Undeniably, one of the greatest evolutionary mysteries is the origin of birds. The earliest bird to first be discovered is Archaeopteryx. The 150 million year old fossil was discovered in 1861 in southern Germany, and it provided the first real clue. Archaeopteryx is clearly a primitive bird but did possess unique bird characteristics: reduced fingers, a wishbone, feathers and wings. However, Archaeopteryx also had teeth, three digits with claws, and a long bony tail, which are all traits characteristic of reptiles, not birds. Therefore, this important discovery was dubbed the "missing link" between birds and reptiles. Of course different people had different theories, a shared ancestry with dinosaurs being one of them, but it wasn’t until the late 1960s when paleontologists unearthed their next crucial clue. Paleontologist Dr. J.H. Ostrom compared Deinonychus, a small bipedal dinosaur belonging to the family of theropods, to Archaeopteryx and noted that both had hollow bones, long arms, similar hip and shoulder bones, and were lightly built. With this information he then concluded that birds evolved from theropods, the group of dinosaurs that includes T. rex and Velociraptor.
By the mid 1990s, more evidence started pouring in to support the evolutionary link between birds and dinosaurs. New dinosaur species all belonging to the theropod family, such as Sinosauropteryx, were discovered in China and, interestingly enough, all were covered in feathers! These fossils were also dated at 120 million years old, showing us that these bird-like theropods were living right alongside their Archaeopteryx relatives.
More evidence emerged showing the connection between theropods and modern day birds. For example, fossils show that theropods laid their eggs in the same way as birds and those eggs looked very similar to modern eggs. Also numerous fossilized theropods have been found in brooding poses, just like a chicken brooding over her eggs.
All the evidence scientists have and continue to discover further cements the theory that our modern day birds descend from the same lineage that includes the large, formidable T. rex and the agile pack hunters known as Velociraptor. So, according to this theory, dinosaurs haven’t really gone anywhere. They are still living and present in our backyards, hopping around underneath our cars, bathing themselves in puddles, and snatching other animals right off the ground.
Dinosaurs are still here. We just call them birds.