Evolution and escalation, an ecological history of life

The Miocene epoch (23.03–5.33 Ma) was a time interval of global warmth, relative to today. Continental configurations and mountain topography transitioned towards modern conditions, and many flora and fauna evolved into the same taxa that exist today. Miocene climate was dynamic: long periods of early and late glaciation bracketed a ∼2 Myr greenhouse interval – the Miocene Climatic Optimum (MCO). Floras, faunas, ice sheets, precipitation, pCO2, and ocean and atmospheric circulation mostly (but not ubiquitously) covaried with these large changes in climate. With higher temperatures and moderately higher pCO2 (∼400–600 ppm), the MCO has been suggested as a particularly appropriate analogue for future climate scenarios, and for assessing the predictive accuracy of numerical climate models – the same models that are used to simulate future climate. Yet, Miocene conditions have proved difficult to reconcile with models. This implies either missing positive feedbacks in the models, a lack of knowledge of past climate forcings, or the need for re‐interpretation of proxies, which might mitigate the model‐data discrepancy. Our understanding of Miocene climatic, biogeochemical, and oceanic changes on broad spatial and temporal scales is still developing. New records documenting the physical, chemical, and biotic aspects of the Earth system are emerging, and together provide a more comprehensive understanding of this important time interval. Here we review the state‐of‐the‐art in Miocene climate, ocean circulation, biogeochemical cycling, ice sheet dynamics, and biotic adaptation research as inferred through proxy observations and modelling studies.

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The Miocene: The Future of the Past

Evolution and Escalation

An impediment to understanding the origin and dynamics of the latitudinal diversity gradient (LDG)-the most pervasive large-scale biotic pattern on Earth-has been the tendency to focus narrowly on a single causal factor when a more synthetic, integrative approach is needed. Using marine bivalves as a model system and drawing on other systems where possible, we review paleobiologic and biogeographic support for two supposedly opposing views, that the LDG is shaped primarily by (a) local environmental factors that determine the number of species and higher taxa at a given latitude (in situ hypotheses) or (b) the entry of lineages arising elsewhere into a focal region (spatial dynamics hypotheses). Support for in situ hypotheses includes the fit of present-day diversity trends in many clades to such environmental factors as temperature and the correlation of extinction intensities in Pliocene bivalve faunas with net regional temperature changes. Support for spatial dynamics hypotheses includes the age-frequency distribution of bivalve genera across latitudes, which is consistent with an out-of-the-tropics dynamic, as are the higher species diversities in temperate southeastern Australia and southeastern Japan than in the tropical Caribbean. Thus, both in situ and spatial dynamics processes must shape the bivalve LDG and are likely to operate in other groups as well. The relative strengths of the two processes may differ among groups showing similar LDGs, but dissecting their effects will require improved methods of integrating fossil data with molecular phylogenies. We highlight several potential research directions and argue that many of the most dramatic biotic patterns, past and present, are likely to have been generated by diverse, mutually reinforcing drivers.

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Shaping the Latitudinal Diversity Gradient: New Perspectives from a Synthesis of Paleobiology and Biogeography.

Coordinated biotic and abiotic change during the Great Ordovician Biodiversification Event: Darriwilian assembly of early Paleozoic building blocks

Polar transport of the phytohormone auxin is a well-known physiological phenomenon recorded in different extant plant groups including bryophytes and pteridophytes. Earlier, this phenomenon has bee...

