Amongst all the disciplines in Earth Sciences, paleontology and sedimentary geology share a particularly striking and complicated frontier. On the one hand, some of the topics that they encompass are apparently separated by huge gulfs in methods and expertise: multiple degrees of separation need to be counted to get from, say, molecular phylogeny to sediment diagenesis, or paleophysiology to sequence stratigraphy. Yet there are arguably further areas where the boundary between the subjects is far more porous, consisting of sub-disciplines that refuse to be pigeon-holed and instead demand consensus between paleontologists and sedimentary geologists. This hazy border zone is the natural territory of PALAIOS, the remit of which is to emphasize “the impact of life on Earth's history as recorded in the paleontological and sedimentological records”, and which has previously published seminal advances in topics such as ichnology, taphonomy, and carbonate sedimentology. Recognizing this, this first of two thematic sets in the journal, which seek to explore how the sedimentary rock record has chronicled ancient life and sediment interactions, might seem unnecessary. Yet what makes these collected papers distinct is that they defy classification within any particular sub-discipline: rather these are either ‘paleontological’ papers that pay additional attention to sedimentological context or ‘sedimentological’ papers that emphasise the importance of life in sedimentary environments. In each instance they demonstrate the potential to understand much more about ancient Earth when the procedures of the two disciplines are undertaken in unison, and hopefully showcase avenues of exploration to inspire further research in this vein.