The effects of locomotion on the structural characteristics of avian limb bones

Despite the wide range of locomotor adaptations in birds, little detailed attention has been given to the relationships between the quantitative structural characteristics of avian limb bones and bird behaviour. Possible differences in forelimb relative to hindlimb strength across species have been especially neglected. We generated cross‐sectional, geometric data from peripheral quantitative computed tomography scans of the humerus and femur of 127 avian skeletons, representing 15 species of extant birds in 13 families. The sample includes terrestrial runners, arboreal perchers, hindlimb‐propelled divers, forelimb‐propelled divers and dynamic soarers. The hindlimb‐propelled diving class includes a recently flightless island form. Our results demonstrate that locomotor dynamics can be differentiated in most cases based on cross‐sectional properties, and that structural proportions are often more informative than bone length proportions for determining behaviour and locomotion. Recently flightless forms, for example, are more easily distinguished using structural ratios than using length ratios. A proper phylogenetic context is important for correctly interpreting structural characteristics, especially for recently flightless forms. Some of the most extreme adaptations to mechanical loading are seen in aquatic forms. Penguins have forelimbs adapted to very high loads. Aquatic species differ from non‐aquatic species on the basis of relative cortical thickness. The combination of bone structural strength and relative cortical area of the humerus successfully differentiates all of our locomotor groups. The methods used in this study are highly applicable to fossil taxa, for which morphology is known but behaviour is not. The use of bone structural characteristics is particularly useful in palaeontology not only because it generates strong signals for many locomotor guilds, but also because analysing such traits does not require knowledge of body mass, which can be difficult to estimate reliably for fossil taxa. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 153 , 601–624.     

Microanatomy of the amniote femur and inference of lifestyle in limbed vertebrates

The femoral microanatomy of 155 species of extant amniotes (57 species of mammals, 15 species of turtles, 56 species of lepidosaurs, and 27 species of birds) of known lifestyle is studied to demonstrate a possible link between some basic parameters of bone structure and specific lifestyles, as well as phylogenetic relationships between taxa. Squared change parsimony with random taxon reshuffling and pairwise comparisons reveal that most compactness and size parameters exhibit both phylogenetic and ecological signals. A discriminant analysis produces several inference models, including a ternary model (aquatic, amphibious, terrestrial) that yield the correct lifestyle in 88% of the cases. These models are used to infer the lifestyle of three extinct Permian temnospondyls: Eryops megacephalus, Acheloma dunni, and Trimerorhachis insignis. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 644–655.     

Speciation and evolution of eco‐climatic ranges in the intertropical African dung beetle genus,Diastellopalpus van Lansberge

We investigate how late Cenozoic orogenics and climatic change might have influenced the history of taxon diversification and current species ranges of an endemic, Afrotropical, insect genus. Diastellopalpus van Lansberge is a near basally‐derived taxon in the dung beetle tribe Onthophagini (Coleoptera: Scarabaeidae: Scarabaeinae) that has diversified into 32 known species primarily centred on intertropical forests. Basal dichotomies in both published and re‐analysed phylogenies divide the species into clades that are geographically centred either to the east or west of the south‐east highlands that underwent uplift from the Miocene. There is broad climatic overlap between many of the species but clear separation along a minimum spanning tree in ordinal space where they are divided into taxa with either lowland or highland centres of distribution. Observed spatial distributions of six defined species groups mostly differ from predicted climatic ranges, presumably as a result of historical constraints on species dispersal. A trend from dominance of montane or wet lowland forest associations in species lineages derived from more basal nodes (Groups A–C) to dominance of drier upland forest and moist woodland associations in species lineages derived from a more terminal node (Groups D–F) is perhaps linked to the stepped trend to cooler, dryer climate in the late Cenozoic. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 407–423.     

