On the Origin of Species: Lileep and Cradily
The creativity and imagination of Game Freak, in my opinion, is most evident when it comes to the Fossil Pokémon. We've been reviving Pokémon from fossils since Red and Blue, and yet it wasn't until Generation IV that we actually got the things that most people associate with fossils: dinosaurs. Up until then, the games had introduced us to a variety of other prehistoric creatures that reflect the remarkable range of fossils that exist in the real world. When you consider that an estimated 99.9% of species that have ever existed are now extinct, you can probably appreciate that there's more to fossils than just dinosaurs.
Lileep and Cradily were inspired by one such group of strange beasts. And "beasts" is the correct word, because despite appearances and a Grass typing, these Pokémon aren't based on plants. Their design comes from the crinoids, a class of animals that once thrived across the globe, covering the sea floors. And, although we're most familiar with them from their fossils, a small subset of crinoids still survive to this day.
The most immediately noticeable thing about most crinoids is that they barely look like animals at all. In fact, they look much more like plants, having a stem, a flower-like 'head' and seemingly being rooted to a single spot. This has earned them the common name of "sea lilies". They're a little reminiscent of sea anemones, also flower-like creatures that attach themselves to the sea floor, but they belong to a very different lineage. Crinoids are members of the Echinodermata, meaning that some of their closest relatives are starfish. Though the resemblance might not be immediately apparent, crinoids do posses the fivefold symmetry that characterizes the starfish and their relatives. They also have an internal skeleton, a feature common only to the Echinodermata and their distant cousins... vertebrates. Yes, strange as it may seem, you and I are more closely related to sea lilies and starfish than we are to insects.
The main part of any crinoid's body is the calyx or 'cup'. This contains the mouth, digestive and reproductive organs, and most of the creature's nervous system. Nerves also extend up into the multiple arms that extend around the calyx, surrounding the mouth. There may be between ten and twenty such arms depending on the species, all of them covered in fine hairs used to trap passing morsels of food and guide it into the mouth. Finally, there is a tough, bony stem, used to anchor the creature to the sea floor.
Or at least, that's how it used to be. A great number of crinoid species alive today have no stem, or just the vestigial remains of one. They still prefer to stay still most of the time, clamping themselves onto rocks, but they needn't remain fixed to the spot if they decide they'd like to move. By contrast, almost all of the crinoid fossils we've found have stems. And there are plenty of crinoid fossils. Their stems fossilize particularly well, and there are limestone deposits across Europe and North America that are literally full of ancient crinoid stems.
Indeed, the Root Fossil from which Lileep can be revived is likely based on such limestone, though it's possible that the term 'root' is a slight mistranslation. Crinoids don't have roots, not being plants, but the Japanese term used, nekko no kaseki (ねっこのカセキ), can also be translated as "stump fossil" or "stub fossil". To me, it seems that these are probably closer to the intended meanings... but it's hard to say for certain.
So, if most ancient crinoids remained fixed in one place with their stems, and most modern crinoids can move around freely, what might have prompted this change? Well, first we have to consider why a creature might choose to be immobile in the first place. Sedentary crinoids are descended from free-living animals, and indeed, their larvae are able to swim before attaching themselves to the sea floor. So at some point, it must have been beneficial for these creatures to take up this particular lifestyle. Why might this have happened? Well, we only need to look at nature to see that staying still can actually be an excellent strategy. It certainly works for plants and fungi. As long as food is always within reach, staying still means that an organism doesn't have to expend energy on movement, or waste resources on making complicated muscular systems that it doesn't need to use. It can simply stay where it is, and put all of its excess energy into reproducing. This was evidently a successful strategy for the prehistoric crinoids, because 300 million years ago they were thriving, with countless species colonizing the sea floor at a wide range of depths.
One big disadvantage to staying still, however, is that you become an easy target for predators. Fossil evidence shows us that creatures such as sea urchins began to view the stationary sea lilies as an easy meal: many crinoid fossils from the Triassic period show evidence of teeth-marks! It seems that this is why some crinoids became motile again. Some, such as the feather stars, have become reasonably adept swimmers: not especially quick or graceful, but enough to make a break for it if things seem to be getting dangerous. Other species have been seen to slowly walk along the sea floor using their multiple arms. This gradual progression towards motility seems to be referenced in the Pokédex entries of Lileep and Cradily, too... while Lileep is stated to be immobile, numerous references are made to Cradily moving around (albeit inelegantly).
It was recently discovered that even crinoids with stems - that usually remain fixed to their spot no matter what - can move if it becomes necessary. Archive footage taken from a submersible shows a crinoid with a snapped stem inching its way along the sea floor on its arms. Perhaps this is how the ancestors of modern motile crinoids started out, before doing away with their stems altogether. Either way, it's a powerful reminder that though they may look like plants, these lilies are indeed animals: animals that can eat, think and move... if the mood takes them.