Molecular Divergence Dates Research Articles

A new fossil from the early Oligocene of Provence (France) increases the diversity of early Gruoidea and adds constraint on the origin of cranes (Gruidae) and limpkin (Aramidae)

Cranes (Gruidae) have a poor early fossil record, and the oldest ascertained fossils hitherto referred to the family (either as crown or stem-representatives) date back to the early or middle Miocene. Other Gruoidea have an even scarcer fossil record. Psophiidae and Aramidae are virtually unknown as fossils, and other fossil representatives of the Gruoidea are difficult to place. Here, we describe a new fossil that sheds new light on the early history of stem Gruidae, a right coracoid in dorsal view preserved on slab in limestone laminites of the early Oligocene « Calcaires de Campagne-Calavon» (Alpes de Haute Provence, France). It is compared with extant and fossil morphologically related taxa, and appears to differ from all extant and fossil relatives in the Gruoidea. The new fossil represents, among the Gruoidea, a new genus and species, Palaeogeranos tourmenti, placed within the clade (Aramidae + Gruidae) that is referred to as epifamily Gruoidae. Within Gruoidae, placement is tentative and we give arguments leading to propose a possible position as a stem Gruidae, a hypothesis to be tested with further discoveries. In this hypothesis, aged around 30 million years, the new fossil suggests that the stem of the Gruidae would date back to at least the earliest Oligocene, which is still compatible with current molecular phylogenetic divergence dates estimations, given the confidence intervals. Palaeogeranos will potentially help refining future calibrations for molecular phylogenetic studies, at least concerning the earliest Gruoidae (Aramidae + Gruidae).

Biogeographic mechanisms involved in the colonization of Madagascar by African vertebrates: Rifting, rafting and runways

AbstractAimFor 80 years, popular opinion has held that most of Madagascar's terrestrial vertebrates arrived from Africa by transoceanic dispersal (i.e. rafting or swimming). We reviewed this proposition, focussing on three ad hoc hypotheses proposed to render this unlikely scenario more feasible: (a) Could hibernation have helped mammals to reach Madagascar? (b) Could the aquatic abilities of hippopotamuses have enabled them to swim the Mozambique Channel? (c) How valid is the Ali‐Huber model predicting that eastward Palaeogene surface currents allowed rafts to reach Madagascar in 3–4 weeks? Finally, we explored the alternative hypothesis of geodispersal via short‐lived land bridges between Africa and Madagascar.LocationEast Africa, Madagascar, Mozambique Channel.TaxaFish, amphibians, reptiles, birds, mammals.MethodsWe established colonization timeframes using molecular divergence dates estimated for Malagasy vertebrate lineages. We reviewed the likelihood of the “torpid waif” and “swimming hippopotamus” hypotheses, and re‐investigated Ali and Huber's model of Eocene jet‐like currents by tracking particle trajectories in currents simulated using the Institut Pierre‐Simon Laplace Earth System Model. Finally, we summarized recent geological findings from the Mozambique Channel, and used them to compile palaeosedimentological maps using PLACA4D.ResultsMadagascar's vertebrate fauna has complex origins. Hibernation is probably an adaptation to Madagascar's hypervariable climate, rather than a facilitator of mammal dispersal. Hippopotamus physiology precludes the ability to cross an oceanic channel deeper than 4 m and hundreds of km wide. The Ali‐Huber model of Palaeogene currents considerably underestimated the time required to cross the Mozambique Channel under simulated palaeogeographic conditions. New geological data indicate the existence of three short‐lived land bridges between Africa and Madagascar at 66–60 Ma, 36–30 Ma and 12–05 Ma.Main conclusionThe three Cenozoic land bridges afford a more grounded hypothesis for the dispersal of Madagascar's extant biota than transoceanic rafting or swimming, although vicariance, island hopping and limited rafting also played a role.

