Ancient method of encipherment with a message wrapped around a cylinder / WED 12-27-23 / Crystalline mineral deposits in some caves / Novelist King who wrote "Caretakers" and "One on One" / Some handoff recipients in football, for short / "Great" 10th-century emperor / Japanese exporter of diesel engines

Constructor: Kareem Ayas

Relative difficulty: Medium

THEME: THESAURUS (33D: Writer's reference ... or what each row of shaded [in my case, circled] letters is missing?) — shaded letters spell out the first part of dinosaur names ... minus THE "SAURUS" part. Also those shaded dinosaur name parts break across black squares, which I guess are supposed to represent the ASTEROID that caused the dinosaurs to go extinct? (4D: What had a major impact on this puzzle's theme), but I could be making that part up ... 

Theme answers:

• LEBRON / TOE (15A: "King James" / 16A: Word before nail or after steel)
• ALARMIST / EGOISM (24A: Voice of doom / 27A: It's a me problem)
• MARTYR / ANNOTATE (44A: One dying for a cause / 47A: Leave a mark on?)
• GAL / LOAFER (58A: Jug unit: Abbr. / 59A: Comfy shoe)

Word of the Day: SCYTALE (40D: Ancient method of encipherment with a message wrapped around a cylinder) —

In cryptography, a scytale (/ˈskɪtəliː/; also transliterated skytale, Ancient Greek: σκυτάλη skutálē "baton, cylinder", also σκύταλον skútalon) is a tool used to perform a transposition cipher, consisting of a cylinder with a strip of parchment wound around it on which is written a message. The ancient Greeks, and the Spartans in particular, are said to have used this cipher to communicate during military campaigns.

The recipient uses a rod of the same diameter on which the parchment is wrapped to read the message. (wikipedia)

A very cute revealer pun, but the theme feels kind of muddled or confusing because of the ASTEROID / black square stuff. The puzzle *leads* with the ASTEROID bit ... and then immediately afterward, I get the dinosaur name parts, and those name parts have a big hole in them (i.e. they're each broken by a black square), which I assume represents some kind of ASTEROID crater (???). So it looks like "this puzzle's theme" is an asteroid impact / dinosaur extinction theme. But then I get this punny revealer, which, again, I like, but ... is the ASTEROID thing a mirage? Are the dino name parts broken across black squares Just Because? I guess there's really no other way you're gonna get something like "TYRANNO" in the grid *except* to break it across a black square, but still, I feel like the ASTEROID bit is a cutesy little self-referential "bonus" answer that made matters confusing. I know no one can lay off puns, and the "had a major impact" pun [wink wink nudge nudge get it!?] was probably irresistible, but all it led to for me was disappointment that the ASTEROID did not, actually, have a major impact on this theme. Or it's being coy about it? If it were thematic, truly thematic, I'd expect it to be *symmetrical* to THESAURUS, but it's not. It's symmetrical with PRITZKER, which is ironic, as I think the architecture today is kinda wobbly. Or the concept is. Or it's trying to do too much. Or does too little. Or gets caught in no man's land. The ASTEROID is too big an element to bring in and *not* have it be meaningful, so maybe I should just stand by my initial (if tentative) impression—that's it's a "no SAURUS" theme on two levels (SAURUS missing from the dino names, and all the SAURUSes missing from the earth on account of the ASTEROID). Whatever is going on, the THE / SAURUS revealer is clever and inventive.