Fossils reveal wondrous dinosaur diversity just before mass extinction

A more complete picture of what the world looked like in the age of dinosaurs is being created by palaeontologists in fossil rich Patagonia in the southernmost reaches of South America.

Scientists like Marcelo Leppe, director of the Antarctic Institute of Chile, says the fossil record is key to understanding life today. This latest research provides a glimpse into the dinosaurs and birds that lived in the region during the Late Cretaceous just before the mass extinction 66 million years ago which saw the disappearance of non-avian dinosaurs.

“We still need to know how life made its way in that apocalyptic scenario and gave rise to our southern environments in South America, New Zealand and Australia,” Leppe says.

But we can now build a snapshot of the diverse dinosaurs that roamed prehistoric Patagonia thanks to the study led by Leppe and palaeontologists at the University of Texas at Austin.

Patagonia has been a treasure trove of fossil discoveries for decades. Among the significant fossils found in southern Argentina and Chile are Dreadnoughtus, a 70 tonne long-necked sauropod thought to be the largest land animal ever, and one the largest carnivorous dinosaurs, Giganotosaurus, which, at 14 metres from nose to tail, is longer than T. rex!

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This latest study focuses on the late Cretaceous period 66 to 75 million years ago.

The region where they were found is believed to be an ancient river delta.

Among the fossils are the first recorded theropods from Chile. Theropods are the dinosaur group that includes both modern birds and their close non-avian dinosaur relatives. Most famous among them are Tyrannosaurus rex, Allosaurus and the raptors such as Velociraptor.

Included in the finds are giant megaraptors with large sickle-like claws and birds closely related to modern species.

“The fauna of Patagonia leading up to the mass extinction was really diverse,” says lead author Sarah Davis. “You’ve got your large theropod carnivores and smaller carnivores as well as these bird groups coexisting alongside other reptiles and small mammals.”

As a group, theropods are mostly carnivorous. The top predators found in the Patagonian study included dinosaurs from two groups – megaraptors and unenlagiines.

The megaraptors reached lengths of over seven metres, making them among the larger theropod dinosaurs in South America’s Late Cretaceous.

Unenlagiines ranged from chicken-sized to more than three metres tall and were likely covered with feathers. The unenlagiine fossils found in Patagonia are the southern-most found in the world.

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Bird fossils also came in two groups – enantiornithines and ornithurines.

Enantiornithines are now extinct, but were the most diverse and abundant birds millions of years ago. They resembled sparrows, but with toothed beaks.

Ornithurines includes all birds living today. The fossils are too fragmentary to tell for sure, but the palaeontologists believe the ones living in ancient Patagonia may have been similar in appearance to geese or ducks.

Davis says the team found mainly small fossil fragments including teeth, toes and small bone pieces. The enamel on dinosaur teeth glinted out of the rocks, making them easier to spot.

Some scientists suggest that climatic changes in the southern hemisphere after the asteroid impact 66 million years ago were less extreme and more gradual than in the north.

Patagonia and other places in the southern hemisphere, including Australia and Antarctica, may have been a refuge for birds, mammals and other creatures which survived the extinction. Davis says this study is another piece in the puzzle and may help investigate this theory.

The study is published in the Journal of South American Earth Sciences.

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