John-Paul Zonneveld, Aswan, Russell L. Ciochon, Riley Morton, Yan Rizal, Maria Rodriguez, Yahdi Zaim, Neil H. Shubin
Amphibious fishes, with varying degrees of terrestriality, occur in a broad variety of marginal lacustrine and marginal marine settings. Most of these rely on axially driven locomotion (tail and torso bending) in terrestrial movement. Oxudercid gobiids (mudskippers) are distinctive in that their normal terrestrial locomotion is driven primarily by a pulling motion of their pectoral fins resulting in movement termed ‘crutching’. This contribution is focused on the traces emplaced in sand and mud by mudskippers, formed during the locomotory activity of the two most terrestrialized mudskipper genera: Periophthalmus and Periophthalmodon. The traces produced were compared with Devonian ichnofossils in order to frame the discussion of the nature and timing of the earliest vertebrate invasion of terrestrial realms. Mudskipper traces emplaced by large (. 20 cm body length) Periophthalmodon in subaerial, wet, but unsaturated mud produced exceptionally distinctive traces. These traces are characterized by distinct central tail and body grooves, bordered by small distinct pelvic fin traces and larger, arcuate pectoral fin traces. Fin traces in mud substrates commonly retain discrete fin ray impressions. The unique crutching motion results in an approximately symmetrical trace, with paired fin traces on each side of the central grooves. Traces made by smaller Periophthalmus may look similar or may be less distinctive due to the lighter weight of the animals. Traces made in sand may lack pelvic fin impressions and, in some cases may be limited to the central body groove. Mudskipper locomotion traces are similar to the arthropod ichnogenera Siskemia and Stiaria. We note the similarity of some mudskipper tracks to some trackways previously inferred to be made by tetrapods. Assessing the traces that modern amphibious fishes make can inform the search for similar behaviors recorded by Devonian traces and by traces made by previously unrecognized amphibious fishes throughout the post-Devonian interval. Copyright © 2025, SEPM (Society for Sedimentary Geology)
Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, Canada; Department of Geology, Institut Teknologi Bandung, Indonesia; Department of Anthropology, University of Iowa, Iowa City, IA, United States; Department of Geology, Institut Teknologi Sumatera, ITERA, Lampung, Indonesia; Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL, United States