The Protodonata - giant near-dragonflies swooping down like great predatory birds

Protodonatans are stock characters in paleontological art. They're those gigantic dragonflies that can be seen buzzing over Carboniferous and Permian landscapes, looking (and sounding) for all the world like miniature helicopters. In time-travel stories, a giant dragonfly buzzing past is often among the first inklings that Something is Afoot. And giant dragonflies make decent kaiju and horror monsters - such as in the adjacent picture, from the infamous Dinosaurs Attack! card series (in which the dragonflies are named Sigillaria... seriously, what the hell?) They deserve the purple prose in the title of this post.

So what, exactly, are protodonatans? Popular literature refers to them as "giant dragonflies". While many of them certainly are gigantic by insect standards, protodonatans were not true dragonflies, but instead formed a stem group to the dragonflies in the Odonata. To eliminate the confusions of the common name, Grimaldi and Engel (2005) suggested the name "griffenfly" as a substitute, which is pretty awesome. Use it whenever possible.

The order Protodonata has long been suspected to be paraphyletic, and the possibility of its inclusion among the Odonata as a suborder has been the subject of debate. With several suborders pruned from Protodonata, it appears to be monophyletic, with families Meganeuridae and Paralogidae. Whether or not it is an order on its own is another question. F. M. Carpenter, who provided most of the literature on the North American griffenflies, supported the ordinal status of the Protodonata (Carpenter, 1960). Griffenflies lack the pterostigma present in dragonflies (Grimaldi and Engel, 2005). Rehn (2003) defined them on the basis of a lobe on the outside edge of the costal axalare, and intercalary longitudinal veins between IR2 and RP2, and established them as a sister group to odonatans. It must be mentioned that they may yet prove to be paraphyletic stem-odonatoids (Grimaldi and Engel, 2005).

Most griffenfly fossils consist of wings or fragments of wings, dating from the Carboniferous and Permian. Judging by the instances where the rest of the insect has been preserved, it would seem that griffenflies, apart from their more primitive wing venation, are similar to dragonflies. With large eyes and spiny legs, they were certainly active predators - the eagles of their time, feeding on anything unlucky enough to be smaller than them. No larvae are known; however, if griffenflies had aquatic larvae to the same scale of modern dragonfly nymphs, they would be some 18 inches long in the largest species (Grimaldi and Engel, 2005). The mind boggles as to what they were eating.

Picture of Meganeura monyi, the first-known and best-known of griffenflies, from Wikipedia.

Griffenflies also have the distinction of being among the first endothermic animals to appear. Like modern-day dragonflies, many of which are endothermic, griffenflies likely had the capacity to regulate their body temperature, allowing a high level of activity. However, given their size and habitat, they were easy targets for overheating. It has been suggesting that hunting at dusk, gliding on occasion, and specialized cooling systems (such as ventilating hemolymph in the abdomen) could have warded off thermal stress (May, 1982).

Of course, if you ever saw a griffenfly (a highly unlikely possibility, as will be explained), the first thing you'd notice would not be the wing venation, but the creature's sheer size. Griffenflies rank as the largest flying insects ever to exist. The Carboniferous Meganeura monyi and the even-larger Permian Meganeuropsis permiana could reaches wingspans of around 71 cm, and likely fed on small vertebrates as well as other insects. When Charles Brongniart discovered Meganeura back in 1893, he was apparently so impressed by its size that he included a life-size fold-out reconstruction in his dissertation (Grimaldi and Engel, 2005).

The existence of giant insects during the Paleozoic has also been scrutinized. While's it's a common misconception that the Paleozoic was an age of giant arthropods, there's no denying that many arthropods did grow much larger than anything today, from Meganeura and Meganeuropsis to the myriapod Arthropleura. High oxygen levels during the Carboniferous and Permian were responsible for this, allowing arthropods to grow to remarkable sizes (Dudley, 1998; Chapelle and Peck, 1999). A drop in oxygen levels near the end of the Permian led to the demise of the large griffenflies. This was good news for the dragonflies, though, as they radiated after the extinction of their larger cousins (Grimaldi and Engel, 2005).

Image of Meganeura from BBC's Walking with Beasts series, taken from Wikipedia.

So, if you do ever get around to seeing a griffenfly in the flesh - er, exoskeleton, remember this: either it's choking, or you are. Insects of that size would not survive on the world we live in; which of course negates an episode of Prehistoric Park and pretty much every time-travelling encounter with griffenflies.

Oh, and did I mention that they're named after mythical beasts that are half-eagle and half-lion? They're that awesome.


References

Carpenter, F. M. (1960) Studies on North American Carboniferous Insects. I. The Protodonata. Psyche 67:98-110, 1960

Chapelle, G. and Peck, L. S. (1999) Polar gigantism dictated by oxygen availability. Nature 399: 114-115.

Dudley, R. (1998) Atmospheric oxygen, giant Paleozoic insects and the evolution of aerial locomotor performance. The Journal of Experimental Biology 201, 1043–1050

Grimaldi, D. and Engel, M. S. (2005). Evolution of the Insects. Cambridge University Press

May, M. L. (1982) Heat exchange and endothermy in Protodonata. Evolution, 36(5), pp. 1051-1058

Rehn, A. C. (2003) Phylogenetic analysis of higher-level relationships of Odonata. Systematic Entomology, 28, 181-239