GEOL 104 Dinosaurs: A Natural History

Fall Semester 2006
Sauropodomorpha: Size matters

Sauropodomorpha:

  • Name means "sauropod form"; Sauropoda means "lizard feet", even though their feet do not look much like lizard feet!
  • Characterized by:
  • Herbivores (early forms maybe omnivores)
  • Primitive forms are facultative bipeds; later forms were so large they were obligate quadrupeds
  • Were the largest herbivores ever to live on land; by the end of the Late Triassic had surpassed all previous land living animals in size, and kept on going…

    The most primitive known sauropodomorph is Saturnalia of the Late Triassic of Brazil. (Some fragments from the Middle Triassic of Madagascar might be VERY early sauropodomorphs, but might instead be from some non-dinosaurian herbivorous archosaurs).

    Basal sauropodomorphs are often called "prosauropods". However, there does not appear to be a true clade "Prosauropoda". Instead, basal sauropodomorphs form a paraphyletic grade leading to the Sauropoda; this grade has at its base small bipedal forms such as Saturnalia, Thecodontosaurus, Efraasia, and Plateosauravus, followed by larger-bodied (3-10 m) long facultative bipeds such as Plateosauridae, Riojasauridae, Massospondylidae, and Melanorosaurus.

    Basal sauropodomorphs are characterized by:

    Basal sauropodomorphs were the first large-bodied dinosaurs. Their long necks would allow them to browse higher in trees than any contemporaneous herbivores. Also, larger size would give them bigger guts to digest more plants and defense against predators.

    These three selective seem to have led to the evolution of the true Sauropoda. Primitive sauropods are known from the Late Triassic, but sauropods do not become common outside of the southern regions of Pangaea (modern South America, southern Africa, Australia) until the Middle Jurassic.

    Sauropods are characterized by:

    Antetonitrus of the Late Triassic of Africa is among the best known early sauropod. Unfortunately, its skull and most of its neck are not known, so it isn't certain if the following features are present in it, or in the next more advanced group of sauropods:

    Shunosaurus of the Middle Jurassic of China is a good example of an early sauropod. The giant size of sauropods would allow them to feed even higher in trees, digest more plants, and serve as defense against ever-larger predators. (Some sauropods developed additional defenses: Shunosaurus, for instance, had a tail club).

    Different clades of sauropods had different solutions to tree-feeding. Some added extra neck vertebrae; some increased forelimb length; some reared up on hind legs; and many had combinations of these.

    The main sauropods of the Late Jurassic and the Cretaceous belong to the clade Neosauropoda. Neosauropods are characterized by:

    There are two main clades of neosauropods: Diplodocoidea and Macronaria.

    Diplodocoids:

    Within the diplodocoids are several clades:

    Dicraeosaurids (Late Jurassic-Early Cretaceous of South America and Africa), with relatively short necks and very tall neural spines (forming fins or sails in Amargasaurus of the Early Cretaceous of Argentina) were relatively small, as were rebbachisaurids. However, the Diplodocidae (best known from the Late Jurassic of western North America), included some gigantic forms:

    Macronarians ("big noses") are characterized by:

    Camarasaurus of the Late Jurassic of western North America, Europe, and Africa is a typical primitive macronarian, as is Jobaria of the Early Cretaceous of Africa. The more advanced macronarians (the Titanosauriformes), and are characterized by expanded snouts and nares placed on top of their skulls. Titanosauriforms include some of the largest dinosaurs (rivalled only by the largest diplodocids), and are divided into:

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    Last modified: 9 January 2007