Aquatic stem group myriapods close a gap between molecular divergence dates and the terrestrial fossil record

Identifying marine or freshwater fossils that belong to the stem groups of the major terrestrial arthropod radiations is a longstanding challenge. Molecular dating and fossils of their pancrustacean sister group predict that myriapods originated in the Cambrian, much earlier than their oldest known fossils, but uncertainty about stem group Myriapoda confounds efforts to resolve the timing of the group's terrestrialization. Among a small set of candidates for membership in the stem group of Myriapoda, the Cambrian to Triassic euthycarcinoids have repeatedly been singled out. The only known Devonian euthycarcinoid, Heterocrania rhyniensis from the Rhynie and Windyfield cherts hot spring complex in Scotland, reveals details of head structures that constrain the evolutionary position of euthycarcinoids. The head capsule houses an anterior cuticular tentorium, a feature uniquely shared by myriapods and hexapods. Confocal microscopy recovers myriapod-like characters of the preoral chamber, such as a prominent hypopharynx supported by tentorial bars and superlinguae between the mandibles and hypopharynx, reinforcing an alliance between euthycarcinoids and myriapods recovered in recent phylogenetic analysis. The Cambrian occurrence of the earliest euthycarcinoids supplies the oldest compelling evidence for an aquatic stem group for either Myriapoda or Hexapoda, previously a lacuna in the body fossil record of these otherwise terrestrial lineages until the Silurian and Devonian, respectively. The trace fossil record of euthycarcinoids in the Cambrian and Ordovician reveals amphibious locomotion in tidal environments and fills a gap between molecular estimates for myriapod origins in the Cambrian and a post-Ordovician crown group fossil record.

Lower Cretaceous fossils from China shed light on the ancestral body plan of crown softshell\xa0turtles (Trionychidae, Cryptodira)

Pan-trionychids or softshell turtles are a highly specialized and widespread extant group of aquatic taxa with an evolutionary history that goes back to the Early Cretaceous. The earliest pan-trionychids had already fully developed the “classic” softshell turtle morphology and it has been impossible to resolve whether they are stem members of the family or are within the crown. This has hindered our understanding of the evolution of the two basic body plans of crown-trionychids. Thus it remains unclear whether the more heavily ossified shell of the cyclanorbines or the highly reduced trionychine morphotype is the ancestral condition for softshell turtles. A new pan-trionychid from the Early Cretaceous of Zhejiang, China, Perochelys hengshanensis sp. nov., allows a revision of softshell-turtle phylogeny. Equal character weighting resulted in a topology that is fundamentally inconsistent with molecular divergence date estimates of deeply nested extant species. In contrast, implied weighting retrieved Lower Cretaceous Perochelys spp. and Petrochelys kyrgyzensis as stem trionychids, which is fully consistent with their basal stratigraphic occurrence and an Aptian-Santonian molecular age estimate for crown-trionychids. These results indicate that the primitive morphology for soft-shell turtles is a poorly ossified shell like that of crown-trionychines and that shell re-ossification in cyclanorbines (including re-acquisition of peripheral elements) is secondary.

33 million year old Myotis (Chiroptera, Vespertilionidae) and the rapid global radiation of modern bats.

The bat genus Myotis is represented by 120+ living species and 40+ extinct species and is found on every continent except Antarctica. The time of divergence of Myotis has been contentious as has the time and place of origin of its encompassing group the Vespertilionidae, the most diverse (450+ species) and widely distributed extant bat family. Fossil Myotis species are common, especially in Europe, beginning in the Miocene but earlier records are poor. Recent study of new specimens from the Belgian early Oligocene locality of Boutersem reveals the presence of a relatively large vespertilionid. Morphological comparison and phylogenetic analysis confirms that the new, large form can be confidently assigned to the genus Myotis, making this record the earliest known for that taxon and extending the temporal range of this extant genus to over 33 million years. This suggests that previously published molecular divergence dates for crown myotines (Myotis) are too young by at least 7 million years. Additionally, examination of first fossil appearance data of 1,011 extant placental mammal genera indicates that only 13 first occurred in the middle to late Paleogene (48 to 33 million years ago) and of these, six represent bats, including Myotis. Paleogene members of both major suborders of Chiroptera (Yangochiroptera and Yinpterochiroptera) include extant genera indicating early establishment of successful and long-term adaptive strategies as bats underwent an explosive radiation near the beginning of the Early Eocene Climatic Optimum in the Old World. A second bat adaptive radiation in the New World began coincident with the Mid-Miocene Climatic Optimum.

