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.     

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.     

Incongruence in the pattern and timing of intra-specific diversification in bronze frogs and bullfrogs (Ranidae)

We compare patterns of lineage divergence in mitochondrial DNA (mtDNA) sequences of two protein-encoding mitochondrial genes (cyt b and ND2) in two ecologically similar, co-distributed, and closely related ranid frogs (Rana clamitans and Rana catesbeiana), that are geographically widespread, and frequently syntopic. We identified three lineages in R. clamitans, separated by 0.5% to 2.1% net corrected sequence divergence, comparable to two R. catesbeiana lineages separated by 0.6%. The geographic pattern of lineage distribution differed notably between the two species. In R. clamitans, we found a Coastal Plain-Appalachian (CPA) lineage restricted to south and east of the Appalachian Mountains and a widespread lineage that encompassing nearly all the sampled range. A third distinct and divergent lineage was detected in one location in the southwest portion of the range (Louisiana). This pattern contrasts with the east-west pattern in R. catesbeiana, and reflects possible differences in refugial dynamics and patterns of range expansion. Although both species have undergone range expansion and population growth, coalescent reconstruction of N(e) reflects larger lineages but more recent divergence in R. clamitans relative to R. catesbeiana, reflecting significant differences in population history or divergent patterns of molecular evolution at mtDNA.     

Evolutionary dental changes.

In the evolution of primates there has been a tendency towards reduction in jaw length and prognathism, mandibular canine size and first molar cusp number, and third molar presence. These oral structures were contrasted, and compared with cranial size, body height and weight, and finger length in 118 males and 102 females of the Burlington Growth Centre. Body weight was significantly related to canine width and to jaw length and prognathism. These relationships were stronger in the males than in the females. The evolutionary reduction in these dental dimensions may result from an evolutionary reduction in genetically determined body size. In the males the number of molar cusps was related to finger length and cranial height. Agenesis of third molars was related to the length of the maxilla in both sexes. In the females, canine width was related to the number of cusps of the first molars, agenesis of third molars, and length of a finger. Simultaneous reductions in dental structures were more frequent in the females.     

Evolution of a dental character in the beaver Castor fiber L. (Mammalia: Rodentia)

Variation in morphology of beaver cheek teeth has been examined in respect of ontogeny, geographical variation and geological time. When the effects of ontogeny are taken into account, certain patterns of dental variation are found to be restricted in space and time. An isolated loop of enamel ubiquitously present in the lower third molars of European beavers from the present interglacial seems to be a "new" acquisition which is lacking in Recent Siberian and North American beavers, as well as in Western European specimens from earlier interglacials.
Whilst the genetic basis of such morphological details is presumed rather than established, they may be helpful in tracing past population movements and are also of potential stratigraphic importance. Changes in range associated with Pleistocene climatic oscillations have led to the "sudden" appearance of this and other castorid dental characters in the Western European fossil record. The morphological discontinuity in the fossil record should be taken as evidence of climatic change rather than evidence for the operation of a certain pattern of evolution.     

Evolutionary Divergence and Convergence in Shape and Size Within African Antelope Proximal Phalanges

Morphological convergence amongst species inhabiting similar environments but having different evolutionary histories is a concept central to evolutionary biology. Cases of divergent evolution, where there is morphological divergence between closely related species exploiting different environments, are less well studied. Here we show divergent evolution in the morphology of the proximal phalanges of several closely related African antelope species inhabiting different environments. This morphological divergence was consistently observed in both a neutral morphospace and an externally ordinated morphospace. Divergence, but not convergence, was also observed when size and shape were considered independently. Finally, convergent evolution of the morphology of the proximal phalanges was observed, but only in the externally ordinated morphospace. Size shows less correlation with phylogeny than does shape. Therefore, we suggest that divergence in size will occur more readily when a species encounters new environmental conditions than divergence in shape. These findings are compatible with observations of rapid dwarfing on islands (Foster’s rule).     

