Tapejara wellnhoferi, a small azhdarchoid pterodactyloid from the Early Cretaceous Santana Formation of Brazil, provides critical information about the aerodynamic function of its spectacular head crest. The cranial c...Tapejara wellnhoferi, a small azhdarchoid pterodactyloid from the Early Cretaceous Santana Formation of Brazil, provides critical information about the aerodynamic function of its spectacular head crest. The cranial crests in pterodactyloids were sexually dimorphic and are thought to have evolved in adult males in response to female mate choice. However, the location of cranial crests in front of the center of gravity would create instability in the yaw axis during flight and may seem like a handicap. Vertically aligned webbed feet probably suppressed the yawing rotations and instability from the crest. Here we show that the crest functioned as a front rudder to make agile turn and mediate flight control. A computer simulation model suggests that Tapejara had a large excess of muscle power available above the power required for continuous flapping flight. It could easily takeoff from a perch, ground, or water surface and land safely on the ground. It was an excellent glider with a gliding angle close to 4~ and a cruising speed of 27 km/h. Tapejara could soar efficiently on the windward side of cliffs or circle on rising thermals over tropical waters for efficient long-distance flight. Various control surfaces in the wings of Tapejara analogous to the slat, aileron, elevator, fin, rudder, and horizontal stabilizer of an aircraft made pterodactyloids versatile flyers.展开更多
Microscopic charcoal preserved in sediments of the Lashly Formation(Middle to Late Triassic)of South Victoria Land(SVL),Antarctica provides a proxy record of palaeofire.These charred fragments derived from wood and le...Microscopic charcoal preserved in sediments of the Lashly Formation(Middle to Late Triassic)of South Victoria Land(SVL),Antarctica provides a proxy record of palaeofire.These charred fragments derived from wood and leaf pieces along with spores and pollen grains are part of the buried plant biomass preserved in the shale and carbonaceous shale of fluvial/lacustrine deposits.The evidence of paleofire in Antarctica during the Triassic Period is supported by the presence of a thin bed of silicic tuff interlayered with Dicroidiumbearing shale.The detailed morphology and comparative anatomy of least to high thermally altered plant fragments observed under the light,fluorescence and scanning electron microscope demonstrates the evidence of effect of fire on the vegetation during Middle to Late Triassic(240-200 million years).Most of the charred particles retain identifiable structures with well-preserved to distorted cellular details.Such plant fragments are dark brown,blackish brown,quadrangular-multiangular,equi-dimensional,opaque up to the edges and nonfluorescent.The pollen grains recorded from several sedimentary sequences(but the new data come from only one level i.e.,member C of Lashly Formation)show distorted exinal sculptures and are light to dark brown in colour indicating intensive thermal effect.The detailed microscopic images of such fire-affected plant remains also explain their preservation biases in the sediments.The magnitude of the charred pieces and their abundance peaks from various locations in Allan Hills is related solely to the production and amount of burnt material embodied in the sediments.The high peaks indicate severity of fire and production of maximum charcoal of the standing vegetation in Allan Hills.展开更多
文摘Tapejara wellnhoferi, a small azhdarchoid pterodactyloid from the Early Cretaceous Santana Formation of Brazil, provides critical information about the aerodynamic function of its spectacular head crest. The cranial crests in pterodactyloids were sexually dimorphic and are thought to have evolved in adult males in response to female mate choice. However, the location of cranial crests in front of the center of gravity would create instability in the yaw axis during flight and may seem like a handicap. Vertically aligned webbed feet probably suppressed the yawing rotations and instability from the crest. Here we show that the crest functioned as a front rudder to make agile turn and mediate flight control. A computer simulation model suggests that Tapejara had a large excess of muscle power available above the power required for continuous flapping flight. It could easily takeoff from a perch, ground, or water surface and land safely on the ground. It was an excellent glider with a gliding angle close to 4~ and a cruising speed of 27 km/h. Tapejara could soar efficiently on the windward side of cliffs or circle on rising thermals over tropical waters for efficient long-distance flight. Various control surfaces in the wings of Tapejara analogous to the slat, aileron, elevator, fin, rudder, and horizontal stabilizer of an aircraft made pterodactyloids versatile flyers.
基金funded by the National Science Foundation and Birbal Sahni Institute of Palaeobotany.
文摘Microscopic charcoal preserved in sediments of the Lashly Formation(Middle to Late Triassic)of South Victoria Land(SVL),Antarctica provides a proxy record of palaeofire.These charred fragments derived from wood and leaf pieces along with spores and pollen grains are part of the buried plant biomass preserved in the shale and carbonaceous shale of fluvial/lacustrine deposits.The evidence of paleofire in Antarctica during the Triassic Period is supported by the presence of a thin bed of silicic tuff interlayered with Dicroidiumbearing shale.The detailed morphology and comparative anatomy of least to high thermally altered plant fragments observed under the light,fluorescence and scanning electron microscope demonstrates the evidence of effect of fire on the vegetation during Middle to Late Triassic(240-200 million years).Most of the charred particles retain identifiable structures with well-preserved to distorted cellular details.Such plant fragments are dark brown,blackish brown,quadrangular-multiangular,equi-dimensional,opaque up to the edges and nonfluorescent.The pollen grains recorded from several sedimentary sequences(but the new data come from only one level i.e.,member C of Lashly Formation)show distorted exinal sculptures and are light to dark brown in colour indicating intensive thermal effect.The detailed microscopic images of such fire-affected plant remains also explain their preservation biases in the sediments.The magnitude of the charred pieces and their abundance peaks from various locations in Allan Hills is related solely to the production and amount of burnt material embodied in the sediments.The high peaks indicate severity of fire and production of maximum charcoal of the standing vegetation in Allan Hills.
