Sexual dimorphism of Tyrannosaurus "x"

Tyrannosaurus "x" is a dubious type of tyrannosaurid first introduced in the 1970s by Robert T. Bakker. He noticed differences between BHI 3033 and AMNH 5027 and gave out a new epithet to the latter. AMNH 5027, by Bakker, was distinct in having a smaller nasal opening; smaller, more tightly packed teeth with more of them than T. rex. Also, a smaller lateral lachrymal pneumatic foramina; an extra incisor; smaller fenestrae and a more pronounced horn ridge on the back of the head. All of this, together with a gracilic 

AMNH 5027, a (so-called) specimen of Tyrannosaurus "x", is distinguishable from T. 

rex because of a smaller nasal opening; smaller, more tightly packed teeth with more of them than 

body has made some believers out of the theory such as Peter Larson. Others such as Jack Horner think that T. "x"' is nothing more than a male T. rex. If so, this implies sexual variation in the genus Tyrannosaurus. The ones who encourage the Tyrannosaurus "x" theory scowl at the idea of gender dimorphism in the species, because of one factor. Theropod's (two-legged saurischian dinosaurs such as T. rex) closest relatives are birds and crocodilians, and there is no recognition of these reptiles having gender variation. Those who support the T. "x" hypothesis also point out the scarcity of the gracile-like specimens. To date, only around five specimens represent this "species" (including AMNH 5027, MOR 008, SDSM 12047 and Samson), while in the robust form, there are over twenty-five specimens. The supporters say males and females would be roughly the same number (in total specimens), but since they are not, this (to them) represents a new, more endangered species.

(source:wikipedia)