Comparative pollen morphology and ultrastructure of the Callitrichaceae

The Callitrichaceae are an aquatic family of dicots that include the single, geographically cosmopolitan genus Callitriche. Callitriche contains 40-50 terrestrial, amphibious, and obligately submersed species, and it is the only known genus in the plant kingdom with co-occurring aerial and hydrophilous pollination syndromes. Pollen morphology and ultrastructure were described for 13 Callitriche species using scanning electron and transmission electron microscopy. Representative taxa of each growth form were examined; these included three terrestrial species (C. deflexa, C. peploides, and C. nuttallii), nine amphibious species (C. brutia, C. cophocarpa, C. cophocarpa-stagnalis hybrid, C. cribrosa, C. hamulata, C. heterophylla var. heterophylla, C. lusitanica, C. marginata, and C. trochlearis), and one obligately submersed species (C. truncata). Of the amphibious taxa, C. heterophylla var. heterophylla and C. trochlearis had internal geitonogamy, a type of internal self-fertilization. Pollen from all taxa was spheroidal, small, intectate, and lacked well-defined apertures. Taxa primarily differed with respect to exine thickness, surface ornamentation, and the presence or absence of aperture-like regions. The pollen of terrestrial species, as well as that of C. marginata, had well-developed exines with thick sculptured and basal layers. In general, amphibious taxa produced pollen with distinct, but thinner, exines than that of terrestrial taxa. Pollen of the amphibious taxa with internal geitonogamy had a thicker basal layer than species without internal geitonogamy, whereas the overall exine was reduced in C. hamulata and absent in C. brutia and C. lusitanica. Pollen of the obligately submersed C. truncata also lacked an exine. These palynological data were correlated with growth habits and related pollination biologies, as well as with phylogenetic interpretations of Callitrichaceae. Exine reduction or loss has evolved at least twice in the family, and it is associated with aneuploid reduction in chromosome number.     

The evolutionary history of Fagus in western Eurasia: Evidence from genes, morphology and the fossil record

 Fagus (beech) is among the most abundant and economically important genera of broad-leaved trees in northern hemisphere temperate forests. The number of modern taxa present in Europe and Asia Minor has long been a matter of debate and up to five species have been recognised. To resolve taxonomic and phylogenetic relationships we conducted morphological and molecular genetic analyses in western Eurasiatic taxa and evaluated palaeontological evidence. To place our findings from western Eurasiatic populations in a broader context additional East Asiatic and North American species of the same subgenus Fagus as well as two species of the subgenus Engleriana were included in our study. The morphological features exhibited in western Eurasiatic populations of Fagus show a west-east gradient that is characterised by strongly overlapping variability between geographical races. Fagus populations from Asia Minor exhibit an even higher variability that is also reflected in their genetic variability of nuclear rDNA internal transcribed spacer (ITS) sequences. The intraspecific genetic variability recorded here is in conflict with previous ITS studies in Fagus. The high amount of ITS polymorphism within Fagus from western Eurasia along with the clinal variation observed for morphological characters suggest the presence of only a single species, Fagus sylvatica L., in Europe and Asia Minor. Previously recognised taxa such as F. orientalis Lipsky and Fagus moesiaca (Maly) Czeczott should therefore be treated as synonyms of Fagus sylvatica. Although species belonging to the subgenus Engleriana were genetically distinct from species of the subgenus Fagus, relationships within the subgenus Fagus could not be clearly resolved. A reason for this could be the low rate of diversification in Fagus during the early phase of range expansion of the genus in the Oligocene period as indicated by the uniformity of leaf and cupule/nut fossils. This may account for the low overall ITS divergence and the high degree of polymorphism encountered in the subgenus Fagus and points to a late differentiation of western Eurasiatic and eastern Asiatic species. Area disruptions during the Pleistocene and the post-glacial recolonisation of western Europe appear to have caused the west-east gradient that is apparent in modern Fagus of western Eurasia but absent in Late Tertiary ancestors of Fagus sylvatica. Received June 22, 2001 Accepted February 25, 2002     

Preface: The phylogeny, fossil record and ecological diversity of ostracod crustaceans

After more than two centuries of research, more than 65,000 living and fossil ostracod species have been described and studied, yet much remains to be learned about this ancient, widespread and diverse group of bivalved arthropods. Their higher classification and phylogeny are subjects of vigorous debate, as is their position in the broader picture of crustacean phylogeny. At the same time, major advances in our understanding of ostracod lineages and their relationships are resulting from the application of innovative approaches and techniques. This preface provides a contextual overview of the 15 contributions to this volume, which resulted from the 14th International Symposium on Ostracoda (ISO2001) held in 2001at Shizuoka, Japan. As such it provides a cross-section of topics at the forefront of research on the evolution and diversity of Ostracoda, and indicates directions for future work.     

