Early hominin auditory capacities

Studies of sensory capacities in past life forms have offered new insights into their adaptations and lifeways. Audition is particularly amenable to study in fossils because it is strongly related to physical properties that can be approached through their skeletal structures. We have studied the anatomy of the outer and middle ear in the early hominin taxa Australopithecus africanus and Paranthropus robustus and estimated their auditory capacities. Compared with chimpanzees, the early hominin taxa are derived toward modern humans in their slightly shorter and wider external auditory canal, smaller tympanic membrane, and lower malleus/incus lever ratio, but they remain primitive in the small size of their stapes footplate. Compared with chimpanzees, both early hominin taxa show a heightened sensitivity to frequencies between 1.5 and 3.5 kHz and an occupied band of maximum sensitivity that is shifted toward slightly higher frequencies. The results have implications for sensory ecology and communication, and suggest that the early hominin auditory pattern may have facilitated an increased emphasis on short-range vocal communication in open habitats

Macromammalian faunas, biochronology and palaeoecology of the early Pleistocene Main Quarry hominin-bearing deposits of the Drimolen Palaeocave System, South Africa

The Drimolen Palaeocave System Main Quarry deposits (DMQ) are some of the most prolific hominin and primate-bearing deposits in the Fossil Hominids of South Africa UNESCO World Heritage Site. Discovered in the 1990s, excavations into the DMQ have yielded a demographically diverse sample of Paranthropus robustus (including DNH 7, the most complete cranium of the species recovered to date), early Homo, Papio hamadryas robinsoni and Cercopithecoides williamsi. Alongside the hominin and primate sample is a diverse macromammalian assemblage, but prior publications have only provided a provisional species list and an analysis of the carnivores recovered prior to 2008. Here we present the first description and analysis of the non-primate macromammalian faunas from the DMQ, including all 826 taxonomically identifiable specimens catalogued from over two decades of excavation. We also provide a biochronological interpretation of the DMQ deposits and an initial discussion of local palaeoecology based on taxon representation.The current DMQ assemblage consists of the remains of minimally 147 individuals from 9 Orders and 14 Families of mammals. The carnivore assemblage described here is even more diverse than established in prior publications, including the identification of Megantereon whitei, Lycyaenops silberbergi, and first evidence for the occurrence of Dinofelis cf. barlowi and Dinofelis aff. piveteaui within a single South African site deposit. The cetartiodactyl assemblage is dominated by bovids, with the specimen composition unique in the high recovery of horn cores and dominance of Antidorcas recki remains. Other cetartiodactyl and perissodactyl taxa are represented by few specimens, as are Hystrix and Procavia; the latter somewhat surprisingly so given their common occurrence at penecontemporaneous deposits in the region. Equally unusual (particularly given the size of the sample) is the identification of single specimens of giraffoid, elephantid and aardvark (Orycteropus cf. afer) that are rarely recovered from

Dental Ontogeny in Pliocene and Early Pleistocene Hominins

Until recently, our understanding of the evolution of human growth and development derived from studies of fossil juveniles that employed extant populations for both age determination and comparison. This circular approach has led to considerable debate about the human-like and ape-like affinities of fossil hominins. Teeth are invaluable for understanding maturation as age at death can be directly assessed from dental microstructure, and dental development has been shown to correlate with life history across primates broadly. We employ non-destructive synchrotron imaging to characterize incremental development, molar emergence, and age at death in more than 20 Australopithecus anamensis, Australopithecus africanus, Paranthropus robustus and South African early Homo juveniles. Long-period line periodicities range from at least 6–12 days (possibly 5–13 days), and do not support the hypothesis that australopiths have lower mean values than extant or fossil Homo. Crown formation times of australopith and early Homo postcanine teeth fall below or at the low end of extant human values; Paranthropus robustus dentitions have the shortest formation times. Pliocene and early Pleistocene hominins show remarkable variation, and previous reports of age at death that employ a narrow range of estimated long-period line periodicities, cuspal enamel thicknesses, or initiation ages are likely to be in error. New chronological ages for SK 62 and StW 151 are several months younger than previous histological estimates, while Sts 24 is more than one year older. Extant human standards overestimate age at death in hominins predating Homo sapiens, and should not be applied to other fossil taxa. We urge caution when inferring life history as aspects of dental development in Pliocene and early Pleistocene fossils are distinct from modern humans and African apes, and recent work has challenged the predictive power of primate-wide associations between hominoid first molar emergence and certain life history variables

Average crown formation times (in days) determined by histological methods.

