Supplementary Information Exceptional fossil preservation demonstrates a new mode of axial skeleton elongation in early ray-finned fishes Erin E. Maxwell, Heinz Furrer, Marcelo R. Sánchez-Villagra Supplementary Figure S1. Horizontal septum and flanking multilayer in Saurichthys curionii. Anteriormost preserved abdominal myosepta of PIMUZ T 5806; anterior is to the right 1
Supplementary Note 1. List of morphological characters coded for phylogenetic analysis. Cranial 1. Skull fineness (ordered): ratio of the length of the antorbital segment to the height of the maxilla + preoperculum in lateral view 0-0-1; 1-2-9; 2- greater than 10. 2. Supraorbital bone: 0-present; 1-absent (modified from 32 ) 3. Orbits: 0-opening dorsally, such that the interorbital distance is approximately half as wide as the width of the skull roof immediately posterior to the orbits; 1-interorbital constriction of frontals minimal 4. Parietals: 0-paired; 1-fused (modified from 32 ) 5. Posterior margin of dermopterotic: 0- U-shaped; 1- V-shaped 6. Posterior margin of dermopterotic: 0- distance between posterior projections less than anterior-posterior length along midline; 1- distance between posterior projections greater than anterior- posterior length along midline 7. Post-temporal bone: 0-present; 1-absent 32 8. 9. Ratio of the length of the postorbital segment to maximum height of postorbital segment, measured between the dorsal margin of the preoperculum and the ventral margin of maxilla (ordered): 0-1.2; 1-1.2-2; 2-2=2 10. Robust marginal dentition: 0- subnarial; 1- beginning anterior to external nares 11. Maxilla: 0- bearing robust marginal dentition; 1- maxilla edentulous or only bearing denticles 12. Preopercle: 0- with anterolateral exposure greater than 1/3 height of maxilla; 1- reduced 13. Operculum: 0-higher than long; 1-longer than high 14. Operculum: 0-straight anterior margin; 1-anterior edge angular 15. Operculum: 0-posterior margin angular, giving the element a triangular outline; 1- posterior margin rounded, giving the element a D-shaped outline 16. Angular: 0- excluded from lateral view posterior to the orbital margin; 1- visible in lateral view ventral to the orbit 17. Mandibular rami: lateral shelf reducing space between rami 0- present; 1- absent 18. Length of mandibular symphysis as a proportion of total mandibular length (ordered): 0-0.2; 1-0.4 19. Jaws: with crypts for opposing tooth 0- present; 1- absent Vertebral Column 20. Neural spines: 0- rectangular and flattened in cross-section; 1- thin and rounded in crosssection 21. Prezygapophyses anterior to the median fins: 0- absent, 1- present and elongate (modified from 32 ) 22. Neural arches + spines immediately posterior to the skull: 0- approximately half the height of neural arches and spines between the pelvic and anal fins; 1- little change in the height of neural spines along the length of the column. 23. Anterior abdominal neural arches: 0- neural spine present; 1- box-like 24. Neural spines in region of the abdominal-caudal transition: 0- approximately twice the height of the neural arches; 1- much shorter 25. Interdorsals: 0- resembling neural arches; 1- small, poorly ossified 26. Interventrals: 0- resembling haemal arches; 1- significantly distinct from haemal arches 2
27. Haemal arches anterior and dorsal to anal fin: 0- box-like; 1- bearing elongate haemal spines; 2- unossified 28. Haemal arches posterior to anal fin but anterior to caudal fin: 0-box-like; 1- bearing short haemal spines; 2- unossified 29. Abdominal-caudal osteological transition: 0- corresponding to location of pelvic fins, 1- anterior to pelvic fins. Dorsal and anal fins 30. Fringing fulcra: 0- present; 1- absent 32 31. Segmentation of the lepidotrichia in the dorsal and anal fins (ordered): 0-6-10 segments; 1-2-5 segments; 2- unsegmented. 