Sink or swim?
Bone density as a mechanism for buoyancy control in early cetaceans
Noel-Marie Gray cs 2007
Anat Rec 290:638-653 doi 10.1002/ar.20533.

Previous analyses have shown:
secondarily aquatic tetrapods (incl. whales) exhibit osteological adaptations to life in water, as part of their complex buoyancy control systems.
These structural specializations of bone span hyperostosis through osteoporosis.
The past 15 yrs of paleontological effort has provided an unprecedented opportunity to examine the osteological transfm of whales:
the transition to an obligate aquatic lifestyle over a 10-My period.
Do whales manifest their osteological specialization in the same manner as extant semi- & fully aquatic mammals?
We present a micro-structural analysis of bone in early & late archaic Cetacea, in a comparative sample of modern terrestrial, semi-aquatic & aquatic mammals.
Bone histology was examined from the ribs of 10 fossilized individuals of 5 early cetacean families: Pakicetidae, Ambulocetidae, Protocetidae, Remintonocetidae, Basilosauridae.
Comparisons were made with rib histology from 9 genera of extant mammals: Odocoileus (deer), Bos (cow), Equus (horse), Canis (dog), Lutra (river otter), Enhydra (sea otter), Choeropsis (pygmy hippo), Trichechus (sea cow), Delphinus (dolphin).
Results:
the transition from terrestrial, to semi- to bligate aquatic locomotion in Archaeocetes involved a radical shift in bone function, achieved by means of profound changes at the micro-structural level.
Surprisingly, micro-structural change predates gross anatomical shift in archaeocetes ass.x swimming.
Histological analysis shows:
- high bone density is an aquatic specialization that provides static buoyancy control (ballast) for animals living in shallow water,
- low bone density is ass.x dynamic buoyancy control for animals living in deep water:
there was a shift from the typical terrestrial form, to osteopetrosis & pachyosteosclerosis, and then to osteoporosis in the 1st quarter of cetacean evol.history.

_____

IOW, only ridiculous kudu runners deny:
H.erectus' osteopetrosis & pachyosteosclerosis (POS) indicates shallow-diving.

Sorry for the title (becoming too old? too fast? too angry?):
should be: "incredible" instead of "incridibly", of course...

Op zondag 9 april 2023 om 11:25:02 UTC+2 schreef littor...@gmail.com:
> Sink or swim?
> Bone density as a mechanism for buoyancy control in early cetaceans
> Noel-Marie Gray cs 2007
> Anat Rec 290:638-653 doi 10.1002/ar.20533.
>
> Previous analyses have shown:
> secondarily aquatic tetrapods (incl. whales) exhibit osteological adaptations to life in water, as part of their complex buoyancy control systems.
> These structural specializations of bone span hyperostosis through osteoporosis.
> The past 15 yrs of paleontological effort has provided an unprecedented opportunity to examine the osteological transfm of whales:
> the transition to an obligate aquatic lifestyle over a 10-My period.
> Do whales manifest their osteological specialization in the same manner as extant semi- & fully aquatic mammals?
> We present a micro-structural analysis of bone in early & late archaic Cetacea, in a comparative sample of modern terrestrial, semi-aquatic & aquatic mammals.
> Bone histology was examined from the ribs of 10 fossilized individuals of 5 early cetacean families: Pakicetidae, Ambulocetidae, Protocetidae, Remintonocetidae, Basilosauridae.
> Comparisons were made with rib histology from 9 genera of extant mammals: Odocoileus (deer), Bos (cow), Equus (horse), Canis (dog), Lutra (river otter), Enhydra (sea otter), Choeropsis (pygmy hippo), Trichechus (sea cow), Delphinus (dolphin).
> Results:
> the transition from terrestrial, to semi- to bligate aquatic locomotion in Archaeocetes involved a radical shift in bone function, achieved by means of profound changes at the micro-structural level.
> Surprisingly, micro-structural change predates gross anatomical shift in archaeocetes ass.x swimming.
> Histological analysis shows:
> - high bone density is an aquatic specialization that provides static buoyancy control (ballast) for animals living in shallow water,
> - low bone density is ass.x dynamic buoyancy control for animals living in deep water:
> there was a shift from the typical terrestrial form, to osteopetrosis & pachyosteosclerosis, and then to osteoporosis in the 1st quarter of cetacean evol.history.
>
> _____
>
> IOW, only ridiculous kudu runners deny:
> H.erectus' osteopetrosis & pachyosteosclerosis (POS) indicates shallow-diving.

littor...@gmail.com wrote:

> Sorry for the title (becoming too old? too fast? too angry?):
> should be: "incredible" instead of "incridibly", of course...

Apparently I was too old too fast in the 1990s...

What was I going to say? Oh yes:

i was going to start a thread but that seems impossible these
days so I might as well just ask you about Denisovans.

Supposedly Tibets "Adapted" to high altitude at least partly by
acquiring some useful DNA for doing just that, and getting this
DNA from the Denisovans.

Why would the Denisovans have it? They seem nearly entirely
associated with warmer climates -- southeast Asia and the
pacific -- but then some odd group took to the mountains?

So what I am speculating on here, more or less just tossing it
out there, is what if the adaptations that allowed for exploiting
low levels of oxygen was an emergent trait? You know, like they
dove a lot, perhaps swam a lot and water not being a great spot
for breathing, adapted to cope with low levels of oxygen?

It's the kind of evolutionary quirk I'd look for, rather than Intelligent
Design.

The thing is, it's kind of necessary for them to acquire the
adaptation so they could experience the selective pressure to
acquire the adaption, in the mountains. Not so in the sea. They
could dive without it, swim without it but not as well... so they
could perform the act AND experience selective pressure to be
better at performing it.

But, high altitude cultures?

-- --

https://jtem.tumblr.com/post/714091698115035136