A recent study has revealed how the first marine vertebrates, such as ostracoderms, swam and the hydrodynamic mechanisms that allowed them to be the first vertebrates to rise beyond the seabed, colonizing the so-called water column, much earlier than done so far. ., it was believed.
The work is the work of Francisco Huera of the Rovira i Virgili University (URV) of Tarragona, Héctor Botella, of the Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia, Spain, and Richard A. Fariña, of the University of Republic in Montevideo, Uruguay.
After exposing 3D models of these extinct fish to water currents, the researchers determined that, despite their morphology, they were skilled enough swimmers to occupy the layers closest to the surface. The results of the study lead to a change in the conception that was held about the first marine vertebrates and help to understand how they evolved to live, in the long run, out of the water.
The Devonian is the geological period in which the first insects appeared and in which the vertebrates, which inhabited the sea, began to develop limbs. On land, some plants developed woody tissues and the ability to reproduce through seeds, which gave rise to the first forests on Earth. Oceanic ecosystems, populated by bryozoans, brachiopods, corals and trilobites, led to the appearance of the first vertebrates, including fish called ostracoderms.
Traditionally, scientific literature describes fish in this class as clumsy swimmers who limited themselves to crawling on the bottom, due to the configuration of their skeleton. Ostracoderms – a name that derives from the Greek “shell skin” – had a rigid exoskeleton that covered the front part of the body, limiting their mobility. These animals, now extinct, did not have a jaw, nor did they have any fins other than the tail, that is, their own tail.
Researchers around the world have long suspected that ostracoderms played a major role in colonizing the water column of the marine pelagic zone, or, in other words, those parts of the sea that do not lie on a continental shelf, offshore. However, the swimming mechanisms they must have used to expand their seafloor habitat down to the shallowest layers were unclear. Biologists, in fact, attribute the colonization of the water column to more modern fish.
3D model of an Ostracoderm. (Photo: URV / Universitat de Valencia / University of the Republic of Montevideo)
“As soon as I saw an ostracoderm I thought it could swim very well,” confesses Francisco Huera. Huera is not a biologist, but rather studies fluid dynamics, that is, how air or water behaves in a series of conditions, such as those that occur in the flight of an airplane, in the operation of a wind turbine or in the behavior of fish when they swim. The research team worked with full-scale models built from fossil remains of ostracoderms to determine the extent to which their morphology allowed them to ascend beyond the seafloor.
In the water channel of the URV Laboratory of Fluid-Structure Interaction (LIFE) research group, Huera exposed the models to water currents and was able to determine the hydrodynamic behavior of prehistoric animals. In this way, they demonstrated that, although ostracoderms lacked fins, they possessed a fairly sophisticated control system, which allowed them to swim in a far from primitive way: “They work like a hang glider; The shape of the head generates vorticity, a spiral rotational current, which exerts additional lift. This same mechanism is what some of the most advanced aircraft exploit,” explains Huera. The researchers reconstructed the most likely way in which these fish must have swum: “they waved their caudal fin, jerkily, and tilted their heads to generate more or less lift.”
The colonization of the water column of the pelagic zone represents one of the most important transitions in the evolution of life on Earth. The research results identify and explain the mechanisms through which the first fish managed to expand their habitat in this area and demonstrate that this occurred much earlier than previously thought, during the transition between the Silurian and Devonian periods, more than 400 million years ago years.
The study is titled “Delta Wing Design in Early Nektonic Vertebrates.” And it was published in the academic journal Communications Biology. (Source: URV)
Interview between the Time.news Editor and Francisco Huera, Fluid Dynamics Expert
Editor: Welcome, Francisco! Thank you for joining us today to discuss your groundbreaking research on ostracoderms. To start, could you tell us what inspired you to explore the swimming mechanisms of these ancient marine vertebrates?
Francisco Huera: Thank you for having me! My fascination with fluid dynamics—how fluids behave under various conditions—led me to consider ostracoderms. When I first encountered their fossils, I couldn’t shake the intuition that these creatures, despite their peculiar morphology, might have had impressive swimming abilities. It ignited a desire to test that hypothesis using modern technology.
Editor: That’s incredibly intriguing! Traditionally, ostracoderms have been depicted as clumsy swimmers. Your study challenges that notion. What were some of the key findings that shifted our understanding of their swimming capabilities?
Francisco Huera: Our study revealed that ostracoderms were much more adept at navigating the water column than previously thought. By creating 3D models of these creatures and exposing them to controlled water currents, we observed that they could indeed swim skillfully, occupying layers close to the surface. This suggests that they were not just limited to the seabed but played a crucial role in colonizing the water column much earlier than scientists had believed.
Editor: It’s fascinating to think of these ancient fish occupying such different ecological niches. How does this newfound understanding of ostracoderm swimming impact our views on vertebrate evolution?
Francisco Huera: It has significant implications! It indicates that the evolutionary adaptations we often attribute to more modern fish may have roots in these early vertebrates. The ability to swim well in the open water likely paved the way for further adaptations, including the development of limbs, which would eventually lead to vertebrates colonizing land.
Editor: The Devonian period was a transformative time for life on Earth, with the first forests emerging alongside these early fish. Can you elaborate on how your findings connect with the broader ecological changes occurring during that era?
Francisco Huera: Absolutely! The Devonian was a crucial period not just for marine life, but for the emergence of terrestrial ecosystems. As ostracoderms and other early vertebrates began to exploit the water column, they might have contributed to nutrient cycling in marine ecosystems. This, in turn, could have supported the burgeoning land ecosystems by maintaining biodiversity in the oceans, ultimately influencing evolutionary trajectories across multiple domains of life.
Editor: It sounds like your research opens up new avenues for understanding our planet’s evolutionary history. Were there any surprises during your research process?
Francisco Huera: Definitely! One of the most surprising elements was how a creature with a rigid exoskeleton could still exhibit such agility. Their morphology—often seen as a limitation—actually allowed for unique swimming strategies. It challenged the narrative that adaptation is always about flexibility; instead, sometimes it can be the balance of trade-offs that leads to unexpected capabilities.
Editor: That’s a refreshing perspective! what do you hope will be the next steps in this area of research?
Francisco Huera: I hope this study encourages more interdisciplinary approaches within paleontology, combining fluid dynamics, biomechanics, and evolutionary biology. There’s still much to learn about early vertebrates not just through fossil analysis but also by employing tech like simulations and 3D modeling to further explore their behaviors and interactions with their environments.
Editor: Thank you, Francisco, for sharing your insights. It’s exciting to see how technology is reshaping our understanding of the past. We look forward to following your future research!
Francisco Huera: Thank you! I appreciate the opportunity to discuss our work, and I’m excited about what lies ahead in this fascinating field!