The most complete ontogenetic series of flagellicaudatan sauropods? A set of five juvenile specimens from the Morrison Formation, Wyoming, USA, and their implications for the systematics and evolution of the group

• Applicant: Dr. Emanuel Tschopp
• Subject Area: Palaeontology ; Systematics and Morphology (Zoology)
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 566342267

The largest terrestrial animals that ever existed were sauropod dinosaurs. Reaching weights of up to 70 tons, they increased their body mass about 2500-fold throughout their growth. Their skeletons had to adapt to cope with this weight increase, as well, so some bones probably changed their shape considerably while growing. Unfortunately, however, we know little about these morphological changes because finds of juvenile sauropods are very rare. If they are found, identifying to what species they belonged is very challenging. Some of the changes these animals underwent during growth correspond to changes that happened during the evolution of the group, meaning that juvenile individuals had some traits that occurred in species that existed earlier in time than those they actually belonged to. A recently acquired collection of five juvenile flagellicaudatan sauropods from the Upper Jurassic Morrison Formation in Wyoming, USA, provides a unique opportunity to identify these changes and their impact on phylogenetic analyses. The collection of five specimens of three distinct growth stages (1hatchling, 2 early juveniles, 2 subadults) was excavated from a single locality. Preliminary analysis suggests they may all be from a single species, which would mean that this is one of the most complete growth series of flagellicaudatan sauropods. All skeletons preserved parts of all skeletal regions, including cranial, axial, and appendicular material, which is also exceedingly rare. Additionally, the skeletons will be prepared over the coming 3-4 years, allowing access to every single bone. Given that they will be mounted in museum displays in future, such access will be very limited after that. The project is thus as scientifically important as it is timely. Together with a PhD student, the PI of this project will conduct a series of tests to identify traits that vary through growth. A range of weighting methods will then be tested to decrease the impact of such variable traits on the phylogenetic analysis. The PhD student will describe the specimens in detail as part of the thesis project, and run a final phylogenetic analysis to identify to which species these specimens belong. The student will use this analysis to update existing ontogenetic frameworks for flagellicaudatan sauropods and to assess whether certain parts of the skeleton change more considerably throughout growth than others. As such, this project combines classic descriptive paleontology with state-of-the-art approaches for phylogenetic and systematic research, forming an important and concise PhD project. It will also provide the basis for promising future studies on the same material regarding their internal bone structure and how it changed in response to the enormous increase in weight of these species.

• DFG Programme: Research Grants
• International Connection: Switzerland
• Cooperation Partner: Dr. Loïc Costeur
• Co-Investigator: Professorin Dr. Stefanie Kaboth-Bahr