Exceptionally well-preserved pinaceous leaves and seed cones are abundant in unconsolidated Early... more Exceptionally well-preserved pinaceous leaves and seed cones are abundant in unconsolidated Early Cretaceous lignites in central Mongolia. These fossils include two seed cones, both of which have helically arranged bract–scale complexes with two winged seeds on the adaxial surface. The larger of the two seed cones, described as Picea farjonii sp. nov., is cylindrical to ellipsoidal, and was borne terminally on a stout shoot. The bract is small and tridentate. Leaf bases on the shoots are helically arranged, and attached leaves are linear and flattened. In all of the morphological and anatomical features that are preserved, P. farjonii is very similar to extant Picea. The smaller seed cone, described as Pityostrobus stockeyae sp. nov., shows features of several genera of extant Pinaceae. This cone is ellipsoidal and was borne terminally on a long, slender shoot. The bract is thin and triangular proximally, but the distal portion is thicker, needle-like, and deciduous. Picea farjonii ...
The global extent and distribution of forest trees is central to our understanding of the terrest... more The global extent and distribution of forest trees is central to our understanding of the terrestrial biosphere. We provide the first spatially continuous map of forest tree density at a global scale. This map reveals that the global number of trees is approximately 3.04 trillion, an order of magnitude higher than the previous estimate. Of these trees, approximately 1.39 trillion exist in tropical and subtropical forests, with 0.74 trillion in boreal regions and 0.61 trillion in temperate regions. Biome-level trends in tree density demonstrate the importance of climate and topography in controlling local tree densities at finer scales, as well as the overwhelming effect of humans across most of the world. Based on our projected tree densities, we estimate that over 15 billion trees are cut down each year, and the global number of trees has fallen by approximately 46% since the start of human civilization.
Evolution; international journal of organic evolution, Jan 22, 2015
Integration influences patterns of trait evolution, but the relationship between these patterns a... more Integration influences patterns of trait evolution, but the relationship between these patterns and the degree of trait integration is not well understood. In order to explore this further, we study a specialized pollination mechanism in conifers whose traits are linked through function but not development. This mechanism depends on interactions among three characters: pollen that is buoyant, ovules that face downward at pollination, and the production of a liquid droplet that buoyant grains float through to enter the ovule. We use a well-sampled phylogeny of conifers to test correlated evolution among these characters and specific sequences of character change. Using likelihood models of character evolution, we find that pollen morphology and ovule characters evolve in a concerted manner, where the flotation mechanism breaks down irreversibly following changes in orientation or drop production. The breakdown of this functional constraint, which may be facilitated by the lack of dev...
Exceptionally well-preserved pinaceous leaves and seed cones are abundant in unconsolidated Early... more Exceptionally well-preserved pinaceous leaves and seed cones are abundant in unconsolidated Early Cretaceous lignites in central Mongolia. These fossils include two seed cones, both of which have helically arranged bract–scale complexes with two winged seeds on the adaxial surface. The larger of the two seed cones, described as Picea farjonii sp. nov., is cylindrical to ellipsoidal, and was borne terminally on a stout shoot. The bract is small and tridentate. Leaf bases on the shoots are helically arranged, and attached leaves are linear and flattened. In all of the morphological and anatomical features that are preserved, P. farjonii is very similar to extant Picea. The smaller seed cone, described as Pityostrobus stockeyae sp. nov., shows features of several genera of extant Pinaceae. This cone is ellipsoidal and was borne terminally on a long, slender shoot. The bract is thin and triangular proximally, but the distal portion is thicker, needle-like, and deciduous. Picea farjonii ...
The global extent and distribution of forest trees is central to our understanding of the terrest... more The global extent and distribution of forest trees is central to our understanding of the terrestrial biosphere. We provide the first spatially continuous map of forest tree density at a global scale. This map reveals that the global number of trees is approximately 3.04 trillion, an order of magnitude higher than the previous estimate. Of these trees, approximately 1.39 trillion exist in tropical and subtropical forests, with 0.74 trillion in boreal regions and 0.61 trillion in temperate regions. Biome-level trends in tree density demonstrate the importance of climate and topography in controlling local tree densities at finer scales, as well as the overwhelming effect of humans across most of the world. Based on our projected tree densities, we estimate that over 15 billion trees are cut down each year, and the global number of trees has fallen by approximately 46% since the start of human civilization.
Evolution; international journal of organic evolution, Jan 22, 2015
Integration influences patterns of trait evolution, but the relationship between these patterns a... more Integration influences patterns of trait evolution, but the relationship between these patterns and the degree of trait integration is not well understood. In order to explore this further, we study a specialized pollination mechanism in conifers whose traits are linked through function but not development. This mechanism depends on interactions among three characters: pollen that is buoyant, ovules that face downward at pollination, and the production of a liquid droplet that buoyant grains float through to enter the ovule. We use a well-sampled phylogeny of conifers to test correlated evolution among these characters and specific sequences of character change. Using likelihood models of character evolution, we find that pollen morphology and ovule characters evolve in a concerted manner, where the flotation mechanism breaks down irreversibly following changes in orientation or drop production. The breakdown of this functional constraint, which may be facilitated by the lack of dev...
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