Brief communication: Possible third molar impactions in the hominid fossil record

Impacted third molars affect 15%–20% of modern Americans and Western Europeans. In contrast, third molar impactions have not been reported in the early hominid fossil record. It is uncertain whether the lack of reports reflects an absence of impactions or a failure to recognize them. This communication is intended to raise awareness of the possibility of impactions by describing the appearance of impacted teeth and by noting two possible instances of impaction in early hominids. Specifically, the mandibular third molars of the Sterkfontein specimen, STS52b (Australopithecus africanus), and the left maxillary third molar of the Lake Turkana specimen, KNM-WT17400 (Australopithecus boisei), are positioned in a manner which suggests that they would not have erupted normally. Both specimens also exhibit strong crowding of the anterior dentition, providing further support for the view that these individuals lacked sufficient space for normal eruption of the third molars. Other published reports of dental crowding in the hominid fossil record are noted, and it is suggested that more attention be paid to dental impaction and dental crowding in hominid evolution. © 1993 Wiley-Liss, Inc.     

The mixed dentition and associated skull fragments of a juvenile fossil hominid from Sterkfontein,South Africa

In April–May 1983, the late A.R. Hughes and his field team recovered more than 40 bone fragments and teeth from a single solution pocket of the Sterkfontein Formation. After preparation and reconstruction by JMC, it was recognised that these fragments represent a single juvenile individual (Stw 151), consisting of more than 40 cranial and dental parts, with mixed dentition. It constitutes the most complete set of jaws and teeth of an early hominid child since the Taung child was recovered in 1924. In this paper, the morphological and metrical features of the individual teeth are described. The other associated skull fragments (right ramus of the mandible, left petrous bone, right glenoid region) are also described. Comparisons are made with other South (and East) African fossil hominids. The beautiful preservation simultaneously of most of the deciduous teeth and of the permanent teeth exposed in their crypts allows an accurate analysis of the developmental sequence. A report on the dental developmental status of this juvenile is presented. On the basis of the microanatomical study of the developing permanent teeth, the estimated age at death is 5.2–5.3 years. Reconstructions of the maxillary and mandibular arcades are also offered. The morphological and metrical features of Stw 151 raise the possibility that it may represent a hominid more derived towards an early Homo condition than the rest of the A. africanus sample from Member 4. Am J Phys Anthropol 106:425–465, 1998. © 1998 Wiley-Liss, Inc.     

The biological and chronological maturation of early hominids

Recent studies on the rate and pattern of dental development indicate that the growth and maturation of early hominids were more similar to the extant apes than to modern humans. This contrasts with the previously held opinion derived from combined dental development, pattern and attrition studies claiming that early hominids were more hominine in their development (Mann, 1975). This paper explores the origin of this difference of opinion and reviews immature hominid dentitions with the benefit of improved radiographs and new data on the pattern and rate of pongid dental development. Paranthropus and Australopithecus specimens are shown to possess an ape-like development pattern but incisor development is specialized in the former and superficially human-like in pattern. The present and recent studies on dental development rate and pattern justify the position that early hominids were more ape-like in their growth and development. Therefore, ages at death calculated from pongid dental development schedules are provided for most immature early hominids. More detailed studies of early hominid developmental biology are now possible. It is suggested that divergent heterochronic processes characterize changes in brain/body proportions during hominid evolution. Relative rates of bone remodeling processes can now be identified on early hominid skeletons. The paleodemographic analysis of early hominids is little changed by the developmental model one chooses.     

The eruption pattern of the permanent incisors and first permanent molars in Australopithecus (Paranthropus) robustus

This study aims to reassess the claim that the eruption sequence of the permanent incisor and first permanent molar teeth of Australopithecus (Paranthropus) robustus is identical with that in modern Homo sapiens. Eight fossil hominid mandibles of equivalent dental developmental age were chosen for comparative study. Emphasis has been placed upon the comparative timing of events within the growth period rather than eruption sequence alone. The results of this study indicate that Homo sapiens and Australopithecus (Paranthropus) robustus share the same pattern of permanent molar and incisor eruption and that this is significantly different from the pattern of eruption shared by the great apes, Australopithecus africanus and Australopithecus afarensis.     