Rowing locomotion by a stonefly that possesses the ancestral pterygote condition of co-occurring wings and abdominal gills

A leading hypothesis for the origin of insect wings is that they evolved from thoracic gills that were serial homologues of the abdominal gills present in fossil pterygotes and in the nymphs of some modern mayflies, damselflies and stoneflies. Co-occurrence of thoracic wings and abdominal gills is the primitive condition for fossil pterygote insects, whereas the winged stage of modern insects almost exclusively lacks abdominal gills. Here we examine the locomotor behaviour and gill morphology of a stonefly, Diamphipnopsis samali (Plecoptera), which retains abdominal gills in the winged adult stage. This species can fly, but also uses its forewings as oars to accomplish rowing locomotion along the surface of water. The abdominal gills are in contact with both air and water during rowing, and their elaborately folded surface suggests an ability to contribute to gas-exchange. D. samali nymphs also have behaviours that place them in locations where their gills are exposed to air; they forage at night at the stream margin and within bubble curtains in rapids. These traits may exemplify an early pterygote condition in which gill and protowing function overlapped in an amphibious setting during a transition from aquatic to aerial locomotion and gas exchange. Rowing locomotion provides a novel and mechanically intermediate stage for the wings-from-gills and surface-skimming hypotheses for the origin of insect wings and flight.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 79, 341–349.     

Fitting the bill: do different winter food resources influence juniper titmouse (Baeolophus ridgwayi) bill morphology?

Divergent adaptive selection is a prominent mechanism influencing patterns of morphological diversity. We used the juniper titmouse [Baeolophus ridgwayi (Richmond, 1902)], a nonmigratory passerine that inhabits woodlands throughout western North America, to investigate variation in bill morphology in relation to diet and geography. We gathered data from museum specimens and used morphometric techniques to determine the relative strength of support for competing hypotheses using information theoretics: (1) differences in bill morphology are predicted by a key winter food resource that each regional population consumes (seeds of different juniper tree species); or (2) bill morphology scales with body size, and both increase along a latitudinal gradient. Juniper species emerged as the variable with the most support explaining variation in bill size, supporting the hypothesis that seed sizes influence bill size, independently of body size. The shape analysis revealed no distinct patterns in bill shape variation, but employed a powerful method for evaluating the strength of support for numerous candidate models. The differences in bill size of juniper titmice across their range are likely to reflect adaptive variation, because bill morphology is highly heritable in birds, juniper titmouse gene flow appears to be relatively low, and there is a clear mechanistic explanation for why bill sizes may differ among the ranges of the three juniper species. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 667–679.     

Shiny wing scales cause spec(tac)ular camouflage of the angled sunbeam butterfly,Curetis acuta

The angled sunbeam butterfly, Curetis acuta (Lycaenidae), is a distinctly sexually dimorphic lycaenid butterfly from Asia. The dorsal wings of female and male butterflies have a similar pattern, with a large white area in the female and an orange area in the male, framed within brown–black margins. The ventral wings of both sexes are silvery white, which is caused by stacks of overlapping, non‐pigmented, and specular‐reflecting scales. With oblique illumination, the reflected light of the ventral wings is strongly polarized. We show that the silvery reflection facilitates camouflage in a shaded, foliaceous environment. The ecological function of the silvery reflection is presumably two‐fold: for intraspecific signalling in flight, and for reducing predation risk at rest and during hibernation. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 279–289.     

Social bonds in birds are associated with brain size and contingent on the correlated evolution of life‐history and increased parental investment

In birds, large brains are associated with a series of population‐level phenomena, including invasion success, species richness, and resilience to population decline. Thus, they appear to open up adaptive opportunities through flexibility in foraging and anti‐predator behaviour. The evolutionary pathway leading to large brain size has received less attention than behavioural and ecological correlates. Using a comparative approach, we show that, independent of previously recognized associations with developmental constraints, relative brain size in birds is strongly related to biparental care, pair‐bonding, and stable social relationships. We also demonstrate correlated evolution between large relative brain size and altricial development, and that the evolution of both traits is contingent on biparental care. Thus, biparental care facilitates altricial development, which permits the evolution of large relative brain size. Finally, we show that large relative brain size is associated with pair‐bond strength, itself a likely consequence of cooperation and negotiation between partners under high levels of parental investment. These analyses provide an evolutionary model for the evolution of and prevalence of biparental care, altricial development, and pair‐bonding in birds. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 111–123.     

