Post by Deinobrontornis on Jun 1, 2012 11:19:19 GMT -5
Meganeura
Meganeura is a genus of extinct insects from the Carboniferous period approximately 300 million years ago, which resembled and are related to the present-day dragonflies. With wingspans of up to 65 cm (2.1 ft), M. monyi is one of the largest known flying insect species; the Permian Meganeuropsis permiana is another. Meganeura were predatory, and fed on other insects, and even small amphibians.
Fossils were discovered in the French Stephanian Coal Measures of Commentry in 1880. In 1885, French paleontologist Charles Brongniart described and named the fossil "Meganeura" (large-nerved), which refers to the network of veins on the insect's wings. Another fine fossil specimen was found in 1979 at Bolsover in Derbyshire. The holotype is housed in the Muséum national d'histoire naturelle, Paris.
Size:
Controversy has prevailed as to how insects of the Carboniferous period were able to grow so large. The way oxygen is diffused through the insect's body via its tracheal breathing system puts an upper limit on body size, which prehistoric insects seem to have well exceeded. It was originally proposed (Harlé & Harlé, 1911) that Meganeura was only able to fly because the atmosphere at that time contained more oxygen than the present 20%. This theory was dismissed by fellow scientists, but has found approval more recently through further study into the relationship between gigantism and oxygen availability.[1] If this theory is correct, these insects would have been susceptible to falling oxygen levels and certainly could not survive in our modern atmosphere. Other research indicates that insects really do breathe, with "rapid cycles of tracheal compression and expansion".[2] Recent analysis of the flight energetics of modern insects and birds suggests that both the oxygen levels and air density provide a bound on size[3].
A general problem with all oxygen-related explanations of the giant dragonflies is the circumstance that very large Meganeuridae with a wing span of 45 cm also occurred in the Upper Permian of Lodève in France, when the oxygen content of the atmosphere was already much lower than in the Carboniferous and Lower Permian.[4]
Bechly (2004) suggested that the lack of aerial vertebrate predators allowed pterygote insects to evolve to maximum sizes during the Carboniferous and Permian periods, maybe accelerated by an evolutionary "arms race" for increase in body size between plant-feeding Palaeodictyoptera and Meganisoptera as their predators.
Meganeura is a genus of extinct insects from the Carboniferous period approximately 300 million years ago, which resembled and are related to the present-day dragonflies. With wingspans of up to 65 cm (2.1 ft), M. monyi is one of the largest known flying insect species; the Permian Meganeuropsis permiana is another. Meganeura were predatory, and fed on other insects, and even small amphibians.
Fossils were discovered in the French Stephanian Coal Measures of Commentry in 1880. In 1885, French paleontologist Charles Brongniart described and named the fossil "Meganeura" (large-nerved), which refers to the network of veins on the insect's wings. Another fine fossil specimen was found in 1979 at Bolsover in Derbyshire. The holotype is housed in the Muséum national d'histoire naturelle, Paris.
Size:
Controversy has prevailed as to how insects of the Carboniferous period were able to grow so large. The way oxygen is diffused through the insect's body via its tracheal breathing system puts an upper limit on body size, which prehistoric insects seem to have well exceeded. It was originally proposed (Harlé & Harlé, 1911) that Meganeura was only able to fly because the atmosphere at that time contained more oxygen than the present 20%. This theory was dismissed by fellow scientists, but has found approval more recently through further study into the relationship between gigantism and oxygen availability.[1] If this theory is correct, these insects would have been susceptible to falling oxygen levels and certainly could not survive in our modern atmosphere. Other research indicates that insects really do breathe, with "rapid cycles of tracheal compression and expansion".[2] Recent analysis of the flight energetics of modern insects and birds suggests that both the oxygen levels and air density provide a bound on size[3].
A general problem with all oxygen-related explanations of the giant dragonflies is the circumstance that very large Meganeuridae with a wing span of 45 cm also occurred in the Upper Permian of Lodève in France, when the oxygen content of the atmosphere was already much lower than in the Carboniferous and Lower Permian.[4]
Bechly (2004) suggested that the lack of aerial vertebrate predators allowed pterygote insects to evolve to maximum sizes during the Carboniferous and Permian periods, maybe accelerated by an evolutionary "arms race" for increase in body size between plant-feeding Palaeodictyoptera and Meganisoptera as their predators.
