Nature 2014 Long JA

LETTERdoi:10.1038/nature13825

Copulation in antiarch placoderms and the origin ofgnathostome internal fertilizationJohn A. Long1,2,3, Elga Mark-Kurik4, Zerina Johanson5, Michael S. Y. Lee6,7, Gavin C. Young8, Zhu Min9, Per E. Ahlberg10,Michael Newman11, Roger Jones12, Jan den Blaauwen13, Brian Choo1 & Kate Trinajstic14,15

Reproduction in jawed vertebrates (gnathostomes) involves eitherexternalor internal fertilization1. It is commonly argued that internalfertilization can evolve from external, but not the reverse.Male copu-latory claspers are present in certain placoderms24, fossil jawed ver-tebrates retrieved as a paraphyletic segment of the gnathostome stemgroup in recent studies58. This suggests that internal fertilizationcould be primitive for gnathostomes, but such a conclusion dependsondemonstrating that copulationwasnot just a specialized featureofcertain placoderm subgroups. The reproductive biology of antiarchs,consistently identified as the least crownwardplacoderms58 and thusof great interest in this context, has until now remained unknown.Here we show that certain antiarchs possessed dermal claspers in themales,while femalesborepaireddermalplates inferred tohave facili-tated copulation.These structures are not associatedwithpelvic fins.Theclaspermorphology resembles that ofptyctodonts, amore crown-ward placoderm group7,8, suggesting that all placoderm claspers arehomologous and that internal fertilization characterized all placo-derms. This implies that external fertilization and spawning, whichcharacterize most extant aquatic gnathostomes, must be derivedfrom internal fertilization, even though this transformation has beenthought implausible. Alternatively, the substantial morphologicalevidence for placoderm paraphyly must be rejected.Among living fish (non-tetrapod vertebrates) internal fertilization

is mostly effected by copulatory structures representing modificationsof the pelvic fins (chondrichthyans9) or anal fins (the gonopodiumof some teleost fishes10,11). The discovery in arthrodiran3 and ptycto-dont placoderms2,4 of copulatory structures (claspers) originally3,12 butincorrectly4 interpreted as modified pelvic fins implied that any pla-coderms lacking pelvic appendages would have also lacked claspers,and therefore reproduced externally by spawning. This was thoughtto be the case with the antiarchs, recently considered the sister group ofall other jawed vertebrates58. Deposits where small antiarch juvenilessuffered mass mortality have been interpreted as nurseries associatedwith mass spawning events13.

Microbrachius, a small bothriolepidoid antiarch, is known from com-plete articulated specimens from theMiddleDevonian (Givetian) periodof Scotland14, the EarlyMiddle Devonian of China15,16 and by isolatedplates from the Essi Farm site in Estonia (Extended Data Figs 1 and 2provide geological background for sites of specimens described herein).Numerous new articulated specimens from the Eday Flags, Orkney Is-lands, Scotland, UK, show eithermale dermal claspers or female genitalplates in life position (Figs 1 and 2 and Extended Data Fig. 3), and onespecimen from Estonia shows an isolated right posterior ventrolateral(PVL)platewith anattacheddermal clasper (Fig. 1ac) (SupplementaryInformation A1 and A2 and Extended Data Figs 1 and 2).

The clasper ofMicrobrachius is a deeply grooveddermal bone (Fig. 1ac, hm) that curves laterally, similar to themain hooked dermal clasperelement of ptyctodontid placoderms2,4. The groove (gr, Fig. 1l, m)mayhave served to transfer sperm, or encased a structure that carried thesperm canal. The articulated specimens show some of the claspers inmesial contact, sutured in the midline (Fig. 1i, k) indicating they werenot mobile. The extended wing of the clasper extends laterally as far asthe width of the trunkshield (Fig. 1h, j, k), potentially enabling a maleMicrobrachius clasper to reach the cloaca of a female if the two indivi-duals were side by side (Fig. 3). Ventrally the claspers have well defineddermal ornamentation of small posteriorly directed spines, and havea series of larger spines along the distal margin (Fig. 1i, m). Variationin clasper size probably reflects individual sexual maturity (ExtendedData Fig. 3).FemaleMicrobrachius dicki (Figs 2eg and 3a, b) showpaired blade-

