Like many previous articles on sauropods, this article begins with "Sauropod dinosaurs were by far the largest animals to ever roam the Earth." The heaviest terrestrial animals weighed four times as much as the largest sauropods (and other largest dinosaur species). The unusually long neck paired with a relatively small head, which can reach lengths of over 14 meters in some species, has the characteristic body design of sauropods (Fig. 1). The neck is often held horizontally or at a low angle. Like an elephant's, four pillars supported a large but rather short trunk.
The forelimb bones of sauropods were vertically oriented, and some of the last forms walked only on their metacarpals after losing their finger bones (middle bones of the hand). Semi-erect foot on hind leg that bears most of the weight. As with most other true land vertebrates, the femur (thigh bone) was the largest bone in the skeleton (amniotes). The long tail stabilizes the long neck, the sole of which acts as the fulcrum of the massive muscles that push the hind foot back as it walks.
Although sauropods are sometimes portrayed in popular culture as the ultimate failure of evolution, the opposite is true. By far, and by any standard, no other herbivore in the history of terrestrial animals has been so successful. Sauropods lived at least 201 million years between the beginning of the Jurassic 66 million years ago and the end of the Cretaceous 135 million years ago. For most of this time, sauropods dominated all continents as the dominant herbivores, with hadrosaurs only challenging them on a few landmasses in the Late Cretaceous.
With hundreds of known species, sauropods are the most diverse group of extinct dinosaurs (other than non-avian theropods), despite having massive bodies that are inversely proportional to the diversity in modern mammals. Presumably, size is an indicator of evolutionary progress. A “large” sauropod starts at 20 tons, a “giant” sauropod starts at 50 tons, and a “super-giant” sauropod reaches over 80 tons, the mass of a large whale. However, there is no official size classification. Surprisingly, large body size was a feature of nearly all sauropod lineages from the beginning of their evolutionary history. Some of the earliest sauropods had already crossed the 20-ton barrier, making them larger than any previous land animal.
The exceptions were mostly island-dwarf dwarf species, and most sauropods were gigantic to supergiant.
The diversity of sauropods in time and space
Ornithischia or bird-hipped dinosaurs and Saurischia or lizard-hipped dinosaurs are the two main groups of dinosaurs. Theropods and sauropods form a large bifurcation at the base of the saurischians known as sauropodomorphs. Birds are theropods or meat-eating dinosaurs. Thus, birds are living dinosaurs, but not related to dinosaurs with bird-like hips (Figure 2).
Along with theropods, sauropodomorphs first appear in the fossil record at least at the beginning of the Late Triassic, or 237 million years ago. From that point on, these originally bipedal creatures, ranging in size from deer to rhinoceros (such as Plateosaurus), diversified and spread geographically.
True sauropods arose in the Early Jurassic, 201 million years after the end-Triassic mass extinction, as evidenced by their fossilized bones. However, traces and trails from the Greenland Late Triassic point to an earlier existence. One of the best-known early sauropods, Vulcanodon lived in Southern Africa during the Early Jurassic period and exhibits many of the group's distinguishing features, particularly fully upright legs that indicate quadrupedal mobility. Toward the end of the Early Jurassic, 180 million years ago, early branching sauropodomorphs disappeared, most likely due to an extinction event that occurred during the Toarcian phase. At that time, sauropods were allowed to roam freely and evolved rapidly (Fig. 2).
Kaynak: cell.com/current-biology/fulltext/S0960-9822(22)01960-1
Günceleme: 03/02/2023 13:59
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