[N] 2006 Guanlong a Tyrannosauroid or a subadult Monolophosaurus?
Carr, T. (2006) Is Guanlong a Tyrannosauroid or a subadult Monolophosaurus? JVP 26(3) Abstracts pp.48
Guanlong wucaii is a purported Late Jurassic basal tyrannosauroid from the Shishugou Formation of northwestern China. Guanlong bears a tall and fenestrated nasal crest that extends along the top of the snout, as in Monolophosaurus jiangi, a carnosaur that is about twice the size as Guanlong, from a lower level in the same unit. The original cladistic analysis of Guanlong used a data matrix relevant to resolving the relationships among basal theropods, which reconstructed it as a basal tyrannosauroid. However, the similarities shared between Guanlong and Monolophosaurus in the crest prompted a test of the original hypothesis using a data matrix based on characters relevant for resolving ingroup relationships of Tyrannosauroidea.
The data matrix includes 201 characters and 34 theropod species. The matrix was analyzed in PAUP* 4.0b under a heuristic search; Guanlong was reconstructed as a carnosaur, and as the sister species of Monolophosaurus. This relationship is supported by the shape of the rostral ramus of the maxilla; a sagittal, elongate, pneumatic, and fenestrate crest along the top of the snout; and a foramen in the pubic process of the ischium. Monolophosaurus is distinguished from Guanlong by a longer crest that includes the premaxilla and lacrimal, a rostrally-positioned maxillary fenestra, a deep maxilla, a long jugal process of the quadratojugal, and a subocular process on the postorbital. Guanlong is distinguished from Monolophosaurus by a wide snout tip, short squamosal process of the postorbital, a concave orbital margin of the postorbital, a cornual process on the jugal, the antorbital fossa is deeply excavated into the jugal, absence of a caudal surangular foramen, fewer dentary teeth, apneumatic cervical centra, presence of a rostrodorsal notch in the ilium, and the presence of a pubic tubercle.
These results suggest two alternative hypotheses for Guanlong: it is either the sister taxon, or it is a subadult, of Monolophosaurus.