Researchers show dinos hatched eggs less efficiently than modern birds

Research using dinosaur body model suggests that – unlike modern birds – bird-like dinosaurs may have used the sun’s warmth to help hatch eggs, shedding light on the evolution of avian-style incubation.

Frontiers

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Lateral view of the clutch. The eggs were molded from casting resin. 

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Credit: Chun-Yu Su.

What do we really know about how oviraptors – bird-like but flightless dinosaurs – hatched their eggs? Did they use environmental heat, like crocodiles, or body heat from an adult, like birds? In a new Frontiers in Ecology and Evolution study, researchers in Taiwan examined the brooding behavior and hatching patterns of oviraptors. They also modelled heat transfer simulations of oviraptor clutches and compared hatching efficiency to modern birds. To do so, they experimented with a life-sized oviraptor incubator and eggs.

“We show the difference in oviraptor hatching patterns was induced by the relative position of the incubating adult to the eggs,” said senior author Dr Tzu-Ruei Yang, an associate curator of vertebrate paleontology at Taiwan’s National Museum of Natural Science.

“Moreover, we obtained an estimate of the incubation efficiency of oviraptors, which is much lower than that of modern birds,” added first author Chun-Yu Su, who attended Washington High School in Taichung when the research was conducted.

Building a dinosaur

The reconstructed oviraptor Heyuannia huangi lived between 70 and 66 million years ago in what today is China. Estimated to be around 1.5 meters long and weighing around 20kg, it built semi-open nests made up of several rings of eggs.

The incubating oviraptor’s trunk was made from polystyrene foam and wood for the skeletal frame and cotton, bubble paper, and cloth for the soft tissue. Eggs were molded from casting resin. In the two clutches used in the experiments, eggs were arranged in double-rings based on real oviraptor clutches.

“Part of the difficulty lies in reconstructing oviraptor incubation realistically,” said Su. “For example, their eggs are unlike those of any living species, so we invented the resin eggs to approximate real oviraptor eggs as best as we could.”

When the team ran experiments to find out if clutch attendance of a brooding adult or different environmental circumstances may have impacted hatching patterns, they found that in colder temperatures, where a brooding adult attended the clutch, the eggs’ temperatures in the outer ring differed by up to 6°C, which could have resulted in asynchronous hatching, a pattern where eggs in the same nest hatch at different times. In warmer conditions, the difference in egg temperatures in the outer ring was just 0.6°C, suggesting that oviraptors living in warmer conditions may have exhibited a different pattern of asynchronous hatching because they could use the sun as an additional, powerful heat source.

“It’s unlikely that large dinosaurs sat atop their clutches. Supposedly they used the heat of the sun or soil to hatch their eggs, like turtles. Since oviraptor clutches are open to the air, heat from the sun likely mattered much more than heat from the soil,” Yang explained.

Better hatchers?

The team also investigated how oviraptor incubation efficiency compares to that of modern birds. Most birds use thermoregulatory contact incubation (TCI), where adults sit directly on the eggs to transfer heat. TCI requires three prerequisites – the adult bird must be in contact with every egg, be the main heat source, and maintain all eggs within a constrained temperature range – which oviraptors didn’t fulfil. For example, their egg arrangement prevented the adult from making full contact with all eggs in the clutch.

“Oviraptors may not have been able to conduct TCI as modern birds do,” said Su. Instead, these dinosaurs and the sun may have been co-incubators – a less efficient incubation behavior than that displayed by modern birds. Yet, the combination of adult incubation and an ambient heat source – perhaps a behavioral adaptation associated with the evolution from buried to semi-open nests – isn’t necessarily worse.

“Modern birds aren’t ‘better’ at hatching eggs. Instead, birds living today and oviraptors have a very different way of incubation or, more specifically, brooding,” Yang pointed out. “Nothing is better or worse. It just depends on the environment.”

The team pointed out that their findings are specific to the reconstructed nest and are limited by the fact that today’s climate does not resemble the Late Cretaceous climate, which may have impacted the results. Oviraptors also exhibited a longer incubation period than modern birds.

