skeleton The neck of Giganotosaurus was strong, and the axis bone (the neck vertebra that articulates with the skull) was robust. The rear neck (cervical) vertebrae had short, flattened centra (the "bodies" of the vertebrae), with almost hemispherical articulations (contacts) at the front, and pleurocoels (hollow depressions) divided by laminae (plates). The back (dorsal) vertebrae had high neural arches and deep pleurocoels. The tail (caudal) vertebrae had neural spines that were elongated from front to back and had robust centra. The transverse processes of the caudal vertebrae were long from front to back, and the chevrons on the front were blade-like. The pectoral girdle was proportionally shorter than that of Tyrannosaurus, with the ratio between the scapula (shoulder blade) and the femur being less than 0.5. The blade of the scapula had parallel borders, and a strong tubercle for insertion of the triceps muscle. The coracoid was small and hook-shaped. The ilium of the pelvis had a convex upper border, a low postacetabular blade (behind the acetabulum), and a narrow brevis-shelf (a projection where tail muscles attached). The pubic foot was pronounced and shorter at the front than behind. The ischium was straight and expanded hindwards, ending in a lobe-shape. The femur was sigmoid-shaped, and had a very robust, upwards pointing head, with a deep sulcus (groove). The lesser trochanter of the femoral head was wing-like, and placed below the greater trochanter, which was short. The fourth trochanter was large and projected backwards. The tibia of the lower leg was expanded at the upper end, its articular facet (where it articulated with the femur) was wide, and its shaft was compressed from front to back. Classification Coria and Salgado originally found Giganotosaurus to group more closely with the theropod clade Tetanurae than to more basal (or "primitive") theropods such as ceratosaurs, due to shared features (synapomorphies) in the legs, skull, and pelvis. Other features showed that it was outside the more derived (or "advanced") clade Coelurosauria. In 1996, Sereno and colleagues found Giganotosaurus, Carcharodontosaurus, and Acrocanthosaurus to be closely related within the superfamily Allosauroidea, and grouped them in the family Carcharodontosauridae. Features shared between these genera include the lacrimal and postorbital bones forming a broad "shelf" over the orbit, and the squared front end of the lower jaw. As more carcharodontosaurids were discovered, their interrelationships became clearer. The group was defined as all allosauroids closer to Carcharodontosaurus than Allosaurus or