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Early jawless fish from the 'Age of Fishes' were likely filter feeders

Jawless fish, specifically a species known as Rhinopteraspis dunensis, are at the heart of a study that illuminates their ancient feeding behaviors. Recently published in the Proceedings of the Royal Society B, the study featured advanced CT scanning techniques.

Subsequently, a team of paleontologists from the University of Birmingham led the research, achieving detailed 3D reconstructions of the mouthparts of vertebrates from the early Devonian epoch — about 400 million years ago, a period often referred to as the Age of Fishes.

Evolution of jawless fish

Jawless fish, also known as agnathans, are ancient vertebrates without jaws. They are categorized into two main groups: the extinct ostracoderms and the extant lampreys and hagfish.

These fish possess cartilaginous skeletons, with most ostracoderms featuring heavy bony armor. Conversely, lampreys and hagfish display a simplified body structure, lacking paired fins and using a notochord as their primary axial support.

Moreover, jawless fish are crucial for understanding vertebrate evolution. They highlight the transition from simple organisms to more complex vertebrate structures.

CT scans reveal new details

The research reveals that these early fish likely employed bony projections surrounding their mouths to alter the mouth’s shape as they gathered food. This suggests a filter-feeding mechanism rather than active hunting or scavenging.

Consequently, this challenges long-standing theories that vertebrates progressively evolved from passive to active feeding strategies.

Dr. Ivan Sansom, the project lead, highlights the significance of non-destructive CT scanning in revealing these ancient life forms. He states, “The application of CT scanning techniques to the study of fossil fish is revealing so much new information about these ancient vertebrates and giving us the opportunity to study precious and unique specimens without destructive investigation.”

Diets of jawless fish

Dr. Richard Dearden, lead author of the study, elaborated on their findings. He explained, “These methods have allowed us to assemble all the small bones of this animal’s mouth together, and understand how it fed from this integrated system rather than by examining isolated bones.

Contrary to a steady trend towards ‘active food acquisition’ — scavenging or hunting — we observe a real diversity and range of feeding behaviors among our earliest vertebrate relatives.”

The 3D images revealed the structure of finger-like bones projecting from the fish’s lower ‘lip.’ These projections helped shape the mouth to capture food from the water.

Furthermore, the reconstructions indicate that the bony plates around the mouth allowed limited movement, suggesting these animals were not capable of biting.

Instead, they likely used these plates to strain food from the water, similar to how modern flamingos or oysters feed.

More about jawless fish

Jawless fish, or agnathans, offer a fascinating glimpse into the early stages of vertebrate evolution. Here are some additional intriguing aspects about them that were not covered in the initial research summary:

Ecological role

Beyond their feeding mechanisms, jawless fish play specific roles in their ecosystems. Lampreys, for instance, impact the populations of other fish, which can have cascading effects on aquatic ecosystems. Meanwhile, hagfish contribute to the ocean floor’s nutrient cycle by breaking down dead animals.

Reproductive habits

The reproductive behaviors of jawless fish are quite unique. Lampreys, for example, migrate from saltwater to freshwater environments to spawn, reminiscent of salmon. They build nests by moving stones with their mouths, and after spawning, they typically die, similar to the lifecycle of salmon.

Anatomical features

The anatomical structure of jawless fish provides insight into the minimalist design of early vertebrates. For example, they have a single nostril and a early brain that lacks the complexity found in jawed vertebrates. Their sensory systems are also specialized; lampreys have well-developed eyes, whereas hagfish are mostly blind and rely heavily on their sense of smell and touch.

Conservation status of jawless fish

Some species of lampreys are considered endangered due to habitat destruction, pollution, and barriers like dams that block their migratory paths. Conservation efforts are crucial to maintaining the diversity and ecological roles of these ancient creatures.

Research applications

The unique properties of jawless fish have led to various research applications, including the study of their cartilage for insights into human cartilage repair and regeneration.

Moreover, the slime produced by hagfish is being studied for potential applications in materials science due to its unique properties, such as its incredible strength and flexibility.

Jawless fish thus not only provide a window into the past but also continue to influence scientific research and ecological conservation efforts today. Their study helps refine our understanding of evolutionary biology and offers potential applications in medicine and technology.

Challenging traditional views

The findings challenge the prevailing hypothesis that vertebrate evolution predominantly moved from passive to increasingly predatory behavior.

Additionally, the diversity in feeding strategies observed in these ancient vertebrates suggests a complex scenario. This indicates a more nuanced process of evolutionary adaptation.

New perspective on vertebrate history

The implications of this research are vast, offering a new lens through which we can view the early evolutionary stages of vertebrates. This perspective applies long before the advent of jawed creatures.

The diversity of feeding behaviors observed underscores the complexity of early vertebrate life. Additionally, it challenges the linear narratives of evolutionary progression traditionally favored in scientific discourse.

The full study was published in the journal Proceedings of the Royal Society B Biological Sciences.


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