32. Number of dorsal axonosts (ordered): 0-15; 1-10-13; 2-9 33. Dorsal fin axonosts: 0- located mostly anterior to fin position; 1- ventral to fin position 34. First dorsal axonost: 0- massively expanded; 1- not differentiated from succeeding axonosts. 35. Anal fin, anterior axonosts: 0- almost half the length of the fin; 1- short relative to the fin. Caudal Fin 36. Segmentation of the lepidotrichia in the caudal fin (ordered): 0-10; 1-2-6; 2- unsegmented 37. Caudal radials: 0- clearly differentiated; 1- reduced or absent 38. Caudal fin: 0- clearly bifurcated (v-shaped); 1- essentially triangular 39. Caudal fin: 0- body axis extending into dorsal lobe of fin; 1- body axis straight Paired fins 40. Cleithrum: 0- with posterior process straight; 1- with posterior process descending; 2- with flat posterior margin 41. Cleithrum: 0- with dorsal process curving anteriorly; 1- with dorsal process straight or posteriorly inclined 42. Pelvic fins: 0-located closer to the anal fin than half the length of the tail stock, 1- located further anteriorly than half length of tail stock 43. Pelvic fin: 0- well-ossified radials present; 1- absent 44. Segmentation of the lepidotrichia in the pelvic fin: 0- present; 1- absent Squamation 45. Squamation (ordered): 0- complete, 1- six rows; 2- four rows; 3- three rows; 4- two rows; 5-0 rows. Coded such that only one side of the fish is taken into account (modified from 32 ) 46. Mid-dorsal and mid-ventral scales, abdominal region (ordered): 0- laterally broad; 1- elongate, but still relatively wide; 2- needle-like 47. Mid-dorsal scales anterior to median fins: 0- tubercular ornamentation on mid dorsal scales present; 1- absent. 48. Approximate relationship between the abdominal scales of the lateral row the dorsal scales of the medial row: 0-1:1 1-1:2 or more 49. Mid-lateral scales anterior to median fins: 0- tubercular ornamentation present; 1- absent 3
50. Mid-lateral scales, abdominal region (ordered): 0- dorsoventrally high and rectangular; 1- dorsoventrally high and tapering; 2- rib-like; 3- taller than long, but very reduced in height; 4- small and rounded. 51. Ventrolateral scales: 0- dorsoventrally higher than mid-lateral scales; 1-reduced. If both lateral scale rows are absent anterior to the median fins, this character is coded as unknown. 52. Anal loop scales: 0- not significantly differentiated from the ventral scale row; 1- at least one highly modified scale present 53. Tail stock: 0- reinforced by highly modified scutes; 1- no sudden divergence from the caudal squamation immediately posterior to the dorsal fin 4
Supplementary Note 2. Character matrix used in phylogenetic analysis. #NEXUS Begin data; dimensions ntax=17 nchar=52; format missing=? symbols= 0~5 ; MATRIX Australosomus 0110??000000?01???10100111101001100000001000010100?1 Birgeria 00100001000110010110100111100011100000211005???????? S._paucitrichus 20??1?1111?001???1010000012011111111010?1102201021?0 S._costasquamosus 10011011011001101001?000011011?111110111110210102110 S._krambergi 1??????11100011??001000??22?112001111101111321?14110 S._striolatus 201????1?1?1011??1?0?11??22?12????2111??111321?14110 S._dawaziensis 10????011110011??001?0100020001?0?0101011?0320104100 S._curionii 101101110110111?110100000110111111110111111221114111 S._macrocephalus 101100110110011??001000001?01111?1110110010221113111 Si._longipectoralis?1?00000?110111?1001?0001110010111110120011200103111 Si._longimedialis 111000000110111??101??0011000101111?01210?1200103111 Si._minuta 1110000001101111?1???????10?0111111101210?1200103111 Saurorhynchus_brevirostris 101101?11110111??0110000011112211?200101011421?????0 S._madagascariensis??001001?110000???01??0000??001?11?????????0000040?? S._ornatus?11011020100001???01??0000??0?????????0??0032010410? S._orientalis????????11?010????01?????????1????????0????20000110? S._calcaratus?0????01?11101???????????00?12?00121?1011?1311??41?0 ; end; ctype ord: 1 8 17 30 31 35 44 45 49; begin trees; tree tnt_1 = [&U] (1,(2,(16,((((3,4),(9,(8,(13,(5,(6,17)))))),(10,(11,12))),(14,(7,15)))))); end; 5