Saturday 28 March 2015

Preservation of cellular structures in a fossil Sponge from the Middle Ediacaran of Guizhou Province, China.

Sponges are considered to be the sister group to all other groups of Animals, which is to say all other animals are more closely related to one-another than they are to Sponges and all Sponges are more closely related to one-another than to other Animals, but Sponges and other Animals are more closely related to one-another than they are to anything else. Phylogenetic studies have suggested that the common ancestor of Sponges and other Animals lived in the deep Cryogenian (the geological period that lasted from 850 to 635 million years ago) and a number of putative Sponge fossils have been found from the Cryogenian and Ediacaran (635-540 million years ago), which tends to support this hypothesis. However the simple organization of Sponge bodies, which lack specific tissues and can reform if squeezed through a sieve, makes it very hard to determine if these putative Sponges are true members of the group, or ‘Sponge-grade organisms’, which may be ancestral to Sponges, other Animals, both or neither.

In a paper published in the Proceedings of the National Academy of Sciences of the United States of America on 9 March 2015, Zongjun Yin and Maoyan Zhu of the State Key Laboratory of Palaeobiology and Stratigraphy of the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences, Eric Davidson of the Division of Biology at the California Institute of Technology, David Bottjer of the Department of Earth Sciences at the University of Southern California, Fangchen Zhao, also of the State Key Laboratory of Palaeobiology and Stratigraphy of the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences, and Paul Tafforeau of the European Synchrotron Radiation Facility describe a Sponge-like fossil from the Doushantuo Formation of Guizhou Province, China.

The Doushantuo Formation outcrops across much of South China, and has produced a large number of spectacular microfossils showing a remarkable level of cellular preservation, including fossils interpreted as possible embryos, dating from between 635 and 551 million years ago. Unlike other fossil sites producing such remarkable levels of preservation, it is interpreted as having formed in a high-energy, wave dominated environment, which led to the preservation of small biological particles in phosphatised granules, but not the preservation of larger structures such as body fossils of non-microscopic Animals. The possible Sponge comes from a gray oolitic dolomitic phosphorite layer exposed at the Badoushan Phosphorite Mining Quarry in Weng’an County in Central Guizhou, which is interpreted to be about 600 million years old.

The fossil is named Eocyathispongia qiania, where ‘Eocyathispongia’ means ‘Dawn-cup-shaped-Sponge’ and ‘qiania’ is a term for Guizhou Province. It is approximately 1.2 mm by 1.1 mm, and comprises three cup-shaped tubes emerging from a common base. These tubes have numerous pore-like openings, which if this organism was biologically similar to a modern Sponge would be inflow channels through which the filter-feeding Animal drew water prior to expelling it through the larger openings at the end of each tube. The outer surface of the fossil is covered by flattened cells 8–12 μm in diameter; these are split into two classes, with oval cells being consistently larger than circular ones, implying that cellular differentiation was present (something found in all Animals, including Sponges, but not usually in colonies of single-celled organisms).

Scanning electron micrograph of Eocyathispongia qiania showing the main tubular chamber with a large opening and additional chambers viewed from the exterior. Yin et al. (2015).

Based upon the available data, Yin et al. interpret Eocyathispongia qiania as being a genuine Sponge, albeit one that lived prior to the differentiation of the group into its modern orders. The cellular structure of the fossil resembles modern Sponges, though it does not show preserved choanocyte cells (flagella bearing cells which drive the movement of water through the Sponge) would be the best indicator of a true Sponge, it does have a structure that would be difficult to interpret in any other way, and dates from approximately the same time as the earliest Doushantuo specimens interpreted as Cnidarians (the group that includes modern Jellyfish, Corals and Sea Anemones) and Bilaterians (all animals other than Sponges, Cnidarians and Ctenaphores – Comb Jellies).

See also…

An enigmatic animal from the Australian continental shelf, with possible similarities to some members of the Ediacaran Fauna.

The Ediacaran Fauna comprises a group of fossils from the Late Ediacaran Period, found at sites around the world and pre-dating the Cambrian Explosion, which is considered to indicate the origin of the majority of modern animal groups, and in particular those with mineralized skeletons. Some biologists have suggested that these organisms represent an entirely separate experiment...

The fossils of the Ediacaran Period record the first widespread macrofossils in the rock-record. Many of these fossils do not appear to belong to any modern group, but instead are thought to belong to an extinct taxa (sometimes known as ‘Vendobionts’), which may-or-may-not be related to modern Animals, though some fossils have been linked to Sponges (a group which also has...

Sponges are curious creatures. They are considered to be animals as they are multicellular and some of them have fixed body shapes, however they show no cell differentiation, and can be broken down into individual cells (by, for example, forcing them through a sieve) and they will re-assemble themselves without apparent...

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