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Sauropods: the long-necked giants
giants from c. 190 million years ago· Organism or group· Animals
Well establishedStrong fossil, genetic or geological evidence.
Long-necked, four-legged plant-eating dinosaurs, the largest animals ever to walk on land.
See it on the Life map →What happened
Sauropods descend from smaller, two-legged sauropodomorphs of the late Triassic; giants appeared in the early Jurassic. Familiar ones include Brachiosaurus and Diplodocus of the Jurassic; Cretaceous titanosaurs such as Argentinosaurus and Patagotitan reached about 30–37 m and 50–80 tonnes, though estimates vary. Long necks let them sweep wide areas of plants without moving. They swallowed food unchewed, and bird-like air sacs hollowed their bones, saving weight. They laid many small eggs, and young grew fast.
Why it matters
They show how large a land animal can become: a combination of air sacs, no chewing, many small eggs and fast growth let them far outgrow any land mammal.
The evidence (fossils, genes, rocks)
Skeletons, wide trackways, nesting grounds with embryos such as Auca Mahuevo in Argentina, and bone growth rings; body mass estimated from leg-bone thickness.
Still debated
How they pumped blood up such long necks, whether necks were held high or low, and their true maximum weights are debated.
Connections (2)
▸Eoraptor & the first dinosaurs (Argentina) may resemble the ancestors of Sauropods: the long-necked giantsDebated
The connection
A 2011 reanalysis placed Eoraptor on the sauropodomorph branch, the line that later produced the long-necked giants. If correct, sauropods trace back to small, two-legged, partly plant-eating ancestors much like Eoraptor, and only grew huge over the following 40 million years.
When and how
Proposed by Ricardo Martínez and colleagues in Science (2011), in the paper describing Eodromaeus, also from Argentina's Ischigualasto Formation.
How sure are we?
Features of its teeth and skull hint at sauropodomorph links, but early dinosaurs share so many traits that the placement is uncertain.
Debates and open questions
Other analyses place Eoraptor as an early theropod or near the base of all dinosaurs; its position shifts as new fossils are added.
▸End-Triassic extinction opened the Jurassic to Sauropods: the long-necked giantsStrong evidence
The connection
With rival large plant-eaters gone, sauropodomorphs expanded. True sauropods appeared in the early Jurassic, and by about 190–180 million years ago they were reaching giant sizes, becoming the main large plant-eaters on land for the rest of the Jurassic.
When and how
Early Jurassic, from about 200 million years ago; early sauropods such as Vulcanodon come from Zimbabwe, with others from elsewhere in Africa and Asia.
How sure are we?
Sauropod bones and wide-gauge footprints become common in early Jurassic rocks, after the extinction removed other large herbivores.
Debates and open questions
Large sauropodomorphs such as Ingentia, about 210 million years old, already existed in the late Triassic, so how much the extinction mattered is debated.