Morphology and histology of acanthodian fin spines from the late Silurian Ramsasa E locality, Skane, Sweden Anna Jerve, Oskar Bremer, Sophie Sanchez, Per E. Ahlberg To cite this version: Anna Jerve, Oskar Bremer, Sophie Sanchez, Per E. Ahlberg. Morphology and histology of acanthodian fin spines from the late Silurian Ramsasa E locality, Skane, Sweden. Palaeontologia Electronica, Coquina Press, 2017, 20 (3), pp.20.3.56A-1-20.3.56A-19. 10.26879/749. hal-02976007 HAL Id: hal-02976007 https://hal.archives-ouvertes.fr/hal-02976007 Submitted on 23 Oct 2020 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. Palaeontologia Electronica palaeo-electronica.org Morphology and histology of acanthodian fin spines from the late Silurian Ramsåsa E locality, Skåne, Sweden Anna Jerve, Oskar Bremer, Sophie Sanchez, and Per E. Ahlberg ABSTRACT Comparisons of acanthodians to extant gnathostomes are often hampered by the paucity of mineralized structures in their endoskeleton, which limits the potential pres- ervation of phylogenetically informative traits. Fin spines, mineralized dermal struc- tures that sit anterior to fins, are found on both stem- and crown-group gnathostomes, and represent an additional potential source of comparative data for studying acantho- dian relationships with the other groups of early gnathostomes. An assemblage of iso- lated acanthodian fin spines from the late Silurian Ramsåsa site E locality (southern Sweden) has been reconstructed in 3D using propagation phase contrast synchrotron X-ray microtomography (PPC-SRµCT). The aim is to provide morphological and taxo- nomical affinities for the spines by combining morphology and histology with the taxo- nomical framework previously established for the site mainly based on isolated scales. The high-resolution scans also enable investigations of the composition and growth of acanthodian fin spines when compared to similar studies of extinct and extant gnatho- stomes. In total, seven fin spine morphotypes that have affinities to both Climatiidae Berg 1940 and Ischnacanthiformes Berg 1940 are described. The majority are inter- preted as median fin spines, but three possible paired spines are also identified. The spines display differences in their compositions, but generally agree with that pre- sented for climatiids and ischnacanthiforms in previous studies. Their inferred growth modes appear to be more similar to those of fossil and extant chondrichthyan fin spines than to those described from placoderms and stem-osteichthyans, which is con- gruent with the emerging view of acanthodians as stem-chondrichthyans. Anna Jerve. Biology Department, Imperial College London, Silwood Park Campus, Buckhurst Road, Ascot, SL5 7PY, United Kingdom. [email protected] Oskar Bremer. Department of Organismal Biology, Uppsala University, Norbyvägen 18A, 752 36, Uppsala, Sweden. Corresponding author. [email protected] Sophie Sanchez. Science for Life Laboratory and Uppsala University, Department of Organismal Biology, Norbyvägen 18A, 752 36 Uppsala, Sweden and European Synchrotron Radiation Facility, 71 Avenue des Martyrs, 38000 Grenoble, France. [email protected] Per E. Ahlberg. Department of Organismal Biology, Uppsala University, Norbyvägen 18A, 752 36, Uppsala, Sweden. [email protected] Jerve, Anna, Bremer, Oskar, Sanchez, Sophie, and Ahlberg, Per E. 2017. Morphology and histology of acanthodian fin spines from the late Silurian Ramsåsa E locality, Skåne, Sweden. Palaeontologia Electronica 20.3.56A: 1-19. https://doi.org/10.26879/749 palaeo-electronica.org/content/2017/2062-ramsasa-acanthodian-fin-spines Copyright: November 2017 Palaeontology Association. This is an open access article distributed under the terms of Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0), which permits users to copy and redistribute the material in any medium or format, provided it is not used for commercial purposes and the original author and source are credited, with indications if any changes are made. creativecommons.org/licenses/by-nc-sa/4.0/ JERVE ET AL.: RAMSÅSA ACANTHODIAN FIN SPINES Keywords: fin spines; histology; acanthodians; 3D-reconstructions; Silurian; Baltic Basin Submission: 2 December 2016 Acceptance: 7 November 2017 INTRODUCTION southern Sweden, include well preserved, albeit fragmentary and isolated remains of acanthodian Acanthodians were once considered to form a spines and shoulder girdles, together with other clade found worldwide in rocks ranging in age from isolated vertebrate remains. Vergoossen (2004) Silurian