GEOL 104 Dinosaurs: A Natural History

Fall Semester 2000
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 of other early sauropodomorphs from Madagascar might be as old as the Middle Triassic, but the age of the rocks they are from is not certain).

    Basal sauropodomorphs are often called prosauropods. They may form a paraphyletic grade leading to the Sauropoda; they may form their own monophyletic group Prosauropoda; or there may be a combination of both.

    Prosauropods are characterized by:

    Prosauropods 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. The oldest known sauropod is from the end of the Late Triassic, but sauropods do not become common until the Middle Jurassic.

    Sauropods are characterized by:

    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:
    Euhelopodidae is a clade of Middle Jurassic-Early Cretaceous sauropods from eastern Asia. They had round fat bodies for support and many extra cervicals to make their necks extremely long (the longest of any known animal).

    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:

    Macronarians ("big noses") are characterized by:

    Camarasaurus of the Late Jurassic of western North America, Europe, and Africa is a typical primitive macronarian. The more advanced macronarians form Titanosauriformes, and are characterized by expanded snouts and nostrils 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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