1 Supplementary information 2 3 Dental diversity in early chondrichthyans 4 and the multiple origins of shedding teeth 5 6 Dearden and Giles 7 8 9 This PDF file includes: 10 Supplementary figures 1-5 11 Supplementary text 12 Supplementary references 13 Links to supplementary data 14 15 16 Supplementary Figure 1. Taemasacanthus erroli left lower jaw NHMUK PV 17 P33706 in (a) medial; (b) dorsal; (c) lateral; (d) ventral; (e) posterior; and (f) 18 dorsal and (g) dorso-medial views with tooth growth series coloured. Colours: 19 blue, gnathal plate; grey, Meckel’s cartilage. 20 21 Supplementary Figure 2. Atopacanthus sp. right lower or left upper gnathal 22 plate NHMUK PV P.10978 in (a) medial; (b) dorsal;, (c) lateral; (d) ventral; and 23 (e) dorso-medial view with tooth growth series coloured. Colours: blue, 24 gnathal plate. 25 26 Supplementary Figure 3. Ischnacanthus sp. left lower jaw NHMUK PV 27 P.40124 (a,b) in lateral view superimposed on digital mould of matrix surface 28 with Meckel’s cartilage removed in (b); (c) in lateral view; and (d) in medial 29 view. Colours: blue, gnathal plate; grey, Meckel’s cartilage. 30 Supplementary Figure 4. Acanthodopsis sp. right lower jaw NHMUK PV 31 P.10383 in (a,b) lateral view with (b) mandibular splint removed; (c) medial 32 view; (d) dorsal view; (e) antero-medial view, and (f) posterior view. Colours: 33 blue, teeth; grey, Meckel’s cartilage; green, mandibular splint. 34 35 Supplementary Figure 5. Acanthodes sp. Left and right lower jaws in 36 NHMUK PV P.8065 (a) viewed in the matrix, in dorsal view; (b) superimposed 37 on the digital mould of the matrix’s surface, in ventral view; and (c,d) the left 38 lower jaw isolated in (c) medial, and (d) lateral view. Colours: grey, 39 endoskeleton; green, dermal skeleton; white, matrix/mould. 40 41 42 43 Supplementary text 44 Section 1 – Full description of jaw elements 45 Taemasacanthus 46 Taemasacanthus erroli is known from eight isolated jaws from the Emsian 47 (Lower Devonian) Murrumbidgee Group in New South Wales, Australia (1). 48 Other species, also based on isolated jaw bones, have been assigned to the 49 genus (2,3), but no articulated animals are known. Taemasacanthus is 50 understood to be an ischnacanthid on the basis of its similarity to well-known 51 members of that grade. NHM UK PV P.33706, described here, is a lower right 52 jaw, and is comprised of two main parts: a dermal gnathal plate and the 53 articular ossification of Meckel’s cartilage. The external morphology of this 54 jawbone in Taemasacanthus is fully described by Long (1986), but is briefly 55 redescribed here to contextualise our new information. 56 The gnathal plate is approximately half the full depth of the jaw, and is 57 sinusoidal in dorsal view (Figs. 1a,b,S1). A circular ridge, which Long (1986) 58 suggests might be for a labial cartilage, is present on the lateral surface 59 approximately ¼ of the way along its length (Fig. S1c). Anterior to this, the 60 gnathal plate curves medially to follow the outline of the jaw, with the lateral 61 tooth row positioned on its dorso-lateral surface. Posteriorly, the gnathal plate 62 curves laterally and broadens to wrap around the articular (Fig. S1b). The 63 lateral expansion is larger than the medial expansion, and both are rounded 64 posteriorly. Ventrally, a groove formed by the posterior confluence of these 65 two processes runs underneath the entire length of the gnathal plate, and 66 would have overlain Meckel’s cartilage (Fig. S1d). The greatest part of the 67 gnathal is approximately trapezoid in cross section, and bears three rows of 68 teeth. Histologically this comprises heavily vascularised dermal bone, similar 69 to that observed in thin sections of other ischnacanthid jaw elements (4–6), 70 with a relatively thin layer of less vascularised bone around the plate margins. 71 The vascularisation comprises an interlinked network of tubules, which are 72 strongly polarised along the anteroposterior length of the element (Fig. 1c). In 73 transverse section these are near-horizontal, running the width of the element, 74 and are interlinked. The circular ridge is formed of avascular bone, but is 75 otherwise a similar tissue to that forming the outer margin of the gnathal plate. 76 The dermal bone is broken anteriorly, exposing the histology and shearing 77 through a tooth. 78 Three rows of teeth are present in Taemasacanthus, all starting approximately 79 at the level of the mesial ridge: a lateral row, medial row, and lingual row 80 (Figs. 1, S1a,f,g). The mesial ridge is formed by the dorsal corner of the 81 underlying gnathal plate, and bears a disorganised row of irregular cusps. 