The braincase of the chondrichthyanDoliodusfrom the Lower Devonian Campbellton Formation of New Brunswick, Canada

Abstract

Maisey, J.G., Miller, R.F. and Turner, S. 2009. The braincase of the chondrichthyan Doliodus from the Lower Devonian Campbellton Formation of New Brunswick, Canada. -Acta Zoologica (Stockholm) 90 (Suppl. 1): 109-122

The characters of Palaeozoic jawed vertebrates

“…8A; Stensiö, 1963Stensiö, , 1969Denison, 1978;Goujet, 1984a;Young, 1986). This contrasts with chondrichthyans (Schaeffer, 1981;Maisey, 2005Maisey, , 2007Maisey et al, 2009), osteichthyans (Jarvik, 1980;Gardiner, 1984b), osteostracans (Janvier, 1985a, b), and galeaspids (Gai et al, 2011), in which such a division is absent. Interestingly, this character has been dismissed as a placoderm synapomorphy in favour of being a generalized vertebrate character (Goujet, 2001).…”

“…In shark-like chondrichthyans (Maisey, 2005(Maisey, , 2007Maisey et al, 2009), actinopterygians (Gardiner, 1984b), and Acanthodes (Miles, 1973b;Davis et al, 2012), the neurocranium exhibits a well-developed lateral projection where the orbits meet the otic capsules (Figs 6, 7), termed the postorbital process. The process termed an 'anterior postorbital process' in arthrodires (Goujet, 1984a) and some other placoderms (Stensiö, 1969;Ørvig, 1975) supports the hyoid arch articulation.…”

A reappraisal of the origin and basal radiation of the Osteichthyes

“…Lungfishes show a secondary exception to this condition (Miles, 1977), as do limbbearing tetrapods and most post-Devonian actinopts (Poplin, 1974;Hamel and Poplin, 2008). The generalized osteichthyan arrangement differs from that found in the early chondrichthyans Cladodoides (Maisey, 2005), Tamiobatis (Romer, 1964;Schaeffer, 1981), Akmonistion (Coates and Sequeira, 1998), possibly Pucapampella ; and a similar braincase: Maisey and Anderson, 2001), and Dolidous (Maisey et al, 2009), where large parts of the nasal capsules appear to have not been enclosed by the ethmoid, as well as Acanthodes (Miles, 1973b), where the ethmoid is unmineralized. 'Placoderms' combine a fissure that separates the ethmoid from the sphenoid along with ventrally open nasal capsules (Goujet, 1984(Goujet, , 2001, further implying that the condition observed in crown osteichthyans is derived.…”

“…These characters are absent in both 'placoderms' and basal chondrichthyans and imply osteichthyan total-group membership. Symmoriiform chondrichthyans have anatomically tropibasic neurocrania (Masiey, 2007(Masiey, , 2008, but this is not the case in early chondrichthyans such as Pucapampella , Cladodoides (Maisey, 2005), and Doliodus (Maisey et al, 2009), or in 'placoderms' (e.g., Stensiö, 1963Young, 1979Young, , 1980Goujet, 1984).…”

Precise occlusion and trophic niche differentiation indicate specialized feeding in Early Devonian jawed vertebrates

“…The surface meshes were then sculpted using Geomagic until the curvature of the cartilages in the ischnacanthiform jaw reconstructions (Fig. 3) more closely resembled the curvature of the jaws in related Devonian fossil specimens that were preserved in three dimensions or dorsoventrally exposed, including Ptomacanthus anglicus (Miles 1973), redescribed by Brazeau (2009); Doliodus problematicus (Woodward 1892), based on CT data presented by Maisey et al (2009Maisey et al ( , 2014; and Gogoselachus lynbeazleyae (Long et al 2015a). Although the more laterally flattened MOTH ischnacanthiform jaws may have been less curved than the jaws of these specimens in life, the purpose of curving the jaw reconstructions was to determine whether and how it affected the occlusion of the jaws, not to attempt to recreate an entirely accurate life position.…”