like structures in the same region corresponding to the male clasper(Fig. 2g). These blades carry a distinctive ornament of curving ridgesand marginal tubercles on their dorsal (that is, internal) surfaces: theonly internally facing ornament in their dermal skeleton. Identicalinternal ornament is seen in Pterichthyodes14, where it occurs on sepa-rate dermal plates preserved atop the dorsal (internal) side of the sub-anal lamina of the PVLplates (Fig. 2ad) in similar position as themaleclaspers. Within other placoderms, where separate male and femaledermal elements are known, they are similarly positioned2,4. Thesedermal plates are flat and taper tomeet the lateral ends of the transverseventral ridge inside the lateral lamina of the PVL plate (Fig. 2fh). Weinterpret these structures inMicrobrachius andPterichthyodes as femalegenital plates, similar to the post-pelvic plates found in some femaleptyctodonts4, and suggest that the claspers attached to them duringmating by gripping the internal ornament which faced into the cloacalchamber (Fig. 3e and Extended data Fig. 9).Two specimens of the LateDevonian antiarchBothriolepis also show

small semicircular plates sitting on the distal area of the subanal laminaof the PVL plates (Fig. 2hj). They are only visible in dorsal view, andshow a slight thickening anteriorly with a line of roughened pits forligamentous ormuscle attachment near the anteriormargin.We inter-pret these as female genital plates as they do not resemblemale claspersinMicrobrachius, and occupy the same topology as the paired genitalplates in female Pterichthyodes. We also identify new features on thesubanal lamina of the PVL plates in other antiarchs, which probablyrelate to their reproductive anatomy (Extended Data Fig. 4 and Sup-plementary Information B4).We thus have compelling evidence for a clasper-based system of

internal fertilization inMicrobrachius, strong circumstantial evidencefor the same system in Pterichthyodes and plausible evidence for the

1School ofBiological Sciences, FlindersUniversity, 2100, Adelaide, SouthAustralia5001, Australia. 2NaturalHistoryMuseumof LosAngelesCounty, 900ExpositionBoulevard, LosAngeles, California9007,USA. 3Museum Victoria, PO Box 666, Melbourne, Victoria 3001, Australia. 4Institute of Geology at Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia. 5Department of Earth Sciences,Natural History Museum, London SW7 5BD, UK. 6South Australian Museum, North Terrace, Adelaide, South Australia 5000, Australia. 7School of Earth and Environmental Sciences, The University ofAdelaide, South Australia 5005, Australia. 8Research School of Earth Sciences, The Australian National University, Canberra, Australian Capital Territory 0200, Australia. 9Key Laboratory of EvolutionarySystematics of Vertebrates, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, PO Box 643, Beijing 100044, China. 10Department of Organismal Biology,Evolutionary Biology Centre, Uppsala University, Norbyvagen 18A, 752 36 Uppsala, Sweden. 11Vine Lodge, Vine Road, Johnston, Haverfordwest, Pembrokeshire SA62 3NZ, UK. 126 Burghley Road,Wimbledon, London SW195BH, UK. 13University of Amsterdam, Science Park 904, 1098XH, Amsterdam, TheNetherlands. 14Western Australian Organic and IsotopeGeochemistry Centre, Department ofChemistry, Curtin University, Perth, Western Australia 6102, Australia. 15Earth and Planetary Sciences, Western Australian Museum, Perth, Western Australia 6000, Australia.

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same in Bothriolepis. Although male claspers have not been described inantiarchsother thanMicrobrachius, even fromtaxasuchasBothriolepis17,18,Asterolepis19 and Remigolepis20 known from hundreds of articulatedspecimens with tails preserved, we suggest that internal fertilization

is general for the Antiarchi. As the dermal skeleton is quite reduced inadvanced antiarchs, we propose that the claspers in some forms mighthave alsobeencartilaginous and thusnotwell preserved. Further evidencefor internal fertilization in antiarchs comes from their large hatchlings13

(Supplementary Information B4).The clasper inMicrobrachius is clearlydifferent fromthe pelvic girdle

and fin, known only in one antiarch: Parayunnanolepis from the EarlyDevonian of China21. More derived asterolepidoid and bothriolepioidantiarchs lack pelvic girdles and fins, which are thus assumed to be lost(secondarily absent) in these groups19. In chondrichthyans, the clasperis attached to the posterior extremity of the pelvic finmetaptyerygium9,22,23.In ptyctodont and arthrodire placoderms, the clasper is immediatelyposterior to the pelvic fin4, and has previously been interpreted as anelaboration of the pelvic fin skeleton2,3. However, new evidence showsthat the clasper of arthrodires does not articulate directlywith the pelvicgirdle or fin4. In ptyctodonts the endoskeleton of the clasper (if present)

