Gerromorpha (STYS & KERZHNER, 1975)

Damgaard, Jakob, 2008, Evolution of the semi-aquatic bugs (Hemiptera: Heteroptera: Gerromorpha) with a re-interpretation of the fossil record, Acta Entomologica Musei Nationalis Pragae 48 (2), pp. 251-268 : 252-254

Fossil Gerromorpha

While the Nepomorpha (aquatic bugs) has a very extensive fossil record dating back into the Triassic ( POPOV 1971), the Gerromorpha has by comparison left much fewer fossils ( GRIMALDI & ENGEL 2005: Fig. 8.62). Those fossils that are available range from beautiful amber inclusions with lots of details preserved (e.g. ANDERSEN & POINAR 1992) to rock impressions of various qualities (e.g. ANDERSEN 1998, WAPPLER & ANDERSEN 2004). According to GRIMALDI & ENGEL (2005), the oldest fossil gerromorphan bug is Karanabis kiritschenkoi Bekker-Migdisova, 1962 from the Upper Jurassic (152 million Ma) of Kazakhstan, which was initially assigned to Nabidae (BEKKER- MIGDISOVA 1962), but transferred to Gerridae by POPOV (1968) and later to Mesoveliidae by POPOV & BECHLY (2007: 325). Another fossil, Engynabis tenuis Bode, 1953 from the Lower Jurassic, Posidonia Shales of northern Germany ( BODE 1953) was considered as ‘closely related to Karanabis ’ by POPOV & WOOTTON (1977: 350), and as ‘undoubtedly a member of Mesoveliidae’ by POPOV & BECHLY (2007).ANDERSEN (1998: 93) however, hesitated to accept such taxonomic assignments. According to DOLLING (2000), ANDERSEN (1998) overlooked Brodie’s mention ( BRODIE 1845), without description, of ‘ Hydrometra ’ and ‘ Velia (?)’

from the Jurassic of Britain and stated that ‘if genuine, Brodie’s fossils would be both the earliest recognition of fossil Gerromorpha in print and the oldest known representatives of the group’. BRODIE (1845: 121) mentions several specimens coming from the ‘Wealden’ and which ‘appear from their proportions to be those of species of Velia and Hydrometra , but their veins were not sufficiently clear to be figured with precision’. Brodie’s use of the term ‘Wealden’ was much broader than the definition of the term today, and it is very likely that he was referring to the Purbeck Beds of Dorset (S. W. Heads, pers. comm.). Nevertheless, both the Purbeck and Wealden groups of southern England are now considered to be Early Cretaceous in age and not Jurassic as previously thought ( MILNER & BATTEN 2002).

The earliest fossil gerromorphan bug accepted by ANDERSEN (1998) was Duncanovelia extensa Jell & Duncan, 1986 from the Lower Cretaceous (120 Ma) Koonwarra Lägerstätte of Victoria, Australia, which was assigned to Mesoveliidae by the authors ( JELL & DUNCAN 1986). Two incomplete fossils assigned to ‘ Veliidae sp.’ from the same deposit were likewise accepted with some reservations by ANDERSEN (1998: 88-89) as the oldest fossils of the Veliidae-Gerridae clade. Cretaceometra brasiliensis Nel & Popov, 2000 and Incertametra santanensis Perez Goodwyn, 2002 (both Hydrometridae ) were described from quarries in the Nova Olinda Member laminated limestone in the Araripe Basin of northeastern Brazil. These and other authors assigned all fossils from the site to the ‘Santana Formation’, thus causing considerable confusion as to the composition of the respective assemblages and their relative ages. Today it is well established that the deposition of the older (Aptian) Crato Formation (110 Ma) and the younger (?Albian) Santana Formation are discontinuous and separated by a thick series of evaporates, now called the Ipubi Formation and a stratigraphic disconformity ( MARTILL 1993, MARTILL et al. 2007: 27). Fossil from the Crato Formation were named ‘limonite (iron oxide) mummies’ by NEL & POPOV (2000: 2316) apparently due to their three dimensional structure, which differs technically from two-dimensional compression fossils. It is nearly always the cuticle that is preserved, with the soft tissues rotted away and the void space left behind filled with calcite. Specimens recovered from the weathered, creamy buff-coloured limestone are preserved as reddish-brown replacements of the initial iron sulphide (pyrite) preservations with goethite (one of the main mineral components of limonite). Fossils from the blue-grey unweathered levels of the Nova Olinda Member are preserved as a mixture of organic material and extremely fine-grained iron sulphide (pyrite or perhaps mackinawite or greigite). This oxidises in situ, and results in a specimen that is essentially replaced by goethite. In both cases goethite is the major component of the fossils, and the term ‘limonite mummies’ is therefore appropriate for this type of fossils (S. W. Heads and D. Martill, pers. comm.).

