Temporal range: Late Triassic – Late Cretaceous
|Several species of Sauropodomorph|
The Sauropodomorpha, meaning 'lizard-foot form', is a genus of dinosaurs used to group and identify the group of long-necked, herbivorous dinosaurs that eventually evolved into quadrupedal creatures that became the largest animals that ever walked the earth.
Much like modern-day giraffes, the sauropodomorphs evolved to adapt to the high foliage and fauna available on the high trees of their time. The animals developed exceptionally long necks in order to be able to reach and browse for sustenance at heights no other creature could remotely reach. Such a feeding pattern is supported by their basic defining characteristics, such as a light, tiny skull on the end of an elongated neck, which featured ten or more elongated cervical vertebrae, as well as a long tail that was used to counterbalance to length of the creatures' necks, as well as for defense from larger predatory dinosaurs.
Sauropodomorph teeth were generally weak, and shaped like leaves or spoons. As these teeth were not useful for grinding their food, the creatures had stomach stones known as gastroliths, similar to the gizzard stones of modern birds or crocodiles, to help grind and digest tough plant fibers swallowed by the animals. The sauropodomorphs' upper portion of their mouth bent down, in what may have been a beak. This is similar to other herbivorous dinosaurs' jaw structure, which allowed the creatures to rip and tear fauna much more effectively.
The earliest known sauropodomorph, Saturnalia, was a relatively small ancestor of the species, at 1.5 metres long, in comparison to its later-developing relatives. However, by the end of the Triassic Period, the sauropodomorphs were the largest dinosaurs of their time, and increased in size as a species by the time of the Jurassic and Cretaceous periods. Ultimately, the largest sauropods ever discovered, such as the Supersaurus, Diplodocus hallorum, and Argentinosaurus, were capable of reaching 30–40 metres, or 100–130 feet, in length, and 60,000–100,000 kilograms or more in mass.
Sauropodomorphs were initially bipedal like many other dinosaur species, but, due to the vast increases in size faced by the species, they evolved to become graviportal quadrupeds, similar to modern elephants. As the sauropodomorphs share common ancestors with the therapods, the other saurischian lineage, it is possible that early sauropodomorphs were actually omnivorous, and developed into a solely herbivorous species when their increasing size and neck length made plant grazing easier and game hunting more difficult.
The sauropodomorphs also had large nostrils, and most likely increased olfactory senses in tow, as well as a retained thumb from ancestor generations which featured a large claw possibly used for defense. However, due to the creatures' overwhelmingly massive size, their primary defensive adaptation would be the intimidation factor such size provides, as well as their sizeable tail.
The sauropodomorphs were one of the very first dinosaurs to evolve in the late Triassic Period, roughly 230 million years ago, and became the dominant herbivores mid-way through the Triassic Period. Despite evidence pointing to a decline in the species during the Cretaceous period, it is noted that, while the creatures' numbers appear to have dwindled in Europe or North Maerica, they were still the dominant herbivores in the Gondwana landmasses. A spread of flowering plants and competition from the evolving ornithischian species are likely not a major factor in the sauropod decline in northern continents.
The most basal sauropodomorph known, Saturnalia, a sort of forerunner of the species, was discovered in 1999, and is dated to have live during the late Triassic. Saturnalia, had the teeth, backbone, pelvis, and legs of traditional prosauropods, while lacking all of the unique sauropod characteristics. This lends support to its placement as the basal sauropodomorph, as it would be the first of the line, and hence least evolved. However, fragmentary remains from Madagascar may represent an even earlier sauropodomorph from the middle Triassic.
Sauropodomorpha is one of the two major clades within the order Saurischia. The sauropodomorphs' sister group, the Theropoda, includes bipedal carnivores like Velociraptor and Tyrannosaurus. However, Sauropodomorpha also share a number of characteristics with the Ornithischia, so a small minority of palaeontologists like Bakker place both sets of herbivores within Phytodinosauria (or Ornithischiformes), effectively dividing dinosaurs by their predatory or herbivorous tendencies.
While the sauropodomorphs are still grouped into prosauropods and sauropods for convenience, most modern classification schemes break the prosauropods into a half-dozen groups that evolved separately from one or more common ancestors. While they have a number of shared characteristics, the evolutionary requirements for giraffe-like browsing high in the trees may have caused convergent evolution, where similar traits evolve separately because they faced the same evolutionary pressure, instead of homologous traits derived from a shared ancestor.
- Suborder Sauropodomorpha
- Infraorder Prosauropoda
- Infraorder Sauropoda