Some ostracoderms - primitive vertebrates without fins or jaws - first colonized the marine pelagic environment more than 400 million years ago. These fishes optimized their cephalic shells to rise from the bottom and move efficiently in oceanic waters, thus compensating for their lack of fins. This is the main result of a study led by a team from the Cavanilles Institute of Biodiversity and Evolutionary Biology, located at the University of Valencia Science Park, which has just been published in the journal Nature Communications Biology. The work has been carried out using 3D models of fossils and advanced techniques of digital particle image velocimetry
The colonization of the pelagic environment - mid-water near the ocean surface - by vertebrates was a milestone in the establishment of complex aquatic ecosystems. Although this transition has always been related to the appearance of fins and jaws during the evolutionary process of fishes, recent studies suggest that the first active swimmers to occupy the water column were some ostracoderms, primitive fishes without jaws or fins other than the caudal fin, their own tail. However, the hydrodynamic mechanism used by these agnates to rise from the benthic zones to the pelagic environment remained unclear.
The work now published in Nature Communications Biology reveals the hydrodynamic mechanism used by ostracoderms to generate lifting forces by means of their large cephalic shells and from the generation of vortices or whirlpools called LEVs (Leading Edge Vortices). The study, carried out jointly from paleobiology and fluid mechanical engineering, used 3D-printed models of fossils more than 420 million years old. It also used DPIV -Digital Particle Image Velocimetry- technology, a technique that allows precise measurement of two-dimensional velocity fields and was applied in a water tunnel environment to study the flow around fish body structures.
“While swimming, the fish generated vortices on the front edges of their cephalic shields, through which they stabilized their swimming and acquired a surprising lifting capacity, similar to that produced in the triangular delta wings used by some of the most modern airplanes and space vehicles”, comments Héctor Botella, professor of Paleontology, researcher at the Cavanilles Institute of Biodiversity and Evolutionary Biology (ICBiBe), located at the University of Valencia Science Park, and co-author of the article.
“While swimming, the fish generated vortices on the front edges of their cephalic shields, through which they stabilized their swimming and acquired a surprising lifting capacity, similar to that produced in the triangular delta wings used by some of the most modern airplanes and space vehicles”
During the last decades science has shown that LEVs represent a hydro-aerodynamic mechanism universally exploited by many species. The present study demonstrates that the first vertebrates already exploited LEVs more than 400 million years ago to make up for the lack of mobile appendages and colonize the water column.
The results of this research open new perspectives to the study of the evolution of the first aquatic vertebrates and their ability to adapt to the pelagic marine environment. The discovery that ostracoderms used principles similar to those used by hang gliders in aeronautics underlines the complexity and diversity of evolutionary strategies and may, according to the authors, provide a source of bio-inspiration for the design of underwater vehicles.
In addition to the Paleobiology Unit of the Cavanilles Institute of Biodiversity and Evolutionary Biology (ICBiBe) of the University of Valencia, the Department of Paleontology of the University of the Republic (Montevideo, Uruguay) and the Department of Mechanical Engineering of the University Rovira i Virgili (URV, Tarragona) have participated in the research.
Delta wing design in earliest nektonic vertebrates. Héctor Botella, Richard A. Fariña & Francisco Huera-Huarte. Communications Biology volume 7, Article number: 1153 (2024)