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 programme 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 were probably the extrinsic limitation of available ecospace and intrinsic controls of genomic and developmental plasticity that enabled trace-maker morphological and behavioural novelty.Financial support for the initial part of this project was provided to N.J.M. through a Government of Canada Post-doctoral Research Fellowship under the Canadian Commonwealth Scholarship Program. Additional funding was provided by the Natural Sciences and Engineering Research Council (NSERC) Discovery Grants 311726-05/08/15 and 311727-05/08/13 (to L.A.B. and M.G.M., respectively). M.R.G also acknowledges funding from an NSERC Discovery Grant. This is Earth Sciences Sector contribution number 20160255 and contribution 314 of the Evolution of Terrestrial Ecosystems Consortium of the National Museum of Natural History, Washington DC

Intra-trackway morphological variations due to substrate consistency: the El Frontal dinosaur tracksite (Lower Cretaceous, Spain).

An ichnological and sedimentological study of the El Frontal dinosaur tracksite (Early Cretaceous, Cameros basin, Soria, Spain) highlights the pronounced intra-trackway variation found in track morphologies of four theropod trackways. Photogrammetric 3D digital models revealed various and distinct intra-trackway morphotypes, which reflect changes in footprint parameters such as the pace length, the track length, depth, and height of displacement rims. Sedimentological analyses suggest that the original substrate was non-homogenous due to lateral changes in adjoining microfacies. Multidata analyses indicate that morphological differences in these deep and shallow tracks represent a part of a continuum of track morphologies and geometries produced by a gradient of substrate consistencies across the site. This implies that the large range of track morphologies at this site resulted from similar trackmakers crossing variable facies. The trackways at the El Frontal site present an exemplary case of how track morphology, and consequently potential ichnotaxa, can vary, even when produced by a single trackmaker