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Madagascar’s climate at the K/P boundary and its impact on the island’s biotic suite
... However, evidence from divergence time estimates in plants suggests an older origin of dry and humid forests (see Buerki et al., 2013 for a review). In line with this proposal, Ohba et al. (2016) suggested that mesic habitats (similar to the climatic conditions of the extant subhumid forest of the central highlands) were spread over most of the island during the early Paleogene, and that dry deciduous forests were present only in parts of the west and north-west of Madagascar, while the sub-arid spiny thicket and the rainforest were likely not yet existing (Ohba et al., 2016). Assuming that our study group is indicative of the environment in which it currently occurs, our results support the hypothesis that the arid biome may be younger, and that the rainforest biome may be older than traditionally thought (Wells, 2003;Ohba et al., 2016) Overall, our ancestral range reconstruction suggested that Madagascar's biomes and past large-scale climatic changes played a role in the diversification of Malagasy Scincinae (Fig. 5). ...
... However, evidence from divergence time estimates in plants suggests an older origin of dry and humid forests (see Buerki et al., 2013 for a review). In line with this proposal, Ohba et al. (2016) suggested that mesic habitats (similar to the climatic conditions of the extant subhumid forest of the central highlands) were spread over most of the island during the early Paleogene, and that dry deciduous forests were present only in parts of the west and north-west of Madagascar, while the sub-arid spiny thicket and the rainforest were likely not yet existing (Ohba et al., 2016). Assuming that our study group is indicative of the environment in which it currently occurs, our results support the hypothesis that the arid biome may be younger, and that the rainforest biome may be older than traditionally thought (Wells, 2003;Ohba et al., 2016) Overall, our ancestral range reconstruction suggested that Madagascar's biomes and past large-scale climatic changes played a role in the diversification of Malagasy Scincinae (Fig. 5). ...
... In line with this proposal, Ohba et al. (2016) suggested that mesic habitats (similar to the climatic conditions of the extant subhumid forest of the central highlands) were spread over most of the island during the early Paleogene, and that dry deciduous forests were present only in parts of the west and north-west of Madagascar, while the sub-arid spiny thicket and the rainforest were likely not yet existing (Ohba et al., 2016). Assuming that our study group is indicative of the environment in which it currently occurs, our results support the hypothesis that the arid biome may be younger, and that the rainforest biome may be older than traditionally thought (Wells, 2003;Ohba et al., 2016) Overall, our ancestral range reconstruction suggested that Madagascar's biomes and past large-scale climatic changes played a role in the diversification of Malagasy Scincinae (Fig. 5). Today's asymmetric distribution of species across the island bioclimatic zonation supports the hypothesis that different biomes contributed differently to the in situ diversification of the group. ...
Most of the unique and diverse vertebrate fauna that inhabits Madagascar derives from in situ diversification from colonisers that reached this continental island through overseas dispersal. The endemic Malagasy Scincinae lizards are amongst the most species-rich squamate groups on the island. They colonised all bioclimatic zones and display many ecomorphological adaptations to a fossorial (burrowing) lifestyle. Here we propose a new phylogenetic hypothesis for their diversification based on the largest taxon sampling so far compiled for this group. We estimated divergence times and investigated several aspects of their diversification (diversification rate, body size and fossorial lifestyle evolution, and biogeography). We found that diversification rate was constant throughout most of the evolutionary history of the group, but decreased over the last 6–4 million years and independently from body size and fossorial lifestyle evolution. Fossoriality has evolved from fully quadrupedal ancestors at least five times independently, which demonstrates that even complex morphological syndromes – in this case involving traits such as limb regression, body elongation, modification of cephalic scalation, depigmentation, and eyes and ear-opening regression – can evolve repeatedly and independently given enough time and eco-evolutionary advantages. Initial diversification of the group likely occurred in forests, and the divergence of sand-swimmer genera around 20 Ma appears linked to a period of aridification. Our results show that the large phenotypic variability of Malagasy Scincinae has not influenced diversification rate and that their rich species diversity results from a constant accumulation of lineages through time. By compiling large geographic and trait-related datasets together with the computation of a new time tree for the group, our study contributes important insights on the diversification of Malagasy vertebrates.
... They sometimes appear as white-water channels and occasionally as waterfalls (Figures S9a, S9b, and S9c in Supporting Information S1). Orographic precipitation on the escarpment side (Ohba et al., 2016) adds to the relatively rapid erosion of the steep escarpment. ...
... In addition to the inhibited physical erosion due to area loss, chemical weathering may have been encouraged by the stable climatic conditions of the high plateau, where the modern climate is characterized by hot summer and moderate humidity. The modern hot moderate climate of the high plateau was established by ∼66 Ma although the island has drifted northward for ∼20 latitudinal degrees since Cretaceous rifting (Ohba et al., 2016). ...
A great escarpment at a rift margin can correspond directly to a major water divide, but at many margins, including in Madagascar, the escarpment often appears as a steep knickzone on rivers that have their main water divides into the interior of the high plateau. We hypothesize that this variability in morphology is a reflection of the frequency and size of the drainage area captured from the high plateau over the escarpment. To test this hypothesis, we document morphological features and weathering conditions of river sediment in Madagascar. We propose that the existence of a weathered, weak surface layer of crystalline bedrock encourages river reversal and large river captures from the upper plateau, leading to a high frequency of knickpoint‐type rivers. We demonstrate that this is feasible using 2D landscape evolution models and show that an easily eroded surface layer is prone to fast divide migration through frequent river capture and reversal. A positive scaling relationship between the captured area and escarpment retreat rate is found from the models. We demonstrate that this scaling is also observed in the great escarpments of Madagascar and India. This divide migration mechanism provides a new explanation for the morphology of river profiles and great escarpments.
... Forested biomes (dry deciduous and rainforest) were reconstructed as the oldest ancestral ranges where the diversification of the group has probably started. The oldest reconstruction of the sub-arid spiny thicket biome dates to ca. 18 Mya (Fig. 4.4) (Ohba et al., 2016). Our results support the hypothesis that the arid biome is younger and the humid forest biome is older than traditionally thought (Wells, 2003). ...
... However, evidence from divergence times estimates in plants suggests an older origin of dry and humid forests (see Buerki et al., 2013 for a review). In line with this proposal,Ohba et al. (2016) suggested that mesic habitats (similar to the habitat of extant subhumid forest of the central highlands) were spread in most of the island during the early Paleogene and suggested that dry deciduous forests were present in part of western and north-western Madagascar, while the sub-arid spiny thicket and the rainforest were likely not yet existing ...
... The annual precipitation decreases from east to west, and also from north to south (Figure 2b). In the study area, the eastern coastal plain and the escarpment are rainy yearround, due to an orographic effect (Figures 2a and 3, Ohba et al., 2016). Annual rainfall in the northern portion of the high plateau is mostly from the summer monsoon during November to April, whereas the southern part of the central high plateau is subtropical and dry (Nassor & Jury, 1998). ...
... Paleomagnetic studies have reconstructed the paleolatitude of Madagascar to be between 30° and 40°S at Chron 34 (∼84 Ma) (Schettino & Scotese, 2005). The northward drift of Madagascar pulled it out of subtropical latitudes to the present tropical zone progressively during the Cenozoic (Ohba et al., 2016). 10.1029/2021GC009979 4 of 25 ...
The eastern margin of Madagascar has a prominent relief change from the flat coastal plain to the low‐relief high plateau, characterizing a typical great escarpment topography at a passive margin. A quantification of the spatial distribution of erosion rates is necessary to understand the rate of landscape evolution. We present catchment‐averaged erosion rates from detrital cosmogenic ¹⁰Be concentrations, systematically covering distinct morphological zones of the escarpment. Erosion rates are differentiated across the escarpment, where the high plateau and the coastal plain are slowly eroding with an average rate of 9.7 m/Ma, and the escarpment basins are eroding faster with an average rate of 16.6 m/Ma. The Alaotra‐Ankay Graben related basins have the highest erosion rate with an average rate of 27 m/Ma. The spatial pattern of erosion rates indicates a retreating escarpment landscape. Retreat rates calculated from the ¹⁰Be concentrations are from 182 to 1,886 m/Ma. The rates of escarpment retreat on Madagascar are consistent with a model of a steady retreat from the coastline since the time of rifting, similar to the Western Ghats escarpment on its conjugate margin of the India Peninsula.
... The annual precipitation decreases from east to west, and also from north to south (Figure 2b). In the study area, the eastern coastal plain and the escarpment are rainy yearround, due to an orographic effect (Figures 2a and 3, Ohba et al., 2016). Annual rainfall in the northern portion of the high plateau is mostly from the summer monsoon during November to April, whereas the southern part of the central high plateau is subtropical and dry (Nassor & Jury, 1998). ...
... Paleomagnetic studies have reconstructed the paleolatitude of Madagascar to be between 30° and 40°S at Chron 34 (∼84 Ma) (Schettino & Scotese, 2005). The northward drift of Madagascar pulled it out of subtropical latitudes to the present tropical zone progressively during the Cenozoic (Ohba et al., 2016). 10.1029/2021GC009979 4 of 25 ...
The eastern margin of Madagascar has a prominent relief change from the flat coastal plain to the low-relief high plateau, characterizing a typical great escarpment topography at a passive margin. A quantification of the spatial distribution of erosion rates is necessary to understand the rate of landscape evolution. We present catchment-averaged erosion rates from detrital cosmogenic 10Be concentrations, systematically covering distinct morphological zones of the escarpment. Erosion rates are differentiated across the escarpment, where the high plateau and the coastal plain are slowly eroding with an average rate of 9.7 m/Ma, and the escarpment basins are eroding faster with an average rate of 16.6 m/Ma. The Alaotra-Ankay Graben related basins have the highest erosion rate with an average rate of 27 m/Ma. The spatial pattern of erosion rates indicates a retreating escarpment landscape. Retreat rates calculated from the 10Be concentrations are from 182 m/Ma to 1886 m/Ma. The rates of escarpment retreat on Madagascar are consistent with a model of a steady retreat from the coastline since the time of rifting, similar to the Western Ghats escarpment on its conjugate margin of the India Peninsula.
... That answer may lie in the limits to plasticity. Despite being considered a hypervariable environment, much of Madagascar is rather warm (Ohba et al., 2016). In fact, Madagascar's climate is thought to have changed very little since tenrecs first colonized the island 30-56 MYA (Everson et al., 2016;Ohba et al., 2016). ...
... Despite being considered a hypervariable environment, much of Madagascar is rather warm (Ohba et al., 2016). In fact, Madagascar's climate is thought to have changed very little since tenrecs first colonized the island 30-56 MYA (Everson et al., 2016;Ohba et al., 2016). We found tenrecs appear highly stressed when T a or T b is <8°C or >34°C as cold animals may cease ventilating and hot animals pant and breathe irregularly (Kayser, 1961;Oelkrug et al., 2013;Scholl, 1974;M.D.T., L.S., B.B. and F.v.B., personal observations). ...
