Sauropodomorpha

Plateosaurus by Todd Marshall (2004)

CHARACTERISTICS

• Very large nares (nasal cavities)
• Extremely long neck
• Teeth shaped like pegs and suited to herbivorous lifestyle
• Largest terrestrial animals ever to exist

PROSAUROPODS

These animals were the predecessors of the sauropods. Early prosauropods were partially bipedal, with functional hands, but once they reached the great sizes found in later forms, they were obligate quadrupeds. The teeth retained the primitive serration, a feature lost in the sauropods. The prosauropods died out in the Middle Jurassic.

Plateosaurus skeleton by P. Olsen (2004) based upon Galton (1990), Cranial photo by P.M. Galton

CHARACTERISTICS

• Long neck with a small head, counterbalanced by a long tail
• Functional hand with a large thumb claw
• Small leaf-shaped teeth with mild serrations
• Very few sacral vertebrae (hip vertebrae)
• Broad pelvis with an 'apron'-like shape

SAUROPODS

Diplodocus by P. Olsen (2004) based upon Hatcher (1901)

The sauropods were completely quadrupedal, and they include the largest land animals ever. They were herbivores, and thrived throughout the Jurassic, diminishing in numbers during the Cretaceous. Some forms had body armour, and other physical defenses. Shunosaurus had a club-like tail, while others used their long tails in a whip-like fashion, which has also been hypothesized to have been used for communication. Some species of sauropods lived in herds, as suggested by multiple sets of trackways made by many animals.

CHARACTERISTICS

• Huge body size, with the neck and tail balancing the animal like a suspension bridge
• Tiny head at the end of an extremely long neck (meters long in some species) due to extra cervical vertebrae
• Nares (nostril cavities) located very high up in the skull
• Teeth lined up so that biting mechanisms are more functional for stripping plants of their leaves

Cladogram courtesy of T.Holtz Jr 2004 (http://www.geol.umd.edu/~tholtz/G104/10421saur.htm)

(1) NEOSAUROPODS

• Hands evolved specifically for walking and carrying weight, with columnar metacarpals (hand bones)
• The teeth were all gathered at the front of the mouth
• The animal walks with a digitigrade (on the toes) posture as opposed to a plantigrade (on the ball of the foot) posture

Diplodocus carnegii by Todd Marshall (2004)

DIPLODOCOIDS

• Small elongated teeth all gathered at the front of the mouth
• Extremely long and whip-like tails
• Arms much shorter than hind legs
• Clades

• Rebbachisauridae - Teeth very similar to hadrosaurs
• Dicraeosauridae - Shorter necks than other diplodocoids, very tall spines on the neck (Example : Amargasaurus)
• Diplodocidae - Very long necks, and long thinner skulls than other diplodocoids (Examples: Diplodocus, Apatasaurus)

Apatosaurus louisae by Todd Marshall (2004)

(2) MACRONARIANS ("big noses")

• The nares were much larger than in any other group of sauropods, some even larger than their eye sockets
• Metacarpals (hand bones) were elongate in order to support the increased weight of the animals
• Teeth shorter and thicker, and often rounded
• Example : Camarasaurus, a shorter, animal with a thicker, stumpier skull than its relatives

(1) BRACHIOSAURIDAE

• Forelimbs were longer than hindlimbs
• Example : Brachiosaurus

Brachiosaurus by P.Olsen (2004) based on Paul (1988), skull based on McIntosh (1990)

(2) TITANOSAURIA

• These sauropods had wider hips than the brachiosaurs, and had more flexible spinal columns
• Some species in this group had armour
• The only group of sauropods that were common in the Cretaceous, and include the largest member of Sauropoda, Argentinosaurus from Argentina.

Argentinosaurus and Giganotosaurus by Todd Marshall (2004)

NEXT : THEROPODA

• Characters/ anatomy
• Major subgroups in the phylum
• Fossil record
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Author: Emma Schachner
Last updated: 13 November 2004
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