Baltic Ordovician compound sponges as erratics on Gotland (Sweden), in northern Germany and the eastern Netherlands

Abstract

Compound orchocladine sponges are unusual in the Early Palaeozoic. In Europe, silicified material of Late Ordovician age has hitherto been referred to as Aulocopium aurantium Oswald, 1847 and the invalid Aulocopium compositium Conwentz, 1905. An examination of new material has resulted in the recognition of a new genus, Hydraspongia, with two new species, H. polycephala and H. erecta, and a third new species, Perissocoelia megahabra, to which most specimens can now be assigned. These taxa form part of rich erratic sponge assemblages, which originate from unknown source areas in the Baltic, and have been collected in northern and western Europe from fluvial sandy deposits of the Eridanos River system, which drained the Baltic area from the Middle Miocene to Early Pleistocene.

A new Silurian (Llandovery, Telychian) sponge assemblage from Gotland, Sweden

“…Hydraspongia Rhebergen, 2007 includes compound sponges that usually form bulbous oscular heads and show conspicuously distinct growth stages. Postperissocoelia n. gen. resembles Hydraspongia in general form, but the latter is composed of dendroclones and chiastoclones, and didymoclonelike spicules are absent.…”

“…Canals that achieved their maximum length induced the formation of a new cluster of excurrent canals, in order to drain the newly formed parts. This continuous growth apparently caused the development of new oscular heads, while the formation of stacked skeletal trabs series continued uninterrupted (Rhebergen 2007).…”

“…Rhebergen & van Kempen (2002) summarized a discussion between Lindstr€ om, Schmidt (1891) and Stolley (Stolley 1900(Stolley , 1929 on the age and lithostratigraphical origin of the sponges. Lindstr€ om probably intended to describe at least part of the sponge assemblage, because he had drawings made by Lilljeval, but did not complete the work (Rhebergen 2007). Schl€ uter (1884) reported on a remarkable sponge specimen, Astylospongia gothlandica, which has been figured by Rauff (1894) as an aberrant form of the Ordovician species Caryspongia diadema.…”

Unusual Deep Water sponge assemblage in South China—Witness of the end-Ordovician mass extinction

“…Many fossils have been found from the rocks chronostratigraphically corresponding to the interval from the first episode of the end-Ordovician mass extinction to the latest Ordovician, such as brachiopods, trilobites, corals, graptolites and so on 6 7 8 . Sponges are rare in this interval, and only lithistids and stromatoporoids have been sporadically documented 9 10 11 . Although many new discoveries show that the non-lithistid spicular sponges (especially the Burgess Shale-type faunas) are known from a broad range of times, and not restricted to the Cambrian, there are still large gaps in the fossil records of non-lithistid spicular sponges during the Late Ordovician 12 13 14 .…”