4 ms·...and mammals were all 3" or smaller. Not a world we'd want to live in.by JoeAltmaier 5y ago...and mammals were all 3" or smaller. Not a world we'd want to live in.ProAm 5y agoSpeak for yourself.notdang 5y agowho said that the planet needs the mammals?Koshkin 5y agoTo be fair, mammals just appeared around that time, so no wonder.