QA_Vol 24_No 1_July 2007 - Australasian Quaternary Association

ResultsMicrofossilsThe quantitative yields of ostracods and molluscs(fragments and intact shells) recovered from outcropsamples of the Slippery Dip section are presented inTable 2 and Figure 4 (overleaf). (Photomicrographs ofrepresentative fauna are shown in Plates 1 (ostracods)and 2 (molluscs), available online at: www.aqua.org.auThroughout the lower 202 cm of the section there isan abundance and diversity of microfossils, bothostracods and molluscs, although there does seem tobe a slight increase in diversity of mollusca between202 and 338 cm above its base (Austropyrgus sp. adultsbecome more numerous). This diversification coincideswith a marked drop-off in ostracod species diversity.Nine species of ostracods are identified here, includingone that is apparently new.The mollusca in the lower unit belong mainly to thegastropod family Hydrobiidae. In addition, there arerare specimens of the land snail family Charopidae.The zone of least diversity is just below the palaeosol.Above this level, there is a gradual increase in microfossilabundance. Fossils in the thinly bedded upperunit above the palaeosol are less well preserved andmore fragmented than those below.Ostracods(Plate 1: see www.aqua.org.au)Candonids (possibly Candonopsis sp. or Candonopsistenuis). Candonopsis tenuis: is only known as a freshwaterform (De Deckker, 1982a).Candonocypris novaezelandiae: a freshwater, benthicspecies common in farm dams and eutrophic waterbodies; often found grazing on decaying vegetabledebris and black organic-rich mud; adults have notbeen observed to swim, in contrast to juveniles, whichare good swimmers (De Deckker, 1981a, 1982c).Cypretta sp.: good swimmer in freshwater, includingslowly flowing river; uncommon in temporary pools (DeDeckker, 1982a).Darwinula sp.: found mostly in freshwater, but are alsofairly tolerant of a wide range of conditions; their eggscannot tolerate desiccation such that their presenceindicates a permanent water body (De Deckker, 1982a;Yilmaz and Külköylüo lu., 2006). The Darwinula of thislocality are similar to the type described by De Deckker(1982a) from Tasmania.Gomphocythere sp.: potentially a new ostracod genus orspecies (P. De Deckker, pers. com.). Park and Martens(2001) have described a similar extant form from LakeTanganyika. The new endemic species there has beennamed Gomphocythere woutersi and was collectedfrom a water depth of 18 m on a sandy substrate. It ischaracterised by the pitted tubercle ornamentation onits valves. As no species like it, either extant or extinct,has been described in Australia, its value as a paleoenvironmentalindicator is uncertain. It is interestingto note, however, that its occurrence along the sectionparallels that of Gomphocythere sp.Gomphodella maia: presence generally indicatespermanent water conditions, although it is possiblethat they burrow in sediment during times of desiccation;they require permanent water to reproduce.De Deckker (1980, 1981c, 1982a,b).Ilyodromus viridulus: considered a freshwater speciesand has never been found in brackish waters (DeDeckker, 1982c). Most Ilyodromus species in Australiaare freshwater forms that favour organic-rich sedimentsas substrates (De Deckker, 1982b).Lymnocythere mowbrayensis: a benthic species stillextant in South Australia (De Deckker, 1981b). It cannotswim and is usually found crawling among filamentousalgae in permanent fresh water, but can tolerate watersof up to 6% salinity in ephemeral locations (De Deckker,1981b, 1982b).Mesocypris sp.: taxonomy of this form is uncertain butthis genus is found in slow flowing fresh waters andswampy areas (De Deckker, 1982a).Mollusca(Plate 2: see www.aqua.org.au)The main molluscs identified in this section belongto two families of gastropods, the Hydrobiidae and theCharopidae.Austropyrgus sp. seems to be the most prominentspecies of Hydrobiidae, with both adult and juvenileforms present. Extant examples live mainly in streamsand springs, including those of the Flinders Ranges.It needs permanent water.A second new genus or species of gastropod also seemsto be present in the section. It looks like a living phreaticspecies from the Flinders Ranges, presently beingdescribed by Dr Winston Ponder at the AustralianMuseum, Sydney. What it indicates about the environmentis still unknown.A few unassigned examples of the Charopidae wereidentified. These are native land snails associated withdamp vegetation (W.F. Ponder, pers. comm.).23 | Quaternary AUSTRALASIA 24 (2)