A revision of Vernicomacanthus Miles with comments on the characters of stem-group chondrichthyans Richard Dearden, Jan Blaauwen, Ivan Sansom, Carole Burrow, Robert Davidson, Michael Newman, Andy Ko, Martin Brazeau To cite this version: Richard Dearden, Jan Blaauwen, Ivan Sansom, Carole Burrow, Robert Davidson, et al.. A revision of Vernicomacanthus Miles with comments on the characters of stem-group chondrichthyans. Papers in Palaeontology, Wiley, In press, 10.1002/spp2.1369. hal-03274825 HAL Id: hal-03274825 https://hal.archives-ouvertes.fr/hal-03274825 Submitted on 30 Jun 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. [Papers in Palaeontology, 2021, pp. 1–28] A REVISION OF VERNICOMACANTHUS MILES WITH COMMENTS ON THE CHARACTERS OF STEM-GROUP CHONDRICHTHYANS by RICHARD P. DEARDEN1,2 , JAN L. DEN BLAAUWEN3,IVANJ.SANSOM4 , CAROLE J. BURROW5 ,ROBERTG.DAVIDSON6, MICHAEL J. NEWMAN7 , ANDY KO1 and MARTIN D. BRAZEAU1,8 1Department of Life Sciences, Imperial College London, Silwood Park Campus, Buckhurst Road, Ascot SL5 7PY, UK; [email protected] 2CR2P, Centre de Recherche en Paleontologie–Paris, Museum National d’Histoire Naturelle, Sorbonne Universite, Centre National de la Recherche Scientifique, CP 38, 57 rue Cuvier, F75231, Paris Cedex 05, France; [email protected] 3University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, The Netherlands; 4School of Geography, Earth & Environmental Sciences, University of Birmingham, Birmingham, B15 2TT, UK; 5Geosciences, Queensland Museum, 122 Gerler Road, Hendra, Qld 4011, Australia; 635 Millside Road, Peterculter, Aberdeen, AB14 0WG, UK; 7Vine Lodge, Vine Road, Johnston, Haverfordwest, SA62 3NZ, UK; 8Department of Earth Sciences, Natural History Museum, London, SW7 5BD, UK; Typescript received 5 October 2020; accepted in revised form 1 April 2021 Abstract: The ‘acanthodian’ fishes provide key anatomi- differences between V. uncinatus and its congeneric, cal insights into the deepest branches of the chon- V. waynensis, which include potentially phylogenetically sig- drichthyan stem group. We review the anatomy of the nificant characters of the shoulder girdle and spines, are acanthodian Vernicomacanthus uncinatus from the Lochko- sufficient to erect a new genus for V. waynensis: Dobun- vian (Lower Devonian, 419.2–410.8 Ma) of Scotland based nacanthus gen. nov. The scales of Vernicomacanthus are on eight articulated fossils, one of which is newly described. identical to those of the ‘shark’ scale genus Altholepis,sug- Broadly, the anatomy of V. uncinatus fits with that of con- gesting that some such scales may instead belong to taxa temporaneous acanthodians such as Climatius and Parexus, with acanthodian-like gross anatomies. Based on these with a head covered by robust tesserae, an enlarged postor- scales we highlight potential patterns in chondrichthyan bital scale, an armoured shoulder girdle, and many pairs of scale evolution, in particular the axial addition of odon- ventrolateral spines. However, it departs from this anatomy todes. Anatomical similarities between Vernicomacanthus in key respects. Its pectoral fin spines are obliquely ridged and gyracanths, highlighted by previous authors, may indi- and posteriorly denticulated, similarly to Carboniferous cate the existence of a grade including these and similar gyracanth stem-group chondrichthyans. Its scales consist of acanthodian-grade taxa placed relatively crownwards in the multiple anteroposteriorly aligned odontodes, similarly to chondrichthyan stem-group. many Palaeozoic ‘sharks’. And its endoskeletal shoulder gir- dle may have a posterolateral angle, previously observed Key words: stem-group chondrichthyan, Lower Devonian, only in shark-like chondrichthyans. We propose that the Acanthodian, scales, shoulder girdle, Scotland. O VER the last decade, evidence has mounted that ‘acan- conceals how acanthodians are related to one another as thodians’ (a collection of poorly understood fishes previ- well as to ostensibly more shark-like stem- ously grouped with bony fishes, cartilaginous fishes, stem- chondrichthyans, leading to poorly resolved phylogenetic gnathostomes, or all three) are in fact all stem-group relationships (Brazeau 2009; Davis et al. 2012; Zhu et al. chondrichthyans (Zhu et al. 2013; Brazeau & Friedman 2013; Giles et al. 2015; King et al. 2016; Chevrinais et al. 2014; Coates et al. 2018). These taxa have the potential to 2017; Coates et al. 2018; Dearden et al. 2019, Frey et al. provide insight into the evolution of chondrichthyan 2020). The best hope for broadly comparable phylo- morphology, as well as that of gnathostomes (jawed verte- genetic characters, outside of rarely preserved endoskeletal brates) more broadly. However, a lack of traits widely structures, lies in the detailed microanatomy of acantho- comparable with outgroup taxa (i.e. endoskeletal data) dians. However, few studies have been able to document © 2021 The Authors. doi: 10.1002/spp2.1369 1 Papers in Palaeontology published by John Wiley & Sons Ltd on behalf of The Palaeontological Association. