Fossil hominids from the Laetolil Beds

Leakey, Meave G.; Hay, Richard L.; Curtis, Garniss H.; Drake, Robert E.; Jackes, Mary; White, T. D.

doi:10.1038/262460a0

Cited by 201 publications

(69 citation statements)

References 14 publications

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“…Whereas their pattern of locomotion is likely to have included some arboreality, they were fully bipedal and did show many signs of advanced bipedal bone structure. The 3.5 million-year-old Laetoli footprints of Australopithecus afarensis show human-like proportions, arches, heel strike, and convergent big toes (40). Comparative anatomical analysis of human, apes, and fossil hominids indicate that A. afarensis had significant features of bipedality (39,41).…”

Section: Discussionmentioning

confidence: 99%

Inactivation of CMP- N -acetylneuraminic acid hydroxylase occurred prior to brain expansion during human evolution

Chou

Hayakawa

Díaz

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

319

236

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Humans are genetically deficient in the common mammalian sialic acid N-glycolylneuraminic acid (Neu5Gc) because of an Alu-mediated inactivating mutation of the gene encoding the enzyme CMP-N-acetylneuraminic acid (CMP-Neu5Ac) hydroxylase (CMAH). This mutation occurred after our last common ancestor with bonobos and chimpanzees, and before the origin of present-day humans. Here, we take multiple approaches to estimate the timing of this mutation in relationship to human evolutionary history. First, we have developed a method to extract and identify sialic acids from bones and bony fossils. Two Neandertal fossils studied had clearly detectable Neu5Ac but no Neu5Gc, indicating that the CMAH mutation predated the common ancestor of humans and Neandertals, Ϸ0.5-0.6 million years ago (mya). Second, we date the insertion event of the inactivating human-specific sahAluY element that replaced the ancestral AluSq element found adjacent to exon 6 of the CMAH gene in the chimpanzee genome. Assuming Alu source genes based on a phylogenetic tree of human-specific Alu elements, we estimate the sahAluY insertion time at Ϸ2.7 mya. Third, we apply molecular clock analysis to chimpanzee and other great ape CMAH genes and the corresponding human pseudogene to estimate an inactivation time of Ϸ2.8 mya. Taken together, these studies indicate that the CMAH gene was inactivated shortly before the time when brain expansion began in humankind's ancestry, Ϸ2.1-2.2 mya. In this regard, it is of interest that although Neu5Gc is the major sialic acid in most organs of the chimpanzee, its expression is selectively down-regulated in the brain, for as yet unknown reasons. hominid evolution ͉ sialic acids ͉ Alu sequences

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Section: Discussionmentioning

confidence: 99%

Inactivation of CMP- N -acetylneuraminic acid hydroxylase occurred prior to brain expansion during human evolution

Chou

Hayakawa

Díaz

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

319

236

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“…17). This was one of the features that led to the preliminary attribution of the Laetoli and part of the Hadar hominid collections to the early part of the Homo lineage (Leakey et al, 1976;Johanson and Taieb, 19761, and in Finally, we are not at all certain that the anteriorly and superiorly placed inferior transverse torus cited by Wolpoff is a genuine synapomorphy because this structure is rudimentary in H. habilis, whereas in A. africanus and "robust" Australopithecus species it is usually well developed.…”

Section: Africanus)mentioning

confidence: 95%

Cranial morphology of Australopithecus afarensis: A comparative study based on a composite reconstruction of the adult skull

Kimbel

White

Johanson

1984

American J Phys Anthropol

157

111

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The Pliocene hominid species Australopithecus afarensis is represented by cranial, dental, and mandibular remains from Hadar, Ethiopia, and Laetoli, Tanzania. These fossils provide important information about the cranial anatomy of the earliest known hominids. Because complete crania or skulls are not known, we produced a composite reconstruction of an adult male skull based on 13 specimens from the Hadar Formation. The reconstruction serves as a testable hypothesis regarding functional relationships in the A. afarensis skull and is the basis for the comparative study presented here. We examine six major aspects of cranial and mandibular anatomy. We combine our results with those of White et al. (1981) in a discussion of alternate hypotheses of early hominid phylogeny. In the cranium, jaws, and teeth A. afarensis exhibits a morphological pattern that we interpret as primitive for the Hominidae. Homo habilis retains a number of these primitive features for which A. africanus, A. robustus, and A. boisei share derived character states, particularly in the masticatory apparatus. Homo and "robust" species of Australopithecus share a suite of derived cranial base features. These shared traits may relate to upper facial orthognathium which is also common to these taxa and are probably indicative of parallelism rather than a close phylogenetic relationship. The cranial base characteristics of A.L. 333-45 do not, contrary to Olson's (1981) claims, provide evidence for an A. afarensis--"robust" Australopithecus sister group. When the range of mastoid variation in extant African pongids and A. afarensis is examined thoroughly, the Pliocene hominid appears to retain a primitive, rather than derived, morphology.

