Aepyornis femora of the Oxford Museum of Natural History
March 18, 2018
By contrast to the very delicate pelican humerus and ulna in the previous post, here is the left femur of Aepyornis OUMNH 4950 — an “elephant bird” from Antolanbiby, Madagascar. It’s just a couple of meters away from the pelican, in the same Oxford gallery:
This is of course a ludicrously robust bone, as befits a gigantic ground-dwelling bird. But the fun thing is that it, too, is very pneumatic. You can see this in lots of ways: the foramina up at the top, the little patch of stretched texture at mid-length, and most of all in the honeycomb structure of the inside of the bone, which we can see where the cortex has broken off at both proximal and distal ends.
Birds: they’re made of air.
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March 18, 2018 at 3:42 pm
I have a developmental question about pneumaticity.
When in the life of an individual (dinosaur, bird, or mammal) do pneumatic cavities first become (only) air-filled, rather than (as I presume they begin) fluid-filled?
As newborns have to void their lungs of fluid to take their first breath, is that the same for hatchlings?
Are birds hatched (and were dinosaurs hatched) with their lungs AND all air sacs and pneumatic spaces filled initially with amniotic fluid, that then had to be drained somehow? Quite a workout, I imagine!
Or do/did the pneumatic systems of bird/dinosaur individuals start really simple (just their trachea, lungs and major air-sacs) and then, as they grow/grew up, expand into the various diverticulae? (Increasingly numerous, more elaborate and larger, over their lifespan?)
March 18, 2018 at 4:03 pm
Great questions! Perhaps the literature on extant birds contains the answers. If it does, Matt may well know about it — I certainly don’t. But you can start with Wedel 2006
March 18, 2018 at 4:35 pm
As far as I know, the development of pneumatic spaces always comes after hatching (for birds and crocs) or birth (for mammals). That is certainly true for human sinuses and postcranial pneumaticity in birds. See papers by John A. Bremer in the 1940s, A.S. King in the 1950s, and D.A. Hogg in the 1980s on chicken pneumaticity. Most of these will be cited in my dissertation, which is free and easy to find (would give a link but I’m in a hurry).
EDIT: Oh, Schepelman (1990) on pigeons is also good, and helps demonstrate that the post-hatching pneumatization seen in pigeons does generalize to at least some other birds. And the link to my dissertation, which cites all of the above, is here: https://sauroposeidon.files.wordpress.com/2010/04/wedel-2007-dissertation1.pdf
March 19, 2018 at 3:37 am
Whoa, humans are born without sinuses? or do we drain them after birth?
March 19, 2018 at 3:58 am
Some sources say that the excavation of the sinuses starts before birth, but if so, it is extremely minimal. Even at one year old, our frontal and maxillary “sinuses” are just tiny, shallow pockets on the walls of our nasal cavities – you could fairly call them pneumatic fossae. From that point, expansion of the sinuses basically follows growth of the facial bones. So in someone 10 years old, you’d expect the sinuses to be only 1/2 to 2/3 as extensive as they are in most adults. There are good images of the development of the sinuses in the better anatomy textbooks, and you can find lots by doing an image search for “sinus development”.
March 20, 2018 at 4:44 pm
I wonder if that might put some kind of size limit on how large a tetrapod can be when it is born. After all, if you can’t be born with sinuses, and if you need hollowed bones/sinuses/whatever (e.g., elephant sinuses, in addition to the examples mentioned here) to reach a certain size, then that’s going to put a hard limit on how large your offspring can be at birth.
March 20, 2018 at 4:47 pm
I’m not following. Why can’t you be born small and apneumatic, then develop pneumaticity as you grow? As indeed, sauropods did and birds do?
March 20, 2018 at 5:30 pm
Well, elephants have apneumatic postcranial skeletons, and so did indricotheres. Presumably a full-term fetus of some hypothetical giga-mammal could be the size of an adult indricothere without suffering any penalty from the presumed no-pneum-before-birth rule. And that’s assuming that indricothere adult size was biomechanically limited, which it probably was not.