Sauropods are best described as gigantic, long-necked herbivores with long tails and tree-trunk legs. The largest sauropods were over 30 meters (~100 feet) long and may have weighed over 30 metric tons (nearly 60,000 lbs)! Unlike whales, these dinosaurs were land-lubbers, and their skeletons had to resist gravity.
Sauropods represent the extreme of a trend towards gigantism in dinosaurs. The word “dinosaur” and “giant” go together in the public imagination, and for good reason – the average dinosaur weighed in at over 1 metric ton (~ 2,000 lbs)! For comparison, the average mammal weighs less than 1 kilogram (~ 2 lbs.).
What is it about dinosaurs that allowed them to get so big so often?
Certainly, metabolism, diet, and a warm global climate must have been significant factors that influenced the evolution of dinosaur gigantism. But these aspects of dinosaur lives are difficult to get at directly. On the other hand, the shapes and associations of the limb bones and backbones of dinosaurs can be examined first-hand.
By the time sauropod dinosaurs were giants the following skeletal adaptations had occurred:
- A mouth capable of a wide gape
- The mouths of sauropods are not like those of herbivorous mammals like cows where the teeth grind food. Instead, the teeth of sauropods slide past one another and stick forwards to help them grab and gulp food (technically called bulk-browsing). Their jaws can open wide – and probably did not have a cheek.
- A quadrupedal posture with interlocking forearm bones
- The earliest dinosaurs were bipeds, striding about on their hindlimbs. Sauropods reversed this trend, dropping down on to all-fours to better distribute their weight. The interlocking forearm bones reinforced the forelimb and prevent the now weight-bearing hand from twisting.
- Specialized bracing joints between the backbones
- To hold up their backbone against their weight and gravity, sauropods developed extra bracing joints that reinforced their vertebral column.
- Column-like femur (thigh bone)
- The thigh bone of sauropods looks like a column and was loaded vertically during movement, just as in elephants. Bones are strongest when loaded vertically.
- Hind feet flattened with the most robust toes on the inside of the foot
- The hind feet of sauropods, like those of elephants, were flattened and splayed out against a fat pad to distribute the stresses of weight-bearing and walking. Sauropod footprints show the impression of a large heel pad. Unlike elephants, the most robust toes are on the inside of the foot and bear large claws, probably because:
- the center of sauropod mass was close to the midline of the body and
- the feet of sauropods were turned outwards – with the inner toes leading the way, thereby absorbing the brunt of the stress.
- this provided additional traction in certain sediments.
Want a more detailed and illustrated overview? See Fredric Heeren’s Nature article, “Dinosaurs: Rise of the Titans.”