Before the Cambrian, with its trilobites, and opabinia,
there was an even stranger era, the Ediacaran.
My recent fascination with the Ediacaran ironically started with a creationist’s comment about how his doubts of evolution began when he looked at the Cambrian Explosion. “How could life go from almost nothing to all the creatures we see in the Cambrian?” It seemed a fair question, inquiring minds want to know.
What I found first was that the Cambrian Explosion was no faster than any of the other era in animal history. It was an explosion that played out over more than 70 million years in a world where oxygen was only starting to become abundant. The second thing I found was that there was complex life before the Cambrian.
Before the Cambrian there was a diverse world full of ephemeral live. A world that puzzles scientist because some of the species do not appear to fit in anywhere. Before the Cambrian there was the Garden of the Ediacaran. It was an age of alien creatures so strange that they often defy classification. But it was not alien, it happened right here on Earth, and it is fascinating.
In 1868 Scottish geologist Alexander Murray found spiral fossils in Newfoundland that were in a layer of rock older than the Cambrian. They were dismissed as air bubbles or inorganic concretions. Then in 1933, Georg Gürich discovered specimens in Namibia, but he was already old and set in his ways, and assigned them to the Cambrian. Reg Sprigg noticed "jellyfishes" in the Ediacara Hills of Australia, but once again he assigned them to the Cambrian. More fossils were found in England's Charnwood Forest. These were a bit more problematic because there was no question that they predated the Cambrian era. Finally in 1959 Martin Glaessner put it all together. There was complex life before the Cambrian.
Here would be a good place to talk about how the fossils formed. Ediacaran life were soft-bodied organisms and left only molds of their forms. There are no skeletons. The earliest finds where formed in sand, leading to the idea that their was a microbial mat holding the sand together, and are course in their details. More recently found fossils formed when volcanic ash quickly cover the Ediacaran life, and finer details are found in them. Perhaps more interestingly are the trace fossils which are not of the creature itself, but of its movement, like burrowing or crawling.
Starting in the 1960's serious attention was given to the Ediacaran, but the research is still evolving. By the time I post this diary, some of the information will already be obsolete. There seems to have been a desire to fit the life forms of the Ediacaran into the outline we already know. The Ediacaran life was considered earlier forms of the well know Cambrian life. This lead to this picture, which is something that looks a bit familiar to us.
But as more fossils with finer details started to appear form Canada and Russia, this assumption was challenged.
Where does the three segmented Tribrachidium fit in?
It doesn't.
And even more problematic is the highly successful Dickinsonia, the fossil Sprigg thought was a jellyfish.
It dose not have a mouth an anus, or even a gut, but it is clearly not a plant because it was found in water too deep for sunlight to have been useful. It is often found with trace fossils trailing it. It seems to have been able to move. Is it an animal, or maybe something else altogether?
Was Thectardis an early sponge?
Did Ausia live a symbiotic life with plants living inside its bulb, or is it the predecessor of coral?
There are more questions than answers.
The trace fossils are enigmatic too. Were there worms borrowing, and crawly little critters with legs? Maybe not. Here is a video of a Sea Anemone 'walking'.
Some Ediacarn life does appear to be predecessors of existing spices.
The Kimberella is now thought to be an early mollusk and clearly is bilaterian.
Parvancorina might well be a trilobite-like arthropod.
All this has led to a picture of the Ediacaran that looks a bit more like this.
Or maybe this - it is still hard to say
But all the evidence of Ediacaran life abruptly ends at the beginning of the Cambrian. What happened? The world got cold, that we know. Another theory goes that they did not disappear, but we just can't find them because the Cambrian become much more active, destroying the soft-body Ediacarnan life forms fossils. I think both of those play a part, but there was another thing that happened – the arms race of the animals. Late in the Garden of the Ediacaran, a new species appeared, the Cloudinid.
Cloudinids had mineralized skeletons. And not only that, there are fossils of bore holes in the skeletons. Cloudinids developed armor to guard against predators. The predators came into their own with the beginning of the Cambrian, hence the 'arms race of the animals' that fueled the Cambrian explosion. The Garden of the Ediacaran was the salad bar.
So, to summarize by the beginning of the Ediacaran oxygen had finally reach the point where it could support complex life. Early complex life began largely without predators. These early life forms were so friggin' weird that they might be plants, they might be animals, they might be halfway between plants and animals, or they might be something else altogether. And it all happen here on Earth about 600 million years ago.
Finally, I will leave you with this slightly silly. but catchy song by paleontologist Ron Schmidtling....