Wyoming's Fossil Lake has revealed yet another astonishing find — one of the earliest known passerine birds.
Perching birds, or passerines, include species such as sparrows, finches, robins and crows. All told the birds with feet made for hanging onto limbs make up about 6,500 of the 10,000 bird species alive today.
That wasn't always the case. They were once rare, and scientists are still learning about their origins.
Fifty-two million years ago, in a period known as the Early Eocene, one of these then-rare birds was preserved in sediment in southwest Wyoming's Green River geologic formation.
"This is one of the earliest known perching birds," said Lance Grande, Field Museum Neguanee Distinguished Service Curator. "It's fascinating because passerines today make up most of all bird species, but they were extremely rare back then. This particular piece is just exquisite. It is a complete skeleton with the feathers still attached, which is extremely rare in the fossil record of birds."
Grande is one of the authors of a new paper published in "Current Biology" that describes two new fossil bird species — one from Germany that lived 47 million years ago, and the other that lived in what's now Wyoming.
The Wyoming bird, Eofringillirostrum boudreauxi, is the earliest example of a bird with a finch-like beak, similar to today's sparrows and finches. This legacy is reflected in its name; Eofringilllirostrum means "dawn finch beak." Meanwhile, boudreauxi is a nod to Terry and Gail Boudreaux, longtime supporters of science at the Field Museum.
The fossil birds' finch-like, thick beaks hint at their diet.
"These bills are particularly well-suited for consuming small, hard seeds," said Daniel Ksepka, the paper's lead author and curator at the Bruce Museum in Connecticut.
Anyone with a bird feeder knows that lots of birds are nuts for seeds, but seed-eating is a fairly recent biological phenomenon.
"The earliest birds probably ate insects and fish, some may have been eating small lizards," Grande said. "Until this discovery, we did not know much about the ecology of early passerines. E. boudreauxi gives us an important look at this."
"We were able to show that a comparable diversity of bill types already developed in the Eocene in very early ancestors of passerines," said co-author Gerald Mayr of the Senckenberg Research Institute in Frankfurt.
"The great distance between the two fossil sites implies that these birds were widespread during the Eocene, while the scarcity of known fossils suggests a rather low number of individuals," Ksepka added.
While passerine birds were rare 52 million years ago, E. boudreauxi had the good luck to live and die near Fossil Lake, a site famous for perfect fossilization conditions.
"Fossil Lake is a really graphic picture of an entire community locked in stone — it has everything from fishes and crocs to insects, pollen, reptiles, birds, and early mammals," Grande said. "We have spent so much time excavating this locality that we have a record of even the very rare things."
Grande noted that Fossil Lake provides a unique look at the ancient world — one of the most detailed pictures of life on Earth after the extinction of the dinosaurs (minus the birds) 65 million years ago.
"Knowing what happened in the past gives us a better understanding of the present and may help us figure out where we are going for the future," he said.
With that in mind, Grande plans to continue his exploration of the locale.
"I've been going to Fossil Lake every year for the last 35 years, and finding this bird is one of the reasons I keep going back," Grande said. "It's so rich. We keep finding things that no one's ever seen before."