What is the axial skeleton?

The axial skeleton is one of the two sections of the entire dinosaur skeleton. It is made up of the trunk, spine, and tail, essentially forming the foundation to which the animals limbs and skull were attached. In other words, it includes the so-called backbone of the dinosaur and the ribs. The backbone (or vertebral column) is divided into four segments: the neck (cervical), the back (dorsal), hip (sacral), and the tail (caudal). It included numerous individual bones known as vertebrae. The ribs were long, narrow bones attached to the vertebrae of the cervical and dorsal segments. These were paired bones one on each side of the backbone and extended downward to protect the internal organs. They included the neck ribs and the belly ribs (gastralia, or the bones that protected the digestive tract and other internal organs).

What were the vertebrae of a dinosaur?

Vertebrae were the numerous individual bones that made up the backbone (vertebral column) of the dinosaur. Each individual vertebra was a roughly cylindricalshaped piece of bone (centrum); on top of the vertebrae were neural arches, triangular arches of bone covering the spinal cord. The spinal cord in a dinosaur would run between the centrum and neural arch. A bony neural spine projected up from the neural arch and was where the back muscles were attached. Some dinosaurs, in addition to these basic features, had very complex vertebrae with all sorts of ridges and projections.

Each segment along the backbone had vertebrae that were specifically shaped to help that segment function. For example, the hip (sacral) vertebrae were fused together in dinosaurs in a structure called a sacrum; this provided support and strength for the hips. The neck (cervical) vertebrae were specifically shaped to provide flexibility, allowing the dinosaur to move its head around freely.

Its impossible to pinpoint how many vertebrae each dinosaur had, as they varied greatly among all groups. In general, the neck bones held 9 to 19 vertebrae, the back had 15 to 17 of these bones, the hips held 3 to 10 vertebrae, and the tail had from 35 to 82 vertebrae, depending on the dinosaur.

How was the vertebral column in ornithischian dinosaurs strengthened?

The vertebral column in ornithischian dinosaurs was strengthened by means of structures called ossified tendons. These were actually tissues that connected the vertebrae together. They became filled with calcium, literally turning to bone (called ossifying). The result of this was a stiffening and strengthening of the connection between vertebrae, resulting in a strengthened backbone.

On ornithischian dinosaurs, ossified tendons appear as bony strands that look like spaghetti. Different names are given to them depending on where they are located on the dinosaur. For example, those between the tail vertebrae are called hypaxial tendons. In ornithischian dinosaurs, one purpose of the ossified tendons was to stiffen the base of the tail, making it more rigid with respect to the hips, while the tip of the tail was left mobile and flexible.

How were connections between theropod dinosaur vertebrae strengthened?

Some advanced species of theropod dinosaurs had strengthened vertebrae connections, but this was not accomplished by means of ossified tendons, as with the ornithischian dinosaurs. The theropods prezygapophyses elongated and grew over several vertebrae sometimes as many as 12 vertebrae and it strengthened and stiffened the area.

What are some of the richest dinosaur bone areas in the world?

Some of the richest dinosaur bone graveyards are found in three diverse regions of the world: the Patagonia region of Argentina, the Gobi Desert in China, and the western United States. Most recently, scientists have found one of the largest plant-eating dinosaurs, the Argentinosaurus, and the largest carnivore, the Gigantosaurus carolinii, in the Patagonia region of Argentina, which has one of the richest and longest-term fossil records in the Southern Hemisphere. No doubt more dinosaur bones will be discovered in these three unique places in the future.

Most dinosaurs walked on their toes rather than on the soles of their feet, which allowed them to move with greater speed (iStock).

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