A phylogenetic tree of arachnid-like monsters in monster hunter and how their body segmentation and limb specialization developed. (I’m not delving into the heated debate of whether or not frontier is canon).
Figure 1) The earliest ancestor of pseudo-arachnids that probably appears during the Cambrian. It has 8 eyes, biramous limbs, and 8 abdominal segments.
Figure 2) A more derived ancestral body plan and probably the body plan pseudo-arachnids had before the big split. The first two limb pairs have been adapted into mouth parts not unlike centipede forcipules, and limb pairs 3-7 have been completely lost so the thorax can form a sort of pseudo neck used for striking and reaching places the main body can’t fit in. Limb pairs 8-12 bear the weight of the organism. Only limb pair 8 has remained biramous and is used for grabbing and manipulating the environment.
Figure 3) The basic ancestral false-spider body plan. Limb pair 8 has been ditched in favor of striking with the pseudo-neck and devastating mouthparts. Limb pairs 9-12 are the weight bearing limbs. Multiple groups of false-spiders would lose or reduce limb pair 12 as they increased in size (such as nerscylla and rakna). Ironically, later pseudo-spiders would reduce their pseudo-neck and develop limb pair 9 into raptorial appendages not unlike the false-scorpions. They also develop silk.
Figure 4) The basic false-scorpion body plan. Two pairs of eyes have been ditched (forgot to illustrate that) and the pseudo-neck has been reduced and in later forms lost entirely. Unlike early false-spiders, false-scorpions favored their biramous limb pair 8 for striking and dispatching prey. The reason I think it’s a biramous limb and not a normal arthropod claw is because the two ends of the claws on the larger scorpion monsters move independently of each other and the arm.
Rakna is a basal false-spider that evolved into megafauna independently of the rest of the group and is also independently reducing their 12th limb pair. Rakna is basal, but not so basal as to not have developed raptorial limbs.
The puppet spider is a good early example of the second wave of giant false-spiders with its reduced neck.
Nerscylla is a proper second wave giant false-spider. With its reduced neck, and absence of the 12th limb pair.
Baelidae is… a very weird one. It’s supposedly a crab monster, but it has more eyes than crabs and mouthparts different from a crab too. So I interpreted it as a heavily derived false-spider adapted for digging that has also finally lost the pseudo-neck entirely and formed a true cephalothorax like actual spiders. However, it could also be interpreted as a derived false-scorpion.
Kusubami was weird as it had way too many body segments and limb segments on its raptorial limbs. It threw a wrench in my theory, but then I remembered that house centipedes have defensive plating over their actual body plates that doesn’t match up with their actual segmentation. I imagine that kusubami evolved something similar as a form of defense and something that can slough off when their main predator, the Gasurabazura, tries to eat them.
There’s not much to be said about Jebia and Vashimu.
Think of this as a continuation and conclusion to this series of posts.
I updated this post and redid the tree and diagrams. The fact that I decided to prioritize this out of the blue might clue in on what’s happening in the near future.
It was all to help with this episode!
I also want to point out that all the skulls I make wouldn’t be possible without all the work @krmoaten-blog and @freaky-owl put into getting me amazing reference pictures!
Now time to update the frog skulls…