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University of Michigan researchers have used an AI tool to demonstrate that birds in the group Passeriformes evolved in rapid evolutionary bursts and that these bursts frequently coincided with climate shifts throughout Earth's history.
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Evolutionary theory predicts that the evolution of organisms occurs in pulsed bursts followed by slowdowns—something researchers have seen hints of in the fossil record.
Now, looking at passerines, University of Michigan researchers have identified these evolutionary bursts by examining data gleaned from skeletal measurements of contemporary bird specimens. The researchers also observed that these bursts coincided with historical climate change.
"This is really important for evolutionary theory because there's a long history, going back 100 years, that predicts the emergence of new groups, called evolutionary radiations, is often associated with an explosive burst of diversification. Evolutionary theory predicts that adaptive radiations may account for a large portion of the diversity of life on Earth," said Jake Berv, lead author of the study and postdoctoral fellow in the U-M School for Environment and Sustainability.
"This could be because of a new ecological opportunity, or it could be because a group dispersed to a new continent, resulting in dramatic accelerations in their rate of evolution. The idea is that, over time, there's less opportunity as evolution proceeds, and so it slows down, and that this occurs in pulses across time. That's what theory predicts, and that seems to be what we see in the data as well."
The findings, deduced using artificial intelligence and a large-scale statistical model, are published in Nature Ecology & Evolution.
Seeing with Skelevision
To trace how this group of birds evolved, the U-M scientists, including senior author Brian Weeks, examined more than 2,000 species and collected more than 170,000 individual skeletal measurements. To create such a large dataset, the team used an AI tool called Skelevision, which Weeks' lab developed with David Fouhey's lab at New York University.
Skelevision uses a camera to photograph specimens—for this study, bird skeletons—against a background grid that provides a common scale. Over a seven-year collaboration, Weeks and Fouhey developed an AI model that can precisely measure a dozen bones across the avian skeleton.
The researchers used Skelevision to scan and measure more than 15,000 individual museum specimens, most of which came from the U-M Museum of Zoology collections. Scanning each specimen takes only about 45 seconds, which makes it possible to digitize entire collections.
A method to the madness
Berv then developed a new statistical method called bifrost that enabled researchers to examine a species' entire skeleton at once. This allowed the researchers to estimate the evolution of body shape over the approximately 45-million-year history of Passeriformes.
"The whole organism is an integrated, complex morphology, and each of the individual pieces is interrelated to every other part in the body," Berv said. "The question from the model's perspective is, 'What is the sequence of evolutionary changes that needs to happen to explain the variation we can see today?'"
The researchers found that passerines underwent rapid bursts of body-shape evolution roughly 35 million years ago, coinciding with the Eocene–Oligocene transition. During this time, Earth experienced intense global cooling. Then, the statistical analysis showed a cluster of evolutionary slowdowns that occurred about 15 million years ago and coincided with another important geological event.
"Our findings have definitely shifted my thinking about how the world works," said Weeks, associate professor of ecosystem science and management at U-M's School for Environment and Sustainability.
"This pattern we found with rare, big increases in the rates of evolution and lots of small decreases in the rates of evolution is really consistent with a pattern where lineages are exploring new ecological space and changing rapidly to take advantage of that opportunity."
A bonus discovery
To test their results, the researchers then examined the skeleton dataset worldwide. They found that where birds live also predicts their average rate of morphological evolution—that is, communities at more extreme latitudes and with greater seasonal temperature fluctuations tend to host species that evolve more quickly than those near the equator.
The similar patterns the researchers found across time and space suggest that the shared influence of environmental variation may be an important cause of changes in body shape.
"It looks like there's a connection between latitudinal gradients and rates of morphological evolution that has been underappreciated," Weeks said. "I hope our findings will inspire a new integration of rates of morphological change into other big areas of interest, things like the very well-known latitudinal gradients in biodiversity."
The study itself points to the importance of investing in museum collections, Weeks says, and how advances in artificial intelligence can help researchers better leverage these resources.
"It's especially clear how important it is to invest in museums when you think about the scale of an analysis like this; it's so far beyond the scope of what can be done using specimens contributed by an individual collector," he said.
"It's also fun to imagine what early collectors would make of how we're using the specimens they collected—I imagine it would blow their minds to learn that a computer has analyzed a photograph of these specimens. It's just another example of how impossible it is to foresee the full future value of a specimen."
The researchers say the study may also offer lessons for how species respond to our current era of intense climate change.
"Right now, we're in this moment in human history where there's dramatic global climate change, and we don't know what's going to happen over even a 10-year period, let alone over a 10-million-year period," Berv said.
"To have a chance of understanding the long-term impact of human activity on Earth, we have to study the relationship between events in Earth's history and evolutionary transitions."
More information: Rates of passerine body plan evolution in time and space, Nature Ecology & Evolution (2026). DOI: 10.1038/s41559-026-03110-5
Provided by University of Michigan
This story was originally published on Phys.org.
