So I can agree that the ear of a dinosaur was probably worse than the ear of a mammal, as they had not our 3 ear bones, but I wouldn't be so sure in the case of the eyes. In the case of the brain, well, today the brain full of circunvolutions of a mammal seems to be superior and more able to develop inteligence than the smooth brain of a bird (or a dinosaur, or a crocodyle), but where was the mammal brain 65 million years ago? I don't know if there is any mold of a mammal brain in the fossil record from that age. It can be a more recent adaptation... an adaptation that an alternate lineage of post K/T dinosaurs could develop as well.
Nonsense, the basic design of the placental mammals and the typical brain of the placental mammals was already around in the mid-, perhaps even the early Cretaceous, and the lineages of placental mammals were already growing apart
long before the K-T mass extinction,
(relatively recent genetic research and recent fossil findings strongly suggest that the lineages of the marsupials and the placental mammals split about 175 million years ago, and the same genetic research suggests that the four major lineages (the four cohorts that were proposed on the basis of genetic analysis) of placental mammals grew apart IIRC at least 100 million years ago), and because all the mammals from these lineages (i.e. all the known placental mammals) clearly share this same brain type, the simplest and most propable explanation for that is that this basic brain type was present in their common ancestor.
And the advanced brain of the placental mammals did not just come out of the blue. Basically, after the dinosaurs began to dominate in the Triassic, all the ancestors of the mammals did was evolve to become more efficient and make up for no longer being the biggest and strongest beast around, and evolving more efficient brains was part of that whole evolution.
And then about the propability of a branch of dinosaurs developing such a complex brain: assuming for a while that there is 75 million years between the (proto-)placental mammals separating from the marsupials, and the point that the common ancestor of all modern mammals lived, then the whole process of developing the typical mammalian brain took *at most* 75 million years, and propably somewhere around 50 or 60 million years (but that's a guesstimate), so it's not exactly something the dino's would 'just do' in a few million years...
And even if it was an ancient adaptation, does it really matter? 60% of present day mammals, if not more, are rodents as dumb as the mammals who lived with the dinosaurs. Is the equation mammal brain = more inteligence = superiority really correct? Probably not.
Actually, about 50% of the present day mammalian species are rodents, then about 25% are bats and all the other mammals make up the remaining 25% of the mammalian species.
And many rodents aren't exactly dumb (just look at rats), and I'm pretty certain that today's rodents are on average a lot smarter than most of the mammals that scurried around during the Mesozoic, although most mammals that lived during this age (even the Cretaceous) were not placental mammals...
However, to come to your point: the advantage of a greater intelligence is that an animal with a greater intelligence can learn a few tricks and thus be better and more efficient at a certain thing as a similar animal that is less intelligent. It's not a guarantee, but statistically, it will give a clear advantage, and that is also one of the main reasons why small dinosaurs never outcompeted the mammals.
And another reason is that more adaptable types of brains evolve far more easily into larger, more efficient brains. In other words: there's more than just the intelligence of the average mammal that we're talking about here, it's also the efficiency of the basic design of the mammalian brain, so it's also an evolutionairy advantage we're talking about.
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Nonetheless, I agree that the (relatively) big brains of the placental mammals didn't do much againest the larger dinosaurs except that they may have frustrated their dinosaur predators a little more than the average frog or lizard would have, and that it wasn't intelligence alone that made the mammals dominate the Earth after the dinosaurs went extinct.
But nonetheless, their intelligence was one of the evolutionairy advantages (along with being warm-blooded, evolving at a very fast rate, efficient hearing, etc.) that allows mammals to bounce back from a disaster like a climate change or mass-extinction far more quickly than any 'rival' animal group, giving mammals an advantage in changing environments.