Scientists have made a significant discovery in their ongoing debate about the decline of dinosaurs before the asteroid impact that ended the Cretaceous period. The study, focusing on a set of hindlimb bones, has revealed the existence of a new species, challenging previous assumptions about dinosaur diversity.

The bones were found in South Dakota and date back to the final two million years of the Cretaceous period. Initially, the scientists identified them as belonging to a group of birdlike dinosaurs known as caenagnathids, specifically the species Anzu, also dubbed the "chicken from Hell." Caenagnathids were characterized by their toothless beaks, long legs, and short tails, and were covered in complex feathers, similar to modern birds.

However, upon closer examination, the researchers discovered that the bones belonged to an entirely new species, which they named Eoneophron infernalis, meaning "Pharaoh's chicken from Hell." This newfound dinosaur had distinct features, including ankle bones fused to the tibia and a well-developed ridge on one of its foot bones.

The discovery of Eoneophron infernalis prompted a reassessment of other dinosaur bones previously attributed solely to Anzu. It became clear that there were multiple caenagnathid dinosaurs living in western North America during the late Cretaceous period. This included a smaller, unnamed species, as well as the larger Anzu, which was comparable in size to a grizzly bear, and Eoneophron, which was human-like in weight.

Comparisons with older fossil formations, such as the Dinosaur Park Formation of Alberta, revealed striking similarities in both the number of species and the size classes of caenagnathids. This suggests that the diversity of caenagnathids remained stable throughout the last part of the Cretaceous period.

The findings challenge previous beliefs that dinosaur diversity was declining before the asteroid impact. The presence of new and yet-to-be-discovered species indicates that there is still much to learn about these ancient creatures. The researchers argue that the apparent decrease in diversity could be attributed to sampling and preservation biases, rather than an actual decline in dinosaur populations.

This study adds compelling evidence to the ongoing debate on dinosaur extinction. While many questions remain, the discovery of Eoneophron infernalis suggests that caenagnathids were thriving before the cataclysmic event that ultimately wiped out dinosaurs from the Earth.

As paleontologists continue to uncover and analyze fossils, the story of the dinosaurs and their demise continues to evolve, shedding new light on the world that existed millions of years ago. With each new discovery, our understanding of the Earth's ancient inhabitants deepens, and the mysteries of the past become a little less obscure.