ABST R AC T VOLU M E 4th INTERNATIONAL
PALAEONTOLOGICAL CONGRESS
The history of life: A view from the Southern Hemisphere
September 28 – October 3, 2014 MENDOZA, ARGENTINA
4th IN T E R NAT IONAL PAL AEON TOLOGIC AL CONGR ESS T H E H ISTORY OF LI F E : A V I E W F ROM T H E SOU T H E R N H E M ISP H E R E
ABST R AC T VOLU M E Compiler
Esperanza CERDEÑO | IANIGLA, CCT-CONICET Mendoza. Argentina
Graphic design: Remedios MARÍN | CCT-CONICET Mendoza. Argentina Text composition: Silvina Laura PEREYRA | CCT-CONICET Mendoza. Argentina
Open sessions / Oral
M I DDLE EOC EN E L A K E DE POSI TS F ROM T H E GI R A F F E PI P E C R AT E R , NORT H E R N C A NADA : A W I N DOW ON F R ESH WAT E R SPONGE EVOLU T ION Andrzej Pisera1, Peter Siver2 and Alexander Wolfe3 1. Institute of Paleobiology, Polish Academy of Sciences, ul. Twarda 51/55, Warszawa, 00-818, Poland.
[email protected] 2. Connecticut College, Botany Department, New London, Connecticut 06320, USA. 3. Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada.
The fossil record of freshwater organisms is usually less complete relative to marine counterparts, and sponges are a good example of such a situation. Today, freshwater sponges are a significant component of biotas in numerous freshwater habitats and are well studied worldwide, but their fossil history is poorly known. Marine sponges are documented since the Precambrian, but the earliest freshwater sponges do not appear in the fossil record until the Permo-Carboniferous of Europe. Mesozoic occurrences of these sponges are known from the Late Jurassic of USA, and the Lower Cretaceous of England and Patagonia. In this last region the oldest preserved gemmules (resting bodies of sponges) were found. More common freshwater sponges have been uncovered in Tertiary deposits, with records from Germany, Siberia, Japan, Chile and South Africa. Recently, middle Eocene (about 40 Ma old) lake sediments (laminated shales and massive organic mudstones) from a maar lake nestled within a kimberlite diatreme in northern Canada referred to as the Giraffe locality, have been discovered to contain a rich assemblage of siliceous microfossils, including diatoms, chrysophytes and euglyphids. In addition, these deposits contain a highly diverse association of freshwater sponge spicules, many of which display pronounced modern affinities. The sponges are represented exclusively by loose spicules; including numerous morphotypes of megascleres, amphidiscs, non-amphidisc gemmuloscleres, and microscleres. At least 8 distinct taxa can be identified based on spicule morphology, the most common belonging to Ephydatia (most probably the Recent species E. facunda Weltner), but also Radiospongilla, Spongilla, Paleospongilla, among other undiagnosed spicules. Most belong to the family Spongillidae Gray, but some belong to the family Potamolepidae Brien, know previously only from the Miocene of Japan. The diversity of the Giraffe sponge assemblage is the highest known in the fossil record and comparable with that of the present-day sponge fauna of all of Canada (15 species). Such high diversity indicates that radiation of freshwater sponges predates the middle Eocene, and that a rich, as of yet unknown, history of freshwater sponges exists. Due to its richness, diversity, and excellent preservation, the Giraffe Eocene sponge fauna is crucial in understanding the evolution of freshwater sponges.
4th INTERNATIONAL PALAEONTOLOGICAL CONGRESS, Mendoza, Argentina. 2014
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