April 4, 2022 Scott Kraus

Seismosaurus Was Likely A Large Diplodocus

Seismosaurus (pronounced Size-mow-Sore-uss) was a giant saurischian sauropod named from the Greek language for its size which can be translated as “(earth) quake lizard”. Seismosaurus was once thought to have been a new genus of dinosaur but in recent years it has been agreed upon by most palaeontologists that Seismosaurus was most likely a particularly large species of Diplodocus though it’s type species name of S. hallorum has yet to be officially changed. Originally thought to have measured up to 50 meters in length making it the longest dinosaur ever recorded, Seismosaurus has been down-sized in recent years to a more respectable 35 meters in length.

Quick Facts

What did Seismosaurus Look Like?

Similar in looks to other Diplodocid dinosaurs and having been compared to “the dachshund of a giant dinosaur”. Seismosaurus was enormous having an extremely long slender neck with a small head and a large bulky body with short front legs and taller rear ones as well as a long heavy whipped tail. Its feet, like a modern-day elephant, had five toes with one toe on each foot having a claw, thought to be for protection.

Physical Attributes of Seismosaurus

Palaeontologists have questioned whether Seismosaurus heart would have been strong enough to pump blood to its head via its extremely long neck if it held it vertically. If not they have suggested that it must have held its neck almost parallel to the ground moving its head back and forth so that blood could reach its brain and head.

Seismosaurus backbone had extra bones below it with chevron shaped bony protrusions running backwards and forwards thought to have been for extra support and mobility in its neck and tail. It’s tail had at least one rather unusual wedge-shaped bones that gave it a kink, also thought to be used for protection – It thought that if Seismosaurus swung it’s tail at a potential predator it would have been able to do so with such force that it would have cracked the predator’s ribcage.

It is thought that Seismosaurus like other sauropods had a low intelligence with a very small brain, one of the lowest among all of the dinosaurs in fact, it’s intelligence being measured relative to its brain to body weight.

What did Seismosaurus Eat?

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 gingkos (a type of Chinese tree similar to the conifer), seed ferns, cycads (a palm-like plant), ferns, club mosses and horsetails.

It’s long agile neck would have been used to poke into the forests to reach foliage – Seismosaurus having the advantage of being able to reach high-growing foliage that the other large Sauropods wouldn’t have been able to reach, their large size and shorter necks preventing them from entering the forests and reaching the foliage.

Due to its huge 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.

Palaeontologists have discovered gastroliths (small round stomach stones) fossilized in the center of its skeleton, which it is thought Seismosaurus would have swallowed to have helped crush and digest the tough plant matter.

How did Seismosaurus Move?

Seismosaurus was a slow moving quadrupedal meaning he walked on four legs. Though leg-bone fossils have yet to be recovered, it is thought that Seismosaurus had short legs, the front shorter than the back, to help stabilize this huge dinosaur.

Where did Seismosaurus Live?

Seismosaurus lived about 150 million years ago during the late Jurassic period in what is now known as New Mexico in the United States.

It is thought that Seismosaurus may have traveled together in herds and may have migrated when their food supplies became depleted though their only being the one holotype this isn’t known for sure.

Seismosaurus would have lived at the same time as Stegosaurus, Allosaurus, Brachiosaurus and many others but Seismosaurus didn’t have to worry about predators thanks to its huge size.

The Discovery of Seismosaurus

Seismosaurus remains were found in New Mexico in 1979 by a group of four hikers Arthur Loy, Jan Cummings, Frank Walker and Bill Norlander. The group reported their discovery to the Bureau of Land Management but the government body lacked the proper tools and perhaps funding to remove the bones so it wasn’t until 1985 that the bones were excavated by palaeontologist David Gillette who took them to the New Mexico Museum of Natural History.

So far only a partial skeleton has been recovered for Seismosaurus including the front part of the tail, the pelvis and stomach region along with back vertebrae and some ribs. It is quite a rare find as the skeleton is articulated meaning it is joined and it also has many gastroliths (gizzard stones) within the stomach area.

The fossils for Seismosaurus took 13 years to remove from the ground and prepare due to the size of the remains and the hardness of the rock so it wasn’t until 1991 that this dinosaur was formally described and given the species name of S. hallorum.

The fossils are still being prepared to date at the New Mexico Museum of Natural History and palaeontologists hope to recover the front legs, neck and skull of this dinosaur in the future.

Basing his observations on a few tail vertebrae and parts of the hips Gillette originally announced that he had discovered a new dinosaur; Seismosaurus the largest sauropod dinosaur ever known being 150-200% larger than it’s cousin Diplodocus.

However as further work was done on the skeleton paleontologists noticed that the dinosaur was beginning to shrink in size. It turns out that what Gillette thought to be the large tail bones found down in the tail actually came from closer to the hips. This meant that the original estimated size had to be down-shifted quite dramatically giving the dinosaur an estimated length of about 35 metres, down from the originally estimated length of up to 50 meters.

Paleontologists were also finding that the characteristics which made this dinosaur distinct and unique warranting a new genus were diminishing. In 2004, amidst some controversy, it was announced that Seismosaurus was actually a very large Diplodocus.

The Importance of Seismosaurus

Seismosaurus reminds us that mis-identification’s are sometimes made but that as more evidence is found and palaeontologists re-examine evidence along with new formulas and technology being invented science self-corrects as it goes along, enabling Paleontologists to find out the true evolution and paleobiology of dinosaurs.