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Insects
Insects, which had first appeared during the preceding Carboniferous, increased in diversification during this Permian period and gave birth to 'modern' insects
Read in conjunction with 'Origin of Insects' from previous period.
Hemimetaboly
Hemimetaboly
The dominant insects during the Permian Period were all hemimetabolous, including representatives like mayflies (ephemeroptera) and dragonflies (odonata), grasshoppers crickets (orthoptera), earwigs and beaked insects, seen in the Carbiniferous but now more plentiful. Towards the end of the Permian, there was a substantial drop in both origination and extinction rates. This is likely due to competition from some other hemimetabolins, ‘true bugs (Hemiptera), due to their similar mouthparts and ecology.
Hemimetabolous insects are those that emerge form an egg and go through a varying number of nymphal stages, where they throw off their previous covering, changing slightly at each stage, until they reach a final winged stage. Examples include cockroaches and earwigs, and are generally considered ‘more primitive’.
Holometabolous insects have a ‘whole’ life cycle so lay eggs which become larvae which get bigger but then go through a ‘pupa’ stage before emerging as a quite different character, like bees and butterflies, generally considered ‘advanced’. The question was always:” what is the relation between the two?” There is much argument how holometabolous insects arose from hemimetabolous forms. Perhaps my hypothesis (right) can throw some light on the matter.
The insects about in this period are nearly all 'hemi-metabolic - going through various growing stages, each a bit more developed There may be several or quite numerous stages of 'nymphs'. The main soil arthropods, both springtails and mites, just go through a series of nymphal stages before maturing.
There have been all sorts of questions about the relation between hemimetabolous or holometabolous. I remember winning a bet at school that I could get both these terms in an essay three times, but my teacher was somewhat bemused.
The insects emerging during this period took flight after going through a series of nymphal stages. The expansion of hemi-metabolic winged insect in this period is notable, but may have been due to the oxygen. Later insects would not have that advantage. It was from about 300 mya ago that the expansion of winged insects with a complete life cycle – holometabolous – started.
My hypothesis
My hypothesis
My hypothesis of this part of insect evolution, is that the hemi-metabolous forms emerged from soils (sometimes water) developing a final nymphal stage which had rudimentary wings. This got them to new places.
Holometabolous insects evolved with distinct growing forms, one for feeding and one for sex, each suitable for different environments. This gave them more environment to live in. The wings became stronger to produce regularly flying adults, to take over the airwaves and come back to earth as a secondary source for their larvae to grow.
It is all about how wings emerged – which ‘remains an intriguing problem for further study.. (Bradley et al 2009)
Holometaboly
Holometaboly
The first signs ever of an holometabolous insect was found at the beginning of this period. (Labandeira& Phillips 1996) Philipps 1996. This was of a larva in a fern leaf, not a lot to go on. Holometabolous insects go through 4 distinct stages of growing up. The first stage, egg, hatches to a larva, which pupates before turning into a distinct adult.
Holometabolous insects emerged well after hemimetabolous insects which had been wandering round for quite a few million years.
Ghilarov said this was a ‘secondary’ coming to earth. They now had something to come back to – not only rich plant life but also a whole new dynamic soil environment.
“The earliest holometabolans appeared in the Late Carboniferous, all minute and as scarcely-recognizable stem groups, but by the Permian (300-250mya) more familiar-looking species make their debut, including primitive beetles, lacewings, and varied mecopteroid-like relatives of Antliophora and Amphiesmenoptera" (Engel 2016)
According to Tim Cockerill, talking with Brain Cox, this complete metamorphosis is probably one of the reasons insects have become so successful. The four most diverse groups of animals on the planet - wasps, beetles, flies and moths, all do it. The most important things for species to survive is to eat and to reproduce. These creatures have one half of their life cycle designed - by natural selection, to take on as much food as possible.
1st Holometablous
1st Holometablous
Most of the insects we know today are holometabolous, and these 'modern' insects started to diversify in this period. They also called the Endopterygota because they develop their wings inside their body, during pupation. These insects with internally developed wings, and external mandibles are one of the most successful groups of animals on the planet. They constitute the most diverse insect superorder, with over 1 million living species divided between 11 orders, containing insects such as butterflies, flies, fleas, bees, and ants, which we will come about later. And beetles..
It is easy to see how the first holometabolous insects would came back to earth and lived in decaying wood. The fact that the origin of beetles is in decaying wood would be the most readily available food for their offspring to grow up in. Beetles don’t fly particularly often, as their hard front wings (hence ‘coleoptera meaning hard wings) are probably more about protection than strong sustained flight. That would come later.
Then came the beetles. Yeahyeahyeah. Beetles have hard wings and are called coleo (hard) ptera (wing). The earliest known beetles, appear at the beginning of the Permian and included members of Permocupedidae (left) which fed on decaying wood. The most diverse group of insects - beetles – originated by making the most of decaying wood, which would be abundant. The earliest holometabolous insects invaded decaying wood. This became a sort of stepping stone to living plants and soil.
More about the 'Early Beetles'
"More than one insect extinction events, accompanied by significant diversity drop and turnovers of faunal compositional, occurred in the Permian and Triassic". Gui et al 2023
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