记江苏泗洪首次发现森林古猿类化石

本文记述了在江苏泗洪松林庄发现的一种古猿类化石,它以个体小、颊齿宽、有发达的齿带等特征有别于我国云南的腊玛古猿、西瓦古猿;它也有别于在同一地点、同一层位发现的双沟醉猿。其形态与非洲的Proconsul属接近,根据这些形态特点和它的地史分布,我们订立了一新属一新种:Platodontopithecus jianghuaiensis,地质时代为中新世。     

Morphological integration in the hominin dentition: evolutionary, developmental, and functional factors

As the most common and best preserved remains in the fossil record, teeth are central to our understanding of evolution. However, many evolutionary analyses based on dental traits overlook the constraints that limit dental evolution. These constraints are diverse, ranging from developmental interactions between the individual elements of a homologous series (the whole dentition) to functional constraints related to occlusion. This study evaluates morphological integration in the hominin dentition and its effect on dental evolution in an extensive sample of Plio- and Pleistocene hominin teeth using geometric morphometrics and phylogenetic comparative methods. Results reveal that premolars and molars display significant levels of covariation; that integration is stronger in the mandibular dentition than in the maxillary dentition; and that antagonist teeth, especially first molars, are strongly integrated. Results also show an association of morphological integration and evolution. Stasis is observed in elements with strong functional and/or developmental interactions, namely in first molars. Alternatively, directional evolution (and weaker integration) occurs in the elements with marginal roles in occlusion and mastication, probably in response to other direct or indirect selective pressures. This study points to the need to reevaluate hypotheses about hominin evolution based on dental characters, given the complex scenario in which teeth evolve.     

A new morph of Telmatochromis temporalis (Cichlidae; Cichliformes) from Lake Tanganyika

Telmatochromis temporalis is a cichlid fish endemic to Lake Tanganyika. Two morphs of this species, normal and dwarf, form a good model for the study of ecological speciation through divergent natural selection on body size. This study reports a third morph of this species, slender morph, which was collected from deep waters off Kasenga, Zambia, whereas the normal morph inhabits shallow waters of the same locality. This study examined morphological characters and mitochondrial DNA sequences in 18 populations of the three T. temporalis morphs and two closely related species. The slender morph was morphologically similar to the normal and dwarf morphs of the same species, but clearly differed from closely related species. Genetic analyses showed that the slender morph was closest to but significantly different from the parapatric normal morph, suggesting reproductive isolation between them. Due to the lack of colour differences between morphs and of obvious geographical barriers between habitats, reproductive isolation between these morphs may be attributed to ecological factors, rather than sexual or geographical segregation. Further studies examining the evolution of the slender morph may deepen our knowledge of initial stages of speciation, like in the dwarf morph.

     

Evolution of larger sperm in response to experimentally increased sperm competition in Caenorhabditis elegans

Sperm morphology evolves rapidly, resulting in an exceptional diversity of sperm size and shape across animal phyla. This swift evolution has been thought to prevent fertilizations between closely related species. Alternatively, recent correlative analyses suggest that competition among sperm from more than one male may cause sperm diversity, but these hypotheses have not been tested. Here, we test experimentally the effect of sperm competition on sperm-size evolution using the nematode Caenorhabditis elegans. This worm has a three day generation time, which allowed the study to cover many generations. Sperm volume increased nearly 20% over 60 generations in lines genetically induced to have high levels of sperm competition compared with those of control lines. These results show that sperm competition can and does cause morphological evolution of sperm and, therefore, can explain much of the diversity in sperm morphology.     

A DEVELOPMENTAL ANALYSIS OF AN EVOLUTIONARY TREND: DIGITAL REDUCTION IN AMPHIBIANS

In this study, we integrate information from phylogeny, comparative ontogeny, and experimental embryology in an attempt to elucidate the mechanisms controlling evolutionary trends towards digital reduction and loss observed in amphibians. Frogs and salamanders that have lost phalanges and even whole toes have done so in a very ordered manner, i.e., certain skeletal elements are lost prior to others. This pattern of morphological diversity is described and trends elucidated. It is concluded that the process is characterized by striking intraordinal convergences coupled with substantial differences between the trends observed in frogs as compared to urodeles. We argue that this pattern is essentially a reflection of the differences in the ontogenies of the two orders. Similarly, the convergences within urodeles and within anurans can be explained as the result of regulation of developmental parameters in a resilient developmental program. We further explore this hypothesis by experimentally perturbing the number of cells in the embryonic limb primordium to show that reduction in the number of mesenchymal cells secondarily affects the developmental process of pattern formation causing a rearrangement of the skeletal morphology of the foot. The same experimental manipulation has different effects in frogs as compared to salamanders. However, in both cases, the experimentally generated morphologies tend to parallel the phenotypes and trends observed in nature. Our conclusion is that most of the patterns of diversity in the digital morphology of amphibians can be explained as a reflection of developmental properties. In general, we present a methodology that attempts to empirically address the issue of identifying developmental constraint in morphological evolution.     

