Labocania anomala, Molnar, 1974

Holtz, TR jr., 2004, Tyrannosauroidea, The Dinosauria, University of California Press, pp. 111-136 : 3

Labocania anomala ,

based on a frontal, a quadrate, an incomplete maxilla and dentary, a hemal process, a proximal ischium, metatarsal II, and other fragments from the Campanian “La Bocana Roja” Formation, near Arroyo del Rosario, Baja California, Mexico (Molnar 1974), shows several tyrannosauroid features: a hollow quadrate, a triangular obturator process on the ischium, and the semicircular scar on the caudolateral surface of the proximal ischium. These features are also found in other coelurosaurs, however.The flattened lateral surface of metatarsal II is reminiscent of the buttressing surfaces of tyrannosaurid arctometatarsi but would also be consistent with the general tetanuran condition of metatarsal III being slightly compressed within the metatarsus (as in Allosaurus or Sinraptor ). In some features, however, Labocania differs from tyrannosaurids and resembles abelisaurids such as Majungatholus , Carnotaurus , and Abelisaurus : the frontals are thick, and the fragmentary quadrate indicates that it was markedly angled caudoventrally, not vertical as in tyrannosaurids. The dorsal surface of the frontal shows no sign of the supratemporal muscle scar that is present in all tyrannosaurids. The hemal process is L-shaped with a longer distal than cranial extension, similar to those in the end of the proximal portion of the series in tyrannosaurids or the middle of the series in carnosaurs but unlike the vertical and tapered hemal processes of ceratosaurs. The maxillary teeth are ziphodont, unlike those of Tyrannosauridae ; the premaxillary teeth lack the U-shaped cross section of tyrannosaurid teeth and are more similar to those of carnosaurs, basal tetanurans, or ceratosaurs. Although the possibility exists that Labocania represents some highly apomorphic member of the tyrannosauroid clade, there are no potential synapomorphies uniting the Mexican taxon to Tyrannosauroidea that are not found in other taxa (in part or as a whole). The phylogenetic position of this enigmatic and poorly known form, even whether it is abelisaurid, coelurosaurian, or some other taxon, remains uncertain.