Mattresses, the Universe and Everything: the fossils of the Ediacaran Biota

Life on Earth 600 million years ago comprised enigmatic mattress-like organisms, but some modern ecological rules did apply

In Life, the Universe and Everything, Douglas Adams has left Marvin the Paranoid Android stranded and walking in circles (literally) on Sqornshellous Zeta. This is a swampy planet, where the dominant life form is the mattress. Marvin chats with Zem, a perky and affable pocket-sprung mattress, who encourages him to be ‘more mattressy*’. In an infinite universe, Adams tells us, very few things are manufactured, since everything has evolved somewhere, including mattresses. They are harvested and shipped out to be slept on across the galaxy.

Douglas Adams certainly liked to play around with ideas in evolution. The unlikely evolution of the babel fish was the cause of a theological existential crisis, and his bureaucratic and bad-tempered Vogons were effectively disowned by evolution as soon as they left the primordial seas of Vogsphere. What I don’t know is whether Douglas Adams had ever read about the Ediacaran biota: fossils from a time when Earth was, briefly, the planet of the mattresses.

The Ediacaran period spans nearly 100 million years below the base of the Cambrian period, 542 million years ago. Its upper boundary is defined by the appearance of preserved complex burrows (evidence of “modern” animal behaviour), while its base is marked by the end of a global, 15-million-year glaciation event. In between those two marker points, life was quite, well, mattressy.

These fossils were first studied from the Ediacara Hills of the Flinders Ranges, north of Adelaide, Australia in the 1940s. Similar assemblages were soon discovered in the Leicestershire in the UK, Newfoundland, Canada, and Namibia, and are now known worldwide, They are imprints of what, in the absence of any mineralised body parts, appear to be soft bodies, but usually preserved on the undersides of slabs of coarse-grained rocks like sandstone and quartzite, with no organic matter preserved.

The best way to describe them is as quilted organisms. Some are round blobs, others seem to have bilateral symmetry, and some even seem to have a “head end”. Dickinsonia is a common form, and is a bilaterally symmetrical oval ranging from mere millimetres to well over a metre in length.

Classifying these quilted organisms has been a challenge to palaeontologists. Early researchers did their best to refer them to modern groups: jellyfish, sea-pens and annelid worms were popular choices. Other researchers set up their own classifications: Dolf Seilacher proposed a separate kingdom: the Vendobionta. He interpreted their quilted appearance as a compartmentalised, pressurised, hydrostatic skeleton, like an inflatable mattress. With their high surface area to volume ratio, perhaps they photosynthesised, or chemosynthesised, in a gentler world without predators to burst their bubble (literally).

Other researchers had different interpretations. In the 1980s, Mikhail Fedonkin decided to forego any biological interpretations and formulated a descriptive classification based on symmetry, while in the 1990s Greg Retallack made a controversial proposal, on the basis that there seemed no natural upper limit on their growth and on details of their preservation, that the ediacarans were actually lichens (a symbiotic relationship between fungi and algae and/or cyanobacteria). The consensus now is that most of the ediacarans were animals, and that many were colonial organisms (as are modern sea-pens), but that they are a separate early branch of the animal kingdom.

At the Ediacara sites, the rocks tell us that the organisms lived in a shallow sea, near to shore, and prone to storms and slumping sediments which buried communities intact and in situ. A recent study by Lily Reid and co-authors puts a bit more of the palaeobiological jigsaw together, by considering how sea-floor communities responded to these environmental disturbances in the Ediacaran period. They described a 6.5m2 slab of sandstone (known as the Crisp Wall in its home, the Southern Australian Museum) which is dominated by small, presumed to be juvenile, forms of Dickinsonia costata. Other organisms are also present, including taxa with wonderfully descriptive informal names: “Striped Banana” and “Fried Eggs”.

By applying statistical techniques, they compared the abundance and diversity of organisms in this slab with other Ediacaran beds. They concluded that the Crisp Wall represents an early stage in an Ediacaran ecological succession. The small individuals from few species are the pioneers colonising a pristine new layer of sea-bed sediment, following an environmental disturbance, with other species joining the party as a more mature, and eventually a climax, community is established. Modern ecological responses to environmental upheavals seem to have been in place, even on the planet of the mattresses.

*I’m going with Dirk Maggs’s superlative radio dramatisation here. In the original novel, Zem says “mattresslike”, but “mattressy” sounds much floopier.


Susannah Lydon

The GuardianTramp

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