Monolophosaurus

Phylogeny: Dinosauria > Saurischia > Theropoda > Neotheropoda > Tetanurae > Avetheropoda (?) > Carnosauria (?)

Overview: Fossilized remains belonging to this medium-sized theropod are known from the region of Xinjiang, in western China. The holotype and so far only specimen of Monolophosaurus consists of a decent portion of the animal’s skull and body, excavated over the course of the 1980’s. Rock layers surrounding the bones date to the Middle Jurassic, geologists attributing them to the larger Shishugou Formation, preserving a semi-arid and seasonal environment. Monolophosaurus may’ve lived alongside notable dinosaurs like Limusaurus, Guanlong and Sinraptor, though these dinosaurs are often attributed to slightly younger sections of the Shishugou. With a length of about five to six meters, Monolophosaurus was probably going after smaller and medium-sized herbivores. Sources of food may’ve included smaller theropods, stegosaurs, early ceratopsians and young sauropods.

Monolophosaurus, the “single-crested lizard”, was named in reference to its most notable trait – a large, bony crest growing along the length of its snout. This crest was low, thin and bore a handful of openings, which in life may’ve been covered by keratin or other such tissues. Its exact purpose is unknown, but the keratin covering it may’ve been brightly colored or patterned, allowing it to signal its health and vitality to potential mates or ward off rivals. The aforementioned Guanlong, which was a fair bit smaller than Monolophosaurus, also had a similar crest. Some speculate that it was a juvenile of this genus, but the fossils referred to Guanlong were from a fully grown individual. On top of that, Guanlong is usually seen as an early tyrannosaur. Monolophosaurus has a somewhat more unstable phylogenetic status. It has been classified as a basal tetanuran, a relative of the allosauroids, related to the megalosauroids or even close to the spinosaurids.