Re: Two more gaps in the fossil record

Jonathan Clarke (
Sun, 17 Oct 1999 09:05:39 +1000

Hi Glenn

A terminology question here. What is meant by "hollow bones"? Many bones have a
central cavity, filled in life by marrow. All bones also are porous. What
distinguishes the follow bones of birds from these? I recall reading somewhere
that the hollowed bones of birds contain air sacs. This was supposedly to aid
high respiration rates. Is this correct for all hollow bones in birds? If true,
is a different adaptation to aerial life than simply reduction in weight, a
feature found in other flying vertebrates like bats and pterosaurs. Did these
taxa also have how bones in the same sense as birds?

God Bless

Jonathan wrote:

> At 07:59 PM 10/15/1999 -0700, Cliff Lundberg wrote:
> >As to the matter of hollow bones, one may wonder which came first, the
> >light hollow bones that facilitate flight and rapid respiration, or the
> flight
> >that brought selection pressure for such bones. There may have been niches
> >in which lightness and high metabolism was advantageous for a terrestrial
> >organism. For example, in trees or in dry open country, neither of which are
> >likely spots for fossilization.
> Hollow bones break easily, they are a decided disadvantage to a land-living
> creature. If there were an advantage, why no hollow boned mammals today?
> glenn
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