Stretching the time span of hominin evolution at Kromdraai (Gauteng,South Africa): Recent discoveries

The Plio-Pleistocene locality of Kromdraai B has yielded the type specimen of Paranthropus robustus, as well as 27 additional fossil hominin specimens. In a number of both cranial and dental features, the states shown by the Kromdraai Paranthropus are more conservative when compared to the more derived conditions displayed by both South African conspecifics and the post-2.3 Ma eastern African Paranthropus boisei. Since 2014, we excavated the earliest known infilling of the Kromdraai cave system in a previously unexplored area. This new locality provided as yet 2200 identifiable macrovertebrate fossils, including 22 hominins, all tied in the earliest part of the stratigraphic sequence, representing three distinct depositional periods. Since we report here, for the first time, the occurrence of fossil hominins in Members 1 and 2, our discoveries stretch the time span of hominin evolution at Kromdraai and contribute to a better understanding of the origin of Paranthropus in southern Africa.     

Relative dental development of Upper Pleistocene hominids compared to human population variation

The relative development of permanent teeth in samples of Neandertal/archaic Homo and Early Modern/Upper Paleolithic hominids is compared to the range of variability found in three recent human samples. Both fossil hominid samples are advanced in relative M2 and M3 development compared to white French-Canadians, but only the Neandertal/archaic Homo M3 sample is advanced when compared to black southern Africans. Both fossil hominid samples are delayed in relative I1 and P3 development compared to the recent human samples. Two hypotheses concerning the significance of the advanced M3 and M2 development found in both hominid groups and southern Africans compared to French-Canadians are discussed. The first postulates that the differences in relative molar development are due simply to variation in tooth/jaw size relationships. The second postulates that the relatively advanced M3 and M2 development found in the fossil hominids and southern Africans is a correlate of their potential for advanced skeletal maturation compared to French-Canadians and other European-derived populations. It appears that dental development patterns have continued to evolve from the Upper Pleistocene to present times, and that Neandertals and Early Moderns shared similar patterns of relative dental development. © 1996 Wiley-Liss, Inc.     

Paranthropus boisei: An example of evolutionary stasis?

Of the presently recognised early hominid species, Paranthropus boisei is one of the better known from the fossil record and arguably the most distinctive; the latter interpretation rests on the numbers of apparently derived characters it incorporates. The species as traditionally diagnosed is distributed across approximately one million years and is presently confined to samples from East African sites. The hypodigm has been examined for evidence of intraspecific phyletic evolution, with particular emphasis on the areas best represented in the fossil record, namely the teeth and mandible. The results of this examination of 55 mandibular and dental variables, which uses the Γ test statistic for the detection of trend, and nonparametric spline regression (Loess regression) for investigating pattern and rate of temporal change, show that within Paranthropus boisei sensu stricto most evidence of temporally related morphological trends relates to the morphology of the P₄ crown. There is little or no evidence of any tendency to increase in overall size through time. Fossils from the Omo Shungura Formation and West Turkana which have been recovered from a time period earlier than the P. boisei sensu stricto hypodigm resemble the latter taxon in some features, but differ from it in aspects of cranial morphology. There is insufficient fossil evidence of the earlier taxon to tell whether it changes through time, but when trends of 47 mandibular and dental variables are assessed across the combined East African “robust” australopithecine sample, there is evidence for a relatively abrupt change around 2.2–2.3 Myr in approximately 25% of the dental and mandibular remains. Some of these changes correspond with the temporal trends within P. boisei sensu stricto, but others, such as mandible height, do not. If the earlier material is ancestral to P. boisei sensu stricto, evidence from the teeth and jaws is consistent with a punctuated origin for the latter taxon. © 1994 Wiley-Liss, Inc.     

Molar microwear textures and the diets of Australopithecus anamensis and Australopithecus afarensis

Many researchers have suggested that Australopithecus anamensis and Australopithecus afarensis were among the earliest hominins to have diets that included hard, brittle items. Here we examine dental microwear textures of these hominins for evidence of this. The molars of three Au. anamensis and 19 Au. afarensis specimens examined preserve unobscured antemortem microwear. Microwear textures of these individuals closely resemble those of Paranthropus boisei, having lower complexity values than Australopithecus africanus and especially Paranthropus robustus. The microwear texture complexity values for Au. anamensis and Au. afarensis are similar to those of the grass-eating Theropithecus gelada and folivorous Alouatta palliata and Trachypithecus cristatus. This implies that these Au. anamensis and Au. afarensis individuals did not have diets dominated by hard, brittle foods shortly before their deaths. On the other hand, microwear texture anisotropy values for these taxa are lower on average than those of Theropithecus, Alouatta or Trachypithecus. This suggests that the fossil taxa did not have diets dominated by tough foods either, or if they did that directions of tooth–tooth movement were less constrained than in higher cusped and sharper crested extant primate grass eaters and folivores.     

