Nice and tough, just like a Friday ought to be, with a great 1A, FOSHIZZLE (1A: "Definitely, dawg!"). ATHANAEUM (15A: Reading room) is another very nice word, and STANDINGO (17A: Reward for knocking 'em dead), well... I guess that's how you'd spell that.
There are a few things that we scowled at, like ETALII (24A: Name dropper's phrase) (mostly saved by the great clue), CELLI (10D: Parts of many chamber groups) (seems a little cheap), WANS (36D: Pales) (so "wan" is a verb now?), and we're not quite convinced that "learn" is a true ANTONYM of "teach" (45D: Learn to teach?).
But the puzzle was so good in other ways that we're (at least I am, anyway) letting it slide. How 'bout that clue for MANO (55A: A leader and follower?), and I see that "supply" is given as an alternate form of "supplely," but the latter would not have been so devilish in 18A: Moving supply (LITHE). Egad! The whole right side took the lion's share of the time today. I finally got CANST (10A: Art enabled), and that opened it up a little, but "student" fit where SCHOLAR (13D: 15-Across frequenter, maybe) belonged, and then those two quotes were very slow in coming.
Lastly, I didn't realize that marmot was the name of a large class of animals, as well as being the name of quite a few species. Neither did I know that the woodchuck and the groundhog were the same thing, and that it is also sometimes called a land-beaver, or a whistle-pig. You learn something new every day!
Again, we enjoyed the challenge today. Good, tough, Friday.