Let’s look at some animals!
February 20, 2012
An important new paper is out:
R. Kent Sanders and Colleen G. Farmer. 2012. The pulmonary anatomy of Alligator mississippiensis and Its similarity to the avian respiratory system. The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology (advance online publication). doi:10.1002/ar.22427
(It’s paywalled, naturally, but let’s just assume that everyone who reads this blog is affiliated with a big university and has access.)
First of all, congratulations to the authors on doing this properly: publishing a proper paper (sixteen pages) to follow up their big-splash Science paper of just over a year ago. As Mickey Mortimer has shown, follow-through rates when people publish in Science and Nature are generally not at all good, and it’s always encouraging to see an exception.
Here’s the abstract:
Using gross dissections and computed tomography we studied the lungs of juvenile American alligators (Alligator mississippiensis). Our findings indicate that both the external and internal morphology of the lungs is strikingly similar to the embryonic avian respiratory system (lungs + air sacs). We identified bronchi that we propose are homologous to the avian ventrobronchi (entobronchi), laterobronchi, dorsobronchi (ectobronchi), as well as regions of the lung hypothesized to be homologous to the cervical, interclavicular, anterior thoracic, posterior thoracic, and abdominal air sacs. Furthermore, we suggest that many of the features that alligators and birds share are homologous and that some of these features are important to the aerodynamic valve mechanism and are likely plesiomorphic for Archosauria.
The main reason I want to post this (apart from the fact that it’s an important finding) is because someone had to blog David Marjanovic’s classic response on the Dinosaur Mailing List (quoted with permission, since David doesn’t have his own blog):
See, this is the kind of thing where I’m totally baffled that it wasn’t figured out a hundred years ago, or 120 or 130.
I suppose the logic that has prevented people from dissecting crocodilian lungs for so long went like this:
1) Crocodilians are reptiles.
2) So, crocodilians have reptile lungs, not mammal lungs or bird lungs.
3) What are reptile lungs like? Let’s dissect the nearest reptile and find out!
4) We’re in Europe, so let’s just take the nearest lacertid, perhaps the nearest “colubrid” and maybe the nearest viperid and cut them open.
5) <snip> <snip>
6) Hooray! We’ve figured out what reptile lungs are like!
7) Textbook describes and illustrates generic non-varanid squamate lung as “reptile lung”.
8) Everyone believes it is known what reptile lungs are like.
9) Everyone believes it is known what crocodilian lungs are like, because crocodilians are reptiles.
Ceterum censeo Reptilia esse nomen delendum.
If you must keep the name, follow Joseph Collins and restrict it to Squamata or Lepidosauria. Otherwise, destroy it. Kill it with fire.
We could draw a whole lot of conclusions from this analysis, but let’s just concentrate on one: look at animals. See how they behave. Then cut them open and see what’s inside. Don’t assume. Don’t guess. Find out. To quote the splendid motto of the Kirkcaldy Engineering Works, “FACTS, NOT OPINIONS”.
Seriously. Who’d have though there was a Science paper and an Anatomical Record paper just in cutting open an alligator and having a poke around in there? Sometimes, science doesn’t progress by paradigm shifts; sometimes it progresses just by looking at things.