Meganisoptera is an extinct order of very large to gigantic insects, occasionally called griffinflies. The order was formerly named Protodonata, the "proto-Odonata", for their similar appearance and supposed relation to modern Odonata (damselflies and dragonflies). They range in Palaeozoic (Late Carboniferous to Late Permian) times. Though most were only slightly larger than modern dragonflies, the order includes the largest known insect species, such as the late Carboniferous Meganeura monyi, Megatypus, and the even larger early Permian Meganeuropsis permiana, with wingspans of up to 71 centimetres (28 in).
The forewings and hindwings are similar in venation (a primitive feature) except for the larger anal (rearwards) area in the hindwing. The forewing is usually more slender and slightly longer than the hindwing. Unlike the true dragonflies, the Odonata, they had no pterostigma, and a somewhat simpler pattern of veins in the wings.
Most specimens are known from wing fragments only; with only a few as complete wings, and even fewer (of the family Meganeuridae) with body impressions. These show a globose head with large dentate mandibles, strong spiny legs, a large thorax, and long and slender dragonfly-like abdomen. Like true dragonflies, they were presumably predators.
Although sometimes included under the dragonflies, the Protodonata lack certain distinctive wing features that characterise the Odonata. Grimaldi & Engel 2005 point out that the colloquial term "giant dragonfly" is therefore misleading, and suggest "griffinfly" instead.
|Illustration of a Meganeura species|
Controversy has prevailed as to how insects of the Carboniferous period were able to grow so large. The way oxygen is diffused through the insect's body via its tracheal breathing system puts an upper limit on body size, which prehistoric insects seem to have well exceeded. It was originally proposed in Harlé (1911) that Meganeura was only able to fly because the atmosphere at that time contained more oxygen than the present 20%. This theory was dismissed by fellow scientists, but has found approval more recently through further study into the relationship between gigantism and oxygen availability. If this theory is correct, these insects would have been susceptible to falling oxygen levels and certainly could not survive in our modern atmosphere. Other research indicates that insects really do breathe, with "rapid cycles of tracheal compression and expansion". Recent analysis of the flight energetics of modern insects and birds suggests that both the oxygen levels and air density provide a bound on size.
A general problem with all oxygen related explanations of giant griffinflies is the circumstance that very large Meganeuridae with a wingspan of 45 cm also occurred in the Upper Permian of Lodève in France, when the oxygen content of the atmosphere was already much lower than in the Carboniferous and Lower Permian.
Bechly 2004 suggested that the lack of aerial vertebrate predators allowed pterygote insects to evolve to maximum sizes during the Carboniferous and Permian periods, maybe accelerated by an "evolutionary arms race" for increase in body size between plant-feeding Palaeodictyoptera and meganeurids as their predators.
Amphiesmenoptera is an insect superorder, established by S. G. Kiriakoff, but often credited to Willi Hennig in his revision of insect taxonomy for two sister orders: Lepidoptera (butterflies and moths) and Trichoptera (caddisflies). In 2017, a third fossil order was added to the group, the Tarachoptera.Trichoptera and Lepidoptera share a number of derived characters (synapomorphies) which demonstrate their common descent:
Females, rather than males, are heterogametic (i.e. their sex chromosomes differ).
Dense setae are present in the wings (modified into scales in Lepidoptera).
There is a particular venation pattern on the forewings (the double-looped anal veins).
Larvae have mouth structures and glands to make and manipulate silk.Thus these two extant orders are sisters, with Tarachoptera basal to both groups. Amphiesmenoptera probably evolved in the Jurassic. Lepidoptera differ from the Trichoptera in several features, including wing venation, form of the scales on the wings, loss of the cerci, loss of an ocellus, and changes to the legs.Amphiesmenoptera are thought to be the sister group of Antliophora, a proposed superorder comprising Diptera (flies), Siphonaptera (fleas) and Mecoptera (scorpionflies). Together, Amphiesmenoptera and Antliophora compose the group Mecopterida.Archodonata
Archodonata is an extinct order of palaeozoic paleopterous insects, sometimes included in Odonata.Bohemiatupus
Bohemiatupus is an extinct genus of griffenfly in the family Meganeuridae and containing a single species Bohemiatupus elegans. The species is known only from the Late Carboniferous, Bolsovian stage, Kladno Formation near the village of Radnice in the Radnice Basin, Czech Republic.Dicondylia
The Dicondylia are a taxonomic group (taxon) that includes all insects except the jumping bristletails (Archaeognatha). Dicondylia have a mandible attached with two hinges to the head capsule (dicondyl), in contrast to the original mandible with a single ball joint (monocondyl).Eumetabola
Eumetabola is an unranked category of Neoptera. Two large unities known as the Paurometabola and Eumetabola are probably from the adelphotaxa of the Neoptera after exclusion of the Plecoptera. The monophyly of these unities appears to be weakly justified.Meganeura
Meganeura is a genus of extinct insects from the Carboniferous period (approximately 300 million years ago), which resembled and are related to the present-day dragonflies. With wingspans ranging from 65 cm (25.6 in) to over 70 cm (28 in), M. monyi is one of the largest-known flying insect species. Meganeura were predatory, with their diet mainly consisting of other insects.
