Early bursts of diversification defined the faunal colonization of land

The colonization of land was one of the major events in Earth history, leading to the expansion of life and laying the foundations for the modern biosphere. We examined trace fossils, the record of the activities of past life, to understand how animals diversify both behaviourally and ecologically when colonizing new habitats. The faunal invasion of land was preceded by excursions of benthic animals into very shallow, marginal-marine environments during the latest Ediacaran Period and culminated in widespread colonization of non-marine niches by the end of the Carboniferous Period. Trace-fossil evidence for the colonization of new environments shows repeated early-burst patterns of maximal ichnodisparity (the degree of difference among basic trace-fossil architectural designs), ecospace occupation, and level of ecosystem engineering prior to maximal ichnodiversity. Similarities across different environments in the types of behavioural programmes employed (as represented by different trace fossils), modes of life present, and the ways in which animals impacted their environments, suggest constraints on behavioural and ecological diversification. The early-burst patterns have the hallmark of novelty events. The underlying drivers of these events likely were the extrinsic limitation of available ecospace and intrinsic controls of genomic and developmental plasticity that enabled trace-maker morphological and behavioural novelty.