While modern amphibians start life in a larval stage, a new fossil study suggests these tadpole-like stages were not present in earlier times. In studying the origin of tetrapods, including the transition from water to land, an important hypothesis has been that early tetrapods may have exhibited gradual metamorphosis – including an aquatic larval stage. The larval stage was characterized by transient organs that were lost in a later transition to adulthood, and it has been hypothesized that this transition may have facilitated the larger transition from water to land. To seek evidence for this larval stage, Jason Pardo et al. looked at many fossils of stem tetrapods from the Mazon Creek Lagerstatte in Illinois. Their soft tissue was especially well-preserved. In these tissues, the authors found no evidence of larval morphological change. Instead, both before and after the fin-to-limb transition, growth from hatchling to adult proceeded through a direct development model, say the authors. Their findings suggest that acceleration of limb development may have been a prerequisite for completing the transition to land in early tetrapods.

For reporters interested in research integrity-related themes, Pardo told SciPak: “Research integrity is a critical part of the work we do. For us, our work relies on ensuring our interpretations of fossils are replicable by other researchers. We achieve this by ensuring our specimens are in public museums and research collections. We have worked closely with amateur collectors to ensure that the scientifically important fossils we report here will always be available to any researcher by making certain that they have been donated to public museums. We would like to see more partnerships like this.”