Yet, the study advances our understanding of oviraptor brooding strategies through innovative approaches. It represents an important bridge between physics-based simulations and paleontological interpretations, potentially enabling paleontologists to investigate topics for which approaches were limited until now.  

“It also truly is an encouragement for all students, especially in Taiwan,” concluded Yang. “There are no dinosaur fossils in Taiwan but that does not mean that we cannot do dinosaur studies.”

Lateral view of the clutch with the incubator on top

Photograph of the generalized clutch after Experiment III.

Dorsal view of the incubator.

Credit

Chun-Yu Su.

The arrangement of thermometers in the incubation experiments. Thermometers 1 (with thicker outlines) were used in Experiment II. Thermometers 2 (with lighter outlines) were the additional thermometers used in Experiment III. The schematic presents a lateral view of the clutch and the incubator.

Credit

Su et al.,2026.

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Journal

Frontiers in Ecology and Evolution

DOI

10.3389/fevo.2026.1351288 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Heat transfer in a realistic clutch reveals a lower efficiency in incubation of oviraptorid dinosaurs than of modern birds

Article Publication Date

17-Mar-2026

 

Tiny’ dinosaur, big impact: 90-million-year-old fossil rewrites history

New study says Alnashetri originated when the continents were still connected as the supercontinent Pangaea

University of Minnesota

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A new study of fossils from a bird-like dinosaur, called Alnashetri, provides new insight into how its lineage evolved, shrank and spread across the ancient world.

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Credit: Gabriel Díaz Yantén, Universidad Nacional de Río Negro.

MINNEAPOLIS / ST. PAUL (02/25/2026) — A team co-led by University of Minnesota Twin Cities researcher Peter Makovicky and Argentinean colleague Sebastian Apesteguía has identified a 90-million-year-old fossil that provides the “missing link” for a mysterious group of prehistoric animals. 

The study, published in the peer-review journal Nature, details the discovery of a complete skeleton of Alnashetri cerropoliciensis. Alnashetri belongs to a group of bird-like dinosaurs, known as alvarezsaurs, that are famous for their tiny teeth and stubby arms ending in a single large thumb claw. For decades, they have remained a mystery because most of the well-preserved fossils were found in Asia, while records from South America were fragmented and difficult to interpret.

In 2014, the almost complete fossil of Alnashetri was discovered in the northern part of Patagonia, Argentina, at a site that is world-renowned for its exquisite Cretaceous fossils. The species was originally named a few years prior based on fragmentary remains, but this newer, more complete specimen allowed the team to finally map the group's strange anatomy. The team spent the last decade carefully preparing and piecing together the fossils to avoid damaging the small bones.

“Going from fragmentary skeletons that are hard to interpret, to having a near complete and articulated animal is like finding a paleontological Rosetta Stone,” said Peter Makovicky, lead author on the paper and a professor in the University of Minnesota Department of Earth and Environmental Sciences. “We now have a reference point that allows us to accurately identify more scrappy finds and map out evolutionary transitions in anatomy and body size.”

The discovery of this nearly complete skeleton opens up a new understanding of how its lineage evolved, shrank and spread across the ancient world.

• Unlike its later relatives, Alnashetri had long arms and larger teeth. This proves that some alvarezsaurs evolved to be tiny long before they developed these specialized features thought to be adaptations for an "ant-eating" diet.

• Microscopic analysis of the bones confirmed the animal was indeed an adult of at least four years old. These animals are not just among the tiniest non-avian dinosaurs, but they never get any bigger—the largest species are the size of an average human, very small for dinosaurs, and Alnashetri itself weighed less than 2 lbs making it one of the smallest dinosaurs known from South America.

• By identifying previously found alvarezsaurs fossils in museum collections from North America and Europe, the team proved these animals originated much earlier than expected when the continents were still connected as the supercontinent Pangaea. Their distribution was caused by the breakup of the earth's landmasses, not unlikely treks across oceans.

