Evolution of the mandibular third premolar crown in early Australopithecus

The Pliocene hominins Australopithecus anamensis and Australopithecus afarensis likely represent ancestor-descendent taxa—possibly an anagenetic lineage—and capture significant change in the morphology of the canine and mandibular third premolar (P₃) crowns, dental elements that form the canine honing complex in nonhuman catarrhines. This study focuses on the P₃ crown, highlighting plesiomorphic features in A. anamensis. The A. afarensis P₃ crown, in contrast, is variable in its expression of apomorphic features that are characteristic of geologically younger hominins. Temporal variation characterizes each taxon as well. The A. anamensis P₃ from Allia Bay, Kenya expresses apomorphic character states, shared with A. afarensis, which are not seen in the older sample of A. anamensis P₃s from Kanapoi, Kenya, while spatiotemporal differences in shape exist within the A. afarensis hypodigm. The accumulation of derived features in A. afarensis results in an increased level of P₃ molarisation. P₃ molarisation did not evolve concurrent with postcanine megadontia and neither did the appearance of derived aspects of P₃ occlusal form coincide with the loss of canine honing in hominins, which is apparent prior to the origin of the genus Australopithecus. A. afarensis P₃ variation reveals the independence of shape, size, and occlusal form. The evolution of the P₃ crown in early Australopithecus bridges the wide morphological gap that exists between geologically younger hominins on the one hand and extant apes and Ardipithecus on the other.     

New hominid fossils from Woranso‐Mille (Central Afar,Ethiopia) and taxonomy of early Australopithecus

The phylogenetic relationship between Australopithecus anamensis and Australopithecus afarensis has been hypothesized as ancestor‐descendant. However, the weakest part of this hypothesis has been the absence of fossil samples between 3.6 and 3.9 million years ago. Here we describe new fossil specimens from the Woranso‐Mille site in Ethiopia that are directly relevant to this issue. They derive from sediments chronometrically dated to 3.57–3.8 million years ago. The new fossil specimens are largely isolated teeth, partial mandibles, and maxillae, and some postcranial fragments. However, they shed some light on the relationships between Au. anamensis and Au. afarensis. The dental morphology shows closer affinity with Au. anamensis from Allia Bay/Kanapoi (Kenya) and Asa Issie (Ethiopia) than with Au. afarensis from Hadar (Ethiopia). However, they are intermediate in dental and mandibular morphology between Au. anamensis and the older Au. afarensis material from Laetoli. The new fossils lend strong support to the hypothesized ancestor‐descendant relationship between these two early Australopithecus species. The Woranso‐Mille hominids cannot be unequivocally assigned to either taxon due to their dental morphological intermediacy. This could be an indication that the Kanapoi, Allia Bay, and Asa Issie Au. anamensis is the primitive form of Au. afarensis at Hadar with the Laetoli and Woranso‐Mille populations sampling a mosaic of morphological features from both ends. It is particularly difficult to draw a line between Au. anamensis and Au. afarensis in light of the new discoveries from Woranso‐Mille. The morphology provides no evidence that Au. afarensis and Au. anamensis represent distinct taxa. Am J Phys Anthropol 2010. © 2009 Wiley‐Liss, Inc.     

New fossils of Australopithecus anamensis from Kanapoi,West Turkana,Kenya (2003–2008)

Renewed fieldwork from 2003 through 2008 at the Australopithecus anamensis type-site of Kanapoi, Kenya, yielded nine new fossils attributable to this species. These fossils all date to between 4.195 and 4.108 million years ago. Most were recovered from the lower fluvial sequence at the site, with one from the lacustrine sequence deltaic sands that overlie the lower fluvial deposits but are still below the Kanapoi Tuff. The new specimens include a partial edentulous mandible, partial maxillary dentition, two partial mandibular dentitions, and five isolated teeth. The new Kanapoi hominin fossils increase the sample known from the earliest Australopithecus, and provide new insights into morphology within this taxon. They support the distinctiveness of the early A. anamensis fossils relative to earlier hominins and to the later Australopithecus afarensis. The new fossils do not appreciably extend the range of observed variation in A. anamensis from Kanapoi, with the exception of some slightly larger molars, and a canine tooth root that is the largest in the hominin fossil record. All of the Kanapoi hominins share a distinctive morphology of the canine–premolar complex, typical early hominin low canine crowns but with mesiodistally longer honing teeth than seen in A. afarensis, and large, probably dimorphic, canine tooth roots. The new Kanapoi specimens support the observation that canine crown height, morphology, root size and dimorphism were not altered from a primitive ape-like condition as part of a single event in human evolution, and that there may have been an adaptive difference in canine function between A. anamensis and A. afarensis.     