Physiological plasticity allows organisms to respond to diverse conditions. However, can being too plastic actually be detrimental? Malagasy common tenrecs, Tenrec ecaudatus, have many plesiomorphic traits and may represent a basal placental mammal. We established a laboratory population of T. ecaudatus and found extreme plasticity in thermoregulation and metabolism, a novel hibernation form, variable annual timing, and remarkable growth and reproductive biology. For instance, tenrec body temperature (Tb) may approximate ambient temperature to as low as 12°C even when tenrecs are fully active. Conversely, tenrecs can hibernate with Tbs of 28°C. During the active season, oxygen consumption may vary 25-fold with little or no changes in Tb During the Austral winter, tenrecs are consistently torpid but the depth of torpor may be variable. A righting assay revealed that Tb contributes to but does not dictate activity status. Homeostatic processes are not always linked e.g. a hibernating tenrec experienced a ∼34% decrease in heart rate while maintaining constant body temperature and oxygen consumption rates. Tenrec growth rates vary but young may grow ∼40-fold in the 5 weeks until weaning and may possess indeterminate growth as adults. Despite all of this profound plasticity, tenrecs are surprisingly intolerant to extremes in ambient temperature (<8 or >34°C). We contend that while plasticity may confer numerous energetic advantages in consistently moderate environments, environmental extremes may have limited the success and distribution of plastic basal mammals.
... When continental drift moved Madagascar north and directly into the trade wind zone, the spiny forest ecosystem contracted (3). However, the humid forest has been found to contain taxa belonging to lineages that date back to the Paleocene, and further evidence from climate reconstructions suggests that Madagascar was moderately humid at the K-Pg boundary (11,30) (Fig. 1A). ...
Madagascar's biota is hyperdiverse and includes exceptional levels of endemicity. We review the current state of knowledge on Madagascar's past and current terrestrial and freshwater biodiversity by compiling and presenting comprehensive data on species diversity, endemism, and rates of species description and human uses, in addition to presenting an updated and simplified map of vegetation types. We report a substantial increase of records and species new to science in recent years; however, the diversity and evolution of many groups remain practically unknown (e.g., fungi and most invertebrates). Digitization efforts are increasing the resolution of species richness patterns and we highlight the crucial role of field- and collections-based research for advancing biodiversity knowledge and identifying gaps in our understanding, particularly as species richness corresponds closely to collection effort. Phylogenetic diversity patterns mirror that of species richness and endemism in most of the analyzed groups. We highlight humid forests as centers of diversity and endemism because of their role as refugia and centers of recent and rapid radiations. However, the distinct endemism of other areas, such as the grassland-woodland mosaic of the Central Highlands and the spiny forest of the southwest, is also biologically important despite lower species richness. The documented uses of Malagasy biodiversity are manifold, with much potential for the uncovering of new useful traits for food, medicine, and climate mitigation. The data presented here showcase Madagascar as a unique "living laboratory" for our understanding of evolution and the complex interactions between people and nature. The gathering and analysis of biodiversity data must continue and accelerate if we are to fully understand and safeguard this unique subset of Earth's biodiversity.
... Madagascar became increasingly wetter as it moved above the arid subtropical zone (30° south latitude) and the northward movement of India allowed the trade winds of the Indian Ocean to bring moisture (Buerki, Devey, Callmander, Phillipson, & Forest, 2013;Wells, 2003). Alternatively, the distribution of climate regimes seen today may have been relatively stable in deep time, though cooler and with less distinct precipitation gradients and seasonality than today (Ohba, Samonds, LaFleur, Ali, & Godfrey, 2016). Despite the antiquity of arid climates in Madagascar, the extant lemur lineages that converged on the hot, arid niche diverged between 15 and 2 mya. ...
Aim
To test the hypothesis that adaptive convergent evolution of climate niches occurred in multiple independent lemur lineages.
Location
Madagascar.
Taxon
Lemurs.
Methods
I collected climate and altitude data from WorldClim and summarized the niches of almost all living lemurs (83 species) into phylogenetically controlled principal components. To test for convergent evolution, I searched for multiple, similar climate optima using multi‐peak Ornstein–Uhlenbeck models (surface, l1‐ou, bayou). I compared the observed level of climate convergence to that simulated under neutral and single‐optimum models. To test if behavioural or morphological traits were related to climate niches, I used phylogenetic regressions with activity pattern, diet, and body size.
Results
From an ancestral niche with high rainfall and low seasonality, four lemur lineages independently converged on climate niche optima characterized by high temperatures and low rainfall, supporting adaptive evolution in southwest deciduous and arid habitats. The observed level of convergence was more frequent than expected under Brownian motion and single‐optimum simulations, which illustrates that the results are likely not a result of stochastic evolution over long time periods. Nocturnal and cathemeral activity patterns were common among lineages in the arid climate niche.
Conclusion
Lemur climate niche evolution demonstrated that convergence explains the distribution of four independent clades in hot, arid environments of southwest Madagascar. The timing of these convergent shifts coincided with the origination of modern arid‐adapted plant genera, some of which are important lemur food sources. These communities have high endemicity and are especially threatened by habitat loss. Arid environments are arenas in which convergent evolution is predicted to occur frequently.
Madagascar is a biogeographically unique island with a remarkably high level of endemism. However, endemic taxa in Madagascar are massively threatened due to unprecedented pressures from anthropogenic habitat modification and climate change. A comprehensive phylogeny-based biodiversity evaluation of the island remains lacking. Here, we identify hotspots of taxonomic and phylogenetic plant diversity and neo- and paleo-endemism by generating a novel dated tree of life for the island. The tree is based on unprecedented sampling of 3,950 species (33% of the total known species) and 1,621 genera (93% of the total known genera and 69% of endemic genera) of Malagasy vascular plants. We find that island-endemic genera are concentrated in multiple lineages combining high taxonomic and phylogenetic diversity. Integrating phylogenetic and geographic distribution data, our results reveal that taxon richness and endemism are concentrated in the northern, eastern, and southeastern humid forests. Paleo-endemism centers are concentrated in humid eastern and central regions, whereas neo-endemism centers are concentrated in the dry and spiny forests in western and southern Madagascar. Our statistical analysis of endemic genera in each vegetation region supports a higher proportion of ancient endemic genera in the east but a higher proportion of recent endemic genera in the south and west. Overlaying centers of phylogenetic endemism with protected areas, we identify conservation gaps concentrated in western and southern Madagascar. These gaps should be incorporated into conservation strategies to aid the protection of multiple facets of biodiversity and their benefits to the Malagasy people.
Madagascar exhibits high endemic biodiversity that has evolved with sustained and stable rates of speciation over the past several tens of millions of years. The topography of Madagascar is dominated by a mountainous continental rift escarpment, with the highest plant diversity and rarity found along the steep, eastern side of this geographic feature. Using a process-explicit model, we show that precipitation-driven erosion and landward retreat of this high-relief topography creates transient habitat organization through multiple mechanisms, including catchment expansion, isolation of highland remnants, and formation of topographic barriers. Habitat isolation and reconnection on a million-year timescale serves as an allopatric speciation pump creating the observed biodiversity.
Societal Impact Statement
Madagascar is famous for its unique forests and their fauna. Most of the island is covered by flammable grassy ecosystems long considered to be of human origin and threatening the remaining forests. Yet new studies show that many plants and animals of the grassy systems are unique to Madagascar and restricted to these open habitats. Open grassy ecosystems have markedly different management requirements from forests and bring different contributions to society. We argue that the grassy ecosystems can benefit Madagascar if understood and managed wisely using expanded knowledge bases that also include collaboration with locals.
Summary
Until recently, nearly all research and interests in Madagascar focused on forested habitats. To help place Madagascar's grassy ecosystems in context, we provide a summary of the origin, development, and evolution of open tropical, C4 grassy ecosystems elsewhere, especially those from Africa; we summarize similarities and differences with the distribution of C3 and C4 grasses in the Malagasy landscape, their plant traits, and inferences on the evolutionary legacy of grasses. We also discuss the animal communities that use and have coevolved in these grassy systems; to help resolve controversies over the pre‐settlement extent of grassy ecosystems, we suggest a variety of complementary geochemical, palaeobotanical, and molecular genetic tools that have been effectively used elsewhere to untangle forest/grassy ecosystem mosaics and the ecological and evolutionary processes that influence them. Many of these tools can and should be employed in Madagascar to fully understand the spatio‐temporal dynamics of open, grassy, and closed forest systems across the island; as regards conservation, we discuss the ecosystem services provided by grassy systems, which are too often ignored in general, not only as a biome, vis‐à‐vis forests, but also for their global importance as a carbon sink and role they play in water management and providing goods to local villagers. We conclude by outlining the necessary research to better manage open ecosystems across Madagascar without threatening endangered forest ecosystems.
Evolutionary shifts in chromosome compositions (karyotypes) are major drivers of lineage and genomic diversification. Fusion of ancestral chromosomes is one hypothesized mechanism for the evolutionary reduction of the total chromosome number; a frequently implied karyotypic shift. Empirical tests of this hypothesis require model systems with variable karyotypes, known chromosome features, and a robust phylogeny. Here we used chameleons, diverse lizards with exceptionally variable karyotypes (2n = 20-62), to test whether chromosomal fusions explain the repeated evolution of karyotypes with fewer chromosomes than ancestral karyotypes. Using a multidisciplinary approach including cytogenetic analyses and phylogenetic comparative methods, we found that a model of constant loss through time best explained chromosome evolution across the chameleon phylogeny. Next we tested whether fusions of microchromosomes into macrochromosomes explained these evolutionary losses using generalized linear models. Multiple comparisons supported microchromosome fusions as the predominant agent of evolutionary loss. We further compared our results to various natural history traits and found no correlations. As such, we infer that the tendency of microchromosomes to fuse was a quality of the ancestral chameleon genome, and that the genomic predisposition of ancestors is a more substantive predictor of chromosome change than the ecological, physiological, and biogeographical factors involved in their diversification.
There is disparity between the estimated time of origin
of the ‘superclade’ Dipterocarpaceae sensu lato, that
includes Sarcolaenaceae, Cistaceae, Pakaraimaea, Bixaceae,
Cochlospermaceae and Sphaerosepalaceae, as determined by
recent molecular phylogenies (100−85 million years ago, Ma) and
its strongly tropical, South American-African-Madagascan-SE Asian
distribution that indicates an older Gondwanan origin (>110 Ma).
We used several paleobiogeographic approaches, including
recently reported fossil records, to explore the hypothesis that
Dipterocarpaceae sl has a Gondwanan/early-Cretaceous origin.
We created molecular phylogenies for this group, assigned
each genus/family to the tectonic plate on which it is extant, and
subjected the cladogram to areogram analysis. We also assessed
ecological, mycotrophic and morphological traits, and global
circulation patterns, as these might affect this group’s distribution.
The initial analysis (omitting fossil evidence) showed that the
crown of Dipterocarpaceae sl occurred concurrently on the South
American and Madagascan plates. Including fossils from Africa and
India changed this to a South American-African origin. Collectively,
these origins represent NorthWest Gondwana with South America,
Africa and Madagascar remaining conjoined until ≥105–115 Ma,
setting the minimum age for this superclade with some evidence
that it may be much older. We also show that the immediate
ancestors of the three daughter lineages [Dipterocarpaceae-
Sarcolaenaceae (in Africa/Madagascar, ≥115 Ma), Cistaceae-
Pakaraimaea (South America/Africa/Eurasia, ≥105 Ma) and
Bixaceae-Cochlospermum-Sphaerosepalaceae (South America/
Africa, ≥105 Ma)] also arose in NorthWest Gondwana.
The immediate ancestors or basal species in Sarcolaenaceae,
Sphaerosepalaceae, Dipterocarpaceae (both its subfamilies) and
Bixaceae migrated from (South America)/Africa to Madagascar
and we propose that the Dipterocarpoideae proceeded from
Africa to India while still linked to Madagascar. In addition, much
subsequent diversification of this superclade has occurred on the
Eurasian, Indian, SE Asian (Sunda) and North American plates
post-Gondwanan breakup.
