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PubMed1999

Ontogeny and phylogeny of femoro-tibial characters in humans and hominid fossils: functional influence and genetic determinism.

Three different human femoro-tibial characters are selected as functionally relevant and derived hominid characters: femoral bicondylar angle, shape of the femoral distal epiphysis, and the tibial insertion of the lateral meniscus. The timing and mode of formation of these characters are investigated during human ontogeny and are shown to differ considerably. The available hominid fossils (Australopithecus afarensis and early Homo) are interpreted in the light of this ontogenetic analysis with the conclusion that, during hominid evolution, different modes of selection of these features must have occurred. In modern humans, the femoral bicondylar angle proves to be an epigenetic functional feature, which develops during early childhood growth. It is present in all australopithecines and we suggest that it developed following a change in their locomotor behavior and not upon a genomic change: the early practice of bipedal walking, with adducted knee joints, in the locomotor repertoire of infant australopithecines, was sufficient to promote this angle. Later in hominid evolution, the knee joint evolved from having a single insertion of the lateral meniscus on the tibia to a double one. While Australopithecus afarensis exhibits a single insertion, early Homo clearly exhibits a double insertion of the lateral meniscus on the tibia. The double insertion restricts the mobility of the meniscus on the tibial plateau, indicating a habitual practice of full extension movements of the knee joint. Among modern humans, the posterior insertion of the lateral meniscus appears early in fetal life. Consequently in early Homo, this new selected feature developed directly as a result of a genomic change. The derived shape of human distal femoral epiphysis includes a prominence of the lateral lip of the femoral trochlea, an elliptical profile of the lateral condyle, and an anteroposterior lengthening of the epiphysis. Analysis of human fetal and neonatal distal epiphyses shows that the prominence of the lateral lip of the trochlea arises before any use, and thus appears to be genetically determined. However, the postnatal development of this joint shows that this feature is also modified epigenetically by use. It is argued that the hominid femoro-patellar joint would have been reshaped following the process of genetic assimilation (Waddington [1942] Nature 3811:563-565). The prominence of the lateral lip of the femoral trochlea was probably selected following a two-staged process-first epigenetic, then genetic. Far from being a Lamarckian explanation, this concept applies precisely to adaptive characters that are induced by an external stimulus during a single lifetime and are replaced through natural selection by genetically based equivalent characters. The nature of the structures involved in the studied features is shown to be an important parameter determining their mode of development and selection.

Adaptation, Physiological↗

PubMed1999

Microscopic investigation in fossil hominoidea: a clue to taxonomy, functional anatomy, and the history of diseases.

Ten selected samples of fossilized bones (including Australopithecus, Homo erectus, Homo neandertalensis, and Homo sapiens sapiens) were examined by light microscopy using plane and polarized light. The histomorphological findings show that microscopic research adds much to what can be ascertained by marcoscopic examination or by X-ray techniques. In particular, emphasis was placed on taxonomy, functional anatomy of bones, and causes of some of the diseases of early hominids. Anat Rec (New Anat): 257:225-232, 1999.

Anatomy↗

PubMed2001

Origin of anthropoidea: dental evidence and recognition of early anthropoids in the fossil record, with comments on the Asian anthropoid radiation.

Among the earliest fossil anthropoid primates known are Catopithecus browni, Serapia eocaena, Arsinoea kallimos, and Proteopithecus sylviae, from the late Eocene quarry L-41, Fayum Depression, Egypt. Two of these taxa, C. browni and S. eocaena, may be the oldest known members of the Propliopithecidae and Parapithecidae, respectively, while A. kallimos and P. sylviae are archaic anthropoids of less certain familial affiliation. Dental features of C. browni, S. eocaena, A. kallimos, and P. sylviae are compared with those of younger propliopithecids and parapithecids from the Fayum in order to determine the morphocline polarities of dental features among these early anthropoids. From this, a basal African anthropoid dental morphotype is constructed. Among the features of this morphotype are: dental formula of 2.1.3.3; incisors subvertically implanted and somewhat spatulate; p2 as large as p3, both lacking paraconids; p4 weakly obliquely oriented but not exodaenodont; all lower molars with small paraconids present; upper anterior premolars lacking protocone; upper molars with small, cingular hypocones, all cheek teeth nonbunodont; and canines projecting but not necessarily sexually dimorphic. Comparisons are made between this African anthropoid morphotype and two of the best-represented proposed basal anthropoids, Eosimias and Djebelemur, with the result that neither appears to be a good candidate to have been ancestral to the African anthropoids. Other possible basal simians such as Algeripithecus, Tabelia, and Biretia also are evaluated but are too poorly known for adequate analysis. The larger-bodied Asian primates Pondaungia, Amphipithecus, and Siamopithecus also are not likely ancestors for African anthropoids, but like Eosimias they may share a common ancestry. Despite many recent claims of an Asian origin for anthropoids, the evidence remains far from compelling. The true origins of Anthropoidea remain obscure.