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“…Subsequent to this, A. anamensis, a species more derived than A. ramidus and probably transitional to A. afarensis, has been reported from the 3.9-4.2 myr interval (Leakey et al, 1995). A. afarensis becomes widespread by circa 3.5 myr, as represented by the Ethiopian and Tanzanian fossil record (Leakey et al, 1976;Johanson and White, 1979;White et al, 1993). Kimbel et al (1994) reported A. afarensis to have existed a t Hadar at circa 2.95 myr, exhibiting no detectable morphological difference from the circa 3.4 myr condition.…”

Section: The Early Recordmentioning

confidence: 96%

Mandibular postcanine dentition from the Shungura Formation, Ethiopia: Crown morphology, taxonomic allocations, and Plio-Pleistocene hominid evolution

Suwa

White

Howell

1996

Am. J. Phys. Anthropol.

212

119

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Over 200 hominid specimens were recovered by the International Omo Expedition of 1967-1976. Despite the fragmentary nature of this primarily dental collection, these hominid remains represent a major body of evidence about hominid evolution in eastern Africa during the 2-3 myr time period. Our analysis of the Omo dental collection is based on a large comparative sample of 375 quantifiable mandibular postcanine teeth of A. afarensis, A. africanus, A. aethiopicus, A. boisei, A. robustus, and early Homo. A total of 48 isolated mandibular premolars and molars of the Omo collection spanning the 2-3 myr time period is sufficiently preserved to allow reliable serial allocations and intertaxon comparisons and is the object of study in this paper. We present taxonomic identifications of these teeth and seven other mandibular specimens preserving tooth crowns. Metric analyses of this study include cusp area and crown shape variables taken on occlusal view diagrams. Nonmetric analyses were based on simultaneous observations of all relevant material to ensure accuracy of categorical evaluations. First, a combined metric and morphological evaluation was conducted to allocate each Omo tooth to either robust or nonrobust categories. Further taxonomic affinities were then examined. Our results indicate that nonrobust and robust lineages cooccur by circa 2.7 myr. We consider the Shungura robust specimens from Members C through F to represent A. aethiopicus. A significant phenetic transformation occurs at circa 2.3 myr, with the mosaic emergence of the derived A. boisei morphology across Member G times. Characterization of the East African nonrobust lineage is more difficult because of the comparatively subtle morphological differences seen among the dentitions of A. afarensis, A. africanus, and early Homo. The earlier Members B and C nonrobust specimens are difficult to evaluate and are considered indeterminate to genus or species. Both molars and premolars from Members E through G exhibit phenetic similarities to the early Homo condition and are considered as aff. Homo sp. indet. At present, there is no indication of multiple species in the Omo nonrobust sample at any time horizon. The 2-2.4 myr Omo nonrobust specimens exhibit some similarities to the stated Homo "rudolfensis" condition in size and morphology and are likely to represent the ancestral condition of the genus Homo. The bearing of these results on interpretations of early hominid evolution and diversification is considered.

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Fossil hominids from the Laetolil Beds

Cited by 201 publications

References 14 publications

Inactivation of CMP- N -acetylneuraminic acid hydroxylase occurred prior to brain expansion during human evolution

Inactivation of CMP- N -acetylneuraminic acid hydroxylase occurred prior to brain expansion during human evolution

Cranial morphology of Australopithecus afarensis: A comparative study based on a composite reconstruction of the adult skull

Mandibular postcanine dentition from the Shungura Formation, Ethiopia: Crown morphology, taxonomic allocations, and Plio-Pleistocene hominid evolution

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