for cercopithecoid evolution and biogeography are discussed, with a particular emphasis on these two fossil taxa.

The massive fossil humerus from the Oldowan horizon of Gombore I, Melka Kunture (Ethiopia, >1.39 Ma)

A well-preserved distal portion of a left humerus was discovered in 1976 during excavations directed by J. Chavaillon at the Gombore I site, in the Melka Kunture area (Ethiopia). The specimen, labelled Gombore IB-7594 (formally Melka Kunture 3, or MK3), was found in situ within unit 2 of level B, which is dated to >1.39 Ma and includes a rich Oldowan Paleolithic assemblage. Although MK3 has never been described in detail, it appeared in the literature several times and, from a taxonomic point of view, has been alternatively regarded as Homo, Australopithecus or Paranthropus. According to our analysis, MK3 exhibits a suite of features that fit the variability of the genus Homo and does not display any clear Australopithecus/Paranthropus affinity. Nevertheless, MK3 adds a great deal of variability to the genus Homo, at least as far as the Early Pleistocene fossil record is concerned. In particular, our quantitative approach, which combines traditional morphometric analyses and geometric morphometrics, highlights traits that are uncommon among the Plio-Pleistocene fossil record, while affinities with Mid-to-Late Pleistocene representatives of Homo are observed. In addition, the large size of MK3 suggests that this humerus belonged to an individual whose body weight approached 90 kg, far from the range of body size known for Homo representatives in the Early Pleistocene and as big as those of extant humans or even gorillas. We suggest that such peculiar features are of interest when regarded from an ecological perspective; thus, dimension and morphology of MK3 may be considered as an exaptation that became useful when early humans dispersed to high altitudes such as those of the upper Awash basin on the Ethiopian plateau, at heights above 2000 m.

Plio-Pleistocene climatic change had a major impact on the assembly and disassembly processes of Iberian rodent communities

Comprehension of changes in community composition through multiple spatio-temporal scales is a prime challenge in ecology and palaeobiology. However, assembly, structuring and disassembly of biotic metacommunities in deep-time is insufficiently known. To address this, we used the extensively sampled Iberian Plio-Pleistocene fossil record of rodent faunas as our model system to explore how global climatic events may alter metacommunity structure. Through factor analysis, we found five sets of genera, called faunal components, which co-vary in proportional diversity over time. These faunal components had different spatio-temporal distributions throughout the Plio-Pleistocene, resulting in non-random changes in species assemblages, particularly in response to the development of the Pleistocene glaciations. Three successive metacommunities with distinctive taxonomic structures were identified as a consequence of the differential responses of their members to global climatic change: (1) Ruscinian subtropical faunas (5.3–3.4 Ma) dominated by a faunal component that can be considered as a Miocene legacy; (2) transition faunas during the Villafranchian–Biharian (3.4–0.8 Ma) with a mixture of different faunal components; and (3) final dominance of the temperate Toringian faunas (0.8–0.01 Ma) that would lead to the modern Iberian assemblage. The influence of the cooling global temperature drove the reorganisation of these rodent metacommunities. Selective extinction processes due to this large-scale environmental disturbance progressively eliminated the subtropical specialist species from the early Pliocene metacommunity. This disassembly process was accompanied by the organisation of a diversified metacommunity with an increased importance of biome generalist species, and finally followed by the assembly during the middle–late Pleistocene of a new set of species specialised in the novel environments developed as a consequence of the glaciations.

Did shell-crushing crabs trigger an escalatory arms race in the aftermath of a Late Neogene regional mass extinction event? An experimental test

