Out of all the interesting features that birds have, their mobile beaks are one the most defining ones, being shared by more than 99% of all birds. The somewhat complex mechanism that enables a mobile beak is thought to have evolved beginning with the extinction of the dinosaurs (or at least the non-avian ones — all birds are dinosaurs).
However, an unsuspecting tiny fossil nestled inside a rock the size of a grapefruit just torpedoed this long-standing assumption that has been etched onto biology textbooks for nearly a century.
A mighty mobile bird jaw — with teeth!
According to researchers at the University of Cambridge and the Natuurhistorisch Museum Maastricht, mobile beaks actually first evolved before the mass extinction event that wiped out the dinosaurs 66 million years ago. Their proof? The CT scan of the fossilized palate, or the roof of the mouth, of a large ancient bird called Janavis finalidens.
This was one of the last toothed birds to ever flap its wings and was contemporary with dinosaurs. When the researchers closely analyzed the palate bones, they were shocked to find its beak was mobile and dexterous, exactly like that of modern birds.
Birds, old and new
There are nearly 11,000 bird species known to science that are still alive on Earth today. Based on the arrangement of their palate bones, birds can be split into only two groups. First, there’s the palaeognath, or ‘ancient jaw’ group, represented by birds like ostriches and emus, which have their palate bones fused together into a single solid mass (just like us humans, by the way). Then there’s the neognath, or the ‘modern jaw’ group, meaning their palate bones are connected by a mobile joint. The vast majority of birds belong to this latter group, making their beaks much more dexterous than the more ancestral birds, giving them an edge when it comes to grooming, nest-building, food-gathering, predation and defense, and just about anything that involves manipulating using their beaks.
This classification is literally as old as the theory of evolution. It was originally proposed by naturalist Thomas Huxley, also known as “Darwin’s Bulldog” for his staunch support of natural selection. Huxley first published a classification of birds into either “ancient” or “modern” jaw groups in 1867, arguing that the former configuration was the original condition for all birds, out of which the “modern” jaw evolved later.
“This assumption has been taken as a given ever since,” said Dr. Daniel Field from Cambridge’s Department of Earth Sciences, the new study’s senior author. “The main reason this assumption has lasted is that we haven’t had any well-preserved fossil bird palates from the period when modern birds originated.”
But then came Janavis. Its humble beginning was inconspicuous enough. The fossils were first unearthed from a limestone quarry close to the Belgian-Dutch border in the 1990s and sat in storage until they could be properly examined in the leary 2000s. The problem was that paleontologists couldn’t make much of it since it was almost completely encased in rock, with only some fragments of the skull and shoulder bone sticking out.
As such, Janavis’s fossils were set for a very unremarkable life as yet another museum item, to be locked and forgotten in some dark corner. Luckily, the fossils were given a fresh look some two decades later when they were loaned to Cambridge.
“Since this fossil was first described, we’ve started using CT scanning on fossils, which enables us to see through the rock and view the entire fossil,” said Juan Benito, now a postdoctoral researcher at Cambridge, and the paper’s lead author. “We had high hopes for this fossil—it was originally said to have skull material, which isn’t often preserved, but we couldn’t see anything that looked like it came from a skull in our CT scans, so we gave up and put the fossil aside.”
After this initial setback, the world outside the researchers’ lab shook: the COVID-19 pandemic was upon England and, by early 2020, across the rest of the world. With nothing better to do, Benito and Field gave the fossil yet another chance, partly because there were still some puzzling things about it.
“The earlier descriptions of the fossil just didn’t make sense—there was a bone I was really puzzled by. I couldn’t see how what was first described as a shoulder bone could actually be a shoulder bone,” Benito said.
Old after new
But then the researchers finally realized where they saw a similar bone before: inside a turkey skull. When the researchers brought out a turkey bone, which apparently can be found in ample amounts inside Cambridge biology labs, the two bones proved almost identical. In other words, the newly identified species Janavis had a “modern jaw”.
This blew everyone’s minds. It means “ancient jaw” birds like ostriches and their relatives actually evolved after, and not before, “modern jaw” birds.
However, this doesn’t mean that Janavis was exactly like a modern bird — not quite. While Janavis had a mobile jaw, it still had teeth, which is a feature of primitive, pre-mass extinction birds.
“Evolution doesn’t happen in a straight line,” said Field. “This fossil shows that the mobile beak—a condition we had always thought post-dated the origin of modern birds, actually evolved before modern birds existed. We’ve been completely backwards in our assumptions of how the modern bird skull evolved for well over a century.”
This discovery is about to rewrite our understanding of a key evolutionary feature now sported by virtually every modern bird alive today on Earth. And it’s all thanks to an unsuspecting fossil that few were interested in giving a second glance. There may be hundreds of thousands of other fossils like it scattered across museum collections.
As for Janavis, it sadly was wiped out with the rest of the dinosaurs. It was a rather large bird, about the size of a modern-day vulture, so it couldn’t adapt to a new calorie-deprived world in which only small birds and a group of lowly subordinate creatures, known as mammals, could survive.