My "Inability to read"? Why are you abusive?
I read it.
Then you would know that your claim regarding Cambrian was refuted.
Our view of the sequence of events in the Cambrian has thus been transformed in the last few decades,
with the basal rocks now being known to contain a suite of trace fossils of moderate diversity, and an increasing diversity of small shelly fossils, including a large number of tubes, plates and cap-shaped fossils (e.g. [17]). The affinities of these early fossils are much debated as soft parts are unknown, but at least molluscs seem to represented.
For decades, researchers have been extracting small, sometimes fragmentary fossils preserved as organic carbon, from siliceous rocks using hydrofluoric acid (HF).
The characteristic fossils recovered in this way – termed acritarchs – are a heterogeneous assemblage of pro- and eukyarotic taxa that probably include cyanobacteria, green algae, and other related groups, and their record extends deep into the Precambrian (e.g. [20]). More recently, remarkably-preserved organic fossils have been recovered using somewhat gentler HF methods from Cambrian rocks (e.g. [21]), and these promise to extend and complement the Burgess Shale-type material. The most significant find is of fragments that can be confidently assigned to crown-group crustaceans [22], and this has extended the record of many of these groups back at least to the middle Cambrian.
A particularly exciting recent development has been to calibrate the absolute age of this carbon isotope curve, using the co-occurrence of rocks suitable for isotopic evaluation with volcanic ash-beds lying within them, most particularly in Morocco. This dated carbon curve has been used to set up a global reference for faunas in many area of the world, especially in China, Mongolia and Siberia. In detail, this method is not free from difficulties, and some of the results have been somewhat surprising (for example, the rocks in Mongolia, which bear a rather standard set of fossils, have been suggested to be somewhat older than similar rocks in Siberia),
but the broad outlines of the sequence of events, and their timing, are now becoming somewhat clearer.
As the base of the Cambrian became reliably dated (e.g. [
6,
7]), its age relationship to the underlying Ediacaran rocks and their perplexing biotas became clearer.
These include both the huge frond
Charnia wardi [
35], some specimens of which are over 2m in length, as well as an assemblage of what appear to be juvenile specimens of
Charnia masoni [
38].
Charnia masoni-like fronds are also known from the White Sea area from about 549 Ma [
39,
40], making this an extremely long-lived morph. Rather than representing a relatively short-lived burst of “failed evolutionary experiments”, the Ediacara-like biota was both long lived and cosmopolitan.
More recently still, a biota from the Lantian Formation of South China has been suggested to be almost certainly older than this assemblage from Newfoundland [42]. It contains some macroscopic taxa that are probably algal in affinity, but also a more diverse range of organisms that are more intriguing. Indeed, one form (Fig. 3E3E of [42]) has recently been suggested to be related to the conulariids, a group of Cambrian problematica that are often compared to cnidarians [43]. If the dating and affinities can be sustained, this would suggest that both stem-group cnidarians and bilaterians were present almost all the way through the Ediacaran Period (635-541), which would be a signficant advance in our our understanding of early animal evolution. Once again, this is an area that would be worthy of further investigation.
Increasingly firm control on the dating of Ediacaran assemblages (reviewed in [
36]) suggests a definite temporal distribution of the various clades they identify. The oldest assemblages in Newfoundland are dominated by “rangeomorphs”, although, rather curiously,
Charniodiscus-like fronds are also present. In the later, “White Sea” and “Nama” assemblages, apparently bilaterally symmetrical and (presumably!) non-frondlike taxa such as
Spriggina appear, and these are joined by the truly complex
Kimberella [
64].
An obvious explanation of this distribution, is that this diversification truly represents a radiation of basal animal groups, from sponge-grade at the bottom (rangeomorphs and potential sponges themselves) through stem-group eumetazoans and stem-group bilaterians.
Gould's view was that the Cambrian exceptional record revealed an unparalled explosion of different body plans, giving rise to a substantial diversity and disparity that was then pruned by later extinction.
The problem with this view is that it has since become apparent that, rather than representing entirely distinct clades, most if not all of the known record represents stem groups to living groups (e.g. [48]). As a result, the Gouldian view has largely faded from the palaeobiological literature, even if it lingers elsewhere.
Nobody is claiming the picture is clear. It's not expected to be so far back in the past. But there is zero reason for skepticism given what is known so far.
