Monday 30 April 2012

An Assassin Bug from the Palaeocene of Spitsbergen Island.

The fossil Hymenopterites deperditus was first described from the Middle Palaeocene Firkanten Formation at Kapp Starostin on Spitsbergen Island in 1870. At the time it was believed to be the forewing of a wasp. In 1977 a review of H. deperditus suggested it might in fact be the wing of a seed, similar to that of a Sycamore.

In a forthcoming paper in the journal Acta Palaeonontoligica Polonica, a team of scientists lead by Torsten Wappler of the Steinmann-Institut für Geologie, Mineralogie und Paläontologie at Universität Bonn, re-examine H. deperditus and come to the conclusion it is in fact an Assassin Bug.

The Assassin Bugs, Reduviidae, are carnivorous True Bugs, often noted for their ability as mimics. Wappler et al. were not confident enough about the classification of H. deperditus to place it within a specific subfamily, but are confident enough to assign it to the Emesine-Saicine group, probably most closely related to the modern Saicinae.

(A-D) Modern Saicinid Assassin Bugs. (A) Tagalis.
inornata. (B) Polytoxus wahlbergi. (C) Saica tibialis. (D) Wings of Tagalis sp. (E-H) Hymenopterites deperditus. (E) Whole specimen with original labeling. (F) Close up of wing under normal light conditions. (G) Close up under alcohol. (H) Line drawing of wing. Abbreviations. –– Veins: Cu, cubitus; M, Media; Pcu, Postcubitus; R, Radius; Rs, radial sector; Cells: (M) cell between Cu and M; (t) triangular cell between Pcu and Cu. Scale Bars equal 1 mm.

The Saicinae are often wasp-mimics, which helps toe explain the original diagnosis of the wing as that of a wasp. The modern Saicinae are almost entirely tropical in distribution, with no known species surviving anything cooler than a Mediterranean climate. If the same is true for H. deperditus then subarctic Spitsbergen must have been considerably warmer in the Palaeocene; this is not a total surprise, other fossils from the Palaeocene of Spitsbergen have also suggested a warmer climate.

A fossil Assassin Bug has previously been described from the Cretaceous of China, but this is now thought to have been inaccurate. Assassin Bugs have also been reported from the Cretaceous of Mongolia, but not yet formally described. This makes the Palaeocene H. deperditus the oldest yet described Assassin Bug, the next members of the group appearing in the Eocene Messel Shale. The Saicinae are thought to be highly derived members of the group, suggesting that Assassin Bugs must have been around for quite a while before H. deperditus. This fits well with the known biogeography of the Assassin Bugs; they are found throughout the tropics, suggesting that the group must have come into existence before the breakup of Gondwanaland, about 100 million years ago.

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