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Extraordinary dinosaur fossils discovered from the end of the Cretaceous era

In a significant paleontological discovery, researchers have found a fossil site in South Argentina that may provide insight into life in the final days of non-avian dinosaurs.

Matthew Lamanna is a paleontologist and the principal dinosaur researcher at the Carnegie Museum of Natural History. He explained the importance of the fossil finds from the Cañadón Tomás Quarry in southern Argentina’s Patagonia region to understanding the last days of the non-avian dinosaurs.

“In general, dinosaurs and other continental vertebrates from the Cretaceous tend to be less known from the Southern Hemisphere than they are from the Northern, and that creates an imbalance in our understanding of biodiversity, evolution, and paleobiogeography,” said Lamanna.

“We know enough about continental vertebrates in the Late Cretaceous to know that there were some very different kinds of animals thriving in the Southern Hemisphere. One thing that we’d really like to know is, how did non-avian dinosaurs in the southern half of the world fare at the Cretaceous-Paleogene boundary?”

Cañadón Tomás Quarry 

The growing interest in petroleum across South Argentina led to the first discovery of the Cañadón Tomás Quarry. What was supposed to be a paleontological impact study by oil companies turned out to be a discovery of dinosaur fossils.

Neoliza Cardozo is a PhD student at the UNPSJB and member of the Cañadón Tomás research team. He said, “The paleontological impact study was done by people from the Museo de La Plata, and they found some bones belonging to hadrosaurs (large-bodied duck-billed dinosaurs).”

“This information was shared with the paleontology crew of the Universidad Nacional de la Patagonia San Juan Bosco (UNPSJB), who started to explore the area, finding some bones. At the end of 2020, a few bones were recovered in the outcrop that today is Cañadón Tomás, and little by little, we began to expand that excavation, hoping to find something interesting,” she added.

Dinosaurs living in the late Cretaceous

Researchers have found several bones from hadrosaurs on the fossil site. Hadrosaurs, or “duck-billed dinosaurs,” are herbivorous dinosaurs that lived during the late Cretaceous period.

These large animals possess specialized dentition and keratinous beaks that help break down plants for food. They are less known from the Southern Hemisphere sites of the Late Cretaceous period compared to the Northern Hemisphere sites.

The hadrosaur bones from the Cañadón Tomás suggest the individuals were different sizes. Lamanna also reported the discovery of the fossils of two dinosaurs that did not belong to the non-avian predatory population. They found a claw that might belong to a noasaurid or a baby abelisaurid and a tooth that might belong to an abelisaurid.

Non-dinosaur species discovered

In addition to the dinosaur fossils, the team also picked up fossils of rare and small-bodied vertebrates. These include a snake’s vertebra suspected to belong to a madtsoiid. The madtsoiid is the first Cretaceous snake discovered in the Patagonia region.

Also worthy of mention is the discovery of the upper jaw of a small mammal known as a reigitheriid. Cardozo describes this as “the most exciting discovery” from the site. Lammana also described the jaw as one of the best fossils of this kind of mammal ever discovered.

Excavation work continues

The team believes there is still much to uncover at the Cañadón Tomás site. 

“Cañadón Tomás is a site of great interest not only for the great diversity but also for the great quantity of materials that are being discovered at the site,” said study co-author Bruno Alvarez.

“As excavation work continues, more and more materials are being found. There is still a lot of work left to do at Cañadón Tomás with a lot of fieldwork to complete, and we suspect there will be many more fossils to discover and study,” he added.

Lamanna believes the Cañadón Tomás holds great potential. This is particularly true for using fossils to understand the Cretaceous-Paleogene faunal and extinction dynamics in the Southern Hemisphere and discover new animal species.

“Right now, it’s one of the sites I’m involved with that has me the most excited and fired up,” said Lamanna.

More about dinosaurs living in the cretaceous

The Cretaceous period spanned from approximately 145 to 66 million years ago. It stands out as one of the most dynamic eras in Earth’s history. This is primarily due to the diverse species of dinosaurs that thrived during this time. The Cretaceous witnessed the climax of the dinosaurs’ evolutionary innovation, occurring immediately before the mass extinction that brought their reign to an end.

Dominant dinosaurs of the Cretaceous

Among the various dinosaur species that roamed the planet, certain groups were particularly prominent during the Cretaceous period.

Tyrannosaurs ruled the land

Tyrannosaurs, one of the most iconic carnivores, prowled the territories of what is now North America and Asia. Tyrannosaurus rex is the most famous member of this group. This massive dominated due to its massive size, powerful jaws, and sharp, serrated teeth, capable of crushing bone.

Herbivores flourished

On the other end of the spectrum, herbivorous dinosaurs roamed in herds. This group included the duck-billed hadrosaurs and the horned ceratopsians, like Triceratops. They grazed the land with their specialized teeth and jaws, ideal for processing tough plant matter. These creatures evolved defensive mechanisms, such as horns, frills, and body armor, to deter the era’s formidable predators.

Rise of the raptors

The Cretaceous also saw the emergence of smaller but incredibly agile predators, the dromaeosaurids, commonly known as raptors. Deinonychus and Velociraptor were known for their sharp claws and keen hunting strategies. They were a stark contrast to the giant predators but equally deadly.

Evolutionary marvels: Wings and feathers

One of the most revolutionary developments of the Cretaceous was the evolution of flight. While the famous Archaeopteryx lived earlier, numerous bird-like dinosaur species thrived in the Cretaceous skies. These avian relatives, such as the toothed Ichthyornis, displayed advanced flying abilities and exhibited the diversification of birds from their dinosaur ancestors.

Environmental backdrop and biodiversity

The Cretaceous world was one of extreme environmental changes, with rising sea levels creating shallow inland seas and a warmer climate. These conditions resulted in diverse habitats, from vast coastal swamps to open woodlands, allowing for an incredible biodiversity among dinosaur populations.

Flowering plants emerge

A significant ecological shift occurred with the appearance of the first flowering plants, or angiosperms. These plants created new ecosystems, contributing to the evolution of plant-eating dinosaurs due to changes in diet and foraging strategies.

End of an era: Mass extinction

Despite the thriving biodiversity, the Cretaceous period ended in a mass extinction event. The Cretaceous–Paleogene extinction event is normally attributed to a catastrophic asteroid impact combined with intense volcanic activity. This event marked the end of the dinosaurs, making way for the rise of mammals and eventually, humankind.

The Cretaceous era, rich with life and evolutionary advancements, continues to fascinate scientists and laypersons alike. The fossils preserved from this time, whether of a mighty T. rex or the first flowers, serve as a powerful reminder of Earth’s dynamic history and the ever-changing nature of life on our planet.

The research was presented at the 2023 meeting of the Geological Society of America.

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