This long vicariant history is supported by fossil, ecological,
mycotrophic and morphological traits, and global circulation
patterns that show negligible propensity for transoceanic dispersal
to explain this clade’s wide intercontinental distribution.
We conclude that all these areocladogram/plate-breakup/
ecomorphological/circulation features are consistent with
a Gondwanan/early-Cretaceous (>115 Ma) origin for the
Dipterocarpaceae-Cistaceae-Bixaceae superclade plus its three
daughter clades. Future analyses at the species level, exploring
alternative diversification dates from both fossils and platetectonic
dynamics, are needed to refine these findings.
For most of the 20th century, the hypothesis was accepted that Madagascar's extensive grass‐dominated ecosystems were of anthropogenic origin, carved out of pristine forests after a mere two millennia of human settlement. We tested an alternative hypothesis that these C4 grassy ecosystems were part of the general Late Miocene expansion of tropical grassy biomes, using diverse data from published sources (Bond et al. 2008). Joseph and Seymour (2021) criticised this paper, which they see as seminal to subsequent studies on the grasslands. Here we respond to their critique of our study. We also briefly note diverse studies since 2008 pointing to the ancient origin of Madagascar's C4 grasses and the ecosystems they dominate. We conclude with key research needs that will help promote open‐minded research on these long neglected grassy biomes. The answers would be of considerable scientific and public interest but may also contribute to enlightened management of forest/grassland mosaics.
We present a study to estimate the large‐scale landscape history of a continental margin, by establishing a source‐to‐sink volume balance between the eroding onshore areas and the offshore basins. Assuming erosion as the primary process for sediment production, we strive to constrain a numerical model of landscape evolution that balances the volumes of eroded materials from the continent and that deposited in the corresponding basins, with a ratio imposed for loss of erosion products. We use this approach to investigate the landscape history of Madagascar since the Late Cretaceous. The uplift history prescribed in the model is inferred from elevations of planation surfaces formed at various ages. By fitting the volumes of terrigenous sediments in the Morondava Basin along the west coast and the current elevation of the island, the landscape evolution model is optimized by constraining the erosion law parameters and ratios of sediment loss. The results include a best‐fit landscape evolution model, which features two major periods of uplift and erosion during the Late Cretaceous and the middle to late Cenozoic. The model supports suggestions from previous studies that most of the high topography of the island was constructed since the middle to late Miocene, and on the central plateau the erosion has not reached an equilibrium with the high uplift rates in the late Cenozoic. Our models also indicate that over the geological time scale, a significant portion of materials eroded from Madagascar was not archived in the offshore basin, possibly consumed by chemical weathering, the intensity of which might have varied with climate.
Interspecific associations may limit the dispersal of individual species, but may also facilitate it when entire co-evolved systems expand their geographic ranges. We tested the recent proposal that episodic land bridges linked Africa and Madagascar at three stages during the Cenozoic by comparing divergence estimates of Madagascar’s angiosperm taxa with their dispersal mechanisms. Plants that rely on gravity for seed dispersal indicate at least two episodes of land connection between Africa and Madagascar, in the Early Palaeocene and Early Oligocene. Seed dispersal by strepsirrhine primates possibly evolved in the Palaeocene, with the divergence of at least one endemic Malagasy angiosperm genus, Burasaia (Menispermaceae). This genus may have facilitated the lemur colonization of Madagascar. Frugivory, nectarivory and gummivory probably generalized in the Oligocene, with the co-evolution of modern lemurs and at least 10 new Malagasy angiosperm families. In the Late Miocene, more angiosperms were probably brought from Africa by birds via a discontinuous land connection, and radiated on Madagascar in diffuse association with birds (asities) and dwarf nocturnal lemurs (cheirogaleids). During the same connective episode, Madagascar was probably colonized by hippopotamuses, which both followed and re-seeded a variety of plants, forming the grassy Uapaca ‘tapia’ forest and ericoid ‘savoka’ thicket.
The Indian Ocean has a complex geological history that has drawn the attention of naturalists for almost a century now. Due to its tectonic history, many geological elements and processes have been evoked to explain the exchange of species between landmasses. Here, we revisited previous studies on twenty-three taxa to investigate trends across time since the Gondwana breakup. We investigated these datasets by applying a time-calibrated Bayesian framework to them and reconstructing their ancestral ranges. We conclude that ecological transformations have presented opportunities for the establishment of migrants. The role of donating and receiving migrants has shifted several times according to these transformations. Time-specific trends show weak evidence for the stepping-stones commonly suggested as physical routes between landmasses. However, before its collision with Asia, India may have served as an intermediary for such exchanges.
Aim
For 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.
Location
East Africa, Madagascar, Mozambique Channel.
Taxa
Fish, amphibians, reptiles, birds, mammals.
Methods
We 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.
Results
Madagascar'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 conclusion
The 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.
Background:
Was there a mid-Cenozoic vertebrate extinction and recovery event in Madagascar and, if so, what are its implications for the evolution of lemurs? The near lack of an early and mid-Cenozoic fossil record on Madagascar has inhibited direct testing of any such hypotheses. We compare the terrestrial vertebrate fauna of Madagascar in the Holocene to that of early Cenozoic continental Africa to shed light on the probability of a major mid-Cenozoic lemur extinction event, followed by an "adaptive radiation" or recovery. We also use multiple analytic approaches to test competing models of lemur diversification and the null hypothesis that no unusual mid-Cenozoic extinction of lemurs occurred.
Results:
Comparisons of the terrestrial vertebrate faunas of the early Cenozoic on continental Africa and Holocene on Madagascar support the inference that Madagascar suffered a major mid-Cenozoic extinction event. Evolutionary modeling offers some corroboration, although the level of support varies by phylogeny and model used. Using the lemur phylogeny and divergence dates generated by Kistler and colleagues, RPANDA and TESS offer moderate support for the occurrence of unusual extinction at or near the Eocene-Oligocene (E-O) boundary (34 Ma). TreePar, operating under the condition of obligate mass extinction, found peak diversification at 31 Ma, and low probability of survival of prior lineages. Extinction at the E-O boundary received greater support than other candidate extinctions or the null hypothesis of no major extinction. Using the lemur phylogeny and divergence dates generated by Herrera & Dàvalos, evidence for large-scale extinction diminishes and its most likely timing shifts to before 40 Ma, which fails to conform to global expectations.
Conclusions:
While support for large-scale mid-Cenozoic lemur extinction on Madagascar based on phylogenetic modeling is inconclusive, the African fossil record does provide indirect support. Furthermore, a major extinction and recovery of lemuriforms during the Eocene-Oligocene transition (EOT) would coincide with other major vertebrate extinctions in North America, Europe, and Africa. It would suggest that Madagascar's lemurs were impacted by the climate shift from "greenhouse" to "ice-house" conditions that occurred at that time. This could, in turn, help to explain some of the peculiar characteristics of the lemuriform clade.
Aim Describe the main geo‐physical features of the various sorts of marine islands that are associated with the continents and consider how the ontogenetic pathways of each landmass type might have shaped the hosted biotas.
Location Global.
Methods Review of the literature that underpins understanding of the “continental” marine islands, particularly those publications with biological, geological, geophysical, oceanographical and palaeoceanographical foci.
Results Based on their geo‐physical settings, islands with continental basements/close connections to the continents can be assigned to one of nine categories: shelf, shelf volcano, orogenic margin, continental arc, continental fore‐arc, rifted arc‐raft, isolated raft atoll, isolated block and micro‐continental terrane. As each functions in a distinctive manner, this must have strongly imprinted the native biotas.
Main conclusions “Continental” marine islands can be allocated to one of nine groups based on their respective geo‐physical locations. When geological time is considered, then the unique histories of each insular landmass type will have played a critical role in moulding the land‐locked faunal assemblages that have amassed and evolved atop them. Researchers investigating insular biotas, particularly those exploring biodiversity growth, may wish to accommodate these insights.
Geographic patterns of biodiversity result from broad-scale biogeographic and present-day ecological processes. The aim of this study was to investigate the relative importance of biogeographic history and ecology driving patterns of diversity in modern primate communities in Madagascar. I collected data on endemic lemur species co-occurrence from range maps and survey literature for 100 communities in protected areas. I quantified and compared taxonomic, phylogenetic, and functional dimensions of intra- and intersite diversity. I tested environmental and geographic predictors of diversity and endemism. I calculated deforestation rates within protected areas between the years 2000 and 2014, and tested if diversity is related to forest cover and loss. I found the phylogenetic structure of lemur communities could be explained primarily by remotely sensed plant productivity, supporting the hypothesis that there was ecological differentiation among ecoregions, while functional-trait disparity was not strongly related to environment. Taxonomic and phylogenetic diversity also increased with increasing topographic heterogeneity. Beta diversity was explained by both differences in ecology among localities and potential river barriers. Approximately 3000 km² were deforested in protected areas since the year 2000, threatening the most diverse communities (up to 31%/park). The strong positive association of plant productivity and topographic heterogeneity with lemur diversity indicates that high productivity, rugged landscapes support greater diversity. Both ecology and river barriers influenced lemur community ecology and biogeography. These results underscore the need for focused conservation efforts to slow the loss of irreplaceable evolutionary and ecological diversity.
Ancient environmental and sea-level changes are very likely to have played key roles in primate speciation, extinction, adaptation, and dispersal. Most modern primates are ecologically dependent on trees and inhabit tropical environments, and the same was true for many extinct primates. In the warm Paleocene and Eocene when the tropical broadleaf forest biome extended to high latitudes, primates inhabited North America and northern Eurasia. Ranges then contracted into lower latitudes in the Eocene and Oligocene when global cooling caused a commensurate reduction in suitable tree cover, only to expand again in the Miocene, when most primates across Africa, Eurasia, and South America exploited diverse forest and woodland environments, which may have been very different to those observed in similar regions today. By the end of the Miocene through to the Pleistocene, grassland expansion allowed more terrestrial and open habitat primates to radiate, although most retained some ecological dependence on trees. Sea-level changes occurring since the origin of primates, causing events such as the closure of the eastern Tethys Sea, appearance of the Isthmus of Panama, and shifts in Southeast Asian archipelagos, influenced primate dispersal and diversification. Changes to ocean circulation caused by sea-level change may have impacted global climate, which in turn would have altered primate environments.
Lemurs, the diverse, endemic primates of Madagascar, are thought to represent a classic example of adaptive radiation. Based on the most complete phylogeny of living and extinct lemurs yet assembled, I tested predictions of adaptive radiation theory by estimating rates of speciation, extinction and adaptive phenotypic evolution. As predicted, lemur speciation rate exceeded that of their sister clade by nearly twofold, indicating the diversification dynamics of lemurs and mainland relatives may have been decoupled. Lemur diversification rates did not decline over time, however, as predicted by adaptive radiation theory. Optimal body masses diverged among dietary and activity pattern niches as lineages diversified into unique multidimensional ecospace. Based on these results, lemurs only partially fulfil the predictions of adaptive radiation theory, with phenotypic evolution corresponding to an 'early burst' of adaptive differentiation. The results must be interpreted with caution, however, because over the long evolutionary history of lemurs (approx. 50 million years), the 'early burst' signal of adaptive radiation may have been eroded by extinction.
Aim
We studied the gecko genus Ebenavia to reconstruct its colonization history, test for anthropogenic versus natural dispersal out of Madagascar, and correlate divergence date estimates of our phylogeny with geological age estimates of islands in the region.
