Culturally that’s a big one. From Carolyn Gramling at ScienceNews:
The once-lengthy list of “definitely a dinosaur” features had already been dwindling over the past few decades thanks to new discoveries of close dino relatives such as Teleocrater. With an April 2017 report of Teleocrater’s skull depression (SN Online: 4/17/17), yet another feature was knocked off the list.
“I often get asked ‘what defines a dinosaur,’ ” says Randall Irmis, a paleontologist at the Natural History Museum of Utah in Salt Lake City. Ten to 15 years ago, scientists would list perhaps half a dozen features, he says. “The only one to still talk about is having a complete hole in the hip socket.”
The abundance of recent discoveries of dinosauromorphs, a group that includes the
dinosaur-like creatures that lived right before and alongside early dinosaurs, does more than call diagnostic features into question. It is shaking up long-standing ideas about the dinosaur family tree.
To Nesbitt, all this upheaval has placed an even more sacred cow on the chopping block: the uniqueness of the dinosaur.
“What is a dinosaur?” Nesbitt says. “It’s essentially arbitrary.”
Paleontologists once assumed the dinosaurs were somehow superior, with physical features that helped them outcompete the other reptiles. “But that’s not borne out by new dinosaur relatives,” Nesbitt says. More.
Why did the paleontologists assume that dinosaurs were “somehow superior”? Because fundamental to Darwinism is the notion that life forms succeed if they “outcompete” other life forms, much as if they were all entered in the Kentucky Derby and one of them gets to eat the roses.
But nature doesn’t quite work that way. It features vast numbers of ecologies, growing and shrinking, in which countless life forms have a place—not principally by competition but by membership in a local chain of life. Competition is not a war of all against all; it usually happens for a given space on the chain. That space may go to a life form that is either “superior” or inferior according to an irrelevant, external standard. Many factors cause changes over time (evolution) and some may lead to devolution, in which case, the spot on the chain is occupied successfully by a genetically devolved life form.
To understand dinosaurs, it may be better to just forget Darwinism. Sorry, NCSE.
See also: Dinosaurs are tearing paleontology apart?
Sauropod dinosaurs had small, agile ancestors?