to late Permian, and united partly by the described the micro-remains in residues from presence of median and paired fin spines (Deni- Ramsåsa site E samples with the aim of providing son, 1979). However, paired fin spines have now a paleontological and taxonomical framework for been described from early chondrichthyans (Miller both the micro-vertebrate and macro-remains. et al., 2003) and paired and median spines have Besides reporting osteostracans, thelodonts, and been discovered on a handful of fossil osteich- anaspids, Vergoossen (2004) also described sev- thyans (Zhu et al., 1999, 2009). These discoveries, eral acanthodian scales and fragments, and along with cranial data, have led to the rejection of referred them to a number of scale-based taxa. a monophyletic Acanthodii (Brazeau, 2009; Davis However, most of the macro-remains have et al., 2012) and to new ideas about how these ani- remained undescribed and have not yet been taxo- mals relate to osteichthyans and chondrichthyans. nomically identified. The working hypothesis of vertebrate phylogeny Here, we describe the morphology of seven has now shifted to accept acanthodians as a para- fin spine morphotypes identified from the Ramsåsa phyletic assemblage within the chondrichthyan collection held at the Naturhistoriska Riksmuseet total group (Zhu et al., 2013; Giles et al., 2015; Bur- (NRM) in Stockholm, Sweden. With the aid of the row et al., 2016; Qiao et al., 2016). micro-vertebrate framework presented by Vergoos- Osteichthyans and placoderm fossils are sen (2004), and by comparing them to described known by their bony skeletons, but chondrich- articulated material (see later sections), we aim to thyans and acanthodians have only a few skeletal give these vertebrate remains taxonomical and elements that commonly preserve, including morphological assignments. Given the current scales, teeth, jaws, head tesserae, scapulae, and close phylogenetic position of acanthodians to fin spines. The presence of fin spines and spiny chondrichthyans based on recent hypotheses (Zhu elements in all these groups of jawed vertebrates et al., 2013; Giles et al., 2015; Burrow et al., 2016; has highlighted the importance of understanding Qiao et al., 2016) it is necessary to understand their development and evolution. Studies of the how similar their fin spines are in terms of morphol- development and growth of extant chondrichthyan ogy and growth. The morphology and histology are fin spines (Markert, 1896; Maisey, 1979; Jerve et investigated (where possible) from synchrotron- al., 2014) has provided a framework from which to microtomography data collected from the Euro- understand fossil spines. Furthermore, the use of pean Synchrotron Radiation Facility in Grenoble, propagation phase-contrast synchrotron X-Ray France. These data are used to compare the microtomography technology as a nondestructive Ramsåsa fin spines to other fossil taxa and the cur- tool for studying the 3D microstructure of fossils rent growth models for extant sharks described by has made it possible to understand aspects of their Maisey (1979), Tovar-Ávila et al. (2008), and Jerve overall architecture that might not be observed et al. (2014). from traditional 2D thin section (e.g., Sanchez et al., 2012; Qu et al., 2015). This technique has been GEOLOGICAL SETTING used to study the histology of a number of fossils, including scales (e.g., Qu et al., 2013, 2015), der- The Öved-Ramsåsa Group crops out in three mal plates (e.g., Dupret et al., 2010; Giles et al., areas in Skåne, Southern Sweden: the Ringsjö 2013; Chen et al., 2016), fin bones and rays (San- area, the Bjärsjölagård-Övedskloster area, and the chez et al., 2014), and fin spines (Jerve et al., Ramsåsa area. The Ramsåsa area (Figure 1) is 2016), and has provided valuable information on the southeasternmost of these and is represented the morphology, vascularization, and growth of by a series of old quarries (sites A-H in Grönwall, these structures. 1897). The only site still accessible (site F) is Fossils collected from the now inaccessible referred to as Ramsåsa 8 in Jeppsson and Laufeld late Silurian Ramsåsa site E locality in Skåne, (1986). This is also where the first Ramsåsa fish 2 PALAEO-ELECTRONICA.ORG FIGURE 1. Map modified from Mehlqvist et al. (2014) showing the location of the Ramsåsa area (1), and the Ramsåsa localities of Grönwall (1897) with an arrow indicating site E (2) adapted from Vergoossen (2004). faunas were described from by Lehman (1937). Laufeld, 1986).