Coping with Heat – How Some Dinosaurs Stayed Cool
As temperatures soar in the United Kingdom and the southern part of the country endures temperatures in excess of 30 degrees Celsius, lots of media space is dedicated to the subject of how to keep cool in what looks like to be the hottest days of our all to brief British Summer. Although, the weather has certainly been hot in places like central London, when the temperatures recorded at midday in Britain are compared with other places in the world where we have been, (Kenya, Canada, USA), for example, the hot UK weather is put more into context.
For some dinosaurs, keeping cool may have presented them with some serious difficulties to overcome. Whilst horses in a field will often seek out the shade and shelter of a tree during the hottest part of the day, a Brachiosaurus for example, may not be fortunate enough to find a tree canopy big enough, or indeed tall enough to stand under. A typical brachiosaurid, such as Sauroposeidon, Brachiosaurus or Camarasaurus would have held their heads many metres above the ground. In the case of Sauroposeidon, from the fossil evidence gathered to date, it has been estimated that this creature could have raised its head to over 20 metres above the ground. Wandering around in the mid-day Early Cretaceous sun, it is surprising that the brains of these animals did not cook inside the skulls. These dinosaurs and indeed many other families of dinosaurs must have had ways in which they could modify and maintain a constant body temperature.
An Illustration of a Typical Brachiosaur
Picture Credit: Everything Dinosaur
Having a stable, almost constant body temperature is important in vertebrates, whether they are endothermic or ectothermic (warm-blooded or cold-blooded). A stable internal body temperature will allow the animal’s chemical processes to work efficiently and constantly. Chemical reactions in the body are controlled by enzymes and these are very temperature sensitive. Birds and mammals maintain stable internal temperatures and it is believed that dinosaurs did too. The trouble for a huge herbivore like a brachiosaurid is that it would have generated a lot of heat irrespective of the weather. For starters, these animals had huge guts, basically a series of fermentation chambers. The fermentation of digested and digesting remains of plants would have produced a lot of heat. Secondly, just moving around, an animal as big as a brachiosaur would have generated a lot of heat in its huge leg muscles and this would have to be dissipated somehow.
With such a large surface area to volume, a brachiosaur may have struggled to cool down, but just like many large animals that live in hot climates today, these dinosaurs had survival strategies for coping with heat. Some of these strategies would involve anatomical changes in their bodies to help regulate body heat, other strategies would be related to the way these animals behaved.
African elephants for example, have evolved large ears, these act as radiators, permitting blood to be circulated close to the surface of the skin and subsequently cooled. Some scientists have speculated that the long, cylindrical neck and tail of a brachiosaurid would have made effective radiating surfaces, particularly if blood could be selectively channelled under the skin, as it can be in some extant reptiles. This could be an example of an anatomical adaptation with regards to thermal regulation.
Brachiosaurs may have sought relief from the harshest part of the dry season by migrating to cooler, higher regions perhaps. They may have wadded in lakes in order to cool down, an adult Brachiosaurus would certainly have nothing to fear from the crocodiles and other lake predators.
To keep the head cool, after all, it was perched high up in the full glare of the sun, brachiosaurids may have had another trick up their sleeve, or to be more precise up their noses. Brachiosaurids are classified as Macronaria (big noses), they have a distinctive, box-like head shape with the holes in the skull representing the nostrils far bigger than the holes in the head for the eyes (orbits). Could a brachiosaur keep a cool head by allowing blood to circulate in special channels close to the skin in these large, moist nostrils?
These big, moist, nasal cavities would have cooled the air that the animal breathed in and if blood was channelled into special tissues close to the internal surface of the nostril, this may have proved to be an effective cooling device. The process would be similar to the ears of an elephant, which can act as a radiator to cool the blood. By flapping its ears an elephant creates airflow which can accelerate this process. Perhaps a brachiosaur could have cooled its small brain simply by breathing in and out in a regimented manner, permitting a greater airflow over the moist membranes and thus increasing the speed of the cooling. A head at 20 metres off the ground is generally moving through cooler air than the body, this difference in temperature between the head and the top of the neck compared to the bulky body, may also have had a role to play in helping to regulate temperature.
When a hot period of weather breaks, there is often a thunderstorm. If you are 20 metres tall you could have been the highest thing around on the Late Jurassic or Early Cretaceous plains. This could be dangerous especially if there was any forked lightning around. Perhaps big brachiosaurids were occasionally struck by lightning.
To read about a newly discovered genus of early sauropod that may have had a trouble keeping warm, as it lived in Antarctica (Glacialisaurus): A long-necked dinosaur from the Antarctic.