Primoptynx poliotauros: 55-Million-Year-Old Fossil of Large-Sized Owl Found in Wyoming

Saturday, August 1, 2020

The 55-million-year-old skeleton of Primoptynx poliotauros. Image credit: Senckenberg Research Institute / Tränkner.

A new genus and species of owl that lived 55 million years ago (Eocene epoch) has been identified from a partial skeleton found in Wyoming, the United States. The discovery is reported in a paper in the Journal of Vertebrate Paleontology.

Named Primoptynx poliotauros, the ancient owl species was about 60 cm (23.6 inches) tall.

It belongs to a group of owls closely related to the extinct family Protostrigidae.

“The fossil owl was about the size of a modern snowy owl (Bubo scandiacus). However, it is clearly distinguished from all extant species by the different size of its talons,” said lead author Dr. Gerald Mayr, an ornithologist in the Senckenberg Research Institute and Natural History Museum Frankfurt.

“While in present-day owls the talons on all toes are approximately the same size, Primoptynx poliotauros has noticeably enlarged talons on its hind toe and second toe.”

Dr. Mayr and colleagues hypothesize that Primoptynx poliotauros used its feet to dispatch prey items in a hawk-like manner, whereas living owls kill prey with their beak.

“Owls today have four toes with claws of equal size to catch relatively small preys and kill them with the beak,” said co-author Dr. Thierry Smith, a paleontologist at the Royal Belgian Institute of Natural Sciences.

Primoptynx poliotauros has a longer first and second toe, as seen in hawks and other members of the family Accipitridae.”

“Those more developed toes are used to pin down prey, which are punctured by the talons. So it was an owl that hunted like a hawk on medium-sized mammals.”

“The lifestyle of this extinct owl clearly differed from that of its modern relatives,” Dr. Mayr added.

The partial skeleton of Primoptynx poliotauros was found by U.S. paleontologists at Bighorn Basin in Wyoming about 30 years ago.

The fossil shows that during the Early Eocene there were already many species of owls, of different sizes, which occupied different ecological niches.

“The success of the owls runs parallel to that of the mammals, which became very diverse after the fifth mass extinction, which wiped out the dinosaurs,” the researchers said.

“The later extinction of Primoptynx poliotauros and other proto-owls may have been due to the emergence of daytime birds of prey in the Late Eocene.”

“It is not clear why owls changed their hunting technique in the course of their evolution,” Dr. Mayr said.

“However, we assume that it may be related to the spread of diurnal birds of prey in the Late Eocene and Early Oligocene, approximately 34 million years ago.”

“Competition for prey with diurnal birds of prey may have triggered feeding specializations in owls, possibly also leading to these charismatic birds’ nocturnal habits.”

The discovery of Primoptynx poliotauros also revealed a high level of diversity among the owls in the Early Eocene of North America: from the small species Eostrix gulottai, measuring a mere 12 cm (4.7 inches), to the newly-discovered large species.


Gerald Mayr et al. Skeleton of a new owl from the early Eocene of North America (Aves, Strigiformes) with an accipitrid-like foot morphology. Journal of Vertebrate Paleontology, published online July 28, 2020; doi: 10.1080/02724634.2020.1769116