All land-living vertebrates, or tetrapods, possess the same set of bones. While these bones range wildly in shape, size, and function amongst tetrapods, they are homologous, or they share a common origin. So the same bones in your arms and legs were the same bones in the giant thundering limbs of an Apatosaurus.
However, dinosaurs and humans have different styles of locomotion, so the anatomical directions have different orientations in space. Compare the diagrams of Allosaurus fragilis and Homo sapiens.
The following terms are useful when referring to an anatomical structure in reference to another structure. For instance, the skull is anterior to the rib cage, and the hand is distal to the shoulder.
Anterior (Superior): Towards the head.
Posterior (Inferior): Towards the tail or rear
Dorsal: Towards the back
Ventral: Towards the stomach
Medial: Towards the midline
Lateral: Away from the midline
Distal: Away from center mass
Proximal: Towards the center mass
All tetrapods have an axial skeleton and an appendicular skeleton. The axial skeleton is composed of the skull, the vertebral column (backbone), and the ribcage. The appendicular skeleton is composed of the shoulder girdle, the pelvis, the forelimbs, and the hindlimbs.
Bones have features that function as attachments for muscles and other soft tissues. The bones themselves are attached to one another via features of articulation or connection.
The tetrapod skull is composed of a variety of different bones that are sutured together and vary wildly depending on the organism’s ecological role. The skull functions as a mechanism for ingestion, the beginning of the digestive process, as well as protection for the brain.
In a dinosaur, and many other vertebrates, the vertebral column is composed of cervical (neck), dorsal (back), sacral (hip), and caudal (tail) vertebrae. These different kinds of vertebrae are highly modified to support their given function, but they all have homologous features. The round and thick body of the vertebrae is called the centrum. The thin, upward pointing structure above the centrum is called the spinous process. The structure pointing horizontally out of either side of the centrum are called transverse processes. The function of the vertebral column is to provide structural support and muscle attachment for an animal’s appendicular skeleton, as well as providing protection for the central nervous system.
The ribcage is an assemblage of bones that house the internal organs of the thoracic cavity, and articulate with the vertebrae, via the rib head. Their function is to protect internal organs and soft tissues.
The hind limbs originate from the pelvis. The pelvis is a compilation of bones which interact with the upper leg bone, the femur. The processes vertebrae near the pelvis fuse together to form a structure called the sacrum. The sacrum articulates with a bone called the ilium, and the ischium, which is posterior to the ilium, and the pubis, which is posterior to the ilium and ventral to the ischium. In a dinosaur, these bones all articulate together to form an opening called the acetabulum, where the femur articulates and the hindlimb is attached to the axial skeleton.
The hindlimb is composed of the upper leg bone, the femur. The femur articulates with a pair of lower leg bones, the more robust tibia, and the more delicate fibula. The tibia and fibula articulate with a pair of bones called the astragalus and the calcaneum. These bones articulate with the metatarsals, which form the arch of the human foot, but are off the ground in theropod dinosaurs like Allosaurus. The metatarsals articulate with the bones of the toes, the phalanges.
Like the pelvis, the shoulder girdle is a structure is a complex structure with significant variation among dinosaurs and other tetrapods. It is composed of the scapula, or the shoulder blade, and the clavicle, the collarbone. The clavicle is reduced or absent in many dinosaurs, and the clavicles fused together in theropod dinosaurs to form the furcula or the wishbone. The scapula articulates with the uppermost arm bone, the humerus. the humerus articulates with the bones of the lower arm, the radius and ulna. The radius is medial (in a human, towards the thumb) to the ulna. The radius and ulna articulate with the carpals or the wrist bones. The carpals articulate with the metacarpals (in a human, the palm), which articulate with the bones of the fingers, the phalanges.
Dinosaurs display a tremendous range of shape and size of corresponding bones. The thundering forward pair of arms Apatosaurus and the long, grasping, viciously-clawed arms Allosaurus are made of the exact same bones! So when you stare up at the wall of bones at the Carnegie quarry, don’t think of them as alien, but rather a display of common evolutionary heritage that you and the “terrible lizards” of the Jurassic share.