Phylogeny of early Australopithecus: new fossil evidence from the Woranso-Mille (central Afar,Ethiopia)

The earliest evidence of Australopithecus goes back to ca 4.2 Ma with the first recorded appearance of Australopithecus ‘anamensis’ at Kanapoi, Kenya. Australopithecus afarensis is well documented between 3.6 and 3.0 Ma mainly from deposits at Laetoli (Tanzania) and Hadar (Ethiopia). The phylogenetic relationship of these two ‘species’ is hypothesized as ancestor–descendant. However, the lack of fossil evidence from the time between 3.6 and 3.9 Ma has been one of its weakest points. Recent fieldwork in the Woranso-Mille study area in the Afar region of Ethiopia has yielded fossil hominids dated between 3.6 and 3.8 Ma. These new fossils play a significant role in testing the proposed relationship between Au. anamensis and Au. afarensis. The Woranso-Mille hominids (3.6–3.8 Ma) show a mosaic of primitive, predominantly Au. anamensis-like, and some derived (Au. afarensis-like) dentognathic features. Furthermore, they show that, as currently known, there are no discrete and functionally significant anatomical differences between Au. anamensis and Au. afarensis. Based on the currently available evidence, it appears that there is no compelling evidence to falsify the hypothesis of ‘chronospecies pair’ or ancestor–descendant relationship between Au. anamensis and Au. afarensis. Most importantly, however, the temporally and morphologically intermediate Woranso-Mille hominids indicate that the species names Au. afarensis and Au. anamensis do not refer to two real species, but rather to earlier and later representatives of a single phyletically evolving lineage. However, if retaining these two names is necessary for communication purposes, the Woranso-Mille hominids are best referred to as Au. anamensis based on new dentognathic evidence.     

Human evolution

The common ancestor of modern humans and the great apes is estimated to have lived between 5 and 8 Myrs ago, but the earliest evidence in the human, or hominid, fossil record is Ardipithecus ramidus, from a 4.5 Myr Ethiopian site. This genus was succeeded by Australopithecus, within which four species are presently recognised. All combine a relatively primitive postcranial skeleton, a dentition with expanded chewing teeth and a small brain. The most primitive species in our own genus, Homo habilis and Homo rudolfensis, are little advanced over the australopithecines and with hindsight their inclusion in Homo may not be appropriate. The first species to share a substantial number of features with later Homo is Homo ergaster, or ‘early African Homo erectus’, which appears in the fossil record around 2.0 Myr. Outside Africa, fossil hominids appear as Homo erectus-like hominids, in mainland Asia and in Indonesia close to 2 Myr ago; the earliest good evidence of ‘archaic Homo’ in Europe is dated at between 600–700 Kyr before the present. Anatomically modern human, or Homo sapiens, fossils are seen first in the fossil record in Africa around 150 Kyr ago. Taken together with molecular evidence on the extent of DNA variation, this suggests that the transition from ‘archiac’ to ‘modern’ Homo may have taken place in Africa.     

Anterior dental evolution in the Australopithecus anamensis–afarensis lineage

Australopithecus anamensis is the earliest known species of the Australopithecus–human clade and is the likely ancestor of Australopithecus afarensis. Investigating possible selective pressures underlying these changes is key to understanding the patterns of selection shaping the origins and early evolution of the Australopithecus–human clade. During the course of the Au. anamensis–afarensis lineage, significant changes appear to occur particularly in the anterior dentition, but also in jaw structure and molar form, suggesting selection for altered diet and/or food processing. Specifically, canine tooth crown height does not change, but maxillary canines and P₃s become shorter mesiodistally, canine tooth crowns become more symmetrical in profile and P₃s less unicuspid. Canine roots diminish in size and dimorphism, especially relative to the size of the postcanine teeth. Molar crowns become higher. Tooth rows become more divergent and symphyseal form changes. Dietary change involving anterior dental use is also suggested by less intense anterior tooth wear in Au. afarensis. These dental changes signal selection for altered dietary behaviour and explain some differences in craniofacial form between these taxa. These data identify Au. anamensis not just as a more primitive version of Au. afarensis, but as a dynamic member of an evolving lineage leading to Au. afarensis, and raise intriguing questions about what other evolutionary changes occurred during the early evolution of the Australopithecus–human clade, and what characterized the origins of the group.     

