The Caudal (Tail) Region

(Click name)

| Back to Skeleton Page | Home |

The tail region is fairly similar in all dinosaurs. The caudal vertebrae tend to become less specialized towards the tip of the tail and all of the ascending processes (the neural spines etc.) tend to become reduced and even lost. In some species, however, where the tail needs to be stiffened to act as a counterbalance for running, there can be a great deal of modification of these processes so that they act like links in a chain (see fig. B).

Centrum: The core of the vertebra. The centrum is typically round, but mid-tail centra can be polygon shaped and towards the tip of the tail the centrum can be quite flattened.{top}

Ascending Processes

The ascending processes of the caudal vertebrae are the bones that sit atop the centrum. Depending on the particular species of dinosaur, these structures can either become reduced towards the tip of the tail (fig. C) or they can be modified to stiffen the tail (fig. B). In species where the processes are reduced, some of the tip-ward vertebrae can lose the fusion between the processes and the centrum so they are help together only by cartilage.

Figure B shows the expansion of the pre- and post- zygapophyses in the ostrich-like dinosaur Ornithomimus. In Ornithomimus, the expansion of these structures allows them to interlock like a chain and when further strengthened by tendons that become hardened by the addition of calcium, the entire tail becomes stiff and rod-like. In this way, the tail becomes a counterweight that is held off the ground to allow bipedal running. See the illustration of Deinonychus at right.{top}

Neural Spine: The tall projection upwards from the centrum, above the neural canal. The neural spine tends to be reduced and eventually lost in the vertebrae closest to the tip of the tail.{top}

Prezygapophysis: The process at the front (anterior) end of the vertebra. It typically exists as a pair, but can be reduced and fused into a single structure as in fig. B.{top}

Postzygapophysis: The process at the back (posterior) end of the vertebra. It too is typically paired and fusion is not generally known. This means that if what you're looking at has two bits on one end and one bit on the other, the two bits face the back!{top}

Other Bones of the Tail

Chevrons: The chevrons are V-shaped bones that attach to the bottom (ventral) side of the centrum. Their size and shape varies somewhat between species and in Ankylosaurs the chevrons are fused to the centrum itself, forming a single solid structure.{top}

Ossified Tendons: Most species of dinosaurs have specialized tendons in the back and tail that harden by absorbing calcium. They form a mesh-like network that strengthens and stiffens the region they cover. In some species they are so numerous they essentially form a soild structure so the tail then becomes a solid counterweight.{top}

| Top of Page | Back to Skeleton Page | Home |