Every day I’m home, I’m surrounded by cats. The clowder is rarely more than a few feet away while I tap away on the keyboard. One of them is lounging on the back of my chair as I write this, considering whether she wants to oust me from my seat or not. So you can believe me when I tell you that I’m very familiar with whiskers, and seeing feline faces all day got me wondering about whether one of my other favorite groups of animals sported stiffened structures on their faces, too.
Whiskers – technically called vibrissae in mammals – are an important part of my cats’ sensory arrays. When Margarita abruptly tears across the apartment for reasons I can only speculate about, her whiskers can tell her if she’s cutting to close to a wall so that she doesn’t run headlong into the doorway. And they’re certainly useful when she plays fetch. She fans her whiskers forward so that those hairs send vibrations back to the skin and she can orient her mouth just right to catch her “prey”, and the vibrissae on her arms help her triangulate the right angle of attack.
Such sensory structures aren’t unique to mammals, though. Some birds independently evolved feathers that act like whiskers.
While prominent feathers on birds’ faces might look showy, in many cases they actually carry alternate – or, at least, additional – functions. Simple, whisker-like feathers around the eye and nose can help keep out dust and dirt. And the motion of these bristle-like feathers can be felt in the skin, helping birds like the whiskered auklet navigate tight spaces. Now here’s where Velociraptor and company come in.
Non-avian dinosaurs keep getting fluffier and fluffier. Protofeathers and feather-like body coverings keep popping up all over the dinosaur family tree. While paleontologists have often focused on how these feathers may have been useful for insulation, display, and, in some cases, flight, the similarities between the ways my cats and whiskered auklets use their independently-evolved bristles made me wonder if predatory dinosaurs such as Velociraptor and Tyrannosaurus might have had specialized, whisker-like feathers on their arms or faces to help them make precision movements of claw and jaw when taking down prey.
Bird facial feathers trap debris and can be touch-sensitive. Was the same true of non-avian dinosaurs? From Persons and Currie, 2015.
I wasn’t the only one entertaining such scenarios. In a new Evolution article, University of Alberta paleontologists W. Scott Persons and Philip Currie speculate that some non-avian dinosaurs partially felt their way around the Mesozoic world with brushes of facial feathers. More than that, Persons and Currie suggest that the very first feather forerunners might have had more to do with touch than keeping warm.
Since the discovery of fluffy little Sinosauropteryx in 1996, paleontologists have centered on two different functions for the first feathers. A downy coat was probably useful for insulation, and, as reinforced by work on fossil feather colors as well as the anatomy of these structures, protofeathers could have been startling display feathers.
Each of these scenarios presents unresolved issues for feather origins. For protofeathers to be effective as insulation, Persons and Currie write, the fluff had to cover a significant part of the dinosaur. Perhaps fuzz really did start out this way, in swaths rather than as isolated wisps, but we need more exceptionally-preserved early dinosaurs to find out. And as for display, flashy dinosaur plumage is often said to be some sort of sexual or signaling structure without much further investigation. Given that paleontologists have been entertaining an ongoing debate about whether or not bizarre dinosaur structures can be considered signs of sexual selection, experts shouldn’t assume that what stands out to us was therefore the result of dinosaurian style preferences without more detailed investigation.
As an alternative, Persons and Currie suggest that feathers may have started as simple sensory structures. (They call them “bristles”, but paleontologists often use that as a general term for structures on dinosaurs like Psittacosaurus. Given the functional interpretation of the protofeathers, I’m going to keep calling the facial feathers whiskers here.) Cylindrical, whisker-like feathers on a non-avian dinosaur’s face may have had the dual benefits of trapping debris and providing another way to detect nearby prey or avoid smacking into a tree. From there, the researchers propose, additional fluff may have spread over dinosaurian bodies, eventually being co-opted to become warm coats, biological billboards, and structures useful for taking to the air.
While speculative, the idea that some dinosaurs had feathery whiskers isn’t outlandish. Today’s avian dinosaurs have feathers modified for this purpose, and perhaps some of their non-avian forerunners and relatives independently evolved the same structures. But the idea that whiskers were the original feathers is a little shakier.
No one, Persons and Currie point out, has found dinosaur whiskers yet. This might be because non-avian dinosaurs didn’t actually have them. But it may be that whiskers are only rarely preserved or haven’t been recognized just yet. For now, we can only hope that researchers stay on the lookout for possible dinosaur whiskers – and other odd plumage – as they continue to discover and study fossil dinosaurs.
The real test may be dinosaurs like Sinosauropteryx and Sciurumimus. These small dinosaurs had extensive coverings of simple protofeathers, but they haven’t yet shown any sign of whiskers on their arms or faces (where an enhanced sense of touch would be most advantageous). Either the structures haven’t been found or they were absent.
If the latter option is the case, it would be strange for carnivorous dinosaurs to evolve useful structures for detecting prey and then later lose those structures. Mammals offer a parallel case. The origins of hair are murky, too, but one hypothesis proposes that vibrissae were the first hairs. Rather than losing whiskers, though, mammals – particularly predatory beasts – retained them as fur covered the rest of their bodies. A lack of sensitive face feathers on archaic dinosaurs coated in fluff is a hurdle to the hypothesis that whiskers came first.
Whether dinosaurs had whiskers and what those plumes had to do with the origin of feathers are questions that may not be resolved for years to come. But there has never been a more wonderful and productive time for dinosaur paleontology. New finds and analyses are coming out at a rapid-fire rate, and Persons and Currie have formally articulated a hypothesis than can be checked against the fossil record. We’ve learned time and again that non-avian dinosaurs were stranger than we possibly could have imagined, and I wouldn’t be shocked if one day paleontologists came forward with whiskery, kitten-faced dinosaur.
[In a similar vein, I wrote about the possible acoustic properties of non-avian dinosaur feathers here.]
Persons, W., Currie, P. 2015. Bristles before down: a new perspective on the functional origin of feathers. Evolution. doi: 10.1111/evo.12634