page_title: Giganotosaurus
section_title: Skull
hierarchical_section_title: Giganotosaurus / Description / Skull
caption_attribution_description: A Giganotosaurus skull cast.
context_page_description: Giganotosaurus is a genus of theropod dinosaur that lived in what is now Argentina, during the early Cenomanian age of the Late Cretaceous period, approximately 98 to 97 million years ago. The holotype specimen was discovered in the Candeleros Formation of Patagonia in 1993, and is almost 70% complete. The animal was named Giganotosaurus carolinii in 1995; the genus name translates as "giant southern lizard" and the specific name honors the discoverer, Rubén D. Carolini. A dentary bone, a tooth and some tracks, discovered before the holotype, were later assigned to this animal. The genus attracted much interest and became part of a scientific debate about the maximum sizes of theropod dinosaurs.
  Giganotosaurus was one of the largest known terrestrial carnivores, but the exact size has been hard to determine due to the incompleteness of the remains found so far. Estimates for the most complete specimen range from a length of 12 to 13 m, a skull 1.53 to 1.80 m in length, and a weight of 4.2 to 13.8 t. The dentary bone that belonged to a supposedly larger individual has been used to extrapolate a length of 13.2 m.
context_section_description: Though incompletely known, the skull of Giganotosaurus appears to have been low. The maxilla of the upper jaw had a 92 cm (36 in) long tooth row, was deep from top to bottom, and its upper and lower edges were almost parallel. The maxilla had a pronounced process (projection) under the nostril, and a small, ellipse-shaped fenestra (opening), as in Allosaurus and Tyrannosaurus. The nasal bone was very rugose (rough and wrinkled), and these rugosities continued backwards, covering the entire upper surface of this bone. The lacrimal bone in front of the eye had a prominent, rugose crest (or horn) that pointed up at a backwards angle. The crest was ridge-like, and had deep grooves. The postorbital bone behind the eye had a down and backwards directed jugal process that projected into the orbit (eye opening), as seen in Tyrannosaurus, Abelisaurus, and Carnotaurus. The supraorbital bone above the eye that contacted between the lacrimal and postorbital bones was eave-like, and similar to that of Abelisaurus. The quadrate bone at the back of the skull was 44 cm (17 in) long, and had two pneumatic (air-filled) foramina (holes) on the inner side. 
   
  The skull roof (formed by the frontal and parietal bones) was broad and formed a "shelf", which overhung the short supratemporal fenestrae at the top rear of the skull. The jaw articulated far behind the occipital condyle (where the neck is attached to the skull) compared to other theropods. The condyle was broad and low, and had pneumatic cavities. Giganotosaurus did not have a sagittal crest on the top of the skull, and the jaw muscles did not extend onto the skull roof, unlike in most other theropods (due to the shelf over the supratemporal fenestrae). These muscles would instead have been attached to the lower side surfaces of the shelf. The neck muscles that elevated the head would have attached to the prominent supraoccipital bones on the top of the skull, which functioned like the nuchal crest of tyrannosaurs. A latex endocast of the brain cavity of Giganotosaurus showed that the brain was similar to that of the related genus Carcharodontosaurus, but larger. The endocast was 29 mm (1 in) long, 64 mm (3 in) wide, and had a volume of 275 ml (9.7 imp fl oz).
  The dentary of the lower jaw expanded in height towards the front (by the mandibular symphysis, where the two halves of the lower jaw connected), where it was also flattened, and it had a downwards projection at the tip (which has been referred to as a "chin"). The lower side of the dentary was concave, the outer side was convex in upper view, and a groove ran along it, which supported foramina that nourished the teeth. The inner side of the dentary had a row of interdental plates, where each tooth had a foramen. The Meckelian groove ran along the lower border. The curvature of the dentary shows that the mouth of Giganotosaurus would have been wide. It is possible that each dentary had twelve alveoli (tooth sockets). Most of the alveoli were about 3.5 cm (1.3 in) long from front to back. The teeth of the dentary were of similar shape and size, except for the first one, which was smaller. The teeth were compressed sideways, were oval in cross-section, and had serrations at the front and back borders, which is typical of theropods. The teeth were sigmoid-shaped when seen in front and back view. One tooth had nine to twelve serrations per mm (0.039 in). The side teeth of Giganotosaurus had curved ridges of enamel, and the largest teeth in the premaxilla (front of the upper jaw) had pronounced wrinkles (with their highest relief near the serrations).
caption: Reconstructed skull in Japan, based on large size estimates
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