Eocene lantern fruits from Gondwanan Patagonia and the early origins of Solanaceae

The nightshade family Solanaceae holds exceptional economic and cultural importance. The early diversification of Solanaceae is thought to have occurred in South America during its separation from Gondwana, but the family's sparse fossil record provides few insights. We report 52.2-million-year-old lantern fruits from terminal-Gondwanan Patagonia, featuring highly inflated, five-lobed calyces, as a newly identified species of the derived, diverse New World genus Physalis (e.g., groundcherries and tomatillos). The fossils are considerably older than corresponding molecular divergence dates and demonstrate an ancient history for the inflated calyx syndrome. The derived position of these early Eocene fossils shows that Solanaceae were well diversified long before final Gondwanan breakup.

A Possible Role for Stochastic Astrophysical Ionizing Radiation Events in the Systematic Disparity between Molecular and Fossil Dates.

Major discrepancies have been noted for some time between fossil ages and molecular divergence dates for a variety of taxa. Recently, systematic trends within avian clades have been uncovered. The trends show that the disparity is much larger for mitochondrial DNA than for nuclear DNA, also that it is larger for crown fossil dates than stem fossil dates. It has been argued that this pattern is largely inconsistent with incompleteness of the fossil record as the principal driver of the disparity. A case is presented that, given the expected mutations from a fluctuating background of astrophysical radiation from such sources as supernovae, the rate of molecular clocks is variable and should increase back to a few million years, before returning to the long-term average rate. This is a possible explanation for the disparity. One test of this hypothesis is to look for an acceleration of molecular clocks at 2 to 2.5 Ma due to one or more moderately nearby supernovae known to have happened at that time. Another is to look for reduced disparity in benthic organisms of the deep ocean. In addition, due to the importance of highly penetrating muon irradiation, the disparity should be magnified for megafauna. Key Words: Extreme events in Earth history-Molecular clock-Radiation physics-Evolution. Astrobiology 17, 87-90.

Papio Cranium from the Hominin-Bearing Site of Malapa: Implications for the Evolution of Modern Baboon Cranial Morphology and South African Plio-Pleistocene Biochronology.

A new partial cranium (UW 88-886) of the Plio-Pleistocene baboon Papio angusticeps from Malapa is identified, described and discussed. UW 88-886 represents the only non-hominin primate yet recovered from Malapa and is important both in the context of baboon evolution as well as South African hominin site biochronology. The new specimen may represent the first appearance of modern baboon anatomy and coincides almost perfectly with molecular divergence date estimates for the origin of the modern P. hamadryas radiation. The fact that the Malapa specimen is dated between ~2.026–2.36 million years ago (Ma) also has implications for the biochronology of other South African Plio-Pleistocene sites where P. angusticeps is found.

Flying rocks and flying clocks: disparity in fossil and molecular dates for birds.

Major disparities are recognized between molecular divergence dates and fossil ages for critical nodes in the Tree of Life, but broad patterns and underlying drivers remain elusive. We harvested 458 molecular age estimates for the stem and crown divergences of 67 avian clades to explore empirical patterns between these alternate sources of temporal information. These divergence estimates were, on average, over twice the age of the oldest fossil in these clades. Mitochondrial studies yielded older ages than nuclear studies for the vast majority of clades. Unexpectedly, disparity between molecular estimates and the fossil record was higher for divergences within major clades (crown divergences) than divergences between major clades (stem divergences). Comparisons of dates from studies classed by analytical methods revealed few significant differences. Because true divergence ages can never be known with certainty, our study does not answer the question of whether fossil gaps or molecular dating error account for a greater proportion of observed disparity. However, empirical patterns observed here suggest systemic overestimates for shallow nodes in existing molecular divergence dates for birds. We discuss underlying biases that may drive these patterns.

