Middle Jurassic fossils document an early stage in salamander evolution

Area of Science:

• Paleontology
• Evolutionary Biology
• Vertebrate Zoology

Background:

• Salamanders are crucial model organisms, but their evolutionary origins and early radiation are poorly understood.
• Early fossil records of stem-salamanders are incomplete, hindering insights into Lissamphibia's origins.
• Existing fossils often represent larval or fragmentary specimens, limiting anatomical understanding.

Purpose of the Study:

• To describe the near-complete skeleton of the stem-salamander Marmorerpeton from the Middle Jurassic of Scotland.
• To reconstruct the 3D anatomy of Marmorerpeton, focusing on poorly characterized features like the braincase and jaw.
• To resolve the phylogenetic relationships of early and stem-salamanders using comprehensive anatomical and imaging data.

Main Methods:

• Computed tomography (CT) scanning for high-resolution 3D anatomical visualization of Marmorerpeton fossils.
• Detailed morphological analysis of key skeletal elements, including the braincase, scapulocoracoid, and lower jaw.
• Phylogenetic analysis incorporating fossil and extant species data, utilizing advanced imaging of modern amphibians.

Main Results:

• Marmorerpeton fossils provide near-complete skeletal information, revealing detailed anatomy of early salamanders.
• Phylogenetic analysis places Marmorerpeton with other Middle Jurassic-Cretaceous Asian taxa, indicating an early radiation of neotenous stem-salamanders.
• The study identifies greater diversity among Jurassic stem-salamanders than previously recognized, with some sharing traits with extant giant salamanders.

Conclusions:

• The findings advance understanding of evolutionary changes within the salamander lineage.
• This research provides critical data on early salamander evolution and the origins of Batrachia and Lissamphibia.
• The diversity and specialized morphologies of early stem-salamanders are highlighted, cautioning against using single taxa as representative.