Abstract
BackgroundMany extant male animals exhibit exaggerated body parts for display, defense or offence in sexual selection, such as male birds of paradise showing off colorful and elegant feathers and male moose and reindeers bearing large structured antlers. For insects, male rhinoceros and stag beetles have huge horn-like structure for fighting and competition and some male Leptopanorpa scorpionflies have very long abdominal terminal segments for sexual display and competition. Fossil records of insects having exaggerated body parts for sexual display are fairly rare. One example is two male holcorpids with elongate abdominal segments from sixth (A6) to eighth (A8) and enlarged male genitalia from Eocene, suggesting evolution of these characters occurred fairly late.Principal FindingsWe document two mecopterans with exaggerated male body parts from the late Middle Jurassic Jiulongshan Formation in northeastern China. Both have extremely extended abdominal segments from A6 to A8 and enlarged genitalia, which might have been used for sexual display and, to less extent, for fighting with other males in the competition for mates. Although Fortiholcorpa paradoxa gen. et sp. nov. and Miriholcorpa forcipata gen. et sp. nov. seem to have affinities with Holcorpidae, we deem both as Family Incertae sedis mainly due to significant differences in branching pattern of Media (M) veins and relative length of A8 for F. paradoxa, and indiscernible preservation of 5-branched M veins in hind wing for M. forcipata.Conclusions/SignificanceThese two new taxa have extended the records of exaggerated male body parts of mecopterans for sexual display and/or selection from the Early Eocene to the late Middle Jurassic. The similar character present in some Leptopanorpa of Panorpidae suggests that the sexual display and/or sexual selection due to extremely elongated male abdominal and sexual organs outweigh the negative impact of bulky body and poor mobility in the evolutionary process.
Highlights
Holcorpidae is an enigmatic and controversial extinct family in Mecoptera, which has been documented and debated since 1878
All specimens are deposited in the Key Lab of Insect Evolution & Environmental Changes, College of Life Sciences, Capital Normal University, Beijing, China (CNU, Dong Ren, Curator)
The second is the abdominal segments 6 (A6) to A8 exceedingly elongate and male genitalia enlarged, which are present in some species of Orthophlebiidae from the late Middle Jurassic of Inner Mongolia, China
Summary
Holcorpidae is an enigmatic and controversial extinct family in Mecoptera, which has been documented and debated since 1878. Many authors have subscribed to the view of not considering Holcorpa as a panorpid, and have mentioned the name ‘‘Holcorpidae’’ in some cases It is Willmann [5] who provided a description distinguishing and defining the family as required by article 13 of the International Code of Zoological Nomenclature [6] for family names published after 1930. In 2010, Archibald distinguished Holcorpa from all known Panorpidae by a combination of diagnostic characters: (1) fore-, and hind wing media veins with five branches; (2) abdominal segments 6 (A6) to 8 (A8) elongate (both male, female), with A8 distinctly longest; (3) male: extended, slender dististyli, lacking basal tooth [7]. Male rhinoceros and stag beetles have huge horn-like structure for fighting and competition and some male Leptopanorpa scorpionflies have very long abdominal terminal segments for sexual display and competition. One example is two male holcorpids with elongate abdominal segments from sixth (A6) to eighth (A8) and enlarged male genitalia from Eocene, suggesting evolution of these characters occurred fairly late
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