Toward an Ecological Model of African Plio-Pleistocene Hominid Adaptations

What was the environmental complex in which the Plio-Pleistocene hominids were evolving? What situations selected f o r increasing variation in hominid morphology? A n ap-preciation of ecological dynamics is important to develop answers to those questions. The circumstances that accompany periodically more severe semiarid successions appear to have promoted a shqt in early australopithecine morphology toward hyper-robust forms. Successional dynamics (including ameliorated conditions) may have resulted in repeated sympat y of potentially competing lines. Through the process of character divergence, some earliergracile populations appear to have emerged more Homo-like by the end of the Pliocene. Palaeodemographic analysis combined with detailed ecological modeling offers new possibilities f o r explorato y retrodictions concerned with common and divergent hominid adaptations. [australopithecines. palaeoecology, early Homo]     

颧根与侧颅底重要结构的解剖学测量

目的：通过测量颧根与侧颅底各重要结构间的距离关系,为临床侧颅底外科手术治疗提供定位参考。方法：取成人颅骨标本50例（去颅盖标本8例,整颅42例）100侧,用游标卡尺、圆规和直尺测量颧根与侧颅底重要结构的距离。结果：实验测得左右侧颧根与外耳门前缘中点、乳突尖、茎突、翼突外侧板根部、舌下神经管外口、茎乳孔、颈静脉孔外缘、颈动脉管外口后缘、棘孔、卵圆孔、破裂孔的距离分别为22.30±2.84mm和22.02±3.27mm、40.37±3.21mm和40.56±3.54mm、32.53±2.78mm和32.92±2.68mm、35.13±3.14mm和35.19±2.74mm、49.29±2.88mm和48.98±2.87mm、32.92±2.44mm和33.05±2.61mm、35.15±2.86mm和34.68±3.13mm、33.17±2.78mm和33.17±2.72mm、28.83±2.62mm和28.68±2.63mm、31.15±2.76mm和31.49±2.73mm、43.67±3.32mm和44.15±3.02mm,左右侧数据无差异（P〉0.05）。结论：颧根可以作为侧颅底外科手术的定位标志,为直视条件下经颞下等入路的侧颅底外科手术提供解剖学依据。     

Petite bodies of the “robust” australopithecines

The “robust” australopithecines are often depicted as having large and powerfully built bodies to match their massive masticatory apparatus, but until 1988 the sample of postcranial remains attributed with certainty to this group was very limited. Almost nothing was known about the body of the East African “robust” australopithecine because taxonomic attribution of the postcrania was so uncertain. The body of the South African “robust” australopithecine had to be reconstructed from about a dozen isolated fragments of postcrania. Now a partial skeleton is attributed with confidence to the East African “robust” group along with several isolated bones. The South African sample has more than tripled. Analyses of this vastly expanded sample reveal that a large portion of postcrania attributed to “robust” australopithecines from Swartkrans Member 1 (35%) are from extraordinarily small-bodied individuals similar in size to a modern Pygmy weighing as little as 28 kg. These small elements include parts from the forelimb, spine, and hindlimb. About 22% of these Swartkrans 1 “robust” australopithecines are about the same size as a modern human weighing about 43 kgs and about 43% are larger than this standard but less than or equal to a 54 kg modern human. Approximately the same pattern is true for the Swartkrans 2 hominids, but taxonomic attribution is less certain. All of the Member 3 specimens are similar in size to the 45 kg standard. The partial skeleton of the East African “robust” australopithecine (KNM-ER 1500) has hindlimb joints that would correspond to a modern human of 34 kgs although the actual weight may be 5 to 10 kgs greater judging from shaft robusticity and forelimb size. The largest postcranial element attributed with some certainty to the East African “robust” australopithecine group (the talus, KNM-ER 1464) is about the same overall size as a modern human of 54 kgs, although its tibial facet is slightly smaller. Although many previous studies have hinted at the possibility that “robust” australopithecines had relatively small bodies, the new fossils provide substantial evidence that these creatures ranged from quite small to only moderate in body size relative to modern humans. These were the petite-bodied vegetarian cousins of our ancestors. Sexual dimorphism in body size appears to be greater than that in modern humans, similar to that in Pan, and less than that in Gorilla or Pongo, although such comparisons are of limited value given the small samples, poorly known body proportions, time averaging, and many other problems.     