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Figure 1 | Male reproductive structures in antiarchs and ptyctodontids.ac, Microbrachius sp. right PVL plate, GIT 628-24 in (a) dorsal view,(b) interpretive drawing and (c) lateral view. dg, Dermal clasping elementsof ptyctodont Austroptyctodus gardineri, NHMUK PV P57665; d, dermalhooked elements in dorsal and ventral (g) views; e, large hooked dermalelement in ventral view; f, reversed image. hm, Male M. dicki specimensshowing claspers with close-up views of some specimens. h, i, NHMUK PVP73397; j, NHMUK PV P77402; k, NHMUK PV P77401; l, m, NHMUK PVP77405. Abbreviations: cls, dermal clasping elements; clsd, distal claspingelement; clst, terminal hooked clasping element; gr, groove;mls,midline suture;orn, ornament; PVL, posterior ventrolateral plate; ri, ridge; sp., spines; sut,suture between clasper and PVL; tvr, transverse lateral ridge; vl, ventral lamina;vlr, ventrolateral ridge.

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Figure 2 | Female reproductive structures in MiddleLate Devonianantiarchs. a, c, Pterichthyodes milleri; NHMUK PV P32544; b, d, UMZC 687.eg, M. dicki; e, f, NHMUK PV P73398; g, NHMUK PV P73399.h, i, Bothriolepis canadensis, V11127 (Smithsonian), showing armour (h) andfemale genital plates (i). j, Bothriolepis sp. ANU V1040, close up of pairedfemale genital plates. Abbreviations: fgp, female genital plates; l.PVL, leftposterior ventrolateral plate.

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was unossified12,making itmore difficult to determine its precise relation-ship to neighbouring structures, but the dermal components of the clas-pers are consistently preserved some distance posterior to the pelvis2,4,12.All known placoderm claspers thus differ from chondrichthyan clas-pers in being independent from the pelvis and pelvic fin. The principledermal element of the ptyctodont clasper is a large curved, groovedplate (Fig. 1e, f) that distinctly resembles and is thus probably homo-logous to the dermal clasper of Microbrachius, whereas arthrodireclaspers have a much smaller but plausibly homologous dermal bonetip3,4. Based on similarities in position (behind and independent ofpelvic region), and materials (dermal bone), the claspers of antiarchs,ptyctodonts and arthrodires are most probably homologous with eachother, but not homologous with the claspers of chondrichthyans.

To evaluate the evolution of claspers and reproductive biology acrossgnathostomes, we expanded upon a recently published phylogeneticanalysis8 with the addition of 14 placoderm taxa, three new characters(256258), andone character (122) split into two (122, 159) (Supplemen-tary Information C7, 8). Our analyses of both expanded and originaldata sets yielded very similar trees, which supported placoderm para-phyly andplaced antiarchs as the sister group to all other gnathostomes(Extended Data Figs 5 and 6 and Supplementary Information C7, 8).Our analyses found shorter trees for the original data set8, supporting amore orthodox position for ptyctodonts lower on the gnathostomestem (Extended Data Figs 7 and 8 and Supplementary Information C8).The shortest tree indicates that bony claspers separate from the pelvicfin arose in themost recent common ancestor of jawed vertebrates andwere lost in the most recent common ancestor of crown gnathostomes(Fig. 4 and Extended Data Figs 5 and 6).These results have intriguing biological implications. The implied

loss of bony claspers and implied reversion to external fertilization incrown gnathostomes appears heterodox: loss of internal fertilizationand acquisition of external fertilization is not widely accepted, at least

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Figure 3 | Male and female sexual dimorphism in M. dicki. Reconstructionof femaleM. dicki in (a) dorsal and (b) ventral views; c, d, maleM. dicki ventralviews showing variations in clasper development; e, hypothetical matingposition for Microbrachius. Abbreviations as for Figs 1 and 2 plus pec.ap,pectoral appendage.

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Figure 4 | Phylogeny of major lineages of gnathostomes, based on analysisof an expanded version of the data set from ref. 8. Distribution andmorphology of two kinds of clasper aremapped on the phylogeny. Claspers aremost parsimoniously inferred to have evolved in the most recent commonancestor of all gnathostomes, then lost before or at the node of crown groupgnathostomes. Claspers developed as a modified part of the pelvic fin skeletonappear as a synapomorphy of all chondrichthyans. The full tree with branchsupports and states for all terminal taxa is shown in ExtendedData Figs 5 and 6.See Supplementary Information for further details of the analysis.

