Copulation in antiarch placoderms and the origin of gnathostome internal fertilization

The diplacanthid fishes (Acanthodii, Diplacanthiformes, Diplacanthidae) from the Middle Devonian of Scotlan

“…Shortest tree length was 641 steps. Both strict consensus and 50% majority rule trees support a topology with acanthodians+chon-drichthyans as a clade with 100% bootstrap support (Figures 39, 40, 41), with chondrichthyans forming a monophyletic group within the clade (also 100% bootstrap support), paralleling the results of Zhu et al (2013) and Long et al (2015). For acanthodians, Acanthodiformes, Diplacanthiformes, and Climatiidae clades are supported in all analyses, with 100% bootstrap support, and an Ischnacanthiformes clade is supported in our majority rule tree (58% bootstrap support).…”

“…The analyses by Brazeau (2009), Davis et al (2012) showed a paraphyletic Acanthodii, with one group as stem osteichthyans and another as stem chondrichthyans. Zhu et al (2013) and Long et al (2015) resolved all acanthodian taxa as stem chondrichthyans, and the analysis by Dupret et al (2014) showed a monophyletic Chondrichthyes and monophyletic Acanthodii as sister groups. Here we present a new analysis incorporating additional information for acanthodians in the character and coding lists (Appendix 2) and in the data matrix (Appendix 3).…”

“…In recent years, a number of cladistic analyses of gnathostome relationships have been published, including Brazeau (2009), Davis et al (2012), Zhu et al (2013), Dupret et al (2014), and Long et al (2015). The first two of these papers primarily focussed on redescriptions of the braincase of two acanthodians, Ptomacanthus anglicus Miles, 1973a and Acanthodes bronni Agassiz, 1833, respectively.…”

“…Cladoselache has been coded (? ), after Long et al (2015). The extra and revised codings added by the latter have not been included.…”

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

“…Several phylogenetic analyses have suggested that acanthodians as a group most likely represent a paraphyletic assemblage of stem chondrichthyans (Brazeau 2009;Davis et al 2012;Zhu et al 2013;Giles et al 2015;Long et al 2015b;Burrow et al 2016). It has become increasingly clear that understanding acanthodians is integral to our understanding of early gnathostome phylogenetic relationships, and that conditions in acanthodians may reflect the primitive conditions for at least some crown group gnathostomes.…”