Pectoral Morphology inDoliodus: Bridging the ‘Acanthodian’-Chondrichthyan Divide

Abstract

Doliodus problematicus (NBMG 10127), from the Lower Devonian of New Brunswick, Canada (approx. 397-400 Mya) is the earliest sharklike jawed vertebrate (gnathostome) in which the pectoral girdle and fins are well preserved. Its pectoral endoskeleton included sharklike expanded paired coracoids, but Doliodus also possessed an "acanthodian-like" array of dermal spines, described here for the first time. Doliodus provides the strongest anatomical evidence to date that chondrichthyans arose from "acanthodian" fishes by exhibiting an ana¬ tomical mosaic of "acanthodian" and sharklike features.

A critical appraisal of appendage disparity and homology in fishes

“…latispinosus, which also possesses prepectoral and possibly admedian spines (Burrow et al, 2017;Maisey et al, 2017), and W. priscus (Potvin-Leduc, 2017). latispinosus, which also possesses prepectoral and possibly admedian spines (Burrow et al, 2017;Maisey et al, 2017), and W. priscus (Potvin-Leduc, 2017).…”

“…D. latispinosus, which also possesses prepectoral and possibly admedian spines (Burrow et al, 2017;Maisey et al, 2017), and W. priscus (Potvin-Leduc, 2017). Notably, it has also been suggested based on the results of a phylogenetic analyses on cranial morphological characters that D. latispinosus may occupy a more stemward position in the chondrichthyan phylogeny, prior to the Euchondrocephali-Elasmobranchii split (Maisey, Turner, Naylor, & Miller, 2014;Pradel, Tafforeau, Maisey, & Janvier, 2011).…”

An early chondrichthyan and the evolutionary assembly of a shark body plan

“…The early evolution of the Chondrichthyes (cartilaginous fishes) has long been obscured by an impoverished fossil record [1][2][3]. This has only recently been improved through discoveries of partly articulated bodies [4][5][6][7] and braincases from the Lower and Middle Devonian [8][9][10], coupled with computed tomography (CT) [11][12][13][14][15][16]. The Lower and Middle Devonian record of chondrichthyans remains sparse, but the influx of high-quality data from slightly younger material, especially from the Upper Devonian and Carboniferous [14][15][16][17], combined with insights from earlier studies [18][19][20][21] has transformed our understanding of the early evolution of the crown group (Holocephali and Elasmobranchii).…”

Morphology and histology of acanthodian fin spines from the late Silurian Ramsåsa E locality, Skåne, Swede

“…The morphology of this spine suggests that the ridge formed a growth center, but scan data is needed to confirm this. A similar morphology was identified in prepectoral spines of Doliodus, leading the authors to suspect that the ridge formed an apical growth center (Maisey et al, 2017). This is similar to the growth in spines of the placoderm Romundina, where the vascularization shows that the growth center is positioned along the upper portion of the anterior midline with new tissue being deposited posteriorly and proximally (Jerve, 2016;Jerve et al, 2016).…”

“…Paired pectoral fin spines were identified on Doliodus, a fossil probable stem-group chondrichthyan (Miller et al, 2003). A segmentation analysis revealed additional pairs of separate dermal spines in this taxon, which consequently combines shark-like characters with a set of acanthodian-like dermal spines (Maisey et al, 2017). All extant chondrichthyans have only median dorsal spines, with sharks having one per each of the two dorsal fins and holocephalans having one anterior to the first dorsal fin.…”