This is Mazon Monday post #276.  What’s your favorite Mazon Creek fossil?  Tell us at email:esconi.info@gmail.com.

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Cal So, Postdoctoral Scientist in the Research & Collections Department of The Field Museum, Chicago, gave us an informative presentation in June 2025.  The title of his presentation was “Taxonomic diversity and development of Late Carboniferous amphibamiforms from the Mazon Creek Lagerstätte”.  He spoke about the history and recent developments in the science of Mazon Creek amphibamiform temnospondyls.  There’s still much more to learn!

Summary: Late Paleozoic amphibamiform temnospondyls have a critical role in the research and discourse on the origin of lissamphibians. Previous research has started to form a consensus that amphibamiforms acquired lissamphibian traits in a stepwise evolutionary pattern. However, Cal’s recent research found that the internal relationships of amphibamiforms may not be as robust as previously thought, weakening support for a linear acquisition of a derived lissamphibian body plan and subsequently destabilizing interpretations on the evolutionary origins of lissamphibians. The exceptional preservational setting in the Francis Creek Shale of the Mazon Creek Lagerstätte (~309 Ma) offers a unique window into the morphology of Late Paleozoic amphibamiforms. Cal is revisiting the morphology of Amphibamus gran diceps using new fossils, including larval forms, from the Francis Creek Shale to improve the understanding of stem-lissamphibian condition. Cal is also describing and analyzing the development and ontogeny of Amphibamus grandiceps. Combined, these studies will shed light on the interplay between the evolution of amphibamiform temnospondyls in the Late Paleozoic Era and the evolutionary and developmental origins of modern lissamphibian anatomy, development, ontogeny, and physiology.