Africa↗

PubMed1996

Fossilization processes in siliceous thermal springs: trends in preservation along thermal gradients.

To enhance our ability to extract palaeobiological and palaeoenvironmental information from ancient thermal spring deposits, we have studied the processes responsible for the development and preservation of stromatolites in modern subaerial thermal spring systems in Yellowstone National Park (USA). We investigated specimens collected from silica-depositing thermal springs along the thermal gradient using petrographic techniques and scanning electron microscopy. Although it is known that thermophilic cyanobacteria control the morphogenesis of thermal spring stromatolites below 73 degrees C, we have found that biofilms which contain filamentous thermophiles contribute to the microstructural development of subaerial geyserites that occur along the inner rims of thermal spring pools and geyser effluents. Biofilms intermittently colonize the surfaces of subaerial geyserites and provide a favoured substrate for opaline silica precipitation. We have also found that the preservation of biotically produced microfabrics of thermal spring sinters reflects dynamic balances between rates of population growth, decomposition of organic matter, silica deposition and early diagenesis. Major trends in preservation of thermophilic organisms along the thermal gradient are defined by differences in the mode of fossilization, including replacement, encrustation and permineralization.

Bacteria↗

PubMed2002

From fins to limbs to fins: limb evolution in fossil marine reptiles.

Limb osteology and ontogenetic patterns of limb ossification are reviewed for extinct lineages of aquatically adapted diapsid reptiles. Phylogenies including these fossil taxa show that paddle-like limbs were independently derived, and that the varied limb morphologies were produced by evolutionary modifications to different aspects of the limb skeleton. Ancient marine reptiles modify the limb by reducing the relative size of the epipodials, modifying the perichondral and periosteal surface of elements distal to the propodials, and evolving extremes of hyperphalangy and hyperdactyly. Developmental genetic models illuminate gene systems that may have controlled limb evolution in these animals.

Alligators and Crocodiles↗

PubMed2004

Relationships between the fossil colobine Mesopithecus pentelicus and extant cercopithecoids, based on dental metrics.

Maxillary dental measurements from six specimens of Mesopithecus pentelicus, 64 cercopithecines, 59 African colobines, and 64 Asian colobines were analyzed by means of a "nested research design" that was specifically designed to explore the affiliation between fossils and extant cercopithecoids at different systematic levels. The results showed that the variation among taxonomic groups was mainly associated with size; however, in addition, interesting shape differences emerged, molars were shown to be important discriminators, Mesopithecus was confirmed as a colobine (as expected) and found to be closer to Asian species than to African ones, and the odd-nosed colobines were found to share more dental similarities with Mesopithecus than other colobines. The last finding is in contrast to previous studies, in which it was proposed that M. pentelicus is morphologically closely related to the African colobus and the gray langur (Semnopithecus).

Africa↗

PubMed2003

Scaling relationships between craniofacial sexual dimorphism and body mass dimorphism in primates: implications for the fossil record.

Craniofacial remains (the most abundant identifiable remains in the fossil record) potentially offer important information about body size dimorphism in extinct species. This study evaluates the scaling relationships between body mass dimorphism and different measures of craniofacial dimorphism, evaluating taxonomic differences in the magnitude and scaling of craniofacial dimorphism across higher taxonomic groups. Data on 40 dimensions from 129 primate species and subspecies demonstrate that few dimensions change proportionally with body mass dimorphism. Primates show general patterns of greater facial vs. neurocranial and orbital dimorphism, and greater dimorphism in lengths as opposed to breadths. Within any species, though, different craniofacial dimensions can yield very different reconstructions of size dimorphism. There are significant taxonomic differences in the relationships between size and craniofacial dimorphism among primate groups that can have a significant impact on reconstructions of body mass dimorphism. Hominoids tend to show lower degrees of facial dimorphism proportional to size dimorphism than other primates. This in turn implies that strong craniofacial dimorphism in Australopithecus africanus could imply very strong body size dimorphism, conflicting with the relatively modest size dimorphism inferred from postcrania. Different methods of estimating the magnitude of size dimorphism from craniofacial measurements yield similar results, and yield comparatively low percent prediction errors for a number of dimensions. However, confidence intervals for most estimates are so large as to render most estimates highly tentative.

