Owner Comments:
In pursuing this thematic collection of coins featuring dinosaurs, one thing that has become readily apparent is that while there are many coins available with excellent depictions of surviving avian dinosaurs, there are very, very few coins which depict non-avian dinosaurs accurately. While there have been huge scientific advances in what we know about dinosaurs in the past two decades, outdated, scaly, traditionally reptilian depictions sadly continue to dominate outside of scientific circles, where it is arguably the most important to have accurate, up-to-date depictions. These outdated depictions are the worst where theropods are concerned, making it very hard to show the shared features between birds and their closest extinct relatives. However, there are some coins that have been minted in recent years that feature accurate depictions of dinosaurs which have a place in this collection and this silver $20 coin from Canada is among the best of these.
This coin depicts Albertosaurus Sarcophagus, a Tyrannosaurid which is a Coelurosaurian Theropod that is a relatively distant relative of Avians as Tyrannosaurids are outside of the clade Maniraptora, though it should be noted that some paleontologists state that a case can be made to include any Coelurosaur within Maniraptora based on many shared features, which the Albertosaurus on this coin displays. Unlike the surviving avians, Albertosaurus was a very large dinosaur, reaching lengths of over 30 feet and with weight estimates of up to 1.9 tons. It was of a lighter build and, likely, higher speed than its close relative Tyrannosaurus and was likely the apex predator of its time and range, which appears to have been restricted to the current Canadian province of Alberta but this can never be stated conclusively due to the incompleteness of the fossil record. Timewise, Albertosaurus existed from 71 to 68 million years ago, during the Late Cretaceous period.
In looking at the Albertosaurus on the coin, several similarities to living birds become readily apparent. The first one that jumps out at me are the legs and feet. Though they are more robust, as would be needed for a very large animal, they are virtually identical to the legs of most modern birds, featuring three toes in the front, a digitigrade walking stance and a pattern of scalation that is identical to that seen in modern birds, though many modern birds have different patterns of toe arrangement and the fourth toe, on the back of the foot typically, is important for perching. Albertosaurus had this fourth toe too, but it was a reduced, vestigial dewclaw on the inside of the foot as an animal as large as Albertosaurus wasn't flying around or perching in trees. Secondly, the body shape of Albertosaurus exhibits the distinctive theropod body plan that is shared among all theropod dinosaurs, including modern birds. The stance seen in Albertosaurus and many other non-avian theropods is slightly more horizontal than that seen in modern dinosaurs because of the long tail that they have, which needed to be balanced. Modern birds no longer have this long tail, instead having a pygostyle, which is a shortened, fused and compacted tail which supports their tail feathers.
The next obvious shared feature between Albertosaurus and its modern avian cousins is plumage. In this depiction, a fluffy coat of feathers can be seen on the neck, back and tail of the Albertosaurus. While it is a virtual certainty that Albertosaurus and other Tyrannosaurids had feathers, currently the only Tyrannosaurs known from specimens with preserved with feathers are Dilong paradoxus and Yutyrannus huali, both of which are evolutionarily older than Albertosaurus, meaning that it can be implied that later Tyrannosaurs also had feathers. So, the exact coat of feathers on the Albertosaurus in the depiction is hypothetical. They could have had more plumage in life, though it’s unlikely that they had less. Some researchers argue that due to the large size of Tyrannosaurs, it’s likely that most of them were scaly rather than feathered based on the almost total hairlessness of very large mammals today. However, there are serious flaws in this theory. The first is that comparing mammals and their hair to dinosaurs and their feathers is an apples and oranges kind of comparison. Feathers are much more efficient regulators of heat than hair is. While an African Elephant covered in hair in its hot environment would likely overheat, a feathered dinosaur of a similar size would likely not face that problem as feathers allow for more efficient thermoregulation.
Also, though mammals and theropods are both endothermic, that endothermy is of a different nature in the two groups as their last common ancestor lived over 300 million years ago. Mammals and theropods, and their ancestors, have been following their own evolutionary paths for over 300 million years, meaning that they share very little in common. The higher metabolic rate and thinner skin of theropods tends to cause them to lose heat faster than mammals do, so their main problem would be keeping the heat in rather than radiating it out. The second problem with a “scaly” Albertosaurus is that the previously mentioned Yutyrannus was almost exactly the same size as Albertosaurus and it had feathers all over its body aside from its face, hands and feet. I’d say that Albertosaurus and the other large Tyrannosaurs likely were covered in feathers over most of their bodies as well, making this depiction a little scalier and balder than the animal likely was in life. But it still has feathers, so that’s a huge plus!
While it is uncertain is Albertosaurus exhibited this next behavior or not, another feature that birds, especially raptors, share with other theropods is the regurgitation of pellets to expel the non-digestible parts of prey swallowed whole or in large pieces, such as bones, fur and feathers. The reason that it is uncertain if Albertosaurus produced pellets or not is that fossil pellets are impossible to assign to a specific animal. However, fossil theropod pellets have played an important role in paleontology as there are species of pterosaurs, fish and small dinosaurs that are only known from fossilized theropod pellets.
The last shared feature that I’d like to discuss with this coin is one that isn’t as obvious, but it is one that all Coelurosaurs share. That is the way they carry their hands. All Coelurosaurs have hands that are held with the two palms facing each other with the fingers running parallel. The hands are also very immobile and inflexible at the wrist. To have their palms face the ground, any Coelurosaur would have to lift their whole arm up perpendicular to the body. Birds have these same kinds of hands, but they are not visible as the three fingers of modern birds are all fused together skeletally and covered in flesh and skin, making them invisible in living specimens. However, it should be noted that the hands in Tyrannosaurs like Albertosaurus were likely vestigial and nearly useless to them while the hands of modern birds are a vital portion of their wing anatomy.
For centuries, humans have tried to discern where birds fit in the evolutionary history of life. Because of several features that they have that are unique among animals that humans have encountered, this has been a difficult task. However, the reason that birds have appeared to fit nowhere is that all of the animals that have shared features with them are extinct and have been for at least 66 million years. Thankfully, now the fossil record and diligent and excellent research and scholarship has filled in the gaps and decisively shown us exactly where avians fit; with their theropod relatives as members of the Dinosauria.