Medullary bone

Medullary bone is a specialized type of bone tissue found in many bird species. It is a temporary, easily mobilized source of calcium that female birds use to produce eggshells. Medullary bone is unique to birds and has been used as evidence of the bird-like reproductive habits of some dinosaurs.

Structure and Function

Medullary bone is characterized by its spongy, lattice-like structure. Unlike other types of bone, it is not involved in support or movement. Instead, its primary function is to serve as a reservoir of calcium and other minerals necessary for the production of eggshells.

During the breeding season, female birds deposit calcium into the medullary bone. This calcium is then mobilized and transported to the oviduct during eggshell formation. The presence of medullary bone can therefore be an indicator of reproductive status in birds.

Evolutionary Significance

The presence of medullary bone in birds and its absence in other vertebrates has been used as evidence of the unique reproductive strategies of birds. Some scientists have suggested that the development of medullary bone may have been a key factor in the evolutionary success of birds.

Fossil evidence has also revealed the presence of medullary bone in some dinosaurs, including Tyrannosaurus rex and Allosaurus. This has been used as evidence of the bird-like reproductive habits of these dinosaurs, and supports the theory that birds are the modern descendants of dinosaurs.

See Also

• Bird anatomy
• Dinosaur
• Eggshell
• Oviduct