Location
Madagascar and surrounding islands of the Western Indian Ocean (Comoros, Mayotte, Mauritius, Pemba).
Methods
We reconstructed the phylogeny of Ebenavia covering its entire geographical range using a molecular data set of three mitochondrial and two nuclear markers. We estimated divergence times based on calibrations using (1) previously calculated mutation rates of mitochondrial markers, (2) a combination of these rates with old or (3) young geological age estimates for some of the islands inhabited by the genus, and (4) an independent data set with fossil outgroup calibration points.
Results
Ebenavia inunguis , one of two recognized species of the genus, comprises multiple ancient evolutionary lineages. The earliest divergence within this complex (Miocene, 13–20 Ma; 95% credibility interval [ CI ]: 4–29 Ma) separates the population of the Comoros Islands, excluding Mayotte, from all other lineages. The age estimates for island lineages coincide with the geological age estimates of the islands except for Grand Comoro, where the age of the local clade (3–5 Ma; 95% CI : 2–7 Ma) significantly predates the estimated island age (0·5 Ma). A clade from north Madagascar + Mayotte + Pemba is estimated to have diverged from an eastern Malagasy clade in the Miocene.
Main Conclusions
Our results suggest that Grand Comoro Island is geologically older than previously estimated. The islands of the Comoros and Pemba were probably colonized via natural dispersal out of Madagascar (> 1000 km in the case of Pemba). Mauritius was most likely colonized only recently from eastern Madagascar via human translocation.
Torpor, the controlled depression of virtually all bodily function during scarce periods, was verified in primates under free-ranging conditions less than two decades ago. The large variety of different torpor patterns found both within and among closely related species is particularly remarkable. To help unravel the cause of these variable patterns, our review investigates primate torpor use within an evolutionary framework. First, we provide an overview of heterothermic primate species, focusing on the Malagasy lemurs, and discuss their use of daily torpor or hibernation in relation to habitat type and climatic conditions. Second, we investigate environmental characteristics that may have been involved in shaping the high variability of torpor expression found in lemurs today. Third, we examine potential triggers for torpor use in lemurs. We propose the "torpor refugia hypothesis" to illustrate how disparate primate torpor patterns possibly evolved in response to environmental cues during glacial periods, when animals were restricted to different refuge habitats along riverine corridors. For example, individuals enduring harsher conditions at higher altitudes likely developed seasonal hibernation, whereas those inhabiting lower elevation river catchments might have coped with unfavorable conditions by employing daily torpor. The ultimate stimuli triggering torpor use today likely differ between the different habitats of Madagascar. The broad diversity of torpor patterns in lemurs among closely related species, both within the same and in distinctly different habitat types, provides an ideal base for research into the stimuli for torpor use in endotherms in general. Our hypothesis highlights the importance of considering the environmental conditions under which ecosystems and species evolved when trying to explain physiological adaptations seen today.
Skeletal histology supports the hypothesis that primate life histories are regulated by a neuroendocrine rhythm, the Havers-Halberg Oscillation (HHO). Interestingly, subfossil lemurs are outliers in HHO scaling relationships that have been discovered for haplorhine primates and other mammals. We present new data to determine whether these species represent the general lemur or strepsirrhine condition and to inform models about neuroendocrine-mediated life history evolution. We gathered the largest sample to date of HHO data from histological sections of primate teeth (including the subfossil lemurs) to assess the relationship of these chronobiological measures with life history-related variables including body mass, brain size, age at first female reproduction, and activity level. For anthropoids, these variables show strong correlations with HHO conforming to predictions, though body mass and endocranial volume are strongly correlated with HHO periodicity in this group. However, lemurs (possibly excepting Daubentonia) do not follow this pattern and show markedly less variability in HHO periodicity and lower correlation coefficients and slopes. Moreover, body mass is uncorrelated, and brain size and activity levels are more strongly correlated with HHO periodicity in these animals. We argue that lemurs evolved this pattern due to selection for risk-averse life histories driven by the unpredictability of the environment in Madagascar. These results reinforce the idea that HHO influences life history evolution differently in response to specific ecological selection regimes.
Inferring the behavior of extinct organisms is a formidable task, even under the best of circumstances (Rudwick, 1964; Stern and Susman, 1983; Kay, 1984; Thomason, 1995). Nevertheless, and in spite of inevitable complications and limitations, such inferences remain the ultimate goal of paleobiologists if we are to understand fossils as integrated organisms rather than isolated bones and atomized character states. In this chapter we attempt to breathe life back into the osteological remains of recently extinct (or “subfossil”) prosimian primates from the Quaternary of Madagascar. Subfossil lemurs provide many special opportunities to the optimistic functional morphologist, but they also present their own unusual set of complications and potential frustrations. Approximately one-third of Madagascar’s known primate species were driven to extinction in the late Holocene by the lethal interaction of aridification and human colonization (Burney, 1997; Dewar, 1997; Simons, 1997), including all taxa of large body size (> 9 kg). Two new extinct species from northern Madagascar (Babakotia radofilai and Mesopropithecus dolichobrachion) have been discovered and described in the last decade (Godfrey et al., 1990; Simons et al., 1995), and a third new species from the northwest will be diagnosed soon (Jungers et al., in prep.). Sixteen currently recognized subfossil species of Malagasy primates are represented in museum collections, most by numerous individuals, including a growing tally of specimens with associated craniodental and postcranial elements (e.g., MacPhee et al., 1984; Simons et al., 1992,Simons et al., 1995; Wunderlich et al., 1996). Table I summarizes the current taxonomy of the extinct lemurs. Aspects of morphology suggest that cheirogaleids are more closely related to galagos and lorises than to other Malagasy primates (Szalay and Katz, 1973; Cartmill, 1975; Schwartz and Tattersall, 1985; Yoder, 1992). Molecular results, as well as “total evidence” analyses that combine morphological and molecular data, argue instead that the Malagasy primates are probably monophyletic (Yoder, 1994,Yoder, 1996). Regardless of the placement of the cheirogaleids within strepsirrhines, the precise relationships among the various ancient clades of Malagasy primates remain somewhat fuzzy, even from a biomolecular perspective (Yoder, 1997; Yoderet al., 1999).
New constraints on the timing of the Cre-taceous-Paleogene mass extinction and the Chicxulub impact, together with a particularly voluminous and apparently brief erup-tive pulse toward the end of the " main-stage " eruptions of the Deccan continental fl ood ba-salt province suggest that these three events may have occurred within less than about a hundred thousand years of each other. Partial melting induced by the Chicxulub event does not provide an energetically plausible explanation for this coincidence, and both geochronologic and magnetic-polarity data show that Deccan volcanism was under way well before Chicxulub/Cretaceous-Paleogene time. However, historical data document that eruptions from existing volcanic systems can be triggered by earthquakes. Seismic model-ing of the ground motion due to the Chicxu-lub impact suggests that the impact could have generated seismic energy densities of order 0.1–1.0 J/m 3 throughout the upper ~200 km of Earth's mantle, suffi cient to trigger volcanic eruptions worldwide based upon comparison with historical examples. Triggering may have been caused by a transient increase in the effective permeability of the existing deep magmatic system beneath the Deccan province, or mantle plume " head. " It is therefore reasonable to hypothesize that the Chicxulub impact might have triggered the enormous Poladpur, Ambenali, and Ma-habaleshwar (Wai Subgroup) lava fl ows, which together may account for >70% of the Deccan Traps main-stage eruptions. This hypothesis is consistent with independent strati-graphic, geochronologic, geochemical, and tectonic constraints, which combine to indicate that at approximately Chicxulub/Creta-ceous-Paleogene time, a huge pulse of mantle plume–derived magma passed through the crust with little interaction and erupted to form the most extensive and voluminous lava fl ows known on Earth. High-precision ra-dioisotopic dating of the main-phase Deccan fl ood basalt formations may be able either to confi rm or reject this hypothesis, which in turn might help to determine whether this singular outburst within the Deccan Traps (and possibly volcanic eruptions worldwide) contributed signifi cantly to the Cretaceous-Paleogene extinction.
The Chicxulub asteroid impact (Mexico) and the eruption of the massive Deccan volcanic province (India) are two proposed causes of the end-Cretaceous mass extinction, which includes the demise of nonavian dinosaurs. Despite widespread acceptance of the impact hypothesis, the lack of a high-resolution eruption timeline for the Deccan basalts has prevented full assessment of their relationship to the mass extinction. Here we apply U-Pb zircon geochronology to Deccan rocks and show that the main phase of eruptions initiated ~250,000 years before the Cretaceous-Paleogene boundary and that >1.1 million km(3) of basalt erupted in ~750,000 years. Our results are consistent with the hypothesis that the Deccan Traps contributed to the latest Cretaceous environmental change and biologic turnover that culminated in the marine and terrestrial mass extinctions.
Copyright © 2014, American Association for the Advancement of Science.
Simulations of the Early Cretaceous (120,000,000 years before the present day: 120 Ma) and the Last Creta-ceous (65 Ma) have been performed using an atmospheric general circulation model (AGCM) coupled with a 1.5-layer reduced-gravity ocean model. After the initial spin-up period, both the runs are integrated for approxi-mately 70 years. The simulation results confirm the occurrence of first-order changes in tropical atmospheric cir-culation in response to changes in the land/sea distribution. The simulation results show that the continental drift during the Cretaceous strongly a¤ects the Walker and Hadley circulations. The birth of the Atlantic resulting from the breakup of the Gondwana continent causes splitting of a Walker circulation cell into two, and this in turn reduces the zonal gradient of the equatorial SST over the Pacific. The resultant SST warming in the equato-rial Pacific enhances the Hadley circulation. The northward drift of the Indian continent causes significant SST warming in the Indian Ocean and intensifies the monsoon precipitation over Asia. It is also shown that the sea-sonal variations in the Asian monsoon are much stronger in the 65-Ma run than in the 120-Ma run. Interestingly, continental breakups cause the mega-monsoon system to split into distinct monsoon systems such as the Indian, South American, and African monsoon systems.
A new member of the Upper Cretaceous (Maastrichtian) Maevarano Formation is proposed to accommodate a distinctive succession of strata exposed along the shores of Lac Kinkony in northwestern Madagascar. The new Lac Kinkony Member overlies fully terrestrial sandstones of the Anembalemba Member of the Maevarano Formation, and is capped by marine dolostones of the Berivotra Formation. In the stratotype section, the base of the Lac Kinkony Member consists of siltstone interbeds that host networks of Ophiomorpha. Siltstone facies pass up-section to distinctive white sandstones packed with dolomitic mud matrix that exhibit rhythmic clay drapes, flaser and wavy bedding, and oppositely-oriented ripples developed on the toes of larger foresets. Thin flat interbeds of microgranular dolostone and claystone comprise the uppermost facies of the Lac Kinkony Member, and a laterally traceable ravinement bed mantled by cobbles of rounded dolostone marks the contact with the superjacent Berivotra Formation. Deposits of the Lac Kinkony Member are interpreted to represent siliciclastic and carbonate tidal flats dissected by tidally-influenced rivers. Vertebrate fossils are abundantly preserved in these coastal deposits, and are locally concentrated in microfossil bonebeds that have the potential to yield thousands of small identifiable specimens. In addition to many taxa already known from the Maevarano Formation, the Lac Kinkony Member has yielded a wealth of phyllodontid albuloid fish skull elements, the distal humerus of a new frog taxon, five vertebrae representing two new snakes, a tooth of a possible dromaeosaurid, and a complete skull of a new mammal. The discovery of several new vertebrate taxa from this new member reflects the fact that it samples a previously unsampled nearshore, peritidal paleoenvironment in the Late Cretaceous of Madagascar.