Animals↗

PubMed2003

Functional capabilities of modern and fossil hominid hands: three-dimensional analysis of trapezia.

Three-dimensional (3D) trapezium models from Homo sapiens, Gorilla gorilla, Pan troglodytes, Australopithecus afarensis (A.L.333-80), and Homo habilis (O.H.7-NNQ) were acquired through laser digitizing. Least-square planes were generated for each articular surface, and the angles between the planes were compared. Each extant species displays an overall pattern that distinguishes it from the others. The observed angles in G. gorilla and P. troglodytes are more similar to one other than either is to H. sapiens. Our results, obtained from using new 3D modeling and analytical tools, raise interesting questions about the functional capabilities of the fossil trapezia. Multivariate statistical analyses indicate that A.L.333-80 is morphologically more similar to that of modern humans, whereas the O.H.7 trapezium is more similar to that of the gorilla. Significant differences between A.L.333-80 and the extant species occur, but some similarities to humans suggest the ability to form the distinctively human forceful pad-to-side and three-jaw chuck grips. Some key morphological differences from humans highlighted and quantified by our research suggest limitations in the functional capabilities of the O.H.7 trapezium, particularly in those that facilitate pronation at the base of the second metacarpal. If the O.H.7 trapezium represents part of the hand responsible for manufacturing and using the stone tools found at Olduvai, our results suggest that the hand manipulated the stones in a way for which we have no modern analog. Alternative considerations are that the O.H.7 trapezium is not representative of other trapezia from its species (i.e., N=1), or that it represents another primate or hominid species.

Animals↗

PubMed1976

A fossil hominid frontal from Velika Pećina (Croatia) and a consideration of Upper Pleistocene hominids from Yugoslavia.

Fossil hominid remains dating to the Upper Pleistocene in Yugoslavia are reviewed. Particular emphasis is placed on the assessment of a hominid frontal from the site of Velika Pećina in northwestern Croatia. This specimen represents the earliest absolutely-dated hominid associated with the Upper Paleolithic in Europe. Also the hominid material from the site of Veternica is discussed, and data are presented on the new remains from Sandalja. It is concluded that no Neandertal remains, except for Krapina, have been found in Yugoslavia.

Cephalometry↗

PubMed1979

Studies on the condition and structure of bone of the Saldanha fossil cranium.

The external surface of the Saldanha cranium shows extensive exfoliation and cracking. In a few places remnants of the probable original bone surfaces can be observed. These are orange-brown in color, contrasting with the nearly white color of exposed deeper layers, and are subdivided into small segments with pits in their centers. Causes of the color differences are uncertain but merit investigation. The surface cracking and exfoliation probably result from weathering before fossilization. This conclusion is based on the observation that the endocranial surfaces show no such effects, despite the scattering of the cranial fragments at the time of discovery. A depressed fracture in the frontal bone indicates a heavy blow at or shortly after the time of death. This blow probably created some of the fragments, but there are also incomplete fracture cracks which may have resulted from the blow. Unresolved taphonomic problems include the manner in which the cranium held together after decay of soft tissues allowed weathering, and the manner in which the fragments were subsequently scattered. Chips from the cranial vault indicate that the outer table was very thick, tending to support recent proposals that the specimen and assoicated fauna and tools are from a considerably earlier time period than originally believed. The surface damage to the brow ridges gives information on the structure of deeper layers. These are lacking orientation, supporting the hypothesis that hominid brow ridges are not primarily a response to masticatory forces, but may afford protection for the eyes.

Animals↗

PubMed1982

Allometric scaling in the dentition of primates and prediction of body weight from tooth size in fossils.

Tooth size varies exponentially with body weight in primates. Logarithmic transformation of tooth crown area and body weight yields a linear model of slope 0.67 as an isometric (geometric) baseline for study of dental allometry. This model is compared with that predicted by metabolic scaling (slope = 0.75). Tarsius and other insectivores have larger teeth for their body size than generalized primates do and they are not included in this analysis. Among generalized primates, tooth size is highly correlated with body size. Correlations of upper and lower cheek teeth with body size range from 0.90-0.97, depending on tooth position. Central cheek teeth (P44 and M11) have allometric coefficients ranging from 0.57-0.65, falling well below geometric scaling. Anterior and posterior cheek teeth scale at or above metabolic scaling. Considered individually or as a group, upper cheek teeth scale allometrically with lower coefficients than corresponding lower cheek teeth; the reverse is true for incisors. The sum of crown areas for all upper cheek teeth scales significantly below geometric scaling, while the sum of crown areas for all lower cheek teeth approximates geometric scaling. Tooth size can be used to predict the body weight of generalized fossil primates. This is illustrated for Aegyptopithecus and other Eocene, Oligocene, and miocene primates. Regressions based on tooth size in generalized primates yield reasonable estimates of body weight, but much remains to be learned about tooth size and body size scaling in more restricted systematic groups and dietary guilds.