A regional mass extinction event in the late Neogene western Atlantic is widely thought to have generated evolutionary opportunities for survivors, including enemy-related adaptation (escalation). The Strombus alatus species complex is one potential example of this phenomenon. Strombid gastropods are abundant in the Plio-Pleistocene fossil record and Recent in subtropical Florida, and the percentage of these shells bearing a row of short spines on the last whorl increased from nearly zero to almost 100% over this time. As shell ornamentation is one of the most frequently cited defenses against both peeling and crushing predators, we exposed live spined and spineless S. alatus to the stone crab Menippe, one of its natural enemies and the predator responsible for shells scars commonly found on modern and fossil S. alatus shells, to test whether the increase in expression of shell spines in this species complex is consistent with an adaptive or induced response to intensifying predation pressure from durophagous crabs. We also utilize random variation in prey shell length, diameter, and lip thickness to quantify the relative importance of additional shell parameters thought to deter attacks from durophagous crabs. The central finding of this study is that neither thicker shell lips nor the modern configuration of spines determine whether S. alatus will be more likely to survive Menippe attacks or have less severe shell damage. In our experiments, the only shell trait associated with reduced damage and increased probability of survival was whorl diameter. We conclude that menippid crabs, at least those crabs within the range of large, adult sizes used in this experiment, probably did not play a primary role in the changing expression of Strombus spines on the last whorl in the post-Pliocene of Florida or elsewhere in tropical America. This conclusion is consistent with the position that faunal-scale increases in expression of defensive shell traits in the post-Pliocene of Florida were driven more by differential extinction of lightly armored species than escalatory responses to increasing crab predation pressure. However this conclusion is tentative and additional data are needed to explore this hypothesis fully.

Isoprenoids, steranes, and hopanes as markersof the origin and maturity of sedimentary organic matterFirst report of Lutra simplicidens (Carnivora, Mustelidae, Lutrinae) in the Early Pleistocene of the Upper Valdarno (Italy) and the origin of European otters

Fossil Lutrinae are very rare in the Plio-Pleistocene fossil record. We report here a right mandible of an otter from the Early Pleistocene of the Upper Valdarno Basin (Italy) kept in the collections of the Natural History Museum of London. The specimen, recovered in the XIX century, remained undescribed until today. Morphologic and morphometric characters of the mandible allow us to refer it to Lutra simplicidens Thenius, 1965, a fossil otter recorded in Europe in the late Early to Middle Pleistocene, thus representing the oldest report of this species. This finding adds a new interesting taxon to the late Villafranchian faunal assemblage of the Upper Valdarno and reinforces the hypothesis of an African origin of L. simplicidens , because of its affinities with L. fatimazohrae Geraads, 1997 from Morocco.

Plio-Pleistocene fossil record of large predators in Iberia: Diversity, home range and climatic change

We investigated the patterns of change in diversity and home range-size structure of the latest Miocene–Pleistocene Iberian carnivores to recognize the tempo and mode of the major shifts, and place them in the context of late Cenozoic climatic changes. The database consists of 36 selected and taxonomically revised faunal lists. A general pattern of carnivore diversity from Iberia shows three maxima in diversity that can be correlated with major global changes. The first coincides with the glacial trend during Pliocene, starting at 2.7–2.6Ma, with the onset of glacial cycles of 41ka; second maximum happened at the beginning of the Middle Pleistocene and can be correlated with the switch at 1Ma; third maximum in diversity occurs at the end of Middle Pleistocene, when the amplitude of interglacials shifted from cooler to warmer interglacials. The most significant shifts in Carnivora diversity and home range-size patterns were linked to dispersal phases that were tracked by a renovation of the carnivore guild. From the patterns in home range-size structure it seems that some multifaceted, and not always straight, interactions exist between ecological and climatic change and shifts in home range-size. The onset of the Holocene home range-size structure in Iberian carnivores traces back to a high diversity pulse at the end of the Middle Pleistocene.

Paleoecological significance of coupling metrics of successful and unsuccessful shell-breaking predation: Examples using Neogene bivalve prey

Traces of durophagous predation on molluscan prey have been used as proxies to reconstruct the nature and intensity of predator–prey interactions in both the fossil record and the modern oceans. Available metrics for the quantification of these interactions have focused either on failed/unsuccessful or successful attacks in isolation. Because predator–prey dynamics and subsequent adaptation depend on both the success as well as the failure of the predator, we propose to combine these two components to increase our ability to reconstruct the dynamics of these relationships in the past. In this study, two bivalve clades, Chione and Varicorbula, from Florida's Plio-Pleistocene fossil record are used to show how the combination of repair frequency and estimated crushing mortality serve as better constraints on interpreting changes in predator–prey interactions as compared to the more limited interpretations when these two metrics are used independently. When used in tandem, the two metrics document an overall predation intensity increase from the upper Pliocene Pinecrest Beds (upper Tamiami Formation to the overlying lower Pleistocene Caloosahatchee, and a decrease in successful attack frequency in the upper Pleistocene Bermont Formations. However, patterns were different in the upper Pleistocene Ft. Thompson Formation: successful attacks increased for Chione and decreased for Varicorbula. In detail, however, the overall dynamics for these two predator–prey systems varied, and they also changed differently throughout the studied interval.

