Scientist describe two fossil bird species from 50-million-year-old fossil sites in Germany and North America. These specimens are equipped with finch- like bills and represent the oldest seed-eating birds known to date. The study will be published today in the scientific journal “Current Biology.”
With more than 6,000 species, passerines, or perching birds, are the most species-rich order among modern birds – and their success is partly due to their wide variety of bill designs. The differently shaped beaks allow smaller birds to pursue a broad spectrum of feeding strategies, such as foraging for hard seeds and grains, hunting for insects, or feeding on soft fruit and the nectar of flowers.
The fossil of Eofringillirostrum boudreauxi, the newly described species from the North American
Green River Formation.
Green River Formation.
Photo: Lance Grande
“Based on two avian fossils – one from the Messel Pit in Germany, and another from the Green River Formation, a North American site of approximately the same age – we were able to show that a comparable diversity of bill types already developed in the Eocene in very early ancestors of passerines,” explains Dr. Gerald Mayr of the Senckenberg Research Institute in Frankfurt, and he continues: “The two new species belong to an extinct group of birds whose members are among the oldest known relatives of passerines.”
The fossil skeletons of the two new bird species, described as Eofringillirostrum boudreauxi and Eofringillirostrum parvulum, both possess finch-like bills reminiscent of the modern-day American Goldfinch. “These bills are particularly well-suited for consuming small, hard seeds,” says Dr. Daniel T. Ksepka, the study’s lead author and curator at the Bruce Museum in Greenwich, USA.
Until now, birds with finch-like beaks were only known from the more recent geological past – the two approximately 50-million- year-old fossils therefore represent the oldest seed-eating birds known to date.
Detail of the finch-like bill of Eofringillirostrum boudreauxi.
Photo: Daniel Ksepka.
“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,” according to Ksepka.
The question remains why these Eocene archaic relatives of passerines became extinct despite their adaption to a diverse range of food supplies, only to be replaced in the same ecological niches by true passerines. According to the team of researchers, one possible explanation can be found in breeding biology of passerines’, which build complex nest constructions that facilitate nesting in tree branches and shrubs.
The fossil of Eofringillirostrum parvulum, the new species from Messel.
“Unlike modern passerines, the Eocene birds may still have nested in tree cavities. A difference in breeding behavior could possibly be indicated by the different morphology of the fossil feet of the fossil species, whichhad a grasping foot with two toes pointing backward. A similar foot anatomy is found in certain extant bird groups that nest in cavities, such as woodpeckers or parrots,” explains Mayr.
Dr. Lance Gande, the study’s co-author from the Field Museum of Natural History in Chicago, adds: “We hope to discover additional fossils like these that shed more light on the as yet very poorly understood early evolution of passerines.”
Contacts and sources:
Dr. Gerald Mayr / Judith Jördens
Senckenberg Research Institute and Nature Museum in Frankfurt
Citation: Oldest finch- beaked birds reveal parallel ecological radiations in the earliest evolution of passerines Daniel T. Ksepka, Lance Grande, Gerald Mayr (2019) Current Biology.