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In the context of human evolution and dispersal in Africa, it is important to understand past climate conditions and changes as possible drivers of these processes. One of the most recent climatic events was the end of the African Humid Period (AHP) at around 5 ka BP. This was marked by a decrease in precipitation following a long wet-phase in northern and eastern Africa, which caused many lakes to decrease in size or even desiccate. Although the termination of the AHP is well known, the timing and rate of the transition from wet to dry conditions is still heavily debated. To investigate the termination of the AHP at a high temporal resolution (subdecadal and subannual), fossil stromatolites and Etheria elliptica shells from paleo-shorelines in the Chew Bahir Basin, southern Ethiopia, were collected. Today, Lake Chew Bahir is a deltaic swamp, however in past pluvials a large lake was present that likely overflowed and connected to other basins similar to other amplifier lakes in the East African Rift System. Radiocarbon dating, oxygen and carbon stable isotope analyses, trace element analyses and petrographic mapping of stromatolite laminae structure were conducted. A strong correlation between δ18O and δ13C shows that paleo-lake Chew Bahir likely experienced highly evaporative conditions and indicate an endorheic state of the basin in times of stromatolite growth at 7.1, 5.8, 4.7 and 4.6 ka BP. Furthermore, our findings suggest highly fluctuating environmental conditions during these times and demonstrate that the transition to drier conditions was not a strictly linear trend. In summary, the stromatolites and Etheria elliptica shells are an excellent environmental archive due to their high temporal resolution, precise dating (± 30 yrs) and an indication of the paleo-lake water depth. These types of records provide insights to past changes in freshwater availability, the variability of which would have had large consequences for humans living in the region.

Investigations on the accumulation of heavy metals in water and sediments of river Ogbese were carried out between December 2010 and February 2011 using Atomic Absorption Spectrophotometer. Etheria elliptica a sessile organism was also used to determine the concentration of heavy metal in the aquatic environmental. In water, Cu had the highest concentration (0.55 – 0.13 mg/l ±0.1) while in sediments, the highest value obtained was in Fe (1.46-3.89mg/l±0.27). The minimum concentrations recorded were in Pb; which was below detectable level. The result also revealed that the shell accumulate more heavy metals than the flesh of the mussel with Cu in the shell exhibiting a negative correlation with all the metals in the flesh. However, the condition factor (K) value is 6.44, an indication of good health. The length-weight relationship is expressed as W = -0.48 x L 1.94 (r2 = 0.29) showing the growth pattern to be negatively allometric., {"references":["Abdel-Baki A. S., Dkhil M. A. and Al-Quaraishy S., Bioaccumulation of\nsome heavy metals in tilapia fish relevant to their concentration in water\nand sediment of Wadi Hanifah, Saudi Arabia African Journal of\nBiotechnology, 10(13) 2011, pp2541-2547.","Asaolu S. S., Ipinmoroti K. O., Adeyinowo C. E., Olaofe O.,\nInterrelationship of heavy metals concentration in water, sediment as\nfish samples from Ondo State coastal Area, Nig. Afr. J. Sci 1, 1997, pp\n55-61.","Asaolu S.S., Chemical Pollution Studies of Coastal Water of Ondo\nState. Ph.D Thesis, Fed. Univ. Technol., Akure, 1998, Pp 45- 52.","Asaolu S. S. and Olaofe O., Biomangification factors of some heavy and\nessential metals in sediments fish and crayfish from Ondo State coastal\nregion Bio. Sci. Res. Comm. 16, 2004, pp 33-39.","Borg, H., E d n, A., Holm., Skold, E., Determination of metals in fish\nlivers by flameless atomic absorption spectroscopy Wat. Res. 15, 1981,\npp1291-1295.","Bourgoln. B. 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S, Sharma B., Analysis of some heavy\nmetals in the riverine water, sediments and fish from river Ganges at\nAllahabad. Environ. Monit. Assess. 157, 2009, pp 449-458.\n[12] Nwajei G. E., Gagophien P. O., Distribution of heavy metals in the\nsediments of Lagos Lagoon, Pak. J. Sc. Ind. Res. 43, 2000, pp 338-340.\n[13] Olawusi-Peters, O. O., Ayo-Olalusi C. I. and Adeyemi T. V.,\nBioaccumulation of some trace element (Zn, Fe, Pb and Cu) in the gills\nand tissues of Clarias gariepinus and Oreochromis niloticus in River\nOgbese, Ondo State, Nigeria. J. Envt. Chem. and Ecotox. 6(2), 2014, pp\n6-12.\n[14] Olowu R. A., Ayejuyo O. O., Adewuyi G. O., Adejoro I. A., Denloye A.\nA., Babatunde A. O., and Ogundajo A. L., , Determination of Heavy\nMetals in Fish Tissues, Water and Sediment from Epe and Badagry\nLagoons, Lagos, Nigeria .E-Journal of Chemistry,7(1), 2010, p p215-\n221.\n[15] Öztürk, M., Özözen, G., Minareci, O. and Minareci, E., Determination\nof heavy metals in fish, water and sediments of Avsar Dam Lake in\nturkey. Iran. Journal of Environment, Health. Science and Engineering\n6(2), 2009, 73-80.\n[16] WHO, Guidelines for Drinking-Water Quality: Recommendations. 2nd\nEdn., World Health Organization, Geneva, ISBN-92: 4 154460, 1993, pp\n51.\n[17] WHO, Guidelines for Drinking-Water Quality: Recommendations. 1st\nEdn., World Health Organization, Geneva, ISBN-10: 9241546387 ,\n2004, pp 515.\n[18] Soumady D. and Asokan S., A study on trace metal accumulation in\nselected organs of Perna viridis in Nagapattinam coastal waters, Tamil\nNadu, India, Inte. Pharm. Sci., 1(2), 2010, pp42-47.\n[19] Dumalaganan H. G. D. and Gonzales A. C., Trace metal content in\nmussels, Perna viridis L., obtained from selected seafood markets in a\nmetropolitan city, Bull.Environ. Contam. Toxicol., 84(1), 2010, pp492-\n496.\n[20] Mihajlo J, Ana S., Slavković-Beskoski L, Ilija T., Sandro D. and Slavka\nS., Mussels as a bio-indicator of the environmental quality of the coastal\nwater of the Boka Kotorska Bay (Montenegro). J. Serb. Chem. Soc. 76\n(6) , 2011, pp933–946.\n[21] Pyatt, F. B, Metealfe, M. R and Pyatt, A, Copper bioaccumulation by the\nfreshwater snail Lymnaea peregra: A toxicological marker of\nenvironmental and human health, Environ. Toxicol. Chem., 22, 2003,\npp561-564.\n[22] Kamaruzzaman B.Y, Mohdzahin M. S., Akbar J. B., Jalal, K. C. A.,\nShahbudin S. M, Al-Barwani and Goddard J. S., Bioaccumulation of\nsome metals by Green mussel Perna viridis (Linnaeus 1758) from Pekan,\nPahang, Malaysia. Int. J. Biol. Chem. 5(1), 2011, pp 51-60.\n[23] Pauly, D., Some simple methods for the assessment of tropical fish\nstock. 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The oxygen isotope ratios in the incremental growth layers in the shells of Etheria elliptica constitute a proxy record of rainfall patterns, and thus a record of seasonality. Analyses of shells of early Holocene age (6800 14 C years BP or 5600 BC) collected from the lower reaches of Wadi Howar, near the confluence of that now-extinct river with the Nile, show an annual pattern of two rainy seasons in the present-day hyperarid southeastern Sahara, similar to that which prevails today in much of East Africa.

