Evaluating trans-tethys migration: an example using acrodont lizard phylogenetics

A phylogenetic tree for acrodont lizards (Chamaeleonidae and Agamidae) is established based on 1434 bases (1041 informative) of aligned DNA positions from a 1685-1778 base pair region of the mitochondrial genome. Sequences from three protein-coding genes (ND1, ND2, and COI) are combined with sequences from eight intervening tRNA genes for samples of 70 acrodont taxa and two outgroups. Parsimony analysis of nucleotide sequences identifies eight major clades in the Acrodonta. Most agamid lizards are placed into three distinct clades. One clade is composed of all taxa occurring in Australia and New Guinea; Physignathus cocincinus from Southeast Asia is the sister taxon to the Australia-New Guinea clade. A second clade is composed of taxa occurring from Tibet and the Indian Subcontinent east through South and East Asia. A third clade is composed of taxa occurring from Africa east through Arabia and West Asia to Tibet and the Indian Subcontinent. These three clades contain all agamid lizards except Uromastyx, Leiolepis, and Hydrosaurus, which represent three additional clades of the Agamidae. The Chamaeleonidae forms another clade weakly supported as the sister taxon to the Agamidae. All eight clades of the Acrodonta contain members occurring on land masses derived from Gondwanaland. A hypothesis of agamid lizards rafting with Gondwanan plates is examined statistically. This hypothesis suggests that the African/West Asian clade is of African or Indian origin, and the South Asian clade is either of Indian or Southeast Asian origin. The shortest tree suggests a possible African origin for the former and an Indian origin for the latter, but this result is not statistically robust. The Australia-New Guinea clade rafted with the Australia-New Guinea plate and forms the sister group to a Southeast Asian taxon that occurs on plates that broke from northern Australia-New Guinea. Other acrodont taxa are inferred to be associated with the plates of Afro-Arabia and Madagascar (Chameleonidae), India (Uromastyx), or southeast Asia (Hydrosaurus and Leiolepis). Introduction of different biotic elements to Asia by way of separate Gondwanan plates may be a major theme of Asian biogeography. Three historical events may be responsible for the sharp faunal barrier between Southeast Asia and Australia-New Guinea, known as Wallace's line: (1) primary vicariance caused by plate separations; (2) secondary contact of Southeast Asian plates with Eurasia, leading to dispersal from Eurasia into Southeast Asia, and (3) dispersal of the Indian fauna (after collision of that subcontinent) to Southeast Asia. Acrodont lizards show the first and third of these biogeographic patterns and anguid lizards exhibit the second pattern. Modern faunal diversity may be influenced primarily by historical events such as tectonic collisions and land bridge connections, which are expected to promote episodic turnover of continental faunas by introducing new faunal elements into an area. Repeated tectonic collisions may be one of the most important phenomena promoting continental biodiversity. Phylogenetics is a powerful method for investigating these processes.     

Biogeographical and geological evidence for a smaller, completely-enclosed Pacific Basin in the Late Cretaceous

Aim To use biogeographical, palaeomagnetic, palaeosedimentary, and plate circuit data from Late Cretaceous regions in and around the Pacific to test the plate tectonic hypothesis of a pre‐Pacific superocean. Location East Asia, Australia, Antarctica, the western Americas, and the Pacific. Methods Literature surveys of the distributions of Cretaceous, circum‐Pacific taxa were compared with palaeomagnetic and palaeosedimentary data. Uncontroversial plate motions based on seafloor spreading data were also used to test the results of the biogeographical and palaeomagnetic analyses. Results The distributions of Cretaceous terrestrial taxa, mostly dinosaurs, imply direct, continental connections between Australia and East Asia, East Asia and North America, North America and South America, South America and Antarctica, and Antarctica and Australia. Palaeomagnetic, palaeosedimentary, and basic plate circuit analyses require little to no latitudinal motion of the Pacific plate with respect to the surrounding continents. Specifically, the data implies that western North America, East Asia, and the Pacific plate all increased in latitude by roughly the same amount (c. 11 ± 5°) since the Campanian – and that the Pacific Ocean Basin has increased in length north‐to‐south. Main conclusions Each of the analyses provides independent corroboration for the same conclusion: the Late Cretaceous Pacific plate was completely enclosed by the surrounding continents and has not experienced significant latitudinal motion with respect to North America, East Asia, or the Bering land bridge. This contrasts significantly with the plate tectonic history of the Pacific, implying instead that the Pacific plate formed in situ, pushing the continents apart as the plate and basin expanded. These results also substantiate recent biogeographical analyses that have concluded that a narrower Pacific Ocean Basin in the Mesozoic and early Tertiary provides the most reasonable explanation for the great number of trans‐Pacific disjunctions of poor dispersing taxa.     

