Fossils of a newly discovered species of dinosaur — a 10-meter-long, elephant-weight predator — were discovered in 1996 along the banks of Argentina’s Rio Colorado, and are now being reported after a long period of careful study. This dinosaur dates to about 85 million years (which falls within the Cretaceous period).
~ A repost, because it is still an amazing dinosaur ~
Perhaps the most interesting feature of Aerosteon riocoloradensis is that it demonstrates the evolution of a bird-like respiratory system in an animal that is definitely not bird-like in most other ways. Indeed, the authors of this paper imply that this dinosaur’s respiratory system represents an early phase in the evolution of the bird’s respiratory system. This is a case of an adaptation arising in one context and later being used in an entirely different context.
This is how evolution often works: An adaptation arises for one reason, and then that adaptation is employed in a similar way but for a very different purpose (it is “exapted” as Stephen Gould would say) in a later organism. In this case, we see a lung adapted for a certain kind of efficiency in a terrestrial organism. Later, if the authors are correct, this same efficiency-enhancing adaptation is used in birds as an adaptation related to flight, an entirely different reason.
This diagram shows a reconstruction of the dinosaur Aerosteon riocoloradensis in outline, with the features identified as related to the pneumatic (breathing-related) adaptations indicated. You can access the original paper on line if you wish to study these features in more detail. Suffice it to say that there are a lot of pneumatic features of interest!
In order to understand the significance of this find, it may be helpful to first discuss some interesting things about tetrapod lungs, and bird lungs in particular.
Continue reading Aerosteon riocoloradensis: A Very Cool Dinosaur from Argentina →