Further analysis of mandibular molar crown and cusp areas in Pliocene and early Pleistocene hominids

Crown and cusp areas of mandibular molars were measured and analyzed on a sample of 249 specimens attributed to Australopithecus afarensis, A. africanus, A. (Paranthropus) robustus, A. (P.) boisei, and early Homo. In addition to intertaxon comparisons, we compared data that had been collected independently by two of the authors using methods that differ slightly in technique of measurement. Interobserver differences were evaluated by the t-test of paired comparisons, method error statistic, percent differences, and principal component analysis. Results suggest that between-technique error of measurement of overall crown area is small. Error estimates for individual cusp area measurements were of larger relative magnitude. However, these were not sufficient to detract from the conclusions derived from comparative analyses. Our results are in general agreement with previous assessments of early hominid dental size. Crown areas of A. africanus, however, exhibit a mosaic pattern, with M1 similar in size to that of A. afarensis and early Homo, and M2 and M3 similar in size to that of A. robustus. Intertaxon comparisons of relative cusp area were undertaken by univariate statistics and principal component analysis. These analyses revealed that while A. (P.) robustus and A. (P.) boisei both possess mandibular molars with cusp proportions significantly different from the ‘non-robust’ taxa, these differences are substantially greater in A. (P.) boisei. © 1994 Wiley-Liss, Inc.     

Experimental perspective on fallback foods and dietary adaptations in early hominins

The robust jaws and large, thick-enameled molars of the Plio–Pleistocene hominins Australopithecus and Paranthropus have long been interpreted as adaptations for hard-object feeding. Recent studies of dental microwear indicate that only Paranthropus robustus regularly ate hard items, suggesting that the dentognathic anatomy of other australopiths reflects rare, seasonal exploitation of hard fallback foods. Here, we show that hard-object feeding cannot explain the extreme morphology of Paranthropus boisei. Rather, analysis of long-term dietary plasticity in an animal model suggests year-round reliance on tough foods requiring prolonged postcanine processing in P. boisei. Increased consumption of such items may have marked the earlier transition from Ardipithecus to Australopithecus, with routine hard-object feeding in P. robustus representing a novel behaviour.     

A Homo habilis maxilla and other newly-discovered hominid fossils from Olduvai Gorge, Tanzania

In 1995, a 1.8 million year old hominid maxilla with complete dentition (OH 65) was excavated from Bed I in the western part of Olduvai Gorge. The molar crowns are small relative to the long flaring roots, and the root of the canine is very long and straight. The broad maxilla with wide U-shaped palate and the form of the tooth roots closely match those of KNM-ER 1470 which, in its parietal size and morphology, matches the type specimen of Homo habilis, OH 7. Thus, OH 65 and KNM-ER 1470 group with OH 7 as representatives of H. habilis while some other Olduvai specimens, such as OH 13 and OH 24, have more in common in terms of morphology and brain size with Australopithecus africanus. Between 1995 and 2007, the OLAPP team has recovered teeth of eight other hominid individuals from various parts of Olduvai Gorge. These have been identified as belonging to H. habilis, Paranthropus boisei, and Australopithecus cf. africanus.     

Endocranial hyperostosis in Sangiran 2, Gibraltar 1, and Shanidar 5

Sangiran hominid 2 (S-2), Gibraltar hominid 1 (G-1), and Shanidar hominid 5 (SH-5) exhibit previously undescribed bilateral, paramedian hyperostosis of the endocranial frontal squama that spares the frontal crest, sagittal sinus, and ectocranial surface. The hyperostosis is localized to the frontal (usually the middle third) and parietal and is consistent with a diagnosis of hyperostosis calvariae interna (HCI), inclusive of hyperostosis frontalis interna. The hyperostosis in these specimens is compared to fossil hominids from Indonesia and Europe and to modern human cases of HCI. The three cases of HCI reported here document the existence and frequency of HCI in fossil hominids and push the antiquity of the disease back to nearly 1.5 millin years. The relatively great incidence of HCI in fossil hominids adds another confounding factor to the problematical issue of the taxonomic significance of cranial vault thickness. Am J Phys Anthropol 102:111–122. © 1997 Wiley-Liss, Inc.     

