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2 Acta Palaeontologica Polonica

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The Australasian muricid gastropod Lepsiella as Pleistocene visitor to southernmost South America

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Gordillo S. , Nielsen S. N.

Acta Palaeontologica Polonica

2013

tom 58

nr 4

Six shells belonging to a muricid gastropod species were recovered from a Pleistocene marine raised beach located on Navarino Island, in southern South America. None of the living species in the Beagle Channel or in the area is close, and none of the fossil species in the vicinity regions shows the diagnostic characters of the Navarino Pleistocene fossils. Our material resembles Lepsiella baileyana from southern Australia, although some differences in the suture and in the spire outline are recognized. Haustrinae were previously confined geographically to New Zealand and to the temperate coast of Australia, now extending its range of distribution to southern South America. This finding of Lepsiella ukika sp. nov. is best explained on the basis of transoceanic migration from Australasia by means of the Antarctic Circumpolar Current perhaps during a Quaternary glacial period. The presence of this Pleistocene visitor in southern South America is important because it clearly demonstrates that transcontinental traverse of taxa with direct (non−planktonic) development might have happened by rafting on kelp that served as transport platforms.

Live-live and live-dead interactions in marine death assemblages: The case of the Patagonian clam Venus antiqua

100%

Gordillo S. , Archuby F.

Acta Palaeontologica Polonica

2014

tom 59

nr 2

In this work we studied bioerosion and encrustation on dead shells of the shallow benthic clam Venus antiqua from Patagonia Argentina with the aim of understanding biotic interactions (live/live interaction) and postmortem encrustation (live/dead interaction). In this regard, drill hole analysis and epibiont distribution in shells from modern death assemblages were performed. Additionally, we analyzed crushing traces in the shells of the drilling gastropod Trophon geversianus, which were caused by another predator. The analysis of drill hole placement and epibiont distribution on V. antiqua shells show drill holes (75%) and the epibiont Crepidula spp. (70.91%) more concentrated in the upper sector of the valve, which might be explained by the vertical position and a semi-infaunal mode of life in this clam. Nevertheless, the presence of drill holes in the lower sector of the valve indicates that clams spent part of the time reclining on the sediment. There is also evidence that clams with Crepidula spp. as commensals are less frequently attacked by drilling gastropods. Besides, a high percentage of articulated clams (30.97%) show signs of attack by drilling gastropods, but incomplete drill holes (7.67%) also suggest failed attempts, resulting in a minimum of 23.30% of successful predation. These incomplete drill holes may suggest failed attempts due to another predator attack upon the snails consuming the clams thus interrupting the feeding activity: more than 60% of marks of crushing in T. geversianus shells could have been produced by other predators, such as crabs. The postmortem encrustation on V. antiqua shells (35%) was mainly produced by calcareous polychaetes, preferably located on the inner side of the valve indicating that the empty shells of V. antiqua served as cryptic environment before they become exposed on the beach. Finally our data show that drilling frequency is very low in Pleistocene assemblages, suggesting changes in burial depth dynamics of this suspension feeder.