A new global palaeobiogeographical model for the late Mesozoic and early Tertiary

Late Mesozoic palaeobiogeography has been characterized by a distinction between the northern territories of Laurasia and the southern landmasses of Gondwana. The repeated discovery of Gondwanan lineages in Laurasia has led to the proposal of alternative scenarios to explain these anomalous occurrences. A new biogeographical model for late Mesozoic terrestrial ecosystems is here proposed in which Europe and "Gondwanan" territories possessed a common Eurogondwanan fauna during the earliest Cretaceous. Subsequently, following the Hauterivian, the European territories severed from Africa and then connected to Asiamerica resulting in a faunal interchange. This model explains the presence of Gondwanan taxa in Laurasia and the absence of Laurasian forms in the southern territories during the Cretaceous. In order to test this new palaeobiogeographical model, tree reconciliation analyses (TRAs) were performed based on biogeographical signals provided by a supertree of late Mesozoic archosaurs. The TRAs found significant evidence for the presence of an earliest Cretaceous Eurogondwanan fauna followed by a relatively short-term Gondwana-Laurasia dichotomy. The analysis recovered evidence for a biogeographical reconnection of the European territories with Africa and South America-Antarctica during the Campanian to Maastrichtian time-slice. This biogeographical scenario appears to continue through the early Tertiary and sheds light on the trans-Atlantic disjunct distributions of several extant plant and animal groups.     

The Gondwanan and South American Episodes: Two Major and Unrelated Moments in the History of the South American Mammals

The first steps in the history of South American mammals took place ca. 130 Ma., when the South American plate, still connected to the Antarctic Peninsula, began to drift away from the African-Indian plate. Most of the Mesozoic history of South American mammals is still unknown, and we only have a few enigmatic taxa (i.e., a Jurassic Australosphenida and an Early Cretaceous Prototribosphenida) that pose more evolutionary and biogeographic questions than answers. The best-known Mesozoic, South American land-mammal fossils are from Late Cretaceous Patagonian beds. These fossils represent the last survivors of non- and pre-tribosphenic Pangaean lineages, all of them with varying endemic features: some with few advanced features (e.g., ?Eutriconodonta and “Symmetrodonta”), some very diversified as endemic groups (e.g., ?Docodonta Reigitheriidae), and others representing vicariant types of well known Laurasian Mesozoic lineages (e.g., Gondwanatheria as vicariant of Multituberculata). These endemic mammals lived as relicts (although advanced) of pangeic lineages when a primordial South American continent was still connected to the Antarctic Peninsula and, at the northern extreme, near the North American Plate. By the beginning of the Late Cretaceous, the volcanic and diastrophic processes that finally led to the differentiation of the Caribbean region and Central America built up transient geographic connections that permitted the initiation of an overland inter-American exchange that included, for example, dinosaurian titanosaurs from South America and hadrosaurs from North America. The immigration of other vertebrates followed the same route, for example, polydolopimorphian marsupials. These marsupials were assumed to have differentiated in South America prior to new discoveries from the North American Late Cretaceous. The complete extinction of endemic South American Mesozoic mammals by the Late Cretaceous-Early Paleocene, and the subsequent and in part coetaneous immigration of North American therians, respectively, represent two major moments in the history of South American mammals: a Gondwanan Episode and a South American Episode. The Gondwanan Episode was characterized by non- and pre-tribosphenic mammal lineages that descended from the Pangeic South American stage (but already with a pronounced Gondwanan accent, and wholly extinguished during the Late Cretaceous-Early Paleocene span). The South American Episode, in turn, was characterized only by therian mammals, mostly emigrated from the North American continent and already with a South American accent obtained through isolation. The southernmost extreme of South America (Patagonia) remained connected to the present Antarctic Peninsula at least up until about 30 Ma., and both provided the substratum where the primordial cladogenesis of “South American” mammals occurred. The resulting cladogenesis of South American therian mammals followed Gould's motto: early experimentation, later standardization. That is to say, early cladogenesis engendered a great variety of taxa with scarce morphological differentiation. After this early cladogenesis (Late Eocene-Early Oligocene), the variety of taxa became reduced, but each lineage became clearly recognizable distinctive by a constant morphologic pattern. At the same time, those mammals that underwent the “early experimentation” were part of communities dominated by archaic lineages (e.g., brachydont types among the native “ungulates”), whereas the subsequent communities were dominated by mammals of markedly “modern” stamp (e.g., protohypsodont types among the native “ungulates”). The Gondwanan and South American Episodes were separated by a critical latest Cretaceous-earliest Paleocene hiatus, it is as unknown as it is important in which South American land-mammal communities must have experienced extinction of the Gondwanan mammals and the arrival and radiation of the North American marsupials and placentals (with the probable exception of the xenarthrans, whose biogeographic origin is still unclear).     

