Dispersal and diversity in the earliest North American sauropodomorph dinosaurs, with a description of a new taxon

Sauropodomorph dinosaurs originated in the Southern Hemisphere in the Middle or Late Triassic and are commonly portrayed as spreading rapidly to all corners of Pangaea as part of a uniform Late Triassic to Early Jurassic cosmopolitan dinosaur fauna. Under this model, dispersal allegedly inhibited dinosaurian diversification, while vicariance and local extinction enhanced it. However, apomorphy-based analyses of the known fossil record indicate that sauropodomorphs were absent in North America until the Early Jurassic, reframing the temporal context of their arrival. We describe a new taxon from the Kayenta Formation of Arizona that comprises the third diagnosable sauropodomorph from the Early Jurassic of North America. We analysed its relationships to test whether sauropodomorphs reached North America in a single sweepstakes event or in separate dispersals. Our finding of separate arrivals by all three taxa suggests dispersal as a chief factor in dinosaurian diversification during at least the early Mesozoic. It questions whether a 'cosmopolitan' dinosaur fauna ever existed, and corroborates that vicariance, extinction and dispersal did not operate uniformly in time or under uniform conditions during the Mesozoic. Their relative importance is best measured in narrow time slices and circumscribed geographical regions.     

Geographic distributions of homosporous ferns: does dispersal obscure evidence of vicariance?

The central problem in biogeography is that interactions between different processes result in the formation of historical patterns, such that it is difficult to discriminate the relative roles of vicariance and dispersal. Ferns are distributed by small wind-dispersed propagules that are produced in very large numbers and capable of dispersing thousands of kilometers. Thus, most taxon distributions in ferns are assumed to be a function of dispersal rather than vicariance. Here, we review some case examples that provide good evidence for vicariance and dispersal in ferns. We then ask whether dispersal is so extensive in ferns that vicariance is no longer detectable in most cases. Although we think that too few studies have been carried out to make generalizations at this stage, we outline the criteria for an effective research programme that can address this issue. Phylogenetic and distributional data are needed, not only because they are lacking in an evolutionarily important group of organisms, but also because data from ferns and other cryptogams are likely to be crucial in making broad biogeographic statements.     

Coming to America: multiple origins of New World geckos

Geckos in the Western Hemisphere provide an excellent model to study faunal assembly at a continental scale. We generated a time-calibrated phylogeny, including exemplars of all New World gecko genera, to produce a biogeographical scenario for the New World geckos. Patterns of New World gecko origins are consistent with almost every biogeographical scenario utilized by a terrestrial vertebrate with different New World lineages showing evidence of vicariance, dispersal via temporary land bridge, overseas dispersal or anthropogenic introductions. We also recovered a strong relationship between clade age and species diversity, with older New World lineages having more species than more recently arrived lineages. Our data provide the first phylogenetic hypothesis for all New World geckos and highlight the intricate origins and ongoing organization of continental faunas. The phylogenetic and biogeographical hypotheses presented here provide an historical framework to further pursue research on the diversification and assembly of the New World herpetofauna.     

New insight into the phylogenetic and biogeographic history of genus Ficus: Vicariance played a relatively minor role compared with ecological opportunity and dispersal

Studies on the evolution of tropical taxa emphasize the role ofvicariance and the break-up of Gondwana in explaining modern distributions.Earlier studies on figs (Ficus spp.) support this view.In the current study,we used an expanded sample (208 spp.) and improved molecular dating techniques to reconstruct the phylogenetic and biogeographic history of Ficus.Consistent with previous studies,our biogeographic analysis indicated that the ancestor of Ficus was present in Gondwana.However,a relaxed clock analysis relying on uncorrelated rates in BEAST suggested that the Neotropical section Pharmacosycea split-off in South America 86.67 Mya,and that other Ficus lineage ancestors originated in India.Most of the basal lineages appeared to have diverged following KT extinction,then rapidly diversified after India collided with continental Asia.The Afrotropical species most likely evolved initially in the Indian subcontinent then dispersed to Africa,either in the late Cretaceous of Madagascar or even later,following the Eocene collision of India with Asia.The Neotropical section Americana,either islandhopped to South America or took a northern route to the Americas through Europe prior to the terminal Eocene global cooling event.Ficus may have arrived in eastern Malesia following the collision of India with Asia,then widely dispersed thereafter.Given the wide ranges in our date estimates,several other scenarios are possible.However,contrary to earlier reports,our analyses suggest that vicariance played a relatively minor role compared with ecological opportunity and dispersal in the diversification of genus Ficus.     

