Copelatus convexus ( Foerster , 1891) Foerster, 1891

Martin, Fikacek, Hajek, Jiri & Schmied, Heiko, 2011, On the identity of the fossil aquatic beetles from the Tertiary localities in the southern part of the Upper Rhine Graben (Coleoptera, Hydrophilidae, Dytiscidae), ZooKeys 78, pp. 15-25 : 16-18

Copelatus convexus ( Foerster, 1891) comb. n. Figs 1-4

Escheria convexa Förster 1891: 359, plate XI, Figs 9a,b (original description from Brunstatt); Handlirsch 1908: 767 (catalogue).

Hydrobius convexus : Théobald 1937: 168, plate XII, Fig. 29 (transferred to Hydrobius , recorded from Kleinkems); Hansen (1999: 319, catalogue).

WWW site on Wikispecies.

http://species.wikimedia.org/wiki/Copelatus_convexus

Material examined.

Neotype, by present designation (NHMB): R91 (imprint) + R74 (counter-imprint) from the locality of Kleinkems (SW Germany, ca. Eocene-Oligocene boundary): fossil of the whole beetle in dorsal view, head, pronotum and elytra almost completely preserved; appendages missing.

Redescription.

Body oblong-oval, broadest in basal third of elytra. Head relatively broad; compound eyes large, not exceeding body outline; clypeus rounded. Pronotum broadest between posterior angles, lateral margins regularly, moderately curved. Mesoscutellar shield well preserved, broadly triangular. Base of elytra as broad as pronotal base; lateral margins of elytra moderately curved. Only mesocoxae, part of metathoracic anepisternum, and probably part of apical abdominal ventrite perceptible from ventral part of body (Figs 1-4).

Surface sculpture. Pronotum with distinct longitudinal median impression, and poorly perceptible short longitudinal striolae on disc. Elytra with 12 moderately impressed longitudinal striae.

Measurements. TL: 6.3 mm, TL-h: 5.6 mm, TW: 3.2 mm. EL: 5.2 mm.

Notes on the type material.

Theneotype corresponds well with the original description and drawings by Förster (1891) in the following characters: (i) general body shape; (ii) shape of the pronotum with projecting anterior angles; (iii) elytra with large number of longitudinal striae [preserved only in posterior portion of elytra in the holotype and their number is therefore estimated by Förster (1891) to be at least 10; 12 striae are present in the specimen from Kleinkems]; (iv) shape and proportion of the scutellar shield [much wider than long]; (v) body size [TL = 6.5 mm, EL = 4.3 mm, TW = 3.8 mm for the specimen from Brunstatt according to Förster (1891)]. The body proportions differ slightly between both specimens (the specimen from Brunstatt is relatively wider), but this may easily have been caused by deformation during the fossilization process or by the inaccuracy of the drawings by Förster (1891) which is quite usual for historic authors (e.g., compare the drawings by Théobald (1937) in Figs 6 and 12 with the actual appearance of the respective fossils). Moreover, Förster (1891) mentioned that his fossil resembles the dytiscid genus Agabus in most characters and did not assign it to the Dytiscidae merely because of its ventral morphology which was reconstructed by him as resembling that of Polyphaga (Fig. 5). It seems that Théobald (1937) examined Förster’s types as he mentioned certain details which are absent in Förster’s (1891) original publication, and his opinion about the conspecificity therefore also has to be considered as a strong argument.

The reasons provided above together with the same age, geological origin and geographical proximity of both outcrops (Brunnstatt and Kleinkems) provide strong support for the conspecificity of both specimens mentioned by Théobald (1937). As the specimen from Brunstatt (i.e., the holotype) is lost, we consider it adequate to designate the specimen from Kleinkems as the neotype.

Generic attribution.

The preserved characters of the ventral morphology, i.e. the narrow metathoracic anepisternum arising from the median coxal cavity and the anepisterno-metaventral suture directed lateroposteriad correspond closely with the ventral morphology of the Dytiscidae (see, e.g., Fig. 7.6.1 in Balke (2005)). The hydrodynamic body shape, large eyes, broad mesoscutellar shield, medium body size and distinct elytral striae enable us to classify the specimen without any doubt as belonging to the genus Copelatus Erichson, 1832 of the family Dytiscidae .

Copelatus is currently pantropical in its distribution and contains more than 400 described species ( Nilsson 2001). Most species of Copelatus are characterised by longitudinal elytral striae whose number has been used to group the species into species groups ( Sharp 1882); only a few species have smooth elytra (e.g., Hájek et al. 2010). Although the presence and number of elytral striae provides only limited evidence of phylogeny ( Balke et al. 2004), the species groups delimited by number and position of elytral striae are frequently used as a tool for better orientation within the genus (e.g., Guignot 1961; Guéorguiev 1968; Nilsson et al. 1997). The European species previously classified in Copelatus have elytra without striae and have been transferred to the genus Liopterus Dejean,1833 by Balke et al. (2004); they are not closely related to the fossil dealt with in this study.

Comparison with other Copelatus species.

Altogether five species of fossil Copelatus species are known: Copelatus aphroditae Balke, 2003 from Baltic amber (Eocene), Copelatus predaveterus Miller, 2003 from Dominican amber (Miocene) ( Miller and Balke 2003), and Copelatus fossilis Říha, 1974, Copelatus ponomarenkoi Říha, 1974 and Copelatus stavropolitanus Říha, 1974 from the Miocene deposit of Stavropol ( Říha 1974). The differences between all known species are summarized in Table 1.

Copelatus convexus differs from all known fossil and extant species of the genus in the presence of 12 longitudinal striae on each elytron. Sharp (1882) erected a group characterized by 12 discal striae (group 7) for a single species Copelatus interruptus Sharp, 1882 which is, however, currently classified in the genus Exocelina Broun, 1886 ( Nilsson 2007). In contrast to the fossil Copelatus convexus , this recent species has elytra with numerous short striolae rather than ‘true’ striae, see, e.g. Wewalka et al. (2010). Therefore, Copelatus convexus might be provisionally classified in a separate Copelatus convexus -group. However, it is necessary to point out that the counting of the precise number of lateral elytral striae is problematic in compressed fossils as the imprint of the submarginal stria may coincide with the lateral margin of the body or with the epipleuron. Therefore, we cannot rule out that a short submarginal stria was present in Copelatus convexus although it is not perceptible in the fossil. In this case, Copelatus convexus would belong to the Copelatus simoni -group sensu Nilsson (2001).