2005.03 Synthetic apparent polar wander (APW) paths for North America, South America, Eurasia, India, Central Africa, Australia and Antarctica for the last 200 Myr are proposed. Computation of these APW paths is based upon the latest version (4.5a) of the Global Paleomagnetic Database (GPMDB), a revised global plate tectonic model since the Early Jurassic, and a new technique for generating smoothed APW paths. The smoothing technique includes the following steps: (1) pre-selection of palaeopoles, including pre-filtering parameters (number of sites, number of samples per site, 95 per cent confidence circle about mean direction, cleaning procedure, and time uncertainty); (2) generation of palaeolatitude and declination plots for a reference site on each continent that combines palaeopoles via a global plate tectonic circuit; (3) independent spline regression analyses of the palaeolatitude and declination plots; (4) removal of palaeolatitude or declination data that deviate by more than 10° from the regression curves (post-filtering process); (5) generation of synthetic APW paths from the resulting palaeolatitude and declination plots. These synthetic APW paths are then rotated into African coordinates to determine the best-fit APW path and a global palaeomagnetic reference frame. Four representative plate tectonic reconstructions and global plate velocity fields are presented for the three time intervals that correspond to globally synchronous changes in plate motion.
The Lake Alaotra–Ankay rift valley of Central Madagascar forms a NE–SW oriented depression filled with Neogene to recent sediments and is part of a more regional post-Miocene graben system that strikes N–S across much of the central part of the island. The region is characterized by a number of small earthquakes, active hot springs, steep fault-scarp bounded valleys, and several levels of terraces. Young, deeply incised topography related to intense tropical weathering, is largely concentrated near active fault systems. The origin and evolution of this extensional structure and its morphological expressions, however, have not been clearly documented. Mountain front sinuosity values indicate that the eastern side of the rift valley is tectonically more active than the western side, and that rapid erosion under subtropical conditions is causing rapid weathering of fault scarps. The active river network within the Alaotra–Ankay rift shows clear signs of surface re-adjustment to recent tectonic activity. The drainage network is asymmetric, with most channels on the east sides of valleys and controlled by regional eastward tilting. First-order rivers flow parallel to the basin axis. Zones of intense lavaka (erosional gully) formation are correlated with active fault systems and seismicity. Extension in the Ankay–Alaotra rift is oriented roughly the same as in the morphologically similar East African rift system, located only 500km to the west. The eastern edge of the African continent is moving somewhat independently from the rest of Africa and the portion of the African plate east of the East African rift is regarded as a separate plate, the Somali plate. However, few plate configurations have clearly defined the southern extension of the Africa-Somali plate boundary to where it must join the Southwest Indian Ocean ridge, a necessary requirement of any true microplate bounded by plate boundaries. Instead, the southeast part of the African plate, including the Somali microplate, seems to be dominated by a number of individual rift systems, overall defining a broad diffusive extensional plate boundary. We suggest that this diffusive plate boundary includes one segment that extends off the coast of Africa through the Comores, then cuts through northern Madagascar and extends down the active Ankay–Alaotra rift to the fault-block dominated southeastern coast of Madagascar, then extends southeastward to the Southwest Indian Ocean Ridge. Thus, the southeastern part of the African plate is considerably more fragmented by plume-related uplift and diffuse extensional boundaries than previously envisaged.
The Madagascan genus Sauvagella is revised and a new species, Sauvagella robusta, from the Ambomboa River (Sofia drainage) described. Preliminary analysis suggests Sauvagella is an ehiravin and that the pellonuline tribe Ehiravini is monophyletic. The immediate relationships of Sauvagella appear to lie with the single other ehiravin genus from Madagascan waters, Spratellomorpha. Reports of the occurrence of Gil- christella in Madagascan waters are in error. A MONG the least well-known components of Madagascar's freshwater ichthyofauna are the small, and admittedly somewhat nonde- script, pellonuline clupeids of the tribe Ehira- vini. Prior to the present study, the ehiravin fau- na of Madagascar was reported to comprise three species: the endemic Madagascan round herring, Sauvagella madagascariensis (Sauvage); the two-finned round herring, Spratellomorpha bianalis (Bertin); and the estuarine round-her- ring Gilchristella aestuarius (Gilchrist). Review of pertinent literature and of museum collections provides no confirmation of the presence of Gil- christella in Madagascan waters. The Madagascan record cited by Poll et al. (1984), and uncriti- cally followed by Stiassny and Raminosoa (1994), probably results from a confusion fol- lowing Bertin's (1943) introduction of the com- bination, Gilchristella madagascariensis, for S. mad- agascariensis. Whatever the case, Gilchristella aes- tuarius is restricted to the inland coastal waters of southern Africa and does not occur on Mad- agascar. Similarly, records of the occurrence of Gilchristella in India (Blaber, 1997) are of dubi- ous validity. Of the endemic genus Sauvagella, the subject of the present study, little is known. Beyond the observation that the genus is endemic to the freshwaters of Madagascar and is possibly tol- erant of brackish water, Whitehead (1985) had little to add other than that more specimens and data are needed. Based on a series of recently collected mate- rials and examination of museum collections two species are recognized: the type species, S. madagascariensis, which is widely distributed in fresh and brackish waters in eastern coastal drainages and throughout the interconnecting Pangalanes; and a second species, Sauvagella ro- busta n. sp. from freshwaters in a northwestern drainage of the island.
Analyses of phylogenetic topology and estimates of divergence timing have facilitated a reconstruction of Madagascar's colonization events by vertebrate animals, but that information alone does not reveal the major factors shaping the island's biogeographic history. Here, we examine profiles of Malagasy vertebrate clades through time within the context of the island's paleogeographical evolution to determine how particular events influenced the arrival of the island's extant groups. First we compare vertebrate profiles on Madagascar before and after selected events; then we compare tetrapod profiles on Madagascar to contemporary tetrapod compositions globally. We show that changes from the Mesozoic to the Cenozoic in the proportions of Madagascar's tetrapod clades (particularly its increase in the representation of birds and mammals) are tied to changes in their relative proportions elsewhere on the globe. Differences in the representation of vertebrate classes from the Mesozoic to the Cenozoic reflect the effects of extinction (i.e., the non-random susceptibility of the different vertebrate clades to purported catastrophic global events 65 million years ago), and new evolutionary opportunities for a subset of vertebrates with the relatively high potential for transoceanic dispersal potential. In comparison, changes in vertebrate class representation during the Cenozoic are minor. Despite the fact that the island's isolation has resulted in high vertebrate endemism and a unique and taxonomically imbalanced extant vertebrate assemblage (both hailed as testimony to its long isolation), that isolation was never complete. Indeed, Madagascar's extant tetrapod fauna owes more to colonization during the Cenozoic than to earlier arrivals. Madagascar's unusual vertebrate assemblage needs to be understood with reference to the basal character of clades originating prior to the K-T extinction, as well as to the differential transoceanic dispersal advantage of other, more recently arriving clades. Thus, the composition of Madagascar's endemic vertebrate assemblage itself provides evidence of the island's paleogeographic history.
Vertebrate fossils are remarkably abundant and exceptionally well preserved within the Upper Cretaceous Maevarano Formation of northwestern Madagascar. The vast majority of these fossils, including all of the currently known bone beds, are entombed within deposits of fine-grained cohesive debris flows. These deposits are typically massive and are characterized by very poor sorting and a significant montmorillonite-dominated silt-clay (mud) fraction ranging from 17% to 46% by weight. Deposition is attributed to recurrent exceptional rainfall events that prompted erosion and flooded ancient channel belts with sediment-laden flows. These extraordinary burial events shielded vertebrate remains from destructive surface processes and also afforded protection for soft tissues. Taphonomic attributes of associated bone concentrations suggest that debris flows had limited transport potential and generally entombed subaerially exposed bone assemblages. The remarkable and recurrent association of bone beds and debris-flow deposits likely reflects marked seasonality in this Late Cretaceous terrestrial ecosystem, with prolonged dry spells prompting mortality and subsequent rains setting debris flows in motion.
We performed a population genomics study of the aye-aye, a highly specialized nocturnal lemur from Madagascar. Aye-ayes have low population densities and extensive range requirements that could make this flagship species particularly susceptible to extinction. Therefore, knowledge of genetic diversity and differentiation among aye-aye populations is critical for conservation planning. Such information may also advance our general understanding of Malagasy biogeography, as aye-ayes have the largest species distribution of any lemur. We generated and analyzed whole-genome sequence data for 12 aye-ayes from three regions of Madagascar (North, West, and East). We found that the North population is genetically distinct, with strong differentiation from other aye-ayes over relatively short geographic distances. For comparison, the average FST value between the North and East aye-aye populations-separated by only 248 km-is over 2.1-times greater than that observed between human Africans and Europeans. This finding is consistent with prior watershed- and climate-based hypotheses of a center of endemism in northern Madagascar. Taken together, these results suggest a strong and long-term biogeographical barrier to gene flow. Thus, the specific attention that should be directed toward preserving large, contiguous aye-aye habitats in northern Madagascar may also benefit the conservation of other distinct taxonomic units. To help facilitate future ecological- and conservation-motivated population genomic analyses by noncomputational biologists, the analytical toolkit used in this study is available on the Galaxy Web site.
The three members of the Malagasy genus Aglyptodactylus (Aglyptodactylus madagascariensis, Aglyptodactylus laticeps, Aglyptodactylus securifer) form, together with Laliostoma labrosum, the subfamily Laliostominae within the Mantellidae (Ranoidea: Anura). In this paper, the morphology, life history, and ecology of sympatric tadpoles of A. laticeps and A. securifer are described and compared to those of A. madagascariensis and L. labrosum. Tadpoles of all Aglyptodactylus species are morphologically more similar to each other than to L. labrosum. However, all species differ with respect to habitat, feeding habits, and life history.
The relationships of Madagascan plant and animal taxa have been the object of much fascination, Madagascar shar-ing numerous lineages with Africa, others with Asia, Australia, or the Americas, and many others being of uncertain relationships. In commonly accepted global regionalization schemata, Madagascar is treated together with Africa for animals, and with Africa, tropical Asia and the Pacific islands in the case of plants. Here we examine the similarities between the biotic assemblages of (i) tropical Africa, (ii) Madagascar, and (iii) the rest of the world, on a basic taxonomic level, considering the families of vascular plants and vertebrates as analysis units. The percentages of endemic families, families shared pair-wise between regions, or pre-sent in all three, are roughly similar between the two broad groups, though plant families with ranges limited to one region are proportionally fewer. In dendrograms and multidimensional scaling plots for different groups, Madagascar clusters together with Africa, Asia or both, and sometimes with smaller Indian Ocean Islands, but quite often (though not in plants) as a convincingly separate cluster. Our results for vertebrates justify the status of full zoogeographic region for Madagascar, though an equally high rank in geobotanical regionalization would mean also treating Africa and Tropical Asia as separate units, which would be debata-ble given the overall greater uniformity of plant assemblages. Beyond the Madagascan focus of this paper, the differences be-tween plant and vertebrate clusters shown here suggest different levels of ecological plasticity at the same taxonomic level, with plant families being much more environmentally-bound, and thus clustering along biome lines rather than regional lines [Current Zoology 58 (3): 363−374, 2012].
