The fact that birds are the direct descendants of dinosaurs is now and overwhelmingly supported theory in palaeontology, though most will not know much beyond the recent plethora of discoveries of feathered dinosaurs. While these are obviously a wonderful example, the ancestry of birds is more than skin (or feather) deep and since mostly palaeontologists work from bones it may not be a surprise to learn that you can see plenty of dinosaurian traits in your Christmas dinner.
A typical roasting turkey is already missing the head, probably the neck and the feet, all of which contain some key traits to identify them as dinosaurs. Still, as you carve your way through your dinosaurian dinner there are plenty of features remaining that can point you to the evolutionary history of the main course. Although birds have the best part of 140 million years of adaptation to flight behind them (and then quite a lot of change wrought by domestic breeders) there are multiple features that can easily be traced between them and their predecessors. Let’s start with one that should be familiar to everyone – the wishbone.
Properly called the furcula, this is actually a fusion of two bones into one the collarbones or clavicles. For a long time this was considered to be absent in dinosaurs as none could be found even though other reptiles retained clavicles. However, a plethora of recent discoveries shows that in fact it was common in dinosaurs and multiple animals close to birds possessed this unusual bone. In fact we now even have multiple examples of Tyrannosaurus with a furcula, and while it obviously has a few differences, the characteristic V or U-shape and little paddle-like plates at the ends, mark this clearly as a bone shared by birds and their antecendents.
Sticking to the chest, the huge breastbone of birds is linked to the huge flight muscles that anchor there, but this is also, albeit rather smaller, a feature of the more bird-like dinosaurs. The small feathered dinosaurs like Velociraptor and Microraptor and quite unlike earlier forms had a huge pair of plate-like bones that sat below the furcula in the chest. Other dinosaurs lack this feature but those closest to the origins of the birds expanded this area considerably and the huge, and now keeled, sternum of birds harks back to this.
Lastly in the torso are the ribs with their unusual reversed processes. Few may see this normally, but boil down your carcass for soup or a stew and the rib cage should become clear of the remnants of lunch and show off the bizarre shape. Each rib rather than the simple curved rod of most animals has a little (or even quite large) extension from them, making the long piece like a very odd and stretched out lower case ‘t’. These go by the name of uncinated processes and are another feature seen in birds, their nearest dinosaurian predecessors (including Velociraptor again) and, well, not much else (oddly a few digging mammals also have these, they help strengthen the ribcage).
Anyone who ends up with a wing can also have a look at the end of the humerus (upper arm bone) closest to the shoulder joint. If you clean it up a bit there should be a rather obvious large cavity going into the bone. This is one of many pneumatic openings in birds (you may find a few others if you hunt around, including on the various bits of the backbone but this is a nice and obvious one) which allows extensions of the lungs to penetrate into the bones which are thin and hollow. Yes, birds literally have air-filled bones and if you crack one open you will see just how thin the bones are and in part why birds are so light for their size.
Finally the feathers might be present in your dinner (unless something went rather badly wrong) but their presence can still be seen, or at least felt. If you get hold of the wing bones and locate the ulna (the larger and straighter of the two bones below the humerus) run your finger along its outer edge. Unlike the shafts of other long bones in your turkey this will not be smooth and straight but will have a series of humps along the surface. These are called quill knobs and mark the point at which some of the largest flight feathers in the wing actually articulate with the bones. These are also found in some dinosaur fossils, so even when the feathers are not preserved we can see the traces in the bones of their original presence.
These are the easiest features to spot though a few more like the very wide range of motion in the shoulder and the shape of the wrist bones (if you can dig them out) are also key features of some of the most bird-like dinosaurs. Incidentally, it’s not just the turkeys that have these traits either, all birds share these features at some level so those sitting down with a goose, duck or chicken will also see the same things, although anyone plumping for lamb might struggle to find uncinated processes or a furcula.
That birds really are dinosaurs is a critical part of our understanding of the evolution of these amazing groups but it can be hard to comprehend so hopefully this will make things a little more clear with some nice anatomy to help while away the post-lunch respite while we all wait for the inevitable Bond film to start up.
Merry Christmas to all the Lost Worlds Revisited readers and more palaeontological features will be appearing in the coming week and new year. For more details on dinosaurian traits in a turkey, try this feature by palaeontologist Dr Tom Holtz.