Reconstruction of past environments is an essential part of evaluating the ecology of organisms including early man and assessing the pressures for evolutionary change. In this study we have demonstrated that Etheria elliptica , the freshwater oyster of equatorial Africa, accretes layers of shell having a lunar month periodicity. Separation and oxygen isotopic analyses of the individual monthly layers affords a qualitative picture of seasonal change. Fourteen monthly samples of E. elliptica , collected near Kisumu on the Winam Gulf of Lake Victoria, gave oxygen isotope ratios in the penultimate layer of their shells in excellent agreement with the individual layers of a shell whose growth covered the same period. The variation in isotope ratios correlates clearly with the rainfall pattern of that region of East Africa.

Shells of two species of freshwater bivalve ( Unio willcocksi Bullen Newton and Etheria elliptica Lamarck) from the predynastic Gerzean (Nagada II) Decorated Tomb at Hierakonpolis, Egypt have given dates of 5000±90 bp for the tomb, and 12,900±120 bp for an episode of Nile terrace accumulation (correlated here with the Sahaba-Darau aggradation event). The archaeological and geological significance of these results is discussed, together with an outline of problems associated with radiocarbon dating of shell. Comparisons are made with the few other radiocarbon dates available for the Predynastic period in Egypt and possible reasons for the presence of shells in the tomb are considered.

Acostaea rivoli (Desh.) is an etheriid bivalve which occurs, cemented to the substrate, in the basin of the River Magdalena in Colombia. The animal, apart from the shell, is here first described and compared with the two closely related species, the similarly monomyarian Pseudomulleria dalyi (Smith) from Mysore, India and the dimyarian Etheria elliptica Lam. widely distributed in tropical Africa. Attaching at an unusually late stage and by either valve, all three pass from initial bilaterial symmetry to a state of extreme bilateral and– apart from Etheria–also antero-posterior asymmetry. In Acostaea (and Pseudomulleria) this involves exclusively posterior and, because settlement is anterior end downward in a depression, topographically upward growth with a change of around 90 in the disposition of the valves as these flatten out over the substrate. This necessitates formation of a new hinge between the anterior spur which is composed of the earlier growth of both valves, and the horizontal extent of the upper valve. With loss of the anterior adductor, the monomyarian condition is achieved in a unique manner. Evidence indicates that the family Etheriidae arose from edentulous Unionidae with the adoption of a pleurothetic cemented habit, this permitting exploitation of a hard substrate often, although not invariably, in rushing water.