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in vertebrates1,11 although it could have happened multiple times ininvertebrates24. The shared, unique morphology and post-pelvic posi-tion of claspers in all placoderms ismore consistentwith a single origin,and thus represents a potential synapomorphy supporting placodermmonophyly25.If all placodermclaspers are homologous, aswe suggest, this gives rise

to alternative implications with equally startling significance for earlyvertebrate evolution. If placoderm paraphyly is accepted, on the basisof the optimal trees here (and consistent with the majority of recentanalyses58), then external fertilization and spawning employed by themajority of recent bony fishes and many lissamphibians must haveevolved from clasper-mediated internal fertilization. If claspers areaccepted as prima facie evidence of placodermmonophyly25, the trans-formation of cranial architecturewithin thePlacodermi documentedbyseveral recent analyses58must be entirely convergent oncrowngnathos-tomes, as the antiarchs belong to the cluster of primitive placodermswith posteriorly placed rostronasal capsules and a trabecular upperlip8. Placodermmonophyly is also inconsistentwith the co-occurrenceof placoderm and osteichthyan characteristics in Silurian taxa such asEntelognathus7. Resolutionof the status of placoderms,whichwill requiredata both from fossil anatomyand the reproductive physiology of extantfishes, is one of the most pressing tasks currently facing early gnathos-tome palaeontology.

Online ContentMethods, along with any additional Extended Data display itemsandSourceData, are available in theonline versionof thepaper; referencesuniqueto these sections appear only in the online paper.

Received 27 January; accepted 29 August 2014.

Published online 19 October 2014.

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3. Ahlberg, P. E., Trinajstic, K., Johanson, Z. & Long, J. A. Pelvic claspers confirmchondrichthyan-like internal fertilization in arthrodires. Nature 460, 888889(2009).

4. Trinajstic, K. M., Boisvert, C., Long, J. A., Maksimeko, A. & Johanson, Z. Pelvic andreproductive structures in placoderms (stem gnathostomes). Biol. Rev. http://dx.doi.org/10.1111/brv12118 (2014).

5. Brazeau, M. D. The braincase and jaws of a Devonian acanthodian and moderngnathostome origins. Nature 457, 305308 (2009).

6. Davis, S. P., Finarelli, J. A.&Coates,M. I.Acanthodes and shark-like conditions in thelast common ancestor of modern gnathostomes. Nature 486, 247250 (2012).

7. Zhu, M. et al. A Silurian placoderm with osteichthyan-like marginal jaw bones.Nature 502, 188193 (2013).

8. Dupret, V., Sanchez, S., Goujet, D., Tafforeau, P. & Ahlberg, P. E. A primitiveplacoderm sheds light on the origin of the jawed vertebrate face. Nature 507,500503 (2014).

9. Freitas, R., Zhang, G. & Cohn, M. J. BiphasicHoxd gene expression in shark pairedfins reveals an ancient origin of the distal limb domain. PLoSONE 2, e754 (2007).

10. Meyer, A. & Lydeard, C. The evolution of copulatory organs, internal fertilizationplacentae and viviparity in killifishes (Cyprinodontiformes) inferred from a DNAphylogeny of the tyrosine kinase gene X-src. Proc. R. Soc. Lond. B 254, 153162(1993).

11. Parenti, L. R., LoNostro, F. L. & Grier, H. J. Reproductive histology of Tomeurus gracilisEigenmann, 1909 (Teleostei: Atherinomorpha: Poeciliidae) with comments onevolution of viviparity in atherinomorph fishes. J. Morphol. 271, 13991406 (2010).

12. Miles, R. S. & Young, G. C. Placoderm interrelationships reconsidered in the light ofnew ptyctodontids fromGogo,Western Australia. Linn. Soc. Symp. Ser.4,123198(1977).

13. Downs, J. P., Criswell, K. E. & Daeschler, E. B. Mass mortality of juvenile antiarchs(Bothriolepis sp.) from theCatskill Formation (Upper Devonian, FamennianStage),Tioga county, Pennsylvania. Proc. Acad. Nat. Sci. Philad. 161, 191203 (2011).