82 These cusps are continuous with the underlying dermal bone, and only the 83 more posterior few are vascularised. The cusps extend along roughly the 84 posterior half of the mesial ridge – anteriorly the ridge is smooth. The lateral 85 tooth row comprises around twelve cusps, mounted on the dorso-lateral face 86 of the gnathal plate. Posteriorly these are approximately the size as the 87 mesial ridge cusps, but they become progressively larger anteriorly. This tooth 88 row follows the outside of the gnathal plate, and teeth are joined by a ridge 89 which, along with the teeth themselves, is laterally continuous with the plate’s 90 outer surface. The lingual side of each cusp is rounded, and ornamented with 91 a number of ridges, which become progressively more tuberculated on 92 anterior cusps. The lingual row comprises ten cusps which become 93 progressively larger anteriorly, and which curve antero-medially along the 94 dorso-lingual surface of the underlying dermal plate. Cusps are similar in 95 shape and ornament to those of the lateral row, but without the outer ridge, 96 instead being completely surrounded by the ridged ornament. The histology of 97 the lateral and lingual tooth rows is similar, comprising a vascular internal 98 tissue, seemingly without a continuous enameloid covering (Fig. 1c). In both 99 rows, teeth are added anteriorly, with anterior cusps overlying posterior ones. 100 In what is probably a pathology, the eighth cusp of the lingual row is 101 incomplete, and is either damaged or its growth appears to have been 102 aborted (Fig. 1a)). The ninth cusp in the row has instead grown over the 103 incomplete eighth as well as the tenth cusp. This is in fact the youngest cusp 104 in the entire row, and is oriented notably more medially. 105 Only the posteriormost portion of the Meckel’s cartilage, the articular 106 ossification, is preserved (Figs. 1, S1). It is formed from a sheath of 107 perichondral tissue, and would have been filled with cartilage in life. Some 108 spongy texture is apparent on the interior surface of the perichondral bone. A 109 shallow groove on the posterior surface does not appear to continue ventrally, 110 making it unlikely to have accommodated a mandibular splint (as suggested 111 by Long 1986). Articulation with the palatoquadrate appear to be via a an 112 open, oval, fossa (Long 1986) (Fig. S1b). The tissue forming this is however 113 notably ill-formed, and appears to lack a solid perichondral covering, meaning 114 that it could well, as Burrow (2004) suggests, be a typical ischnacanthid 115 process that has lost its tip. An additional ventral fragment of the articular (as 116 figured in Long 1986) has become detached from the rest of the ossification. 117 Atopacanthus 118 The genus Atopacanthus is known throughout the Middle-Upper Devonian (7). 119 The type species, Atopacanthus dentatus, is known from several jaws from 120 near Hamburg, New York (8,9). Articulated fossils of Atopacanthus sp. from 121 the Upper Devonian are also known (10), their attribution to this genus is 122 questionable (11). The specimen described here, NHMUK PV P.10978, was 123 collected from Elgin, Scotland, in making it Middle Devonian in age. It was 124 originally labelled as possibly dipnoan, before later being referred to 125 Atopacanthus, and its morphology conforms with that of other specimens 126 described as Atopacanthus. 127 This specimen comprises a dermal jawbone (Figs. 1d-f, S2). It is not 128 associated with any endoskeletal material, making it impossible to tell whether 129 it is from a right lower jaw or upper left jaw. For ease of comparison with other 130 specimens, we describe its morphology as if it were a lower jaw element. As 131 in Taemasacanthus, the gnathal plate is robust, and likely occupied most of 132 the full depth of the jaw. It is trapezoid in cross-section, but flatter and taller 133 proportionate to its length than in Taemasacanthus, and is slightly medially 134 convex. The element appears to be broken both anteriorly and posteriorly, 135 with internal histology visible at both ends. The anterior fifth of the element is 136 toothless and tapers slightly. A narrow, shallow groove to accommodate the 137 mandibular cartilage runs along the ventral surface of the element (Fig. S2d). 138 Internally the histology is similar to Taemasacanthus, being heavily 139 vascularised antero-posteriorly oriented tubules (Fig. 1f). However, the 140 lamination of this vascularisation is more pronounced, and they are clearly 141 oriented in an antero-dorsal direction. Towards the surface of the element 142 vascularisation is less dense, and not polarised. On the lingual face of the 143 element is a thin lingual plate. This is still heavily vascularised, but tubes are 144 instead polarised across the dorso-lingual surface of the main dental plate.