Fossilized eggshells from Argentina’s Chorrillo Formation reveal that giant titanosaurs nested at 55–60 degrees south latitude, the southernmost confirmed site for dinosaur eggs, according to a study led by Kohei Tanaka of the University of Tsukuba. The discovery shows these massive dinosaurs used buried nests heated by decaying vegetation to survive cold, high-latitude environments.
The Chorrillo Formation near El Calafate, Argentina, has yielded 255 fragments of Fusioolithus eggshells, the most definitive dinosaur egg remains found in the southern hemisphere. Dating to the Late Cretaceous, about 70 million years ago, the site lay at 55–60 degrees south latitude—a region characterized by milder climate but with long periods of absence of sunlight that posed nesting challenges for non-avian dinosaurs, according to a study published in The Royal Society Open Science.
Southern Argentina eggshells suggest giant titanosaurs buried eggs to
Researchers determined the eggs were incubated in covered nests, likely using heat from decaying plant matter rather than solar radiation or parental brooding. The shells’ high porosity, matched to modern crocodilian and megapode bird nesting strategies, suggests they were buried in nesting materials to retain moisture, as reported by Earth.com. They’re too big. The nest would be one big omelet,
said Darla Zelenitsky, a University of Calgary paleontologist and co-author, explaining why titanosaurs could not sit on their eggs like birds, per Earth.com.
The study’s micro-CT scans and microscopic analysis of shell pores supported the buried-nest theory, as an exposed egg with such porous shell would lose water dangerously fast. The site, located approximately 29 km (18 miles) to the southeast of El Calafate in Santa Cruz Province, featured a previously waterlogged or marshy plain during the Late Cretaceous, with an average annual temperature of 56 degrees Fahrenheit, according to Earth.com. Researchers classified the shells as Fusioolithus, a fossil egg type commonly associated with titanosaurs, though no embryos were found. Titanosaur bones and teeth from the same formation, however, support the link.
Patagonian Titanosaur Eggs Reveal a Polar Nesting Secret
The Chorrillo site represents the highest paleolatitude area to produce definitive dinosaur egg remains from the southern hemisphere. While northern high-latitude nesting—such as in Siberia, Alaska, and Alberta, Canada—has been documented, less evidence exists for high-latitude nesting in the southern hemisphere, in part owing to the lack of definitive dinosaur eggshells/eggs from the regions of Antarctica or Australia, the study noted. Few discoveries have yielded fossil evidence of non-avian dinosaurs nesting at high paleolatitudes,
the researchers wrote, highlighting the Chorrillo findings as a rare glimpse into how dinosaurs adapted to polar environments.
The team measured all 255 shell fragments, examined selected pieces with microscopes, and used micro-CT imaging to view the inside of one fragment in three dimensions. They also compared the shells with the global record of Fusioolithus nesting sites, which helped show that the Chorrillo eggs were notable not just for their location but also for what they suggest about how giant dinosaurs adapted to cold environments. The study’s authors argued that decomposing vegetation was a plausible heat source.
Titanosaurs Nested Far South of Equator, Fossil Eggshells Reveal
Even the absolute largest dinosaurs figured out a way to not only reproduce or nest in the lower latitude environments but also in these higher-latitude environments, which are usually more challenging, Zelenitsky observed, underscoring the adaptability of titanosaurs. The discovery adds to evidence that titanosaurs nested at higher latitudes than previously known, with the Chorrillo Formation’s location closer to the pole than any other place on Earth known to preserve definitive dinosaur eggs in the southern hemisphere. Researchers estimated that eggs of this type were 4.3 to 9.1 inches across and 1.6 to 14.7 pounds, though no complete eggs were found.
The study’s authors acknowledged gaps in the findings, including the absence of complete eggs, intact nests, or embryos, which leaves uncertainties about clutch size, nest form, or the titanosaur species. The same formation also contains fossils believed to belong to the giant Nullotitan glaciaris, though researchers are currently unable to link the eggshells to any specific species. Future research may focus on linking the eggshells to specific titanosaur species and exploring how these strategies influenced dinosaur distribution across ancient polar regions, as noted by Earth.com.