Martian stick-like structures are not trace fossils: a new protocol for testing ichnogenicity synthesized from paleosol ichnology

There are different criteria that are usually analysed independently before identifying a new trace fossil, such as morphological regularity, completeness, dispersion, recurrence and complexity, surface morphology, and context. The synthesis of these criteria, as utilized in paleosol ichnology, composes a protocol that is presented herein for the first time and can be used for testing the ichnogenicity of trace-like structures in any paleoenvironment of Earth or Mars. As a study case, the Martian ‘stick-like structures’ do not fulfil any of the requirements posed by this protocol to be postulated as trace fossils. The ichnogenicity test, focussed exclusively on morphology and context, is simpler but equally useful as the biogenicity ones. It may be applied in the future with other potential cases before carrying on more complex analyses or to evaluate the astrobiological interest of trace-like structures.