Owner Comments:
Given that what we know of dinosaurs other than extant avians comes from fossils, discovering behaviors in extinct non-avian dinosaurs to link to their still living relatives is a difficult task. A fossil is often skeletal remains or footprints, which can give rough ideas of how fast an animal moved, how it may have looked in life and its size in life along with a very rough idea of what it ate. Overall, fossils are poor things to deduce behaviors from. In considering this, we have to take what we can get as far as shared behaviors but we are fortunate that some amazing fossils have allowed us to make an important link to a behavior shared by birds and other dinosaurs: nesting, brooding of eggs and parental care of the young once they hatched.
Fossilized eggs have been found from all three major groups of dinosaurs: theropods, sauropods and ornithischians. Nests have been found for both theropods and ornithischians. The lack of sauropod nests and the way the fossil eggs are positioned and located seems to indicate that sauropods simply laid their eggs as they moved, buried them and moved on, similar to how most modern turtles handle the task of reproduction. Obviously, this behavior is very different from what we see in modern dinosaurs, which all exhibit complex parental care behaviors. Much of what is known about breeding behaviors in ornithischians comes from some remarkably preserved fossil material from the Late Cretaceous hadrosaur Maiasaura peeblesorum. These amazing fossils show that Maiasaura built nests of rotting vegetation similar to those made by extant crocodilians, which are close evolutionary relatives of dinosaurs. These fossils didn’t just include the nest and eggs, it included fossils of babies with underdeveloped legs and worn teeth. This indicates that the babies both required parental care and received it and the worn teeth show that the babies were fed food brought to them by the adults in this species.
However, with this set, it’s the theropods that are important as birds are theropods. In the early days of dinosaur research, theropods got a bad rap when it came to eggs. While dinosaur nests associated with Oviraptorosaurs and Dromaeosaurs were found rather early in the study of dinosaurs, the assumption was that these Maniraptoran theropods were stealing the eggs of another dinosaur to consume. In fact, the name Oviraptor means “Egg Thief”. However, as it became known that these theropods were related to birds, these fossils were reexamined. In particular, there are two fossils of named species associated with nests, the Oviraptorosaur Citipati osmolskae and the Dromaeosaur Deinonychus antirrhopus.
When these fossils were reexamined, it was found that in both cases the dinosaurs were sitting on their own eggs and that they had died on top of their nests, protecting their young to the very end of their lives. The positions of the skeletons of the parent in both cases show a very bird-like brooding position and are further proof that these dinosaurs had feathers and that their long wing feathers were used for protecting and brooding their eggs. Further fossils of nests, eggs and groups of theropods with individuals of different ages, have come to light and been subject to examination, leading most paleontologists to believe that all theropods brooded their eggs and exhibited complex and extended parental behaviors. This certainly would be expected when observing extant avian theropods and the great care and protection that they give their eggs and babies.
Of all dinosaurs, theropods have the most advanced brains and are the most intelligent group of dinosaurs. They also often have young born in a very undeveloped state, much like we humans do. This reproductive strategy requires a high level of parental care. Also, like many extant avians, non-avian theropods appear to have had more learned behaviors and fewer instinctual ones when compared with sauropods and ornithischians as a result of their more advanced brains. This seems to be particularly true of Coelurosaurs, which is the group that includes birds. Many theropods likely needed to be taught how to hunt and kill prey, how to preen and care for their feathers and how to fly in flighted species. This fits with the growth process that many birds of prey, corvids and parrots, three of the most intelligent living dinosaur groups, have to go through in growing up.
These breeding behaviors are some of the most important behavioral links we have between birds and other dinosaurs because they are some of the only ones that the fossil record can tell us. I think that this gorgeous little 1/10th ounce Gold Eagle is the perfect coin to tell this part of the story as it has an excellent depiction of Bald Eagles, one of my favorite modern theropods, engaging in nesting behaviors much like those of their extinct relatives. However, the meaning of the depiction has a slight inaccuracy. The four eagles on the coin are meant to represent the four different sized Gold Eagle coins and, from what I read, the male eagle is supposed to represent the largest coin, the 1 Ounce $50 piece. With raptors such as the Bald Eagle, the female is almost always considerably larger than the male and this is true with the Bald Eagle, so the 1 Ounce should be the female’s coin and the male should get the half ounce. My coin obviously gets the little tiny fuzzy baby eagle!