I have strong memories of this book from my childhood, which would have been mid to late 70's I guess, which are just images mainly. I think that I got it from my school library, so it is likely to have been published around the late 60's, early 70's. There were pictures in the book, but I think it was more a paperback with pen and ink drawings than a younger child's picture book. This is a weak memory though as it could be that the pictures were in my imagination. The book would have been written in English and was read in the UK.
The story is set in a future where animals can now talk. The main protagonist is (I think) a penguin who lives in a giant clam shell which is his house, or maybe just his room. There are humans, but eating animals is now relegated to the history books. There are a couple of humans who find a butchers knife in a museum (maybe?) and hatch a plan to use it to kill and eat an animal.
The humans were definitely thwarted in their aim. I think there was a team of animals, led by the penguin who discovered the plot and defeated the humans. I think the humans were a husband and wife. They were possibly trying to eat a cow.