Ever since the birdlike dinosaur Archaeopteryx was first discovered in 1861, paleontologists have tried to decipher the evolutionary origins of modern birds—the only surviving descendants of the dinosaurs.
Now, paleontologists based out of the Chinese Academy of Sciences (CAS) have reached a new milestone in this quest. The CAS team has discovered the oldest fossils from the Ornithuromorpha group of dinosaurs, the common ancestor of all modern bird species.
The two specimens date back 130 million years to the Early Cretaceous period, when pterosaurs still dominated the skies. They belong to a new species named Archaeornithura meemannae, a feathered wading bird that lived in what is now northeastern China. The CAS team, led by paleontologist Min Wang, published a detailed analysis of the new specimens today in Nature Communications.
"The new taxon […] constitutes the oldest record of the Ornithuromorpha," Wang and his colleagues wrote in the study.
Because the deep history of birds is so muddled and murky, a quick clarification is order up top. The new species is not the oldest evidence of birds full stop—that honor still goes to the 145-million-year-old Archaeopteryx, which still holds the hallowed title of "Urvogel," or "Original Bird."
However, as Wang told me over email, Archaeornithura meemannae has its own significance as the oldest known ancestor of all living birds. The lineage that included Archaeopteryx, in contrast, was snuffed out with the rest of the dinosaurs. Those forged in the Ornithuromorphid crucible, however, soldiered on to produce the entire spectacular diversity of birds alive today.
"The new specimen is discovered from the 130.7 million years ago deposits which represents the oldest record of Ornithuromorpha," Wang told me. "Previously, the earliest record is 125 million years ago. Therefore, the new finding pushed back the origination date of Ornithurmorpha by at least five million years."
So with this find, Wang and his co-authors have identified the oldest known relative of all extant avian species, and have conclusively proven that modern birds have evolutionary roots at least as far back as the Early Cretaceous.
What's more, the two specimens are unusually well preserved, featuring nearly completely intact feathered plumages. Mesozoic birds, like modern ones, tended to have light, fragile bones, so it is rare to find their remains at all, let alone with the kind of detail displayed by the Archaeornithura meemannae specimens.
Even the animal's alula, or "bastard wing," is exquisitely preserved. These small winglets are located on the anterior edge of many modern bird species, and function in much the same way as the leading-edge slats on an aircraft.
"The alula is a kind of feather attached to the first manual digit of birds, and it serves critical function in low speed flight and maneuverability," Wang told me. "[I]t is amazing to find such beautiful feathers in a bird lived 130.7 million years ago."
But though Wang and his colleagues lucked out with the plumage, they were not so fortunate with the preservation of the skulls. The lack of a well-preserved head makes it tricky to speculate about the diet and behavior of this early bird, but Wang thinks it was probably a seed-eating herbivore, based on its larger family tree.
"There is no direct evidence about its diet," he told me. But, he said, the new specimen is closely related to the Hongshanornithdae group of birds, and paleontologists have found gastroliths—stomach stones—from this group.
"In living birds, gastroliths are mainly used for grinding hard food items, like seeds, which may have suggested that Hongshanornithidae is a herbivore," Wang said, making it a likely bet that Archaeornithura meemannae was a veggiesaurus too. Without further evidence, however, it's impossible to be sure.
Along those lines, Wang hopes to shed more light on this mysterious bird ancestor through all possible channels, including computer modelling.
"Our future work is trying to incorporate statistical methods to estimate the divergence date of major Mesozoic avian groups and compare the evolutionary date in different groups," Wang told me.
"Currently, there are some theoretical methods about how to estimate the divergence date for fossils, and we are trying to use them to see how early the major Cretaceous avian groups appeared," he added.
With this discovery, Wang and his team have set a new evolutionary benchmark for the rise of the modern avian family. So while Archaeornithura meemannae may not have snagged Urvogel status, it has claimed an equally important title—the new grandpoppy of every bird alive today.