Aerosteon riocoloradensis: a new dinosaur from Argentina

Flesh rendering of the predator Aerosteon with the body wall removed to show a reconstruction of the lungs (red) and air sacs (other colors) as they might have been in life.

Flesh rendering of the predator Aerosteon with the body wall removed to show a reconstruction of the lungs (red) and air sacs (other colors) as they might have been in life.

Greg Laden has the scoop on the new Argentine dinosaur that was featured on Daily Planet. It is called Aerosteon riocoloradensis.

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).

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.

Aerosteon riocoloradensis also represents a previously unknown group of South American dinosaurs, which may be ancestral to allosaurs.

Bora Zivkovic at A Blog Around the Clock also has an article: a new dinosaur with hollow bones.

I always get excited when Paul Sereno publishes a paper in PLoS ONE and today is one such day – his third paper in this journal within a span of less than a year (the first was the paper with detailed description of Nigersaurus and the second was the article on Green Sahara cemeteries). Today’s paper is also the second time PLoS ONE publishes a taxonomy paper, i.e., a monograph that describes a new species:

Evidence for Avian Intrathoracic Air Sacs in a New Predatory Dinosaur from Argentina:

Paul Serano, you’ll remember, is National Geographic’s Explorer in Residence.


6 Responses to “Aerosteon riocoloradensis: a new dinosaur from Argentina”

  1. freidenker85 Says:

    What I don’t get is what did that Dinosaur do with those brittle little arms? if that sketch is any indication to the fossil, that is. Even enormous predators have to grab their prey.

    A fascinating aspect of dinosaur/avian evolution would be the intermediate stages between scaly arms to feathered wings (or even sky-divers!) I remember archeopteryx to be a good example of the intermediate stages of “birds slowly losing their bones” on their way to avian supreme power flight, but I don’t know much of what the “half a wing” with the reptilian traits was like.

  2. monado Says:

    Well, let’s see. Snakes and crocodiles don’t use arms to grab their prey; neither do wolves. I think that the allosaur and tyrannosaur dinosaurs just lunged; they look well balanced for it. There has been lots of discussion about why they have those little arms; in particular I remember the observation that the arms of Tyrannosaurus were too small to reach its mouth! We can’t go back and observe them but I believe that biomechanical analysis supports the hypothesis that they were used to brace the dinosaur against sliding forward when it rose from a resting position on the ground.

    It’s important to remember that each of the organisms in the past was a fully functioning member of an ecology on its own, and not half-way to anything in its opinion. I doubt if a seal thinks it’s half-way to a whale, for example. It can go on being a seal forever as long as the competition for fish doesn’t get to be too much.

    It’s pretty clear that feathers developed on small, non-flying dinosaurs for any number of other reasons. In my opinion, insulation was probably first. Fossils have been found with a layer of fuzz like a bird’s down — soft, short, multi-branched feathers. Then there are ones with strong feathers that have a central shaft, which would form a thicker and more adjustable insulation. But all the feathers are symmetrical, which means they weren’t used for flying, which needs unequal air flow to provide lift. (When we see feathers with a short side and a long side, it’s an adaptation for flight.) Once there were feathers, they could be selected for colour differences that provided camouflage, seasonal colour change, mating displays, etc. I’ve seen with my own eyes fossils with feather impressions that have dark and light colour bands like a hawk’s feathers, which in a living bird would make a coloured pattern. Sexual displays of fitness might encourage the development of large, flashy feathers on the arms, legs, and tail.

    Many of the adaptations that allowed flight, such as hollow bones and efficient breathing, came long before it. The allosaurs had hollow bones, which was an adaptation to give strength without weight, like a bicycle’s frame. It’s not given as a reason in the article, but I think that the flow-through oxygen system helped large, fast-running dinosaurs to dump heat from their interior mass. Similarly, many of the skeletal changes that we see in birds start in these large, running dinosaurs, e.g. extension of the ankle bone up the shin. There’s a real continuum.

    Finally, there’s still a controversy about how flight developed. We are groping our way through the evidence. Some people think that a small, running dinosaur “took off” after using feathered forelegs for balance or to run up steep surfaces. I lean towards the other idea, that climbing birds learned to glide and then to control their glide. The hoatzin is a South American bird in which the nestlings have retained a couple of claws at the wing “wrist” and are very agile clambering about and getting back into the nest if they fall. Several years ago, a fossil nestling with three claws at the “wrist” was found. I thought it was very interesting that the claws were shorter near the shoulder and longer near the wrist, so that a bird hanging by its claws would be nicely level. I don’t remember the species name.

    Finally, look up Microraptor – they’re cute. Someone predicted that early flyers would have primary feathers on the legs as will, but I can’t remember who.

    All this writing makes me want to go and look up links to my previous articles for you.

  3. freidenker85 Says:

    This was FASCINATING! Thank you so much! I wonder if there’s anywhere I can have a clear explanation for the biomechanics of flight. For starters, I don’t understand why birds need free air flow in their wings to allow for flight. How deep into aerodynamics must I delve in order to understand this?

    About microraptor: is the “wrist” some sort of a vestige for a “hand” that was lost? If these nestlings can fly, how come they had any “vestigial fingers” (claws, in this case) left? Or maybe I’m mixing up vertebrate anatomy here.

    Your detailed explanation about the evolution of flight was beautiful, I’m going to copy it into a text file!

  4. monado Says:

    The basic principle is something pretty simple in physics. Look up “airfoil.” Bernoulli’s Principle says that the faster air flows over a surface, the lower the pressure on that surface. It sounds wrong, but you can prove it mathematically. What that means for airplanes and birds is this: The top and bottom of the wing have to be shaped differently. Air has to travel farther over the top surface, so that it travels faster. That lowers the pressure and creates lift: the higher pressure on the under surface pushes the wing up.

    Does that make sense?

  5. freidenker85 Says:

    Actually, it does! Although I think I might be able to understand it better if you get a bit more mathy on me. I have secondary school level physics, so this mechanics thingie could make sense. I still don’t see how a higher flux of air (which on the surface seems to imply that there’s greater pressure on the surface of the air) can possibly decrease the pressure. This seems to contradict basic physics to me.

  6. monado Says:

    Just look up “Bernoulli’s Principle.” It is basic physics.

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