Molecular phylogeny of osteoglossoids: a new model for Gondwanian origin and plate tectonic transportation of the Asian arowana

One of the traditional enigmas in freshwater zoogeography has been the evolutionary origin of Scleropages formosus inhabiting Southeast Asia (the Asian arowana), which is a species threatened with extinction among the highly freshwater-adapted fishes from the order Osteoglossiformes. Dispersalists have hypothesized that it originated from the recent (the Miocene or later) transmarine dispersal of morphologically quite similar Australasian arowanas across Wallace's Line, but this hypothesis has been questioned due to their remarkable adaptation to freshwater. We determined the complete nucleotide sequences of two mitochondrial protein genes from 12 osteoglossiform species, including all members of the suborder Osteoglossoidei, with which robust molecular phylogeny was constructed and divergence times were estimated. In agreement with previous morphology-based phylogenetic studies, our molecular phylogeny suggested that the osteoglossiforms diverged from a basal position of the teleostean lineage, that heterotidines (the Nile arowana and the pirarucu) form a sister group of osteoglossines (arowanas in South America, Australasia, and Southeast Asia), and that the Asian arowana is more closely related to Australasian arowanas than to South American ones. However, molecular distances between the Asian and Australasian arowanas were much larger than expected from the fact that they are classified within the same genus. By using the molecular clock of bony fishes, tested for its good performance for rather deep divergences and calibrated using some reasonable assumptions, the divergence between the Asian and Australasian arowanas was estimated to date back to the early Cretaceous. Based on the molecular and geological evidence, we propose a new model whereby the Asian arowana vicariantly diverged from the Australasian arowanas in the eastern margin of Gondwanaland and migrated into Eurasia on the Indian subcontinent or smaller continental blocks. This study also implicates the relatively long absence of osteoglossiform fossil records from the Mesozoic.     

Genetic variability,local selection and demographic history: genomic evidence of evolving towards allopatric speciation in Asian seabass

Genomewide analysis of genetic divergence is critically important in understanding the genetic processes of allopatric speciation. We sequenced RAD tags of 131 Asian seabass individuals of six populations from South‐East Asia and Australia/Papua New Guinea. Using 32 433 SNPs, we examined the genetic diversity and patterns of population differentiation across all the populations. We found significant evidence of genetic heterogeneity between South‐East Asian and Australian/Papua New Guinean populations. The Australian/Papua New Guinean populations showed a rather lower level of genetic diversity. F_ST and principal components analysis revealed striking divergence between South‐East Asian and Australian/Papua New Guinean populations. Interestingly, no evidence of contemporary gene flow was observed. The demographic history was further tested based on the folded joint site frequency spectrum. The scenario of ancient migration with historical population size changes was suggested to be the best fit model to explain the genetic divergence of Asian seabass between South‐East Asia and Australia/Papua New Guinea. This scenario also revealed that Australian/Papua New Guinean populations were founded by ancestors from South‐East Asia during mid‐Pleistocene and were completely isolated from the ancestral population after the last glacial retreat. We also detected footprints of local selection, which might be related to differential ecological adaptation. The ancient gene flow was examined and deemed likely insufficient to counteract the genetic differentiation caused by genetic drift. The observed genomic pattern of divergence conflicted with the ‘genomic islands’ scenario. Altogether, Asian seabass have likely been evolving towards allopatric speciation since the split from the ancestral population during mid‐Pleistocene.     

The trans-Pacific zipper effect: disjunct sister taxa and matching geological outlines that link the Pacific margins

