More than 400 million years ago, some vertebrates developed airplane-like structures in flight to move more efficiently across water. These are the ostracoderms, armored fish without jaws that inhabited the oceans of the Paleozoic era. This is revealed by a study in which the Cavanilles Institute of Biodiversity and Evolutionary Biology (ICBiBE), located in the scientific-academic area of the Science Park University of Valencia (PCUV), which analyzes how these early vertebrates exploited their skeletons to improve their stability and hydrodynamic performance.
Ostracoderms have traditionally been considered clumsy creatures mainly due to the presence of heavy bony shells covering their heads and the absence of even fins, equivalent to the arms and legs of posterior vertebrates. However, the present study published in Paleobiology questions this view. Through the use of advanced techniques in virtual paleontology and fluid dynamics simulation, this group of paleontologists has discovered that such bony shells, as well as certain extensions thereof, function as hydrodynamic stabilizers, allowing them to glide with greater control and efficiency in the water.
The results show that many species of ostracoderms developed lateral and dorsal extensions in their shields, which, like the wings of an airplane, generated lift and reduced the resistance to advance. In addition, the combination of these processes generated stability situations in turns and changes of direction, analogous to the interaction of the empennage of an aircraft with the rest of the aircraft, which reveals the direct implication of the principles of fluid mechanics in the development and evolution of these animals.
"Our work demonstrates that the evolution of these primitive fish was not simply a race towards more active and faster forms, but that there was a great diversity of locomotor strategies," explains Humberto Ferrón, ICBiBE researcher and co-author of the study. "Many ostracoderms probably swim efficiently in the open sea, taking advantage of their bony structures to stabilize themselves, rather than crawling along the seabed as previously thought".
Comparative analysis of more than 60 three-dimensional ostracoderm models has revealed that different groups evolved into similar structures independently, a phenomenon known as 'evolutionary convergence'. Some species developed frontal extensions that reduced resistance to water while others relied on lateral expansions that increased lift and stability, favouring energy efficiency during the swim.
"When we analyzed the data, we realized that the evolution of these primitive fish was much more complex than previously thought," says Vicente Sánchez-Sánchez, first author of the study. "These fish did not have simple shapes without sophisticated adaptations; in fact, their biomechanics show hydrodynamic solutions that we find today in many aquatic animals".
Simulations also indicate that ostracoderms with large dorsal and lateral extensions would have maintained greater stability in the water column, while those with more compact bodies and no additional structures would have been more manoeuvrable in shallow, coastal environments.
"Our work shows that the evolution of these primitive fish was not simply a race towards more active and faster forms, but that there existed a great diversity of locomotor strategies. Many ostracoderms probably swam efficiently in the open sea, taking advantage of their bone structures to stabilize, instead of crawling along the seabed as previously thought", Humberto Ferrón, ICBiBE researcher and co-author of the study
The article points out that the evolution of early vertebrates did not follow a single direction but rather diversified in relation to interactions with the environment, "Not only did they evolve towards faster and more active forms, but they diversified in their way of acting with the environment. In addition, while some were optimized for speed and stability in open water, others became more agile in complex habitats", adds Óscar Sanisidro, from the University of Alcalá and co-author of the work.
This study not only changes current perceptions about the evolution of early vertebrates, but also shows how nature experimented with hydrodynamic principles long before humans began designing efficient structures to move in water.
The work has been carried out by the MacroFun (Macroevolution and Functional Morphology Research Group), led by Humberto Ferrón at ICBiBE. The team specializes in the analysis of large evolutionary transitions using advanced biomechanics, ecology and evolution tools. In addition to the Science Park team, the University of Alcalá and the University of Bristol (England) participated in the study.
Source: UV News