Hatching asynchrony and growth trade‐offs within domesticated and wild zebra finch,Taeniopygia guttata,broods

The Australian zebra finch, Taeniopygia guttata, is a widely used model organism, yet few studies have compared domesticated and wild birds with the aim of examining its relevance as an evolutionary model species. Domestic and wild broods hatch over approximately 4 and 2 days, respectively, which is important given that nestlings can fledge after as little as 12 days, although 16–18 days is common. We aimed to evaluate the extent to which the greater hatching asynchrony in domestic stock may effect reproductive success through greater variance in size hierarchies, variance in within‐brood growth rates, and partial brood mortality. Therefore, by simultaneously controlling brood sizes and experimentally manipulating hatching intervals in both domesticated and wild birds, we investigated the consequences of hatching intervals for fledging success and nestling growth patterns, as well as trade‐offs. Fledging success was similarly high in domestic and wild broods of either hatching pattern. Nonetheless, between‐brood analyses revealed that domestic nestlings had significantly higher masses, larger skeletal characters, and longer wings than their wild counterparts, although wild nestlings had comparable wing lengths at the pre‐fledging stage. Moreover, within‐brood analyses revealed only negligible differences between domestic and wild nestlings, and larger effects of hatching order and hatching pattern. Therefore, despite significant differences in the hatching intervals, and the ultimate size achieved by nestlings, the domestication process does not appear to have significantly altered nestling growth trade‐offs. The present study provides reassuring evidence that studies involving domesticated zebra finches, or other domesticated model organisms, may provide reasonable adaptive explanations in behavioural and evolutionary ecology. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 763–773.     

Avian eggshell coloration: new perspectives on adaptive explanations

Recent work suggests that the evolution of egg coloration may have been constrained in three important ways that have not yet been critically synthesized in any review. First, on account of birds being able to see in the ultraviolet spectrum, the interaction between the properties of avian vision and the light environment of nests imply different perceptions of egg coloration from those experienced by humans. Second, a new hypothesis to explain blue–green egg coloration interprets it as a sexually selected signal to males of the laying female's genetic quality. Third, evidence from taxa as divergent as sparrowhawks and great tits indicates that protoporphyrin pigments responsible for maculation (spotting patterns) have a structural function in compensating for eggshell thinning, as caused by calcium stress, and, more recently, dichlorodiphenyltrichloroethane. We consider this to be the most convincing explanation for the primary function of spotting, although an important secondary function might arise through the fact that individual patterns of maculation may allow birds to identify their own eggs, effectively serving as signatures in the face of inter‐ or intra‐specific brood parasitism. These constraints or hypotheses are not mutually exclusive, and should not be taken to imply that one, but not other, agents of selection might apply to any one species. However, the sexually‐selected eggshell coloration hypothesis is least plausible for hole‐nesting birds because of the poor light quality available, although such species have been the focus of research in this area, and only a single experimental study has shown a link between egg coloration and male provisioning. Furthermore, the observed relationships between female phenotypic quality and egg traits do not necessarily imply that they have signalling functions. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 753–762.     

Variation in nectar–sugar profile of Anchusa and allied genera (Boraginaceae)

The nectar–sugar profile (fructose, glucose and sucrose) of 14 species of Anchusa and five members of the allied genera Anchusella, Cynoglottis, Hormuzakia and Lycopsis (Boraginaceae: tribe Boragineae) was determined. Most of the species examined (c. 74%) produce sucrose‐dominant nectar, whereas the remaining taxa produce sucrose‐rich nectars. Little variation in nectar–sugar composition was found in some species, even when sampling was repeated in different years and/or localities. Average sucrose concentration was 57.75% (coefficient of variation 19.1%). The only floral morphological character that was correlated with the nectar–sugar profile is the length of the corolla tube, as taxa with relatively long floral tubes produce nectar with lower glucose concentrations. The flowering period is also related to sugar composition, as nectar of late‐flowering species contains lower sucrose concentrations. However, small differences in sugar profiles do not reflect phylogenetic relationships based on molecular studies. It would appear that dry habitats and time of flowering are the main determinants of nectar–sugar composition in the genus Anchusa sensu lato. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 162 , 616–627.     

