The fossil record of land vertebrates may be missing its first chapters

Nature · Published 25 October 2026 Swipe more like this →

In short: We long thought we understood how fish first developed limbs to walk on land. However, new evidence from Poland suggests our timeline is wrong. These tracks reveal that four-legged vertebrates were moving across the earth much earlier than the bones we have found.

For decades, the transition from fins to limbs was defined by specific transitional fossils like Tiktaalik and Panderichthys. These 'elpistostegids' are widely recognized as the precursors to tetrapods—the group of vertebrates that eventually dominated terrestrial life. However, a discovery in Poland is forcing a radical reassessment of this evolutionary timeline. These early tetrapods were vertebrates that possessed limbs instead of paired fins. Their evolution represents one of the most significant milestones in vertebrate history.

Researchers identified well-preserved tetrapod trackways in marine tidal flat sediments at the Zachelmie Quarry. These tracks are dated to the early Middle Devonian (Eifelian stage). Such a chronology matters as it positions these quadrupeds on land roughly 18 million years before any known tetrapod remains, and nearly 10 million years prior to the most ancient elpistostegids. The tracks are approximately 400 million years old. Some specimens show foot morphology similar to the primitive Ichthyostega.

This discrepancy suggests that the well-known transitional forms like Tiktaalik might be late-surviving relics rather than the direct ancestors of land animals. The discovery highlights a major gap in our understanding of early vertebrate history. While the Devonian is often called the 'Age of Fishes' due to the dominance of jawless fish and placoderms, it was also the era when changing freshwater environments fostered the first movement onto land. These findings challenge previous assumptions about the age and identity of early track makers. They also suggest that our current body fossil record is incomplete.

The transition occurred alongside a massive vascular plant explosion that created extensive marshlands. As primitive trees like Archeaosigillaria appeared, they transformed global carbon cycling and created new niches for both invertebrates—like scorpions and spiders—and the first tetrapods to emerge from the water. The period saw a peak in marine diversity with predators like sharks and ammonoids. Brachiopods were among the most abundant organisms during this time.

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