I’ve been thinking a lot about chickens’ feet lately. Not as as a convenient snack, like the vacuum-packed ones left on a hotel pillow (alongside a packet of condoms) for my parents to enjoy on a recent trip to China. But as a little reminder that chickens are actually dinosaurs.
The whole avian dinosaur thing has crept up on us over the years, hasn’t it? Children’s encyclopedia facts shifting under middle aged feet, kooky science factoids becoming simple commonsense. The plastic dinosaurs in the kids’ toy basket, made in the 70s, are discredited heritage items now, with not a feather in sight.
When I was a fledgling, Archeopteryx was the only bird-like dinosaur around. But now, it’s just one of many, and not even the earliest (a title currently held by Aurornis xui, which was covered with fine proto-feathers most likely used for insulation and probably couldn’t fly. Naturally, Aurornis is described as “chicken sized“)
I’ve been reading John Pickrell’s Flying Dinosaurs (University of New South Wales, 2014), and he notes that “there is now good evidence that many carnivorous theropod dinosaurs, even fearsome and well known species – such as Allosaurus and Tyrannosaurus – had feathers” (Pickrell, 2014, 84).
Wow! You could knock me over with one of those proto-feathers.
Dinosaurs did all kinds of bird-like things. Mei Long tucked her head under her elbow to roost for the night (Pickrell, 2014, 48). Fossils show Citipati osmolskae crouching over its eggs like a broody hen (Pickrell, 2014, 179). T.rex seems to have suffered from trichomonosis, a potentially lethal parasite that which rots away the jawbone. Contemporary birds of prey catch it from eating pigeons; T.rex might have got it from gnawing at each others’ faces. (Pickrell, 2014, 60)
I discovered some crazy facts about birds reading this book. For instance, birds have smallest genome of the vertebrates – and bats’ genome is pretty small too. Smaller cells with large relative surface area means better gas exchange and greater efficiency, enabling the high metabolic rate required for flying. Apparently hummingbirds, with the fastest metabolism amongst birds, also have the smallest genome (Pickrell, 2014, 58).
Hard to believe that such tiny tiny changes could make a macro difference, but I guess if you’ve given up teeth and a jawbone to save weight, economising on your genome seems like a mere bagatelle. Inferring genome size from the space of lacunae in bones, researchers have proposed that between 230 and 250 million years ago saurischian dinosaurs – ancestors of the birds – also started to have smaller genomes, while the bones of your triceratops or hadrosaur soldiered on unchanged (Pickrell, 2014, 59).
I was amazed to read that birds don’t breathe like mammals: they have a one-way respiratory system with multiple air sacs that, when inflated, help make them light enough to fly. When birds breathe, the air flows into their their bones! And some dinosaur skeletons reveal the same spongy, pneumatised bones (Pickrell, 2014, 49-50)
It’s perhaps ironic that chickens’ scaly feet scream “dinosaur” to me, because one of the earliest feathered dinosaurs was Anchiornis huxleii which actually had feathers on its hind legs as well as its forelimbs. In fact, there were loads of early feathered dinosaurs that looked like this. Paleontologists are still trying to work out quite how it could have used these rear legs in flight without dislocating its hips – they were probably for used to enhance aerodynmics or to create drag (Pickrell, 2014, 114).
The startlingly speedy progression of our chicks from tiny bundles of fluff to whopping great layers, made sense of the notion of paedomorphosis, a process in which animals reach sexual maturity at an earlier stage of development
In comparison to the slow maturing reptiles, birds, like mammals, grow quickly in early on. Interestingly, as they mature, birds’ heads don’t change much in shape; in comparison most dinosaurs’ skulls morphed dramatically, the comparatively large, spherical noggins of babies elongating into the snouts and jaws of adults (Pickrell, 2014, 54). US researchers Bhart-Anjan Bullar, Mark Norell and Timothy Rowe noticed Archeopteryx’s adult skull is rounded just like the babies of other dinosaur species, and concluded that the ancestors of birds maintained juvenile characteristics later in life. This process of paedomorphosis (or neoteny) often goes along with smaller body size. It seems to allow the emergence of a new and unexpected set of features in an organism. Harvard’s Bhart Anjan-Buller observes “These unique characters may allow the exploitation of radically different ecological niches from other similarly sized organisms” (Pickrell, 2014, 56).
And birds have surely filled those ecological niches. There are aroundabout 10,000 living species of birds, far more types of avian dinosaurs than all the non-avian kind that ever lived. “Dinosaurs are now more successful than they’ve ever been, but they all look the same” says Paul Barrett of the Natural History Museum, “With the exception of a few aberrations, they are all bipedal flyers” (Pickrell, 2014, 28).
And let’s not beat around the bush, a really really big percentage of those living dinosaurs are chickens. There’s a global chicken population explosion: there are now about three times as many chickens as there are humans – in the 1960s we were about eekies. And that’s not even considering the ratio of domesticated to wild animals. According to the RSPB, there are maybe 30 times as many domestic chickens as there are the most numerous kind of wild bird, the African dwelling red-billed quelea.
In fact, best not to dwell on this to prevent yourself being plunged into depression about the forthcoming Age of Loneliness, when we humans will mostly likely have few non-human companions. Better get used to the company of rats, cockroaches, and jellyfish. Maybe we’ll have a few bats – to my surprise, there are more species of bats than any other type of mammal except rodents (Pickrell, 2014, 107). And, of course, chickens. Lucky I love my avian dinosaurs.
(You wouldn’t believe the confused and irritated looks the chickens have given me as I’ve been taking these pictures of their feet. Sorry guys.)