Bone Histology

Histology is the study of tissue structure. With bone this is done by cutting off a thin slice of bone and examining it under a microscope. More detail can be obtained with a (more powerful) electron microscope.

What do you see in modern bones?

In warm-blooded creatures the primary osteons (gl) get grown over and eventually replaced by secondary osteons. This creates a tightly packed structure which is highly vascular (gl).

The bones of cold-blooded creatures show a 'lamellar-zoned' pattern. This pattern consists of a series of growth rings containing osteons (a bit like rings in trees). This indicates that the bone was growing in slow bursts, probably seasonally. Cold-blooded animal's bone is less vascular than that of warm-blooded animals.

What do you see in dinosaur bones?

Even though the organic (gl) part of dinosaur bones has usually rotted away, the bone structure is often preserved. This is because bone is also made from mineral crystals which preserve its structure (despite any chemical alteration).

The tightly packed, highly vascular bone normally seen in warm-blooded animals has been seen in bones from:

• sauriscian dinosaurs
  • e.g. Diplodocus
  • Apatosaurus
• ornithiscian dinosaurs
  • e.g. Iguanodon
  • Stegosaurus
  • Triceratops

BUT

Recent experiments have discovered this type of highly vascular bone in living cold-blooded animals. It seems that this bone type is found in all animals with fast-growth rates and also in animals of large size (to strengthen the bones).

So bone structure cannot be used as evidence at present.