Arthropod phylogeny: An overview from the perspectives of morphology,molecular data and the fossil record

Monophyly of Arthropoda is emphatically supported from both morphological and molecular perspectives. Recent work finds Onychophora rather than Tardigrada to be the closest relatives of arthropods. The status of tardigrades as panarthropods (rather than cycloneuralians) is contentious from the perspective of phylogenomic data. A grade of Cambrian taxa in the arthropod stem group includes gilled lobopodians, dinocaridids (e.g., anomalocaridids), fuxianhuiids and canadaspidids that inform on character acquisition between Onychophora and the arthropod crown group. A sister group relationship between Crustacea (itself likely paraphyletic) and Hexapoda is retrieved by diverse kinds of molecular data and is well supported by neuroanatomy. This clade, Tetraconata, can be dated to the early Cambrian by crown group-type mandibles. The rival Atelocerata hypothesis (Myriapoda + Hexapoda) has no molecular support. The basal node in the arthropod crown group is embroiled in a controversy over whether myriapods unite with chelicerates (Paradoxopoda or Myriochelata) or with crustaceans and hexapods (Mandibulata). Both groups find some molecular and morphological support, though Mandibulata is presently the stronger morphological hypothesis. Either hypothesis forces an unsampled ghost lineage for Myriapoda from the Cambrian to the mid Silurian.     

Comparative pollen morphology and ultrastructure of Mentheae subtribe Nepetinae (Lamiaceae)

This study provides new pollen data of 52 representative species belonging to all 12 genera in the currently classification of the subtribe Nepetinae, and considers the possible presence of orbicules for the first time. Pollen morphology and ultrastructure were investigated with light, scanning electron and transmission electron microscopy. Nepetinae pollen is small to large (P = 16–65 µm, E = 17–53 µm), oblate to prolate (P/E = 0.7–1.6) in shape and mostly hexacolpate (sometimes octocolpate). The exine stratification in all taxa studied is similar and characterized by unbranched columellae and a continuous, granular endexine. Sexine ornamentation in the Nepetinae is bireticulate, microreticulate or perforate. In perforate and microreticulate pattern a tendency towards a bireticulum could be recognized due to trace of secondary tectal connections. The bireticulate pattern is most common with variations of primary muri and secondary reticulum. In Hymenocrater and Schizonepeta the observed variation of sexine ornamentation is particularly valuable at the generic level. Pollen data support Lophanthus and Nepeta as very closely allied and Lallemantia is clearly distinct from Dracocephalum. The formerly suggested infrageneric relationships within Dracocephalum and Nepeta are only partly corroborated by palynological characters. Orbicules are absent in the Nepetinae.     

Comparative morphology and molecular phylogeny of aplanochytrids (Labyrinthulomycota)

Aplanochytrids comprise one of three major subgroups within the Labyrinthulomycota. We have surveyed the diversity of aplanochytrids and have discovered that most isolates are difficult to identify to species because of character plasticity and ambiguity. Ten isolates were studied using molecular phylogenies based on small subunit ribosomal gene sequences (SSU rDNA) and morphological characters derived from light microscopy, SEM and TEM (e.g., colony size, colony shape, colony pattern, agar penetration, cell shape, cell surface patterns, cell inclusion characteristics and ectoplasmic net morphology). Of these isolates, we could positively identify two of them to species, namely Aplanochytrium yorkensis (Perkins, 1973) Leander and Porter, 2000 and A. minuta (Watson and Raper, 1957) Leander and Porter, 2000. We used standardized conditions for growing aplanochytrid isolates in order to minimize environmentally induced phenotypic plasticity in our comparative studies of morphology. By mapping the morphological characters listed above onto a conservative phylogenetic topology derived from SSU rDNA sequences, we were able to identify several synapomorphies (e.g., gross colony characteristics and cell surface patterns) that serve as valuable taxonomic characters for the identification of species and specific clades of aplanochytrids.     

