Long-necked Dinosaurs Successful because they did not Chew their Food
The largest land animals ever to exist, the long-necked dinosaurs owed their success to the ability to grow big very quickly and to do this they needed to process their food efficiently. A new European study into the likely feeding behaviours and growth rates of sauropods, the scientific name for the long-necked dinosaurs, concludes that during the Mesozoic, size really did matter.
A team of scientists believe that these animals grew huge to discourage predators, simply becoming to big for carnivorous dinosaurs to hunt effectively. The paper, to be published in the journal Science this week examines the growth rates of sauropods and postulates that these monstrous leviathans were warm-blooded. They would have needed high metabolic rates to sustain their rapid growth. Gigantism certainly has its advantages, for example African elephants have virtually no natural predators once they reach a certain size. Some of the Everything Dinosaur team members have worked in Kenya and they recall stories of a female elephant being attacked and killed by lions but this was an extremely rare occurrence and one that occurred in exceptional circumstances.
The pride concerned was very big, consisting of approximately 20 lionesses and some other semi-mature animals. There had been a prolonged period of drought which had limited the game available and the elephant attacked and killed was an immature animal believed to be about 15 years old. The attack occurred at night when this young female elephant got separated from the herd after visiting one of the few remaining water holes in the area.
It is probable that some carnivorous dinosaurs may have hunted in packs and large numbers of giganotosaurs or allosaurs would have been formidable adversaries quite capable of tackling an adult sauropod had they attacked as a group. From the few trackways that have been preserved showing sauropods moving in a herd, it seems that the smaller more vulnerable animals were to be found in the middle whilst the larger adults walked towards the outside of the group provided some protection for the younger animals.
Certainly, some of these herbivorous sauropods grew into giants. Although scientists still debate the maximum size and weights of these animals estimates of 80 to 100 tonnes are not uncommon and some of the lighter diplodocids could reach lengths in excess of 33 metres or more.
A scale model of a Brachiosaurus
Picture Credit: Everything Dinosaur
To view a scale model of a Brachiosaurus and other dinosaur models: Dinosaur and Prehistoric Animal Models.
How these gentle herbivores were able to grow so large when they had only a few peg-like teeth in their jaws (most species of sauropod), remains a mystery, but commenting on the article sauropod expert Paul Upchurch from the University College London said:
“most palaeontologists agree that feeding is the key to understanding sauropod gigantism”.
The large bodies and long necks effectively gave these animals an efficient feeding platform, allowing them to strip the vegetation from an area with little movement of their vast bulk, indeed it is thought that different species of sauropod fed on different types of plant matter to limit competition between species. Brachiosaurs for example with their necks held high could browse on the tree tops, stripping away branches and leaves with their peg-like teeth literally combing the food into their mouths. In comparison, other sauropods that shared the same habitat such as Apatosaurus probably fed on the understorey of vegetation.
Martin Sander, a palaeontologist at the University of Bonn (Germany), a co-author of the study, explained that a long-neck made sense if you needed to reach lots of food and a large gut would be required to process all the tough plant matter to extract nutrients. The absence of any large numbers of teeth made sense to the scientists when they considered the physical requirement of keeping a heavy head full of teeth aloft so that the animal could feed.
“You can only have this long neck if you don’t chew your food, otherwise your head would be full of teeth and too heavy to support,” he said.
To help process the bulky plant matter scientists believe that sauropods swallowed stones (called gastroliths), these remained in the stomach or perhaps in a gizzard-like organ and the muscular contractions of the dinosaur’s digestive tract helped grind up and break down the tough plant material. Microbes in the gut would also help break down food, particularly the tough cellulose plant tissues. Such a big powerful gut would process food quite efficiently and this would have helped these animals grow quickly, perhaps fast enough to prevent them falling prey to Theropods.
Microscopic analysis of the internal structure of sauropod bones show growth rings and a study of these rings can give scientists an indication of just how fast these animals may have grown. A 10 kilogramme hatch-ling for example may have taken something less than 30 years to grow into a 100 tonne specimen – a truly astonishing rate of growth. This would equate to human baby growing to the weight of an African elephant by the time they started school.
“This tells us that they must have been warm-blooded and had a high metabolic rate compared to cold-blooded creatures,” said the University of Bonn’s Sander.
Recently published studies involving comparisons between growth rates of hadrosaurs and tyrannosaurids also indicate that the plant-eating ornithopods also adopted a strategy of growing quickly to prevent being eaten. The hadrosaur studied was the lambeosaurine Hypacrosaurus, from Upper Cretaceous strata of North America.
To read more about hadrosaur growth rates: Duck-billed Dinosaurs grew up fast to avoid being eaten by Tyrannosaurs.