The Description ofRovnoeucoila tympanomorphaBuffington and Perkovsky, a New Genus and Species of Fossil Eucoiline, with Observations on the Asynchronous Evolution of Diglyphosematini (Hymenoptera: Figitidae: Eucoilinae)

Abstract. A new genus and species of Eucoilinae, Rovnoeucoila tympanomorpha Buffington and Perkovsky, from a Rovno Amber inclusion, is described. This new taxon differs from extant eucoilines by having a clearly segmented metasoma and singular flagellomere morphology in the antenna. The new taxon is included in the re-analysis of a fossil calibrated, relaxed molecular clock divergence date analysis of Figitidae. The new analysis infers a mean crown group age for Eucoilinae at approximately 10 million years younger than previously estimated. The age of the eucoiline tribe Diglyphosematini does not change substantially in our new dating analysis, and is much younger when compared to the age of its host lineage Agromyzidae (Diptera); we discuss potential implications of this situation within the context of natural enemy selection in biological control projects that include parasitoid Hymenoptera.

Nocturnal claroteine catfishes reveal dual colonisation but a single radiation in Lake Tanganyika

Lake Tanganyika (LT) is a biodiversity hotspot supporting many endemic radiations that provide comparative systems in which to investigate if there are common factors leading to the build-up of its considerable diversity. Despite LT containing the highest diversity of lacustrine catfishes on Earth, the evolutionary relationships of nocturnal catfishes within the sub-family Claroteinae have not been investigated and it is unknown if its constituent genera have diversified via single or independent colonisation events. We report the first molecular phylogeny of the LT claroteine catfishes based on a multigene dataset (three nuclear markers, two mitochondrial totalling 4227bp), including 85 samples from LT and outside of the lake basin. These data support LT claroteine monophyly, with the exclusion of the LT endemic Chrysichthys brachynema that independently colonised the lake but has not radiated. Multiple sampling localities from LT and the use of Bayesian species delimitation methods reveal additional locally restricted diversity within the LT Claroteinae clade. Fossil calibrated molecular divergence dates suggest that diversification occurred within full lake conditions as demonstrated in other LT lineages.

New material of Beelzebufo, a hyperossified frog (Amphibia: Anura) from the late cretaceous of Madagascar.

The extant anuran fauna of Madagascar is exceptionally rich and almost completely endemic. In recent years, many new species have been described and understanding of the history and relationships of this fauna has been greatly advanced by molecular studies, but very little is known of the fossil history of frogs on the island. Beelzebufo ampinga, the first named pre-Holocene frog from Madagascar, was described in 2008 on the basis of numerous disarticulated cranial and postcranial elements from the Upper Cretaceous (Maastrichtian) Maevarano Formation of Madagascar. These specimens documented the presence of a hyperossified taxon that differed strikingly from extant Malagasy frogs in its large size and heavy coarse cranial exostosis. Here we describe and analyse new, articulated, and more complete material of the skull, vertebral column, and hind limb, as well as additional isolated elements discovered since 2008. μCT scans allow a detailed understanding of both internal and external morphology and permit a more accurate reconstruction. The new material shows Beelzebufo to have been even more bizarre than originally interpreted, with large posterolateral skull flanges and sculptured vertebral spine tables. The apparent absence of a tympanic membrane, the strong cranial exostosis, and vertebral morphology suggest it may have burrowed during seasonally arid conditions, which have been interpreted for the Maevarano Formation from independent sedimentological and taphonomic evidence. New phylogenetic analyses, incorporating both morphological and molecular data, continue to place Beelzebufo with hyloid rather than ranoid frogs. Within Hyloidea, Beelzebufo still groups with the South American Ceratophryidae thus continuing to pose difficulties with both biogeographic interpretations and prior molecular divergence dates.

Generation times in wild chimpanzees and gorillas suggest earlier divergence times in great ape and human evolution

Fossils and molecular data are two independent sources of information that should in principle provide consistent inferences of when evolutionary lineages diverged. Here we use an alternative approach to genetic inference of species split times in recent human and ape evolution that is independent of the fossil record. We first use genetic parentage information on a large number of wild chimpanzees and mountain gorillas to directly infer their average generation times. We then compare these generation time estimates with those of humans and apply recent estimates of the human mutation rate per generation to derive estimates of split times of great apes and humans that are independent of fossil calibration. We date the human-chimpanzee split to at least 7-8 million years and the population split between Neanderthals and modern humans to 400,000-800,000 y ago. This suggests that molecular divergence dates may not be in conflict with the attribution of 6- to 7-million-y-old fossils to the human lineage and 400,000-y-old fossils to the Neanderthal lineage.

