Wang and colleagues argue that the mechanisms that regulate beak growth also suppress tooth formation. In adult Sapeornis, there were teeth at the back of the jaw but not at the front of the jaw.Īs modern birds develop inside their eggs, the beak keratin begins to form at the tip of the snout and then grows back to cover both upper and lower jaws. The detailed internal scans of the fossils showed adult Limusaurus had no teeth but still had tooth sockets in their lower jaws, closed off and forming a single canal. Wang and colleagues observed that the theropod dinosaur Limusaurus, which was closely related to birds' ancestors, and the early bird Sapeornis had teeth right to the front of the jaws when they were young but lost them as they grew up.
#Late bird dinosaur series
The CT scans are a closely spaced series of X-rays that allow researchers to construct detailed 3-D models showing every fine detail within the bone. Nowadays, bones are rarely cut up, and it is much more common to use computed tomography (CT) scanning to look inside the bones without damaging them.
But fossil examples show that many toothed dinosaurs actually possessed a minimal beak at the front of the snout.Ĭaenagnathasia jawbone. We typically think of beaks as all-encompassing structures, extending from the pointed tip at the front back to the eyes, and including the nostrils in modern birds. Beaks are composed of keratin, the tough, flexible protein that also makes fingernails and cow horns, as well as feathers and hairs. Meanwhile, many dinosaurs actually did have beaks of some kind. This suggests their ancestors at some point grew teeth naturally. Developmental experiments in the 1980s showed that modern birds could probably generate teeth if their jaw tissue was artificially stimulated with the right molecules. Modern birds all lack teeth, except for the South American hoatzin, Opisthocomus, whose hatchlings have a small tooth that they use to help them escape from their egg and then shed. But other early birds had lost their teeth, such as Confuciusornis, also from the early Cretaceous. The oldest birds actually had reptilian-like teeth – for example Archaeopteryx from the late Jurassic period (150m years ago) and Sapeornis from the early Cretaceous (125m years ago). Over time, this process happened earlier and earlier until eventually the animals emerged from their eggs with a fully formed beak.
They found that some dinosaurs evolved to lose their teeth as they got older and sprouted a small beak.
In a new study, Shuo Wang from the Capital Normal University of Beijing and colleagues studied a series of dinosaur and early bird fossils to see the transition.
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