Siamotyrannus isanensis Buffetaut, Suteethorn, and Tong 1996

Holtz, T. R., 2001, The phylogeny and taxonomy of the Tyrannosauridae, Mesozoic Vertebrate Life, Bloomington: Indiana University Press, pp. 64-83 : 71

Siamotyrannus isanensis Buffetaut, Suteethorn, and Tong 1996 :

Buffetaut et al. (1996) considered this fragmentary form from the Barremian Sao Khua Formation of northeastern Thailand to be a primitive tyrannosaurid. It was found here to lie outside Tyrannosauridae proper (aublysodontines and tyrannosaurines), but shares with it the following synapomorphies: 24.1, 25.1.,27.1.,28.1, and3L.1. Instead of the single midline crest on the ilium in tyrannosaurids, however, the Thai taxon has a pair of crests. Siamotyrannus may indeed be an ancestral member of the tyrannosaur lineage, but lacking additional material (in particular, the skull) such a position remains uncertain.