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Popular Science: Giant dragonflies and their way of life – reconstruction based on fossil findings

The maximum wingspan of dragonflies these days is about 19 cm, but in the Late Palaeozoic (approximately 300 Mya), the largest representatives of the Meganeuridae family had a wingspan of about 71 cm. They were thus the largest known insects ever and previously there were already some hypotheses, based on (unfortunately often incomplete) fossil findings and on comparisons with modern-day species, about how these flying colossuses lived. However, an international French-Czech-US team, together with Jakub Prokop and Martina Pecharová from the Department of Zoology of the Faculty of Science, showed that these speculations were not correct and proposed a more probable scenario.

As you can imagine, it is hard to retrospectively reconstruct the biology of an extinct insect, especially if we can only construct our theories solely on wings or isolated body parts that have been preserved as fossils. Researchers thus usually compare body structures with closest extant related organisms and, based on this analysis, they propose the most likely living conditions of the extinct animal. These conclusions may, however, not always correspond to reality, as the ancient ancestor and descendant can differ greatly and the biology of modern animals cannot be simply extended to extinct organisms without a detailed study of all anatomical details and even other factors like environmental conditions in the respective periods.

Representatives of the family Meganeuridae are distantly related to modern dragonflies and damselflies (order Odonata), so many aspects of odonate biology have been supposed to be similar in the extinct meganeurids. However, these conclusions have been made without knowledge of their detailed body anatomy and based on incompletely preserved fossils. On the other hand, specimens (especially one of them) of the species Meganeurites gracilipes from the Gzhelian (a period at about 300 Mya in the geologic timescale) outcrop of Commentry (France) have demonstrated well preserved head structures, as well as other body parts (e.g. wings, legs). This species has not been revised so far, so it was a great opportunity for the team to potentially reveal the unknown aspects of the meganeurid biology based on the morphological observations of these specimens.

Model of the revised dragonfly species Meganeurites gracilipes in comparison with a human hand. Photo: Petr Šípek.

The authors found some parallels to modern odonates, such as strong and robust mandibles with large, sharply acute teeth and legs with strong spines functioning most likely as a “flying trap” for capturing prey. This indicates a predatory way of life of the examined species, and probably of all other representatives of the family Meganeuridae. The leg position, which is more forward, suggests that it should probably allow the animal to grasp and manipulate objects, such as prey, in front of its head. In order to evade their own predators, who were probably larger species of this family, such as M. monyi (wingspan of approx. 70 cm), they had to have very good vision enabling the detection of predators (but also prey) against a blue sky: enlarged compound eyes with broad dorsal parts known in extant hawker dragonflies (family Aeshnidae).

Even though their flight was probably comparable to current odonates, it was not that “spectacular” - it surely lacked the capacity to twist the wings because of the absence of a node (see the illustration of the body scheme) or to make abrupt directional flight changes. Meganeurids were therefore more likely “hawkers” in open-space, transitional zones between open-space and forest, or areas close to rivers or streams and they were probably patrolling for prey above large rivers, lakes, open forests or canopies.

Nel A, Prokop J, Pecharová M, Engel MS, Garrouste R, 2018: Palaeozoic giant dragonflies were hawker predators. Sci Reports 8:12141.

Darina Koubínová

Published: May 27, 2019 07:05 AM

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