The well-preserved fossil was recovered from the La Buitrera fossil area, a site that has yielded other scientifically critical animals, including primitive snakes and tiny saber-toothed mammals.

“After more than 20 years of work, the La Buitrera fossil area has given us a unique insight into small dinosaurs and other vertebrates like no other site in South America," said Apesteguía, a researcher at Universidad Maimónides in Buenos Aires, Argentina. 

Their work is far from over, as the scientists continue to discover and study fossils from the same area where they discovered Alnashetri. “We have already found the next chapter of the alvarezsaurid story there, and it is in the lab being prepared right now,” added Makovicky.

In addition to Makovicky and Apesteguía, the international team included Jonathan S. Mitchell from Coe College in Iowa; Jorge G. Meso and Ignacio Cerda from Instituto de Investigación, Universidad Nacional de Río Negro and Museo Provincial; and Federico A. Gianechini from Instituto Multidisciplinario de Investigaciones Biológicas de San Luis.

The research was supported by the National Scientific and Technical Research Council (CONICET), The Field Museum, National Geographic, University of Minnesota, United States National Science Foundation and the Fulbright U.S. Scholar program.

Read the full paper entitled, “Argentine fossil rewrites evolutionary history of a baffling dinosaur clade,” on the Nature website

Alnashetri was rapidly covered by an advancing sand dune that preserved it almost intact for 90 million years.

Credit

Peter Makovicky, University of Minnesota

University of Minnesota Professor Peter Makovicky uncovers fossil bones at the La Buitrera fossil area.

Credit

Minyoung Son, University of Minnesota

Alnashetri animation [VIDEO] |

Alnashetri belongs to a group of bird-like dinosaurs, known as alvarezsaurs, that are famous for their tiny teeth and stubby arms ending in a single large thumb claw.

Credit

Universidad Nacional de Río Negro and University of Minneso

Journal

Nature

DOI

10.1038/s41586-026-10194-3 

Article Title

Argentine fossil rewrites evolutionary history of a baffling dinosaur clade

Article Publication Date

25-Feb-2026

 

Bird retinas function without oxygen – solving a centuries-old biological mystery

Neural tissue normally dies quickly without oxygen. Yet bird retinas − among the most energy-demanding tissues in the animal kingdom – function permanently without it. This may be relevant in future treatment of stroke patients.

Aarhus University

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The pecten is a vascular structure within the vitreous humor of the eyes of birds with a previously unknown function..

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Credit: Aleksandrina Mitseva / Nature

In a study published today in Nature, an international research team reveals how birds have solved a biological paradox. The researchers show that the inner parts of the bird retina operate under chronic oxygen deprivation, relying instead on anaerobic energy production.

At the same time, the study overturns a long-standing assumption about a mysterious structure in the eye that has puzzled scientists since the 17th century.

Most animals supply neural tissue with oxygen through dense networks of tiny blood vessels. This is considered essential, as neurons have an exceptionally high energy demand. The retina, a highly specialized extension of the brain, is no exception – and in fact consumes more energy than any other tissue in the body.

Birds, however, present a paradox. Their retinas are avascular, meaning they lack blood vessels within the retinal tissue itself. This feature is thought to improve visual acuity, since blood vessels scatter light in its path to the photoreceptor. But how the retina survives without a blood supply has remained unknown.

“Our starting point was simple,” says biologist Christian Damsgaard, first author of the study and associate professor at Aarhus University in Denmark. “According to everything we know about physiology, this tissue should not be able to function.”

While the starting point may have been simple, the journey to the end point was anything but simple. It has taken Damsgaard and a growing team of researchers, mostly from Aarhus University, 8 years to produce the results, that are now finally published.

No oxygen where it was assumed to be

For centuries, the prevailing explanation has been that a structure called the pecten oculi – a comb-like, highly vascularized organ protruding into the vitreous body of the bird eye – supplies oxygen to the retina. The structure has been known since the 1600s, but its precise function has remained speculative.

One reason, the researchers note, is that no one had directly measured oxygen levels in the bird retina under normal physiological conditions.