Biomechanical behaviour of modern human molars: Implications for interpreting the fossil record

Finite-element models of 29 intact molars were created and subjected to cleavage-type loads in order to assess differences in the biomechanical behaviour of molars. A simulated food particle, which was one-third the size of the intercuspal distance and had the properties of a Mezzettia seed, was pushed onto the occlusal basin of these models at various angles, resulting in either both or one particular cusp being preferentially loaded. In all cases, the maximum tensile stresses occurred in enamel at the intercuspal fissure. With regard to first maxillary molars, supporting (functional) and guiding (nonfunctional) cusps apparently dissipate loads equally well, whereas, in second and third maxillary molars, the guiding cusps are better designed to resist loads. Overall, lingual cusps of maxillary posterior molars dissipate loads poorly. Conversely, loads exerted toward supporting cusps of mandibular molars are consistently well dissipated, regardless of position along the tooth row. Because the directions of loads to which these teeth are best adapted change along the tooth row, it seems reasonable to suggest that these may correlate with the well-documented structural and functional orofacial complex. This study indicates that the biomechanical behaviour of molars and the orofacial skeleton are likely to have undergone complementary directional changes during evolution. Consequently, caution must be exercised in making inferences about dietary adaptations of extinct species on the basis of isolated teeth or fragmentary gnathic remains without proper regard of the orofacial skeleton as a whole. Am J Phys Anthropol 106:467–482, 1998. © 1998 Wiley-Liss, Inc.     

Incidence of allergenic pollen of Acer spp., Fraxinus spp. and Platanus spp. in the city of La Plata, Argentina: preliminary results

This work studies the airborne pollenconcentrations of Acer spp.,Fraxinus spp. and Platanus spp. sincethe pollen of these three taxa has beencharacterized as etiological agents ofpollinosis. These tree species are present inlarge amounts in the streets of La Plata city.The aeropalynological monitoring was performedwith a Hirst-type spore trap (Lanzoni VPPS,2000). The emission period of the three taxaextends from approximately late August to October.The maximum cumulative totalof arboreal pollen was found to be 30824.7from September 12 to 18. This period coincideswith the peak of total pollen concentration.Pollen grains trapped were analysed andexpressed as daily averages of 5-hour bandsper day during the whole year. Maximum pollenconcentration was registered between 10 a.m.and 2 p.m. During the studied period, 67 patients examinedat the Allergy Service of ``Hospital Interzonalde Agudos R. Rossi' (La Plata) showed allergicdisease. These allergenic episodes may beproduced by the large amount of pollen trees inthe city area.     

Pollen aperture morphology in Arecaceae: Application within phylogenetic analyses,and a summary of record of palm-like pollen the fossil

For a monocotyledonous family, the Arecaceae possess unusually varied pollen, not only in aperture number and orientation, but also in exine ornamentation. Although the majority of species have monosulcate pollen, 17 aperture types, and 13 exine types, have been described. The family belongs to a minority of monocotyledonous families in which both successive and simultaneous cytokinesis occur. The aperture types that have been described for the Arecaceae can be separated into those associated with successive, and those associated with simultaneous, cytokinesis. Palms have a long fossil record, mainly leaves and pollen, but also fruits, stems, and roots. Flowers have also been recovered. Distinctive aperture and/or exine combinations, in the pollen of some species, have prompted comparisons with fossil pollen taxa, certainly from the Late Cretaceous onwards. Occurrences of various fossil pollen taxa, frequently associated with palms, are reviewed, and their morphologies, particularly aperture characteristics, are compared with those of living palm pollen. The systematic rarity of most palm aperture types places limitations on their value in cladistic analyses. Nevertheless, certain aperture characters are of value, and do contribute to a better understanding of the evolution and phylogeny of the family. The differences between aperture types and aperture characters are addressed. The seventeen aperture types are described, and the interpretation and use of aperture characters in cladistic analyses of the Arecaceae are discussed.     