Exploring the effects of phylogenetic uncertainty and consensus trees on stratigraphic consistency scores: a new program and a standardized method.

The stratigraphic record of first appearances provides an independent source of data for evaluating and comparing phylogenetic hypotheses that include taxa with fossil histories. However, no standardized method exists for calculating these metrics for polytomous phylogenies, restricting their applicability. Previously proposed methods insufficiently deal with this problem because they skew or restrict the resulting scores. To resolve this issue, we propose a standardized method for treating polytomies when calculating these metrics: the Comprehensive Polytomy approach (ComPoly). This approach accurately describes how phylogenetic uncertainty, indicated by polytomies, affects stratigraphic consistency scores. We also present a new program suite (Assistance with Stratigraphic Consistency Calculations) that incorporates the ComPoly approach and simplifies the calculation of absolute temporal stratigraphic consistency metrics. This study also demonstrates that stratigraphic consistency scores calculated from strict consensus trees can be overly inclusive and those calculated from less-than-strict consensus trees inaccurately describe the phylogenetic signal present in the source most-parsimonious trees (MPTs). Therefore, stratigraphic consistency scores should be calculated directly from the source MPTs whenever possible to ensure their accuracy. Finally, we offer recommendations for standardizing comparisons between molecular divergence dates and the stratigraphic record of first appearances, a promising new application of these methods. © The Willi Hennig Society 2010.

Eastern Beringian biogeography: historical and spatial genetic structure of singing voles in Alaska

AbstractAim Pleistocene climatic cycles have left marked signatures in the spatial and historical genetic structure of high‐latitude organisms. We examine the mitochondrial (cytochrome b) genetic structure of the singing vole, Microtus miurus (Rodentia: Cricetidae: Arvicolinae), a member of the Pleistocene Beringian fauna, and of the insular vole, Microtus abbreviatus, its putative sister species found only on the St Matthew Archipelago. We reconstruct the phylogenetic and phylogeographical structure of these taxa, characterize their geographical partitioning and date coalescent and cladogenetic events in these species. Finally, we compare the recovered results with the phylogenetic, coalescent and spatial genetic patterns of other eastern Beringian mammals and high‐latitude arvicoline rodents.Location Continental Alaska (alpine and arctic tundra) and the St Matthew Archipelago (Bering Sea).Methods We generated and analysed cytochrome b sequences of 97 singing and insular voles (M. miurus and M. abbreviatus) from Alaska. Deep evolutionary structure was inferred by phylogenetic analysis using parsimony, maximum likelihood and Bayesian approaches; the geographical structure of genetic diversity was assessed using analysis of molecular variance and network analysis; ages of cladogenetic and coalescent events were estimated using a relaxed molecular clock model with Bayesian approximation.Results Regional nucleotide diversity in singing voles is higher than in other high‐latitude arvicoline species, but intra‐population diversity is within the observed range of values for arvicolines. Microtus abbreviatus specimens are phylogenetically nested within M. miurus. Molecular divergence date estimates indicate that current genetic diversity was formed in the last glacial (Wisconsinan) and previous interglacial (Sangamonian) periods, with the exception of a Middle Pleistocene split found between samples collected in the Wrangell Mountains region and all other singing vole samples.Main conclusions High levels of phylogenetic and spatial structure are observed among analysed populations. This pattern is consistent with that expected for a taxon with a long history in Beringia. The spatial genetic structure of continental singing voles differs in its northern and southern ranges, possibly reflecting differences in habitat distribution between arctic and alpine tundra. Our phylogenetic results support the taxonomic inclusion of M. miurus in its senior synonym, M. abbreviatus.

Phylogenetic diversification patterns and divergence times in ground beetles (Coleoptera: Carabidae: Harpalinae).