Multiple intercontinental dispersals shaped the distribution area of Hordeum (Poaceae)

The grass genus Hordeum (Poaceae, Triticeae), comprising 31 species distributed in temperate and dry regions of the world, was analysed to determine the relative contributions of vicariance and long-distance dispersal to the extant distribution pattern of the genus. Sequences from three nuclear regions (DMC1, EF-G and ITS) were combined and analysed phylogenetically for all diploid (20 species) and two tetraploid Hordeum species and the outgroup Psathyrostachys. Ages of clades within Hordeum were estimated using a penalized likelihood analysis of sequence divergence. The sequence data resulted in an almost fully resolved phylogenetic tree that allowed the reconstruction of intrageneric migration routes. Hordeum evolved c. 12 million years ago in South-west Asia and spread into Europe and Central Asia. The colonization of the New World and South Africa involved at least six intercontinental exchanges during the last 4 million years (twice Eurasia-North America, North America-South America, twice South America-North America and Europe-South Africa). Repeated long-distance dispersal between the northern and southern hemisphere were important colonization mechanisms in Hordeum.     

Effect of vagility potential on dispersal and speciation in rainforest insects

Explaining global patterns of species diversity is one of the most challenging objectives in biology. Most agree that complex interactions between historical and current processes are responsible for such patterns, although rigorous testing of possible mechanisms has proved difficult. Here we demonstrate that macropterous and flightless insects in the rainforests of north-eastern Australia have dispersed and speciated in similar manners. These results contradict the traditionally held assumption that differences in vagility potential would lead to significant differences in distributional patterns and speciation modes.     

Phylogeny and co-speciation in feather mites of the subfamily Avenzoariinae (Analgoidea: Avenzoariidae)

A cladistic analysis of phylogenetic relationships is carried out for the feather mite subfamily Avenzoariinae. The analysis is made at two different taxonomic levels, for 19 genera of the all family Avenzoariidae and for taxa of species rank for the Avenzoaria and Bychovskiata generic groups. A subsequent comparative analysis of phylogenetic hypotheseis for the subfamily Avenzoariinae and recently accepted phylogenetic hypotheses of the shorebirds Charadriiformes indicates co-speciation of feather mites with their hosts. As a result of the comparative analysis it is suggested, that the subfamily Avenzoariinae originated from an ancestor of the order Charadriiformes and co-speciated with this host order. The expected pattern of parallel evolution is disturbed by different evolutionary events, such as host shifts, extinction of mites and differential evolutionary rates of mite lineages in different phyletic branches of feather parasites.     

What is a node?

Biogeographic nodes can be characterized as sites of biological endemism, high diversity, distribution boundaries, anomalous absences, disjunct populations, taxonomic incongruence, parallelism and altitudinal anomalies. Their interpretation has depended on the evolutionary model used, in particular the mode of speciation: Croizat's vicariance or Mayr's ‘peripatric’ or ‘founder dispersal’ (=Darwin's ‘chance dispersal’, Hennig's ‘speciation by colonization’). All authors agree that the first process, together with movement of individual organisms and diaspores, occurs, but the second is much more controversial, with panbiogeographers and many geneticists denying its importance. Although nodes have often been interpreted as centres of origin – as in refugium theory – this is not accepted here as it fails to account for their constituting both centres and margins of distribution as well as zones of absence. Instead they are interpreted as sites of vicariance related to different kinds of tectonic activity which have been shown to occur in the same locality, such as terrane accretion, subduction, regional metamorphism, granitization, volcanism, faulting, folding, uplift, subsidence and regression of epicontinental seas. It is concluded that the identification of nodes is a more productive approach to biogeographic analysis than dividing a study area into ‘biogeographic regions’, which are usually based firmly on current geography and represent geological and biogeographic composites.