Insect Fossils Classification with Hexapoda

Tree of Life
 
Fossil Insect Classification
Class Insecta and Subphylum Hexapoda


Page within: Tree of Life
Also see Phylum Arthropoda
 

Hemiptera iNSECT fOSSIL FROM cRATO fORMATIONUnlike 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 Flying termite in fossil amberColeoptera 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.

Regarding insect origins, Gaunt and Miles (2002) propose based molecular clock analyses encompassing five insect orders (Blattaria, Orthoptera, Hemiptera, Diptera, and Lepidoptera) that the class insecta common ancestor may have been Anostraca (fairy shrimps) at around the Ordovician-Silurian boundary around 434 to 421 million years ago. This time coincides with the earliest plant megafossil, and is consistent with the long held view that terrestrial transition of the aquatic arthropod ancestor to the insects is associated with the appearance with early vascular plants.

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

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.

Also see: References Phylum Arthropoda