The systematic importance of anatomical data in Gagea (Liliaceae) from the Flora Iranica area

Anatomical features of basal leaves, pedicels and tepals of 22 species of Gagea belonging to four sections (Platyspermum, Plecostigma, Gagea and Didymobulbos) are investigated. Anatomical characters are mapped onto a molecular phylogenetic tree and their evolution is evaluated. The systematic importance of the anatomical characters is discussed. Anatomical characters are more systematically useful in the Irano‐Turanian taxa than in Euro‐Siberian taxa. The presence of collenchyma and/or sclerenchyma and the pentagonal outline of the transverse section of the basal leaf is found in Irano‐Turanian taxa of section Platyspermum and is mostly absent in Euro‐Siberian taxa. A diagnostic key based on combined anatomical characters is provided. The level of variation in anatomical characters is greater in the basal leaf than the pedicel and lowest in the tepals. Convergent evolution in anatomical characters is associated with ecological shifts between sunny, open, dry habitats and closed, humid habitats. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 164 , 155–177.     

Phylogeographic analysis of the nocturnal velvet ant genus Dilophotopsis (Hymenoptera: Mutillidae) provides insights into diversification in the Nearctic deserts

Understanding the history of diversification in the North American deserts has long been a goal of biogeographers and evolutionary biologists. Although it appears that a consensus is forming regarding the patterns of diversification in the Nearctic deserts in vertebrate taxa, little work has been done exploring the historical biogeography of widespread invertebrate taxa. Before a robust model of geobiotic change in the North American deserts can be proposed, it needs to be determined whether the same historical events affected vertebrate and invertebrate taxa in the same way. We explore the phylogeographic patterns in a widespread nocturnal wasp genus Dilophotopsis using two rDNA loci, the internal transcribed spacer regions 1 and 2 (ITS1 and ITS2). We use Bayesian phylogenetic analysis and haplotype network analysis to determine whether a consistent geographic pattern exists among species and populations within Dilophotopsis. We also used molecular dating techniques to estimate divergence dates of the major phylogenetic clades. Our analyses indicates that the species‐level divergences in Dilophotopsis occurred in the Neogene, and likely were driven by mountain building during the Miocene–Pliocene boundary (approximately 5 Mya) similar to the divergences in many vertebrate taxa. The population‐level divergences within species occurred during the Pleistocene (0.1–1.8 Mya). The present study shows that similar patterns of diversification exist in vertebrate and invertebrate taxa. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 360–375.     

Detarieae sensu lato (Fabaceae) from the Late Oligocene (27.23 Ma) Guang River flora of north‐western Ethiopia

New species of caesalpinioid legumes, Cynometra sensu lato and Afzelia, are described from the Late Oligocene (27.23 Ma) Guang River flora in north‐western Ethiopia. Both taxa show leaf characteristics that are shared with extant species in the Guineo‐Congolian, Sudanian and/or Zambezian regions of Africa today. The presence of these two species in Ethiopia during the Palaeogene provides further evidence of the importance of the legume tribe Detarieae in northern and north‐eastern Africa throughout much of the Cenozoic, even although the clade is poorly represented in these regions today. The fossil record documents a significant palaeogeographical and evolutionary history of Detarieae in Africa, especially compared with that of Europe and Anatolia. Based on this evidence, it is unlikely that significant diversification of extant African Detarieae took place on the Eurasian landmass. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 163 , 44–54.     

Failure to cospeciate: an unsorted tale of millipedes and mites

Mites form symbiotic relationships with many animal taxa, including fish, amphibians, reptiles, birds, mammals, mollusks and arthropods. They are often found living on millipedes and it has often been speculated that these two groups of arthropods have, in some cases, undergone coevolution. However, this hypothesis has never been formally tested. Millipedes of the family Xystodesmidae Cook 1895 (Diplopoda: Polydesmida) and their symbiotic mites of the genus Stylochyrus Canestrini & Canestrini 1882 were collected in broadleaf forests of the eastern USA. The DNA from two mitochondrial regions (16S/12S and cox1) was sequenced for all collected millipede and mite specimens. Phylogenetic trees were reconstructed for both millipede and mite taxa using Bayesian inference. Pairwise distance data were used in distance‐based coevolutionary analyses and reconstructed phylogenies were used in tree‐based coevolutionary analyses. The phylogenetic analyses indicate Stylochyrus and xystodesmid millipede evolutionary history is incongruent. Moreover, the evolutionary relationships among mite individuals and populations have very low support values and indicate little to no geographic structuring. The coevolutionary analyses likewise detected no pattern of coevolution among these millipede and mite lineages. Unlike many arthropod species, Stylochyrus mites appear to be highly vagile. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 272–287.     

