It’s weird to think that birds evolved from a group of carnivorous dinosaurs, but what if that really was the case? These dinosaurs are labeled as theropods, and one of the most famous examples of this subdivision is the Tyrannosaurus Rex. Like these carnivorous fiends, birds from 150 million years ago had mouths full of pointy teeth!
After the Great Extinction, which took place about 140 million years ago, these birds were finally able to begin developing their beaks. Over the next 66 million years, they branched into about 11,000 species and survived due to natural advantages like their small size, variety in food options, and ability to fly.
The transition from dinosaur to bird is also marked by a variety of transitional species, one such example being the Ichthyornis, which lived around modern-day Kansas when it was still underwater. This particular transitional species was discovered by a team of scientists led by a man named Bhart-Anjan Bhullar. They were able to produce a high-resolution CT scan of its skull using fossils from the surrounding rock. Overall, they were able to make several discoveries that connected it to both dinosaurs and modern-day birds.
Like birds today, the Ichthyornis had the ability to move its upper beak without impacting the skull, giving it precision in what it pecked. Birds commonly have a larger brain to body size ratio when compared to reptiles, and surprisingly, scientists found that the Ichthyornis also exhibited this advantageous trait. However, like dinosaurs, it still had a strong jaw that could be used to consume prey like fish and shellfish.
Charles Darwin cites the Ichthyornis as one of one of the best supports for his famous theory of evolution, recognizing both its strong jaw and flexible beak as adaptations that helped it to survive in a time when the only prey available were rough fish. Bhullar’s discovery even supported the fact that beaks may have appeared at around the same time as wings, meaning evolution is not an entirely straightforward path.
The loss of teeth in modern birds is commonly attributed to the length of time in incubation. Developing teeth can take up to 60% of the incubation period, and considering the threat that offspring face while they are in eggs, it is more logical to forgo forming teeth altogether. This is why modern bird eggs take only a few days or weeks to hatch while dinosaur eggs took multiple months. Tooth loss, leading to a much quicker incubation period, contributed to the survival rate by making it less likely for the offspring to get snatched from their mothers before they were fully developed.
Seeing as the fossil record is full of gaps, it is extremely difficult or maybe even impossible for scientists to trace the exact point in time when different characteristics like wings, teeth, and feathers were adapted. The environment played an important role in how the bird transitioned, from the available prey to the predators that coveted its eggs. It is only a matter of time before we find a new transitional species, closing even more of the gaps that are present in our current fossil record.