Sauropods were large, long-necked plant-eating dinosaurs that first appeared in the Triassic Period and proliferated in the Jurassic. They had tiny heads that logded even tinier brains, and long tails which counterbalanced their very long necks. To the infraorder of sauropods (“lizard-footed”) belonged the five families of Diplodocids, Brachiosaurids, Carnasaurids, Titanosaurids and Cetiosaurids. The dinosaurian species Apatosaurus belonged to the sauropod family of Diplodocids; they were land-roaming giants that lived in the present day North American region for a relatively brief period during the Jurassic, between about 157 mya and 146 mya.
They were among the largest animals that ever lived on the planet, and are generally considered as the largest type of dinosaur. Apatosaurus reached a length of 70 to 90 feet from the end of their tail to the mouth, with their necks alone being over 20 to 40 feet long. They were about 15 feet tall at hips, weighing around 30 to 35 thousand kilograms, or about the weight of 5 elephants. An interesting feature of diplodocoids, a part of their physiognomy, is that they had their nostrils positioned above their eyes, on the top of their heads.
The name ‘Apatosaurus’, meaning ‘deceptive lizard’ is not particularly apt for these dinosaurs, and was given for some circumstantial reasons associated with their original discovery. However, these giant creatures are also popularly known by another name ‘Brontosaurus’, meaning ‘thunder lizard’, which is a much more appropriate description of the mighty beast. The reason these dinosaurs have two names — only ‘Apatosaurus’ being the scientifically accepted — is that when the first fossil of this species was discovered in latter half of 19th century, it was named Apatosaurus; subsequently another skeleton of a presumably new species of dinosaurs was discovered and was named Brontosaurus, but only much later was it found out that both Apatosaurus and Brontosaurus referred to the same species.
This is one of the well-known stories in the dinosaur lore. In 1870’s in the United States, there was a widespread interest in hunting the dinosaur fossils. Two men worked particularly assiduously and enjoyed prolific results in the pursuit of dinosaurs: Othaniel C. Marsh and Edward D. Cope. These legendary rival professors of paleontology who worked for U.S. geological survey discovered 136 dinosaur species between them, whereas there were only 9 known species before their time. In late 1870’s in Wyoming, Marsh found two very large skeletons of the same animal, and named it Apatosaurus.
Some time afterward, a huge sauropod skeleton was discovered by an expedition working under Cope, and it was named Brontosaurus. In both these independent fossil discoveries, skulls of the animals were not found, and therefore the resemblances were not easily noticed. Decades later, in the early 1900’s, a Brontosaur skeleton was displayed in the Museum of Natural History at Yale.
It came to the notice of an investigator who realized that Brontosaur was the same as Apatosaurus. According to established scientific conventions only the name first given to a species remains valid, however the name Brontosaurus was by then firmly entrenched in the public consciousness (Merriam-Webster, 1991). Therefore the name Brontosaurus was not altogether discarded and was retained as a synonym. However, after a controversy in the 1980’s involving a U.S. postal stamp that labeled the creature as Brontosaurus, the term has become obsolescent.
Apatosaurus / Brontosaurus was so massive that at first scientists conjectured that this animal lived in swamplands where part of its enormous body weight could be supported by the buoyancy of water. However, in the later decades as more fossils of this animal were excavated and none were found near watery areas, this conjecture was dropped. Their skeletons were also not particularly adapted for living in water. Apatosaurus could have been a grazing animal that lived and moved in herds. However, it could also have been a solitary animal, because fossils of Apatosaurus were so far found only in isolation and not in clusters.
However, fossil tracks of sauropodian herds were found. These animals may not have had much difficulty in finding food because the terrain was abundantly covered by plants at that time. However, according to some estimates, an Apatosaurus might have needed to consume in excess of one ton of plant material every day.
To procure such massive amounts of food, these animals might have routinely expended considerable time and effort. And in the process they would have significantly reshaped the landscape around them. They had peg-like teeth which could strip leaves from plants, needles from tree-tops and so on, but these teeth could not chew. Therefore it could be possible that these animals swallowed stones along with their food, which could then help break up the ingested food, a strategy followed by some birds.
A special characteristic of diplodocids in terms of their bone structure is that they had hollows in their vertebrae. Nevertheless, they were strong enough. The cervical vertebrae of Apatosaurus were stronger and shorter than the other diplodocids, for example Diplodocus. Diplodocids had a deep and heavy midsection. Apatosaurus had huge bones in the midsection of their bodies. Their ribs were elongated. Apatosaurus did not have a muscular diaphragm, and had avian type lungs. The estimated total lung volume is about 1400 liters with a dead-space volume of 184 liters (Farlow, Brett-Surman, 1999).
