So, the hole digging club has always been an absurd tendency to waste effort on meaningless tasks right? This month it's framed with Sumida Senpai doing the teachers work so she can devote more time to hole digging (a representation of people's willingness to ignore what must be done in order to continue their pointless endeavors), The teacher's use of it as an escape (a bit more straight forward), and the tendency to refuse to validate what you're doing through finding a productive use of your pointless endeavors is exhibited through their distinction from the archaeology club. Perhaps in the fruit song, it's more important that they're fruits, than what fruits specifically, in which case it's a joke about music with illogical lyrics about sweet things? A joke maybe about love songs? Looking at fruits specifically, Apples can mean beauty or peace in Chinese, but also sin and sensual love in Hebrew and Greek stories. Banana... it's a banana... I'll assume the same jokes apply in Japan. Kiwi I have no earthly clue how to interpret, but Avocados were originally a symbol of love. So maybe there's some story about beauty and love hidden in those fruits? Maybe a glasses wearing Mosasaurus is commentary on the current political climate. I doubt it, but symbolism is really hard, so just about anything could be interpreted from this. All I know is dogs usually represent loyalty. I'd guess dinosaurs are "the past" and Haniwas were buried with people when they died. Maybe, just maybe, the excavations are a metaphor for how often times we continue to do useless things for the sake of loyalty toward traditions which have roots in things which have died. That's a stretch though.