- Main article: Triassic Divergence
The Metasauropoda is a group of surviving dinosaurs known from the Americas. They are nested within the Sauropodomorpha and evolved in South America during its period of long isolation. Genetic variation in neck length and forelimb structure have proved to be two of the hallmarks of this clade.
Natural History Edit
Before the split, sauropodomorphs were rather diverse, with a great deal of size range and variation in posture. During the Triassic-Jurassic Mass Extinction, however, most of their diversity outside of the sauropods was lost. The sauropods followed a general trend of decline in Laurasia with most of their diversity in Gondwana until they became extinct at the end of the Cretaceous
While the sauropodomorphs of Triassic Divergence produced large forms in various lineages throughout the Mesozoic, the majority of their diversity has always remained small. They became extinct in every continent except South America at the end of the Mesozoic, where they are represented by today's Metasauropoda. The Metasauropodomorpha (including the extant Metasauropoda and several extinct lineages) radiated into almost every herbivorous niche in South America, as well as into other ecological niches such as insectivory (in fact, they contain the largest insectivores known in the fossil record) frugivory, and picivory. Much of their diversity was lost when animals from North America migrated into South America, but a few forms did so well that they can be found well into North America
The Metasauropoda are represented today by four living lineages characterized by specialized forelimbs variously used for digging, foraging, or catching fish. The Piscatorosauropoda and Edentasauropoda typically come out as sister groups to each other, while the Arbosauropoda and Frugosauropoda form the monophyletic clade Eumetasauropoda. Outside the Metasauropoda proper, a number of extinct groups are known from the broader Metasauropodomorpha. The Ungulisauropoda includes a number of fossil forms that show adaptations for quick bipedal locomotion and grazing behavior. The Gravisauropoda contains some of the largest land animals known from the Cenozoic, and all seem to have been quadrupedal grazers and browsers. The Rostrosauropoda include a number of poorly-understood beaked forms. Finally, there is a single species, Primopatrus austerus, known from the Oligocene that comes out as the sister group of all other Metasauropodomorphs.
Unlike anything in our timeline, the piscatorosauropods are, as the name suggests, piscivorous metasauropods. They tend to have necks of moderate length, long snouts with elongate, smooth teeth, and robust arms with large claws. They tend to be small, with the largest species reaching about 1.5 m (5 ft) in length and the smallest about 50 cm (20 in).
The Piscatorosauropoda are comparatively restricted in range, found from the Pampas to the Yucatan Peninsula. They are most commonly found in the Amazon watershed.
These small to midsize metasauropods are insectivores. Most have lost teeth completely, while one genus retains teeth at the front of the mouth to strip bark from trees. They typically have narrow snouts, long necks, small eyes, and robust forelimbs, as well as large, sticky tongues that tend to be short and wide rather than long and narrow.
The most far-ranging of the modern Metasauropods, the Edentasauropoda are found throughout South America and into North America as far north as the Great Basin Desert. They remain most diverse in tropical South America, however.
These comparatively large metasauropods are obligate browsers, usually feeding on the leaves of trees and bushes. They have long necks, "leaf-shaped" teeth, and sturdy arms that may or may not have claws. Typically, arbosauropods adopt a quadrupedal stance while walking and a bipedal stance while feeding.
Arbosauropods are found across South America and into the temperate forests of what is to us the southern United States.
Frugosauropods are a highly specialized group of metasauropods that are adapted to feeding on fruits and seeds. The more "basal" genera tend to have almost carnassial teeth throughout the mouth in order to cope with fleshier seed carriers, while the more diverse members of the group have extremely large mechanical advantage in the jaws and comparatively flat teeth to allow for feeding on tough seeds.
Frugosauropods are comparatively restricted in range, limited to the tropical jungles of South and Central America.