A preliminary phylogeny of the Pterasteridae (Echinodermata,Asteroidea) and the first fossil record: Late Cretaceous of Germany and Belgium

The Pterasteridae comprises a diversified group of extant largely deep-sea starfishes. Generic diagnoses have been based classically on soft tissue characters and skeletal architecture. A preliminary phylogeny of sixteen extant species is here worked out by cladistic analysis. The resulting tree suggests monophyly of extant genera and the validity of dissociated plates for identification of genera. Fossil remains of Pterasteridae are here described for the first time. By comparison with extant species, all the skeletal remains from the lower Upper Campanian of Belgium and from the lower Maastrichtian of Germany are tentatively assigned to the genusPteraster. The fossil record of starfishes is poor, but the present Late Cretaceous pterasterids provide one more piece of evidence of the high diversity of starfishes during the Mesozoic. Known Late Cretaceous and Paleogene fossils are broadly similar, which suggests the end-Cretaceous extinction event did not cause major turnover in asteroid faunal composition. As suggested for other starfish groups, both the fossil record of deep-sea Pterasteridae in shelf settings and tree topology imply an onshore-offshore evolutionary trend.      

Phylogeny and biogeography of Zelkova (Ulmaceae sensu stricto) as inferred from leaf morphology, ITS sequence data and the fossil record

To address the evolution and geographical diversification of the genus Zelkova (Ulmaceae) a phylogenetic analysis of morphological data and the sequences of the internal transcribed spacers (ITS1 and ITS2) of nuclear ribosomal DNA were used. Cladistic analyses suggested that the Chinese species Z. schneideriana and Z. sinica are basal within Zelkova. The western Asian Z. carpinifolia either appears nested between the East Asian Z. schneideriana and Z. sinica and a clade formed by the Japanese Z. serrata and two Mediterranean species, Z. abelicea and Z. sicula (ITS), or forms a clade with Z. serrata that is sister to a clade Z. abelicea plus Z. sicula (morphology). Nucleotide data suggested that gene flow occurred between Z. schneideriana and Z. serrata, and Z. carpinifolia and a lineage ancestral to Z. abelicea/sicula. Character evolution in Zelkova appears to have gone from long leaves with numerous secondary veins, coarse to shallow teeth with blunt or slightly pointed apex and small stomata, to leaves that are either long or short with numerous or few secondary veins, coarse teeth with cuspidate or obtuse apex or conspicuously shallow teeth, and dimorphic stomata displaying ‘giant stomata’ surrounded by a ring of small stomata or uniform large stomata. These results are in agreement with fossil data. Early Cainozoic fossils attributed to Zelkova from North America and Central Asia closely resemble the modern Z. schneideriana and Z. carpinifolia. The genus could have originated in the northern Pacific area and migrated to Europe after the Turgai Strait was closed during the Late Oligocene. Geographical differentiation may have started with the isolation of Chinese populations (leading to modern Z. schneideriana and Z. sinica) from high‐latitude Eurasian (North American) populations. This widespread Early Cainozoic type may have diversified into the western Asian Z. carpinifolia and the more derived Japanese and Mediterranean species during the latest Cainozoic. The modern Japanese and European/western Asian species would have differentiated relatively late, while two locally endemic Mediterranean species are the result of the cooling and development of a Mediterranean climate belt in Europe during the Pleistocene. Fossils from the Miocene and Pliocene of Europe resemble modern Z. carpinifolia and Z. serrata. Differentiation of the two Mediterranean species Z. abelicea and Z. sicula in the Late Cainozoic cannot be traced by leaf morphology. © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society, 2005, 147 , 129–157.     

New details on the morphology of fossil onagraceous pollen grains

Fossil onagraceous pollen grains from two Upper Miocene localities in E. Austria were investigated by LM and EM. Exine structure and sculpture as well as viscin threads suggest affinities with the extant genusCircea.     

Vertebrate cranial evolution: Contributions and conflict from the fossil record

In modern vertebrates, the craniofacial skeleton is complex, comprising cartilage and bone of the neurocranium, dermatocranium and splanchnocranium (and their derivatives), housing a range of sensory structures such as eyes, nasal and vestibulo-acoustic capsules, with the splanchnocranium including branchial arches, used in respiration and feeding. It is well understood that the skeleton derives from neural crest and mesoderm, while the sensory elements derive from ectodermal thickenings known as placodes. Recent research demonstrates that neural crest and placodes have an evolutionary history outside of vertebrates, while the vertebrate fossil record allows the sequence of the evolution of these various features to be understood. Stem-group vertebrates such as Metaspriggina walcotti (Burgess Shale, Middle Cambrian) possess eyes, paired nasal capsules and well-developed branchial arches, the latter derived from cranial neural crest in extant vertebrates, indicating that placodes and neural crest evolved over 500 million years ago. Since that time the vertebrate craniofacial skeleton has evolved, including different types of bone, of potential neural crest or mesodermal origin. One problematic part of the craniofacial skeleton concerns the evolution of the nasal organs, with evidence for both paired and unpaired nasal sacs being the primitive state for vertebrates.     