Aim To combine analyses of trans‐Pacific sister taxa with geological evidence in order to test the hypothesis of the existence of a Panthalassa superocean. Location The study is concerned with taxa, both fossil and extant, from East Asia, Australia, New Zealand, South America and North America. Methods Phylogenetic and distributional analyses of trans‐Pacific biota were integrated with geological evidence from the Pacific and circum‐Pacific regions. Results A series of recent biogeographical analyses delineates a zipper‐like system of sister areas running up both margins of the Pacific, with each section of western North and South America corresponding to a particular section from East Asia/Australia/New Zealand. These sister areas coincide neatly with a jigsaw‐like fit provided by the matching Mesozoic coastlines that bracket the Pacific. Main conclusions The young age (<200 Myr) of oceanic crust, the matching Mesozoic circum‐Pacific outlines, and a corresponding system of interlocking biogeographical sister areas provide three independent avenues of support for a closed Pacific in the Upper Triassic–Lower Jurassic. The hypothesis of the existence and subsequent subduction of the pre‐Pacific superocean Panthalassa is not only unnecessary, it conflicts with this evidence. Panthalassa‐based paleomaps necessitate the invention of dozens of additional hypotheses of species‐dependent, trans‐oceanic dispersal events, often involving narrow‐range taxa of notoriously limited vagility, in order to explain repeated examples of the same biogeographical pattern. Removing the vanished‐superocean hypothesis reunites both the matching geological outlines and all the disjunct sister taxa. In brief, what appears to be a multi‐era tangle of convoluted, trans‐oceanic distributions on Panthalassa‐based paleomaps is actually a relatively simple biogeographical pattern that is explainable by a single vicariant event: the opening and expansion of the Pacific.     

THE BIOGEOGRAPHY OF SULAWESI REVISITED: IS THERE EVIDENCE FOR A VICARIANT ORIGIN OF TAXA ON WALLACE'S “ANOMALOUS ISLAND”?

Sulawesi, the largest island in the Indonesian biodiversity hotspot region Wallacea, hosts a diverse endemic fauna whose origin has been debated for more than 150 years. We use a comparative approach based on dated phylogenies and geological constraints to test the role of vicariance versus dispersal in the origin of Sulawesi taxa. Most divergence time estimates for the split of Sulawesi lineages from their sister groups postdate relevant tectonic vicariant events, suggesting that the island was predominantly colonized by dispersal. Vicariance cannot be refuted for 20% of the analyzed taxa, though. Although vicariance across Wallace's Line was only supported for one arthropod taxon, divergence time estimates were consistent with a "tectonic dispersal" vicariance hypothesis from the East in three (invertebrate and vertebrate) taxa. Speciation on Sulawesi did not occur before the Miocene, which is consistent with geological evidence for more extensive land on the island from that time. The Pliocene onset of periodic sea-level changes may have played a role in increasing the potential for dispersal to Sulawesi. A more extensive taxon sampling in Wallacea will be crucial for refining our understanding of the region's biogeography and for testing hypotheses on the origin of taxa on its most important island.     

Allochronic taxa as an alternative model to explain circumantarctic disjunctions

Abstract Most biogeographical studies propose that southern temperate faunal disjunctions are either the result of vicariance of taxa originated in Gondwana or the result of transoceanic dispersal of taxa originated after the breakup of Gondwana. The aim of this paper is to show that this is a false dichotomy. Antarctica retained a mild climate until mid‐Cenozoic and had lasting connections, notably with southern South America and Australia. Both taxa originally Gondwanan and taxa secondarily on Gondwanan areas were subjected to tectonic‐induced vicariance, and there is no need to invoke ad hoc transoceanic dispersal, even for post‐Gondwanan taxa. These different elements with circumantarctic distributions are here called ‘allochronic taxa’– taxa presently occupying the same area, but whose presence in that area does not belong to the same time period. This model allows accommodation of conflicting sources of evidence now available for many groups with circumantarctic distributions. The fact that the species from both layers are mixed up in the current biodiversity implies the need to use additional sources of evidence – such as biogeographical, palaeontological, geological and molecular – to discriminate which are the original Gondwanan and which are post‐Gondwanan elements in austral landmasses.     

Late Cretaceous bioconnections between Indo‐Madagascar and Antarctica: refutation of the Gunnerus Ridge causeway hypothesis

