LONG-NECKED GARGANTUANS
World of Dinosaurs Lecture #14
3 March 2009
SAUROPODOMORPHA: PROSAUROPODS AND SAUROPODS
- Saurischians are divided into Theropoda and Sauropodomorpha.
- Sauropodomorpha includes the sauropods, one of the best known dinosaur groups, as
well as the poorly known prosauropods. Both are thought to be herbivorous.
- The group includes the largest animals ever to walk on land, reaching lengths of up
to 150 feet and perhaps greater than 100 tons!
- Sauropodomorphs appeared with the first dinosaurs (225 mya) and persisted
throughout the dinosaurian reign, until the end of the Cretaceous (65 mya).
SAUROPODOMORPH ANATOMY
Prosauropods
- Plateosaurus was one of the first large dinosaurs, about 25 ft. long.
- Most prosauropods retained the primitive condition of being bipedal.
- The neck is relatively long and the head is small. The eyes are directed sideways
rather than forward, suggesting minimal stereoscopic vision.
- The teeth are quite simple and leaf-shaped, with coarse serrations.
- The femur is longer than the tibia, suggesting that these animals were quite slow.
- Some later prosauropods (e.g., Anchisaurus and Thecodontosaurus) were relatively
smaller and more lightly built than the plateosaurids.
Sauropods
- The sauropods were all long-necked, quadrupedal giants with small heads.
- In broad terms, there are two major functional types of sauropod skulls. The first
type, including Camarasaurus and Brachiosaurus, have shorter, higher skulls with thick
spoon-shaped teeth and the bony external nostril positioned near the front. The
second type, including Diplodocus, have longer, lower skulls with narrow, pencil-like
teeth restricted to the front of the jaws, and a dorsally placed bony nostril.
- During the evolution of sauropods, there was an increase in the number of cervical
vertebra, and each vertebra tended to become long.
- The cervical and dorsal vertebrae tend to be highly pneumatized, composed only of a
series of beams and struts attached by thin sheets of bone.
- Despite some controversy in the past, we are now confident that the limbs were not
sprawled, but rather were upright and pillar-like, as in elephants.
- There are five robust metatarsals arranged so that from above, they form two-thirds
of a circle. Sauropods, like theropods, were digitigrade, walking on their fingertips,
with the "palm of the hand" supported by a large pad. Most sauropods have a large
claw on the end of their second finger that may have functioned as a weapon.
- In contrast, the toes of the hindfeet were somewhat splayed out, so that the animal
was almost plantigrade, like we are.
Lecture 14—Long-Necked Gargantuans—1
- At least one groups of sauropods, the titanosaurids, are unique in having body armor
and some apparently had tail clubs as well.
SAUROPODOMORPH PHYLOGENY
- The ancestry of prosauropods and sauropods is obscure. Prosauropods appear fully
formed in the Late Triassic. By the Middle Jurassic, sauropods are present on every
continent, but their evolutionary roots are still uncertain.
- In contrast to sauropods, prosauropods are specialized in having a reduced fifth digit
of the hind foot. This makes it less likely that one of the prosauropods was directly
ancestral to sauropods.
Saurischia
Sauropodomorpha
Prosauropoda
Riojasaurus
Plateosauria
Massospondylidae (e.g., Massospondylus)
Plateosauridae (e.g., Plateosaurus)
Sauropoda
Vulcanodon
Shunosaurus
Barapasaurus
Neosauropoda
Diplodocoidea (e.g., Dipodocus, Barosaurus)
Camarasauridae (e.g., Camarasaurus)
Brachiosauridae (e.g., Brachiosaurus)
Titanosauria (e.g., Titanosaurus, Alamosaurus)
Lecture 14—Long-Necked Gargantuans—2
SAUROPODOMORPH PALEOBIOLOGY AND PALEOECOLOGY
- The evolution of long necks is probably associated with high browsing. Before
prosauropods, virtually all herbivores were short and squat.
- The ecological roles played by prosauropods in the Late Triassic and Early Jurassic
were filled by sauropods by the Middle Jurassic, and the prosauropods disappeared.
- Sauropodomorphs appear to have preferred low latitudes rather than temporate or
polar regions.
- For a long time, sauropod lifestyles were thought to be largely amphibious. Evidence
cited in support of this view included: gigantic size, weak teeth, and nostrils on top of
the head in some forms (thought to be used as a snorkel).
- Since the 1970’s, sauropods have been viewed as fully terrestrial. Evidence for a landliving mode of life includes: pillar-like legs, narrow feet, pneumatic vertebrae, and
abundant trackways.
- There has been great controversy over whether or not sauropods could rear up onto
their hind legs, forming a tripodal stance with the tail. Problems include: strength to
rear up, problem of coming back down, and pumping blood up the neck to the head.
- Yet Brachiosaurus, with its more vertical neck, also had to get blood up to the head,
and all sauropod males would needed to rear up in order to copulate!
- It is estimated that a sauropods carrying its neck vertically would have required very
high blood pressures (4-5 times greater than a human) to push the blood from the
heart to the brain.
- With regard to feeding, it appears very likely that sauropods used their size to browse
the crowns of tall trees.
- The diet was likely composed of conifer trees, cycads, and high-rising tree ferns.
- Yet the skulls and teeth are not designed for powerful chewing.
- Much food processing took place in the gizzard, aided by gastroliths (stomach stones).
- Further down the gut, the partially processed food would have passed through a
giant intestine, where bacteria would have helped further to break down food.
- So, it is likely that sauropods fed on massive amounts of low quality food that would
have been chopped into small pieces in the mouth, ground up by gastroliths in the
gizzard, and then processed by acids and bacteria in the rest of the gut.
- With regard to group behavior, there are large bonebeds known for several
prosauropods, and trackways show that sauropods frequently traveled in groups.
- With regard to predator defense, the greatest deterrent would have been large size.
- In addition, most sauropods, including juveniles, had a large, trenchant hand claw.
- Finally, it has been postulated that the elongate tail of diplodocids was used as a
whip to create a sonic boom and thereby intimidate predators.
- With regard to growth, it has been suggested that sauropods gave birth to live young,
yet we now have several examples of sauropod eggs, some with embryos. These
show that even the largest dinosaurs were hatched from eggs no bigger than a
football.
- Current evidence suggests that sauropods attained adult size in only 10 years, but we
do not know yet about maximum lifespans.
Lecture 14—Long-Necked Gargantuans—3