Unlike the trilobite that has left a prodigious fossil record, the preservation of insects in sedimentary matrix is relatively rare. The reason for the reletive 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, formerly known as the 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, homopteran 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.
Fossil Orders of Insects
• Blattinopsoda
• Caloneurodea
• Diaphonapterodea
• Glosselytrodea
• Meganisoptera
• Megasecoptera
• Miomoptera
• Monura
• Paleodictyoptera
• Paraplecoptera
• Permothemistida
• Protelytroptera
• Protoblattaria
• Protodonata
• Titanoptera
Alternative Order Names
These order names generally see less usage than the synonyms listed next to them. Some of these names are more widely used in certain regions and others are of more archaic usage.
• Archaeognatha
• Blattodea
• Corrodentia
• Dictyoptera
• Blattaria,
• Embioptera
• Entotropha
• Ephemeroptera
• Notoptera
• Phasmatodea
• Planipennia,
• Psocina
• Zygentoma
Oldet known fossil insect. The specimen, no. In.38234, is preserved in a fragment of Rhynie Chert and mounted on a glass microscope slide. It consists of a pair of jaws or mandibles and other associated structures. It was collected by the Reverend W. Cran and is dated 19/06/1919. Cran found many arthropod remains in the Rhynie Chert and made them available for study to S. Hirst, S. Maulik and D.J. Scourfield. Hirst and Maulik published a paper in 1926 and figured this specimen as the ‘mandibles of supposed larval insect’. They also described and named four other specimens of well-preserved heads as Rhyniella praecursor. Eminent fossil insect expert Robin J. Tillyard then studied these specimens. He named the jaws Rhyniognatha hirsti in 1928 and described it as the portion of a head of a small insect, showing the mandibles and some surrounding structures. He also identified Rhyniella praecursor as a collembolan or springtail. The specimens were donated to the NHM by Scourfield in 1940. The Rhynie Chert is a remarkable rock. It comes from the village of Rhynie in Scotland and consists of beds of silica similar to flint that were deposited by hot springs 400 million years ago. The chert contains exquisitely preserved plants and animals from the beginning of the Devonian Period and are evidence of the earliest known terrestrial ecosystem in the world. Since 1928, no-one has doubted that Rhyniella praecursor was a springtail and thus it has been widely regarded as the oldest known fossil hexapod in the world, however Rhyniognatha hirsti has been largely ignored. Various scientists have mentioned Rhyniognatha but most have regarded it as an arthropod of uncertain affinities. In 2002 two American scientists, Dr Michael Engel from the University of Kansas and Dr David Grimaldi from the American Museum of Natural History Museum, New York, visited the Museum to study the fossil insect collections. One of the specimens they asked to see was Rhyniognatha hirsti . From an initial examination they realised it was interesting and borrowed it to take back to the states to study in more detail. There they realised the true importance of the specimen and wrote a paper for the prestigious journal ‘Nature’ that was published on 12th February 2004.
Engel and Grimaldi found that the mandibles of Rhyniognatha hirsti have two points of articulation which is only known in true insects: silverfish and winged insect. The form of the mandibles is more like that of winged insects than silverfish. Although there is no evidence of wings preserved in the Rhynie Chert, the advanced form of the mandibles of Rhyniognatha indicates that it could have been winged. This is very important as the oldest known fossils of flying insects are 320 million years old ; the presence of true insects as far back as 400 million years ago indicates that wings may have evolved much earlier.