New early Pleistocene hominin teeth from the Swartkrans Formation, South Africa

First articulating os coxae, femur, and tibia of a small adult Paranthropus robustus from Member 1 (Hanging Remnant) of the Swartkrans Formation, South Africa

Since paleontological work began there in 1948, Swartkrans (South Africa) has yielded hundreds of Early Pleistocene hominin fossils, currently attributed to (in ascending order of quantity) cf. Australopithecus africanus, Homo spp., and Paranthropus robustus. The bulk of that large sample comprises craniodental remains, with (mostly fragmentary) postcranial materials being much less abundant at the site. In that context, our announcement here of the first articulating partial os coxae, nearly complete femur, and complete tibia of a young adult hominin (SWT1/HR-2), excavated from the <2.3 to >1.7-million-year-old Hanging Remnant (Member 1) of the Swartkrans Formation, represents an important addition to the understanding of hominin postural and locomotor behavior in Early Pleistocene South Africa. We provide qualitative and quantitative descriptions and initial functional morphological interpretations of the fossils, based mostly on external bone morphology. Epiphyseal fusion data, element dimensions, the crural index, and live body stature and mass estimates that we provide all indicate that SWT1/HR-2 is one of the smallest known adult hominins in the fossil record. We discuss the paleobiological implications of these findings in relation to our taxonomic diagnosis of SWT1/HR-2 as representing P. robustus.

New modern and Pleistocene fossil micromammal assemblages from Swartkrans, South Africa: Paleobiodiversity, taphonomic, and environmental context

The oldest deposit at the hominin-bearing cave of Swartkrans, South Africa, is the Lower Bank of Member 1, dated to ca. 2.2 million years ago. Excavations of this unit have produced a diverse and extensive mammalian fossil record, including Paranthropus robustus and early Homo fossils, along with numerous Oldowan stone tools. The present study focuses on the taxonomic analysis of the micromammalian fossil assemblage obtained from recent excavations of the Lower Bank, conducted between 2005 and 2010, as part of the Swartkrans Paleoanthropological Research Project. The taxonomic composition of this assemblage is dominated by Mystromys, a rodent indicative of grassland environments. Taphonomic analysis indicates an accumulation of prey by Tyto alba (Barn owl) or a related species. Environments inferred from this evidence reflect an open landscape primarily covered by grassland vegetation, but they also feature components of wooded areas, rocky outcrops, and the proximity of a river. The Swartkrans fossil assemblage is compared with Cooper's D (dated to ca. 1.4 Ma) and a modern coprocoenosis of Bubo africanus (spotted eagle-owl) collected within the Swartkrans cave for taxonomic, taphonomic, and paleoecological perspectives. Contrasting fossil and modern micromammalian data provide a better understanding of accumulation processes and facilitate a diachronic reconstruction of changes in climate and landscape evolution. Issues regarding paleoenvironmental reconstruction methodologies based on micromammals are also discussed.

New hominin dental remains from the ∼2.04-1.95 Ma Drimolen Main Quarry, South Africa

BACKGROUND

The Drimolen Palaeocave site is situated within the UNESCO Fossil Hominid Sites of South Africa World Heritage Area and has yielded numerous hominin fossils since its discovery in 1992. Most of these fossils are represented by isolated dental elements, which have been attributed to either of two distinct hominin genera, Paranthropus and Homo.

AIM

This paper provides morphological descriptions for a further 19 specimens that have been recovered from the ∼2.04-1.95 Ma Drimolen Main Quarry (DMQ) deposits since 2008. This paper also discusses the two primary hypotheses used to explain Paranthropus robustus variation: sexual dimorphism, and micro-evolution within a lineage.

SUBJECTS AND METHODS

These 19 fossils are represented by 47 dental elements and expand the sample of DMQ early Homo from 13 to 15, and the sample of Paranthropus robustus from 69 to 84.

RESULTS

The evidence presented in this paper was found to be inconsistent with the sexual dimorphism hypothesis.

CONCLUSION

Some support was found for the micro-evolution hypothesis.

New hominin dental remains from the Drimolen Main Quarry, South Africa (1999–2008)

Objectives

Twenty‐four dental specimens from the Drimolen Main Quarry (DMQ) are described. This increases the number of DMQ Paranthropus robustus specimens from 48 to 63 and DMQ Homo specimens from 8 to 12. This allows reassessment of the proposed differences between the DMQ P. robustus assemblage and that of Swartkrans. Analysis conducted assesses intraspecific and inter‐locality variation.

Materials and Methods

We examined the P. robustus and early Homo assemblages from South Africa. Morphology was observed using a hand lens and a binocular microscope. Mesiodistal and buccolingual measurements were taken using plastic‐tipped calipers. Summary statistics were generated and patterns of variability in P. robustus were assessed through box plots and Mann–Whitney U tests.

Results

Comparison between the expanded DMQ and Swartkrans P. robustus assemblages demonstrates overlap in size. Ten dental variables show statistically significant differences.

Discussion

The expanded P. robustus sample allowed us to re‐examine previous analyses of differences in tooth size between the samples. While analyses presented here show a high degree of overlap in the MD and BL dimensions of the two assemblages, significant differences were found in the mean values of these variables in the postcanine maxillary teeth—consistent with previous analyses. Two current hypotheses may explain this pattern: 1) dental size increase through the P. robustus lineage or 2) different sample composition between the two sites. Small sample sizes for all permanent dental classes in the DMQ assemblage represents a limitation on this analysis and interpretations thereof. Any addition to the DMQ or the Swartkrans samples may alter these results.