Madagascar is one of the world's hottest biodiversity hot spots due to its diverse, endemic, and highly threatened biota. This biota shows a distinct signature of evolution in isolation, both in the high levels of diversity within lineages and in the imbalance of lineages that are represented. For example, chameleon diversity is the highest of any place on Earth, yet there are no salamanders. These biotic enigmas have inspired centuries of speculation relating to the mechanisms by which Madagascar's biota came to reside there. The two most probable causal factors are Gondwanan vicariance and/or Cenozoic dispersal. By reviewing a comprehensive sample of phylogenetic studies of Malagasy biota, we find that the predominant pattern is one of sister group relationships to African taxa. For those studies that include divergence time analysis, we find an overwhelming indication of Cenozoic origins for most Malagasy clades. We conclude that most of the present-day biota of Madagascar is comprised of the d...
The monotypic genus Tsingymantis is an isolated, microendemic anuran lineage from the karstic limestone area of Ankarana in northern Madagascar that probably separated from other mantellids about 40 million years ago. It was described only in 2006, and basic data on the natural history of this enigmatic frog is still wanting. Field surveys in the late rainy season (February–March 2007) revealed the previously unknown larvae of Tsingymantis antitra, developing in com-paratively small rock pools. The pools had diameters of 20–170 cm and depths of 3–19 cm. Each of the five pools inhabited contained 1–2 (in one case 8) tadpoles and apparently, most of them contained only limited amounts of potential tadpole food. The larvae have an oral disc characterized by the presence of lateral emarginations, completely keratinised and strong jaw sheaths, and double rows of marginal papillae without a ventral gap, and with five rows of anterior and three rows of posterior labial keratodont rows, of which rows 4 and 1 are discontinuous, respectively. Despite a general similarity to gen-eralized tadpoles as observed in Aglyptodactylus and Laliostoma (Mantellidae: Laliostominae), the strongly enlarged and keratinised jaw sheaths with strong serrations in the upper and lower jaw found in Tsingymantis are otherwise typical for oophagous tadpoles. Although no direct evidence exists, the combination of oral morphology and larval habitats could be an indication for oophagy or a predatory feeding mode in tadpoles of Tsingymantis. Our data also suggest that reproducing in small rock pools can be a successful long-term strategy in karstic habitats.
Phylogenetic relationships, divergence times, and patterns of biogeographic descent among primate species are both complex and contentious. Here, we generate a robust molecular phylogeny for 70 primate genera and 367 primate species based on a concatenation of 69 nuclear gene segments and ten mitochondrial gene sequences, most of which were extracted from GenBank. Relaxed clock analyses of divergence times with 14 fossil-calibrated nodes suggest that living Primates last shared a common ancestor 71-63 Ma, and that divergences within both Strepsirrhini and Haplorhini are entirely post-Cretaceous. These results are consistent with the hypothesis that the Cretaceous-Paleogene mass extinction of non-avian dinosaurs played an important role in the diversification of placental mammals. Previous queries into primate historical biogeography have suggested Africa, Asia, Europe, or North America as the ancestral area of crown primates, but were based on methods that were coopted from phylogeny reconstruction. By contrast, we analyzed our molecular phylogeny with two methods that were developed explicitly for ancestral area reconstruction, and find support for the hypothesis that the most recent common ancestor of living Primates resided in Asia. Analyses of primate macroevolutionary dynamics provide support for a diversification rate increase in the late Miocene, possibly in response to elevated global mean temperatures, and are consistent with the fossil record. By contrast, diversification analyses failed to detect evidence for rate-shift changes near the Eocene-Oligocene boundary even though the fossil record provides clear evidence for a major turnover event ("Grande Coupure") at this time. Our results highlight the power and limitations of inferring diversification dynamics from molecular phylogenies, as well as the sensitivity of diversification analyses to different species concepts.
The abelisaurid theropod Majungasaurus crenatissimus inhabited the plains of northwestern Madagascar during the Late Cretaceous. It lived alongside other nonavian dinosaurs, including a small-bodied noasaurid theropod (Masiakasaurus knopfleri) and a titanosaurian sauropod (Rapetosaurus krausei). Although an inhabitant of the expansive floodplains of the Mahajanga Basin, M. crenatissimus also frequented the broad and sandy channel belts that drained Madagascar's central highlands. These shallow rivers were populated by a variety of aquatic and semi-aquatic animals, including fish, frogs, turtles, and several species of both large and small crocodyliforms. These animals were likely adapted for seasonal fluctuations in water availability because the sediments that entomb their remains (fine-grained debris flow deposits intercalated with stream flow deposits) indicate a strongly variable discharge regime. Associated oxidized calcareous paleosols with localized accumulations of carbonate nodules suggest that the ambient climate was semiarid. The numerous bonebeds preserved in these same sediments are indicative of localized and recurrent pulses of mortality. M. crenatissimus fed on carcasses preserved in these bonebeds, and there is good indication from a wealth of tooth-marked bone derived from two conspecific individuals that it focused on the well-muscled axial skeleton in a fashion similar to that of many modern vertebrate carnivores. This evidence for intraspecific feeding renders M. crenatissimus the only theropod dinosaur with demonstrated cannibalistic tendencies.
Paleontologists reconstruct the locomotor and postural behavior of extinct species by analogy with living forms and biomechanical analyses. In rare cases, behavioral evidence such as footprints can be used to confirm fossil-based reconstructions for predominantly terrestrial orders of mammals. For instance, the chalicothere prints from Laetoli show that these perissodactyls supported their body weight on the metacarpals, as previously reconstructed.1 Unfortunately, primates are mostly arboreal and rarely leave footprints. The cercopithecid and hominin prints at Laetoli are a rare exception. We have recently shown that the semicircular canal system can be used to test and augment locomotor reconstructions based on postcranial material or to provide first estimations of locomotor behavior for taxa not known from the postcranium. Using a sample of modern primates, we have been able to demonstrate that the radii of curvature of the semicircular canals are significantly correlated with both body mass and agility of locomotion.2 This paper reviews those results and examines the relationship between semicircular canal morphology and other evidence in efforts to reconstruct locomotor behavior in subfossil lemurs from the Holocene of Madagascar and fossil lorisoids from the Miocene of Africa.
The degree of chemical weathering in soils increases with mean annual precipitation (P; mm) and mean annual temperature (T; C). We have quantified these relationships using a database of major-element chemical analyses of 126 North American soils. The most robust relationship found was between P and the chemical index of alteration without potash (CIA-K): with . Another strong relationship was found between P and 0.0197(CIA-K) 2 P p 221.12e Rp 0.72 the molecular ratio of bases/alumina (B): with . A Mollisol-specific relationship 2 P p 259.34 ln (B) 759.05 R p 0.66 was found relating P to the molar ratio of calcium to aluminum (C) as follows: with P p 130.93 ln (C) 467.4 . Relationships between weathering ratios and T are less robust, but a potentially useful one was found 2 R p 0.59 between T and the molecular ratio of potash and soda to alumina (S) where with 2 T p 18.516(S) 17.298 R p . Our data also showed that most Alfisols can be distinguished from Ultisols by a molecular weathering ratio of 0.37 bases/alumina of !0.5 or by a chemical index of alteration without potassium !80. Application of these data to a sequence of Eocene and Oligocene paleosols from central Oregon yielded refined paleoprecipitation and paleotem-perature estimates consistent with those from other pedogenic and paleobotanical transfer functions for paleoclimate.
Frogs of the subfamily Mantellinae (Amphibia: Anura: Mantellidae) are a species-rich and diverse lineage endemic to the Madagascan region. The major synapomorphy of this clade is a derived reproductive mode including an unusual mating behaviour (loss of strong mating amplexus, egg deposition outside of water) and associated morphological adaptations (evolution of femoral glands, loss of nuptial pads). However, the evolutionary steps towards this unique character complex remain obscure. We here describe a recently discovered new frog, Tsingymantis antitra gen. nov., sp. nov. from the moderately dry karstic massif Tsingy de Ankarana in northern Madagascar. The new species is not referable to any existing genus or species groups. A phylogenetic analysis, based on DNA sequences of four mitochondrial genes (12S and 16S rRNA, tRNAVal, cytochrome b) and one nuclear gene (rhodopsin) placed Tsingymantis without significant support as sister taxon of the Mantellinae which was found to be a well-defined monophyletic group (100% Bayesian and 99% bootstrap support). The position of Tsingymantis as the most basal clade of the Mantellinae is in agreement with several morphological and osteological characters, suggesting that this subfamily including Tsingymantis may be a monophyletic group whereas the Boophinae could represent the most basal clade of the Mantellidae. We therefore include Tsingymantis in the Mantellinae in a preliminary way, pending further study. In contrast to the large majority of recent mantellid species which are adapted to humid rainforests, the most basal clades of the three subfamilies show adaptations to relatively dry conditions, indicating that the climate during the early radiation of mantellids (probably in the Eocene) may have been drier than in recent times.
The history of the genus Pachypanchax Myers, 1933 in the literature is reviewed and the utility of the diagnostic characters proposed by various authors is evaluated. On the basis of five synapomorphies, four skeletal and one squamational, six of the seven presently known Malagasy aplocheilids are found to be unambiguously referable to the genus Pachypanchax. The seventh, Poecilia nuchimaculata Guichenot 1866, known only from the unique type specimen, displays several peculiar skeletal and squamational features. Pending the acquisition of additional material, it is tentatively assigned to the genus. Of the six species treated here, Pachypanchax omalonotus (Duméril, 1861) and P. sakaramyi (Holly, 1828) are redescribed from recently collected topotypical material; and the following four are described as new: P. varatraza., P. patriciae, P. sparksorum, and P. arnoulti. Data on life colors, distribution, natural history and conservation status on all six Malagasy Pachypanchax species are presented.
A long-term global atmospheric reanalysis, named “Japanese 25-year Reanalysis (JRA-25)” was completed using the Japan Meteorological Agency (JMA) numerical assimilation and forecast system. The analysis covers the period from 1979 to 2004. This is the first long-term reanalysis undertaken in Asia. JMA's latest numerical assimilation system, and specially collected observational data, were used to generate a consistent and high-quality reanalysis dataset designed for climate research and operational monitoring and forecasts. One of the many purposes of JRA-25 is to enhance the analysis to a high quality in the Asian region.
Six-hourly data assimilation cycles were performed, producing 6-hourly atmospheric analysis and forecast fields of various physical variables. The global model used in JRA-25 has a spectral resolution of T106 (equivalent to a horizontal grid size of around 120 km) and 40 vertical layers with the top level at 0.4 hPa. In addition to conventional surface and upper air observations, atmospheric motion vector (AMV) wind retrieved from geostationary satellites, brightness temperature from TIROS Operational Vertical Sounder (TOVS), precipitable water retrieved from orbital satellite microwave radiometer radiance and other satellite data are assimilated with three-dimensional variational method (3D-Var). JMA produced daily sea surface temperature (SST), sea ice and three-dimensional ozone profiles for JRA-25. A new quality control method for TOVS data was developed and applied in advance.
Many advantages have been found in the JRA-25 reanalysis. Predicted 6-hour global total precipitation distribution and amount are well reproduced both in space and time. The performance of the long time series of the global precipitation is the best among the other reanalyses, with few unrealistic variations from degraded satellite data contaminated by volcanic eruptions. Secondly, JRA-25 is the first reanalysis to assimilate wind profiles around tropical cyclones reconstructed from historical best track information; tropical cyclones were analyzed properly in all the global regions. Additionally, low-level cloud along the subtropical western coast of continents is well simulated and snow depth analysis is also of a good quality. The article also covers material which requires attention when using JRA-25.
