Archaeopteryx: The First Bird?

Archaeopteryx reflects one of the most interesting evolutionary stories in the age of dinosaurs. It is also known from one of the most famous and well-known fossils ever discovered. Although scientists doubt the once accepted conclusion that archaeopteryx was the first bird on Earth, the evidence for it being a missing link between dinosaurs and modern birds is still strong.

Archaeopteryx lived during the Jurassic Period, around 150 million years ago. It was small (about the size of a chicken) and possessed a number of characteristics in its fossil record to suggest that it had something in common with modern birds. The first glaring feature of archaeopteryx fossils are the imprints of feathers in the mineral deposit. Before its discovery, the scientific community thought dinosaurs had pebbled, reptilian skin that was devoid of feathers. However, archaeopteryx changed the equation. Feathers were never before seen this early in the fossil record. If this small dinosaur-like animal possessed feathers, could other dinosaurs possess them too? Archaeopteryx also had a wishbone, a specialized bone found in birds today, as well as a partially reversed first toe (used by birds to help perch today).

Archaeopteryx was not a true bird as we know them today. First, its mouth was lined with sharp, needle-like teeth, a trait seen in dinosaurs and pterosaurs but not modern birds. Furthermore, the wingtips of archaeopteryx contained hooked fingertips, which reveals that its wings were evolved from forelimbs of a small, dinosaur-like animal. Modern birds have evolved this finger entirely into their wings, but archaeopteryx still possessed it. Furthermore, the animal possessed a bony tail and three-toed talons. These features are consistent with small therapod dinosaurs, which suggests that this small proto-bird was actually descended from carnivorous dinosaurs with the same body plan as deinonychus and troodon. In addition, the bones of archaeopteryx were not hollow, but contained proto-air sacs that are found in birds. In this respect, their bones were more similar to reptile birds than bird bones.

Archaeopteryx probably evolved its wings in order to better cope with catching its prey which mostly consisted of insects or small animals. Its flight might have begun with running and jumping, and evolutionary mutations would have been responsible for the beginning of feathers to aid in this predation. It is unclear whether the animal was a glider or actually capable of wing-flapping flight.

Classifying archaeopteryx has been problematic, but there is a general consensus that it was somewhere between dinosaur and bird. In any case, it remains one of the most potent pieces of evidence for Darwinian evolution.