Many aspects of the life and habits of the Devonian stem tetrapod Acanthostega remain obscure. Although it had limbs with digits, everything we know about it suggests that it was obligately aquatic. Here Sophie Sanchez and colleagues show that most known Acanthostega specimens come from a single mass-death assemblage, and that their state of ossification suggests that although the largest animal was at least six years old, they were all juveniles—no adults are known. The research provides a poignant snapshot into the life one of the earliest known tetrapods, but raises many questions about the evolution of life history in land vertebrates.
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