Thanks for the reply.
By pointing out a grammatical error (and I don't doubt there were some), he's certainly calling into question my knowledge and learning level (how erudite I am), and this is a common tactic to use when unable to address an argument on its own terms. In that sense I see the point, relating to the turtle discussion, that perhaps the polemics regarding my erudition were to serve as a red herring, distracting from the original object of the posting, which is turtles.
But I don't think he was doing that.
I'd argue that while the whole point of his posting was to call into question the level of my erudition, it was not to distract from the original argument about the turtle, but rather to call into question my account of the reptillian monster. It's as if he were saying, to modify your example: "Well, you have bad grammar, so what you say [regarding turtles] doesn't matter." That, I believe, would amount to an ad hominem fallacy. If you still think otherwise, then I'd chalk it up to semantics, and still sleep soundly.
Of course, I'd be happy if someone actually pointed out my grammatical errors so that I might correct them in the future. By my own admission, this has never been my strong point, and my writing tends toward getting muddled and overly complex. That I quote or refer to other peoples' thoughts and ideas is an open admission that I am not pretending to push original ideas or new, profound thoughts. As the good book says, "There is nothing new under the sun." And that I like to use 'five-dollar words,' says less about the utilization of a thesaurus, than it does about the convenient availability of the local library. I love to read, and I enjoy the economy of a good word. Of course I offer my sincerest apologies if my web forum posting was not nuanced or proof-read to the satisfaction of my friend on the graduate review committee. 
Concerning you, Alotus4u_1975, I feel nothing but warm and sincere affection. I like thinking, for better or worse, and it is always fun to wrestle with a well-learned peer.