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. 2 PAPERS IN PALAEONTOLOGY these anatomical details in the context of articulated spec- The erosion of phylogenetic support for the climatiids imens. has, at least in part, reflected the recent recognition of This paper presents a new description and taxonomic chondrichthyan-like traits in these taxa. Consequently, they re-assessment of Vernicomacanthus Miles, 1973, an acan- have become a focal point in studies of chondrichthyan thodian from the Lower Devonian (Lochkovian, 419– origins. The loss of support for their phylogenetic coher- 411 Ma) Midland Valley of Scotland. Vernicomacanthus is ence has come from two sources. First, there is the recog- known from rare articulated skeletons and provides valu- nition of chondrichthyan scale morphotypes in climatiids able information on the morphological diversity of early such as Kathemacanthus (Hanke & Wilson 2010) and Par- acanthodians and other stem-group chondrichthyans exus (Burrow et al. 2013), or at least a lack of characteristi- (Miles 1973). Miller (1858) first described and figured cally acanthodian superpositional scale growth (e.g. remains that would later be assigned to Vernicomacanthus Brazeau 2012; Burrow et al. 2015; Chevrinais et al. 2017). uncinatus (Powrie 1881; Newman & Davidson 2010), not- Second, there is the identification of climatiid-like hard tis- ing that the inner edge of a pectoral fin spine from Bal- sue structures in the articulated skeleton of Doliodus (an ruddery Den had ‘projecting prickles, that resemble sharp undisputed chondrichthyan) showing stout, nodose, ribbed hooked teeth’ (Miller 1858, p. 160). Later, the articulated fin spines with shallow insertions, a complete complement type material was assigned to the species Climatius unci- of ventrolateral and prepectoral fin spines, and a differenti- natus by Powrie (1864) based on a manuscript name by ated head and trunk squamation (Miller et al. 2003; Bur- Egerton; Miles (1973) subsequently found it sufficiently row et al. 2017; Maisey et al. 2017). It remains unclear to distinct from that taxon to erect a new genus. Miles what extent the armoured and heavily spined climatiid (1973) also assigned material from the Welsh borders to conditions reflect shared derived traits of early V. waynensis that we assign to a new genus in the present crown-group chondrichthyans, or whether these are ple- paper. This reassignment reflects anatomical differences in siomorphic traits of the chondrichthyan total group. the shoulder girdle, spines, and size that distinguish the Climatiid-like taxa variably appear in phylogenies as either two taxa. Furthermore, assuming that these species are nested close to crown-group chondrichthyans (Giles et al. monophyletic in the absence of clear evidence could be 2015; King et al. 2016; Chevrinais et al. 2017; Coates et al. problematic in the context of unsettled stem- 2018; Dearden et al. 2019), with remaining lightly armoured chondrichthyan phylogenetic relationships. acanthodians in a more remote position, or as a basal grade Vernicomacanthus was assigned to the Climatiidae by of the chondrichthyan total group (Burrow et al. 2016; Frey Miles (1973). The Family Climatiidae Berg, 1940, placed et al. 2020), perhaps reflecting their retention of within the Order Climatiida Berg, 1940, are an assem- osteichthyan-like characters such as branchiostegal plates. blage of acanthodians with shoulder girdles carrying der- Here, we redescribe Vernicomacanthus on the basis of a mal plates, skulls clad in dermal tesserae, and pre-pectoral new specimen as well as a re-examination of four speci- fin spines. The Climatiidae in particular have stout fin- mens described previously. Despite having been known spines with the dorsal and anal spines superficially since the nineteenth century, Vernicomacanthus uncinatus inserted into