Were these ancient, diverse tetrapods the true ancestors of modern amphibians and reptiles?

Nature · Published 3 October 2026 Swipe more like this →

In short: Lepospondyls were a collection of small, Paleozoic creatures that thrived in Europe and North America. Ranging from snake-like to lizard-like forms, their evolutionary identity remains a puzzle. Scientists debate whether these distinct animals represent a unified group or a scattered assembly of early ancestors to today's amphibians and amniotes.

Named in 1888 by Karl Alfred von Zittel, the Lepospondyli are defined by their unique, spool-shaped vertebrae. Unlike many other vertebrates, these bones formed as solid cylinders around the notochord rather than ossifying from cartilage. This structural quirk, combined with a fused neural arch, marks them as a distinct, if enigmatic, group of early tetrapods that lived from the Early Carboniferous to the Early Permian.

The classification of lepospondyls is a subject of intense scientific disagreement. Because these creatures arrived in the fossil record already possessing highly developed and specialized physical traits, their exact place on the tree of life is difficult to pin down. Researchers have proposed five major subgroups: the lizard-like Microsauria, the elongated Lysorophia, the limbless Aïstopoda, the aquatic Adelospondyli, and the diverse Nectridea. Whether these groups form a single, monophyletic branch or are a collection of unrelated lineages remains a point of contention.

The debate extends to their relationship with modern life. While the 'temnospondyl hypothesis'—which links modern amphibians to dissorophoid temnospondyls—is currently the most widely accepted, the 'lepospondyl hypothesis' persists. This alternative suggests that modern amphibians evolved from lepospondyl ancestors. Some studies, such as the 1995 work by Robert Carroll, have even argued that lepospondyls are more closely related to reptiles than to amphibians. With recent research continuing to challenge the unity of the group, the true evolutionary story of these Paleozoic survivors remains a work in progress.

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