New fossils from Kromdraai and Drimolen, South Africa, and their distinctiveness among Paranthropus robustus

Most fossil hominin species are sampled with spatial, temporal or anatomical biases that can hinder assessments of their paleodiversity, and may not yield genuine evolutionary signals. We use new fossils from the Kromdraai (Unit P) and Drimolen sites (South Africa) to provide insights into the paleodiversity of the Lower Pleistocene robust australopith, Paranthropus robustus. Our focus is the morphology of the temporal bone and the relationships between size and shape (allometry) of the semi-circular canals (SCC), an aspect that has not yet been investigated among southern African australopiths. We find significant size and shape SCC differences between P. robustus from Kromdraai, Drimolen and Swartkrans. This site-related variation is consistent with other differences observed on the temporal bone. P. robustus from Kromdraai Unit P is distinctive because of its smaller temporal bone and SCC, and its proportionally less developed posterior SCC, independently of age and sex. We emphasize the importance of allometry to interpret paleodiversity in P. robustus as either the consequence of differences in body size, or as yet unknown factors. Some features of the inner ear of P. robustus represent directional selection soon after its origin, whereas the size and shape variations described here may result from evolutionary changes.

The Earliest South African Hominids

The earliest South African hominids (humans and their ancestral kin) belong to the genera Australopithecus, Paranthropus, and Homo, with the oldest being a ca. 3.67 million-year-old nearly complete skeleton of Australopithecus (StW 573) from Sterkfontein Caves. This skeleton has provided, for the first time in almost a century of research, the full anatomy of an Australopithecus individual with indisputably associated skull and postcranial bones that give complete limb lengths. The three genera are also found in East Africa, but scholars have disagreed on the taxonomic assignment for some fossils owing to historical preconceptions. Here we focus on the South African representatives to help clarify these debates. The uncovering of the StW 573 skeleton in situ revealed significant clues concerning events that had affected it over time and demonstrated that the associated stalagmite flowstones cannot provide direct dating of the fossil, as they are infillings of voids caused by postdepositional collapse.

A new absolute date from Swartkrans Cave for the oldest occurrences of Paranthropus robustus and Oldowan stone tools in South Africa

The Early Pleistocene site of Swartkrans in South Africa's Cradle of Humankind World Heritage Site has been significant for our understanding of the evolution of both early Homo and Paranthropus, as well as the earliest archaeology of southern Africa. Previous attempts to improve a faunal age estimate of the earliest deposit, Member 1, had produced results obtained with uranium-lead dating (U-Pb) on flowstones and cosmogenic burial dating of quartz, which placed the entire member in the range of >1.7/1.8 Ma and <2.3 Ma. In 2014, two simple burial dates for the Lower Bank, the earliest unit within Member 1, narrowed its age to between ca. 1.8 Ma and 2.2 Ma. A new dating program using the isochron method for burial dating has established an absolute age of 2.22 ± 0.09 Ma for a large portion of the Lower Bank, which can now be identified as containing the earliest Oldowan stone tools and fossils of Paranthropus robustus in South Africa. This date agrees within one sigma with the U-Pb age of 2.25 ± 0.08 Ma previously published for the flowstone underlying the Lower Bank and confirms a relatively rapid rate of accumulation for a large portion of the talus.

Drimolen cranium DNH 155 documents microevolution in an early hominin species

Paranthropus robustus is a small-brained extinct hominin from South Africa characterized by derived, robust craniodental morphology. The most complete known skull of this species is DNH 7 from Drimolen Main Quarry, which differs from P. robustus specimens recovered elsewhere in ways attributed to sexual dimorphism. Here, we describe a new fossil specimen from Drimolen Main Quarry, dated from approximately 2.04-1.95 million years ago, that challenges this view. DNH 155 is a well-preserved adult male cranium that shares with DNH 7 a suite of primitive and derived features unlike those seen in adult P. robustus specimens from other chronologically younger deposits. This refutes existing hypotheses linking sexual dimorphism, ontogeny and social behaviour within this taxon, and clarifies hypotheses concerning hominin phylogeny. We document small-scale morphological changes in P. robustus associated with ecological change within a short time frame and restricted geography. This represents the most highly resolved evidence yet of microevolutionary change within an early hominin species.

The Oldowan industry from Swartkrans cave, South Africa, and its relevance for the African Oldowan

The oldest recognized artifacts at the Swartkrans cave hominid-bearing site in South Africa have long been known to occur in the Lower Bank of Member 1, now dated with the cosmogenic nuclide burial method to ca. 1.8-2.19 Ma. However, the affinities of this industry have been debated due to small sample size. In this paper we present newly excavated material from the Lower Bank retrieved since 2005 in the Swartkrans Paleoanthropological Research Project. The sample is now large enough to confirm its affinity with the Oldowan industrial complex. The assemblage is highly expedient and core reduction strategies are largely casual. Although freehand flaking is present, the bipolar technique is most significant, even in non-quartz raw materials. The Swartkrans assemblage shows some significant contrasts with the Sterkfontein Oldowan, ca. 2.18 Ma, which can be explained by its closer proximity to raw material sources, its somewhat different geographic context, and its more expedient nature. The Swartkrans Oldowan now provides us with the first good indication of Oldowan variability in southern Africa, where only two sizeable assemblages have thus far been discovered. Comparisons are made with other sites across Africa that help to place this variability within our overall understanding of the Oldowan industrial complex.