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Seismosaurus was a huge plant-eater (herbivore) that lived in North America during the Jurassic period, between about 155 and 145 million years ago.
When initially discovered, the Seismosaurus was believed to be between 130 and 170 feet, which is approximately 40 to 52 meters in length, with most of its range was taken up by its very long neck and tail. Still, the body and head being both comparatively small. Recently, however, there has been discussion among scientists about Seismosaurus, firstly about whether it should be classified as a separate genus from Diplodocus. Secondly, about its length, some recent estimates put its length as only 33.5 meters.
A giant, herbivorous, or plant-eating, dinosaur, Seismosaurus inhabited western North America during the late Jurassic period, approximately 159 to 144 million years ago. It belongs to the order Saurischia the lizard-hipped dinosaurs and the suborder Sauropoda. It is a member of the family Diplodocidae, which includes a better-known dinosaur called Diplodocus.
Seismosaurus may have been the longest species of a dinosaur ever to exist. Fossil evidence shows that some individuals measured more than 150 feet (46 meters) long, equal to half the length of a U.S. football playing field. The enormous size of its hips and sacrum, which supported its massive body as it walked, indicates that the dinosaur would have weighed approximately 100 tons or more, rivaling in size the largest living animal on Earth, the Blue whale. The name Seismosaurus, which comes from the Latin words for “earth-shaking lizard” was inspired by the image of this giant dinosaur causing the ground to shake when it walked. Its sacral vertebrae five bones of the lower spine that form part of the hip region measured 5 feet in length, nearly twice that of the sacral vertebrae found in other diplodocids. Seismosaurus had a very long neck and a tail that each is measuring approximately 70 feet, which is approximately 21 meters in length. Like other diplodocids, Seismosaurus most likely had a small, delicate skull about the size of a modern horse’s head and relatively weak, pencil-shaped teeth.
Seismosaurus was a quadruped, meaning that it stood and walked on all four legs. Its diet consisted of a wide variety of conifers, or evergreen trees, as well as other plants that included ginkgoes, cycads, horsetails, and ferns. Fossil evidence indicates that Seismosaurus swallowed gastroliths, stones that settled in the stomach and helped to grind up the sturdy plant material it consumed—similar to the way modern seed-eating birds require grit in their diet. Some scientists argue that the gastroliths may have also been used to stir up the digestive juices in the dinosaur’s stomach. In one Seismosaurus specimen, paleontologists counted more than 240 gastroliths, which ranged in size from that of a peach pit to the size of a small grapefruit. All were smooth and had rounded edges; some had a dull surface while others were waxy and had a highly polished finish. Paleontologists once believed that during the Jurassic period about 206 to144 million years ago, western North America was utterly tropical and that sauropods such as Seismosaurus had an abundant, steady food supply and always stayed near water.
A row of tail vertebrae was the first evidence of Seismosaurus, discovered in 1979 in the Ojito Wilderness Study Area located in New Mexico in the southwestern United States. Initial excavation of eight exposed tail vertebrae from a sandstone mesa in the Morrison Formation began in 1985 by paleontologist David D. Gillette, who formally named the dinosaur Seismosaurus in 1986. Excavating the remaining partial skeleton of this dinosaur was a challenge because it curved deeply into the mesa. Gillette was able to trace the remainder of the frame into the mesa by using seismic tomography, a method used to locate underground structures with sound waves. This was the first time such technology had been used to find dinosaur remains.
Estimates of Seismosaurus' weight vary, but it is believed to have weighed in at around 100 tons or 200,000 lbs. 200,000 lbs are equal to 40,000 five-pound bags of sugar—the same weight as a small, fully grown adult blue whale.
Seismosaurus was a herbivore meaning it was a plant-eater. This dinosaur would have eaten a diet mostly of conifers, these being the dominant plant during the time that sauropods lived, along with other plant foliage such as ginkgos, seed ferns, cycads (a palm-like plant), ferns, clubmosses, and horsetails. Its long, agile neck would have been used to poke into the forests to reach the foliage. Seismosaurus having the advantage of being able to reach high-growing foliage that the other giant Sauropods wouldn’t have been able to achieve, their large size and shorter necks preventing them from entering the forests and reaching the foliage. Due to its vast size, Seismosaurus must have eaten an extraordinary amount each day to sustain itself. It is thought that Seismosaurus would have swallowed leaves whole, using its blunt peg-like teeth found in the front of its jaw to strip foliage off of nearby trees.
Seismosaurus became extinct at the end of the Cretaceous 65 million years ago, along with all the other dinosaurs and a myriad of other life forms, but they were on their way out long before.
While the long neck has traditionally been interpreted as a feeding adaptation, it was also suggested that the oversized collar of Diplodocus and its relatives might have been primarily a sexual display, with any other feeding benefits coming second. While no evidence indicates Diplodocus nesting habits, other sauropods, such as the Seismosaurus, have been associated with nesting sites. The Seismosaurus nesting sites suggest that they may have laid their eggs communally over a large area in many shallow pits, each covered with vegetation. For Seismosaurus, the size of clutches and individual eggs were surprisingly small for such large animals. This appears to have been an adaptation to predication pressures, as large eggs would require more considerable incubation time and thus would be at higher risk.