The Navaornis fossil represents an astonishing blend of ancient and modern traits. Paleontologists have discovered a remarkably well-preserved enantiornithine bird, Navaornis, from the late Cretaceous period. This discovery is reshaping some of our understanding of avian evolution by filling in previously unknown gaps.
This ancient bird species was about the size of a starling, with a skull measuring about two centimeters. It lived approximately 85–75 million years ago (late Santonian to early Campanian age) and belonged to the Enantiornithes, an interesting group of birds that diverged from modern birds over 130 million years ago. They flourished during the Mesozoic Era but became extinct along with the dinosaurs.
Despite its ancient origin, the Navaornis skull exhibits a range of modern features, providing insights into the evolution of the skull and brain in modern birds.
Discovery
The Navaornis fossil emerged from William’s Quarry, Adamantina Formation, in São Paulo State, southeastern Brazil. The layer containing the fossil is renowned for its preservation of three-dimensional bird fossils. The Navaornis skull is exceptionally well-preserved, making it the best specimen of its kind from that era, unlike many other Mesozoic fossils that often flatten and distort.
In 2016, researchers discovered a complete Navaornis skull and postcranial skeleton. They published a description of the find in 2024. Additionally, a single basicranium found in 2022 also belongs to the Navaornis species (Chiappe, 2022).
The genus name honors William Nava, the historian and director of the Marília Paleontological Museum who discovered the site. The species name, Navaornis hestiae, pays tribute to the Greek Olympian goddess Hestia, symbolizing her duality: both ancient and unexpectedly modern.
A Unique Blend of Ancient and Modern Traits
The Navaornis fossil skull is toothless, with large eyes and a domed skull—a shape very reminiscent of modern birds. However, it retains many primitive features, such as a fixed palate, a reptilian-like skull structure, and a relatively small cerebellum (the part of the brain responsible for movement and balance). Therefore, the complex mechanisms of flight control were not as refined as in modern birds.
These features indicate that, although Navaornis shared similarities with modern birds, it was not yet fully developed compared to their advanced brain and skull configuration.
Notably, Navaornis had a very flexible brain and a well-developed bony labyrinth, structures that control balance and coordination in flying animals. These traits bring it closer to modern birds than to its Mesozoic relatives. Unsurprisingly, its brain was larger than that of Archaeopteryx. Accordingly, its cognitive abilities were more advanced than those of the earliest bird-like dinosaurs.
The Importance of the Navaornis Fossil
Scientists are investing significant effort into understanding how the brains and skulls of modern birds evolved. However, Mesozoic fossils often lack the three-dimensional preservation necessary for detailed study of these structures. The Navaornis fossil, however, provides an opportunity to carefully examine some elements of this critical period of evolution.
This demonstrates that some “modern” features, such as brain shape and skull geometry, began to appear even before the ancestors of modern birds had fully developed some of their other advanced characteristics.
Moreover, the Navaornis fossil shows that evolution does not always proceed in a straight line.
The combination of primitive and modern traits in this species suggests that different elements of the bird’s anatomy evolved at different rates. This process is known as modular evolution. For example, the Navaornis had a relatively advanced brain structure, while its skull retained many primitive features.
A Closer Look at the Skull and Brain
A combination of features: a primitive diapsid skull (with two temporal openings, like reptiles), a fixed palate, but a toothless beak, and a large domed skull, like many modern birds.
The Navaornis brain was heart-shaped and more flexible than that of earlier bird-like dinosaurs such as Archaeopteryx. The optic lobes, responsible for vision, were located farther back in the skull. This is a hallmark of modern birds. However, its cerebellum was still less developed, indicating that some advanced brain features in birds developed later.
Ecological Insights
The quarry where the Navaornis fossil was found contained remains of both toothed and toothless enantiornithines. This suggests that these birds played different ecological roles in their habitat. The toothless beak of Navaornis clearly provided it with feeding strategies distinct from its toothed relatives. As we can see, ancient bird species were highly adaptable and diverse.
What does the Navaornis fossil tell us about the evolution of birds?
The discovery of the Navaornis fossil reveals that the evolution of birds was a complex process. The combination of advanced and primitive features supports the idea that this process was largely mosaic rather than linear. Under the influence of the environment and ecological opportunities, different characteristics evolved at different rates.
By filling in part of a critical gap in the fossil record, Navaornis provides a clearer picture of how modern birds acquired their unique skull and brain structures.
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