Relative cheek-tooth size in Australopithecus

Until the discovery of Australopithecus afarensis, cheek-tooth megadontia was unequivocally one of the defining characteristics of the australopithecine grade in human evolution along with bipedalism and small brains. This species, however, has an average postcanine area of 757 mm², which is more like Homo habilis (759 mm²) than A. africanus (856 mm²). But what is its relative cheek-tooth size in comparison to body size? One approach to this question is to compare postcanine tooth area to estimated body weight. By this method all Australopithecus species are megadont: they have cheek teeth 1.7 to 2.3 times larger than modern hominoids of similar body size. The series from A. afarensis to A. africanus to A. robustus to A. boisei shows strong positive allometry indicating increasing megadontia through time. The series from H. habilis to H. erectus to H. sapiens shows strong negative allometry which implies a sharp reduction in the relative size of the posterior teeth. Postcanine megadontia in Australopithecus species can also be demonstrated by comparing tooth size and body size in associated skeletons: A. afarensis (represented by A.L. 288–1) has a cheek-tooth size 2.8 times larger than expected from modern hominoids; A. africanus (Sts 7) and A. robustus (TM 1517) are over twice the expected size. The evolutionary transition from the megadont condition of Australopithecus to the trend of decreasing megadontia seen in the Homo lineage may have occurred between 3.0 and 2.5 m.y. from A. afarensis to H. habilis but other evidence indicates that it is more likely to have occurred between 2.5 to 2.0 m.y. from an A. africanus-like form to H. habilis.     

Revision of fossil hominid jaws from the plio/pleistocene of hadar,in ethiopia including a new species of the genusHomo (hominoidea: homininae)

The assignment of fossil hominoid jaws from the Plio/Pleistocene of Hadar to a single genus,Australopithecus Dart, 1925, is a misnomer. They are morphologically unrestricted to and inconsistent with the diagnosis and evolutionary trend ofAustralopithecus. The morphological pattern of four large jaws is indeed australopithecine and similar toA. africanus Dart, 1925, but six small jaws reveal a pre-habilis stage of dental development early in theHomo lineage. On the basis of their unique hominine dentition, they are reinterpreted as representing a new species,Homo antiquus n.sp.     

Estimating canine tooth crown height in early Australopithecus

Canine tooth size reduction and the associated reduction in canine dimorphism is a basal hominin character that also provides important evidence for models of behavioral evolution. Two specimens of Australopithecus anamensis (KNM-KP 29287 and KNM-KP 29283) that do not preserve the canine crown, but do preserve the root or alveolus, appear to suggest that canine size variation and canine dimorphism in this species may have been greater than in other hominins. We evaluate canine root and crown dimensions in a series of extant hominoids, and estimate canine crown height in Australopithecus afarensis and A. anamensis. Our results demonstrate that it is possible to generate estimates of canine crown height from basal canine crown and root dimensions with a moderate degree of accuracy. Estimates of maxillary canine crown size for A. anamensis are slightly larger than those of A. afarensis, and are approximately the same size as canines of modern female chimpanzees. Estimated mandibular canine crown height is very similar in the two species. Variation within the A. anamensis sample of estimated canine crown heights is similar to that of modern humans, suggesting a low degree of sexual dimorphism. Inclusion of estimates for KNM-KP 29287 and KNM-KP 29283 does not substantially increase either the estimate of overall canine size or variation for A. anamensis.     

The Old World sparrows (genus Passer) phylogeography and their relative abundance of nuclear mtDNA pseudogenes

The phylogenetic relationships of genus Passer (Old World sparrows) have been studied with species covering their complete world living range. Mitochondrial (mt) cyt b genes and pseudogenes have been analyzed, the latter being strikingly abundant in genus Passer compared with other studied songbirds. The significance of these Passer pseudogenes is presently unclear. The mechanisms by which mt cyt b genes become pseudogenes after nuclear translocation are discussed together with their mode of evolution, i.e., transition/transversion mitochondrial ratio is decreased in the nucleus, as is the constraint for variability at the three codon positions. However, the skewed base composition according to codon position (in 1^st position the percentage is very similar for the four bases, in 2^nd position there are fewer percentage of A and G and more percentage of T, and in 3^rd codon position fewer percentage of G and T and is very rich in A and C) is maintained in the translocated nuclear pseudogenes. Different nuclear internal mechanisms and/or selective pressures must exist for explaining this nuclear/mitochondrial differential DNA base evolutive variability. Also, the phylogenetic usefulness of pseudogenes for defining relationships between closely related lineages is stressed. The analyses suggest that the primitive genus Passer species comes from Africa, the Cape sparrow being the oldest: P. hispaniolensis italiae is more likely conspecific to P. domesticus than to P. hispaniolensis. Also, Passer species are not included within weavers or Estrildinae or Emberizinae, as previously suggested. European and American Emberizinae sparrows are closely related to each other and seem to be the earliest species that radiated among the studied songbirds (all in the Miocene Epoch). Received: 29 November 2000 / Accepted: 22 March 2001     