Psammodinium inclinatum gen. nov. et comb. nov. (=Thecadinium inclinatum Balech) is the closest relative to the toxic dinoflagellate genera Gambierdiscus and Fukuyoa

The heterotrophic sand-dwelling dinoflagellate Thecadinium inclinatum has been re-examined by light and scanning electron microscopy in order to resolve the discrepancies on its plate pattern from the literature, and to obtain its phylogenetic information single-cell PCR technique has been used. The comparison of morphological and molecular information available for other Thecadinium species confirms the genus is polyphyletic and T. inclinatum seems not related to other representatives of the genus sensu lato. Thus, a new genus and combination for the species, Psammodinium inclinatum gen. nov., comb. nov. is proposed. Cells are heterotrophic and strongly laterally flattened, with sulcal pocket. The revised tabulation is: APC 3' 7” 7c 7s? 5”' 1p 2”” with a long-shank fishhook-shaped apical pore and descending cingulum. The cingulum inclines ventrally and declines on the right lateral side producing an asymmetrical epitheca. The epitheca is much smaller than the hypotheca. The phylogenetic results showed a strong relationship with the autotrophic epiphytic genera Gambierdiscus and Fukuyoa, being closely related with the latter. The Gambierdiscus species typically have a tropical and sub-tropical distribution and produce ciguatoxins, causing thousands of intoxications every year by consumption of contaminated fish. Fukuyoa representatives have a wider distribution including warm and temperate waters, and it has been demonstrated that they are also able to produce ciguatoxins, even though at lower amounts. P. inclinatum, which potential toxicity remains to be determined, represents an interesting independent evolutionary branch that resulted in the loss of chloroplasts, the strong lateral compression and the adaptation to sandy habitats in temperate and cold waters.     

Mandibles and molars of the wood mouse, Apodemus sylvaticus (L.): integrated latitudinal pattern and mosaic insular evolution

Aim The distinct nature of island populations has traditionally been attributed either to adaptation to particular insular conditions or to random genetic effects. In order to assess the relative importance of these two disparate processes, insular effects were addressed in the European wood mouse, Apodemus sylvaticus (Linnaeus, 1758). Location Wood mice from 33 localities on both mainland and various Atlantic and western Mediterranean islands were considered. This sampling covers only part of the latitudinal range of A. sylvaticus but included the two main genetic clades identified by previous studies. Islands encompass a range of geographical conditions (e.g. small islands fringing the continent through large and isolated ones). Methods The insular syndrome primarily invokes variations in body size, but ecological factors such as release from competition, niche widening and food availability should also influence other characters related to diet. In the present study, the morphology of the wood mice was quantified based on two characters involved in feeding: the size and shape of the mandibles and first upper molars. The size of the mandible is also a proxy for the body size of the animal. Patterns of morphological differentiation of both features were estimated using two‐dimensional outline analysis based on Fourier methods. Results Significant differences between mainland and island populations were observed in most cases for both the mandibles and molars. However, molars and mandibles displayed divergent patterns. Mandible shape diverged mostly on islands of intermediate remoteness and competition levels, whereas molars exhibited the greatest shape differentiation on small islands, such as Port‐Cros and Porquerolles. A mosaic pattern was also displayed for size. Body and mandible size increased on Ibiza, but molar size remained similar to mainland populations. Mosaic patterns were, however, not apparent in the mainland populations. Congruent latitudinal variations were evident for the size and shape of both mandibles and molars. Main conclusions Mosaic evolution appears to characterize insular divergence. The molar seems to be more prone to change with reduced population size on small islands, whereas the mandible could be more sensitive to peculiar environmental conditions on large and remote islands.     

