Dinosaurs Inside and Out

Growing Bones

How many bones made up the average dinosaur skeleton?

Although the largest dinosaurs may have had a few more bones in their necks and tails, the number of bones in the average dinosaur was approximately 200.

In general, how do scientists decide the bone positions of dinosaur skeletons?

Determining where bones go in a dinosaur skeleton is not an easy task. Scientists have to compare every bone with other dinosaur skeletons, as well as with modern species of reptiles, and hope to find a skeleton in a “death pose” that was close to its living structure. Many times in the past, certain parts of a skeleton were put in the wrong place. For example, heads of certain dinosaurs have been put on the wrong skeleton, and the thumb spike of the Iguanodon was first interpreted as a nose spike.

The positions of bones in dinosaur skeletons are determined using what scientists call an “anatomical direction system,” and only includes what is internal (in other words, it is not based on external conditions). This system uses pairs of names to determine certain directions based on the average (or standard) posture of tetrapods, with the back up, belly down, head pointing forward, and all four legs on the ground.

Each pair of names denotes opposite directions similar to when we refer to north and south. Here are four examples of such paired names:

Anterior and posterior: The direction of anterior is toward the tip of the snout, while the posterior direction is toward the tip of the tail. This is analogous to front and back, respectively.

Dorsal and ventral: Dorsal means toward and beyond the spine, while ventral means toward and beyond the belly. These are analogous to up and down, respectively.

Medial and lateral: These are directions referenced to an imaginary plane located in the center of the body, running from tail to snout. Medial means closer to this central reference; lateral means farther out.

Proximal and distal: These are normally used to indicate directions in the limbs and sometimes the tail. Proximal means closer to the trunk or base of a limb, while distal means farther out from the trunk or from the base of the limb.


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