14. Hemmings,S.K. TheOldRedSandstoneantiarchs ofScotland:PterichthyodesandMicrobrachius. Palaeontogr. Soc. Monogr. 131 (551), 164 (1978).

15. Pan, J. A new species ofMicrobrachius from the Middle Devonian of Yunnan.Vertebr. Palasiat. 22, 813 (1984).

16. Wang, J.-Q. & Zhang, G.-R. Newmaterial ofMicrobrachius from the LowerDevonianof Qujing, Yunnan, China. Vertebr. Palasiat. 37, 200211 (1999).

17. Stensio, E. A. On the Placodermi from the Upper Devonian of East Greenland. II.Antiarchi: subfamilyBothriolepinae.With anattempt at a revisionof thepreviouslydescribed species of the family.Medd. Grnl. 139, 1622 (1948).

18. Long, J. A.&Werdelin, L. AnewLateDevonianbothriolepid (Placodermi,Antiarcha)from Victoria, with descriptions of others from the state. Alcheringa 10, 355399(1986).

19. Lysarkaya, L. A. Baltic Devonian Placodermi. Asterolepididae [in Russian] 1152(Zinatne, 1981).

20. Johanson, Z. New Remigolepis (Placodermi; Antiarchi) from Canowindra, NewSouth Wales, Australia. Geol. Mag. 134, 813846 (1997).

21. Zhu, M., Yu, X., Choo, B., Wang, J. & Jia, L. An antiarch placoderm shows that pelvicgirdles arose at the root of jawed vertebrates. Biol. Lett. 8, 453456 (2012).

22. Leigh-Sharpe,H. Thecomparativemorphologyof the secondary sexual charactersof elasmobranch fishes. The claspers, clasper siphons, and clasper glands.Memoir IIIV. J. Morphol. 36, 190240 (1922).

23. Goodrich, E. S. Studies on the Structure and Development of Vertebrates Vol. 1,1486 (Dover Publications, 1958).

24. Rouse, G.W. Broadcasting fables: is external fertilization really primitive? Sex, size,and larvae in sabellid polychaetes. Zool. Scr. 23, 271312 (1994).

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Supplementary Information is available in the online version of the paper.

Acknowledgements For access to collections we thank E. Bernard, D. Pickering,E. Fitzgerald, L.Grande,W.SimpsonandH.-D.Sues. For photographywe thankP.Hurst,G. Baranov and D. Hubert. We thank M. Brazeau for reviewing an earlier version of thepaper. Travel to Tallinn, London and Washington for J.A.L. to examine specimens wassupported by Flinders University. G.C.Y., J.A.L. and K.T. acknowledge support from theAustralian Research Council.

Author Contributions The project was designed by J.A.L., with material examined anddescribed by J.A.L., E.M.K., Z.J., K.T., B.C. and P.E.A. M.S.Y.L. performed phylogeneticanalyses with input from J.A.L., G.C.Y. and B.C. M.N., J.D.B. and R.J. collected andprepared material, provided site information and input to the discussion. Illustrationswere made by J.A.L. and B.C. with photography supplied for some specimens by theNaturalHistoryMuseum, London, andby the InstituteofGeologyatTallinnUniversityofTechnology. All authors contributed to data interpretation, figures and writing of thepaper.

Author Information Reprints and permissions information is available atwww.nature.com/reprints. The authors declare no competing financial interests.Readers are welcome to comment on the online version of the paper. Correspondenceand requests for materials should be addressed to J.A.L. ([email protected]).

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Extended Data Figure 1 | Location and stratigraphic position of Estonianspecimens ofMicrobrachius. Top, map showing locality of the Essi Farm site,Estonia, and stratigraphical section where the fossils were found. Modifiedfrom ref. 26. Below, Microbrachius sp. plates from Essi Farm, Estonia. a, GIT628-37, sample showing several small plates and fragments; b, GIT 628-9, right

lateral plate, visceral view; c, 628-3, posterior median dorsal plate, dorsalview; d, GIT 628-25, right posterior ventrolateral plate, visceral view; e, GIT628-18, anterior section of anterior ventrolateral plate, lateral view showingbrachial process. All specimens held within the Institute of Geology at TallinnUniversity of Technology, Estonia, collection GIT 628.

