If all these creatures are complex and have all the modern structures like hearts and brains which are very complex and something we see in all modern life then it is showing that the codes for all life have been around for a long time and earlier then evolution has said. There didn't need to be a lot of evolution for mutating all these features. The codes were already there. They suddenly appeared without any trace of where they came from. They have even found evidence of eukaryotes in pre Cambrian layers. So that pushes things back even more. It is the opposite of evolution and making things go from complex to simple rather than simple to complex.
If a brain is evolved so early it would need many stages of evolution to occur. But there is no trace of those stages happening. The point is because there is similar levels of complexity way back when life was suppose to be simple then it is pointing to the code for that life being around from a very early stage and makes it harder to believe that there has been a slow and gradual evolution of things as Darwin said.
Cambrian fossil pushes back evolution of complex brains
The remarkably well-preserved fossil of an extinct arthropod shows that anatomically complex brains evolved earlier than previously thought and have changed little over the course of evolution.
https://www.sciencedaily.com/releases/2012/10/121010131436.htm
Earth's earliest non-marine eukaryotes.
The apparent dominance of eukaryotes in non-marine settings by 1?Gyr ago indicates that eukaryotic evolution on land may have commenced far earlier than previously thought.
http://www.ncbi.nlm.nih.gov/pubmed/21490597
This paper describes how creatures may have had a way of turning on and off existing genetic info when needed. So even from an early stage in existence living things may have had the code to produce complex changes to tap into. Not from random mutations but from existing genetics. This makes more sense in the light of the Cambrian period and the evidence which show that non adaptive forces support how creatures change.
Universal genome in the origin of metazoa: thoughts about evolution.
According to this model, (a) the Universal Genome that encodes all major developmental programs essential for various phyla of Metazoa emerged in a unicellular or a primitive multicellular organism shortly before the Cambrian period;
This model has two major predictions, first that a significant fraction of genetic information in lower taxons must be functionally useless but becomes useful in higher taxons, and second that one should be able to turn on in lower taxons some of the complex latent developmental programs, e.g., a program of eye development or antibody synthesis in sea urchin.
http://www.ncbi.nlm.nih.gov/pubmed/17660714
The paper wasn't meant to go with the paragraphs above. It related to the last sentence above the link about beneficial mutations affecting each other. I had already posted several links for what I was talking about earlier in the above paragraphs on a number of occasions and didn't want to post that again. If you have been following the thread you would see. Even earlier on this page of the one before it. I wanted to add another aspect of why it is hard for mutations to create such fit and more complex living things. It is often claimed that its the beneficial mutations that is the driving force for evolution. These are very rare and even so beneficial mutations can end up having a fitness cost. When they have to work together they will have an effect on each other which ends up diminishing any evolution towards better and fit creatures.