Before they supported bodies, ancient bones functioned as mineral batteries
In short: Today, we view bones as structural scaffolding. But 400 million years ago, the first bones containing living cells may have served a much more energetic purpose: acting as biological batteries to fuel long-distance travel for jawless fish.
In the prehistoric era, bone was far from the internal skeleton we recognize today. Early vertebrates, such as the osteostracans, possessed bone that functioned more like a protective concrete shell on their exterior. These jawless creatures, which researcher Yara Haridy affectionately calls "beetle meriods," featured an armored front end paired with a flexible tail. This external layer of bone tissue was essentially a hard, protective casing for the animal's body.
A recent study published in Science Advances reveals a pivotal shift in vertebrate evolution. While the earliest bone structures lacked osteocytes—the specialized cells that become encased in mineralized tissue during growth—a new type of bone emerged approximately 400 million years ago. These new bones contained living cells that functioned as skeletal batteries, releasing essential minerals into the bloodstream to support the metabolic demands of traveling greater distances. This evolutionary development provided the necessary minerals to sustain life during much longer journeys.
Uncovering this mechanism required a leap from traditional 2D histology to advanced engineering techniques. By employing scanning electron microscopy and focused ion beam milling (FIB-SEM), lead author Yara Haridy produced intricate 3D imagery of fossilised specimens. Although the organic cells themselves decayed millions of years ago, the scans revealed the precise cavities where these ancient osteocytes once resided. This discovery provides a clearer window into how bone transitioned from a simple defensive armor to a dynamic, nutrient-regulating organ. The researchers noticed that the bone tissue surrounding these cell cavities appeared to have been eroded away. This pattern of divots was not indicative of any injury or disease.
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Sources
- Summary by Intellect · source: Bones Began as Mineral Batteries
- Also: Bones evolved to act like batteries, 400-million-year-old fish suggest
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