bird-mammal common ancestor

matt spitzer mwspitze at
Wed Sep 7 23:52:00 EST 1994

In article <memo.212676 at>, rkjb at (Ken
Brown) wrote:

> As for "closest living species", well we're all as close as each other. I
> suppose  the modern species with the nearest niche might be something like a
> monitor lizard, but you & me and the sparrow in the street are just as
> closely related to each other and to the common ancestor as a lizard is.
> That's what we mean by a "common ancestor" :-)

True, but some species, such as the horseshoe crab, are reputed to have
remained  relatively unchanged for millions of years.  So, if the common
ancestor had been an archaic form of horshoe crab, the answer to my
question would have been, well, you get the idea ;^)

The reason that this question came up is a controversy about whether a
brainstem nucleus involved in directional hearing which is similar in birds
and mammals is actually homologous, or simply analogous.  I'm trying to
figure out how to resolve this one, given that its somewhat challenging to
get good histology, let alone single unit recordings, from fossils.

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