Observed and expected variation in hominid evolution

All of the major groups of fossil hominids (australopithecines, pithecanthropines, Neandertals, and early sapiens) were discovered by 1925, and therefore prior to the formulation of the synthetic theory of evolution that revolutionized the concept of the species in systematics. While these fossil finds were being made the framework for their interpretation included several assumptions: (1) that the number of living hominoid species was great, and that intraspecific variation was slight (authoritative sources recognized as many as 14 separate species of chimpanzees and 15 species of gorillas); (2) that the timescale of human evolution was brief (measured in tens or hundreds of thousands of years). As a result of these premises the consensus that hominid evolution was characterized by a large number of sympatric and synchronic species was virtually inevitable.In contrast, recent molecular studies demonstrate that genetic diversity among recent hominoids is so slight that even humans and chimpanzees differ at only about 1% of the loci that have been sampled so far; evidently, very small genetic differences can produce rather great contrasts in morphology. At the same time, geological break-throughs have increased the timescale for human evolution to several million years.It is concluded that morphological differences among fossil hominids, even if very appreciable and complex, do not necessarily reflect a great degree of either genetic or taxonomic diversity. Potential effects of evolutionary change through time should be incorporated into models of hominid evolution as a means of assessing the minimum number of lineages required to account for observed variations among hominid specimens.     

Variability and sexual dimorphism in canine size of Australopithecus and extant hominoids

Among extant hominoids degrees of sexual dimorphism and combined-sex coefficients of variation of canine teeth dimensions are highly correlated. Based on this relationship and coefficients of variation of four species of the genus Australopithecus, we predict degrees of canine dimorphism for these extinct hominids. The estimates show that A. afarensis is as dimorphic as the pygmy chimpanzee, A. boisei slightly less dimorphic than the pygmy chimpanzee, A. robustus slightly more dimorphic than the lar gibbon, while A. africanus overiaps with the lar gibbon as well as a modern human sample. These estimates represent degrees of canine dimorphism substantially lower than results based upon prior sexing of individual specimens. The relationship between canine dimorphism and body weight dimorphism is also analyzed. All four species of Australopithecus are considerably less dimorphic in canine size for their body weight dimorphism than expected. This dissociation of canine size dimorphism and body weight dimorphism is shared with modern humans, and thus represents a unique hominid trait. We interpret the moderate to strong body weight dimorphism in australopithecines as the result of intra- and intersexual selection typical of a polygynous mating structure, while the rather mild canine dimorphism is interpreted in terms of the “developmental crowding” model for reduction in canine size.     

Brief communication: on the optimum number of metacarpals for roentgenogrammetric measurement

Interpretation of dental development of fossil hominids requires understanding of and comparison with the pattern and timing of dental development among living humans and pongids. We report the first study of crown and root calcification in the lower permanent molar teeth among chimpanzees (Pan troglodytes) of known chronological age. A series of 99 lateral head radiographs of 16 captive-born chimpanzees were analyzed. Radiographs were taken at irregular intervals throughout the entire postnatal period of dental development from birth to 13 years of age. Permanent mandibular molars were rated on an eight-point maturation scale from initial radiographic appearance through crown and root calcification and apical closure of the root canals. In addition, we were able to document initial crown calcification and completion, as well as root completion and apical closure in incisors, canines, and premolars. Our results show several differences from the widely cited developmental schedule for pongid dentitions of Dean and Wood (Folia Primatol. 36:111–127, 1981). We found a much greater degree of temporal overlap in calcification of the crowns of adjacent molars, a pattern very unlike that usually seen in human dental development, which is characterized by delays between the onset of crown calcification in the molar series. Also, the ages and durations of crown and root formation in our chimp sample differ from the estimates proposed by Dean and Wood. By more clearly establishing the nature of developmental schedules and the timing of major events in the pongid dentition, these results should aid in the ongoing controversies concerning the human or pongid nature of dental development among Plio-Pleistocene hominids.     

