Abstract
Abstract. A male representative of the extinct species Calomicrus eocenicus Bukejs et Bezděk, 2014 (Chrysomelidae: Galerucinae) is found and described for the first time from Eocene Baltic amber using X-ray microtomography. The aedeagus is well preserved within the body cavity of the specimen, and it is illustrated in detail. This fossil species exhibits distinct sexual dimorphism: the male has a smaller total body size, as well as a copula-adapted modification in abdominal ventrite 5 (apical margin deeply trilobed, with round medial fovea present); meanwhile the female is larger in body size and has a simple abdominal ventrite 5 (without fovea, non-incised and widely rounded apically). Similar sexually dimorphic characters are typical for extant members of the tribe Luperini, and this report is the first time that they are described in an Eocene species. The known sexually dimorphic characters present in Coleoptera within Eocene Baltic amber are briefly discussed.
Highlights
Records of Galerucinae sensu stricto from fossil resins are scarce
Calomicrus eocenicus was originally described based on a single female specimen
Secondary characteristics develop within each sex to facilitate ecological, behavioural and other differences between specimens belonging to each sex. Features such as wing development, antennal length ratios, the form and size of sense organs or mandibles, tarsal setation and dilatation, horns, teeth, and different structural modifications of the exoskeleton, total body size, and colour variability are among the many well-known sexually dimorphic characters in Recent Coleoptera (Arrow, 1951; Crowson, 1981; Klausnitzer, 2002; Gullan and Cranston, 2014)
Summary
Records of Galerucinae sensu stricto (excluding Alticini) from fossil resins are scarce. Until now only four species have been described: Leptonesiotes virkkii Santiago-Blay, Poinar et Craig, 1996 from middle Miocene Dominican amber (20.43–13.65 Ma) (Santiago-Blay et al, 1996); Calomicrus eocenicus Bukejs et Bezdek, 2014 from middle Eocene Baltic amber (Bartonian, 41.2–37.8 Ma) (Bukejs and Bezdek, 2014); Calomicroides danicus Nadein, 2015 from upper Eocene Danish (Scandinavian) amber (37.2– 33.9 Ma) (Nadein et al, 2015); and Taimyraltica calcarata Nadein, 2017 from Upper Cretaceous Taimyr amber (85.8– 84.9 Ma) (Nadein and Perkovsky, 2018). Calomicrus eocenicus was originally described based on a single female specimen. The male of C. eocenicus from Baltic amber is described. The external sexually dimorphic characters are described, and the original species concept (based on the female holotype only) is revised. The available data on sexual dimorphism in fossil Coleoptera from Eocene Baltic amber are briefly discussed. A. Bukejs et al.: Description of the male of fossil Calomicrus eocenicus Bukejs et Bezdek
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