acetabulum n., abbrev. ac the socket on the hip into which the head of the femur fits
amphicoelous adj. describes vertebrae in which the front and back of the centrum are concave. A feature of dinosaur vertebrae that were not supposed to move very much relative to one another, such as posterior dorsals
amphiplatyan adj. describes vertebrae in which the front and back of the centrum are flat.
analogy n. a similar character state present in two or more species of organisms that is derived from different characters in their common ancestor. The opposable digits of Pandas and humans are analogous as the Panda’s digit is formed from bones in the wrist while the human’s is formed from the first digit –analogous adj.
angular bone n., abbrev. mandible bone
anterior adj. forward of; closer to or in the direction of the skull, specifically the tip of the “snout.” For example, the arms are anterior to the legs – cranial syn.
antorbital fenestra n., abbrev. aof fenestration in front of the orbit
appendicular skeleton n. the forelimbs, shoulders, hindlimbs and hip bones
arctometatarsalian adj. describes the condition where the third metatarsal is pinched or compressed between the second and fourth metatarsals. This condition is found in tyrannosaurids, ornithomimids, troodontids, elmisaurids/caenagnathids, Avimimus, Mononykus and their close relatives
astragalocalcaneum n. bone formed by the fusion of the of the anklebones astragalus and calcaneum. This feature was developed convergently in birds and ceratosaurs
axial skeleton n. the spine, including tail, and ribs