Evaluating hypotheses on the origin and diversification of the ringneck snake Diadophis punctatus (Colubridae: Dipsadinae)

Close affinities recognized between taxa in Mexico and the contiguous USA have led to a variety of biogeographical scenarios. One such hypothesis suggests that species that occur in both countries have an origin in central Mexico followed by dispersal into the USA. This study expands upon previous phylogeographical work of the ringneck snake Diadophis punctatus by incorporating new data from previously unsampled areas appropriate to critically assess hypotheses regarding a Mexican origin for this species. Maximum likelihood and maximum parsimony analyses inferred a derived position for the lineage from southern Mexico with constraint tests for alternate evolutionary hypotheses resulting in significantly worse likelihood values. Ancestral area reconstructions inferred an origin for D. punctatus in the south‐eastern USA followed by a south‐east to north‐east then westward directionality of historical migration. The position within the phylogeny and date estimate for the south‐western + Mexico clade suggests a recent invasion into central Mexico with expansion into the Nearctic/Neotropic transition zone. The extensive lineage diversity inferred from the mtDNA suggests that the genus is a complex of cryptic species whose conservational status should be re‐evaluated on both the national and regional levels. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 158 , 629–640.     

Molecules,ecology, morphology,and songs in concert: how many species is Arremon torquatus (Aves: Emberizidae)?

The acceptance of the generalized or unified concept of species (i.e. that species are segments of population lineages) implies that an important task for systematists is to focus on identifying lineages and on testing hypotheses about the acquisition of properties such as phenotypic diagnosability, reciprocal monophyly, or mechanisms of reproductive isolation. However, delimiting species objectively remains one of the most challenging problems faced by biologists. In the present study, we begin to tackle the thorny issue of species delimitation in a complicated group of Neotropical passerine birds (the Arremon torquatus complex, Emberizidae) in which sets of characters vary substantially across space, but do not obviously vary in a concerted fashion. To earlier discussions of species limits in the group, we add a historical perspective offered by a recent molecular phylogeny, present quantitative analyses of morphological and vocal variation, and incorporate ecological niche models as a new tool that aids species delimitation by highlighting cases of ecological distinctiveness and cases where populations appear to be in independent evolutionary trajectories, despite being connected by environments unlikely to represent barriers to gene flow. We demonstrate that at least one pair of taxa (and likely another) currently treated as conspecific are, in fact, distinct lineages that merit species status under essentially any species criterion. However, other pairwise comparisons are not as straightforward owing to nonconcordant patterns of variation in different traits and to the impossibility of distinguishing which characters are causes and which are consequences of reproductive (and evolutionary) isolation. After considering several alternatives, we propose a provisional classification of the complex recognizing eight tentative species‐level taxa. Although this classification is likely to change as more detailed work is conducted, it provides a better foundation for studying the biology of these birds and helps to better describe their diversity, which is obscured when all taxa are subsumed into a single species name. The present study highlights several outstanding challenges, both practical and conceptual, for future studies. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 152–176.     

Australian parasitic Ogyris butterflies: east–west divergence of highly‐specialized relicts

Not all butterflies are innocuous plant‐feeders. A small number of taxa in the family Lycaenidae have graduated from mutualistic partnerships with ants to predatory or parasitic associations. These highly‐specialized life histories, involving butterfly larvae living inside ant colonies, are often associated with rarity and vulnerability to extinction. In the present study, we examined the evolutionary relationships of a poorly‐known group of seven taxa herein referred to as the idmo‐group within the Australian lycaenid genus Ogyris. The idmo‐group has a relictual distribution across southern Australia and includes taxa with highly‐specialized phytophagous and myrmecophagous life histories. A phylogeny based on mitochondrial DNA (cytochrome oxidase I and cytochrome b] and the nuclear DNA locus elongation factor 1α (EF1α), generally agrees with current taxonomy and supports the recent elevation of endangered taxon Ogyris halmaturia to full species status. The transition to myrmecophagy was dated to the mid‐Miocene (approximately 16 Mya), when southern Australia experienced a humid climate and extensive mesic biome. The arid Nullarbor Plain, a major biogeographical feature of central southern Australia, divides the remnants of this mesic biome into south‐eastern and south‐western isolates. Late‐Miocene to Pliocene divergence estimates for polytypic Ogyris species across the Nullarbor were older than estimates made for similarly distributed birds, butterflies, mammals, and reptiles, which mostly date to the Pleistocene. The concept of highly‐specialized life histories as evolutionary dead‐end strategies is well exemplified by the idmo‐group. Data compiled on the known extant subpopulations for idmo‐group taxa show that all of these extraordinary butterflies are scarce and several face imminent threat of extinction. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 473–484.     

