benthic (paleo)ecology, ichnology, paleobiology
I recently came back from the Third International Ichnological Congress, ICHNIA 2012, in Newfoundland (=Terranova). The conference was an excellent opportunity to meet old friends, make new ones, learn about what’s new in the field of ichnology and become an honorary Newfoundlander after going through a difficult initiation ceremony. For me, the conference started with a pre-meeting fieldtrip to explore the Ediacaran and Cambrian fossils of the Avalon and Burin peninsulas. As I wrote in a previous post the Ediacarian-Cambrian transition constitutes the most dramatic change in the history of biosphere. Sometime around 540 million years ago, Earth started to become more ‘earthy’ when the seafloor commenced being populated by animals… Unusual animals, yes… But true animals after all, not so different from a clam, a shark, or a human being. But what was before? A world of microbes and something else: the weird Ediacaran biota, the closest thing to alien life forms that ever lived on Earth, more different from us than any extraterrestrial critter ever invented by science-fiction.
What were Ediacaran creatures? How did they live? We really do not know for sure. They inhabited Earth for several tens of millions of years and their fossils are found all over the world. They were large, soft-bodied, epifaunal organisms whose proper phylogenetic postion is unknown. In the rocky shores of Newfoundland, we had the opportunity to examine fossils of some of these fascinating creatures at different localities thanks to the guidance of Liam Herringshaw, Jack Matthews and Duncan McIlroy. The so-called Avalon-type assemblage records the oldest Ediacarian radiation after the end of the Gaskiers glaciation aroun 580 million years ago.
At Pigeon Cove, we found the Ediacarian version of an Italian ristorante. One single bed exposes numerous irregular, circular fossils known as ivesheadiomorphs, although more commonly referred to as ‘pizza-discs’ (above). The whitish material filling irregularities is not mozzarella but remains of the overlying ash bed that buried the organisms and was thus responsible for their fossilization.
But probably the highlight of the trip was the visit to Mistaken Point. All we needed to enjoy a near-mystic ‘paleoexperience’ was there: a very famous fossil site with a misterious name, the mist half-covering the steep rocky cliffs and thousands of Ediacaran fossils laying quietly as if waiting for our visit. And on top of that, we were requested to take off our boots and put on some soft booties that we were provided for the occassion (pretty comfortable, I must say!). It felt like visiting a temple. And we were not disappointed. Beds D and E were literally covered by Ediacaran fronds, most of them beautifully preserved.
The most abundant fossils were those of the rangeomorph Fractofusus. This has a frond-like morphology with a central axis and a series of bundles arranged in two lateral rows. It has been suggested that it was a benthic recliner.
Another commonly found fossil was Bradgatia with a similar internal structure than Fractofusus but a different overall bush- or lettuce-like morphology . (Look at the beautiful booties in the picture above).
We also observed a third type of fossilized organism, the world-famous Charniodiscus. This is a rangeomorph as well, but it bears a stem and a discoidal holdfast structure, which anchored the organism to the seafloor while the frond was elevated in the water column.
Our last stop at an Ediacarian site was at Ferryland were the discoidal Aspidella terranovica abounded. It has been suggested that they represent the holdfasts of frondose organisms but that is still open to discussion.
Let me finish with this explanatory panel which is part of the small exhibition at the Interpretive Center of the Mistaken Point Ecological Reserve. It shows a reconstruction of how the organisms that we found today as fossils in the shores of Newfoundland are interpreted to have lived. This image is the closest we have to a photograph of Earth 565 million years ago.
Ah! … the good old Earth populated by creatures as alien as they could get in this planet.
I can almost hear the voice of Lieutenant Commander Data to his captain:
– Captain. We reached the orbit of Terranova. Our sensors are reading strange life forms on the surface.
– Commander Riker, Liutenant Worf, prepare a team to beam down…