Meganeura

Meganeura

Overview
Meganeura is a genus of extinct insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s from the Carboniferous period approximately 300 million years ago, which resembled and are related to the present-day dragonflies. With wingspans of more than 75 cm (2.5 ft), M. monyi is one of the largest known flying insect species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

; the Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 Meganeuropsis permiana
Meganeuropsis permiana
Meganeuropsis is an extinct genus of griffenfly, order Protodonata, known from the Early Permian of North America, and represents the biggest known insect of all times. The genus includes two described species:...

is another. Meganeura were predatory, and fed on other insects, and even small amphibians
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...

.

Fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s were discovered in the French Stephanian Coal Measures of Commentry
Commentry
Commentry is a commune in the department of Allier in central France. It lies southwest of Moulins by the Orléans railway.-Population:-Economy:...

 in 1880.
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Encyclopedia
Meganeura is a genus of extinct insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s from the Carboniferous period approximately 300 million years ago, which resembled and are related to the present-day dragonflies. With wingspans of more than 75 cm (2.5 ft), M. monyi is one of the largest known flying insect species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

; the Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 Meganeuropsis permiana
Meganeuropsis permiana
Meganeuropsis is an extinct genus of griffenfly, order Protodonata, known from the Early Permian of North America, and represents the biggest known insect of all times. The genus includes two described species:...

is another. Meganeura were predatory, and fed on other insects, and even small amphibians
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...

.

Fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s were discovered in the French Stephanian Coal Measures of Commentry
Commentry
Commentry is a commune in the department of Allier in central France. It lies southwest of Moulins by the Orléans railway.-Population:-Economy:...

 in 1880. In 1885, French paleontologist Charles Brongniart
Charles Jules Edmée Brongniart
Charles Jules Edmée Brongniart was a French entomologist and paleontologist.He wrote:* Tableaux de zoologie ....

 described and named the fossil "Meganeura" (large-nerved), which refers to the network of veins on the insect's wings
Insect wing
Insects are the only group of invertebrates known to have evolved flight. Insects possess some remarkable flight characteristics and abilities, still far superior to attempts by humans to replicate their capabilities. Even our understanding of the aerodynamics of flexible, flapping wings and how...

. Another fine fossil specimen was found in 1979 at Bolsover
Bolsover
Bolsover is a town near Chesterfield, Derbyshire, England. It is 145 miles  from London, 18 miles  from Sheffield, 26 miles  from Nottingham and 54 miles  from Manchester. It is the main town in the Bolsover district.The civil parish for the town is called...

 in Derbyshire
Derbyshire
Derbyshire is a county in the East Midlands of England. A substantial portion of the Peak District National Park lies within Derbyshire. The northern part of Derbyshire overlaps with the Pennines, a famous chain of hills and mountains. The county contains within its boundary of approx...

. The holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...

 is housed in the Muséum national d'histoire naturelle
Muséum national d'histoire naturelle
The Muséum national d'Histoire naturelle is the National Museum of Natural History in Paris, France.- History :The museum was formally founded on 10 June 1793, during the French Revolution...

, Paris
Paris
Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...

.

Size


Controversy has prevailed as to how insects of the Carboniferous period were able to grow so large. The way oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 is diffused
Diffusion capacity
In biology, diffusion capacity is a measurement of the lung's ability to transfer gases. Oxygen uptake may be limited by diffusion in circumstances of low ambient oxygen or high pulmonary blood flow...

 through the insect's body via its tracheal
Invertebrate trachea
The invertebrate trachea refers to the open respiratory system composed of spiracles, tracheae, and tracheoles that terrestrial arthropods have to transport metabolic gases to and from tissues....

 breathing system puts an upper limit on body size, which prehistoric insects seem to have well exceeded. It was originally proposed (Harlé & 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
Gigantism
Gigantism, also known as giantism , is a condition characterized by excessive growth and height significantly above average...

 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 the giant dragonflies is the circumstance that very large Meganeuridae with a wing span of 45 cm also occurred in the Upper Permian of Lodève
Lodève
Lodève is a commune in the Hérault département in Languedoc-Roussillon in southern France. It is a sub-prefecture of the department.-Geography:...

 in France, when the oxygen content of the atmosphere was already much lower than in the Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 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
Arms race
The term arms race, in its original usage, describes a competition between two or more parties for the best armed forces. Each party competes to produce larger numbers of weapons, greater armies, or superior military technology in a technological escalation...

" for increase in body size between plant-feeding Palaeodictyoptera
Palaeodictyoptera
The Palaeodictyoptera are an extinct order of medium-sized to very large, primitive Palaeozoic paleopterous insects.-Overview:They were characterised by beak-like mouthparts, similarity between fore- and hind wings, and an additional pair of winglets on the prothorax, in front of the first pair of...

 and Meganisoptera as their predators.

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