The Cambrian explosion

The Cambrian explosion

https://reasonandscience.catsboard.com/t2604-the-cambrian-explosion

Xingliang Zhang Current understanding on the Cambrian Explosion: questions and answers 14 July 2021

Was the Darwin’s dilemma resolved?
The contrast between Precambrian rocks almost barren of animal fossils and Cambrian rocks in which they may abound had puzzled scientists for over 100 years and was referred to Darwin’s dilemma (e.g., Schopf 2000; Conway Morris 2006). However, Darwin himself inferred “… if the theory be true, it is indisputable that before the lowest Silurian (revised to Cambrian in later editions) stratum was deposited long periods elapsed, as long as, or probably far longer than, the whole interval from the Silurian (Cambrian) age to the present day; and that during these vast periods the world swarmed with living creatures (Darwin 1859: 287).” The discovery of Eozoon canadense, once identified as fossilized shells of giant foraminiferans and later reinterpreted as a pseudofossil (see discussion in Schopf 2000), in the Precambrian Laurentian Formation of Canada was cited by Darwin to support his inference about the existence of living beings long before the Cambrian Period (Darwin 1872). On the one hand, Darwin thought the Cambrian Explosion was inexplicable using his theory and on the other hand he seemed to firmly believe his explanations. This paradoxical combination may lead him draw a conclusion in the end of the Chapter 9 of On the imperfection of geological record, which stated “On this view the difficulties (to his theory of evolution) above discussed are greatly diminished or even disappear (Darwin 1859: 311)”. Taking this case into consideration, it was difficult to know if Darwin really had a dilemma on the Cambrian Explosion.

The hunt for Precambrian fossils has never been ceasing since 1850s. Specimens of Eozoon were first discovered in 1858, a year before publication of Darwin’s theory of evolution, although their biological interpretation finally collapsed. Since then, of course, much has been learnt. It is, however, a very difficult journey! The existence of life before the Cambrian became widely accepted until 1950s (Schopf 2000). Multidisciplinary investigations did extend the life history deep into Archean (e.g., Shen et al. 2001; Duda et al. 2016; Tashiro et al. 2017; Lepot 2020; Mißbach et al. 2021) but only heightened the sharpness of the beginnings of animal fossils across the Ediacaran–Cambrian transition. All fossil records still point to an explosion of animal life near the beginning of the Cambrian.

What does the fossil record tell us?
Precambrian palaeontologists are at loss to search for animal remains in ancient rocks, but results are somewhat awkward. The findings do not extend the dawn of animal life much further back. Body, trace, and chemical remains of animals are not as ancient as Darwin predicted but have been found in the time slice just before the Cambrian, i.e., late Ediacaran (~ 580.0–538.8 Ma). Moreover, most Ediacaran candidates of animals are a bit weird and thus difficult to be placed in any known animal group. More familiar animals arrived in the early Cambrian.

Most living animal phyla made their first appearance in the fossil record during the first 20 million years of the Cambrian Period (Erwin et al. 2011; Zhang and Shu 2014; Shu et al. 2014). 

What is the nature of the Cambrian Explosion?
Explosion of fossils resulted from explosion of animals! Fossil record does capture the explosive evolution of animal body plans along with biomineralization, body size variation and increase of ecosystem complexity.
However, a major burst of bilateral body plans took place in the first 20 Ma of the Cambrian . Taking the Euarthropoda, the most diversified phylum, for example, molecular clock studies constrained the origin between 561 and 530 Ma , spanning into the Cambrian. The earliest arthropod trace dates to the Fortunian (~ 538.8–529.0 Ma) (Mángano and Buatois 2020). In addition, divergence time analyses using morphological data also recover a Cambrian origin for the Euarthropoda (Wolfe 2017). The estimated timing of origin is remarkably congruent with the fossil record.

Simply there are morphological gaps between phyla. By analyzing the timing of appearance of Linnaean rank taxa in the fossil record, paleontologists realized that the limits on animal disparity were early in animal evolutionary history. By the reinterpretation of the Burgess Shale fauna, Gould suggested a pattern of rapid, maximal disparity in the early history followed by later removal of most groups (stem groups) by extinction that leaves large morphological gaps among high-rank clades. This pattern is applicable to high-rank clades and metazoans as a whole. Particularly, he argued that that the morphological disparity of arthropods at a single locality (Burgess Shale) surpassed all extant arthropods, which inspired considerable efforts to understand disparity. Subsequent quantitative studies have shown that most clades achieved their maximal disparity (or morphological breadth) during a short time interval close to their first appearance in the fossil record in the early Cambrian. A more recent study by mapping of fossil and living metazoan morphospace demonstrated that the majority of phylum-level clades achieved maximal initial disparity in the Cambrian and that the overall disparity was already very broad in the early history of animal evolution, although the envelope of disparity explored by the Metazoa has increased through geological time. It is worth mentioning that new discoveries of weird forms in Cambrian deposits would increase the morphological breadth of Cambrian animals.

