smaller cavities, one at the front, the other at the rear, by curved median processes of the praemaxillae, forming hooks around a passage between the cavities. From the rear cavity the air was transported to below, towards the internal skull cavity. Although it is usually assumed that a single passage served for this purpose, Prieto-Márquez and Wagner saw indications in the form of the nasal that there were paired downward passages, to the inside of the lateral processes of the praemaxillae. From this they concluded that the entire airflow was likely separated, the common medium chamber probably being divided into a left and right section by a cartilaginous septum. The conclusion that the tubular structure in the rear nasal bones was not an air passage, forced Prieto-Márquez and Wagner to find an alternative explanation of its function. They suggested that it would have served to lessen the weight of the crest, such a tube combining relative strength with a low bone mass. Tsintaosaurus would have differed in this from more derived lambeosaurines, which have a front extension of the frontal bone, in the form of a bone sheet, supporting the crest. Other distinctive traits Apart from the crest, Prieto-Márquez and Wagner identified several other distinctive traits (autapomorphies) of Tsintaosaurus. The rim of the upper beak is rounded and thick, wider than the transverse width of the front depression around the nostrils. As far as this depression is situated on the praemaxillae, it is at each side divided lengthwise by two ridges obliquely continuing to below and sideways. Internally, the fused nasal bones form a bony block in front of the braincase. The rear of the nasal bone is clipped by front extensions of the frontal bone, the topmost of which is elevated relative to the skull roof. The ascending branches of the praemaxillae have internal processes pointing to behind, below and slightly inside, dividing a shared chamber at the midline. The prefrontal possesses a flange, continuing from the lower part of the lacrimal bone to the lower part of the ascending process of the prefrontal, and connecting to a process on the side of the praemaxilla to form an elevation on the side of the crest base. The side and the underside of the prefrontal show deep vertical grooves. The supratemporal fenestra is, transversely, wider than long. Classification Tsintaosaurus may form a clade in Lambeosaurinae with the European genera Pararhabdodon