Just a few: rodents and lagomorphs in the Plio-Pleistocene fossil record of the Upper Valdarno Basin

The Plio-Pleistocene vertebrate fossil record of the Upper Valdarno Basin (Tuscany, Italy) is well known because of the large mammal collections. Although the small mammals have a documentation that is not even comparable with that of the large mammals; their record from Upper Valdarno Basin is known since early 1800's papers and includes a number of type specimen of species named by early researchers. We present here an overview of the rodents and lagomorphs distribution within the stratigraphic framework of the Upper Valdarno Basin.

Mitochondrial relationships and divergence dates of the African colobines: evidence of Miocene origins for the living colobus monkeys

The African colobines represent a neglected area of cercopithecid systematics. Resolving the phylogenetic relationships and estimating divergence dates among the living forms will provide insight into the evolution of this group and may shed light upon the evolution of other African primates as well. This is the first molecular assessment of the evolutionary relationships among the modern colobus monkeys, which are comprised of the black-and-white, olive, and red colobus groups. Over 4,000 base pairs of mitochondrial DNA were amplified and sequenced in over 40 colobus monkey individuals incorporating representatives from all commonly recognized species. Gene trees were inferred using maximum likelihood and Bayesian inference, and penalized likelihood was employed to estimate mitochondrial divergence dates among the sampled taxa. The results are congruent with some aspects of previous phylogenetic hypotheses based on morphology and vocalizations, although the relationships among several West and Central African taxa differ to some degree. The divergence date analysis suggests that the black-and-white, olive, and red colobus had diverged from one another by the end of the Miocene, and that by the Plio-Pleistocene many of the species lineages were already present. This demonstrates that the initial extant colobus monkey diversification occurred much earlier than previously thought and was likely part of the same adaptive radiation that produced the diverse colobine taxa seen in the African Plio-Pleistocene fossil record. The lack of early members from the modern lineages in fossiliferous deposits suggests that they resided in part in the forests of Central and West Africa, which also currently harbor the highest levels of colobus monkey diversity. These forests should not be ignored in models of Plio-Pleistocene human and nonhuman primate evolution.

Crab scars reveal survival advantage of left-handed snails

Biological asymmetries are important elements of the structure and function of many living organisms. Using the Plio-Pleistocene fossil record of crab predation on morphologically similar pairs of right- and left-handed snail species, we show here for the first time, contrary to traditional wisdom, that rare left-handed coiling promotes survival from attacks by right-handed crabs. This frequency-dependent result influences the balance of selection processes that maintain left-handedness at the species level and parallels some social interactions in human cultures, such as sports that involve dual contests between opponents of opposite handedness.

Plio-Pleistocene Carnivora of eastern Africa: species richness and turnover patterns

This paper presents an up-to-date and detailed overview of the Plio-Pleistocene fossil record of Carnivora in eastern Africa. Major events in the carnivoran lineages present in the region are discussed and stratigraphic ranges of all species-level taxa are provided. The compiled data are used for quantitative analyses of species richness and turnover. Sampling is considered to be adequate for the interval 3.6–1.5 Mya, and poorer in the half-million-year time slices before and after this interval. Species richness peaks around 3.6–3.0 Mya and declines gradually from that time until the end of the time period analysed. Calculation of origination and extinction rates indicate that there are two peaks of origination: at 3.9–3.3 Mya (although the earlier half of this interval is biased through poor sampling) and at 2.1–1.8 Mya. The origination rate is zero in the interval 3.0–2.4 Mya. The extinction rate peaks at around 3.0 Mya after which it falls slightly, remaining nearly constant until 1.8 Mya, after which it increases considerably. The data support the hypothesis that the modern carnivoran guild of eastern Africa originated relatively recently, mostly within the last million years. There is no support in these data for a turnover pulse in Carnivora between 3 and 2 Mya. © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society, 2005, 144, 121–144.

The Harvey Lecture Series: Reflections on Early Human Ancestors

The study of Plio-Pleistocene hominids has been dominated by arguments about phylogenetic relationships. This is, in part, because other issues have seemed to be generally settled. It is argued that reconstructions of past hominid species, far from being settled, need much more work, especially from a perspective that expects the past to be generally unlike the present. Now that the Plio-Pleistocene fossil record is becoming adequate, it should be possible to improve reconstructions of species; understanding evolutionary transitions is likely to prove less tractable.