Bizarre morphology in extinct Eocene bugs (Heteroptera: Pentatomidae)

Abstract

Newly discovered fossil bugs (Insecta: Hemiptera: Heteroptera:Pentatomidae) from the Eocene of Messel (Germany) andGreen River (North America) exhibit an exaggeratedmorphology including prominent spiny humeral andanterolateral angles of the pronotum and a spiny lateralabdominal margin. Especially the humeral angles are unique;they consist of expansive, rounded projections with strongspines, which is a rare trait among pentatomids. A hypothesisfor the function of this extreme morphology is defence againstsmall vertebrate predators, such as birds or reptiles. The sameprotuberances also produce a disruptive effect camouflagingthe specimen in its environment and provide additionalprotection. Therefore, the extreme morphology providesprimary as well as secondary anti-predator defence. Themorphology ofEospinosus peterkulkaigen. et sp. nov. andE. greenriverensissp. nov. resembles that of Triplatygini, whichtoday occur exclusively in Madagascar, as well as that ofDiscocephalinae or Cyrtocorinae, which today occur in theNeotropics. Due to a lack of conclusive characters, it cannot beexcluded that the fossil species may represent a case ofremarkable convergence and are not related to either taxon.Phylogenetic analyses using parsimony as well as Bayesianalgorithms confirmed that the new genus is a member ofPentatomidae, but could not solve its phylogenetic relationships within Pentatomidae.