New clues to perching evolution

Researchers have discovered one of the earliest known passerines, or perching birds, dating from 52 million years ago in the Early Eocene period.

In fact, the US and German team describes two such fossil finds in a paper published in the journal Current Biology. The second, unearthed in Germany, is a relatively spritely 47 million years old.

This is particularly significant given that, as the authors note, until now “our understanding of early passerine evolution has been hindered by their sparse fossil record”.

The old guy, Eofringillirostrum boudreauxi, was found in what is now the US state of Wyoming and is the earliest example of a bird with a finch-like beak, similar to today’s sparrows and finches.  

This is reflected in its name: Eofringilllirostrum means “dawn finch beak”. 

“This is one of the earliest known perching birds,” says co-author Lance Grande, from the Field Museum in Chicago, US.

“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.”

The German fossil, which was not quite so well preserved, was named Eofringillirostrum parvulum. 

Both birds had finch-like, thick beaks, which hints at their diet, says lead author Daniel Ksepka from the Bruce Museum in Connecticut, US. 

“These bills are particularly well-suited for consuming small, hard seeds,” he says. “Anyone with a birdfeeder knows that lots of birds are nuts for seeds, but seed-eating is a fairly recent biological phenomenon.” 

Grande notes that until now scientists did not know much about the ecology of early passerines. “E. boudreauxi gives us an important look at this,” he says.  

Gerald Mayr, from the Senckenberg Research Institute in Germany, says the team was able to show that a comparable diversity of bill types had developed in the Eocene in very early ancestors of passerines.

Passerines, which also include crows, robins and sparrows, make up about 6500 of the 10,000 species of bird alive today.