Insect Fossils Classification with Hexapoda

Unlike the trilobite that has left a prodigious fossil record, the preservation of insects in sedimentary matrix is relatively rare, and essentially limited to the Lagerstätte sites. The reason for the scarcity of insect fossil is the poor preservation potential of the insect's exoskeleton. Like other Arthropods, insects have an external skeleton called an exoskeleton. Unlike the thick and calcified trilobite exoskeleton, the insect exoskeleton is made of a thin, plastic-like material called chitin, along with a tough protein. This thin, waterproof covering simply does not preserve well in most oxygenated environments, making insect fossils sparse despite the tremendous number that could have been preserved. The exception is in fossil resinite (amber, by street name), where it is possible for even the minutest details to be preserved right down to fragments of DNA. Despite their huge strength to weight ratio, insects were often too small to escape the sticky resin exuded by trees, and which later became a fossil itself, with physical properties akin to modern polymerized plastics. Countering low probability of fossilization is the prodigious fecundity of insects. While lifetime insect fecundity varies enormously across taxa, from less than ten to several millions of eggs, most insects lay between a couple of hundred to a couple of thousand eggs (Hinton 1981).

Insect evolution is a powerful illustration of decent with modification. The earliest known insects are tiny wingless forms from the early and middle Devonian. Insect flight developed with suddenness resembling the Cambrian explosion during the middle Carboniferous, apparently the result of the significant survival advantage that was accrued. By the end of the Carboniferous, the subphylum insecta had evolved into a large number of distinct orders. During the Permian, new insects forms appeared. Blattoid and Orthopteroid orders attained their greatest diversity, and new groups like the Psocoptera, Homoptera, Hemiptera, Mecoptera and Coleoptera became ubiquitous and diverse. The Permian extinction wiped out nine orders of insects, and more orders disappeared in the Triassic or the early Jurassic. However, surviving orders such as Neuroptera, Mecoptera, and Diptera, and Coleoptera underwent further adaptive radiation establishing many families extant in modern times. So exquisite is insect design that most groups were well formed by the Cretaceous and remain largely unchanged in appearance during modern times.

Insect evolution has led to prodigious diversity of this animal group compared with other members of Domain Eukarya. For example, there are believed to be three times as many Dipteran species (true fllies) as there are vertebrate species, and ten times as many Coleopteran species (beetles) as there are vertebrate species.

Taxonomic research on fossil insects has always been relegated to a subordinate role when compared to that of living species. There are large numbers of undetermined fossil insects in many collections throughout the world awaiting descriptions, but only a small fraction of systematic research has ever been devoted to these fossils.

Subphylum Hexapoda - Class Insecta and Class Entognatha

H E X O P O D A	Class	Subclass	Infraclass	Superorder	Order (Links are to Fossils by Order)	Common Names within order	Appearance of Order	Approximate Extant species described
	Entognatha (2)	Collembola	n/a		Collembola	Springtails	Devonian	2,000
			n/a		Diplura	Two-pronged bristletails	Carboniferous	800
			n/a		Protura	Coneheads	Devonian	rare/100
	Insecta	Apterygotes - never had wings (1)	n/a		Archaeognatha	Jumping bristletails	Devonian	350
			n/a		Monura	Enigmatic taxon	Carboniferous	Extinct
			n/a		Thysanura	Silverfish	Lower Devonian	700
			Paleoptera (3)
					Ephemeroptera	mayfly	Devonian	2,100
					Odonata	dragonflies; Damselflies	Devonian	>5,500
		Pterygota (Have or had wings)	Neoptera	Exopterygota	Blattaria	cockroachs	Mississippian	3,700
					Mantodea	mantid	Pennsylvannian	>1,800
					Mantophasmatodea	gladiator	-	-
					Isoptera	termite	Upper Cretaceous	2,000
					Plecoptera	stonefly	Permian	1,600
					Orthoptera	grasshoppers, crickets and locusts	Mississippian	20,000
					Protorthoptera	Grasshopper-like	Carboniferous (extinct)	-
					Embioptera	webspinners	?	300
					Dermaptera	earwigs	Jurrasic	2,000
					Phthiraptera	lice	?	3000
					Notoptera	ice-crawlers & gladiators	?	<30
					Embioptera	webspinners	?	170
					Zoraptera	angel insects	?	1 genus
					Phasmatodea	Walking stick; walking leaf	Lower Triassic	2,500
					Thysanoptera	thrips	Permian	5000
					Psocoptera	booklice, barklicee	Permian	6,000
					Hemiptera	true bugs: Cicada; aphid; plant hopper; leaf hopper; spittlebugs; scale insects; mealy bugs	Upper Pennsylvannian	82,000
				Endopterygota	Hymenoptera	ants; bees; wasps; sawflies	Upper Triassic	130,000
					Homoptera (suborder combined with Hemiptera)	cicadas; aphids; plant hoppers; leaf hoppers; spittlebugs; scale insects; mealy bugs	Permian	33,000
					Coleoptera	Beetles	Lower Permian	350,000
					Neuroptera	Lacewings; antlions	Lower Permian	4,700
					Strepsiptera	twisted-winged parasites	?	?
					Raphidioptera	snakeflies	Jurassic	150
					Mecoptera	Scorpianflies	Pennsylvannian	550
					Siphonoptera	fleas	Miocene (?)	1,750
					Diptera	mosquitos, gnats, midges, etc.	Middle Triassic	240,000
					Trichoptera	caddisflies	Lower Triassic	7,000
					Lepidoptera	Butterfly; moth	Jurassic	180,000
(1) The taxon Apterygota is often applied for a subclass of insects lacking wings in both extant forms as well across their evolutionary history. The earliest occurence in the fossil record is the Devonian period some 417-354 million years ago. The nymphs go through little or no metamorphosis, and thus closely resemble the adults. Apterygotans generally have a thin exoskeleton, giving them a pseudo-translucent characteristic. (2) The Entognatha is a class of arthropods, which, together with insects, makes up the hexapods. They exhibit little or no metamorphosis. The class's three orders: Collembola, Diplura and Protura are currently believed to have independently evolved six legs, and to have independently evolved within each order, making the Entognatha a polyphyletic group. (3) The Palaeoptera comprises a primitive grouping of winged insects (mostly extinct forms) that lack or lacked the ability to fold the wings back over the abdomen as members of Neoptera do. The relationship of the two extant Paleoptera groups (Ephemeroptera and Odonata) to the Neoptera is unresolved; some believe Paleoptera to be paraphyletic such that the grouping should be abandoned.