Survivorship in gracile and robust australopithecines: a demographic comparison and a proposed birth model

The age distributions for the two australopithecine types are examined and found to differ significantly as does the difference in average age at death: 22.9 years for Australopithecus africanus and 18.0 years for Australopithecus robustus. Survivorship curves for the two types are constructed. In addition, the survivorship curve for the australopithecine sample is compared to one group of pre-urban Homo sapiens and found to be much the same, if it is assumed the young australopithecines are not adequately represented. A proposed birth model is presented and it is concluded that both australopithecine types followed a human model of reproduction.     

On a new australopithecine partial endocast.

A newly discovered right parietal/temporal/frontal fragment from an australopithecine natural endocast is described and compared to other australopithecine endocasts. This specimen shows that the central sulcus was arched, rather than straight as previously believed, and reveals frontal lobe convolutions not preserved in other australopithecine endocasts.     

New australopithecine endocast,SK 1585, from Swartkrans,South Africa

The new SK 1585 endocast, found by Dr. Brain at Swartkrans, 1966, is that of a robust australopithecine, matching the endocast of the Olduvai Hominid 5 in volume, and being almost identical to it in morphology. Aside from Olduvai Hominid 5 it is the only robust australopithecine endocast complete enough to permit easy reconstruction, as only a small portion of the frontal lobe is missing. While the gyral and sulcal patterns are not clear, there are a number of features indicating that the brain is not that of a pongid, but that is has been reorganized to a hominid pattern, particularly the occipital, parietal, and temporal lobes.     

Metrical analysis of the basicranium of extant hominoids and Australopithecus

The size and shape of the basicranium (seen in norma basilaris) in Homo, Gorilla, Pan, Pongo, and Australopithecus have been studied by recording the relative disposition of midline and bilateral bony landmarks. Fifteen linear measurements and two angles were used to relate the landmarks. The relatively longer and narrower cranial base of Gorilla, Pan, and Pongo is clearly contrasted with the wider, shorter cranial base in Homo sapiens. When the same observations were made on two “robust” and two “gracile” australopithecine crania, marked differences were found between the taxa. In the two “robust” specimens, the foramen magnum is located relatively further forward, and the axis of the petrous temporal bone is aligned more nearly with the coronal plane than in the two “gracile” crania. The implications of this apparent parallelism in basicranial morphology between Homo sapiens and the “robust” australopithecines are discussed.     

The ischium and hip extensor mechanism in human evolution

Although it is commonly stated that the ischia of the late Pliocene–early Pleistocene hominid fossils are long and ape-like, new interpretations show this view to be fallacious. An important new theory proposed by Robinson concludes that the gracile form of early hominid was an efficient biped, but the robust form was a less efficient biped and was adapted for tree climbing. Interpretation of the ischium is crucial to this idea. The present study shows that (1) the gracile and robust australopithecine ischia had similar relative lengths and (2) that the hamstring mechanism was probably very similar in the two forms of South African early hominid.     

The role of the zygomatic arch in the statics of the skull and its adaptive shape

The zygomatic arch of mammals is usually considered a phylogenetic relic of the fenestrations of the skull roof which may be observed in morphological sequences of primitive vertebrate skulls. If this concept is correct, the element is comparable (though not homologous) to the jugal arches of diapsid reptiles. Two major questions then remain unanswered: why different elements are maintained in reptiles and mammals during evolution, and why the arches are maintained as relics of ancestral forms. It is tempting to respond to the latter question with a very simple answer, namely that the elements function in order to sustain mechanical stresses. In this paper, we raise the questions which quality of stresses occurs in a primate skull within the zygomatic arches and what relationship these stresses hold to the morphology of these bony elements. An answer has been sought by means of finite element stress analysis. We found that the zygomatic arch in primate skulls represents a structure which carries, under all biologically relevant conditions, either compressive or tensile stresses. In a very simple model of the human skull under bite forces, a strip of stresses occurs lateral to the orbits, which seems roughly comparable to the zygomatic arch. Once such a structure exists and is used as an insertion of adductor muscles, it will be exposed to bending stress in side view and in frontal view. Morphological details of the zygomatic arch (curvature, profile, suture) are well suited to sustain the evoked stresses by a minimum of material.     

