Great products though.
A mastodon is a massive, hairy, smelly beast. It's also an extremely well known heavy metal band. For a Twitter clone it makes absolutely no sense. "Toot" as well has some existing connotations I wouldn't think they would want to associate with...just seems like a total non-starter.
Ivy - Naturally grows and spreads and often is seen climbing walls. Maybe in this case it climbs and covers a FB wall :-P Also a play on FB being started at an ivy league school.
Greenfield - Maybe a reasonable name for the protocol that those apps can be built upon? "Ivy's built on the greenfield protocol"
Anyway, that's what I came up with in 10-15 minutes of brainstorming and I would pose that those are much easier, approachable, and just better names than these others that simply don't elicit any sort of emotion (or negative ones).
Names matter, a lot. You need to be able to tell a story that moves people to action. That's what marketing folks do that adds a ton of value. Most open source projects don't have marketing folks so... :-)