Swollen Tarsi in Jurassic Scorpionflies: Fossils Reveal Sexual Selection in Ancient Insects
- 演化之聲
- Mar 14
- 5 min read
More than 160 million years ago, during the Middle Jurassic, a group of scorpionflies (order Mecoptera) became preserved within the fine lacustrine sediments of the Jiulongshan Formation in what is now northeastern China. These fossils, discovered in deposits belonging to the Yanliao Biota, have provided an unexpected window into the reproductive biology of ancient insects. Among eighty-seven fossil specimens examined, researchers discovered a peculiar morphological feature: the first tarsal segment of the hind legs was dramatically swollen in certain individuals, a condition never seen in typical insect legs. Intriguingly, this swollen structure appears exclusively in male specimens. This seemingly minor anatomical detail has allowed paleontologists to infer aspects of mating behavior, sexual dimorphism, and even broader ecological dynamics of Jurassic insect communities.
The eighty-seven specimens studied include eighty-six belonging to the extinct family Orthophlebiidae and a single representative of the rarer family Holcorpidae, represented by the newly described species Conicholcorpa longa. In this species, the sixth through eighth abdominal segments are greatly elongated, forming a conspicuous posterior structure typical of males within that lineage. Even more striking, however, is the pronounced swelling of the first tarsal segment on the hind legs of males in both families. Female specimens show no trace of this modification.
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