Aim To evaluate the Gunnerus Ridge land‐bridge hypothesis, which postulates a Late Cretaceous causeway between eastern Antarctica and southern Madagascar allowing the passage of terrestrial vertebrates. Location Eastern Antarctica, southern Indian Ocean, Madagascar. Methods The review involves palaeogeographical modelling, which draws upon geological and geophysical data, bathymetric charts, and plate tectonic reconstructions, and the evaluation of stratigraphically calibrated phylogenetic analyses to document ghost lineages of select taxa. Results The available geological and geophysical evidence indicates that eastern Antarctica’s Gunnerus Ridge and southern Madagascar were separated for the entire Late Cretaceous by a vast marine expanse. In the mid–Late Cretaceous, the gap was probably punctuated by land on two intervening physiographical highs, the northern Madagascar Plateau and Conrad Rise, the latter of which, although probably large, was still separated from Antarctica’s Riiser‐Larsen Peninsula by c. 1600 km. Recent, stratigraphically calibrated phylogenies including large, terrestrial end‐Cretaceous vertebrate taxa of Madagascar and the Indian subcontinent reveal long ghost lineages that extended into the Early Cretaceous. Main conclusions The view that Antarctica and Madagascar were connected by a long causeway between the Gunnerus Ridge and southern Madagascar in the Late Cretaceous, and that terrestrial vertebrates were able to colonize new frontiers using this physiographical feature, is almost certainly incorrect, as was previously demonstrated for the purported causeway between Antarctica and the Indian subcontinent across the Kerguelen Plateau. Connection across mainland Africa to account for the close relationships of several fossil and extant vertebrate taxa of Indo‐Madagascar and South America is another option, although this too lacks credibility. We conclude that (1) throughout the Late Cretaceous there was no intervening, continuous causeway through Antarctica and associated land bridges between South America to the west and Indo‐Madagascar to the east; and (2) mid‐ to large‐sized, obligate terrestrial forms (e.g. abelisauroid theropod and titanosaurian sauropod dinosaurs and notosuchian crocodyliforms) gained broad distribution across Gondwanan land masses prior to fragmentation and were isolated on Indo‐Madagascar before the end of the Early Cretaceous.     

Evolutionary history of Spalacidae inferred from fossil occurrences and molecular phylogeny

1. The Spalacidae is a family of strictly subterranean rodents with a long evolutionary history. It is unclear how ecological changes have influenced the evolutionary history of these mammals, and the phylogenetic relationship of the subfamilies within Spalacidae is controversial.
2. Through compiling fossil records, reconstructing molecular phylogeny from molecular data, determining the date of divergence, and analysing their geographical evolution based on molecular data and fossil taxa, we explore the origin and evolutionary process of Spalacidae in detail. Diversification within Spalacidae dates to the Late Oligocene, approximately 25 million years ago, based on molecular data.
3. This family originated in South and East Asia in the Late Oligocene, and then split into four clades. The first clade includes Rhizomyinae, which was highly diversified in South Asia in the Early-to-Middle Miocene. Then Rhizomyinae from Asia migrated to northern Africa in multiple waves through the Afro-Eurasian land bridge. Its range largely contracted in the Late Miocene, notably in Central Asia. The second clade includes the extinct Tachyoryctoidinae, which was confined to East and Central Asia, and survived from the Late Oligocene to the Late Miocene. The third clade includes Spalacinae, which have remained around the Mediterranean region since the Late Oligocene with slight trend of northward expansion. The fourth clade is Myospalacinae. Ancient genera of this subfamily in East Asia dispersed eastward during the Late Miocene and reached northern China and south-east Russia.
4. The general distribution pattern of Spalacidae has persisted since the Late Miocene. Extinction of Tachyoryctoidinae and clear range contraction of Rhizomyinae in Central and East Asia are likely to have resulted from increased aridification, while the slight northward expansion of Myospalacinae and Spalacinae since the Quaternary was probably a response to a similar northward expansion of suitable vegetation for these animals.

     

The historical biogeography of sturgeons (Osteichthyes: Acipenseridae): a synthesis of phylogenetics, palaeontology and palaeogeography

Abstract. The historical biogeography of sturgeons is explored using information from palaeogeography, palaeontology and phylogenetic interrelationships. The integration of information from these diverse sources indicates that sturgeons reached a wide Laurasian distribution in the Cretaceous and Tertiary by freshwater and coastal dispersal routes across land connections and along newly forming continental margins. The fossil record also suggests a considerable degree of morphological stasis and also supports an estuarine habit, and perhaps diadromy, as an old and conserved life history trait. While a ‘centre of origin’ for sturgeons remains elusive, phylogenetic relationships indicate that diversification appears to have been associated with fragmentation of biota, and of landmasses and basins, by late Tertiary geological and climatic phenomena, such as orogeny and unequal glaciation over North America, the desiccation of central Asia and alteration of its drainages, and the formation of discrete Ponto-Caspian basins by the fragmentation of the Paratethys. Amphi-oceanic distributions of certain species (Acipenser medirostris Ayres) and sister taxa (e.g. A. oxyrhynchus Mitchill and A. sturio L.) are explained by coastal dispersal and subsequent vicariance by geological (sea-floor spreading and development of new continental margins) and climatic (Pliocene cooling) changes during the Tertiary. An hypothesis is developed for the relationships of the North American sturgeons and their potential relationships with the Siberian sturgeon A. baeri. Late Tertiary climatic and geological phenomena are hypothesized as mediators of vicariance and subsequent diversification of these acipenserids. It appears that although acipenserids are a geologically old group, the historical biogeography of surviving lineages is best explained by more recent geological and climatic changes.     

