Symbol of renewal, eggs also have a lot to say about the past

Eggs have been laid on land by birds, reptiles, dinosaurs and some eccentric mammals for over 200 million years. And humans have used some of these eggs as a nutritious food source and their shells as bowls, bottles and jewelry for most of our history on the planet.

Though often overshadowed by skeletons and bones, fossilized eggshells are a fascinating source of information, illuminating the behavior and diet of ancient creatures, detailing changes in climate, and revealing how our prehistoric relatives lived and communicated. .

This Easter, here are six surprising things eggs reveal about the past:

dinosaur body temperature

Was dinosaur blood cold, like a lizard, or warm, like a bird? It’s a topic that has long divided paleontologists.

An analysis of fossilized dinosaur eggshells suggests it is the latter. By looking at the order of oxygen and carbon atoms in fossilized eggshells, the researchers were able to calculate the internal body temperature of a mother dinosaur. It is a process called “clustered isotope palethermometry”.

“Eggs, being formed inside dinosaurs, act like ancient thermometers,” explains Pincelli Hull, assistant professor in the department of geology and geophysics at Yale University and co-author of the study, published in 2020.

Hull and his colleagues found that the samples tested suggested that the dinosaurs’ body temperature was warmer than the environment would have been.

Research indicates that, unlike reptiles, which rely on the heat of the environment, dinosaurs were able to generate heat internally – more like birds.

Humans created the most dangerous birds in the world

You might think that chickens – or even ducks or turkeys – were the first birds to be domesticated by humans. However, eggshell fragments found at two prehistoric sites in Papua New Guinea suggest that humans may have bred cassowaries – often described as the most dangerous birds in the world because of the dagger-like claw they have. on each foot – already 18,000 years ago.

Territorial, aggressive and often compared to a dinosaur in appearance, the bird is a surprising candidate for domestication. But a study of more than 1,000 fossilized eggshell fragments from Papua New Guinea suggested the birds were deliberately hatched.

To reach their conclusions, the researchers first studied the eggshells of live birds, including turkeys, rheas and ostriches. The inside of the eggshells changes as the developing chicks obtain calcium from the eggshell.

Using high-resolution 3D images and inspecting the insides of the eggs, the researchers were able to build a model of what the eggs looked like during the different stages of incubation.

The scientists tested their model on eggs of modern rheas and ostriches before applying it to fossilized eggshell fragments found in New Guinea. The team found that most of the eggshells found at the sites were all close to maturity – suggesting they were hatched, not eaten.

Some dinosaurs were caring parents

The first fossil oviraptor – from a family of parrot-beaked dinosaurs – was discovered in Mongolia in the 1920s, near a nest egg believed to belong to a rival. Paleontologists at the time assumed the animal had died while trying to loot the nest and called the creature an “egg thief.”

His restoration was only restored in the 1990s when another discovery revealed that the eggs were his. Subsequent discoveries — including an oviraptosaur bent over 24 eggs made public in 2021 — revealed that this specific type of dinosaur was a loving parent.

At least seven of the 24 eggs preserved the bones of partial embryos found inside; it was the first time a fossil had preserved this level of detail. These embryos were at an advanced stage of development, and the proximity of the father confirmed that this dinosaur did indeed incubate its nest like its modern bird cousins.

The tidy layout of the oviraptor nests also suggested that they were hatcheries that lay on eggs to hatch them — even giant oviraptors that weighed 3,000 pounds and laid eggs half a meter long, said Darla Zelenitsky, a dinosaur egg expert. and associate professor in the department of geosciences at the University of Calgary, Canada.

“These fossils also show very precisely arranged eggs, stacked in rings, likely optimized to sit on eggs,” she explained.

The 2-meter-wide giant oviraptor nests had a slightly modified shape to prevent them from being crushed, she added.

Dinosaur eggs – including one with a perfectly preserved baby dinosaur curled up inside – increasingly show that birds have inherited many characteristics from dinosaurs. Not all dinosaurs, however, were caring parents.

Pores on the surface of eggs allow for the diffusion of water, oxygen and carbon dioxide, and the orientation, density and number of pores in the eggs of living animals can reveal whether they are placed in open or underground nests. Applying this knowledge to fossilized dinosaur eggs clarified their nesting behavior.

The analysis suggests that many dinosaurs, including huge herbivorous sauropods, laid their eggs underground in burrows, more like reptiles.

Eggshell accounts formed the first social network

Ostrich eggshells are found at archaeological excavation sites across Africa. Early humans used the large eggs as water bottles, and for tens of thousands of years, ancient humans took the remains and turned them into decorative beads that are still made today.

These beads have been found across Africa – including in areas where ostriches have never lived – raising the question of how they got there.

The answer is hidden in the geochemistry of eggs. The researchers analyzed the signatures of different isotopes or variants of the element strontium in the beads – they vary depending on where the ostriches would feed before laying eggs.

Older rock formations, including granite, have more strontium than younger rocks such as basalt, and this is reflected in the vegetation that grows around them.

The geochemistry of the beads showed that they traveled long distances. They were traded or exchanged in what has been described as an early social network.

understanding extinction

Eggs are a big part of our diet today – something that was also true in the Stone Age.

Indeed, the appetite of ancient Australians for the eggs laid by the 2-meter-tall Genyornis may have been a significant reason why large, flightless birds became extinct 47,000 years ago.

Burning patterns in eggshell fragments from the giant bird found at about 200 sites across Australia were created by humans discarding eggshells around and inside makeshift fires presumably made to cook the eggs.

Chemical signatures of nitrogen and carbon isotopes in fossilized eggshells can also track changes in vegetation, gathering information about past climate change, which can reveal ecological changes that would affect the survival of these species over time.

A study of rheas eggshells found across Australia over a period of 100,000 years does not show a massive shift in climate that researchers believe could have led to the extinction of Genyornis.

This suggests that the extinction of these giant birds was caused by humans, not ecological changes, the study said.

changed climate

Fossilized shells of penguin, ostrich and emu eggs have revealed what the climate was like in ancient Antarctica, South Africa and Australia. Latest egg collections are revealing how the current climate crisis is changing the natural world today.

By comparing bird eggs collected during the Victorian era and modern eggs held by the Field Museum and other institutions, the researchers found that several bird species in the Chicago area nest and lay eggs nearly a month earlier than they did a century ago.

Of the 72 species documented in the data, a third have been nesting at an earlier age, the team found. Birds that changed their nesting habits laid eggs about 25 days earlier, on average.

Similar patterns are seen in insects, which many birds eat, and plants, suggesting that climate change is already altering ecosystems, the study authors said.

*Ashley Strickland and Danya Gainor of CNNcontributed to this report.