Head posture in the Hominoidea

The angle between the antero-posterior plane of the occipital condyles and a vertical axis at right angles to the Frankfort Horizontal was measured in Homo sapiens, Gorilla, Pan, Pongo and casts of two Neanderthal skulls, the Rhodesian skull and three australopithecine skulls. The angle was much greater in adult Homo sapiens and in the Neanderthal and australopithecine casts than in the adult groups of the three apes. In the immature groups, the angle underwent little change with age in Homo sapiens but in Gorilla and Pan the angle decreased markedly during the growth period. These findings can be readily correlated with the habitual bodily posture of each of the extant genera. In Homo sapiens , an upright posture is adopted early in life while in the African apes the young tend to move by brachiation and thus have an habitual posture of the spine closer to the vertical than in the "knuckle walking" adults. The large value of the angle in the Neanderthal casts also correlates well with the now widely held view that this group has a fully upright posture. However, the finding of a relatively low value for the angle in adult Pongo —a brachiator—runs counter to the general thesis that the angle is a direct reflection of overall posture and casts some doubt upon a conclusion that the large value of the angle in the australopithecine fossils necessarily indicates that these creatures stood upright.     

The australopithecines in review

Over the past 75 years since the discovery of the first australopithecine at Taung in southern Africa there has been a growing realisation that there is no simple, linear ancestor-descendant relationship connecting the australopithecines to laterHomo. There are currently at least ten recognised species of australopithecine, including two species of earlyHomo, that have been recently transferred to the genusAustralopithecus. These known species span the period between about 4.2-1.2 Ma and throughout the majority of this period there are multiple contemporaneous hominin species in eastern and southern Africa. This contribution reviews current knowledge about the australopithecine species and their inferred relationships to each other and to the genusHomo. At present it is impossible to resolve the phylogenetic relationships of the australopithecines with any degree of confidence. There is a growing realisation of the ‘bushy’ nature of hominin evolution throughout the australopithecine period and also of the inevitability that additional early hominin species remain to be discovered. Paper submitted for inclusion in the Proceedings of the International Symposium of the Ramón Areces Foundation “Evolution of the Human Family: State of the Art” held in Madrid on the 11–13 March, 1998     

