Last updated May 23, 2018 at 11:09 am
Birds gained an evolutionary advantage over their dinosaur ancestors by skipping tooth development altogether
Why do birds have beaks? Fewer teeth makes for a lighter body, which could have helped in the evolution of flight. But there were birds flying around with some impressive gnashers, so that can’t be the only reason.
Beaks also make for stronger skulls. Beaks that come in a huge range of shapes and sizes certainly help birds adapt to a wide range of habitats and food sources. But recent research suggests that beaks might just be a by-product of the pressure to grow up as quickly as possible.
In an embryo, a developing tooth will grow as new layers of dentin are laid down daily. Like the rings of a tree, the number of these lines (called von Ebner lines) can tell you how long it takes for an embryo to develop.
Ingenious paleontologists with access to dinsoaur fossils from different stages of development figured out that counting these lines is pretty much the only way we have of knowing how long dinosaur incubation times took.
A 2017 study analysed fossils from Protoceratops embryos from Mongolia and Hypacrosaurus embryos from Canada and found that these dinosaurs would have had long incubation times, in the range of three to six months, much like modern reptiles. Modern birds have much shorter incubation times.
Beaks rather than teeth mean shorter egg incubation times
Tzu-Ruei Yang and P. Martin Sander suggest this week in a paper published in Royal Society Biology Letters that this trade off between tooth development and incubation time was a critical driving factor of beak development.
If you’re an animal that lays eggs, the faster they can incubate the less likely they’re going to be eaten by predators, get diseases or be lost to natural disasters.
So there’s an evolutionary advantage to quicker incubation times. The authors suggest that the rate of tooth formation, limited by the rate at which new layers of dentin can be formed, was the main factor holding back quicker incubation times in toothed dinosaurs.
Skipping tooth development altogether allowed birds to reap all the advantages of shorter incubation periods.