ABSTRACT
The Middle Devonian (Emsian?-Late Eifelian-Givetian) chondrichthyan Pucapampella provides new insights into primitive gnathostome cranial morphology, and reveals that the braincase in modern elasmobranchs is considerably more specialized than was previously supposed. Cladistic analysis resolves Pucapampella as a stem chondrichthyan that retains several primitive gnathostome features, including a persistent ventral otic fissure and otico-occipital fissure, a long notochordal canal between the parachordals, a prominent dorsum sellae, endolymphatic ducts enclosed by the dorsal posterior fontanelle, and the presence of palatobasal and hyomandibular articulations. According to this analysis, chondrichthyans are united by prismatic calcification, aortic canals contained in the parachordals, dorsal ridge and lateral otic process. Crown chondrichthyan synapomorphies include the endolymphatic fossa (absent in Pucapampella) and closure of the ventral otic fissure (open in Pucapampella). Apomorphic features of holocephalans include their holostylic jaw suspension and non-suspensory hyoid arch (absent in elasmobranchs and Pucapampella), and absence of the optic pedicel, dorsal ridge, aortic canals and palatine foramen in the postorbital process (all present in elasmobranchs and Pucapampella). Elasmobranch synapomorphies include chondrocranial fusion forming a glossopharyngeal canal, replacement of the crus commune between anterior and posterior semicircular canals by a new connection between the anterior and horizontal canals, and absence of the palatobasal articulation.