Basic features of gymnosperm systematics and phylogeny as evidenced by the fossil record

This paper introduces an integrated system of morphological concepts for gymnosperm fructifications, which does not lean upon any system existing for other higher plants. Comparative analytical treatment of all available characters of the most thoroughly studied fossil genera provided the foundation for an ordered ranking of congregations, each unit being assigned to the status of families, orders and classes. The transformation of the generative and vegetative organs has been traced along various phylogenetic branches. A new large phylogenetic branch (class Ginkgoopsida), beginning with the Lower Carboniferous Calamopityales, has been established. The lineage evolved from this order to Callistophytales and further to Peltaspermales. The family Peltaspermaceae encompasses, among others, plant types formerly regarded as ginkgoaleans. The orders Ginkgoales, Leptostrobales (Czekanowskiales) and Caytoniales evolved from the Peltaspermales. The order Arberiales (glossopterids) evidently evolved from the Calamopityales. In the lineage from Calamopityales to Ginkgoales a common seed type is conserved (platyspermic, non-cupular with two vascular bundles in the integument). Radiospermic seeds are conserved in the class Cycadopsida. In the lineage from Lagenostomales to Trigonocarpales the radially symmetrical cupule underwent modification into an integument of the same type of symmetry. The earliest Lagenostomales with the bilaterally symmetrical cupule evolved into the Cordaitanthales, where the cupule, also undergoing modification, was transformed into a bilaterally-symmetrical integument. In Cordaitanthales and their descendents the Pinales the seeds became secondarily platyspermic (in contrast to the primary non-cupular and primary platyspermic seeds in Ginkgoopsida); their vascularization was progressively reduced. These two orders are grouped into the class Pinopsida. It is believed that angiosperm seeds are in effect radiospermic with a radial cupule, their vascularization also being progressively reduced. If this holds true, the angiosperm ancestry should be sought in the class Cycadopsida. The Caytoniales, Arberiales, Peltaspermales, Leptostrobales and other orders of the class Ginkgoopsida should be excluded from the stock of probable angiosperm ancestors. A new gymnosperm phylogeny has been proposed and the evolution of the phylogenetic branches outlined in terms of the phytochoria system of the geological past. The basic evolutionary innovations took place within the Equatorial Belt and adjacent ecotone areas. Three types of processes, often underrated, have a paramount role in gymnosperm phylogeny. They are defined as follows: (1) homoeotic transformations of organs; corresponding to them are heterotopies, in the morphological aspect, and saltations, in the evolutionary sense; (2) dedifferentiation of the organs (the shift of one ontogenetic program onto various organs); (3) transitive polymorphism (conservation in diversity of a certain organ during phylogeny). These processes probably serve to indicate that rearrangement in the functions of the regulatory genes played an important role in the evolution of gymnosperms.     

Pollen morphology and fossil record of the feathery mistletoe family Misodendraceae

Misodendraceae is a small family of mistletoes in the order Santalales. Its distribution is restricted to the southern South American temperate forests. The family comprises the sole genus Misodendrum with eight species of hemiparasitic shrubs, mainly parasitising the southern beech Nothofagus. This contribution presents palynological evidence from seven species, using light microscopy and scanning electron microscopy. Pollen grains are consistently small, periporate and echinate, although differences in the length of echini and number and size of pores were noted. Pollen features can be used to distinguish groups of species and, in some cases, individual species. Cluster analysis of pollen characters differentiates two main groups: one includes M. brachystachyum, M. oblongifolium and M. quadriflorum; and the other includes M. gayanum, M. linearifolium, M. punctulatum and M. angulatum. Palynological results are compared with previous systematic studies of the family. The South American fossil pollen record is summarised and characters of the fossil pollen are analysed using UPGMA to test the relationships between extant and fossil species. Miocene pollen resulted similar to species of subgenus Angelopogon while Eocene pollen is disimilar to extant species of Misodendraceae.     

