Nav: Home

Most complete enantiornithine bird fossil from North America

November 13, 2018

A 75-million-year-old bird skeleton from a threatened national monument in Utah represents the most complete skeleton ever found in North America for a long-extinct group of birds called enantiornithines. This large, fossilized bird provides important new insight into the evolution of flight. It has several advanced adaptations for flying, which show that the Enantiornithes evolved these features separately from living birds.

Enantiornithine birds ("opposite birds") were a group that existed during the Cretaceous. They were super successful -- so far scientists have found enantiornithine fossils from every continent except Antarctica, and they are known from rocks as old as 130 million years right up to the end of the Cretaceous 65 million years ago. In many ways, they looked quite similar to modern birds and are in fact closely related. They were fully-feathered and flew by flapping their wings like modern birds.

In North America, the enantiornithine fossil record is restricted to the Late Cretaceous - about 100-65 million years ago. Nearly all of these fossils are single bones from the feet, so we don't know what most of these birds looked like. In our new paper published in peer-reviewed journal PeerJ - the Journal of Life & Environmental Sciences, we describe a very special enantiornithine fossil from the Kaiparowits Formation in Utah (~75 million years old), which we named Mirarce eatoni (Meer-ark-ee).

Mirarce pays homage to the incredible, detailed, three-dimensional preservation of the fossil ("mirus" = "wonderful" in Latin), and anatomical evidence that it was an advanced flyer (Arce was the winged messenger of the Titans in Greek mythology). The species name honors Dr. Jeffrey Eaton for his decades of work as a paleontologist on fossils from the Kaiparowits Formation.

Mirarce is unique and important for several reasons. First, it is by far the most complete enantiornithine bird fossil ever discovered in North America. We have bones from almost all regions of the skeleton, except the skull. Additionally, it is also one of the largest birds known from North America from the entire Age of Dinosaurs.

Most Cretaceous birds were the size of chickadees or crows, but Mirarce was significantly bigger, about the size of a turkey vulture or great-horned owl. This fossil also is critical to helping us understand trends in enantiornithine evolution, and bird evolution in general. Though they superficially look like modern birds, enantiornithines have many anatomical differences. Most enantiornithines had a sternum (breast-bone) with a low keel and a wide wishbone. Though they could fly, they weren't as well-adapted for flight as modern birds.

Mirarce, however, shows us that by the Late Cretaceous opposite birds had separately evolved adaptations for advanced flight, similar to what we see in modern birds. The wishbone is narrower, and the sternum has a deeper keel for bigger flight muscles. What is most exciting, however, are large patches on the forearm bones. These rough patches are quill knobs, and in modern birds they anchor the wing feathers to the skeleton to help strengthen them for active flight. This is the first discovery of quill knobs in any enantiornithine bird. Thus, we know that Mirarce was a very strong flier.

This important fossil was found in Grand Staircase Escalante National Monument in Utah, a monument currently under threat of severe size reduction by the national government. Originally discovered in the early 1990s, this find (among many others) contributed to the original establishment of the monument in 1996. Mirarce is one of thousands of fossils discovered from Grand Staircase, and the rocks of the Kaiparowits Formation contain one of the best Cretaceous fossil records in the entire world, underscoring the critical importance of protecting and preserving these parts of our natural heritage. Reducing the size of the protected area puts some of our nation's most valuable natural and scientific resources at risk.

PeerJ is an Open Access publisher of two peer-reviewed journals and a preprint server. PeerJ's mission is to help the world efficiently publish its knowledge. All works published by PeerJ are Open Access and published using a Creative Commons license (CC-BY 4.0). PeerJ is based in San Diego, CA and the UK and can be accessed at

PeerJ is the peer-reviewed journal for Biology, Medicine and Environmental Sciences. PeerJ has recently added 15 areas in environmental science subject areas, including Natural Resource Management, Climate Change Biology, and Environmental Impacts.

PeerJ has an Editorial Board of over 1,900 respected academics, including 5 Nobel Laureates. PeerJ was the recipient of the 2013 ALPSP Award for Publishing Innovation. PeerJ Media Resources (including logos) can be found at:

Media Contacts

For the authors: Dr. Jessie Atterholt -

For PeerJ: email: ,

Note: If you would like to join the PeerJ Press Release list, please register at:


Related Evolution Articles:

Artificial evolution of an industry
A research team has taken a deep dive into the newly emerging domain of 'forward-looking' business strategies that show firms have far more ability to actively influence the future of their markets than once thought.
Paleontology: Experiments in evolution
A new find from Patagonia sheds light on the evolution of large predatory dinosaurs.
A window into evolution
The C4 cycle supercharges photosynthesis and evolved independently more than 62 times.
Is evolution predictable?
An international team of scientists working with Heliconius butterflies at the Smithsonian Tropical Research Institute (STRI) in Panama was faced with a mystery: how do pairs of unrelated butterflies from Peru to Costa Rica evolve nearly the same wing-color patterns over and over again?
Predicting evolution
A new method of 're-barcoding' DNA allows scientists to track rapid evolution in yeast.
Insect evolution: Insect evolution
Scientists at Ludwig-Maximilians-Universitaet (LMU) in Munich have shown that the incidence of midge and fly larvae in amber is far higher than previously thought.
Evolution of aesthetic dentistry
One of the main goals of dental treatment is to mimic teeth and design smiles in the most natural and aesthetic manner, based on the individual and specific needs of the patient.
An evolution in the understanding of evolution
In an open-source research paper, a UVA Engineering professor and her former Ph.D. student share a new, more accurate method for modeling evolutionary change.
Chemical evolution -- One-pot wonder
Before life, there was RNA: Scientists at Ludwig-Maximilians-Universitaet (LMU) in Munich show how the four different letters of this genetic alphabet could be created from simple precursor molecules on early Earth -- under the same environmental conditions.
Catching evolution in the act
Researchers have produced some of the first evidence that shows that artificial selection and natural selection act on the same genes, a hypothesis predicted by Charles Darwin in 1859.
More Evolution News and Evolution Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Climate Mindset
In the past few months, human beings have come together to fight a global threat. This hour, TED speakers explore how our response can be the catalyst to fight another global crisis: climate change. Guests include political strategist Tom Rivett-Carnac, diplomat Christiana Figueres, climate justice activist Xiye Bastida, and writer, illustrator, and artist Oliver Jeffers.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Speedy Beet
There are few musical moments more well-worn than the first four notes of Beethoven's Fifth Symphony. But in this short, we find out that Beethoven might have made a last-ditch effort to keep his music from ever feeling familiar, to keep pushing his listeners to a kind of psychological limit. Big thanks to our Brooklyn Philharmonic musicians: Deborah Buck and Suzy Perelman on violin, Arash Amini on cello, and Ah Ling Neu on viola. And check out The First Four Notes, Matthew Guerrieri's book on Beethoven's Fifth. Support Radiolab today at