Oh, good, I was kind of worried I was the only who saw it that way. To be fair, Pottermore says something like "Slytherins can be very loyal... to their own" which basically summarizes Marco perfectly, so perhaps it's not strictly a Hufflepuff thing. (Or there's a lot more overlap between the houses than we're led to believe, which is my interpretation, but heyyyyy this is comm is about Animorphs not Harry Potter.)

The dinosaurs were what clinched it for me, actually! I was thinking that's such a Ravenclaw thing to do. Plus I'm pretty sure it's mentioned more than once that Tobias used to escape into books, like, all the time.