[lemma=as] [tag=JJ] [tag=","] [tag=RB] [word=□]
[lemma=as] [tag=JJ] [tag=","] [tag=RB] [word=a]
It is my understanding that there was no Cambrian “ explosion ” as such , just a prolongued period ( several million or tens of millions of years ) during which the rate of evolution was a bit higher than the average .