中国更新世兔属化石两新种

中国更新世兔属(Lepus)化石较为丰富,尤其是周口店各化石地点产出了大量的标本。但受条件的限制,缺乏对现生骨骼标本的研究与对比,分类位置混乱或仅鉴定为未定种。详细观察研究了中国科学院动物研究所保存的现生兔属8种的187件头骨标本,归纳整理出Lepus各个种头骨与牙齿特征的个体差异和年龄变化以及稳定的特征。主要稳定特征包括:鼻骨基本形态,如长度、前后相对宽度等;额骨两侧凹陷深浅;眶上突上翘程度;颞窝的深浅及宽度;成年个体上间顶骨愈合,或不完全愈合;门齿前齿沟的形态及白垩质充填的情况;门齿孔宽,腭桥长及翼内窝宽度的比例关系;颧骨高度,浅层咬肌窝及咬肌突腹面三角的形态(反映出咬肌的发育程度);吻部形态;下颌骨基本形态(冠状突、上升支、齿隙骨体、颏孔位置等);颊齿基本形态等。在对现生标本观察研究的基础上,详细描述了周口店第13地点的兔头骨及颅后骨骼,命名一新种德氏兔Lepus teilhardisp. nov.。新种以下列特征区别于已知兔属各种:颅全长平均大于90 mm,眶上突轻微上翘,前支稍短,后支发育;额骨两侧凹陷浅;咬肌突腹面中等大小;颧弓浅层咬肌窝较深;翼内窝宽度明显大于腭桥最小纵径;门齿孔较细长;颞窝上突起较高;枕外结节向下延伸成一低脊;听泡较大;外枕骨较宽,顶视几乎覆盖岩乳骨及部分听泡;I2前齿沟"V"字形,内、外两侧的前缘较平直且几乎持平,充填少量白垩质;下颌骨冠状突倾斜。陕西蓝田陈家窝子发现的翁氏兔(Lepus wongi)也归入该种内。将山东淄博孙家山发现的标本命名为淄博兔Lepus ziboensissp. nov.。该种门齿前齿沟浅窄,充填白垩质;齿隙明显较长;腭桥较长;翼内窝宽度与腭桥长度近乎相等;P2外前褶沟窄浅,内前褶沟亦较浅;p3在1件标本上可见较浅的前内褶沟。根据共生动物群分析,淄博兔的时代为早更新世晚期,参照测年数据德氏兔的时代可能从早更新世晚期至中更新世早期。     

Some implications of relative biomechanical neck length in hominid femora

Demonstration of a size-based influence on relative biomechanical neck length of the femur predicts relatively longer necks for smaller femurs. Fossil hominids through the middle Pleistocene appear to have relatively longer femur necks than expected from this relation, excepting the two small australopithecine females. It is suggested that this variation results from smaller crania at birth in the fossils, and the possibility is raised that australopithecine populations were characterized by marked brain size differences at birth.     

以乳突切迹和翼钩为基点的侧颅底分区方法

目的:探讨以乳突切迹和翼钩为基点的侧颅底分区新方法.方法:在乳突切迹后缘、翼钩、枕骨大孔前缘中点和颧根四个结构间相互连线,区分侧颅底并测量连线的长度.结果:乳突切迹与侧颅底重要结构的关系密切,切迹后缘与翼钩连线和正中线将侧颅底分成内、外侧两个大的三角区,每个区再分成前后两个三角区共四个三角区,即腭和颞下三角、咽三角、关节和听三角、血管神经三角,其中血管神经三角的三边长度左右侧分别为(74.52±5.47)mm和(74.66±5.41)mm、(59.77±3.84)mm和(59.67±3.56)mm、(42.23±3.11)mm和(42.48±2.60)mm.结论:本研究提供了新的侧颅底分区方法,且血管神经三角的区域划分更为科学,为临床侧颅底手术入路和定位提供了解剖学参考.     

Size and shape of the australopithecine pelvic bone

The recovery of several specimens allows to have a good knowledge of australopithecine pelvic bone anatomy. But despite this, differences of opinion still exist regarding locomotory interpretations. The aim of this paper is to present results of a new morphometric analysis of australopithecine pelvic bones to try to understand the reasons of this situation. It appears that australopithecines exhibit the same overall architectural pattern as extant humans, the hominid pattern, just as all African apes also exhibit the same pongid pattern. But, in this pattern, it is possible to clearly depict two subpatterns corresponding to both generaAustralopithecus andHomo. Locomotory interpretations depend on the fact that some studies emphasize traits related to the hominid pattern (concluding then on modern bipedalism) and others focus on trains characterizing australopithecine sub-pattern (concluding then on non-modern bipedalism).     

Body shape shifting during growth permits tests that distinguish between competing geometric theories of metabolic scaling

Metabolism fuels all of life's activities, from biochemical reactions to ecological interactions. According to two intensely debated theories, body size affects metabolism via geometrical influences on the transport of resources and wastes. However, these theories differ crucially in whether the size dependence of metabolism is derived from material transport across external surfaces, or through internal resource‐transport networks. We show that when body shape changes during growth, these models make opposing predictions. These models are tested using pelagic invertebrates, because these animals exhibit highly variable intraspecific scaling relationships for metabolic rate and body shape. Metabolic scaling slopes of diverse integument‐breathing species were significantly positively correlated with degree of body flattening or elongation during ontogeny, as expected from surface area theory, but contradicting the negative correlations predicted by resource‐transport network models. This finding explains strong deviations from predictions of widely adopted theory, and underpins a new explanation for mass‐invariant metabolic scaling during ontogeny in animals and plants.     

