Fossil Ecosystems of North America: Mistaken Point

In this Late Proterozoic Lagerstätten the authors describe some of the most ancient animals fossils on Earth.

The layout for this chapter is very similar to the layout for the previous one: after some background information and the description of the history of its discovery, the geology and the taphonomy of Mistaken Point (Newfoundland, Canada) are outlined, and the single fossils are described. The chapter then analyzes the environment of sedimentation of this Canadian Proterozoic Lagerstätten before taking us north of Adelaide, Australia, for a brief description of the original Ediacaran Fossils.

Both of these localities, Mistaken Point (in Newfoundland, Canada) and the Ediacara Hills (north of Adelaide, Australia) are illustrated in the movie First Life (narrated by David Attenborough, BBC).

part 1 - BACKGROUND: THE FIRST ANIMALS

Animals, when did they start?

What did the development of multicellularity bring?
What did science think about fossils in the Precambrian, up to a few decades ago?
What is found at the base of the Cambrian?
Why was this a problem for Charles Darwin?

The newly discovered soft-bodied organisms of the Late Precambrian also deepened Darwin's dilemma (the lack of a Precambrian fossil record)

Why is that?
How are these organisms collectively known?
Why is Mistaken Point a remarkable locality from the point of view of its Ediacaran Fauna?
What covered the successive stages of the Late Precambrian ocean, thus fossilizing these first animals?
These animals record a critical period in Earth's history, which falls between which two ecosystems?

part 2 - HISTORY OF DISCOVERY OF THE MISTAKEN POINT BIOTA

The Ediacaran Fauna is so called because it was first found in Ediacara, Australia. At the time (1947) it was thought these fossils were Cambrian in age, because of the usual concept that "there were no fossils in the Precambrian". But similar fossils were later found in Britain, and their age was doubtless Precambrian. It was only in 1967 that the fossils at Mistaken Points were found.
So, the fossils at Mistaken Point constitute what we call an Ediacaran Fauna (or Ediacaran Biota) because the first fossils ever of this kind were found in Ediacara. The Ediacaran fauna is Late Precambrian in age (as a matter of fact, see figure to the right, the last Period of the Precambrian has been named Ediacaran.)

modified from
© International Commission on Stratigraphy (2019)

part 3 - STRATIGRAPHIC SETTING AND TAPHONOMY OF THE MISTAKEN POINT BIOTA

A lot of information in this paragraph relies on basic facts you are still not mastering. What you need to get out of this section is that fossils were preserved because of volcanic eruptions that covered the ocean bottom with volcanic ash. Volcanic ash killed and buried the communities on the ocean floor, preserving the detailed morphology of these soft-bodied organisms.

part 4 - DESCRIPTION OF THE MISTAKEN POINT BIOTA

I will not ask about the individual fossil species but you need the know a few basic facts:

The Mistaken point fauna is Ediacaran in age, but many of its species are found only at this location (or, they are endemic to Mistaken Point), and not in Ediacara, Australia, or other places
Only Aspidella, Charnia and Charniodiscus are found at other localities (or, they are cosmopolitan)
The fossils at Mistaken Point occur in two distinct, physically (and temporally) separated assemblages (called respectively Mistaken point Assemblage, and Fermeuse Assemblage), which consist of different forms

Read about the individual fossil species, but I would like you to study and know well only Charnia (how does it look like, what it is, where was the first of them ever found - we can see that, again, in the First Life movie).

part 5 - PALEOECOLOGY OF THE MISTAKEN POINT BIOTA

The Mistaken Point Fauna is part of the so-called Avalonian Terrain. Without getting into further details, you should know that this part of Newfoundland used to be a land mass connected to England, Wales and other European regions, which was separated in two distinct parts due to the opening of the Atlantic Ocean. Newfoundland eventually became part of North America, while England and Wales became part of Europe.
During the Precambrian though, these regions were united and were located at mid-latitudes in the southern hemisphere (that is, approximately where today's Chile and Argentina are in south America, or South Africa and Namibia in Africa).

The fact that ash layers repeatedly covered the Mistaken Point Fauna indicates that there used to be frequent volcanic eruptions, which suggests that this ancient ocean was close to a volcanic arc.

All Ediacaran assemblages found in other parts of the world have been interpreted as shallow water communities which were commonly affected by the action of waves. At Mistaken Point there is no absolutely no evidence of wave action, and many of the rocks are identified as turbidites (graywacke sandstones). As you know, turbidites are deposited -as a rule- in deep waters, at the foot of the continental slope. All of this points towards a much deeper environment of deposition than at other locations (waves indicate a beach, or shallow waters, turbidites indicate the continental rise, or much deeper waters).

part 6 - COMPARISON OF MISTAKEN POINT WITH OTHER LATE PRECAMBRIAN BIOTAS

This section is important because it describes the classic fossil locality of Ediacara, Australia.

Is this Lagerstätten (Ediacara) the same age of the Mistaken Point one, or not?
Are there differences between the two Lagerstätten, and if so, which ones?
Which three forms (we encountered them and named them also in part 4 above) are common to the two Lagerstätten?

Read about the Australian species in the rest of this section, but the final, important point is that this Australian Lagerstätten, being about 10 million years younger than Mistaken Point, seems to be preserving species that are more advanced and that have more in common with some of the Phanerozoic (Cambrian and later) animals which would soon replace them (remember that later animals would not be all that similar to the these Ediacaran faunas)

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