Inferring hominoid and early hominid phylogeny using craniodental characters: the role of fossil taxa

Recent discoveries of new fossil hominid species have been accompanied by several phylogenetic hypotheses. All of these hypotheses are based on a consideration of hominid craniodental morphology. However, Collard and Wood (2000) suggested that cladograms derived from craniodental data are inconsistent with the prevailing hypothesis of ape phylogeny based on molecular data. The implication of their study is that craniodental characters are unreliable indicators of phylogeny in hominoids and fossil hominids but, notably, their analysis did not include extinct species. We report here on a cladistic analysis designed to test whether the inclusion of fossil taxa affects the ability of morphological characters to recover the molecular ape phylogeny. In the process of doing so, the study tests both Collard and Wood's (2000) hypothesis of character reliability, and the several recently proposed hypotheses of early hominid phylogeny. One hundred and ninety-eight craniodental characters were examined, including 109 traits that traditionally have been of interest in prior studies of hominoid and early hominid phylogeny, and 89 craniometric traits that represent size-corrected linear dimensions measured between standard cranial landmarks. The characters were partitioned into two data sets. One set contained all of the characters, and the other omitted the craniometric characters. Six parsimony analyses were performed; each data set was analyzed three times, once using an ingroup that consisted only of extant hominoids, a second time using an ingroup of extant hominoids and extinct early hominids, and a third time excluding Kenyanthropus platyops. Results suggest that the inclusion of fossil taxa can play a significant role in phylogenetic analysis. Analyses that examined only extant taxa produced most parsimonious cladograms that were inconsistent with the ape molecular tree. In contrast, analyses that included fossil hominids were consistent with that tree. This consistency refutes the basis for the hypothesis that craniodental characters are unreliable for reconstructing phylogenetic relationships. Regarding early hominids, the relationships of Sahelanthropus tchadensis and Ardipithecus ramidus were relatively unstable. However, there is tentative support for the hypotheses that S. tchadensis is the sister taxon of all other hominids. There is support for the hypothesis that A. anamensis is the sister taxon of all hominids except S. tchadensis and Ar. ramidus. There is no compelling support for the hypothesis that Kenyanthropus platyops shares especially close affinities with Homo rudolfensis. Rather, K. platyops is nested within the Homo + Paranthropus + Australopithecus africanus clade. If K. platyops is a valid species, these relationships suggest that Homo and Paranthropus are likely to have diverged from other hominids much earlier than previously supposed. There is no support for the hypothesis that A. garhi is either the sister taxon or direct ancestor of the genus Homo. Phylogenetic relationships indicate that Australopithecus is paraphyletic. Thus, A. anamensis and A. garhi should be allocated to new genera.     

A New Horned Crocodile from the Plio-Pleistocene Hominid Sites at Olduvai Gorge,Tanzania

Background

The fossil record reveals surprising crocodile diversity in the Neogene of Africa, but relationships with their living relatives and the biogeographic origins of the modern African crocodylian fauna are poorly understood. A Plio-Pleistocene crocodile from Olduvai Gorge, Tanzania, represents a new extinct species and shows that high crocodylian diversity in Africa persisted after the Miocene. It had prominent triangular “horns” over the ears and a relatively deep snout, these resemble those of the recently extinct Malagasy crocodile Voay robustus, but the new species lacks features found among osteolaemines and shares derived similarities with living species of Crocodylus.

Methodology/Principal Findings

The holotype consists of a partial skull and skeleton and was collected on the surface between two tuffs dated to approximately 1.84 million years (Ma), in the same interval near the type localities for the hominids Homo habilis and Australopithecus boisei. It was compared with previously-collected material from Olduvai Gorge referable to the same species. Phylogenetic analysis places the new form within or adjacent to crown Crocodylus.

Conclusions/Significance

The new crocodile species was the largest predator encountered by our ancestors at Olduvai Gorge, as indicated by hominid specimens preserving crocodile bite marks from these sites. The new species also reinforces the emerging view of high crocodylian diversity throughout the Neogene, and it represents one of the few extinct species referable to crown genus Crocodylus.