Sauropod dinosaurs were the largest animals to ever inhabit the land, culminating in truly gigantic forms in at least three lineages. These giants are unique in exceeding the body mass of any other large terrestrial tetrapods (i.e. large mammals and other dinosaurs) by an order of magnitude.
The diversity and range peak of sauropods is in the Late Jurassic with the famous faunas of the North American Morrison Formation and the African Tendaguru Beds. Although less common on the northern continents during the Cretaceous, sauropods remained diverse and widespread in Gondwana and survived until the very end of this period (about 65 Mio. years ago).
Sauropods thus saw dramatic changes in world geography (break-up of Pangea) and world ecosystems. The latter not only included the changing climates of the Jurassic and Cretaceous (including the Cretaceous hothouse) but also the major ecosystem turnover resulting from the rise of the angiosperms. While from their Late Triassic origin to the Early Cretaceous, sauropods lived in and subsisted on a gymnosperm-dominated environment (with conifers, ferns, cycads, ginkgoes etc.), Late Cretaceous sauropods inhabited angiosperm-dominated environments that may not have looked much different from a modern subtropical forest.
The sauropod body plan is unique among terrestrial tetrapods: A body similar to elephants among mammals is combined with a very small head on a very long neck and a long tail similar to that seen in other dinosaurs (Figure 1). With the exception of brachiosaurid and camarasaurid sauropods, the long neck appears to have been held horizontally, with the long tail acting as a counterbalance. Brachiosaurids and camarasaurids apparently held the neck in an erect pose like a giraffe, the tail being shorter in accordance.
An assemblage of primitive dinosaurs known as the prosauropods are generally hypothesized as the closest relatives of sauropods, and both groups are united in the Sauropodomorpha. Prosauropod dinosaurs existed from the Late Triassic to the Early Jurassic and included such well-known forms as Plateosaurus from the Keuper Beds of Central Europe.
In 2011, the Research Unit 533 published a book on the biology of sauropod dinosaurs and a comprehensive paper on their gigantism, available for free here.
A group termed the prosauropod dinosaurs are generally hypothesized as the closest relatives of sauropods, and both groups are united in the Sauropodomorpha. Prosauropod dinosaurs existed from the Late Triassic to the Early Jurassic and included such well-known forms as Plateosaurus from the Keuper Beds of Central Europe