XingLiang Zhang Causes and consequences of the Cambrian explosion 22 November 2013
https://link.springer.com/article/10.1007/s11430-013-4751-x



Newly Discovered Fossil Species Named After Star Wars Starship
The 500-million-year-old species is a distant relative of today’s crabs, spiders, and insects.
https://www.youtube.com/watch?v=m7zGEITBc9E&t=56s

David F. Coppedge Soft Tissue in Biggest Ever Cambrian Fossil Bonanza March 23, 2019 2

This is in shale rock, but could hardly be better preserved by amber. It looks as though the creatures was buried instantly. If not, this amount of detail would not have survived a day. Nature summarizes the context of this fossil bed, and notes the delicacy of soft-bodied creatures preserved in this fashion. What does it take to preserve details of a jellyfish, or a comb jelly?

‘A stroke of luck’
Finding fossilized nerve tissue from the Cambrian period, which took place between about 543 million and 490 million years ago, is a “rarity,” Ortega-Hernández said. “It’s really a stroke of luck.” Scientists uncovered the first evidence of a fossilized arthropod brain from the Cambrian period about a decade ago, according to a 2012 report in the journal NatureCommunications; 4

Feiyang Chen First report on Guanshan Biota (Cambrian Stage 4) at the stratotype area of Wulongqing Formation in Malong County, Eastern Yunnan, China 5

The Guanshan Biota (Cambrian Series 2, Stage 4) in the Yunnan Province of South China, has produced abundant and diverse, exquisitely preserved fossils that often retain soft tissues and organs. The fossils are preserved by carbonaceous compressions, pyritization, phosphatization and clay mineral replacement, and display high fidelity preservation of soft tissues, similar to that seen in the Chengjiang and other Guanshan Biota localities west of the Xiaojiang Fault. New discoveries of soft-bodied assemblage from the Kanfuqing section on the eastern side of the Xiaojiang Fault has increased the occurrences of the Guanshan Biota, and suggest that similar faunal assemblages were deposited across the basin after the transgression of the eastern Yunnan Sea.


1. https://link.springer.com/article/10.1007/s12542-021-00568-5
2. https://crev.info/2019/03/soft-tissue-in-biggest-ever-cambrian-fossil-bonanza/
3. https://eos.org/articles/newly-discovered-fossil-species-named-after-star-wars-starship
4. https://shomapti.com/500-million-year-old-bug-like-fossils-have-stunningly-preserved-nervous-systems/
5. https://www.sciencedirect.com/science/article/pii/S1674987118302111

Uncommon descent: Fossil Discontinuities: A Refutation Of Darwinism And Confirmation Of Intelligent Design  October 13, 2018 1

The fossil record is dominated by abrupt appearances of new body plans and new groups of organisms. This conflicts with the gradualistic prediction of Darwinian Evolution. Here 18 explosive origins in the history of life are described, demonstrating that the famous Cambrian Explosion is far from being the exception to the rule. Also the fossil record establishes only very brief windows of time for the origin of complex new features, which creates an ubiquitous waiting time problem for the origin and fixation of the required coordinated mutations. This refutes the viability of the Neo-Darwinian evolutionary process as the single conceivable naturalistic or mechanistic explanation for biological origins, and thus confirms Intelligent Design as the only reasonable alternative.