Considerations on the age of the Tiouaren Formation (Iullemmeden Basin,Niger, Africa): Implications for Gondwanan Mesozoic terrestrial vertebrate faunas

Pre-Aptian mid-Mesozoic terrestrial vertebrates from the African continent are still very poorly known. In Niger, the Tiouaren Formation in the Iullemmeden Basin has yielded dinosaur and other vertebrate remains, and this unit has been dated as Early Cretaceous, most probably pre-Aptian, on the basis of its fish fauna and geological relations to other units in the basin. A review of the fish fauna and invertebrates from this formation does not provide any evidence for such an age, and the geological relations only help to constrain the upper limit for the age of the formation (Aptian). In contrast, the described dinosaur taxa are phylogenetically nested with late Middle Jurassic to Early Late Jurassic taxa from other localities, and thus indicate a pre-Kimmeridgian, probably late Middle Jurassic age for the Tiouaren Formation. Under the assumption of such an age, the dinosaur fauna of this formation provides new insights into dinosaur faunal provincialism during the latest Middle Jurassic. Northern Gondwanan faunas of that time seem to have been different from southern Gondwanan faunas, and show closer affinities to Eurasian faunas than to the latter. A possible explanation for this might be a climatically controlled geographic barrier due to pronounced arid conditions and thus desert environments in central Gondwana during this time.     

Marine dispersal as a pre‐requisite for Gondwanan vicariance among elements of the galaxiid fish fauna

Aim The aim of this study was to determine the contributions of Gondwanan vicariance and marine dispersal to the contemporary distribution of galaxiid fishes. This group has been central in arguments concerning the roles of dispersal and vicariance in the Southern Hemisphere, as some taxa have marine life history stages through which transoceanic dispersal may have been facilitated, yet other galaxiids are entirely restricted to freshwaters. Location Southern Hemisphere land masses of Gondwanan derivation. Methods Biogeographic hypotheses of Gondwanan vicariance and marine dispersal were tested using four lines of evidence: (1) concordance of species–area phylogenetic relationships, (2) molecular estimates of lineage divergence times with a priori expectations based on plate tectonics, (3) reconstructions of ancestral dispersal capabilities, and (4) reconstructions of distribution inheritance scenarios (using the dispersal–extinction–cladogenesis model to infer historical ranges and dispersal and extinction events). Results Phylogenetic relationships were reconstructed from 4531 mitochondrial and nuclear nucleotide characters, and 181 morphological characters, across 53 of the 56 presently recognized species. Phylogenetic relationships were generally well resolved and supported among galaxiids using the combined dataset, and conflicting relationships between molecular and morphological datasets typically received low topological support from either or both datasets. Transoceanic disjunctions were exhibited at 16 nodes, but only three pre‐dated relevant continental fragmentation events; furthermore, ancestral distribution inheritance scenarios for two of these nodes reflected cladogenesis within, rather than between, Gondwanan land masses, and ancestral marine dispersal capability could not be rejected for all three. Instead, the four lines of evidence surveyed suggest that Gondwanan vicariance occurred twice, but in both instances was preceded by marine dispersal between land masses, and in at least one instance was initiated by the cessation of marine dispersal subsequent to continental fragmentation. Main conclusions Gondwanan vicariance appears to have been preceded by marine dispersal in the few instances where it may explain contemporary galaxiid distribution, such that these biogeographic mechanisms may sometimes have a synergistic relationship.     

Molecular clocks keep dispersal hypotheses afloat: evidence for trans‐Atlantic rafting by rodents

