|Diplodocus painting by C.R. Knight (1911)|
But the real Sauropods were huge, with long necks and long tails balancing a big, oval body. They are almost certainly the largest animals ever to live on land, and their only competition in terms of size are aquatic mammals like the blue whale. Diplodocus, a common Jurassic sauropod, was up to 170 feet long, and some brachiosaurs were as much as 60 feet tall, four times the height of a modern giraffe. The smallest Sauropods were around 20 feet long. Many of the most famous specimens of Sauropods came from the Jurassic Morrison Formation of western United States, especially in Colorado, Wyoming, and Utah, where Marsh and Cope worked in the 1870s and 1880s.
In contrast to early depictions that indicated these animals were so big they had to live in water to be supported, the modern interpretation is that Sauropods certainly walked on dry land. Or not-so-dry land: the environment of the Morrison Formation was wet mud flats and river flood plains, and sauropod footprints show that they lived in such areas as well as wet, coastal environments.
Although Sauropods appeared in the late Triassic, they diversified and grew to gigantic sizes throughout the Jurassic and into the Cretaceous. By Jurassic time they were widespread. Even though few complete, or even reasonably complete fossils are known, their bones are common enough that we know Sauropods were present on every continent, including Antarctica.
Sauropods appear to have been herd animals that traveled in groups segregated according to age. That fact can be interpreted to suggest that they did not exhibit much parental behavior, and that juveniles quickly began to flock together, but some fossil assemblages include mixtures of individuals of different ages, which could mean there was some parental care for the young. Some of the oldest fossil eggs with well preserved embryos, from the early Jurassic of South Africa, are from prosauropods that are probably an ancestral or sister group to the Sauropods. They’ve been interpreted to suggest that the animals crawled on four feet before learning to walk and rear up on two legs. Sauropods were not bipedal, but they probably could lift themselves on their hind legs to reach high into trees to get at leafy vegetation there.
You might expect sauropods’ feet to be something like those of modern elephants, but that’s not correct. Their front feet did not splay, like elephants’, but in many species were almost a stiff bony column with the digits reduced to near-invisibility. Big stumps, more or less. The hind feed did have claws, and I think that’s the basis for the name, which means “lizard-foot.”
As you can imagine, there’s a vast literature on sauropod dinosaurs and a lot of it is readily available online. What I’ve given here is just a basic outline.
—Richard I. Gibson
Prosauropod eggs and embryos
Painting of diplodocus rearing, by Charles R. Knight, 1911 (public domain via Wikipedia)