When dinosaurs ruled the land, other groups of prehistoric reptiles dominated the waters. Their bones have also fossilised and they reveal much about how these ‘sea dragons’ lived. They tell us about the shape of their bodies, the things they ate and even how they determined their sex. And according to Aurélien Bernard from the University of Lyon, they can tell us whether these reptiles could control their body temperature.
The majority of reptiles are ‘cold-blooded’. Unlike mammals and birds, they can’t generate and retain their own heat, and their body temperature depends on their surroundings. But Bernard thinks that at three groups of marine reptiles – the dolphin-shaped ichthyosaurs, the crocodile-shaped mosasaurs, and the the paddle-flippered plesiosaurs – bucked this trend. Whether in tropical or cold waters, they could maintain a constant body temperature that reached as high as 35-39 degrees Celsius.
Relative to its body size, the huge beak of the toco toucan is the largest of any bird. It allows the toucan to eat both fruit and small animals, and display to both mates and rivals. Darwin himself speculated that it acts as a billboard, shaped by sexual selection to display bright colours that could be attractive to potential mates. But the toucan’s bill has another function that has only been discovered. Like the ears of an elephant, the toucan’s bill is a radiator.
It certainly has all the characteristics of a biological radiator. It’s big and has a surface area that’s 25-40 times larger than normal for a bird of its size; in fact, the bill accounts for 30-50% of the bird’s total surface area. It also lacks any insulating layer of fat, feathers or fur, and beneath its horny exterior, lies a rich network of blood vessels.
These vessels are the means through which the toucan exchanges heat. When it’s warm, it widens the vessels and allows the heat of its blood to radiate into the atmosphere. When it’s too cold, it limits the loss of heat by shutting down the blood flow to its bill.
Rising temperatures and high carbon dioxide emissions are the means through which humans are inadvertently causing the decline of several species. But one animal actively uses both heat and carbon dioxide as murderous weapons – the unassuming honeybee.
With their stings and numbers, bees already seem to be well-defended but they are completely outgunned by giant hornets (right). These two-inch long monsters are three times longer than several times heavier than tiny honeybees and raiding parties can decimate entire hives. European bees mount little in the way of an effective defence, but Japanese bees aren’t so helpless. When their hives are invaded, they launch a mass counterattack.
Swarms of workers dogpile the hornet, pinning it down while vibrating their wing muscles. At the centre of this “heatball”, the frenetic buzzing heats up the hornet to a roasting 45 degrees Celsius.
Scientists have long thought that this manoeuvre bakes the hornet alive, for the bees that surround it are more resistant to high temperatures. But Michio Sugahara and Fumio Sakamoto from Kyoto Gakuen University have found that this isn’t the whole story.
For humans, sex is a simple matter of chromosomes: two Xs and we become female; one X and a Y and we develop into males. But things aren’t so straightforward for many lizards – many studies have found that the temperature of the nest also has a say, even overriding the influence of the chromosomes. But the full story of how the lizard got its sex is even more complicated. For at least one species, the size of its egg also plays a role, with larger eggs producing females, and smaller ones yielding males.
The discovery comes from Richard Shine’s group at the University of Sydney. In earlier work, they showed that if the Eastern three-lined skink (Bassiana duperreyi) incubates its eggs at low nest temperatures, XX carriers develop into males regardless of their chromosomes.
Now, Rajkumar Radder, a former member of Shine’s team, has shown that the amount of yolk also determines the sex of a skink, but only at low temperatures. By deliberately adding and removing yolk from eggs using a syringe, he managed to alter the sex of the hatchlings. This degree of complexity is totally unprecedented – it means that for the skink, sex is a question of its chromosomes, the temperature it was reared under and the amount of yolk it had.