26. Mark-Kurik, E. Psammosteidmicroremains from theMiddle Devonian (Givetian)of Estonia.Mod. Geol. 24, 121 (1999).

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Extended Data Figure 2 | Location and stratigraphic position of newScottish specimens of M. dicki described herein. Top, map of the OrkneyIslands with an asterisk marking the location where the specimens ofM. dicki

described in this paper were collected. Below, stratigraphical column of theupper part of the Middle Devonian in the Orkney Islands with the position ofthe Eday Flagstone Formation fish beds marked by a dotted line.

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Extended Data Figure 3 | Growth of claspers in M. dicki males.a, b, NHMUKVP P 77400, claspers only weakly developed, no lateral wing;close up of claspers in b; c, d, NHMUK VP P 77403 showing further caudally

directed growth of claspers; d, close up of claspers showing fusion in midline.Scale bars, 1 cm.

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Extended Data Figure 4 | New information on pelvic region anatomy inantiarchs. Top, Yunnanolepis porifera, Xitun Formation, Yunnan, China.Specimen IVPP V19359) in (a) dorsal view, (b) ventral view and (c)showing posterior region of trunkshield prepared to show internal side ofthe PVL plates. p.ri, strong ridge on the dorsal surface of the posterior regionof the PVL plates. Below, a, b, Bothriolepis sp., Gogo Formation, Western

Australia (P223045, Museum Victoria, Melbourne); c, B. canadensis,Escuminac Formation, Quebec, Canada (UF 252, Field Museum, Chicago).Abbreviations: m.att?, muscle attachment area; ri.i, internal ridge, ri.o, outerridge; pl, platform; sb.l, subanal lamina; tvr, transverse ridge (5 cristatransversalis interna posterior, Stensio 1948).

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Extended Data Figure 5 | Strict consensus tree from 7,039 trees (L5 640)from analysis of the expanded data set (85 taxa, 259 characters). Numberson branches denote Bremer and bootstrap support. Green squares denotepresence of bony claspers (character 122), red squares denote presence of

cartilaginous claspers (character 259) and white squares denote absence ofboth types of clasper. Circles denote gain/loss of the two types of clasper underthe most-parsimonious optimization.

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CheirolepisDialipina

Ptomacanthus

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Moythomasia

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Meemannia

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Hamiltonichthys

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Microbrachius

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Powichthys

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Youngolepis

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Majority-Rule consensus (and also one of the 7039 MPTS)L=640, CI=0.42, RI=0.82

All nodes found in 100% of MPTs unless otherwise indicatedAll majority-rule groupings shown (including those in

Extended Data Figure 7 | Strict consensus tree from 808 trees (L5 611) from re-analysis of the data set in ref. 8. Numbers on branches denote Bremer andbootstrap support.

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ExtendedData Figure 8 | Majority-rule consensus tree, and one of themost-parsimonious trees (length 611) from analysis of the data in ref. 8. Numbers onbranches indicate percentage of MPTs that contain a particular clade (100% unless otherwise indicated).

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Extended Data Figure 9 | Reconstruction showing hypothetical mating Microbrachius, with male to the right, female on left. Artwork by B. Choo.

LETTER RESEARCH


TitleAuthorsAbstractReferencesFigure 1 Male reproductive structures in antiarchs and ptyctodontids.Figure 2 Female reproductive structures in Middle-Late Devonian antiarchs.Figure 3 Male and female sexual dimorphism in M. dicki.Figure 4 Phylogeny of major lineages of gnathostomes, based on analysis of an expanded version of the data set from ref. 8.Extended Data Figure 1 Location and stratigraphic position of Estonian specimens ofMicrobrachius.Extended Data Figure 2 Location and stratigraphic position of new Scottish specimens of M. dicki described herein.Extended Data Figure 3 Growth of claspers in M. dicki males.Extended Data Figure 4 New information on pelvic region anatomy in antiarchs.Extended Data Figure 5 Strict consensus tree from 7,039 trees (L = 640) from analysis of the expanded data set (85 taxa, 259 characters).Extended Data Figure 6 Majority-rule consensus tree, and one of the most-parsimonious trees (length 640) from analysis of the expanded data set (85 taxa, 259 characters).Extended Data Figure 7 Strict consensus tree from 808 trees (L = 611) from re-analysis of the data set in ref. 8.Extended Data Figure 8 Majority-rule consensus tree, and one of the most-parsimonious trees (length 611) from analysis of the data in ref. 8.Extended Data Figure 9 Reconstruction showing hypothetical mating Microbrachius, with male to the right, female on left.

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Nature 2014 Long JA