The remaining Mesozoic fossils are a few, but excellently preserved, amber inclusions from Lower-Mid Cretaceous, including Carinometra burmensis Andersen & Grimaldi, 2001 ( Hydrometridae ) from Burmese amber ( Myanmar) (100 Ma), Cretogerris albianus Perrichot, Nel & Neraudeau, 2005 (Gerridae) from Archingeay amber ( France) (100 Ma), and a complete but immature specimen from the same deposit assigned to Gerromopha, but without further affinities ( PERRICHOT et al. 2005).

Compared to the Mesozoic, many more fossils have been recorded from the Cenozoic (Tertiary). Some of the earliest fossils from this period are a specimen of Gerrinae from the Palaeocene of Menat ( France) (A. Nel, pers. comm.), and Mo clay impressions from the Palaeocene-Eocene transition (55-54 Ma) of Denmark and Germany (ANDERSEN 1998). These sites have yielded fossils of several families, including Daniovelia morsensis Andersen, 1998 (Macroveliidae) ; Eocenometra danica Andersen, 1982 b , E. longicornis Andersen, 1998 , and Palaeometra madseni Andersen, 1998 (Hydrometridae) ; and Palaeogerris furensis Andersen, 1998 , P. grandis Andersen, 1998 , and P. mikkelseni Andersen, 1998 (Gerridae) . From the Lower/Middle Eocene (52-47 Ma) are several compression fossils from western North America, including Limnoporus wilsoni Andersen, 1998 , Telmatrechus stali (Scudder, 1879) and T. defunctus (Handlirsch, 1910) from British Columbia, Canada, and T. parallelus Scudder, 1890 from Wyoming, USA. Halobates ruffoi Andersen, Farma, Minelli & Piccoli, 1994 (Gerridae) was described from the Middle/Upper Eocene boundary deposits (45 Ma) of Monte Bolca near Verona, northern Italy. Several fossils have been described from the Upper Eocene (40 Ma) Florissant Formation of Colorado, USA, including Metrobates aeternalis Scudder, 1890 , which was interpreted as an exuvium of a gerrine water strider by ANDERSEN (1998: 70); Gerris protobates Cockerell, 1927 , which ANDERSEN (1998: 70-71) found to be too incomplete to be included in Gerris Fabricius, 1794 ; and Steinovelia nigra Scudder, 1890 , which ANDERSEN (1998: 77-78) accepted as a member of Veliidae . The Eocene-Oligocene (40- 35 Ma) Baltic amber contains several inclusions, including Electrovelia baltica Andersen, 1998 (redescribed by ANDERSEN (2000)) and Balticovelia weitschati Andersen, 2000 (both Veliidae ); Hydrometra groehni Andersen, 2003 ; Limnacis succini Germar & Berendt, 1856 ; L. hoffeinsi Popov, 1996 and Metrocephala anderseni Popov, 1996 (redescribed by ANDERSEN (2000)) (all Hydrometridae ); Electrogerris kotaschevichi Andersen, 2000 ; Succineogerris larssoni Andersen, 2000 ; and Gerris sp. (all Gerridae ). Contemporary with Baltic amber are compression fossils from Eckfeld and Messel, Germany of Lutetiabates eckenfeldensis Wappler & Andersen, 2004 , Cylindrobates messelensis Wappler & Andersen, 2004 and a Gerris nymph (all Gerridae ) ( WAPPLER & ANDERSEN 2004). From the Upper Oligocene of France (22.5 Ma) is Protobacillometra oligocenica Nel & Paicheler, 1993 (Hydrometridae) and a Gerridae (A. Nel, pers. comm.), and from the Czech Republic are three fossil Gerridae ( PROKOP & NEL 2007) . From Mid Miocene Dominican amber (20-17 Mya) is a rich fossil record including Electrobates spinipes Andersen & Poinar, 1992 and Brachymetroides atra Andersen, 2001 (both Gerridae ); and Halovelia electrodominica Andersen & Poinar, 1998 , Microvelia polhemi Andersen, 1999 , M. electra Andersen, 2001 , and M. grimaldii Andersen, 2001 (all Veliidae ). The exact age of these deposits has been confused with unsubstantiated claims of Eocene age, but is now known to be of Miocene origin ( GRIMALDI 1994, ITURRALDE- VINENT & MCPHEE 1996, GRIMALDI & ENGEL 2005). Mexican amber is contemporary with Dominican amber, but so far only Stenohebrus glaesarius Polhemus, 1995 (Hebridae) has been described from this material. Also from the Miocene (24-5 Mya) is Aquarius lunpolaensis (Lin, 1981) and Halobates bagonensis Lin, 1981 from the Lunpola Basin, Baingoin Country, Xizang (Tibet), China. ANDERSEN (1998: 72) however, stated that the latter probably was exuvium of the former. Finally, a contemporary specimen assigned to Aquarius (?) sp. from the Karagan Formation in Northern Caucasus, Russia was mentioned by ANDERSEN (1998: 61), but the fossil was too incomplete for a taxonomic assignment.

Table 1 provides a checklist of all fossils that have been convincingly assigned to families and subfamilies of Gerromorpha .