The Quingdao lizard, Tsintaosaurus (1958)
Phylum : Chordata
Class : Reptilia
Order : Ornithischia
Family : Hadrosauridae
Genus : Tsintaosaurus
Species : T. spinorhinus
- Late Cretaceous (83,6 - 72 Ma)
- 10 m long and 3 000 kg (size)
- China (map)
Tsintaosaurus was originally reconstructed with a unicorn-like crest on its skull. The crest, as preserved, consists of an about forty centimetres long process, protruding almost vertically from the top of the rear snout. The structure is hollow and seems to have a forked upper end. Comparable structures with related species are unknown: they possess more lobe-like crests. In 1990, David Weishampel and Jack Horner cast doubt on the presence of the crest, suggesting that it was actually a broken nasal bone from the top of the snout distorted upward by a crushing of the fossil. Their study further suggested that, without the distinctive crest to distinguish it, Tsintaosaurus was actually a synonym of the similar but crestless hadrosaur Tanius. However, in 1993 Eric Buffetaut e.a., after a renewed investigation of the bones themselves, concluded that the crest was neither distorted nor an artefact of restoration; besides, a second specimen with an upright crest part had since been discovered, indicating that the crest was indeed real and Tsintaosaurus is likely a distinct genus.
A new reconstruction in 2013, by Albert Prieto-Márquez and Jonathan Wagner and based on the identification of specimen IVPP V829, a praemaxilla, as a Tsintaosaurus element, came to the conclusion that the unicorn-like bone was just the rear part of a larger cranial crest that started from the tip of the snout. The front of the crest would have been formed by ascending processes of the praemaxillae. These had expanded rhomboid contact facets with the expanded upper parts of the crest processes of the nasal bones, forming the rear of the crest. The rear base of the crest was covered by outgrowths of the prefrontals. The fused nasal bones would have formed a hollow tubular structure. The height of the crest would have exceeded that of the rear skull, measured along the quadrates. Though largely vertical, the crest is directed slightly to the rear; the forward inclination of the holotype crest would be the result of a distortion of the fossil.
The new reconstruction by Prieto-Márquez and Wagner also led to a new hypothesis about the internal air passages of the crest. Yang had assumed that the tubular hollowing in the preserved part of the holotype would have served as the main intake of air. This was rejected by Prieto-Márquez and Wagner who pointed out that the tube was closed at its lower end and that with lambeosaurines in general the air passages are located in a more forward position, the bony nostrils being completely enclosed by the praemaxillae. They assumed that Tsintaosaurus would have had a standard lambeosaurine arrangement in the snout, the air, when inhaling, entering the skull through the paired pseudonares, the “fake nostrils” of the praemaxillae behind the upper beak. From there the air would have been transported through paired passages below the median processes of the praemaxillae to the top of the crest, subsequently entering a common median chamber within the lobe. The rear of the chamber was formed by the nasal bones and probably homologous to the nasal cavity. The chamber was divided into two 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.