“Doing so is technically extremely challenging,” says senior author Jens Randel Nyengaard, professor at Dept of Clinical Medicine, Aarhus University. “You need to keep the animal under stable, normal physiological conditions while performing very delicate measurements.”

In 2020, the team was able to do exactly that, thanks to a collaboration with veterinary anaesthesia expert and assistant professor Catherine Williams, also from Aarhus University. The results were unexpected: the pecten does not deliver oxygen to the retina at all. Measurements showed that the inner layers of the retina exist in a state of permanent oxygen deprivation, with roughly half of the retinal tissue receiving no oxygen.

Each answer raised new questions

If the retina receives no oxygen, how does it produce enough energy to function?

To answer that question, the researchers embarked on a multi-year investigation combining physiology, molecular biology, imaging, and computational analysis. Progress was slow, in part due to the scale and complexity of the data – and in part due to the COVID-19 pandemic, which restricted laboratory access.

Using spatial transcriptomics, the team mapped the expression of thousands of genes across thin sections of the retina, allowing them to see where specific metabolic pathways were active within the tissue.

(Spatial transcriptomics is a technology that maps gene expression directly within intact tissues, revealing both what genes are active and where they are active).

“We were not looking at one or two genes, but at 5,000 to 10,000 genes at once, each mapped to a precise location,” says Damsgaard. “That gave us a kind of molecular GPS.”

The data revealed a striking pattern: genes involved in anaerobic glycolysis – the breakdown of sugar without oxygen – were highly active in the oxygen-deprived inner layers of the retina.

This finding, however, raised yet another problem. Anaerobic glycolysis produces roughly fifteen times less energy than oxygen-based metabolism per sugar molecule.

“This mismatch raised yet another question: How can one of the most energy-hungry tissues in the body survive on such an inefficient process?” Nyengaard says.

A new role for an old structure

The answer emerged through further imaging studies conducted in collaboration with metabolic imaging specialists. Using radiolabelled sugar and autoradiography, the researchers showed that the bird retina takes up glucose at much higher rates than the rest of the brain.

This led the team back to the pecten oculi.

By revisiting their spatial transcriptomics data, the researchers identified high expression of glucose and lactate transporters in the pecten. The structure, they found, serves as a metabolic gateway: delivering large amounts of sugar into the retina and removing lactate, a waste product of anaerobic metabolism, back into the bloodstream.

“The pecten is not an oxygen supplier. It is a transport system for fuel in and waste out,” says Nyengaard.

The discovery fundamentally changes the understanding of a structure that has been misinterpreted for centuries.

“We are essentially collapsing one house of cards and replacing it with another. House of cards, because scientific findings are not set in stone. New results can add new knowledge. That is how science progresses,” Nyengaard adds.

Evolutionary and medical perspectives

The researchers note that avoiding oxygen and blood vessels in the retina likely confers an optical advantage, improving visual sharpness. Evolutionary evidence suggests that this trait arose in the dinosaur lineage leading to modern birds.

While the study is purely fundamental research, the authors point out that the findings may have broader implications.

“In conditions like stroke, human tissues suffer because oxygen delivery is reduced and metabolic waste accumulates,” says Nyengaard. “In the bird retina, we see a system that copes with oxygen deprivation in a completely different way.”

“Nature has solved a physiological problem in birds that makes humans sick.We hope that understanding this evolutionary solution can inspire new ways of thinking about why tissues fail under oxygen deprivation in disease, and how such diseases can be treated” he adds.

  

The study shows that the pecten supplies glucose to the retina at rates that far exceed the glucose supply rates to the brain, as illustrated on the autoradiography images, showing much higher glucose uptake (pink) in the retina compared to the brain.

Credit

Christian Damsgaard and Morten Busk, Aarhus University / Nature

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Journal

Nature

DOI

10.1038/s41586-025-09978-w 

Subject of Research

Animals

Article Title

Oxygen-free metabolism in the bird inner retina supported by the pecten

Article Publication Date

21-Jan-2026