Owing to their fantastically huge size, they had little to fear from predators. Apatosaurus’ enormous tapering tail could serve as a whiplash against any possible attackers. Their main enemy was Allosaurus, which was a ferocious meat-eating dinosaur but very much smaller in size. If indeed these diplodocids traveled in herds, their collectivity could have served as an additional protective measure. However, the speed of their mobility was rather restricted. They had four huge limbs that could support their massive body weight and they walked on all four legs, but understandably enough the adults of the species could only lumber along.
The hind limbs of these animals were larger and longer than their forelimbs. They could walk up to 10 miles or 16 kms a day. Their long tails would stand fully stretched out as they walked, in order balance their bodies. The need to hold their tails up also arose because dragging such a massive tail on ground could have got it entangled in the vegetation or caught up in the cracks of rocks.
Occasionally the tail could have been used as a third limb to support the weight of the body when these animals raised their heads and forelimbs limbs up to grab leaves higher up. The younger ones of the species could become easy prey for Allosaurus or other theropodian predators such as Ceratosaurus, but the juveniles exhibited more agility than the mature ones. Footprint fossils (known as trackways) of Apatosaurian juveniles discovered more recently suggest that while growing, Apatosaurus could run on their hind legs in the manner of some species of lizards today.
These sauropods grew to their full size rather rapidly. It might have taken an Apatosaurus only 15 to 20 years to put on its full body weight of 25 to 35 tons. The average life span of these animals could have been around a 100 years. Scientists still do not have an explanation as to why Tyrannosaurus Rex, Apatosaurus and other huge varieties of dinosaurs were so large and heavy (Zimmer, 2005). But it is clear that to support such gigantic beasts the land must have been extraordinarily rich in vegetation.
Diplodocids were formerly thought to have held their heads high and necks straight up so that they could easily graze from tree tops. But this picture presented some problems because it would not be possible for the blood flow to reach up to the brains in order to oxygenate it if these animals held their long and slender necks nearly vertically up. Accordingly, their necks would have been typically positioned at a 45° angle to their body while grazing from tall trees.
The structure of neck bones also would not have allowed an Apatosaurus to bend its neck further back. In a resting position, the necks would have normally assumed a more comfortable angle, which is being parallel to the ground or actually leaning downwards. Diplodocids generally tended to hold their necks horizontally. Also, these extremely long diplodocid necks had very limited mobility.
Incidentally, in whatever position the neck was placed, pumping blood along its enormous length all the way up to the head and the brain would have presented a great challenge to the animal’s heart. These animals were walking and grazing much of their waking time, and their brains would be situated many meters high above their hearts for many hours a day. Therefore, Apatosaurus’ blood pressure should have been around 4 times higher than humans, and their hearts would have been very powerful machines indeed to sustain such an enormous blood pressure.
Considering that these diplodocids grew at phenomenal rates, growing 20 kg a day and achieving 90% of their adult size only after the first 10 years of their life, they would have required a large amount of energy to maintain their growth rates, and their physiology could have been homeothermic. Large-size sauropods in general could have been inertial homeotherms.
This means that once they were heated by either external environment or internal processes they could maintain this temperature for a long time by fermenting bacteria harbored in their spacious guts. The fact that the surface area / volume ratio was lower in sauropods compared to many other species of dinosaurs would have also helped them maintain the body temperature. In case of overheating, heat venting could have been achieved by means of long necks, tails and legs (Martin, 2006).
Sauropodian eggs were huge, up to one foot in width. It is likely that sauropods did not take care of their eggs.
The states of Wyoming, Colorado, Utah and Oklahoma yielded the most abundant fossils of Apatosaurus as well as other sauropods so far. These beasts may also have lived in a much more extensive area further north and south. Four subspecies of Apatosaurus have been identified: ajax (mostly in Colorado), excelsus (Utah and Oklahoma), louisae (mostly in Colorado), yahnahpin (mostly in Wyoming). Today, Brontosaurus still remains one of the most familiar names of all dinosaurs, perhaps next only to Tyrannosaurus Rex.
Farlow, J.O., Brett-Surman, M.K. (1999). The Complete Dinosaur. Bloomington, IN : Indiana University Press.
Gaines, R. (2001). Apatosaurus. Edina, MN : ABCO Publishing
Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Malden, MA : Blackwell Publishing
Merriam-Webster. (1991). The Merriam-Webster new book of word histories. Springfield, MA : Merriam-Webster, Inc
Zimmer, C. (2005). Dinosaurs. Discover Magazine. April 2005. Retrieved from http://discovermagazine.com/2005/apr/cover
University/College: University of Arkansas System
Type of paper: Thesis/Dissertation Chapter
Date: 21 April 2017
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