Support for the forebrain in gnathostomes is provided by the paired polar bodies and anterior trabeculae.
The two structures of primary importance in the transition from agnathan (jawless) fish to gnathostomes were the mandibular arch (gill arch 2) and the hyoid arch (gill arch 3).
Other paleontologists, however, argue that gnathostomes may not have evolved that early.
He asks why, if gnathostomes existed in the Ordovician, scientists haven't found complete fossils of these animals.
In fact, functional evidence for different aspects of this putative network often conflicts between gnathostome models.
To address the question of whether deployment and function of lamprey cognates of gnathostome neural crest genes are evolutionarily conserved, we performed moderate-throughput transcriptome analysis, identifying more than 50 genes involved in neural crest formation in lamprey.
Myelin basic proteins (MBPs) are abundant in the myelin sheaths of gnathostome
central nervous system (CNS) and peripheral nervous system (PNS) (Waehneldt et al., 1986) and are a logical starting point for this study.
The myelinated nervous system arose in a common ancestor of all modern-day gnathostomes