Last updated March 6, 2017 at 3:20 pm
Our Director Paul Willis is attending the second Palaeo Down Under conference, touching base with his old palaeontology mates. He will be sharing it on social media and blog around this conference for the next few days.
Animal evolutions begins in the Ediacaran faunas.
That’s a bold statement, and something long suspected but lacking the empirical evidence needed to back it up. Until now.
The Ediacaran fauna is a collection of the oldest multicellular fossils now found at several locations around the world. While the first find was in England, the fossils take their name from the Ediacaran Hills in South Australia where the second find was made by geologist Reg Sprigg back in the 1950s. Unlike the British experience, Sprigg recognised the importance of the ancient relicts and thus a whole new branch of palaeontology was created: the study of the most ancient known macro fossils.
No one was really sure what they were because they have body plans that differ from modern living organisms – or anything seen elsewhere in the fossil record. And, to complicate issues, comprehensive study of these fossils has been hampered by lack of quality sites where they can be studied. The original sites in the Ediacara Hills have been picked clean by generations of fossil hunters.
But then, just over a decade ago, palaeontologists found a new, untouched site called Milpeena in the Flinders Ranges. I went there last year and shot the video below. Finally an unsullied site where palaeontologists could take their time and expose whole ancient sea floors to examine these fossils where they lived and died.
What seems to happen at Milpeena is that it was a shallow sea floor – so shallow that it produced ripple marks on the sandy surfaces. The layers or beds where the fossils occur appear to have been bound together by algae; an algal mat must have held the surface together back in the day and many of the fossils found there appear to have been feeding on this gooey green mat. Other Ediacarans appear to be reaching up into the water column and filtering out micro-organisms there.
Fossils have also been found in other ancient environments, delta sands and sheet sands. Not all Ediacarans are found across all environments, some are found across a couple, others only in one. But the take home message is that the Ediacaran fauna is in fact diverse in composition and the environments in which they occur.
At Milpeena, they have 35 separate beds of Ediacaran fauna stacked on top of each other. Among the many amazing aspects of this location is that none of those 35 beds have the same assemblage of creatures, some are dominated by one species or another, others have a higher diversity of species but no two are the same.
And there on these now solid, once gooey surfaces we can now see behaviours and activities from when the Ediacarans were alive. We are now able to see both sexual and asexual reproduction in some of these mysterious fossils as well as systems of aggregation of individuals to form different types of colonies. Feeding trails can be traced across some surfaces and elsewhere there are resting sites of other Ediacarans. Some appear to be anchored into this substrate, reaching up into the water.
But, now we can see some of the details of what these things got up to when they were alive, we can be more confident in saying that they were indeed creatures related to the animals of today rather than plants. We can see mobility and organisation and reproductive patterns that are consistent with the mysterious impressions were once living breathing creatures. And so now we can say with some confidence that animal evolutions really does begin with the Ediacarans.