Paleontologists have found six specimens from three species of ornithuromorph birds — two of which are new to science — at the Changma locality in China’s Gansu province.
The Changma locality in northwestern China is an important place for paleontologists studying bird evolution.
It’s the second-richest Mesozoic fossil bird site in the world, but more than half of the fossils found there belong to Gansus yumenensis, a species of aquatic bird that lived approximately 120 million years ago (Early Cretaceous epoch).
“Gansus yumenensis is the first known true Mesozoic bird in the world, as Archaeopteryx is more dinosaur-like, and now we know what its skull looks like after about four decades,” said Dr. Hai-Lu You, a paleontologist with the Institute of Vertebrate Paleontology and Paleoanthropology and the Center for Excellence in Life and Paleoenvironment at the Chinese Academy of Sciences, and the University of Chinese Academy of Sciences.
Determining which fossils are Gansus yumenensis and which ones aren’t is tricky.
The new six specimens from the Changma site are primarily just skulls and necks, parts not preserved in known specimens of Gansus yumenensis.
The fossils were also somewhat smashed by their time deep in the Earth, which made analyzing them difficult.
“It was a long, painstaking process teasing out what these things were,” said Dr. Jingmai O’Connor, a paleontologist with the Negaunee Integrative Research Center at the Field Museum of Natural History, Chicago, the Institute of Vertebrate Paleontology and Paleoanthropology and the Center for Excellence in Life and Paleoenvironment at the Chinese Academy of Sciences.
“But these new specimens include two new species that increase our knowledge of Cretaceous bird faunas, and we found combinations of dental features that we’ve never seen in any other dinosaurs.”
“These fossils come from a site in China that has produced fossils of birds that are pretty darned close to modern birds, but all the bird fossils described thus far haven’t had skulls preserved with the bodies,” added Dr. Jerry Harris, a paleontologist in the Department of Earth and Environmental Sciences at Dixie State University.
“These new skull specimens help fill in that gap in our knowledge of the birds from this site and of bird evolution as a whole.”
“The Changma site is a special place. The fossil-bearing rocks there tend to split into thin sheets along ancient bedding planes,” said Dr. Matt Lamanna, a paleontologist at the Carnegie Museum of Natural History.
“So, when you’re digging, it’s like you’re literally turning back the pages of history, layer by layer uncovering animals and plants that haven’t seen the light of day in roughly 120 million years.”
The researchers found that four of the new specimens belong to Gansus yumenensis.
The two other specimens are considered new species: Meemannavis ductrix and Brevidentavis zhangi.
Like Gansus yumenensis, both Meemannavis ductrix and Brevidentavis zhangi are ornithuromorph birds — the group that contains modern birds.
Like today’s birds, Meemannavis ductrix was toothless.
Brevidentavis zhangi, on the other hand, had small, peg-like teeth packed close together in its mouth. Along with those teeth came another strange feature.
“Brevidentavis zhangi is an ornithuromorph bird with teeth, and in ornithuromorphs with teeth, there’s a little bone at the front of the jaw called the predentary, where its chin would be if birds had chins,” Dr. O’Connor said.
“At a time when giant dinosaurs still roamed the land, these birds were the products of evolution experimenting with different lifestyles in the water, in the air, and on land, and with different diets as we can see in some species having or lacking teeth,” said Dr. Tom Stidham, a paleontologist with the Institute of Vertebrate Paleontology and Paleoanthropology and the Center for Excellence in Life and Paleoenvironment at the Chinese Academy of Sciences, and the University of Chinese Academy of Sciences.
“Very few fossils of this geological age provide the level of anatomical detail that we can see in these ancient bird skulls.”
“These discoveries strengthen the hypothesis that the Changma locality is unusual in that it is dominated by ornithuromorph birds, which is uncommon in the Cretaceous,” Dr. O’Connor said.
“Learning about these relatives of modern birds can ultimately help us understand why today’s birds made it when the others didn’t.”
The findings appear in the Journal of Systematics and Evolution.
Jingmai K. O’Connor et al. Avian skulls represent a diverse ornithuromorph fauna from the Lower Cretaceous Xiagou Formation, Gansu Province, China. Journal of Systematics and Evolution, published online Decmeber 29, 2021; doi: 10.1111/jse.12823
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