The large lambeosaurine hadrosaur Lambeosaurus lambei, depicting hypothetical deflated (left) and inflated (right) aerostatic expansive external pneumatic tissues (balloon faces). These structures are always paired and parasagittal.
Generalized lambeosaurine hadrosaur skull in profile. Figures depict a strong midline ridge of solid bone with sculpted fossa on either side, and a small aperture, or fontanelle, between the nasal and premaxilla portions of the cranial crest, which may reflect an external aperture for the internal pneumatic cranial sinuses.
The hypothetical lambeosaurine hadrosaurid skull in profile shows the expansion and transformation of the cranial crest from a Lambeosaurus-like forward position to a Tsintaosaurus-like posterior position. The fontanelle is present in most, if not all, depicted lambeosaurines.
Below, a Lambeosaurus skull in three-quarters anterolateral view, showing the skull as it is normally on the left, then overlapped with the internal nasal passage in the middle in light blue; followed by the same with the external extension of the nasal passage into an aerostatic expansive external pneumatic tissue that overlies the crest, bounded by various fossae on the surface.
Head and skull of the saurolophine hadrosaurid dinosaur Maiasaura peeblesorum, showing the aertostatic expansive external pneumatic tissue that arises direction from the anterior end of the nasal passage through the large nostrils, filling the circumnarial fossa, which extends posteriorly on the face to be limited by the bony upward projecting crest. In saurolophines like Brachylophosaurus and Saurolophus, this crest expands posteriorly and forms a long bar, but the ridge and its fossa remain present. These bony rods supported some form of external display tissue, and it's likely that was pneumatic in nature.
Aerostatic expansive external pneumatic tissues in hadrosaurs (and some other #dinosaurs) are not a novel theory of today's paleoartists. It goes back almost 50 years to the late 70s-early 80s. However, it was exclusive to hadrosaurine/saurolophine #hadrosaurs.
#Lambeosaurus #Maiasaura #SciArt