The volcanoes -- well. There's a wonderful book from I think 1998, called
Night Comes To the Cretaceous, which says that in the Deccan, the
iridium-containing K-T boundary layer lies in the middle of a sedimentary
layer between two basalt beds, and the dinosaur fossils continue right up
to
it and stop there. There were no eruptions tens of thousands of years
before
and after the boundary. While global climate and suchlike was probably
affected by the volcanoes, they apparently didn't cause the K-T mass
extinction. _Basta_. =8-)
Someone wrote we have enlarged cerebella just to stay upright. In fact,
they
are smaller than expected for an ape of our size -- climbing seems to
require more RAM.
BTW, off-topic: The 6-million-year-old human has been named *Millennium
ancestor* (I hope they wrote it with nn in the original...). Apparently,
there are other people than HP Ken Kinman who think this find is Most
Important Of The Millennium.