Alienification

Alienification is a phenomenon where a "boring" lineage or one that's considered to be an Earth clone is intentionally altered to a great degree in a small number of evolutions in order to make it more "alien". In most cases, alienification was done with the justification that it "fixed" the previously "bad" organisms. However, this usually came at the cost of making a previously plausible organism completely implausible, and some lineages such as dwellers still suffer from issues stemming from alienification in their ancestry.

Historically, alienification was treated as a "better" alternative to wiping out a lineage using a plague.

Alienification can be thought of as the opposite of Earth cloning.

Examples
Alienification takes many forms, ranging from evolving a single alien feature to drastically changing an organism's body plan. This list is incomplete; you can help by expanding it.


 * Descendants of the Phantom Capiri and especially its later descendant the Wraith Capiri differ dramatically from earlier, "conventional" capiris in that they have evolved a curled-up posture, whip-like organs with no real-world basis said to "confuse predators", and apparently reduced their jaws for no clear reason and turned their tails into their new jaws, in addition to gaining overly-detailed legs and complex feet that seem to have very little to do with the anatomy of their ancestors. They are sometimes considered one of if not the most egregious cases of alienification.
 * Many times, certain nodents have been given strange anatomy or appearances that made them appear more "alien" or "unique" with questionable or very little basis. This includes the diggerundi, the pancakefoot, some descendants of the nectarling, their many respective descendants, and countless one-offs.
 * The Tailhopping Sawclaw and its descendants were randomly made into monopods, and some descendants of the River Tailhopper were given ears derived from their eyes and crests (which, note, would not actually work for picking up sound in real life). And this isn't even getting into the other issues with the lineage.
 * The Chastro is an example of an attempt to alienify shrews, in this case by turning dromaeocanid shrews (which ironically were already among the more alien shrews of the time) into foreleg bipeds and facultative pentapeds with widely spaced eyes.

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 * There are also records of attempts to alienify species that never actually ended up being approved. For example, the Whiskerpick, a key ancestor of living shrews, was apparently nearly turned into an exoskeletal creature with sideways beaked jaws in a single evolution to "fix" it for being "the worst".