Therapsid ESRF_2023

This is a project to take 6 large therapsid skulls to the European Synchrotron Radiation Facility in Grenoble for CT scanning early in July 2023. The aim is to address their neurological adaptations to head-butting and deduce potential behavioural complexity among early therapsids. Details are available in the attached proposal (which has already been accepted by the ESRF, see at the end of this form).

BP/1/5735, BP/1/7141 and BP/1/8125 are relatively small, and will be hand carried to the ESRF by Julien Benoit, Andrew Bolton and Luke Norton.

BP/1/8656, BP/1/1370 and BP/1/1575 are too large and too heavy to be hand carried, and will have to be transported by air cargo to the ESRF using DHL Air Economy

Aim/rationale:

Evidencing intraspecific agonistic behaviours (male to male head-butting combat and sexual display) is the gateway to reconstruct gregariousness and social complexity in extinct species, as it implies the existence of a stratified and hierarchical society. In turns, behaviours like head butting and face biting not only leave visible injuries, but require crucial adaptations of the skull to be used as weapons and withstand these brutal encounters, such as reinforcement and reorientation of the capsules for the cranial nerves, brain, and inner ear. Evolution of these adaptations can be traced through times and the fossil record using SRµCT. The skull of late Permian therapsids, the ancestors of mammals, display a remarkably wide variety of head weapons that remains to be investigated. This includes maxillary bosses (Pachydectes), a frontal horn (Struthiocephalus), a parietal shield (Tapinocaninus and Riebeeckosaurus), tabular bosses (Styracocephalus) and sabre-like canines (Anteosaurus). This diversity in ornamentations is reminiscent to that encountered in social mammals, thus strongly suggesting that the common portrayal of therapsids as solitary animals is an oversimplification.
This project aims at documenting the diversity of agonistic behaviour in early therapsids by providing in depth descriptions and comparisons of the neurological and histological adaptations to social fighting in the above listed species, to find crucial evidence of a great variety of agonistic behaviours. This will, for the first time, demonstrate that therapsids were highly complex, social animals. This will be backed by the study of their encephalisation, as it has been hypothesised that social behaviour would have increased with brain size and intelligence.
Special motivation for BP/1/5735: There is one holotype included in this project, BP/1/5735, the holotype of the biarmosuchian Pachydectes elsi. This specimen is the sole representative of this genus and species and thus is considered sensitive material. It is important to include this specimen in the sampling, however, as it uniquely displays paired pachyostotic maxillary bosses that were likely used for intraspecific combat. As no other therapsids (or even amniotes) display such morphological adaptations to head-butting, BP/1/5735 evidences a unique part of therapsid behavioural diversity. This is why studying its neurology (particularly the maxillary canals) of this specimen is of paramount importance to this project. Unfortunately, the specimen is too large for all the micro-CT lab in the country, and the large size also impedes good contrast. Medical scanners are large enough, but too low in energy to get through the dense sediment. Only the new beamline of the ESRF, BM18, has a stage large enough and enough energy to provide workable results.