<p>Tooth/cusp types: U—upper, L—lower, I—incisor, C—canine, P—premolar, M—molar, buc—buccal cusp, ling—lingual cusp, mb—mesiobuccal cusp, ml—mesiolingual cusp, db—distobuccal cusp, dl—distolingual cusp. <i>Homo sapiens</i> European (EUR) and South African (SA) ranges and sample sizes given in refs. 54, 83. <i>Pan troglodytes</i> data modified from refs. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118118#pone.0118118.ref072" target="_blank">72</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118118#pone.0118118.ref084" target="_blank">84</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118118#pone.0118118.ref085" target="_blank">85</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118118#pone.0118118.ref088" target="_blank">88</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118118#pone.0118118.ref104" target="_blank">104</a>]; <i>Gorilla gorilla</i> data from refs. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118118#pone.0118118.ref010" target="_blank">10</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118118#pone.0118118.ref089" target="_blank">89</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118118#pone.0118118.ref105" target="_blank">105</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118118#pone.0118118.ref106" target="_blank">106</a>]; samples sizes for extant apes are given in parentheses when greater than one. Fossil hominin sample sizes are given in parentheses when greater than one; <i>A</i>. <i>anamensis</i> values reported for periodicity of 5 or 6 days in KNM-KP 34725; StW 151 values based on cuspal daily secretion rates of 5.53 um/day (<i>A</i>. <i>africanus</i>) from ref. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118118#pone.0118118.ref053" target="_blank">53</a>] and 6.06 um/day (early <i>Homo</i>, determined from this study); KB 5223 values based on cuspal daily secretion rates from ref. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118118#pone.0118118.ref057" target="_blank">57</a>] and long-period line periodicity values of 12 or 13.</p><p>Average crown formation times (in days) determined by histological methods.</p

Multiscale synchrotron imaging of a fossil <i>Homo</i> juvenile individual.

<p>DNH 67 (right lower first molar: left), DNH 71 (right upper central incisor: middle), and DNH 70 (left upper first molar: right). Images are from scans performed with the following voxel sizes: 20 μm (upper row), 5 μm (middle row), and 0.7 μm (lower row; DNH 67: left, DNH 70: right). An identical internal developmental defect pattern confirmed that the two molars, which were found isolated but in close proximity, came from the same individual. They also both show an identical long-period line periodicity of 8 days, as 8 light and dark bands (cross-striations illustrated in white brackets) can be seen between successive long-period lines (Retzius lines illustrated by white arrows). It was not possible to determine the age death for this individual due to postmortem loss of the incisor cervix and dentine from all teeth.</p

Ages predicted from extant human molar calcification standards compared to known- or histologically-derived ages.

<p>Two values are presented for <i>A</i>. <i>anamensis</i> KNM-KP 34725 due to uncertainty in the periodicity value. Data on extant human children derive from panoramic X-rays of known-age European and North African children, representing an expanded sample originally detailed in [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118118#pone.0118118.ref054" target="_blank">54</a>]. Fossil <i>Homo sapiens</i> and <i>Homo neanderthalensis</i> samples are from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118118#pone.0118118.ref054" target="_blank">54</a>]; <i>Pan troglodytes</i> are known-age wild western chimpanzees [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118118#pone.0118118.ref072" target="_blank">72</a>].</p

Long-period line periodicity values in Pliocene and early Pleistocene hominins, extant humans, and African apes.

<p>Two values (5 or 6 days) are presented for <i>A</i>. <i>anamensis</i> KNM-KP 34725 due to some uncertainty (indicated by “?”), as shown in Fig. B in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118118#pone.0118118.s001" target="_blank">S1 File</a>. Individual hominin values and sample sizes of extant taxa are given in Tables A and B in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118118#pone.0118118.s001" target="_blank">S1 File</a>, respectively.</p

Average molar crown formation times (in days) in early hominins and extant apes and humans.

<p>UM1 ml cusp = maxillary first molar mesiolingual cusp; LM1 ml cusp = mandibular first molar mesiolingual cusp. UM1 ml cusp of <i>A</i>. <i>anamensis</i> from ref. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118118#pone.0118118.ref065" target="_blank">65</a>]; LM1 ml cusp of <i>A</i>. <i>afarensis</i> from ref. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118118#pone.0118118.ref047" target="_blank">47</a>]. Extant comparative data sources are given in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118118#pone.0118118.t002" target="_blank">Table 2</a>.</p