Take one look at a fossilized Archaeopteryx, and you’re bound to be confused. While its sharp teeth, long snout and lengthy tail look like those of a dinosaur, its feathered wings are reminiscent of a bird. The mix of traits is so strange that even paleontologists have struggled to classify the creature.
Having been described as both a birdish dinosaur and a dinosaur-like bird, Archaeopteryx, whose name translates to “old wing,” is best understood as one of many transitional forms that bridged the evolutionary divide between dinos and birds. And while Archaeopteryx wasn't alone in linking the two lineages, the bizarre beast will be forever famous for revealing the relationship between the dinosaurs and their modern-day descendants.
What Was Archaeopteryx?
Ask any paleontologist about avian origins, and they’ll tell you that today’s birds trace their ancestry to the dinosaurs and represent the only surviving segment of the dinosaur taxon. But it wasn’t until the discovery of Archaeopteryx in the 1860s that those origins were first brought to the surface.
In the simplest of terms, Archaeopteryx was a small, predatory animal that thrived around 150 million years ago. Splitting its time between the shrubbery and the open terrain, the creature inhabited the low-lying shores of salty lagoons and consumed a mostly arthropod diet. But the most amazing aspect of the animal was its strange mesh of dinosaurian and avian traits, indicative of its ties to the dinosaurs as well as the birds.
When Were Archaeopteryx Fossils First Found?
Over the years, paleontologists have found 12 Archaeopteryx fossils, all of which were taken from the sediment formations in and around Solnhofen, Germany. Around 150 million years ago, this area was covered with warm, shallow seas and was scattered with islands where sand slowly accumulated. In time, the sand turned to sediment, trapping the skeletons of ancient animals like Archaeopteryx and transforming them into fossils.
According to paleontologists, the conditions of Solnhofen were such that the 12 Archaeopteryx specimens show an amazing amount of detail. In fact, some are so finely preserved that they feature the imprints of individual feathers.
In 1861, paleontologists described the first fossil Archaeopteryx. That same year, they described the second and branded the specimen as the world’s oldest bird, based on its smattering of feathers. At the time, the ideas of evolution were everywhere. Darwin had just published his On The Origin of Species only a few years earlier, and it made sense to interpret the fossil as the first avian.
Over the years, however, the discovery of new fossils and the reanalysis of old ones have revealed such a strong mix of dinosaurian and avian anatomy that classifying the creature as a dinosaur or a bird has become increasingly difficult. Throughout the decades, as paleontologists gained a greater sense of Archaeopteryx's resemblance to both taxa, they began to believe that the dinosaurs and birds were related, with Archaeopteryx representing a strange, intermediary stage between the two.
Measuring around 20 inches from their snout to their tail, Archaeopteryx fossils indicate that the animal weighed anywhere from 1 to 2 pounds, making them a similar size to an adult raven, according to a PLOS ONE study.
Archaeopteryx shared several anatomical traits with the two-legged theropod dinosaurs, including their long torsos and long tails. They also had a smattering of small, sharp teeth, which were characteristic of theropods, and feathered wings, which were characteristic of birds. Making matters even more muddled, the fossils also bore three taloned fingers atop their wings, representing a unique mishmash of traits.
While some paleontologists now suspect that the 12 Archaeopteryx specimens represent two or more separate species, others say that the specimens belong to the same species, which paleontologists have dubbed A. lithographica. Whatever the number of species, however, the bizarre blend of characteristics make Archaeopteryx a clear candidate for a transitional creature — one that shares traits with both its ancestors and its descendants.
Equally as telling are the abilities of Archaeopteryx. The anatomy of the fossils suggests that the animal’s behavior was stuck somewhere between dino and bird. While specialists say that these strange creatures flew, for instance, the structure of their wings and the arrangement of their feathers imply that the animal wasn't prepared for long periods in the air.
In fact, a 2018 study published in Nature Communications proposed that the bones of Archaeopteryx resembled the bones of pheasants, which jump into the air with awkward jolts of flapping. In other words, while Archaeopteryx wasn't a full-fledged flier, their anatomy allowed for short spurts of flight, to avoid obstacles as well as predators.
The Oldest Bird?
The clues that Archaeopteryx was a transitional creature are built into their bones. But in recent decades, paleontologists have discovered several similar animals that solidify the idea of a slow transformation from dino to bird, with an assortment of strange, jumbled creatures representing distinct stages in the transformation.
Among these critters are Xiaotingia and Aurornis — animals with wings and feathers that some specialists say were as many as 10 to 15 million years older than Archaeopteryx. As a result of these discoveries, paleontologists are starting to see Archaeopteryx not as the world's oldest bird, but as a single member of a much greater group of primitive bird-like animals.
Archaeopteryx and the Evolution of Birds
Ultimately, Archaeopteryx fossils show only one of the various stages in the dinosaur-to-bird transition. Some specialists suspect that the animal was a sort of failed, "dead-end" experiment in that transformation, representing a similar but separate lineage than the lineage that ultimately gave rise to birds. But others insist on Archaeopteryx's importance in the path to bird-hood.
Either way, when considered in combination with finds like Xiaotingia and Aurornis, one thing about Archaeopteryx is incredibly clear: The creature is a testament to the slow, incremental pace of evolution, where the defining traits of the birds emerged bit by bit over the course of millions of years.
As dinosaurs developed the wishbones, breastbones and hollowed-out skeletons filled with air sacs that characterize birds today, they inched closer and closer to what we consider a true avian. In time, they evolved their feathers and wings, and built up their ability for full-fledged flight, taking the first flaps into true bird territory.