Paleontologists have been debating whether the asteroid that killed non-avian dinosaurs took out a varied group of thriving reptiles or one already in decline. Now, researchers say they’ve discovered a new dinosaur species whose very existence disputes the latter argument. The argument is largely based on apparent declines in dinosaur diversity in the 10 million years or so before the asteroid impact. But critics put this down to sampling bias in the incomplete fossil record. Kyle Atkins-Weltman, a 28-year-old PhD student at Oklahoma State University, backs up that claim in a new study describing his discovery of a species from the birdlike caenagnathid family of dinosaurs, dubbed Eoneophron infernalis, or “pharaoh’s dawn chicken from hell,” per the Washington Post.
Only one species of caenagnathid—Anzu wyliei, nicknamed “chicken from hell”—was previously known to exist in the area of the Hell Creek Formation, which stretches across four US states, in the 2 million years before the asteroid impact. So when Atkins-Weltman came across four hind-limb bones from that time and place, which resembled Anzu bones but were much smaller, he assumed they came from a juvenile. When researchers cut into the bones, however, to look for growth arrest lines, which offer clues to an animal’s age, they found lines “spaced progressively closer together, indicating that this animal’s growth had slowed and it was nearly at its adult size,” Atkins-Weltman and Eric Snively, an associate professor of anatomy and cell biology at Oklahoma State, write at Discover.
The bones belonged to Eoneophron which, unlike Anzu, had “ankle bones fused to the tibia, and a well-developed ridge on one of its foot bones,” according to the researchers, who soon found bones attributed to Anzu that they believe point to a third, yet unnamed caenagnathid species even smaller than Eoneophron. As fossils from older formations indicate the same number of caenagnathid species and in the same size classes, the researchers conclude caenagnathid diversity had been stable for millions of years before the impact of 66 million years ago. “These fossils show that there are still new species to be discovered, and support the idea that at least part of the pattern of decreasing diversity is the result of sampling and preservation biases,” write Atkins-Weltman and Snively. (More dinosaurs stories.)