Dinosaur books have become more colourful affairs of late, with the dull greens, browns and greys of yesteryear replaced by vivid hues, stripes and patterns. This has largely been a question of artistic licence. While fossils may constrain an artist’s hand in terms of size and shape, they haven’t provided any information about colour. But that is starting to change.
The fossils of some small meat-eating dinosaurs were covered in filaments that are widely thought to be the precursors of feathers. And among these filaments, a team of Chinese and British scientists have found the distinctive signs of melanosomes, small structures that are partly responsible for the colours of modern bird feathers.
Melanosomes are packed with melanins, pigments that range from drab blacks and greys to reddish-brown and yellow hues. Their presence in dinosaur filaments has allowed Fucheng Zhang to start piecing together the colours of these animals, millions of years after their extinction. For example, Zhang thinks that the small predator Sinosauropteryx had “chestnut to reddish-brown” stripes running down its tail and probably a similarly coloured crest down its back. Meanwhile, the early bird Confuciusornis had a variety of black, grey, red and brown hues, even within a single feather.
Zhang’s discovery also launches another salvo into a debate over the very nature of “feathered” dinosaurs. Beautiful fossils, mainly from China, show that several species of dinosaur had feathers akin to the flight-capable plumes of modern birds. Species like Caudipteryx and the four-winged Microraptor had true feathers with asymmetric vanes arranged around a central shaft.
It’s a dinosaur tooth, and clearly one that belonged to a predator – sharp and backwards-pointing. But this particularly tooth, belonging to a small raptor called Sinornithosaurus, has a special feature that’s courting a lot controversy. It has a thin groove running down its length, from the root to the very tip. According to a new paper from Enpu Gong of the Chinese Academy of Sciences, it was a channel for venom.
Thanks to a certain film that shall remain nameless, a lot of people probably think that we already know that some dinosaurs are venomous. But the idea that Dilophosaurus was armed with poison, much less spat its toxins at its prey, is non-existent. Some scientists had speculated that they were venomous based on their bizarrely notched and allegedly weak jaws. But these notches have since been found in many other species and no one has ever actually measured the strength of Dilophosaurus‘s jaws.
The best sign that a dinosaur was venomous would be the presence of grooved or hollow teeth. With some notable exceptions, most animals with poison bites use grooves like these to channel their toxins from glands in their mouth to whatever they bite. And grooves are exactly what Gong and his colleagues found in Sinornithosaurus‘s well-preserved skull. Bryan Fry, who discovered venom glands in Komodo dragons earlier this year, says, “It is an absolutely fantastic piece of work. I actually got goose-bumps reading it! Other studies have suggested dinosaurs may be venomous but this is the most solid piece of evidence.”
Sinornithosaurus (meaning “Chinese bird-lizard”) is a small feathered dromaeosaurid (or, more commonly, ‘raptor’) and an early distant cousin of the birds. Its teeth are unusually large and Gong says that those in the upper jaw are “so long and fang-like that the animal appears to be saber-toothed”. They’re very similar to the fangs of back-fanged snakes like boomslangs and vine snakes.
Gong says that other aspects of the skull in support of his venom hypothesis. His team noticed that Sinornithosaurus has a small hollow on the side of its jawbone that could have housed a venom gland. They also found a thin groove running along the animal’s jaw, with small pits at the top of each tooth. They interpret this canal as a “collecting duct” that channelled venom from the gland to the teeth, and each pit could have acted as small, local venom reservoirs. David Burnham, a co-author on the paper, says, “Other fossil animals (dinosaurs, lizards, mammals) have been suggested to be venomous simply on the presence grooved teeth but out work found multiple lines of evidence.”