Diverse dentitions in the earliest chondrichthyans

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(1)Diverse dentitions in the earliest chondrichthyans Richard Dearden, Matt Colfer, Sam Giles. To cite this version: Richard Dearden, Matt Colfer, Sam Giles. Diverse dentitions in the earliest chondrichthyans. Palaeontological Association Annual Meeting, Dec 2019, Valençia, Spain. �hal-03218035�. HAL Id: hal-03218035 https://hal.archives-ouvertes.fr/hal-03218035 Submitted on 5 May 2021. HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés..

(2) Diverse dentitions in the earliest chondrichthyans 1 2 3 Richard P. Dearden , Matt Colfer , Sam Giles. @Euphanerops. [email protected]. 1 Museum national d'histoire naturelle, France, 2Department of Earth Sciences, University of Oxford, UK, 3School of Geography, Earth, and Environmental Sciences, University of Birmingham, UK. -Teeth of both the lateral and ? lingual rows added on a dermal bone base, similarly to Compagopiscis (Rücklin et al.) -However, unlike Compagopiscis, they are only added in a single direction, anteriorly.. ES ST OM NA TH O -G ST EM. Atopacanthus. -Teeth in added in a single direction on a bony base, in same manner as other ischnacanthid taxa above -Ischnacanthid "mandibular splint" (Ørvig 1967) appears instead to be the heavily mineralised ventral edge of the Meckelian cartilage. 3 On the basis of the inferred character state distribution we suggest possible state changes in the vertebrate total group.. Acanthodopsis. ?. Acanthodes. -Single row of teeth histologically distinct from mandibular cartilages. ?. -Mandibular splint is dermal (see Acanthodes) -Cartilages identical to Acanthodes (Burrow,2004). -Teeth absent from gape -Mandibular splint appears to be dermal by comparison to endoskeletal tissues -Numerous dermal gill rakers on all pharyngeal arches. Diplacanthus. Mandibular Splint Transverse section. of Ischnacanthus lower jaw. s d i d. o h t. Meckel's Cartilage. n a c. -stem-osteichthyan -Inner dental arcade shed with resorption (Chen et al) -Putative whorl-like growth in marginal bones (Botella et al.), but see Cunningham ? et al.) ?. Compagopiscis -placoderm-grade stem-gnathostome -teeth on dermal plate -added in multiple directions (Rücklin et al. Tooth 2012) shedding. Ischnacanthids. -ray-finned and lobefinned fishes (inc. tetrapods) -Teeth partially resorbed, shed, and replaced -Teeth borne on dermal jaw bones -Tooth whorls in some taxa (e.g. see Doeland et al.). Lophosteus. s d i h ant. c a l ip. D. Left Meckel's cartilage. 8 1 0 2 oates. C. u s n e s " i. i d o nth. a c A ". Mould of Ptomacanthus NHM. P. 24919a showing parallel. tooth whorls of upper jaw. Dermal jaw bone. Crown-chondrichthyans. Doliodus. -"shark-like" stem-chond. Ptomacanthus -Teeth join at base to form -"Acanthodian" stem-chond. parallel rows which grew by -Teeth join at base to form the lingual addition of teeth parallel rows which grew by -Shedding unclear the lingual addition of teeth (Maisey 2014). -Unclear whether teeth or whorls shed (Ørvig 1973).. Inner dental arcade?. Teeth mounted directly on jaw cartilage. -Teeth absent -Curved dermal bone inside gape of Mould of surface Palatoquadrate lower jaw. Curved dermal bone. A. Mineralised ventral edge (crushed). Crown-osteichthyans. 2. Phylogenetic context. 2 We contextualised this data in the broad agreement from recent phylogenetic studies into early vertebrates (see Coates et al. 2018, Dearden et al. 2019). All four scanned taxa are members of the"Acanthodii" sensu Coates et al. 2018, putatively the earliest-branching grade within chondrichthyans.. CROWNOSTEICHTHYANS. CYCLOSTOMES. -Teeth grow similarly to Taemasacanthus -Lingual row added onto a distinct plate of dermal bone, also present (but less obvious) in Taemasacanthus. Ischnacanthus. specimens from the collections of the Natural History Museum (NHM), London, UK. All four taxa are Palaeozoic acanthodian-grade stemchondrichthyans. Data was processed in Mimics (Materialise) and visualised in Blender.. CROWN-GNATHOSTOMES. ?. CROWNCHONDRICHTHYANS. STEM-CHONDRICHTHYANS. Taemasacanthus. 1. We used CT scanning at Bristol University to scan the jaw bones of four. "ACANTHODIANS". The dentition in living chondrichthyans (sharks, rays, and elephant sharks) primitively comprises parallel series of ever-growing (and ever-shedding) teeth. Contrastingly, teeth in their sister group osteichthyans (bony fishes and tetrapods) are resorbed and grow in position. "Acanthodians", a poorly understood grade of Palaeozoic fishes in the chondrichthyan stem-group, have long been recognised as key to reconciling these two different modes of growth and discerning the evolutionary origins of teeth. However, these animals display a profusion of poorly understood dental structures as well as a poorly understood relationships. Here we use computed tomographic (CT) methods to better characterise the diversity of oral structures in acanthodian-grade stem-chondrichthyans, and place this in the context of what is known about early chondrichthyan phylogeny.. Methods. Simplified scheme of vertebrate relationships. From Dearden (2019) PhD thesis. Introduction. -Sharks, rays, chimaeras -Teeth form parallel rows that are shed labially and replaced lingually -Modified into tooth plates in some taxa -Presumed homologous with stem-chond. tooth whorls. Doliodus tooth whorl. shown with cartilage. in Maisey (2014). Series of parallel tooth whorls. Tooth shedding. Conclusions. Resorption Tooth whorls?. 3. Character. distribution. References: Botella et al. 2007 Nature, Burrow 2004 Fossils and Strata, Chen et al. 2017 R. Soc open. sci., Coates et al. 2018 Proc. Roy. Soc. B, Cunningham et al.2012 Biology Letters, Dearden et al. 2019. Nature Comm., Doeland et al. 2019 R. Soc open sci., Maisey et al. 2014 J. Morph., Ørvig 1967 Zoo. J.. Linn. Soc., Ørvig 1973 Pal. Ab. A, Rücklin et al. 2012 Nature Image credits: Phylopic images uploaded by Ghedoghedo, Gareth Monger, and Tony Ayling. Other silhouettes modified from Brazeau (2012), Coates (2018), Gardiner (1984), Gardiner and Miles (1994), Long (1986), Schaeffer and Williams (1977), and Watson (1937).. -Ischnacanthid jaw bones grew by the addition of teeth unidirectionally on an underlying dermal bone, with similarities to both Compagopiscis and chondrichthyan tooth whorls. -Mandibular splints are probably dermal and possibly present only in acanthodids those in ischnacanthids are instead a reinforced region of Meckel's cartilage. -Acanthodopsis teeth are histologically distinct from underlying bone, but are dissimilar to all other chondrichthyan tooth morphologies. Either an unexpected holdout of teeth in an otherwise toothless clade, or alternatively could be adapted gill rakers?. Acknowledgements: Thanks to Emma Bernard at the NHM, London, for access to specimens, and to Tom Davies at Bristol University for help scanning specimens. Thanks also to Christ Church, Oxford, who funded the research via a JRF to SG and the Muséum national d'histoire naturelle, Paris for funding RPD's travel..

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