In molecular analyses Didymelaceae together with Buxaceae form a fairly well-supported clade among families near the base
of eudicots. Only little is known, however, about the flowers and inflorescences of Didymelaceae. In this study, the structure
of the female flowers and inflorescences of Didymeles integrifolia was studied. Flowers are unicarpellate and orientation of the carpel is slightly deflected abaxially as in Proteaceae. Otherwise,
Didymelaceae share many features of the gynoecium with Buxaceae and some other basal eudicots: the carpels are ascidiate in
the lower half; anthetic carpels are completely closed by postgenital fusion; stigma is double-crested and widely decurrent;
stigmatic papillae are unicellular and pear-shaped; the pollen tube transmitting tract is extensive and prominently differentiated;
fruits are fleshy drupes with persistent stigma and style. However, the exceedingly elongate base of the integuments of Didymelaceae
is an unusual feature among basal eudicots and even angiosperms.
The last decade's lemur research includes successes in discovering new living and extinct species and learning about the distribution, biogeography, physiology, behavior, and ecology of previously little-studied species. In addition, in both the dry forest and rain forest, long-term studies of lemur demography, life history and reproduction, have been completed in conjunction with data on tree productivity, phenology, and climate. Lemurs contrast with anthropoids in several behavioral features, including female dominance, targeted female-female aggression, lack of sexual dimorphism regardless of mating system, sperm competition coupled with male-male aggression, high infant mortality, cathemerality, and strict seasonal breeding. Hypotheses to explain these traits include the "energy conservation hypothesis" (ECH) suggesting that harsh and unpredictable climate factors on the island of Madagascar have affected the evolution of female dominance, and the "evolutionary disequilibrium hypotheses" (EVDH) suggesting that the recent megafauna extinctions have influenced lemurs to become diurnal. These hypotheses are compared and contrasted in light of recent empirical data on climate, subfossils, and lemur behavior. New data on life histories of the rain forest lemurs at Ranomafana National Park give further support to the ECH. Birth seasons are synchronized within each species, but there is a 6-month distribution of births among species. Gestation and lactation lengths vary among sympatric lemurs, but all lemur species in the rain forest wean in synchrony at the season most likely to have abundant resources. Across-species weaning synchrony seen in Ranomafana corroborates data from the dry forest that late lactation and weaning is the life history event that is the primary focus of the annual schedule. Lemur adaptations may assure maximum offspring survival in this environment with an unpredictable food supply and heavy predation. In conclusion, a more comprehensive energy frugality hypothesis (EFH) is proposed, which postulates that the majority of lemur traits are either adaptations to conserve energy (e.g., low basal metabolic rate (BMR), torpor, sperm competition, small group size, seasonal breeding) or to maximize use of scarce resources (e.g., cathemerality, territoriality, female dominance, fibrous diet, weaning synchrony). Among primates, the isolated adaptive radiation of lemurs on Madagascar may have been uniquely characterized by selection toward efficiency to cope with the harsh and unpredictable island environment. (C) 1999 Wiley-Liss, Inc.
Troglobitic cavefishes of the genus Typhleotris, endemic to coastal southwestern Madagascar, are taxonomically reviewed and a new darkly pigmented species, Typhleotris mararybe, is described from an isolated karst sinkhole on the coastal plain below the Mahafaly Plateau. The new species, known only from Grotte de Vitane (Vitany) near the town of Itampolo, is unique among blind cavefishes in being uniformly darkly pigmented, rather than fully depigmented or exceptionally light in coloration. In addition to its dark coloration (vs. depigmented, translucent white body in congeners), the new species can be distinguished from its two congeners, Typhleotris madagascariensis and T. pauliani, by the sculpted, bony (vs. fleshy) appearance of its head with strongly protruding lateral ethmoid, sphenotic, and pterotic bones, and an elevated vertebral count.
Although Madagascar is an ancient fragment of Gondwana, the majority of taxa studied thus far appear to have reached the island through dispersal from Cenozoic times. Ancient lineages may have experienced a different history compared to more recent Cenozoic arrivals, as such lineages would have encountered geoclimatic shifts over an extended time period. The motivation for this study was to unravel the signature of diversification in an ancient lineage by comparing an area known for major geoclimatic upheavals (Madagascar) versus other areas where the environment has been relatively stable. Archaeid spiders are an ancient paleoendemic group with unusual predatory behaviors and spectacular trophic morphology that likely have been on Madagascar since its isolation. We examined disparities between Madagascan archaeids and their non-Madagascan relatives regarding timing of divergence, rates of trait evolution, and distribution patterns. Results reveal an increased rate of adaptive trait diversification in Madagascan archaeids. Furthermore, geoclimatic events in Madagascar over long periods of time may have facilitated high species richness due to montane refugia and stability, rainforest refugia, and also ecogeographic shifts, allowing for the accumulation of adaptive traits. This research suggests that time alone, coupled with more ancient geoclimatic events allowed for the different patterns in Madagascar. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
This special issue of the Biological Journal of the Linnean Society (2014, volume 112: issue 4) focuses on advances in vertebrate palaeohistology, a dynamic area of research that relies on an understanding of the constraints acting on vertebrate mineralized tissues, and enables, through comparison with living organisms, access to biological data for fossil taxa. Substantial advances have been made in recent years and the special issue presents new discoveries from some rapidly developing fields of investigation. This introduction briefly reviews the discipline of palaeohistology and then introduces the twelve contributions. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112, 645–648.
This study investigates changes in the frequency and timing of tropical cyclone landfalls over the southwest
Indian Ocean during the last 66 years. Little is known about the spatial and temporal trends of such storm landfalls during recent historical times, specifically the last ca. 100 years. By analysing three storm track records spanning periods of 66–161 years, we establish that much of the perceived change in storm numbers can be attributed to improvements in storm detection methods over the past century. Furthermore, we find no statistically significant trends in the frequency of tropical cyclone landfalls over Madagascar and Mozambique over the past 6 decades, despite more comprehensive records
during the most recent period. There is, however, considerable interannual variability in the number of storms making landfall over the countries investigated; most probably driven by cyclical atmospheric forcing, including El Ni˜no-Southern Oscillation (ENSO) and the Quasi-Biennial Oscillation (QBO). Recent trends indicate an increasing number of tropical cyclones tracking to the south of Madagascar, potentially associated with the southward shift of the 26 ◦C isotherm, combined with a decrease in the steering flow during La Ni˜na years.
A new member of the Upper Cretaceous (Maastrichtian) Maevarano Formation is proposed to accommodate a distinctive succession of strata exposed along the shores of Lac Kinkony in northwestern Madagascar. The new Lac Kinkony Member overlies fully terrestrial sandstones of the Anembalemba Member of the Maevarano Formation, and is capped by marine dolostones of the Berivotra Formation. In the stratotype section, the base of the Lac Kinkony Member consists of siltstone interbeds that host networks of Ophiomorpha. Siltstone facies pass up-section to distinctive white sandstones packed with dolomitic mud matrix that exhibit rhythmic clay drapes, flaser and wavy bedding, and oppositely-oriented ripples developed on the toes of larger foresets. Thin flat interbeds of microgranular dolostone and claystone comprise the uppermost facies of the Lac Kinkony Member, and a laterally traceable ravinement bed mantled by cobbles of rounded dolostone marks the contact with the superjacent Berivotra Formation. Deposits of the Lac Kinkony Member are interpreted to represent siliciclastic and carbonate tidal flats dissected by tidally-influenced rivers. Vertebrate fossils are abundantly preserved in these coastal deposits, and are locally concentrated in microfossil bonebeds that have the potential to yield thousands of small identifiable specimens. In addition to many taxa already known from the Maevarano Formation, the Lac Kinkony Member has yielded a wealth of phyllodontid albuloid fish skull elements, the distal humerus of a new frog taxon, five vertebrae representing two new snakes, a tooth of a possible dromaeosaurid, and a complete skull of a new mammal. The discovery of several new vertebrate taxa from this new member reflects the fact that it samples a previously unsampled nearshore, peritidal paleoenvironment in the Late Cretaceous of Madagascar.
Neither geologists nor biologists have a definition that is capable of classifying Madagascar unambiguously as an island or a continent; nor can they incorporate Malagasy natural history into a single model rooted in Africa or Asia. Madagascar is a microcosm of the larger continents, with a rock record that spans more than 3000 million years (Ma), during which it has been united episodically with, and divorced from, Asian and African connections. This is reflected in its Precambrian history of deep crustal tectonics and a Phanerozoic history of biodiversity that fluctuated between cosmopolitanism and parochialism. Both vicariance and dispersal events over the past 90 Ma have blended a unique endemism on Madagascar, now in decline following rapid extinctions that started about 2000 years ago.
Low-temperature thermochronological data from two profiles across central Madagascar give apatite fission track and apatite (U–Th)/He ages ranging between 258Ma and 176Ma and from 239Ma to 48Ma, respectively. Thermal models derived from these data, as well as modelling of basement denudation and the sedimentary record, indicate that first order topography of central Madagascar developed mainly due to flexural uplift during Mesozoic times. This was in response to successive erosion and depositional loading associated with the sedimentation in the Morondava and Majunga basins, both of which are now exposed along the western margin of Madagascar. Our data suggest that the eastern margin of the island had a similar denudation history and was probably at a similar topographic level before the late Cretaceous break-up of Madagascar and the India/Seychelles block. Cretaceous normal faulting, without major amounts of denudation, led to the development of the present east coast topography defined by a tectonically juvenile escarpment. In the centre of the island Cenozoic tectonics and volcanism has had a minor and localised influence on the landscape of central Madagascar.
Mafic dikes and dike swarms associated with tholeiitic flows of the continental Deccan flood basalt province are studied to understand the timing of lithospheric extension, rifting, and rift activation related to the eruption of the Deccan basalts. Integrated geophysical, tectonic, and geochemical studies and 40Ar/39Ar and K-Ar ages of these mafic dikes and associated Deccan flows along the intraplate Narmada-Tapti rift and western continental margin rift point to flood basalt eruptions between 67 and 64 Ma (peaking at ∼65 Ma) with concurrent lineament reactivation into rifts and dominant N-S and E-W extension of the Indian lithosphere. Correlation of Bouger gravity, shallow and deep seismic, and heat flow anomalies show penetration of elongated and discontinuous mafic bodies between 5 and 6 km deep along the central axis and flanks of the intraplate rift and a long, elongated, and anomalous mantle body into the upper crust along the continental margin rift with upward inflexion of the Moho toward the intersection of the two rifts. Crustal thinning along the rifts ranges between 8 and 25 km. Correlated geophysical and field-structural data show listric faulting and high concentrations of mafic dikes over rift-oriented geophysical anomalies. Field and geochemical relations, and age (67-64 Ma) similarities of many mafic dikes and basal flows, indicate their comagmatic nature and establish many rift-oriented mafic dikes as primary feeders. Geochemical and petrological evidence indicates that the majority of the lower Deccan tholeiites evolved in local and multiple magma chambers close to the surface up to a depth of 7 km, which is consistent with the geophysical evidence. An asthenospheric plume origin under a thinned lithosphere for the parental olivine-tholeiites is possible. Liquid line of descent calculations shown on clinopyroxene-olivine-silica and clinopyroxene-plagioclase-olivine pseudoternary plots and variation diagrams involving MgO and various oxides and elements suggest that the tholeiites of dikes and flows are related by fractional crystallization. The dikes and flows also show evidence of contamination (mainly crustal), which diminishes from the lower Deccan to the Poladpur and the Ambenali flows. Geochemical-stratigraphic relations indicate that the basal flows and dikes in Narmada-Tapti rift region and basal flows in the Gujarat region are older than the Igatpuri flows in the Western Margin rift region. A mantle plume model of laterally spreading magma with propagation of dikes from magma chambers and formation of magma chambers and eruptive centers along lithospheric weak trends is presented to explain copious and rapid eruptive activity over a widely spread area, crustal contamination during ascent, and magma evolution in shallow crustal chambers in the Deccan province.
