Was there a Cambrian explosion on land?

The colonisation of land was a key transition in the history of life. Molecular clock analyses imply a rapid radiation of
arthropods and plants on land in the early Palaeozoic, overlapping with the Cambrian explosion in the sea, but the fossil
record is frustratingly limited. The project will combine palaeontological and computational methods to bridge this gap in
the fossil record and establish a timescale for the evolution of terrestrial ecosystems. Early Palaeozoic terrestrial deposits
will be investigated using a low-manipulation acid extraction procedure to isolate small carbonaceous fossils (SCFs).
SCFs are a unique preservation window for small organisms that rarely fossilise. Arthropod SCFs from numerous
terrestrial deposits have been reported in the 1980 and 1990s but have been overlooked since. Preliminary analyses of
coal balls reveal exceptional SCFs suitable for comparison with extant and Palaeozoic taxa. The phylogenetic position
and non-marine origin of problematic SCFs will be tested using geochemical techniques, providing reliable criteria for
recognising the oldest terrestrial ecosystems. The SCF record will be complemented by revising arthropods from the
Rhynie chert and Mazon Creek biotas in museum collections using tomography. This fossil evidence will provide a set of
robust calibrations for a new timescale of terrestrialisation, which will in turn serve as a backbone for testing hypotheses
about the drivers of the diversification of life on land.