Meganeura is a genus of extinct insects from the
(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,
and fed on 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
4 External links
There has been some controversy as to how insects of the Carboniferous
period were able to grow so large.
Oxygen levels and atmospheric density. 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 (Harlé & Harlé, 1911) that
Meganeura was able to fly only because the atmosphere at that time
contained more oxygen than the present 20%. This hypothesis was
initially dismissed by fellow scientists, but has found approval more
recently through further study into the relationship between gigantism
and oxygen availability. If this hypothesis 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 an upper bound on size. The presence
of very large
Meganeuridae with wing spans rivaling those of Meganeura
during the Permian, when the oxygen content of the atmosphere was
already much lower than in the Carboniferous, presented a problem to
the oxygen-related explanations in the case of the giant dragonflies.
However, despite the fact that meganeurids had the largest-known wing
spans, their bodies were not very large, being smaller than those of
several living Coleoptera; therefore, they were not true giant
insects, only being giant in comparison with their living relatives.
Lack of predators. Other explanations for the large size of
meganeurids compared to living relatives are warranted. Bechly
(2004) suggested that the lack of aerial vertebrate predators allowed
pterygote insects to evolve to maximum sizes during the Carboniferous
Permian periods, perhaps accelerated by an evolutionary "arms
race" for increase in body size between plant-feeding
Meganisoptera as their predators.
Aquatic larvae stadium. Another theory suggests that insects that
developed in water before becoming terrestrial as adults grew bigger
as a way to protect themselves against the high levels of oxygen.
^ Rake 2017, p. 20.
^ Taylor & Lewis 2007, p. 160.
^ Gauthier Chapelle & Lloyd S. Peck (May 1999). "Polar gigantism
dictated by oxygen availability". Nature. 399 (6732): 114–115.
Oxygen supply may also have led to insect gigantism
Carboniferous period, because atmospheric oxygen was 30-35%
(ref. 7). The demise of these insects when oxygen content fell
indicates that large species may be susceptible to such change. Giant
amphipods may therefore be among the first species to disappear if
global temperatures are increased or global oxygen levels decline.
Being close to the critical MPS limit may be seen as a specialization
that makes giant species more prone to extinction over geological
^ Westneat MW, Betz O, Blob RW, Fezzaa K, Cooper WJ, Lee WK (January
2003). "Tracheal respiration in insects visualized with synchrotron
x-ray imaging". Science. 299 (5606): 558–560.
doi:10.1126/science.1078008. PMID 12543973. Insects are known to
exchange respiratory gases in their system of tracheal tubes by using
either diffusion or changes in internal pressure that are produced
through body motion or hemolymph circulation. However, the inability
to see inside living insects has limited our understanding of their
respiration mechanisms. We used a synchrotron beam to obtain x-ray
videos of living, breathing insects. Beetles, crickets, and ants
exhibited rapid cycles of tracheal compression and expansion in the
head and thorax. Body movements and hemolymph circulation cannot
account for these cycles; therefore, our observations demonstrate a
previously unknown mechanism of respiration in insects analogous to
the inflation and deflation of vertebrate lungs.
^ Robert Dudley (April 1998). "Atmospheric oxygen, giant Paleozoic
insects and the evolution of aerial locomotion performance". The
Journal of Experimental Biology. 201 (Pt8): 1043–1050.
PMID 9510518. Uniformitarian approaches to the evolution of
terrestrial locomotor physiology and animal flight performance have
generally presupposed the constancy of atmospheric composition. Recent
geophysical data as well as theoretical models suggest that, to the
contrary, both oxygen and carbon dioxide concentrations have changed
dramatically during defining periods of metazoan evolution. Hyperoxia
in the late Paleozoic atmosphere may have physiologically enhanced the
initial evolution of tetrapod locomotor energetics; a concurrently
hyperdense atmosphere would have augmented aerodynamic force
production in early flying insects. Multiple historical origins of
vertebrate flight also correlate temporally with geological periods of
increased oxygen concentration and atmospheric density. Arthropod as
well as amphibian gigantism appear to have been facilitated by a
Carboniferous atmosphere and were subsequently eliminated by
Permian transition to hypoxia. For extant organisms, the
transient, chronic and ontogenetic effects of exposure to hyperoxic
gas mixtures are poorly understood relative to contemporary
understanding of the physiology of oxygen deprivation. Experimentally,
the biomechanical and physiological effects of hyperoxia on animal
flight performance can be decoupled through the use of gas mixtures
that vary in density and oxygen concentration. Such manipulations
permit both paleophysiological simulation of ancestral locomotor
performance and an analysis of maximal flight capacity in extant
^ Nel A.N., Fleck G., Garrouste R. and Gand, G. (2008): The
Odonatoptera of the Late
Permian Lodève Basin (Insecta). Journal of
Iberian Geology 34(1): 115-122 PDF[permanent dead link]
^ Bechly G. (2004): Evolution and systematics. pp. 7-16 in: Hutchins
M., Evans A.V., Garrison R.W. and Schlager N. (eds): Grzimek's Animal
Life Encyclopedia. 2nd Edition. Volume 3, Insects. 472 pp. Gale Group,
Farmington Hills, MI PDF[permanent dead link]
^ Than, Ker (August 9, 2011). "Why Giant Bugs Once Roamed the Earth".
National Geographic. Retrieved 20 July 2017.
Rake, Matthew (2017). Prehistoric Ancestors of Modern Animals. Hungry
Tomato. p. 20. ISBN 1512436097.
Taylor, Paul D.; Lewis, David N. (2007).
(repeated ed.). Harvard University Press. p. 160.
Media related to
Meganeura at Wikimedia Commons
Picture of life sized model of
Meganeura monyi made for Denver Museum
of Natural History.