Gossiosteology

As on Earth, the science of osteology is the study of bones.  However, on Gossipiboma, there are two main taxa that have independently evolved an internal skeleton.  What is referred to as Gossiosteology is the study of the more dominant taxon with an internal skeleton—the notopeltids, or animals with backbones.  Having adapted to similar environments from a similar ancestor, the notopeltids and vertebrates have much in common skeletally, with a similar spinal column and limbs, but the evolution of their skeleton has much more in common with the evolution of arthropod or calcaripod morphologies.  
Fish
The ancestral notopeltid was probably very similar to an animal such as Flagellodiscus, a small pelagic oceanic motobranch, albeit with the ossification and fusion of the notochords and the ossification of the flagella.  These flagella would later evolve into tails, limbs, and jaws much in the way in which arthropods on Earth or calcaripods on Gossipiboma.    
As time progressed, the flagella of the ancestral notopeltid became more and more ventrally positioned, giving a kind of dog paddle form of locomotion.  To compensate, the trunk had to be more motile and muscular in order to be the main form of locomotion, thus transforming the up and down motion of the ancestor into a more eel-like mode of movement.  In order to make this even more efficient, some of the terminal flagella became more clumped together and were eventually bound with muscle and tendons, forming a kind of compound tail.  Gradually, the unpaired terminal flagellum became more or less fused with the notochord complex, extending the trunk and making the animal a more powerful swimmer.  Because of these new innovations, the propulsive digestive ceca that had once been used for locomotion were now converted into swim bladders to keep the animal afloat.  
  However, at this time, the notopeltids were still jawless filter feeders, and so were not able to get very large.  In order to fully gain advantage of the ocean realm, the bones in the head had to fuse into one solid complex, and there had to be jaws.  To solve this problem, one lineage of jawless fish developed pairs of flagella that became associated with the mouth.   One pair migrated dorsally towards the top of the mouth, while another migrated ventrally to join with the bones at the floor of the buccal cavity.  The wiggling motion of the flagella became transferred to the bones of the head, where they fused and became effective biting devices—jaws.  The segments of the flagella bones became elongated and pointy, like some beetle antennae, in order to catch on prey more easily.   Meanwhile, the lose bones of the head were fusing into a complex that could be described as a skull.  The bones supporting the gills (presumed to be modified ribs) became fused with the back of the braincase, pushing the actual gill tissue to the back of the skull, where it remains to this day.  The skull, at this point, still had the multiple nostrils of the ancestral fish, and was still relatively large and compact.  
The other modified limbs, at this point comprising the tail complex and fins, were undergoing drastic changes as well.  The segments of the flagellar bones in the fins were becoming elongated and featherlike, providing more surface area for accessory propulsion and steering.  The tail complex, on the other hand, was undergoing drastic reduction in some respects.  In the lineage that gave rise to the fortopods, the main terminal flagellum, already ossified, began to dominate in the tail, and began to take on a semblance of the vertebral column.  The other terminal flagella became shorter and more pelvic, and were used as a mode of attachment for the rearmost limbs, allowing the animal to push itself more efficiently around in the water where it stalked its prey.  Like the early tetrapods on earth, these primitive fortopods were presumed to have lived like frogfish, using their limbs to anchor themselves on submerged logs for lunging or for crawling around on the bottom.