Absence of foramen spinosum and abnormal middle meningeal artery in cranial series

In comparative and evolutionary aspects in humans, the middle meningeal artery enters the cranium through the foramen spinosum, whereas in great apes the middle meningeal artery can enter the cranium through foramen spinosum, through foramen ovale or through petrosphenoid fissure. Generally, in nonhuman primates the anterior meningeal system is associated with the ophthalmic branch of the internal carotid artery. The vessels joining the two systems pass through the additional channels: the superior orbital fissure or through the cranio-orbital foramen. In anatomically modern humans, the absence of foramen spinosum involves abnormal development and course of the middle meningeal artery and it is usually accompanied with replacement of the conventional middle meningeal artery with such, arising from the ophthalmic artery system. In these cases the middle meningeal artery most often enters the middle cranial fossa through the superior orbital fissure and rarely through the meningo-orbital foramen. All skulls, investigated in the present study, belonged to adult individuals of both sexes, conditionally grouped into three cranial series--contemporary male, medieval male, and medieval female series. The absence of foramen spinosum was established only among the medieval male and female series--in 1 (0.70%) male and in 1 (0.72%) female skull on the right side and in 3 (2.13%) female skulls on the left side. In 1 (0.72%) female skull, a small atypically located foramen spinosum was established on the right side. In all of the described cases, the intracranial meningeal grooves started from the lateral edge of the superior orbital fissure and probably reflect the ophthalmic origin of the middle meningeal artery.     

A new species of Haborophocoena, an Early Pliocene phocoenid cetacean from Hokkaido, Japan

A new species of phocoenid cetacean Haborophocoena , collected from the Early Pliocene Embetsu Formation, in the close vicinity to the site where the holotype of the type species of the genus Haborophocoena was retrieved, improves our knowledge of the anatomy of this cetacean. The new species, represented by a skull, lacking distal half of the rostrum, ear bones, and teeth, is significantly smaller than, but morphologically similar to, the type species Haborophocoena toyoshimai Ichishima and Kimura 2005 . This new record of Haborophocoena confirms the veracity of the genus Haborophocoena as a biological entity, contributes to understanding the interspecific variation, and suggests that the genus diversified in the northwestern Pacific of early Pliocene time. The adult-like degree of ossification in this small skull precludes it from being a juvenile of Haborophocoena toyoshimai . Autapomorphies of Haborophocoena minutus include narrow premaxilla on the dorsal surface of the rostrum, the anterior position of the premaxillary foramen, and a distinct ridge dividing a fossa on the lateral face of the base of the zygomatic process into the dorsal and the ventral halves, the zygomatic process rectangular in lateral profile, and its small size, which is the most compelling feature, making it a distinct species.     

Sagittal cresting in the South African australopithecines

The evidence for sagittal cresting, and more generally the position of the temporal lines is reviewed in the South African australopithecine sample. The position of the lines is dependent on both the allometric relation of the masticatory apparatus to cranial size and on individual variation. In the Swartkrans specimens, with generally bigger body size, the influence of allometry predominates, actually overshadowing the influence of individual variation. At Sterkfontein and Makapansgat with generally smaller body size and a resulting smaller allometric ratio, individual variation has a greater influence. Of the eleven adult South African specimens, the four largest are crested. The one smaller crested specimen comes from Sterkfontein. The crested Makapan specimen is intermediate in size. The pattern of australopithecine cresting is somewhat different from other hominoids, and is part of a total morphological pattern suggesting adaptation to a diet requiring powerful crushing during mastication.