The endocast from Dana Aoule North (DAN5/P1): A 1.5 million year-old human braincase from Gona,Afar, Ethiopia

The nearly complete cranium DAN5/P1 was found at Gona (Afar, Ethiopia), dated to 1.5–1.6 Ma, and assigned to the species Homo erectus. Its size is, nonetheless, particularly small for the known range of variation of this taxon, and the cranial capacity has been estimated as 598 cc. In this study, we analyzed a reconstruction of its endocranial cast, to investigate its paleoneurological features. The main anatomical traits of the endocast were described, and its morphology was compared with other fossil and modern human samples. The endocast shows most of the traits associated with less encephalized human taxa, like narrow frontal lobes and a simple meningeal vascular network with posterior parietal branches. The parietal region is relatively tall and rounded, although not especially large. Based on our set of measures, the general endocranial proportions are within the range of fossils included in the species Homo habilis or in the genus Australopithecus. Similarities with the genus Homo include a more posterior position of the frontal lobe relative to the cranial bones, and the general endocranial length and width when size is taken into account. This new specimen extends the known brain size variability of Homo ergaster/erectus, while suggesting that differences in gross brain proportions among early human species, or even between early humans and australopiths, were absent or subtle.     

Phylogeny and systematic revision of Eocene Cricetidae (Rodentia,Mammalia) from Central and East Asia: on the origin of cricetid rodents

The origin of the Cricetidae and the relationships among earliest species from Central and East Asia are still disputed. The taxonomic status of some Eocene cricetid taxa is also doubtful. A parsimony analysis based on 65 cranial and dental characters and including 22 early Myomorpha was performed to elucidate these issues. As a result, the North American Elymys, known as the first Myodonta, belongs to dipodoid rodents, although it shares a suite of characters with the first cricetids. This implies that the split between dipodoids and muroids occurred in North America during the early middle Eocene, as previously supposed. The disputed Simimys and Nonomys could constitute an early dipodoid radiation. It appears that the earliest offshoot of the cricetid clade is the Asian genus Palasiomys. This taxon has a more advanced cricetid plan than contemporaneous dipodoids. The genus Raricricetodon no longer exists here because it is polyphyletic; the species are included in Palasiomys (P. minor, P. trapezius) and Pappocricetodon (P. zhongtiaensis). The genus Pappocricetodon displays a complete cricetid plan associated with both the loss of P⁴ and the development of an anterocone on M¹. The disputed genera Eocricetodon and Oxynocricetodon characterize the beginning of the Oligocene radiations of Eucricetodontinae throughout the Holarctic continents.     

Geographic and stratigraphic distributions of the Caribbean species of Cladocora (Scleractinia, Faviidae)

A complete account of the faviid genus Cladocora within the Caribbean is presented. In the Caribbean this genus represents an extant group that had its earliest occurrence during the Campanian-Maastrichtian of Jamaica. Recent forms have been reported throughout the Caribbean. The following forms were found (with stratigraphic ranges in the Caribbean): C. arbuscula (Pliocene-Recent), C. debilis (Pleistocene-Recent), C. gracilis (Middle-Upper Maastrichtian), C. jamaicaensis (Campanian-Maastrichtian and Eocene), C. johnsoni (Pliocene), and C. recrescens (Middle-Upper Oligocene). The occurrence of the genus Cladocora in the Caribbean is largely continuous from the Campanian to Recent, during the majority of the Caribbean species show affinities to European assemblages. For the time intervals Paleocene, Lower Oligocene, and Miocene the taxon has not been reported from the Caribbean.     

Pan paniscus and human evolution

Detailed comparisons of the postcranium, cranium, and dentition of Pan paniscus, Pan troglodytes, and Homo reveal that except for slight differences in fore- and hindlimb proportions and the morphology of the shoulder, the postcranium of the two species of Pan are allometrically scaled variants of the same animal and one does not resemble Homo more than the other. Nor does the postcranium of one species of Pan resemble Australopithecus more closely than the other when the effects of body size are controlled. The over all morphological pattern of the skull and teeth of the two chimpanzees is clearly different, however, but both are about equally distinct from the earliest known members of the family Hominidae.     