Finally – with evidence from genomics complementing the gaps found in the fossil record, no amount of excuses explain why, if we slowly morphed from a fish to a human, why is the empirical evidence for change not show more plasticity? Why Did all the major phyla show up at the first neo-second of geological time, with nothing of interest before, AND nothing at all IN BETWEEN phyla – even Evolutionists said you will never find vertebrates in the cambrian, as the slow and gradual transition from sponge to fish to man excludes this possibility, and vertebrates are a much more advanced body plan – then we found several vertebrates in the Cambrian. Why does genetic data confirm rapid appearance as well? Scientist need to start swallowing their pride, as they could be a part of the most amazing, most awe inspiring, most wondrous discovery in Biology – punctuated equilibrium does not work, as it requires way to small populations and also only accounts for one out of thousands of animals within a population, so even though THAT particular “hopeful monster” showed up, his/her changes would still become invisible to the population – we are talking about many creation events it seems. The history of HomoX, is also now not a smooth progression, but several homoX kinds habitating around similar timeframes, does not exactly fit the notion of some smooth transformation, the fantasy on banners that even Stephen J. Gould hatted as it was just that, pulled from a person’s imagination. To me the idea that a fish is an ancestor of mankind, is a very ancient and pagan idea from various religious ideas that we were all related from the very first life form also linked to notions of Gia. But Orphan Genes, HGT, have put an end to this fantasy, as it is becoming clear, that similarities in protein coding portions of DNA are of little importance, and only represent a toolkit for the organism to use. And suddenly it makes sense why man’s DNA is 50% the same as a banana, but we are infinitely different. It also makes sense why modern chimps have a very similar toolkit as homo sapien sapien, as they require many of the same proteins, but nonetheless does not mean we are a descendant from a common cousin. When the human genome is made up of around 20% (If I remember correctly, maybe 10%) Orphan genes, and so are most mammals, we clearly see an injection of very specific information, not available to our “ancestors”, and that if we are indeed all related, it is only by re-use of the same code, what every programmer does – you don’t throw out code that gets you part of the way to what you need, you simply modify existing code, and add new modules to it.

Gunter Bechly Fossil Discontinuities: Refutation of Darwinism & Confirmation of Intelligent Design  Oct 11, 2018

Evolution is supposed to proceed by random mutation and natural selection. Selection can only work when there is an adaptive value. Some adaptive advantages require two or more coordinated mutations this is known by by experimental data and empirical data and all mutations have two time constraints one is the mutation has to arise in amutations have two time constraints one is the mutation has to arise in a population and the second is the mutation has to spread in the population for the whole species to have this character and these two time constraints are the two waiting times that are involved and now we can look does the fossil record allow to accommodate these waiting times and actually these waiting times pose a dilemma because if you play with the possible variables for example population size if you make the population large then you have a lot of play possibilities for evolutions the mutation can arise more fast but it takes longer to fix the  mutation to spread in a population. If you have a small population it can be fixed a change can be fixed and spread in the population very quickly but you have to wait longer to get the mutation in the first place so your there's no easy way around this problem and you might think well in in be parental species you have recombination a neutral mutation could arise there in the population and they are a population and then they come together by sexual recombination but actually the effect has been studied in a paper already in 1998 and they came to the result that the effect by recombination there is an effect but it is small compared to the other variables like mutation rate and population size so it doesn't solve the waiting time problem to do the math it's actually you need only a few variables like the mutation rate which is new known experimentally and in different groups of organisms you have to know the population size for fossil groups you can make reasonable estimates by comparing them to recent groups so for example a fossil group of early rail  precursors would have had a population size comparable rather to wild boars than to assure it your Coli bacteria and the same with Generation turn over times that would be the third variable you can make a reasonable estimate for let's say for a large weather birth the generation time is some years and not some seconds and then you can do the math.

1. https://uncommondescent.com/evolution/fossil-discontinuities-a-refutation-of-darwinism-and-confirmation-of-intelligent-design/
2. https://www.youtube.com/watch?v=M7w5QGqcnNs

The 12 Strangest Animals of the Cambrian Period
https://www.thoughtco.com/strangest-animals-of-the-cambrian-period-4125717

Libretext: unresolved questions about the animal diversification that took place during the Cambrian period remain. For example, we do not understand how the evolution of so many species occurred in such a short period of time. Was there really an “explosion” of life at this particular time? Some scientists question the validity of the this idea, because there is increasing evidence to suggest that more animal life existed prior to the Cambrian period and that other similar species’ so-called explosions (or radiations) occurred later in history as well. Furthermore, the vast diversification of animal species that appears to have begun during the Cambrian period continued well into the following Ordovician period. Despite some of these arguments, most scientists agree that the Cambrian period marked a time of impressively rapid animal evolution and diversification that is unmatched elsewhere during history.
https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Map%3A_Raven_Biology_12th_Edition/25%3A_The_Origin_and_Diversity_of_Life/25.05%3A_Ever-Changing_Life_on_Earth/25.5.02%3A_The_Evolutionary_History_of_the_Animal_Kingdom