An integrated study of fission-track (FT) dating and structural geology revealed a complex tectono-thermal history preserved in basement rocks of central Madagascar since the amalgamation of Gondwana at the end of the Cambrian. A detailed study of five domains argues for several cooling steps with associated brittle deformations during the separation of Madagascar.Titanite and apatite FT ages range between 483 Ma and 266 Ma and between 460 Ma and 79 Ma, respectively. The titanite FT data indicate that the final cooling after the latest metamorphic overprint was terminated at c. 500 Ma (FC1). A 150 Myr phase of minor cooling (SC2), possibly related to a phase of tectonic quiescence and isostatic compensation, followed episode FC1. Between the Carboniferous and Early Jurassic, when an intracontinental rift developed between East Africa and Madagascar, complex brittle deformation effected the western margin of Madagascar and led to differential cooling of small basement blocks (FC3–FC5). During this period, ductile structural trends were reactivated at the western basement margin and in the centre of the island.A Late Cretaceous thermal event (T1) affected apatite FT data of samples from western–central and the eastern margin of Madagascar. These ages are related to the Madagascar–India/Seychelles break-up, whereby the thermal penetration along the eastern coast was restricted to the west by the Angavo shear zone (AGSZ). The Cretaceous evolution of the eastern margin was associated with minor erosion and was triggered by vertical displacements along brittle structures.
The inferred positions of global paleoshorelines through the 240 million
years of the Mesozoic and Cenozoic are presented within this atlas.
Thirty-one maps, generally corresponding to stratigraphic stages,
provide a snapshot of the continents and their shorelines at
approximately 8 million year intervals. The maps provide a
representation of the gross changes in the distribution of land and sea
throughout the Mesozoic and Cenozoic plotted on Mollweide projections of
paleocontinental reconstruction. They do not distinguish between well
and poorly defined shorelines, but the information sources are set out
in a bibliography numbering more than 2000 primary paleographic
references. This is a global compilation that presents the first attempt
at delineating global shorelines at stage level, and which represents
many years of work sponsored by British Petroleum International (BPI),
and work by BPI themselves between 1981 and 1987.
The degree of chemical weathering in soils increases with mean annual
precipitation and mean annual temperature. We have quantified these
relationships using a database of major element chemical analyses of 126
North American soils. The most robust relationship found was between
mean annual precipitation (P in mm) and the chemical index of alteration
without potash (CIA-K): P = 221.12e0.0197(CIA-K) with
R2 = 0.72. Another strong relationship was found between mean
annual precipitation (P in mm) and the molecular ratio of bases/alumina
(B): P = -259.34Ln (B) +759.05 with R2 = 0.66. A
Mollisol-specific relationship was found relating mean annual
precipitation (P in mm) to the molar ratio of lime to alumina (C) as
follows: P = -130.93Ln (C) + 467.4 with R2 = 0.59. Our data
also showed that most Alfisols can be distinguished from Ultisols by a
molecular weathering ratio of bases/alumina of less than 0.5 or by a
chemical index of alteration without potash less than 80. Application of
these data to a sequence of Eocene and Oligocene paleosols from central
Oregon yielded refined paleoprecipitation estimates consistent with
those from other pedogenic and paleobotanical transfer functions for
paleoclimate.
Madagascar is renowned for its unparalleled species richness and levels of endemism, which have led, in combination with species extinction caused by an unprecedented rate of anthropogenic deforestation, to its designation as one of the most important biodiversity hotspots. It is home to 10 650 species (84% endemic) of angiosperms in 1621 genera (19% endemic). During the last two centuries, botanists have focused their efforts on the provision of a taxonomic framework for the flora of the island, but much remains to be investigated regarding the evolutionary processes that have shaped Madagascan botanical diversity. In this article, we review the current state of phylogenetic and biogeographical knowledge of the endemic angiosperm genera. We also propose a new stratified biogeographical model, based on palaeogeographical evidence, allowing the inference of the spatio-temporal history of Madagascan taxa. The implications of past climate change and extinction events on the evolutionary history of the endemic genera are also discussed in depth. Phylogenetic information was available for 184 of the 310 endemic genera (59.3%) and divergence time estimates were available for 67 (21.6%). Based on this evidence, we show the importance of phylogenetic clustering in the assemblage of the current Madagascan diversity (26% of the genera have a sister lineage from Madagascar) and confirm the strong floristic affinities with Africa, South-East Asia and India (22%, 9.1% and 6.2% of the genera, respectively). The close links with the Comoros, Mascarenes and Seychelles are also discussed. These results also support an Eocene/Oligocene onset for the origin of the Madagascan generic endemic flora, with the majority arising in the Miocene or more recently. These results therefore de-emphasize the importance of the Gondwanan break-up on the evolution of the flora. There is, however, some fossil evidence suggesting that recent extinctions (e.g. Sarcolaenaceae, a current Madagascan endemic, in southern Africa) might blur vicariance patterns and favour dispersal explanations for current biodiversity patterns. © 2013 The Linnean Society of London
Using the most up-to-the-date information available, we present a considerably revised plate tectonic and paleogeographic model for the Indian Ocean bordering continents, from Gondwana's Middle Jurassic break-up through to India's collision with Asia in the middle Cenozoic. The landmass framework is then used to explore the sometimes complex and occasionally counter-intuitive patterns that have been observed in the fossil and extant biological records of India, Madagascar, Africa and eastern Eurasia, as well those of the more distal continents.
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.
Simosuchus clarki is a small, pug-nosed notosuchian crocodyliform from the Late Cretaceous of Madagascar. Originally described on the basis of a single specimen including a remarkably complete and well-preserved skull and lower jaw, S. clarki is now known from five additional specimens that preserve portions of the craniofacial skeleton. Collectively, these six specimens represent all elements of the head skeleton except the stapedes, thus making the craniofacial skeleton of S. clarki one of the best and most completely preserved among all known basal mesoeucrocodylians. In this report, we provide a detailed description of the entire head skeleton of S. clarki, including a portion of the hyobranchial apparatus. The two most complete and well-preserved specimens differ substantially in several size and shape variables (e.g., projections, angulations, and areas of ornamentation), suggestive of sexual dimorphism. Assessment of both external and internal morphological features indicates a habitual head posture in which the preorbital portion of the dermal skull roof was tilted downward at an angle of ∼45°. Functional and comparative assessment of the feeding apparatus strongly indicates a predominantly if not exclusively herbivorous diet. Other features of the craniofacial skeleton of S. clarki are consistent with the interpretation developed from analysis of the postcranial skeleton of a terrestrial habitus, but the current working hypothesis of a burrowing lifestyle is not supported. The atypical appearance of the skull and lower jaw of S. clarki is underscored by the identification of at least 45 autapomorphic features, many of them related to the greatly foreshortened snout.
A new spinicaudatan genus and species, Ethmosestheria mahajangaensis gen. et sp. nov., is described from the Anembalemba Member (Upper Cretaceous, Maastrichtian) of the Maevarano Formation, Mahajanga Basin, Madagascar. This is the first spinicaudatan reported from the post-Triassic Mesozoic of Madagascar. The new species is assigned to the family Antronestheriidae based on the cavernous or sievelike ornamentation on the carapace. Of well-documented Mesozoic spinicaudatan genera, Ethmosestheria mahajangaensis is most closely related to Antronestheria Chen and Hudson from the Great Estuarine Group (Jurassic) of Scotland. However, relatively poor documentation of the ornamentation of most Gondwanan Mesozoic spinicaudatan species precludes detailed comparison among taxa. Ethmosestheria mahajangaensis exhibits ontogenetic trends in carapace growth: a change in carapace outline from subcircular/subelliptical to elliptical, and from very wide juvenile growth bands to narrow adult growth bands. Ornamentation style, however, does not vary with ontogeny. Ethmosestheria mahajangaensis individuals lived in temporary pools in a broad channel-belt system within a semiarid environment; preserved desiccation structures on carapaces indicate seasonal drying out of pools within the river system. Specimens of Ethmosestheria mahajangaensis are preserved with exquisite detail in debris flow deposits; these are the first spinicaudatans reported from debris flow deposits. These deposits also contain a varied vertebrate fauna, including dinosaurs, crocodyliforms, turtles, and frogs. Rapid entombment of the spinicaudatan carapaces likely promoted early fossil diagenesis leading to highly detailed preservation.
Brookesia dwarf chameleons, endemic to Madagascar, were surveyed at the following localities in northern Madagascar (north of 16°S): Montagne d'Ambre, Ankarana, Manongarivo, Tsaratanana, Marojejy and Masoala. A total of 15 species occur in this region. Six new species are described and five new synonyms are identified. The genus Brookesia, the most speciose chamaeleontid genus in Madagascar, contains 23 species.
Almost all the northern Brookesia species are restricted to rainforest and occupy a relatively narrow elevational range. Although the northern rainforests represent just one-third of the total rainforest and about 5% of the total island area, 65% of the Brookesia species occur in this region, and 52% are endemic to the northern rainforest. Five new biogeographic regions of the northern rainforest are identified based on centres of Brookesia endemicity: Montagne d'Ambre, Northwest, Tsaratanana, Northeast and East. Speciation is thought to have been facilitated in the north through geographic isolation, with the Tsaratanana mountain range and the dry forests south of Montagne d'Ambre forming barriers to dispersal, and the Tsaratanana mountains acting as a centre of isolation. The fragmented distribution of several Brookesia species of low altitude rainforest suggests a period in Madagascar's history when the climate was wetter and low altitude rainforest much more widespread.
Recent field studies revealed two new species of the genus Aglyptodactylus (Amphibia: Anura: Ranidae), which was hitherto considered as monotypic and confined to humid eastern Madagascar. Both new species, Aglyptodactylus laticeps sp. n. and Aglyptodactylus securifer sp. n., occur syntopically in the deciduous dry forest of Kirindy in western Madagascar. In comparison to Aglyptodactylus madagascariensis from eastern rainforests, the new species A. laticeps shows a remarkable morphological divergence, which may be partly due to adaptations to burrowing habits in dry environments. Despite of the morphological differentiation, advertisement calls and osteology indicate that all three species of Aglyptodactylus are closely related. A phylogenetic analysis of the Madagascan ranid genera Aglyptodactylus, Mantella, Mantidactylus, Boophis, and Tomopterna (the latter including species from Madagascar, Africa, and Asia) strongly supports a sister group relationship of Aglyptodactylus with the ranine genus Tomopterna. We therefore transfer Aglyptodactylus from the Rhacophorinae to the Raninae and discuss implications of this rearrangement for ranoid systematics. The existence of the endemic genus Aglyptodactylus in Madagascar as well as its close phylogenetic relationships to Tomopterna confirm that the Raninae were already present on the Madagascan plate before its separation from Africa. The Madagascan Tomopterna labrosa shows several important differences both to Asian and to African species of the genus, and is therefore transferred from the subgenus Sphaerotheca (now restricted to Asia) to a new subgenus Laliostoma subgen. n.