Animals↗

PubMed1985

Variation in the developing root cone angle of the permanent mandibular teeth of modern man and certain fossil hominids.

The radiographic appearance of the developing root apex of 461 mandibular teeth was studied using ellipsopantomographs of 77 individuals. The angle formed by the mesial and distal aspects of the developing root cone was measured for each quarter of root development in the permanent mandibular teeth of each subject. Large values for this angle in the more coronal part of the root gradually decreased towards the root apex where values were small in all teeth studied. This gradual decrease in the angle of the developing root cone is concordant with the faster increase in root length but slower rates of dentinogenesis reported for the apical region of human teeth in the literature, as the decrease is likely to reflect the increasing numbers of odontoblasts that become involved in root formation as it proceeds apically. The developing root cone angles of one of the five fossil hominid specimens studied (KMN-ER 820) fall outside the range for the developing root cone angle of the developing premolar and permanent second molar roots in modern Homo sapiens and is evidence of a faster rate of root elongation than is typical for modern man.

Animals↗

PubMed1992

Reassessment of the paleoenvironment and preservation of hominid fossils from Hadar, Ethiopia.

Samples of paleosols from locality AL-333, known for numerous specimens of Australopithecus afarensis, were analyzed in order to reconstruct the original soils and environment of burial of the associated fossil hominids. The bones were found in swale-like features, within the calcareous and coarse-grained basal portion of a paleosol. This is more like an assemblage of bones buried during a single depositional episode, such as a flood, than an assemblage accumulated on a soil over a long period of time by carnivores or other means of death. What killed the hominids remains unclear, but considering the association of originally disarticulated bones of such hydraulically distinct types as phalanges and maxillae, it is very likely that they died and partially rotted at or very near this site. The paleosols at AL-333, here named the Fo and Go clay paleosols, have calcareous rhizoconcretions, granular surface horizons, prismatic peds, and shallow calcareous nodules and stringers like soils now supporting grassy woodland in semiarid regions. Although this group of hominids was buried in streamside gallery woodland, there is evidence from Laetoli, Tanzania, that A. afarensis ventured out into open wooded grassland as well. Evidence for this should be sought from other paleosols at Hadar.

Animals↗

PubMed1993

Body weight prediction in early fossil hominids: towards a taxon-"independent" approach.

The choice of a model taxon is crucial when investigating fossil hominids that clearly do not resemble any extant species (such as Australopithecus) or show significant differences from modern human proportions (such as Homo habilis OH 62). An "interhominoid" combination is not adequate either, as scaling with body weight is strongly divergent in African apes and humans for most skeletal predictors investigated here. Therefore, in relation to a study of seven long bone dimensions, a new taxon-"independent" approach is suggested. For a given predictor, its taxonomic "independence" is restricted to the size range over which the body weight-predictor relationship for African apes and humans converges. Different predictors produce converging body weight estimates (BWEs) for different size ranges: taxon-"independent" estimates can be calculated for small- and medium-sized hominids (e.g., for weights below 50 kg) using femoral and tibial dimensions, whereas upper limb bones provide converging results for large hominids (above 50 kg). If the remains of Australopithecus afarensis really belong to one species, the relationship of male (above 60 kg) to female body weight (approximately 30 kg) does not fall within the observed range of modern hominoids. Considering Sts 14 (22 kg) to represent a small-sized Australopithecus africanus, the level of encephalization lies well above that of extant apes. If OH 62 (approximately 25 kg), with limb proportions less human-like than those of australopithecines, indeed represents Homo habilis (which has been questioned previously), an increase in relative brain size would have occurred well before full bipedality, an assumption running counter to current assumptions concerning early human evolution.

Animals↗

PubMed1994

Comparison of four simple methods for estimating sexual dimorphism in fossils.

