Developmental origin of tetrapod vertebral centra and the phylogenetic relationships of basal tetrapods and lissamphibians

• Applicant: Professorin Dr. Nadia Belinda Fröbisch, since 11/2014
• Subject Area: Palaeontology
• Term: from 2012 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 225144936

Although vertebral evolution in basal tetrapods is crucial for understanding the fish-to-tetrapod transition and early tetrapod history, the development of the complex vertebral centrum in basal tetrapods and their fish-like relatives is still poorly understood. Several efforts were made in the 19th and first half of the 20th century to classify basal tetrapods on the basis of their vertebral morphology. However, different interpretations of centrum formation in basal tetrapods led to conflicting ideas concerning the homology of central elements, and thus precluded using the wide spectrum of centrum morphologies for establishing phylogenetic relationships. Recent advances in developmental biology, especially in research on the early formation of vertebrae, allow new insights into the development of basal tetrapod vertebrae. The proposed project is a combined palaeontological and zoological approach to reconstruct phylogenetic interrelationships between the different lineages of basal tetrapods based on vertebral centrum development and structure. In the palaeontological part of the proposed project, the homology of the particular central components in basal tetrapods will be clarified and it will be shown how the different lineages of basal tetrapods have modified the vertebral centra of their fish-like relatives. For this, vertebral centra of basal tetrapods will be investigated histologically by thin sections and micro-CT scanning and by morphological investigation of growth series. The study will focus on the detection of the different types of mineralised tissue, their modes and timing of ossification and the presumed embryonic soft tissues (notochordal sheath or perichordal tube) from which they were derived. Tetrapodomorph fishes with ossified vertebral centra will be taken for outgroup comparison. It will be assessed if the different modes of vertebral formation, histological structures and vertebral morphologies show derived features that characterise particular lineages of basal tetrapods. In the zoological part of the project vertebral development and histology in basal representatives of the three major groups of extant lissamphibians (caecilians, urodeles and anurans) will be studied in detail and compared with the data of basal tetrapods obtained in the palaeontological part of the project. The knowledge of the homology of central elements and the developmental origin of the tetrapod centrum is important not only for understanding the adaptation of vertebrates to a terrestrial existence, but also for reconstruction of the phylogenetic relationships between different basal tetrapod groups and their affinities with extant lissamphibians, the ancestry of the latter still being one of the most controversially discussed questions in vertebrate palaeontology.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Dr. Florian Witzmann, until 11/2014