Pseudofish evolution

Exercise in designing the evolutionary descent of a critter. Three steps in evolutionary descent, from a simple little “fish” through a more advanced medium-size ambush predator to a large pelagic creature specialized in eating the alien version of surface siphonophorae.

Note the progression of the fins. The earliest stage has a big tail fin for swimming and simple side fins for stability. The next one has a double set, with the new hind side fins becoming the main drive and the old side fins serving as gliding planes, with their front portion becoming claspers. The tail is now used only for quick escape leaps. The final version has the hind side fins enlarged, and the front side fins disappear - only their claspers remain; the gliding plane function is taken up by the greatly enlarged lobes on the jaw capsule that started out as support for stretched olfactory slits.

Other evolutionary progressions include:

- Concentration of eyes. The earliest fish has a few simple eyes scattered all over its main “hull”. The subsequent versions have concentrated triplets of simple eyes.

- Concentration of gills: the three slits of the earliest fish become covered by ducts.

- The mouth is at the end of progressively elongating proboscis. It has a skeletal capsule with strong concentrated muscles working the jaws armed with bony plates, and olfactory slits which become wider with time, until the final critter has a whole glider supporting them.

- Coloration of the earliest fish is primitive, and the two others show progressively complex patterns and camoflage: the ambush predator colored for hiding in still water, the pelagic surface feeder for open ocean.