October 15, 2009
The discovery of new kinds of feathered dinosaurs regularly makes the news these days, but it is important to remember that modern vertebrate paleontology encompasses much more than the search for the origin of birds. Indeed, this week scientists described an equally-spectacular fossil that fills in an important gap in our understanding of ancient life. Dubbed Darwinopterus modularis, this creature from the Middle Jurassic (over 160 million years old) rock of China connects two groups of pterosaurs that have long been divided by a lack of fossil evidence.
Described by Junchang Lu, David Unwin, Xingsheng Jin, Yongqing Liu, and Qiang Ji in the Proceedings of the Royal Society B, Darwinopterus fits snugly between the two major groups of pterosaurs that flew in the sky while dinosaurs ran about on land. The early pterosaurs were characterized by having long tails, short necks, and a separate nasal opening in the skull (among other traits). The later group, called the pterodactyloids, had short tails, long necks, and nasal openings combined with another opening in the skull in front of the eye (technically called the antorbital fenestra). From these forms paleontologists have long predicted that there were creatures of intermediate form between the two groups, and they finally have a good example of such a creature in Darwinopterus.
To put it simply, Darwinopterus possessed a mix of traits from both the earlier and later groups. Its body was like that of the early pterosaurs, including a long tail, but its head was more similar to the pterodactyloids. It had a long snout bearing an array of spiky teeth and had the single nasal/antorbital fenestra opening. Had only the head been found it would have probably been grouped with the pterodactyloids, and had only the body been found the scientists would have said that it was closely related to early pterosaurs, but all together Darwinopterus is an evolutionary mosaic that bears characteristics of both groups.
This means that pterosaurs like Darwinopterus were not evolving as a whole towards any kind of evolutionary goal, a common misconception about how evolution works. Instead different parts of the body were modified to greater or lesser degrees during the evolution of the group, thus why you see a “new” head on an “old” body type. Darwinopterus was not the ancestor of all later pterodactyloids—that is something that we cannot know right now—but its body helps us understand the type of animal the later pterosaurs evolved from. This is why we call it a “transitional form” rather than “ancestor” or “missing link:” it exhibits characteristics that help us understand how a particular group of organisms evolved even if we cannot identify direct ancestors or descendants.
Such a nuanced understanding is missing in most of the popular accounts of Darwinopterus that were published yesterday, and one of the worst offenders was the U.K.’s Daily Mail. “The terrifying flying dinosaur that could unlock the mystery of human evolution” squealed the headline, and it only gets worse from there. The piece states that Darwinopterus could explain why humans evolved so quickly after the last ice age, claiming that the new fossil
… dispels Darwin’s theory that small body parts such as a finger nail or tooth change[d] gradually and could explain how humans developed so quickly from mammals.
There is so much that is wrong here that it is difficult to know where to start. First, Darwinopterus was not a dinosaur. It was a pterosaur, a distinct group of flying reptiles nested within the Archosauria, or the evolutionary group that also contains dinosaurs and crocodiles. Second, the authors say nothing about recent human evolution in the paper. That is entirely the invention of the anonymous writer of the piece.
Furthermore, the new discovery does not do anything to “dispel” Darwin’s theory of evolution by natural selection. If anything, it gives Darwin’s conception of evolution increased influence. The scientists behind the paper consider that the body of Darwinopterus, like other vertebrates, was made up of modules (i.e. skull, neck, back). The form of these parts are regulated by genes that become active during the development of the organism, and slight changes in these regulatory genes could precipitate changes in the body “modules” and thus provide more variation for natural selection to act upon. Also, when we’re talking about evolution, “gradual” means step-by-step, not “slow,” and Darwin knew that rates of evolutionary change differ.
Media misrepresentations aside, Darwinopterus is a wonderful fossil. Not only is it a beautiful transitional fossil represented by multiple specimens, but it provides some key insights into how evolution works. Even better, the discovery of Darwinopterus suggests that there are other transitional pterosaurs out there waiting to be found.
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