Multigene phylogeny reveals convergent evolution in small interstitial catfishes from the Amazon and Atlantic forests (Siluriformes: Trichomycteridae)

Interstitial trichomycterid catfishes of the Glanapteryginae and Sarcoglanidinae with uncommon morphology have been known for long time from taxa endemic to the Amazon. In most recent decades, two genera, Listrura and Microcambeva, respectively, placed in Glanapteryginae and Sarcoglanidinae on the basis of morphological characters, have been described from the Atlantic Forest of eastern South America, about 1,500 km from the area inhabited by those Amazon taxa. Herein, we first test the phylogenetic positioning of Listrura and Microcambeva using a multigene data set, including two nuclear and three mitochondrial genes for nine species of Listrura and Microcambeva and 11 species representing all closely related subfamilies (TSVSG-clade), as well as five used as outgroups. The phylogenetic analyses generated a robust tree with high support values in all nodes, where monophyly of Glanapteryginae and Sarcoglanidinae is refuted. In contrast, Listrura and Microcambeva form a highly supported clade, herein formally described as a new subfamily, sister to a clade containing taxa representing the Glanapteryginae, Sarcoglanidinae, Stegophilinae, Tridentinae and Vandelliinae. This study also indicates that Microcambeva and Listrura exhibit divergent evolutionary trends in ecological and morphological attributes. Species of Microcambeva inhabit patches of loose sand and possess morphological traits that were convergently acquired by Amazon sand-dwelling sarcoglanidines, including loss of body pigmentation and long maxilla. Species of Listrura live burrowed inside small stretches of dense leaf litter and have morphological traits that were convergently acquired by Amazon glanapterygines inhabiting leaf litter bottom rivers, including elongate body, with numerous vertebrae and loss or reduction of all fins.     

Hominid-pongid distinctiveness in the miocene-pliocene fossil record: The lothagam mandible

The Lothagam mandibular fragment, found in 1967 west of Lake Turkana, Kenya, has been dated to 5.5 million years ago. This date is significant because it may lie within the suggested time range during which the hominid and pongid clades diverged. Because of its fragmentary condition and great age, this specimen has run the gamut of taxonomic assignations, from ramapithecine to pongid to hominid. These three nomenclatural categories serve as the basis for three hypotheses tested in this study. First, morphological and metric comparisons between Lothagam and a sample of Euroafrican ramapithecines address the hypothesis of “Lothagam as predi-vergence hominoid.” Second, comparisons with a sample of Pan test the “Lothagam as postdivergence, African protopongid” hypothesis. Finally, samples of Australopithecus afarensis and A. africanus were utilized to evaluate the hypothesis of “Lothagam as postdivergence, early hominid.” Unlike previous studies attempting to ascertain the evolutionary affinities of this enigmatic fossil, this work benefits from the large sample of A. afarensis specimens now generally available for study. Metric and morphological comparisons demonstrate Lothagam's affinity to A. afarensis in sharing derived, hominid states in such features as the mental foramen vertical position, the ascending ramus origin, the breadth of the alveolar margin, the reduction of the hypoconulid, the dimensions of the M₁ and the dimensions of the mandibular corpus. It is suggested that the dental/gnathic features enumerated in this study can be employed to distinguish ancestral hominid from pongid in future Mio/Pliocene paleontological discoveries.     

Morphologic characteristics of the Alaskan Eskimo dentition: IV. Cusp number and groove patterns of mandibular molars

Data on the permanent dentition of 63 coastal and 33 inland Alaskan Eskimos are presented. The number of cusps and groove pattern of the mandibular molars were recorded. Agenesis of the mandibular third molars was classified and the mesiodistal and buccolingual crown diameter was measured on the first and the second mandibular molars. The predominant pattern of the lower first molars was Y5, while for the second molar the dominating patterns were +5 and +4. In the lower third molar, +5 was found in the majority of cases. For M1 and M2, men showed a stronger tendency toward a conservative pattern than did women. In the case of M2, the inland population exhibited a more conservative trait than did the coastal population. No connection was seen between the groove pattern and agenesis of M3, however, a reduction in the mesiodistal crown diameter for the second molars was seen when the number of cusps is reduced from 5 to 4.     