Fossils were discovered in the French Stephanian Coal Measures of Commentry in 1880. In 1885, French paleontologist Charles Brongniart described and named the fossil "Meganeura" (large-nerved), which refers to the network of veins on the insect's wings. Another fine fossil specimen was found in 1979 at Bolsover in Derbyshire. The holotype is housed in the National Museum of Natural History, in Paris.Meganeuropsis
Meganeuropsis is an extinct genus of griffinfly, order Meganisoptera, known from the Early Permian of North America, and represents the biggest known insect of all time. Meganeuropsis existed during the Artinskian age of the Permian period, 283.5–290.1 mya . The genus includes two described species:
Meganeuropsis permiana described in 1937 from Elmo, Kansas. It was one of the largest known insects that ever lived, with a reconstructed wing length of 330 millimetres (13 in), an estimated wingspan of up to 710 millimetres (28 in), and a body length from head to tail of almost 430 millimetres (17 in).Meganeuropsis americana, discovered in Oklahoma in 1940, is most probably a junior synonym of Meganeuropsis permiana. It is represented by a forewing fragment 280 millimetres (11 in) long, which is conserved and displayed in the Harvard Museum of Natural History; the complete reconstructed wing had an estimated total length of 305 millimetres (12.0 in), making it the largest insect wing ever found (with a resulting wing span of 690 millimetres (27 in)).Megatypus
Megatypus is an extinct genus of insect of the order Meganisoptera. Species in this genus were much larger than their modern relatives, dragonflies and damselflies, and reached a wingspan of 70 centimeters (2.3 ft).Myrmeleontoidea
Myrmeleontoidea is a lacewing superfamily in the suborder Myrmeleontiformia.Namurotypus
Namurotypus is an extinct genus of griffenfly. It inhabited the large swamps of the Carboniferous period.Neoptera
Neoptera is a classification group that includes most orders of the winged insects, specifically those that can flex their wings over their abdomens. This is in contrast with the more basal orders of winged insects (the "Palaeoptera" assemblage), which are unable to flex their wings in this way.Odonata
Odonata is an order of carnivorous insects encompassing the dragonflies (Anisoptera) and the damselflies (Zygoptera). The Odonata form a clade, which has existed since the Permian.Dragonflies are generally larger, and perch with their wings held out to the sides; damselflies have slender bodies, and hold their wings over the body at rest.Odonatoptera
The Odonatoptera are a superorder (sometimes treated as an order) of ancient winged insects, placed in the Palaeoptera which probably form a paraphyletic group however. The dragonflies and damselflies are the only living members of this group, which was far more diverse in the late Paleozoic and contained gigantic species, including the griffinflies (colloquially called "giant dragonflies", although they were not dragonflies in the strict sense) of the order Protodonata. This lineage dates back at least to the Bashkirian, not quite 320 million years ago.Palaeoptera
The name Palaeoptera has been traditionally applied to those ancestral groups of winged insects (most of them extinct) that lacked the ability to fold the wings back over the abdomen as characterizes the Neoptera. The Diaphanopterodea, which are palaeopteran insects, had independently and uniquely evolved a different wing-folding mechanism. Both mayflies and dragonflies lack any of the smell centers in their brain found in Neoptera.Panorpida
Panorpida or Mecopterida is a proposed superorder of Endopterygota. The conjectured monophyly of the Panorpida is historically based on morphological evidence, namely the reduction or loss of the ovipositor and several internal characteristics, including a muscle connecting a pleuron and the first axillary sclerite at the base of the wing, various features of the larval maxilla and labium, and basal fusion of CuP and A1 veins in the hind wings. The monophyly of the Panorpida is also supported by recent molecular data.Protodiptera
Protodiptera is an extinct order of insects containing the two genera Permotipula and Permila.Psocodea
Psocodea is a taxonomic group of insects comprising the bark lice, book lice and true lice. It was formerly considered a superorder, but is now generally considered by entomologists as an order. Despite the greatly differing appearance of lice, they are believed to have evolved from within the former order "Psocoptera", which contained the bark lice and book lice. Psocodea contains around 11,000 species, divided among seven suborders.Pterygota
The Pterygota are a subclass of insects that includes the winged insects. It also includes insect orders that are secondarily wingless (that is, insect groups whose ancestors once had wings but that have lost them as a result of subsequent evolution).The pterygotan group comprises almost all insects. The insect orders not included are the Archaeognatha (jumping bristletails) and the Zygentoma (silverfishes and firebrats), two primitively wingless insect orders. Also not included are the three orders no longer considered to be insects: Protura, Collembola, and Diplura.Sinomeganeura
Sinomeganeura is an extinct genus of griffenfly in the family Meganeuridae and containing a single species Sinomeganeura huangheensis. The species is known only from Late Carboniferous, Namurian stage, Tupo Formation near the village of Xiaheyan in Ningxia Hui Autonomous Region, China.