Auxin flow-mediated anatomical modifications in Indian Meso–Cenozoic plants


 The morphological disparity of the marine benthos, through the Phanerozoic, is shaped by multiple abiotic and biotic factors, among which substrate and ecology are key contributors. However, the relationship among substrate, ecology, and morphology is not straightforward—a substrate can be occupied by phylogenetically unrelated families with different life habits, influencing morphological convergence. In contrast, related taxa may differ in substrate and life habits, indicating morphological divergence. Here we evaluate the effect of substrate and ecology on the community-level morphological disparity of 398 Recent marine bivalve species from coastal India, using geometric morphometrics. We further evaluate whether the observed patterns are decoupled from taxonomic identities, i.e., phylogenetic (in)dependence. We find that the Recent marine bivalve assemblages show significant morphological differences while living in different substrates or having different life habit traits. However, while sharing a specific substrate or life habit trait (tiering/motility), different families do not show shape convergence, i.e., families maintain their mean shape, except for families living in soft sediments, for which they show strong substrate-driven morphological convergence. These instances of morphological divergence and convergence suggest that the association among sediment preference, ecology, and shape can be rather complex, and can often transgress phylogenetic boundaries in bivalves.

Substrate- and life habit-induced morphological convergence and divergence in Recent marine bivalve communities

Several burrow morphological features of crab Ocypode ceratophthalma including burrow diameter, orientation, inclination, branching and volume were studied from Chandipur, a sedimentologically and biologically diverse beach on the eastern Indian coast. Burrow morphologies (e.g. I, J, Y) were independent of their positions with respect to the coast line. In addition, no correlation between burrow morphology and burrow diameter was observed; however, diameter of burrow appeared to be a good proxy of the total amount of sediment excavated. Burrow diameters are significantly smaller in the foreshore compared to that of the backshore, suggesting that larger individuals reside along the backshore, where they excavate deeper and large-diameter burrows to minimize chances of desiccation. Smaller burrows are more or less vertical, whereas larger burrows are inclined towards the land, probably to stabilize their domicile from tidal activities, as well as to minimize energy required to excavate sediments. All these suggest that different types of abiotic factors determine the Ocypode burrow morphology and their habitat segregation.

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Burrow Morphology of the Ocypodid Crab Ocypode ceratophthalma at Chandipur Coast, Eastern India and its Implications

Predatory Drilling Traces on Recent Foraminifera from Chandipur Coast, India

Studies on the large-scale latitudinal patterns of gastropod drilling predation reveal that predation pressure may decrease or increase with increasing latitude, or even show no trend, questioning the generality of any large-scale latitudinal or biogeographic pattern. Here, we analyze the nature of spatio-environmental and latitudinal variation in gastropod drilling along the Indian eastern coast by using 76 samples collected from 39 locations, covering ~2500 km, incorporating several ecoregions, and ~15° latitudinal extents. We find no environmental or latitudinal gradient. In fact, drilling intensity varies highly within the same latitudinal bin, or oceanic sub-basins, or even the same ecoregions. Moreover, different ecoregions with their distinctive biotic and abiotic environmental variables show similar predation intensities. However, one pattern is prevalent: some small infaunal prey taxa, living in the sandy-muddy substrate-which are preferred by the naticid gastropods-are always attacked more frequently over others, indicating taxon and size selectivity by the predators. The result suggests that the biotic and abiotic factors, known to influence drilling predation, determine only the local predation pattern. In the present case, the nature of substrate and prey composition determines the local predation intensity: soft substrate habitats host dominantly small, infaunal prey. Since the degree of spatial variability in drilling intensity within any time bin can be extremely high, sometimes greater than the variability across consecutive time bins, temporal patterns in drilling predation can never be interpreted without having detailed knowledge of the nature of this spatial variability within a time bin.

High biogeographic and latitudinal variability in gastropod drilling predation on molluscs along the eastern Indian coast: Implications on the history of fossil record of drillholes.

Subhronil Mondal

Papers

Auxin flow-mediated anatomical modifications in Indian Meso–Cenozoic plants

Substrate- and life habit-induced morphological convergence and divergence in Recent marine bivalve communities

Burrow Morphology of the Ocypodid Crab Ocypode ceratophthalma at Chandipur Coast, Eastern India and its Implications

Predatory Drilling Traces on Recent Foraminifera from Chandipur Coast, India

High biogeographic and latitudinal variability in gastropod drilling predation on molluscs along the eastern Indian coast: Implications on the history of fossil record of drillholes.