Metabolite Profiling Based on UPLC-Q-TOF-MS/MS and the Biological Evaluation of Medicinal Plants of Chinese Dichocarpum (Ranunculaceae)

The genus Dichocarpum is endemic to East Asia, and many species have been used to treat various diseases. However, phytochemical researches of this genus have been limited to date. In the present study, a metabolomic approach based on UPLC-Q-TOF-MS/MS was used to explore the phytochemical profiles of 10 Chinese Dichocarpum species, and cannabinoid receptor (CB1/CB2) agonistic activities evaluation of these plants was performed. A total of 128 features were putatively annotated, belonging to alkaloids, flavonoids, triterpenes saponins, phenolic acids, and others. Semi-quantitative statistics demonstrated that alkaloids and flavonoids were widely distributed, with the former the most abundant, whereas triterpenes saponins were mainly distributed in D. fargesii and D. wuchuanense. The phylogenetic results obtained from DNA sequencing assigned the 10 species to three groups. Further results of in silico annotation revealed three chemical families and helped determine the characteristic features of the three groups. In addition, the plant extracts of nine species from this genus showed agonistic activity on CB2 receptors. This comprehensive analysis revealed the chemotype distribution and pharmacophylogenetic relationship, to provide clues for the prospective resource utilization of the medicinal plants from the genus Dichocarpum.     

Cytological study on the genus Syncalathium (Asteraceae‐Lactuceae), an endemic taxon to alpine scree of the Sino‐Himalayas

Abstract Cytological characters of four species in Syncalathium (Asteraceae: Lactuceae), a small genus with six identified species endemic to alpine scree of the Sino‐Himalayan region, are surveyed in this report. Three species (Syncalathium pilosum, Syncalathium chrysocephalum, and Syncalathium disciforme) are examined for the first time. Combined with our previous counts, five species have been cytologically investigated from the genus and the results indicated that all species are diploid with the basic somatic chromosome number of x=8. The karyotype asymmetry of Syncalathium souliei is 2A, distinct from the other four species of 1A, and the remaining species are divided into two subgroups with different karyotypes, consistent with their morphological features. The significance of the cytological evolution of Syncalathium is briefly discussed.     

Kinematic parameters inferred from enamel microstructure: new insights into the diet of Australopithecus anamensis

The dietary adaptations of Australopithecus anamensis are contentious, with suggestions that range from soft fruits to hard, brittle, tough, and abrasive foods. It is unlikely that all propositions are equally valid, however. Here we extend recent finite element (FE) analyses of enamel microstructure (Shimizu and Macho, 2008) to enquire about the range of loading directions (i.e., kinematics) to which A. anamensis enamel microstructure/molars could safely be subjected. The rationale underlying this study is the observation that hard brittle foods are broken down in crush, while tough foods require shear. The findings are compared with those of Pan and Gorilla.Eighteen detailed FE models of enamel microstructure were created and analysed. The results highlight the uniqueness of A. anamensis dental structure and imply that mastication in this species included a greater shear component than in Pan, as well as a wider range of loading directions; it is similar to that in Gorilla in this respect. These findings are in accord with microwear studies (Grine et al., 2006a). Unlike either of the great apes, however, enamel microstructure of A. anamensis was found to be poorly equipped to withstand loading parallel to the dentino-enamel junction; such loading regimes are associated with mastication of soft fleshy fruits. This, together with broader morphological considerations, raises doubts as to whether A. anamensis was essentially a frugivore that expanded its dietary niche as a result of fluctuations in environmental conditions, e.g., during seasonal food shortages. Instead, it is more parsimonious to conclude that the habitual diet of A. anamensis differed considerably from that of either of the extant African great apes.     

Quantitative and qualitative trends in human sapientization

Sapientization is envisaged as a process leading from the earliest representatives of the genus Homo to the shape and dynamism of Homo sapiens (sapiens). Taking into account the manifestation of the changes occurring in the Homo brain-case, two evolutionary trends can be distinguished: the expansion of the cranial capacity (quantitative sapientization) and the attainment of the recent shape (qualitative sapientization). Evidently, both trends cooperate towards a single objective. The writer suggests that they may come into play in an alternating way.The major changes from the psychic and ethological standpoint seem to be related to stages in qualitative change, namely, to the transition both from Australopithecus to Homo and from H. neanderthalensis to Homo sapiens (sapiens).