Insects Notes

21. Insects Evolution The oldest insect fossil found dates back to 395 million years ago, from the Rhynie Chert in Scotland. The reconstruction shows a clear set of mandibles, whose shape closely match those of a winged insect rather than a non-flying insect. It was called Rhyniognatha. In general, they went through endCretaceous, which is when the asteroid hit earth and the dinosaurs disappeared- no insect went instinct. Maybe cause their eggs can lie dormant over winter - can survive an asteroid winter. They even got through the end-Permian mass extinction - paleodictypterida were hit. Presumably their success could have been because they were aquatic larvae, or they were eggs or pupae that could lie dormant (holometabolous). There is a correlation between environmental change and insect development - when vascular plants formed, winged insects appeared. When Pangaea appeared, angiosperms appeared and holometabolous insects evolved, along with a huge radiation of insects. Rhyniognatha appeared 395 million years ago, hasn't left any immediate ancestors but has branched. In yellow are the hexapods (entognatha) - not insects. They branched off around 410 million years ago, either just before of after they terrestrialised. Archaegnatha are bristle tails and they are also not insects. When vascular plants evolved, massive radiation. Ephemoptera (mayflies) Started off in the water. Nymphs are predatious, carnivorous aquatic larvae that turn into an adult and then a synchronised emergence on a single day, that reduces the predation pressure on the emerging adults. They only live for a day. Paleodictyopterida They are related to dragonflies (odonata). They disappeared at the end-Permian extinction so that suggests they were more vulnerable to the causes of the extinction. This fossil is from 290 million years ago. They could be very large with a wingspan of up to 55cm - giant 'dragonflies'. The idea is they grew so big because of high oxygen levels (up to 30%), but not all insects through gigantism; cockroaches did not get 

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