GEOL 431 Vertebrate Paleobiology

Spring Semester 2021

Vertebrate Skeletal Anatomy III - The Appendicular Skeleton

The Appendicular Skeleton: The skeleton of the pectoral and pelvic girdles and the limbs that attach to them. These, too, are endochondral except that most vertebrates have dermal elements associated with the pectoral girdle.

• Elements of the pectoral girdle:
  • Scapula: The "shoulder blade," the major dorsal endochondral element of the girdle
  • Anterior coracoid: Anterior and ventral to the scapula.
  • Posterior coracoid: Posterior and ventral to the scapula.
  • Clavicle: Dermal element lying anterior to the scapula. (Note: in many primitive vertebrates, other dermal elements are present.
  • Interclavicle: Dermal element lying medial to the clavicles and coracoids on the ventral mid line of the animal.
  • Glenoid fossa: The shoulder socket by which the forelimb articulates with the girdle. The scapula, anterior coracoid, and posterior coracoid can all participate.
  In this case, too, evolution has produced many variation of this theme. In derived land vertebrates, the elements listed above can be lost or fused.

• Elements of the pelvic girdle: All pelvic elements are endochondral. Unlike, the pectoral girdle, the pelvic girdle has a bony connection to the vertebral column via the sacral ribs.
  • Ilium: The element dorsal to the hip socket.
  • Ischium: The element posterior and ventral to the hip socket.
  • Pubis: The element anterior and ventral to the hip socket.
  • Acetabulum: The hip socket. Generally, all three pelvic elements contribute to the acetabulum.

• Elements of the forelimb: In land vertebrates and their closest aquatic relatives, both fore and hindlimbs have a characteristic segmented arrangement of one bone followed by two bones followed by many bones.
  • Humerus: The proximal forelimb element .
  • Radius: The lateral element of the two that articulate with the humerus.
  • Ulna: The medial element of the two that articulate with the humerus. In almost all cases, the "funny bone" of the elbow is formed by the ulna.
  • Carpals: The array of small bones of the wrist.
  • Metacarpals: The long bones forming the palm of the hand.
  • Phalanges (sing. phalanx): The long bones of the fingers.

• Elements of the hindlimb:
  • Femur (pl. femora): Thighbone - The proximal hindlimb element .
  • Fibula: Shankbone - The lateral, and generally smaller element of the two that articulate with the femur.
  • Tibia: The medial element of the two that articulate with the femur.
  • Tarsals: The array of small bones of the ankle.
  • Metatarsals: The long bones forming the sole of the foot.
  • Phalanges (sing. phalanx): The long bones of the toes.

Test yourself:

• Link 6
• Link 7
• Link 8
• Link 9
• Link 10

Eryops sp. right forelimb in anterior view

Forelimb details:

Now some detail:

Manus: the technical term for the "hand."

Tetrapod digits are numbered from I to V (with Roman numerals), with I being the most medial when the manus is in quadruped anatomical position. (E.G.: the human thumb.)

Although there is significant variation over the course of evolution, the tetrapod carpus - the set of carpal elements - ancestrally conforms to a strict pattern where the carpals occupy two distinct rows plus a few:

• Proximal carpals: articulate with the radius and ulna. These are named:
  • Radiale: Medial, articulating with the radius.
  • Ulnare: Lateral, articulating with the ulna.
  • Intermedium: Between ulnare and radius.
  • Centrale 4: When present, articulates with intermedium.
• Distal carpals: articulate with the metacarpals for each digit. These are numbered (with arabic numerals) to correspond to the digit with which they are associated.
• Centralia: (Singular "centrale") Ancestrally, tetrapods had most of a third row between the distal and proximal carpals. These are numbered from medial to lateral. (In tetrapod evolution, these are often reduced or lost.)

Eryops sp. right hindlimb in anterior view

Hindlimb details:

Pes: the technical term for the "foot."

The ancestral pattern of the tetrapod tarsus is similar:

• Proximal tarsals: articulate with the tibia and fibula. These are named:
  • Tibiale: Medial, articulating with the tibia.
  • Fibulare: Lateral, articulating with the fibula.
  • Intermedium: Between fibulare and tibia.
  • Note: In amniotes, the tibiale, intermedium, and at lease one centrale fuse to form the astragalus, but that is a story for later.
• Distal tarsals: articulate with the metatarsals for each digit. Numbered as above.
• Centralia: Up to four, numbered from medial to lateral as in the manus.