Tyrannotitan is a genus of huge (up to around 12.2 metres (40 ft) long) bipedal carnivorous dinosaur of the Carcharodontosauridae family from the Aptian stage of the early Cretaceous period, discovered in Argentina. It is closely related to other newly discovered giant predators Giganotosaurus and Carcharodontosaurus. Its fearsome appearance is reflected in the meaning of its name, "Tyrant titan".

Discovery and species

Tyrannotitan chubutensis was described by Fernando E. Novas, Silvina de Valais, Pat Vickers-Rich, and Tom Rich in 2005. The fossils were found at La Juanita Farm, northeast of Paso de Indios, Chubut Province, Argentina. They are believed to have been from the Cerro Castaño Member, Cerro Barcino Formation (Aptian stage) around 112.2 - 121 million years ago.

The holotype material was designated MPEF-PV 1156 and included partial dentaries, teeth, dorsals 3-8 and 11-14, proximal caudals, ribs and haemal arches, a fragmentary scapulocoracoid, humerus, ulna, partial ilium, a nearly complete femur, fibula, and left metatarsal 2.

Additional material (designated MPEF-PV 1157) included jugals, a right dentary, teeth, atlas vertebra (including neurapophyses), cervical (?) 9, dorsal (?)7, 10, 13, fused sacral centra (5 total), an assortment of distal caudals, ribs, the right femur, a fragmentary left metatarsal 2, pedal phalanges 2-1, 2-2, and 3-3.

This taxon comes standard with: bilobate denticles on the mesial carina, a strong groove for (?) the inferior alveolar nerve along the lateral surface of the dentary, and dorsal neural spines heavily scarred for ligament insertion.

Paleobiology

Little information has yet been released about Tyrannotitan. Only a very brief description of the fossils has been published (four pages). The teeth are less blade-like than those of its kin, and possess odd, lumpy denticles (there is a barely distinguishable groove in the center, dividing each denticle into two parts). Unlike known Carcharodontosaurids, this animal lacks pneumaticity extending into the sacral and caudal centra. The scapulocoracoid is fused, and much better developed than that of Giganotosaurus carolinii, yet the arm is very small. Most of the shaft of the scapula is missing. The acromion curves about 90 degrees from the shaft axis, making it look vaguely Tyrannosaurid-like. Whether the sharp difference between taxa is due to evolution or sexual dimorphism in poorly-sampled populations of both species, has not been determined (the latter seems unlikely). A proximal caudal has a very tall neural spine (about twice the height of its centrum, judging by the figure). The base of the orbital fenestra is a notch of nearly 90 degrees into the body of the jugal, which contrasts with the rounded base restored for Giganotosaurus and agrees with Carcharodontosaurus favorably.

References

1. Mortimer, M. (2004), "The Theropod Database", viewed September 17, 2007. http://home.myuw.net/eoraptor/.