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Molecular Paleobiology and the Cambrian Explosion: 21st Century Answers to 19th Century Problems
Published online by Cambridge University Press: 21 July 2017
Abstract
A number of challenges face us paleontologists as we head into the 21st century. None is more difficult than explaining the Cambrian explosion, the dramatic differentiation of most metazoan animal phyla and classes about 545–530 million years ago. Molecular paleobiology, the experimental and theoretical integration of the geologic and the genetic historical records of life, holds promise to help elucidate the causality of the Cambrian explosion, especially as it relates to understanding how so many animal body plans appeared in such a relatively short period of time, and why these body plans were so stable over the subsequent 500 million years. Three discoveries made over the last few years suggest that the answers to these problems might be right around the corner. First, the notion that phenotypic plasticity was higher early, as compared to later, in a clade's history has finally been confirmed and quantified for trilobites. Second, it has been shown that a recently discovered group of genes, microRNAs, regulate the precision of genic output, turning what is a fairly sloppy process (the number of transcripts derived from any genetic locus) into a precise number of protein molecules. And third, microRNAs are continuously being added to metazoan genomes, with their first major influx occurring at the base of the protostomes and deuterostomes, the very animals that so dramatically make their first appearances in the Early Cambrian. I propose that because phenotypic variation decreases through geologic time, that because miRNAs decrease genic variation in output levels, and because the number of miRNAs found within a genome increases through geologic time, miRNAs might be instrumental in the canalization of development, sacrificing phenotypic variation for developmental precision, and ultimately allowing for increases to morphological complexity. Hence, part of the solution to the Cambrian conundrum might be microRNAs, how they control development through ontogenetic time, and how they evolve through geologic time.
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