Aim In order to resolve disputed biogeographical histories of biota with Gondwanan continental distributions, and to assess the null hypothesis of vicariance, it is imperative that a robust geological time‐frame be established. As an example, the sudden and coincident appearance of hystricognath rodents (Rodentia: Hystricognathi) on both the African and South American continents has been an irreconcilable controversy for evolutionary biologists, presenting enigmas for both Gondwanan vicariance and Late Eocene dispersal hypotheses. In an attempt to resolve this discordance, we aim to provide a more robust phylogenetic hypothesis and improve divergence‐date estimates, which are essential to assessing the null hypothesis of vicariance biogeography. Location The primary centres of distribution are in Africa and South America. Methods We implemented parsimony, maximum‐likelihood and Bayesian methods to generate a phylogeny of 37 hystricognath taxa, the most comprehensive taxonomic sampling of this group to date, on the basis of two nuclear gene regions. To increase phylogenetic resolution at the basal nodes, these data were combined with previously published data for six additional nuclear gene regions. Divergence dates were estimated using two relaxed‐molecular‐clock methods, Bayesian multidivtime and nonparametric rate smoothing. Results Our data do not support reciprocal monophyly of African and South American lineages. Indeed, Old World porcupines (i.e. Hystricomorpha) appear to be more closely related to New World lineages (i.e. Caviomorpha) than to other Old World families (i.e. Bathyergidae, Petromuridae and Thryonomyidae). The divergence between the monophyletic assemblage of South American lineages and its Old World ancestor was estimated to have occurred c. 50 Ma. Main conclusions Our phylogenetic hypothesis and divergence‐date estimates are strongly at odds with Gondwanan‐vicariance isolating mechanisms. In contrast, our data suggest that transoceanic dispersal has played a significant role in governing the contemporary distribution of hystricognath rodents. Molecular‐clock analyses imply a trans‐Tethys dispersal event, broadly confined to the Late Cretaceous, and trans‐Atlantic dispersal within the Early Eocene. Our analyses also imply that the use of the oldest known South American rodent fossil as a calibration point has biased molecular‐clock inferences.     

Origin,Differentiation, and Geographic Distribution of the Chenopodiaceae

Numbers of species and genera,endemic genera,extant primitive genera,relationship and distribution patterns of presently living Chenopodiaceae(two subfamilies,12 tribes,and 118 genera)are analyzed and compared for eight distributional areas,namely central Asia,Europe,the Mediterranean region,Africa,North America,South America, Australia and East Asia． The Central Asia,where the number of genera and diversity of taxa are greater than in other areas,appears to be the center of distribution of extant Chenopodiaceae．North America and Australia are two secondary centers of distribution． Eurasia has 11 tribes out of the 12,a total of 70 genera of extant chenopodiaceous plants,and it contains the most primitive genera of every tribe． Archiatriplex of Atripliceae,Hablitzia of Hablitzeae,Corispermum of Corispermeae,Camphorosma of Camphorosmaea,Kalidium of Salicornieae,Polecnemum of Polycnemeae,Alexandra of Suaedeae,and Nanophyton of Salsoleae,are all found in Eurasia,The Beteae is an Eurasian endemic tribe,demonstrating the antiquity of the Chenopodiaceae flora of Eurasia．Hence,Eurasia is likely the place of origin of chenopodiaceous plants． The presence of chenopodiaceous plants is correlated with an arid climate．During the Cretaceous Period,most places of the continent of Eurasia were occupied by the ancient precursor to the Mediterranean,the Tethys Sea．At that time the area of the Tethys Sea had a dry and warm climate．Therefore,primitive Chenopodiaceae were likely present on the beaches of this ancient land．This arid climatic condition resulted in differentiation of the tribes Chenopodieae,Atripliceae,Comphorosmeae,Salicornieae,etc．,the main primitive tribes of the subfamily Cyclolobeae. Then following continental drift and the Laurasian and Gondwanan disintegration, the Chenopodiaceae were brought to every continent to propagate and develop, and experience the vicissitudes of climates, forming the main characteristics and distribution patterns of recent continental floras. The tribes Atripliceae, Chenopodieae, Camphorosmeae, and Salicornieae of recent Chenopodiaceae in Eurasia, North America, South America, southern Africa, and Australia all became strongly differentiated. However, Australia and South America, have no genera of Spirolobeae except for a few maritime Suaeda species. The Salsoleae and Suaedeae have not arrived in Australia and South America, which indicates that the subfamily Spirolobeae developed in Eurasia after Australia separated from the ancient South America-Africa continent, and South America had left Africa. The endemic tribe of North America, the tribe Sarcobateae, has a origin different from the tribes Salsoleae and Suaedeae of the subfamily Spirolobeae. Sarcobateae flowers diverged into unisexuality and absence of bractlets. Clearly they originated in North America after North America had left the Eurasian continent. North America and southern Africa have a few species of Salsola, but none of them have become very much differentiated or developed, so they must have arrived through overland migration across ancient continental connections. India has no southern African Chenopodiaceae floristic components except for a few maritime taxa, which shows that when the Indian subcontinent left Africa in the Triassic period, the Chenopodiaceae had not yet developed in Africa. Therefore, the early Cretaceous Period about 120 million years ago, when the ancient Gondwanan and Laurasian continents disintegrated, could have been the time of origin of Chenopodiaceae plants.The Chinese flora of Chenopodiaceae is a part of Chenopodiaceae flora of central Asia. Cornulaca alaschnica was discovered from Gansu, China, showing that the Chinese Chenopodiaceae flora certainly has contact with the Mediterranean Chenopodiaceae flora. The contact of southeastern China with the Australia Chenopodiaceae flora, however, is very weak.     

