Whew! there are so many awesome animals all across this era, it gets real hard to just settle for a single favorite! I gotta admit too, as much as I love the obscure little lovelies, I am not very original when it comes to absolute favorite Paleozoic creatures XD. With that confession out of the way, I’d say it’s pretty much a three-way-tie between these:
Inostrancevia alexandri(specifically alexandri because it’s the type species and pretty complete!)
Palaeocast lunchtime lectures - Trilobites - Evo-Devo on a Roll - Prof. Nigel Hughes
The good record of postembryonic development of the trunk region of some trilobite species permits investigation of how mature body form was constructed. The trunk was built progressively via the expression of new exoskeletal segments in a subterminal generative zone, and by their growth and development in subsequent instars. This permits insight into the relationship between the ontogenies of individual taxa and clade history. The controls of trunk segment growth may be explored in order to understand how segment differentiation was determined in early arthropods. Trilobite trunk segments varied from one another in size, shape, and articulation state, and clade evolutionary history suggests a repeated tendency towards greater morphological differentiation within the trunk, along with allocation of a larger proportion of trunk segments to the mature pygidium. This was paralleled by the evolution of secured, encapsulated enrollment. Enrollment in those individuals with small numbers of articulating segments accommodated considerable flexure at each joint, which show differences in form from those joints within segment-rich thoraces. While the developmental evolution of trilobites retains rich research possibilities, we posit that both biomineralization and encapsulated enrollment enhanced protective capability, and that adaptive response to predation pressure was an important driver of trilobite evolution.