Clumping behavior as a strategy against drilling predation: Implications for the fossil record

Drilling gastropod predators are of particular interest to paleontologists, because predatory drill-holes in marine invertebrates serve as one of the rare sources of data for the study of ancient predator-prey interactions. Modern laboratory studies are an important part of predation research providing valuable ecological insight and constraining fossil evidence and interpretations. Previous studies have shown that mussels use clumping behavior against durophagous predation [Okamura, B., 1986. Group living and the effects of spatial position in aggregations of Mylitus edulis. Oecologia 69, 341-347.; Lin, J., 1991. Predator-prey interactions between blue crabs and ribbed mussels living in clumps. Estuar. Coast. Shelf Sci. 32, 61-69.], but its role against drilling predation had not been explored. In this study, we explore the effect of clumping on predator success (drill-hole frequency) and prey handling (drill-hole position) using the mussel, Mytilus trossulus, as prey and the gastropod, Nucella lamellosa, as drilling predator. We assigned mussels to two groups: in one, mussels were allowed to clump together with their byssal threads, and in the other, they were kept separate. We observed a significant decrease in the drilling frequency within the group containing clumped mussels, confirming that clumping acts as a successful anti-predatory strategy against drilling predators. The use of clumping as an effective strategy against multiple types of predators may relax the trade-offs associated with aggregated lifestyles [Bertness, M.D., Grosholz, E., 1985. Population dynamics of the ribbed mussel, Geukensia demissa: the costs and benefits of an aggregated distribution. Oecologia 67, 192-204.]. The increased benefit and unchanged metabolic cost of clumped living alters estimates of individual fitness with evolutionarily significant implications (e.g., eliminating the need to invoke group or species selection to explain the adaptive benefit of an aggregated lifestyle). In spite of potential differences in prey handling and grappling due to clumping, mean drill-hole placement and variation in drill-hole placement showed no significant differences between the two groups. These observations suggest that comparison of predation intensities across clumping and non-clumping taxa must consider the anti-predatory effect of this behavior.     

Pollen morphology and ultrastructure of the Bennettitales: In situ pollen of Cycadeoidea

The micromorphology and ultrastructure of in situ pollen from Cycadeoidea dacotensis are described from permineralized specimens collected from the Lower Cretaceous of North America. Pollen grains are ovoid and relatively small, averaging 25 μm in length and 12 μm in width. Grains are monosulcate with the exine typically invaginated in apertural regions. Exine ornamentation ranges from punctate to psilate. The exine averages 0.73 μm in thickness and is composed of a light-staining sexine and a dark-staining nexine. The sexine consists of a thin, homogeneous tectum, typically with a well-defined inner boundary, and a thicker granular infratectum. The infratectal granules are relatively uniform in size, however, variation occurs in the arrangement of granules. In some grains, the sexine appears homogeneous because there is little lacunal space between the individual granules. The granular infratectum is in direct contact with the underlying nexine. The nexine is uniform in thickness in both apertural and nonapertural regions, and it lacks lamellae throughout. Pollen morphology and ultrastructure are compared with those of the bennettitalean genus Leguminanthus and the dispersed genus Monosulcites. In addition, the fine structure of Cycadeoidea pollen is compared to that of the gymnosperm groups with which the Bennettitales are regarded to be most closely related, including Gnetales, Pentoxylales, and Eucommiidites-type pollen-producing plants.     

Coding of intraspecific nucleotide polymorphisms: A tool to resolve reticulate evolutionary relationships in the ITS of beech trees (Fagus L., Fagaceae)

The internal transcribed spacers ITS1 and ITS2 of the nuclear ribosomal DNA (rDNA) have recently been found to display remarkable intraspecific polymorphism, a feature suggested as limiting their value for phylogenetic reconstructions. A comparative study of oligonucleotide motives and intraindividual nucleotide variability across all species of the tree genus Fagus (beech) shows, however, that this intraspecific ITS polymorphism follows a particular pattern, which can be used to detect reticulation and ancient polymorphism within the genus. Coding ITS polymorphisms as phylogenetically informative characters, moreover, resulted in better‐resolved phylogenies than traditional ‘base‐per‐base’ maximum parsimony and maximum likelihood analyses.     

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.