BackgroundHarpalinae is a species rich clade of carabid beetles with many unusual morphological forms and ecological interactions. How this diversity evolved has been difficult to reconstruct, perhaps because harpalines underwent a rapid burst of diversification early in their evolutionary history. Here we investigate the tempo of evolution in harpalines using molecular divergence dating techniques and explore the rates of lineage accumulation in harpalines and their sister group.ResultsAccording to molecular divergence date estimates, harpalines originated in the mid Cretaceous but did not diversify extensively until the late Cretaceous or early Paleogene about 32 million years after their origin. In a relatively small window of time, harpalines underwent rapid speciation. Harpalines have a relative high net diversification rate and increased cladogenesis in some regions of the clade. We did not see a significant decrease in diversification rate through time in the MCCR test, but a model of diversification with two shift points to lower diversification rates fit the harpaline lineage accumulation through time the best.ConclusionsOur results indicate harpalines are significantly more diverse and have higher diversification than their sistergroup. Instead of an immediate burst of explosive diversification, harpalines may have had a long "fuse" before major lineages diversified during the early Paleogene when other taxa such as mammals, birds, and some flowering plants were also rapidly diversifying.

Integration of Bayesian molecular clock methods and fossil-based soft bounds reveals early Cenozoic origin of African lacertid lizards.

BackgroundAlthough current molecular clock methods offer greater flexibility in modelling evolutionary events, calibration of the clock with dates from the fossil record is still problematic for many groups. Here we implement several new approaches in molecular dating to estimate the evolutionary ages of Lacertidae, an Old World family of lizards with a poor fossil record and uncertain phylogeny. Four different models of rate variation are tested in a new program for Bayesian phylogenetic analysis called TreeTime, based on a combination of mitochondrial and nuclear gene sequences. We incorporate paleontological uncertainty into divergence estimates by expressing multiple calibration dates as a range of probabilistic distributions. We also test the reliability of our proposed calibrations by exploring effects of individual priors on posterior estimates.ResultsAccording to the most reliable model, as indicated by Bayes factor comparison, modern lacertids arose shortly after the K/T transition and entered Africa about 45 million years ago, with the majority of their African radiation occurring in the Eocene and Oligocene. Our findings indicate much earlier origins for these clades than previously reported, and we discuss our results in light of paleogeographic trends during the Cenozoic.ConclusionThis study represents the first attempt to estimate evolutionary ages of a specific group of reptiles exhibiting uncertain phylogenetic relationships, molecular rate variation and a poor fossil record. Our results emphasize the sensitivity of molecular divergence dates to fossil calibrations, and support the use of combined molecular data sets and multiple, well-spaced dates from the fossil record as minimum node constraints. The bioinformatics program used here, TreeTime, is publicly available, and we recommend its use for molecular dating of taxa faced with similar challenges.

Seven new dolphin mitochondrial genomes and a time-calibrated phylogeny of whales.

BackgroundThe phylogeny of Cetacea (whales) is not fully resolved with substantial support. The ambiguous and conflicting results of multiple phylogenetic studies may be the result of the use of too little data, phylogenetic methods that do not adequately capture the complex nature of DNA evolution, or both. In addition, there is also evidence that the generic taxonomy of Delphinidae (dolphins) underestimates its diversity. To remedy these problems, we sequenced the complete mitochondrial genomes of seven dolphins and analyzed these data with partitioned Bayesian analyses. Moreover, we incorporate a newly-developed "relaxed" molecular clock to model heterogenous rates of evolution among cetacean lineages.ResultsThe "deep" phylogenetic relationships are well supported including the monophyly of Cetacea and Odontoceti. However, there is ambiguity in the phylogenetic affinities of two of the river dolphin clades Platanistidae (Indian River dolphins) and Lipotidae (Yangtze River dolphins). The phylogenetic analyses support a sister relationship between Delphinidae and Monodontidae + Phocoenidae. Additionally, there is statistically significant support for the paraphyly of Tursiops (bottlenose dolphins) and Stenella (spotted dolphins).ConclusionOur phylogenetic analysis of complete mitochondrial genomes using recently developed models of rate autocorrelation resolved the phylogenetic relationships of the major Cetacean lineages with a high degree of confidence. Our results indicate that a rapid radiation of lineages explains the lack of support the placement of Platanistidae and Lipotidae. Moreover, our estimation of molecular divergence dates indicates that these radiations occurred in the Middle to Late Oligocene and Middle Miocene, respectively. Furthermore, by collecting and analyzing seven new mitochondrial genomes, we provide strong evidence that the delphinid genera Tursiops and Stenella are not monophyletic, and the current taxonomy masks potentially interesting patterns of morphological, physiological, behavioral, and ecological evolution.

