Ok, So Anyway, I Was Contemplating Pachyostosis

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whut? i'm serios. ever since i discovered that i myself was comprised to some extent of hydroxylapatite, i've been interested in bones and teeth. and occasionally, i would run across a bone that just didn't fit into my worldview. like thissun here -

and then one day it hit me - these things are pachyostotic (no idea if that's really the predicate adjective form of pachyostosis or not - just winged it). so anyway, note that it is obviously a rib bone from a manatee (or a plesiosaur). snapped in half to demonstrate to you the singularly plural lack of trabecular/cancellous/spongy/nameityourself bone. now if you've never majored in structural engineering, you might not realize that this is NOT the way to build a bone if you're looking for structural strength. yes, i realize that's counterintuitive - counterintuitivity is my field of specialization. there was a point in here somewhere...oh! i studied this doctoral thesis paper thingee and learned that manatees get hit by boats too much, that cracks their ribs, in part because their ribs are made for weight to overcome their buoyancy, not for strength to overcome your boat whacks. so this is interesting, and i therefore memorized the attached document, and you should too. and bear in mind while in the process of memorization, that this is precisely why i do not hang out in academia...

light reading

[Auspex]

light reading

[fossisle]

He aint heavy he's my manatee!

[TourmalineGuy]

That is a great title to an article (good article too). I have to ask, how did you ever find it? The topic is somewhat...obscure.

"Drying, heating, freezing, embalming, or storing bone in saline or alcohol solutions can alter the material properties of bone. It is best to use freshly harvested bone when possible. If it is not possible to harvest fresh bone, it is recommended that the bone be wrapped in plastic wrap and stored in airtight bags in a freezer at -20° Celsius (An and Draughn, 2000). Properties will be best maintained with the muscles and soft tissues attached, although hydrating with saline solution after wrapping the bone in gauze is a reasonable alternative if storing the bone for shorter periods of time."

So I'll make sure to "harvest fresh bone" in the future.

Also, I'm happy I'm finally using my structural engineering degree for something.

[Boesse]

Early on in whale evolution, most archaeocete whales were characterized by osteosclerotic and pachyostotic bone. For whatever reason, during evolution of the 'neoceti' (crown-group cetaceans, basically toothed + baleen whales) this trend was reversed, and cetaceans are technically osteoporotic.

Now, not sure how this guy defines pachyostosis, but pachyostosis is typically defined as 'inflation' of the outer surface of the cortical bone, while osteosclerosis is inward expansion of the cortical bone, making the cancellous portion/marrow cavity smaller and narrower in cross section (and thus volumetrically smaller). So, I've heard definitions of this (from paleohistologists) as density-independent.

I just looked up what wikipedia had to say about osteosclerosis, which was density-relative; perhaps this is a medical definition (i.e. opposite of osteoporosis), while the inward expansion of cortical bone may be a histological definition.

Bobby

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bobby - i don't really think i remember pachyostosis defined in the thesis i referenced - i was using the term as i understood it from having read it somewhere else, i think. at any rate, to me anything involving "sclerosis" would be an abnormality - a medical condition.

and it is interesting that the pachyostotic method of addressing buoyancy, etc. was tried and abandoned by the whaley critters, but kept by the sirenians. i would think that would have something to do with a greater need in cetaceans for a stronger skeletal structure, and it might also have something to so with allowing pressure equalization to occur as the animals change depths?

i always cringe when i speculate too much, but it's fun to do.

[Boesse]

In the paleontological literature (I can't speak for the zoological literature) these terms are applied to denote a histological condition, but not necessarily a condition that is abnormal - at least, abnormal relative to the species; they are used (in these cases with marine mammals) to denote a condition relative to 'normal' terrestrial mammals (which, for all intensive purposes, have similar histologies to humans, which are often the regularly used baseline).

It is probable that during the evolution of neoceti, one of two things occurred: 1) a major change in physiology altered the density of their bodies or 2) a major change in behavior required a change in bone density. It is very possible that deep diving became more important for early neoceti, and that osteoporotic bones made rising to the surface to breathe more efficient.

Bobby