Braincase structure of the Middle Jurassic theropod dinosaur Piatnitzkysaurus

The braincase of the Middle Jurassic basal tetanuran theropod Piatnitzkysaurus floresi is described in detail. It exhibits several probable autapomorphic characters of this taxon, including the extremely shortened and narrow basipterygoid processes, the presence of parasphenoid recesses that seem to communicate with each other, and basipterygoid recesses that are approximately as long anteroposteriorly as they are high. The braincase of Piatnitzkysaurus shows two possible synapomorphies with the enigmatic European Middle Jurassic theropod Piveteausaurus, a subrectangular pituitary fossa that is wider than high and the transverse span between the basipterygoid processes being smaller than the width of the basal tubera. A noteworthy aspect of the braincase of Piatnitzkysaurus is the high number of accessory pneumatic recesses, which indicates that the presence of an anterior and dorsal tympanic recess, and possibly also of subcondylar and basipterygoid recesses is plesiomorphic for tetanurans. In contrast, the bones enclosing the brain (e.g., laterosphenoid, prootic, supraoccipital) are very massive and lack internal pneumatic chambers, as they are present in later tetanurans.