PT  - JOURNAL ARTICLE
AU  - Sperling, E. A.
AU  - Pisani, D.
AU  - Peterson, K. J.
TI  - Poriferan paraphyly and its implications for Precambrian palaeobiology
AID  - 10.1144/SP286.25
DP  - 2007 Jan 01
TA  - Geological Society, London, Special Publications
PG  - 355--368
VI  - 286
IP  - 1
4099  - http://sp.lyellcollection.org/content/286/1/355.short
4100  - http://sp.lyellcollection.org/content/286/1/355.full
SO  - Geological Society, London, Special Publications2007 Jan 01; 286
AB  - Well-supported molecular phylogenies, combined with knowledge of modern biology, can lead to new inferences about the sequence of character acquisition in early animal evolution, the taxonomic affinity of enigmatic Precambrian and Cambrian fossils, and the Proterozoic Earth system in general. In this paper we demonstrate, in accordance with previous molecular studies, that sponges are paraphyletic, and that calcisponges are more closely related to eumetazoans than they are to demosponges. In addition, our Bayesian analysis finds the Homoscleromorpha, previously grouped with the demosponges, to be even more closely related to eumetazoans than are the calcisponges. Hence there may be at least three separate extant ‘poriferan’ lineages, each with their own unique skeleton. Because spiculation is convergent within ‘Porifera’, differences between skeletonization processes in enigmatic Cambrian taxa such as Chancelloria and modern sponges does not mean that these Problematica are not organized around a poriferan body plan, namely a benthic, sessile microsuspension feeding organism. The shift from the anoxic and sulphidic deep ocean that characterized the mid-Proterozoic to the well-ventilated Phanerozoic ocean occurs before the evolution of macrozooplanton and nekton, and thus cannot have been caused by the advent of faecal pellets. However, the evolution and ecological dominance of sponges during this time interval provides both a mechanism for the long-term generation of isotopically-light CO2 that would be recorded in carbon isotopic excusions such as the ‘Shuram’ event, and an alternative mechanism for the drawdown and sequestration of dissolved organic carbon within the sediment.