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Journal of Paleontology 91(6):1166–1177


Diplonychus sp. and Hydrocyrius sp. were found to inhabit the lake’s floating hyacinth mats (Orwa et al., 2015). Belostomatids are one of the few groups of aquatic


insects that can tolerate agriculture-affected and polluted water bodies. Belostomatids inhabit the length of the Enfranz River in Ethiopia, from the clean headwaters to the agriculture- dominated mouth (Mehari et al., 2014). Other nepomorphs, such as naucorids and nepids, were only found in the unaffected, upstream areas. Additionally, Belostoma sp. has been collected in the eutrophic Kipkaren River of Kenya (Aura et al., 2011) and Diplonychus sp. was found to inhabit the margins of a number of polluted Bangalore lakes in southern India (Balachandran and Ramachandra, 2010). Perhaps the most extreme case is the collection of Belostoma sp. from hydrogen sulfide-rich Cueva del Azufre in Tabasco, Mexico (Tobler et al., 2007). Belostomatids are also known to inhabit temporary environ-


ments such as rain pools (Fontanarrosa et al., 2009), agricultural fields (Das andGupta, 2010), rice paddies (Hendawy et al., 2005),


and sinkholes (Blinn and Sanderson, 1989), and are common inhabitants of ephemeral playa lakes in arid environments (Haukos and Smith, 1992). Belostomatids have been collected in the stagnant ‘buffalo-wading pools’ of Tarangire National Park on the savanna of northern Tanzania (D.G., personal observation). Merickel and Wangberg (1981) collected Belostoma flumineum along the shores of two playas near Lubbock, Texas, and Richardson et al. (1972) found one juvenile belostomatid in the Jornada Playa of New Mexico. Adult belostomatids disperse to these ephemeral environments via flight, and as a result, are often found at bright lights during the night. A few studies have even reported belostomatids inhabiting


brackish waters. Angelin et al. (2010) collected Diplonychus sp. and Belostoma sp. from an estuary in southern India with a salinity of between 4‰and 8‰(ppt). Siddiqi (2008) reported belostomatids in the marginal areas of India’s Lake Lonar, which is a hyperalkaline, saline, crater lake with a pH of ~10.5 (Siddiqi, 2008) and a salinity of up to ~6‰ (Yannawar and Bhosle, 2013). However, Badve et al. (1993) report that the marginal areas of the lake near the inflow of the freshwater springs have a pH closer to 7.5. It is in these areas that the marshes exist, and it is likely that the belostomatids inhabit these more suitable areas.


Environmental interpretation of ‘Lake Solite’.—Like their modern counterparts, many fossil belostomatids are reported from shallow, lacustrine paleoenvironments (e.g., Grimaldi and Maisey, 1990; Martínez-Delclòs et al., 1995; Prokop and Nel, 2000). However, this contrasts with both interpretations of the paleoenvironment of the Cow Branch Formation. Olsen et al. (1978) first described the environment as a large, deep, chemically stratified lake. This stratification would have produced anoxic bottom waters that prevented bioturbation and therefore allowed for exquisite fossil preservation of delicate insects such as midges and tiny hemipterans. Although unusual for a modern belostomatid habitat, other deep lacustrine paleoenvironments have been reported to contain belostomatid fossils. One such deposit, the late Oligocene Enspel Formation of Germany (Poschmann et al., 2010), has produced ten belostomatid fossils, four of which are adult specimens (Wedmann, 2000).


Recent research by Liutkus et al. (2010) proposed that


the Cow Branch Formation was a shallow, alkaline, saline, rift valley lake. They presented a number of reasons for this interpretation: (1) dominance of terrestrial and nearshore- dwelling insects and terrestrial vascular plants, (2) exquisite fossil preservation, and (3) presence of dolomite and absence of quartz and zirconium throughout the deposit. Based on the environmental preferences of modern


belostomatids, their abundance in the Cow Branch Formation would indicate a shallow, nearshore paleoenvironment. The tolerance of modern belostomatids for polluted and harsh water conditions suggests they may have also been tolerant to extreme environments such as saline, alkaline, rift valley lakes. Because belostomatids breathe air, they would be unaffected by poor water quality. However, harsh water conditions would affect organisms possessing gill respiration (i.e., Ephemeroptera, Plecoptera, Odonata, Trichoptera, etc.), so the lack of gilled insect nymphs of these orders within the deposit is good evidence for poor water quality. The only gilled insect order reported from the Cow Branch Formation is Diptera (Liutkus et al., 2010). However, this appears to be a misidentification of the enigmatic, gilled, larva-like arthropod, which may actually be a crustacean. In addition to belostomatids, the insects preserved in the


Cow Branch Formation are mostly terrestrial adults from the orders Hemiptera (Sternorrhyncha), Diptera, and Coleoptera. A few other taxa have been found to date, including adult members of Blattodea, Odonata, Orthoptera, Plecoptera (Fraser and Grimaldi, 2003), Thysanoptera (Grimaldi et al., 2004), Mecopterida (Grimaldi et al., 2005), Amphiesmenoptera, and Neuroptera. This unique assemblage of terrestrial insects further suggests that the water was toxic to gill-possessing, aquatic larvae and other sensitive groups. Moreover, Fraser and Grimaldi (1999) noted the abundance of conchostracans within the insect bed. Modern members of this group are most commonly found in ephemeral, alkaline water bodies (Tasch, 1969).


Liutkus et al. (2010) discussed the exquisite preservation of


the insect fossils as evidence for a shallow lake. Most insects are completely articulated, which is quite rare for Triassic fossils (cf., Riek, 1974; Brauckmann and Schlüter, 1993; Shcherbakov et al., 1995; Martins-Neto et al., 2008). The lack of disarticula- tion suggests limited postmortem movement. If the lake had been as deep as originally suggested, the insects would likely have decayed, disarticulated, or have been eaten before settling to the benthic zone. Moreover, there are no fossil fish found in the insect layers, further evidence that the insects were buried in very shallow water. The geochemistry of the deposit also supports the


interpretation of a saline, alkaline lake. Liutkus et al. (2010) reported dolomitic claystone throughout the insect bed, and in modern lakes primary precipitation of dolomite occurs most often in waters with elevated salinity, alkalinity, and with abundant magnesium and calcium (DeDeckker and Last, 1989). Furthermore, the surrounding basin is rich in quartz, making its absence in the Cow Branch deposit significant. In addition, albite is abundant in the deposit (Liutkus et al., 2010), which is proposed to have formed by the reaction of clay, quartz, and sodium under alkaline conditions (van de Kamp and Leake,


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