Convergent evolution of sunbird pollination systems of Impatiens species in tropical Africa and hummingbird systems of the New World

The bird pollination systems of the New and Old Worlds evolved independently, and differ in many aspects. New World plants are often presented as those adapted to hovering birds while Old World plants to perching birds. Most Neotropical studies also demonstrate that in hummingbird species rich assemblages, only a small number of highly specialized birds exploits the most specialized plants with long corollas. Nevertheless, recent research on bird–plant pollination interactions suggest that sunbird pollination systems in the Old World have converged more with the highly specialized hummingbird pollination systems than previously thought. In this study we focus on the pollination systems of the bird pollination syndrome Impatiens species on Mt. Cameroon, West Africa. We show that despite the high diversity of sunbirds on Mt. Cameroon, only Cyanomitra oritis appear to be important pollinator of all Impatiens species. This asymmetry indicates the absence of pair wise co‐evolution and points to a diffuse co‐evolutionary process resulting in guilds of highly specialized plants and birds; a situation well known from hummingbirds and specialized plant communities of the New World. Additionally, the herbaceous habits of Impatiens species, the frequent adaptations to pollination by hovering birds, and the habitat preference for understory in tropical forests or epiphytic growth, resemble the highly specialized Neotropical plants. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115 , 127–133.     

Molecular phylogenetics of Uvaria (Annonaceae): relationships with Balonga,Dasoclema and Australian species of Melodorum

An extended molecular phylogenetic analysis of Uvaria (Annonaceae) is presented, using maximum parsimony, maximum likelihood and Bayesian methods, based on sequences of four plastid DNA regions (matK, psbA‐trnH spacer, rbcL and trnL‐F). The additional taxa include the monotypic West African genus Balonga, the monotypic South‐East Asian genus Dasoclema and seven Australian representatives of the genus Melodorum. The results indicate that all of these taxa are nested within a well‐supported clade otherwise consisting of Uvaria species, indicating that their taxonomic treatment needs to be reassessed. The distinguishing morphological characteristics of the taxa are re‐evaluated and interpreted as specialized adaptations of the basic Uvaria structure. The genus Uvaria is accordingly extended following the transfer of these species, necessitating six new nomenclatural combinations and two replacement names. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 163 , 33–43.     

Sculpture and vascularization of dermal bones,and the implications for the physiology of basal tetrapods

Sculpture of dermal bones and their vascularization in basal tetrapods are closely connected. Ontogenetic data suggest that the large vessels that coursed to the superficial bone surface induced the formation of sculptural ridges and tubercles around their openings. Imprints show that the vessels continued on the bone surface and coursed within furrows or pits, where they were protected by the sculpture from mechanical damage. Dermal bone histology indicates a consolidation of the integument in basal tetrapods by strong, mineralized Sharpey's fibres in the sculptural ridges and tubercles, and by the presence of metaplastic tissue in several taxa. Because of the tight integration of bone and dermis, the large vessels were not able to spread over the sculptural elements, but instead had to pass interosseously. The diverse sculptural morphologies depend on the variation in height and width of the ‘nodal points’ and their connecting ridges, and in the size and shape of the enclosed cells and furrows. A principal component analysis (PCA) and discriminant function analysis (DFA) of 47 basal tetrapod taxa with 12 discrete characters shows that dermal sculpture is suited for distinguishing some main basal tetrapod lineages. Taxa that are interpreted as being largely aquatic have generally a more regular sculpture than presumably terrestrial ones. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 160 , 302–340.