Overview
- A peer-reviewed paper published in Science on Thursday, June 18, 2026, reports exceptionally preserved hatchling fossils from the Mazon Creek lagerstätte that lack key amphibian larval traits such as external gills.
- Researchers led by Jason Pardo and Arjan Mann used high-resolution imaging including scanning electron microscopy to show hatchlings already had adult-like skull and skeletal features and in some cases external yolk sacs.
- The study samples hatchlings from several lineages — including embolomeres, a megalichthyid and an aïstopod — which strengthens the case that direct development was widespread among late Carboniferous stem tetrapods.
- The work relied on museum collections and specimens donated by amateur collectors to public repositories to ensure other scientists can reexamine the material and test the conclusions.
- While the findings challenge a long-standing textbook claim that metamorphosis was ancestral to vertebrate land colonization, open questions remain about the very earliest fin-to-limb ancestors, hatchling breathing modes, and how often transitions to land happened.