Ontogeny, skeletochronology and life history traits in temnospondyls

• Applicant: Dr. Nicole Klein
• Subject Area: Palaeontology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 508778113

The origin and early evolution of land vertebrates involved divergent strategies to cope with life at the water-land interface. Central to this is the question what the ancient life cycles of tetrapods were like and how the divergent ontogenies of extant tetrapods evolved. Among these taxa, the temnospondyls have the best documented fossil record of ontogeny. Different life cycles have been reported from many temnospondyls based on morphological examination of size classes from the same locality and horizon. These range from fully aquatic over amphibious to metamorphosing terrestrial taxa. However, in contrast to lissamphibians, most temnospondyls appear to have neither metamorphosed nor did they change their habitats. Aside from metamorphosis, the life history strategy of neoteny has also been identified in at least one clade, the branchiosaurids. Paleohistology holds the key to add primary data on growth and ages at certain life history traits in extinct taxa, and the excellent fossil record and large sample base promise that such studies will greatly enhance our understanding of temnospondyl life cycles. The envisioned project integrates (1) morphological data on ontogenetic phases (larval, neotenic, metamorphosing, adult) in selected taxa with (2) bone histological data (analysis of changes in tissue type and skeletochronology) of the same taxa in order to (3) identify and map the different ontogenies on a phylogeny of temnospondyls. A further step (4) is to provide life history traits for growth modeling, and analysis of life history strategies in a statistical frame in Project. Morphological analysis will add to existing data on temnospondyl ontogenies and focus on poorly studied taxa as well as on species for which growth series are available. Paleohistology will focus on the bone histological growth record, identifying distinct phases in the ancient life cycles as well as analyzing growth marks to detect life history traits. Changes in life style (aquatic-semiaquatic-terrestrial) will be identified for the different ontogenetic phases in collaboration with project D. The morphological and histological data will also provide traits of ancient life histories, which are essential for Project C. Such life history data may include hatchling size, age and size at onset of sexual maturity, age and size when maximum body length was achieved, age and size at death, and maximum life span. In addition, age and size at metamorphosis or at change of habitat will add essential data in taxa with biphasic life cycles.

• DFG Programme: Research Units
• Subproject of: FOR 5581: The evolution of life histories in early tetrapods
• Co-Investigator: Professor Dr. Rainer Schoch