Unique inhibitory cascade pattern of molars in canids contributing to their potential to evolutionary plasticity of diet

Developmental origins that guide the evolution of dental morphology and dental formulae are fundamental subjects in mammalian evolution. In a previous study, a developmental model termed the inhibitory cascade model was established. This model could explain variations in relative molar sizes and loss of the lower third molars, which sometimes reflect diet, in murine rodents and other mammals. Here, I investigated the pattern of relative molar sizes (inhibitory cascade pattern) in canids, a taxon exhibiting a wide range of dietary habits. I found that interspecific variation in canid molars suggests a unique inhibitory cascade pattern that differs from that in murine rodents and other previously reported mammals, and that this variation reflects dietary habits. This unique variability in molars was also observed in individual variation in canid species. According to these observations, canid species have greater variability in the relative sizes of first molars (carnassials), which are functionally important for dietary adaptation in the Carnivora. In conclusion, an inhibitory cascade that differs from that in murine rodents and other mammals may have contributed to diverse dietary patterns and to their parallel evolution in canids.     

Rapid radiation and cryptic speciation in squat lobsters of the genus Munida (Crustacea, Decapoda) and related genera in the South West Pacific: molecular and morphological evidence

Squat lobsters (genus Munida and related genera) are among the most diverse taxa of western Pacific crustaceans, though several features of their biology and phylogenetic relationships are unknown. This paper reports an extensive phylogenetic analysis based on mitochondrial DNA sequences (cytochrome c oxidase subunit I and 16S rRNA) and the morphology of 72 species of 12 genera of western Pacific squat lobsters. Our phylogenetic reconstruction using molecular data supports the recent taxonomic splitting of the genus Munida into several genera. Excluding one species (M. callista), the monophyly of the genus Munida was supported by Bayesian analysis of the molecular data. Three moderately diverse genera (Onconida, Paramunida, and Raymunida) also appeared monophyletic, both according to morphological and molecular data, always with high support. However, other genera (Crosnierita and Agononida) seem to be para- or polyphyletic. Three new cryptic species were identified in the course of this study. It would appear that the evolution of this group was marked by rapid speciation and stasis, or certain constraints, in its morphological evolution.     

Tooth morphology and other aspects of the Teso dentition

The teeth of over 5,000 Teso schoolchildren members of a Nilo-Hamitic tribe in East Africa, were examined for morphological traits. There was a significant difference between the sexes in the number of cusps on the lower first and second molars, in the prevalence of the cusp of Carabelli, and in variability and agenesis of the upper lateral incisor. The results showed that females consistently favoured tooth reduction. There was also a tendency among those possessing extra cusps on one molar to have extra cusps or other molars. Records kept of the prevalence of the tribal custom of extracting lower central incisors indicated that this practise is rapidly dying out. On another group of teeth which had been extracted from adults common variations of root morphology were noted, together with the fissure pattern of the lower molars. Measurements were made of those teeth which were unworn and were not broken down by dental decay, and the lower third molar was found to be the largest tooth of the series. Observations on the pattern of molar tooth wear showed that the buccal as well as the occlusal surface was strongly affected.     

Ecological adaptation and species recognition drives vocal evolution in neotropical suboscine birds

Given that evolutionary divergence in mating signals leads to reproductive isolation in numerous animal taxa, understanding what drives signal divergence is fundamental to our understanding of speciation. Mating signals are thought to diverge via several processes, including (1) as a by-product of morphological adaptation, (2) through direct adaptation to the signaling environment, or (3) to facilitate species recognition. According to the first two hypotheses, birdsongs diversify in different foraging niches and habitats as a product of selection for optimal morphology and efficient sound transmission, respectively. According to the third hypothesis, they diversify as a result of selection against maladaptive hybridization. In this study I test all three hypotheses by examining the influence of morphology, acoustic environment, and the presence of closely related congeners on song structure in 163 species of antbird (Thamnophilidae). Unlike oscine passerines, these Neotropical suboscines make ideal subjects because they develop their songs without learning. In other words, patterns of vocal divergence are not complicated by cultural evolution. In support of the morphological adaptation hypothesis, body mass correlates with the acoustic frequency of songs, and bill size with temporal patterning. These relationships were robust, even when controlling for phylogenetic inertia using independent contrasts, suggesting that there has been correlated evolution between morphological and acoustic traits. The results also support the acoustic adaptation hypothesis: birds which habitually sing in the understory and canopy produce higher-pitched songs than those that sing in the midstory, suggesting that song structure is related to the sound transmission properties of different habitat strata. Finally, the songs of sympatric pairs of closely related species are more divergent than those of allopatric pairs, as predicted by the species recognition hypothesis. To my knowledge, these data provide the first direct evidence that species recognition and ecological adaptation operate in tandem, and that the interplay between these factors drives the evolution of mating signals in suboscine birds.