Insect Fossils
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Insect FossilsClass
Insect and Subphylum Hexapoda |
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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 relative
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 simple 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. Despite their huge strength
to weight ratio, insects were often to small to escape the
sticky
resin exuded by trees, and which later became a fossil itself,
with physical properties akin to modern polymerized plastics.
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. 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 Classification |
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