Bats that walk: a new evolutionary hypothesis for the terrestrial behaviour of New Zealand's endemic mystacinids

BackgroundNew Zealand's lesser short-tailed bat Mystacina tuberculata is one of only two of c.1100 extant bat species to use a true walking gait when manoeuvring on the ground (the other being the American common vampire bat Desmodus rotundus). Mystacina tuberculata is also the last surviving member of Mystacinidae, the only mammalian family endemic to New Zealand (NZ) and a member of the Gondwanan bat superfamily Noctilionoidea. The capacity for true quadrupedal terrestrial locomotion in Mystacina is a secondarily derived condition, reflected in numerous skeletal and muscular specializations absent in other extant bats. The lack of ground-based predatory native NZ mammals has been assumed to have facilitated the evolution of terrestrial locomotion and the unique burrowing behaviour of Mystacina, just as flightlessness has arisen independently many times in island birds. New postcranial remains of an early Miocene mystacinid from continental Australia, Icarops aenae, offer an opportunity to test this hypothesis.ResultsSeveral distinctive derived features of the distal humerus are shared by the extant Mystacina tuberculata and the early Miocene Australian mystacinid Icarops aenae. Study of the myology of M. tuberculata indicates that these features are functionally correlated with terrestrial locomotion in this bat. Their presence in I. aenae suggests that this extinct mystacinid was also adapted for terrestrial locomotion, despite the existence of numerous ground-based mammalian predators in Australia during the early Miocene. Thus, it appears that mystacinids were already terrestrially-adapted prior to their isolation in NZ. In combination with recent molecular divergence dates, the new postcranial material of I. aenae constrains the timing of the evolution of terrestrial locomotion in mystacinids to between 51 and 26 million years ago (Ma).ConclusionContrary to existing hypotheses, our data suggest that bats are not overwhelmingly absent from the ground because of competition from, or predation by, other mammals. Rather, selective advantage appears to be the primary evolutionary driving force behind habitual terrestriality in the rare bats that walk. Unlike for birds, there is currently no evidence that any bat has evolved a reduced capacity for flight as a result of isolation on islands.

Molecular phylogenetics reveal multiple tertiary vicariance origins of the African rain forest trees

BackgroundTropical rain forests are the most diverse terrestrial ecosystems on the planet. How this diversity evolved remains largely unexplained. In Africa, rain forests are situated in two geographically isolated regions: the West-Central Guineo-Congolian region and the coastal and montane regions of East Africa. These regions have strong floristic affinities with each other, suggesting a former connection via an Eocene pan-African rain forest. High levels of endemism observed in both regions have been hypothesized to be the result of either 1) a single break-up followed by a long isolation or 2) multiple fragmentation and reconnection since the Oligocene. To test these hypotheses the evolutionary history of endemic taxa within a rain forest restricted African lineage of the plant family Annonaceae was studied. Molecular phylogenies and divergence dates were estimated using a Bayesian relaxed uncorrelated molecular clock assumption accounting for both calibration and phylogenetic uncertainties.ResultsOur results provide strong evidence that East African endemic lineages of Annonaceae have multiple origins dated to significantly different times spanning the Oligocene and Miocene epochs. Moreover, these successive origins (c. 33, 16 and 8 million years – Myr) coincide with known periods of aridification and geological activity in Africa that would have recurrently isolated the Guineo-Congolian rain forest from the East African one. All East African taxa were found to have diversified prior to Pleistocene times.ConclusionMolecular phylogenetic dating analyses of this large pan-African clade of Annonaceae unravels an interesting pattern of diversification for rain forest restricted trees co-occurring in West/Central and East African rain forests. Our results suggest that repeated reconnections between the West/Central and East African rain forest blocks allowed for biotic exchange while the break-ups induced speciation via vicariance, enhancing the levels of endemicity. These results provide an explanation for present day distribution patterns and origins of endemicity for African rain forest trees. Moreover, given the pre-Pleistocene origins of all the studied endemic East African genera and species, these results also offer important insights for setting conservation priorities in these highly diversified but threatened ecosystems.