Vicariant origin of malagasy reptiles supports late cretaceous antarctic land bridge

Since the acceptance of Wegener's theory of plate tectonics in the 1960s, continental drift vicariance has been proposed as an explanation for pan-Gondwanan faunal distributions. Given the recognition of historical connections among continents, it no longer was necessary to invoke hypotheses of dispersal across nearly insurmountable barriers. The application of continental drift vicariance theory to Gondwanan floral and faunal distributions provided reasonable explanations for such unusual distributions as that of the southern beech (Nothofagus) and chameleons. However, recent studies have demonstrated a significant, if not dominant, role for dispersal in the present-day distributions of these and numerous other "Gondwanan" taxa. The evolutionary histories of three Malagasy groups (boid snakes, podocnemid turtles, and iguanid lizards) commonly have been interpreted as reflecting vicariance because of continental drift associated with the breakup of Gondwana. Bayesian analyses of divergence ages suggest that this pattern is the result of vicariance coincident with the isolation of Madagascar in the Late Cretaceous (approximately 80 million years ago). This represents the first temporal evidence linking the vicariant origin of extant Malagasy vertebrates to a single geologic event. Specifically, our data provide strong, independently corroborated evidence for a contiguous Late Cretaceous Gondwana, exclusive of Africa and connected via Antarctica.     

Bird counts either side of Wallace's Line

Bird counts were made on the islands of Java, Bali, Lombok and Sumbawa during a 16 day study in September 1973 in order to compare bird populations either side of Wallace's Line (running between Bali and Lombok). Evidence was collected which showed that the two westerly islands of Java and Bali share a relatively similar bird fauna, but this differs noticeably from the bird life found more to the east. The conspicuous faunal break which occurs between Bali and Lombok appears to represent a transition from a rich fauna associated with the large continental island of Java, to a somewhat impoverished fauna of the outlying oceanic islands. Marked differences in habitat on the four islands were considered to be primarily important in dictating this change.
Using frequency and abundance estimates for the different bird families it was shown that Java and Bali have a preponderance of Oriental (Asian) birds while Lombok and Sumbawa have more conspicuous Australian elements. However, when the presence or absence of species or families alone are considered all four islands have more Oriental types. It seems that a small range of Australian species including honey eaters, wood swallows, zebra finches and parrots are relatively abundant on Lombok and Sumbawa, and are a sufficiently conspicuous feature of the fauna east of Wallace's Line to impress the visitor that he has entered Australasia.
The bird counts illustrate some of the changes originally described by A. R. Wallace (1860).     

Out of Asia and into India: on the molecular phylogeny and biogeography of the endemic freshwater gastropod Paracrostoma Cossmann, 1900 (Caenogastropoda: Pachychilidae)

Pachychilidae are distributed in the tropical regions of the southern continents implying a Gondwanan history. In the present study, we investigate the phylogenetic relationships of the freshwater pachychilid gastropod Paracrostoma endemic to Southern India using molecular genetic and morphological data, including the first examination of soft body material of the type species, Paracrostoma huegelii . In addition, two new species, Paracrostoma tigrina sp. nov. and Paracrostoma martini sp. nov. , are described. Our systematic revision shows that former taxonomic concepts of Paracrostoma were misleading. We demonstrate that the monophyletic Paracrostoma is restricted to Southern India and nested within a clade of South-east Asian taxa composed of Brotia and Adamietta . The mitochondrial phylogeny is corroborated by the presence of a subhaemocoelic brood pouch that represents a synapomorphy shared by members of only this group of taxa from the Asian mainland and India. Thus, in contrast to several other zoogeographical model cases, our study suggests that pachychilid freshwater gastropods colonized India out of South-east Asia, probably after the collision of both landmasses during the Eocene. By contrast, a simple vicariance scenario involving the Mesozoic raft of originally Gondwanan elements on the drifting Madagascar–India plate and later colonization of Asia from India fails to explain this distributional pattern. Therefore, Pachychilidae do not follow the predictions of the vicariant biotic ferry hypothesis, which has been suggested for a number of other organisms. We conclude that the origins of the Indian biota are more complex and diverse than assumed under the standard Mesozoic vicariance model.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 627–651.