Estimating sexual dimorphism in skeletal and dental features of fossil species is difficult when the sex of individuals cannot be reliably determined. Several different methods of estimating dimorphism in this situation have been suggested: extrapolation from coefficients of variation, division of a sample about the mean or median into two subsamples which are then treated as males and females, and finite mixture analysis (specifically for estimating the maximum dimorphism that could be present in a unimodal distribution). The accuracy of none of these methods has been thoroughly investigated and compared in a controlled manner. Such analysis is necessary because the accuracy of all methods is potentially affected by fluctuations in either sample size, sex ratio, or the magnitude of intrasexual variability. Computer modeling experiments show that the mean method is the least sensitive to fluctuations in these parameters and generally provides the best estimates of dimorphism. However, no method can accurately estimate low to moderate levels of dimorphism, particularly if intrasexual variability is high and sex ratios are skewed.

Animals↗

PubMed2001

New fossil hominid calvaria from Indonesia--Sambungmacan 3.

A morphologically distinct partial calvaria of Homo cf. erectus from Java, Indonesia is described. The fossil hominid Sambungmacan 3 (Sm 3) was first discovered in 1977 from the banks of the Solo River near the village of Poloyo, Sambungmacan district, in central Java. It was later recovered in a New York City natural history establishment in 1999 and quickly returned to the Indonesian authorities. Examination of Sm 3 shows that the calvaria is well preserved with only portions of the cranial base missing. The most striking characteristics of Sm 3 include: the presence of a vertically rising forehead, more open occipital/nuchal and frontal angles, a more globular vault, and a cranial capacity within the Homo erectus range. Most notably absent in Sm 3 are a number of the classic characters attributed to Homo erectus, such as a strongly expressed angular torus and a continuous supratoral sulcus. The absence of such characters would normally place the calvaria outside the range of Homo erectus (sensu stricto), however, overall quantitative and qualitative morphological assessments of Sm 3 place it within the Homo erectus spectrum. The combination of the morphological characters in Sm 3 may be interpreted in several ways: 1.) the known cranial variation of H. erectus from Indonesia and China is extended; 2.) this calvaria shows evidence of evolutionary change within H. erectus; or 3.) more than one species of Homo existed in the (presumed) Middle Pleistocene of Java.)

Animals↗

PubMed2004

High-resolution computed tomography study of the cranium of a fossil anthropoid primate, Parapithecus grangeri: new insights into the evolutionary history of primate sensory systems.

Extant anthropoids have large brains, small olfactory bulbs, and high-acuity vision compared with other primates. The relative timing of the evolution of these characteristics may have important implications for brain evolution. Here computed tomography is used to examine the cranium of a fossil anthropoid, Parapithecus grangeri. It is found that P. grangeri had a relatively small brain compared with living primates. In addition, it had an olfactory bulb in the middle of the range for living primates. Methods for relating optic foramen area and other cranial measurements to acuity are discussed. Multiple regression is used to estimate retinal ganglion cell number in P. grangeri. Given currently available comparative data, P. grangeri seems to have had retinal ganglion cell counts intermediate for living primates, overlapping with the upper end of the range for strepsirrhines and possibly with the lower end for anthropoids.

Animals↗

PubMed2005

Evolutionary innovations in the fossil record: the intersection of ecology, development, and macroevolution.

The origins of evolutionary innovations have been intensively studied, but relatively little is known about their large-scale ecological patterns. For post-Paleozoic benthic marine invertebrates, which have the richest and most densely sampled fossil record, order-level taxa tend to appear first in onshore, disturbed habitats, even in groups that are now exclusively deep-water (so that present-day distributions are not reliable indicators of original environments). New results presented here show that the onshore-origination pattern is robust to shifts in taxonomic methods and to new paleontological discoveries, and the few available studies suggest that this pattern can also be seen in terms of excursions in morphospace or the acquisition of derived character states, without reference to taxonomic categories. The environmental pattern at high levels contrasts significantly with the origin of low-level novelties (such as defined genera and families) in crinoids, echinoids, and bryozoans, where first appearances tend to conform to their clade-specific bathymetric diversity gradients. This discordance seems to eliminate potential driving mechanisms that simply scale up within-population genetic or ecological processes. Little is known about the factors that promote the onshore-offshore expansion of orders across the continental shelf, or that drive some clades to abandon ancestral habitats for an exclusively deep-water distribution. The origin of evolutionary innovation must ultimately reside in developmental changes, but the onshore-origination bias could emerge from two different dynamics: the pattern could be primarily genetic and developmental, i.e., innovations truly arise onshore; or primarily ecological, i.e., innovations arise randomly but preferentially survive onshore. Whatever the ultimate driving mechanisms, these macroevolutionary patterns show that theories of large-scale evolutionary novelty must include an ecological dimension.

Animals↗