Page 1of67 between this versionandtheVersionrecord. Pleasecitethis articleasdoi:10.1002/jmor.20706. through thecopyediting, typesetting, paginationandproofreadingprocess, whichmayleadtodifferences This istheauthormanuscript acceptedforpublicationandhasundergone full peerreviewbuthasnotbeen Kingdom Kingdom Buckhurst Road, SL5 7PY, United Kingdom United7PY,SL5Road, Buckhurst University of Michigan, 1109 Geddes Ave, Ann Arbor, MI Arbor,48109-1079 Ann Ave, Geddes 1109 ofMichigan, University Phone: +44 (0)20 7594 2254 7594+44(0)20 Phone: 4 3 2 1 Brazeau D. Martin architecturepharyngeal andforskeletonitspharyngeal implications primitive gnathostome three-dimensionalA placoderm(stem-group gnathostome) Email: Email: Kingdom. SL5 United 7PY, Road, Buckhurst Park Campus, Silwood London, College Imperial Sciences, Lifeof Department D. Brazeau,Martin to: *Correspondence Kingdom United0DE, OX11 Oxfordshire,

Department of Earth Sciences, Natural History Museum, London SW7 5BD, United United 5BD,London SW7 History NaturalMuseum, Earthof Sciences, Department

AcceptedDidcot,Campus, andScienceInnovation Light Source,Harwell Diamond Sciences, andEnvironmental Earth of andDepartment ofPaleontology Museum ArticleCampus, ParkSilwood London, Imperial College LifeSciences, of Department [email protected] This article isprotected by copyright. All rights reserved. 1,2 *, Matt Friedman Matt*,

Journal ofMorphology

3 , Anna Jerve Anna , 1 , Robert Atwood Robert , 4 rza 1 Brazeau

ABSTRACT— Paraplesiobatis poorly known. Here we describe an articulated, nearly complete pharyngeal skeleton pharyngealnearly complete describean articulated, we Here known. poorly remain stemgroupgnathostomes from skeletons pharyngeal of examples preserved pharyngobranchial) elements are observed. The structure of the pharyngealskeleton ofstructure the The observed. areelements pharyngobranchial) or (epibranchial Nodorsal inchondrichthyans. present as is basihyal branchial arch pair. Unpaired basibranchial bones may be independently derived in in derived bones independently be may Unpaired basibranchial pair. arch branchial reconstruct the threedimensional gill arch architecture of architecture arch gill thethreedimensional reconstruct resolveand we tomography, light synchrotron Using ofGermany.Slate Hunsrück in an Early Devonian placoderm fish, placoderm Devonian Early an in Well data. phylogenetic of a source potential as considerable it offers Furthermore, feeding. vertebrate)(jawed gnathostome ofand theorigin jaws on debates The final and penultimate arches are connected as in osteichthyans. A single median median Asingle in osteichthyans. as archesconnected are penultimate and final The present. archesare branchial least fourat However, preserved. archesnumberof exact the interpreting in uncertainty some scan causes the tomography inresolution Limited arches. branchial seriesof anda ceratohyal) (probable thehyoidarch of elements comprises skeleton pharyngeal Thepreserved othergnathostomes. with it compare

KEY WORDS: Branchial skeleton, Hunsrück Slate, Devonian, hyoid Slate,hyoid arch, Devonian,Hunsrück skeleton, Branchial WORDS: KEY osteichthyans. and chondrichthyans hyoidthefirstand boththeto connection some withprobably character, gnathostome significance of significance phylogenetictaxon. The of thelatter interpretation analternative allowing of AcceptedParaplesiobatis Article

The pharyngeal skeleton is a key vertebrate anatomical system in anatomical isvertebrate key a skeleton pharyngeal The Paraplesiobatis Paraplesiobatis , synchrotron tomography synchrotron , This article isprotected by copyright. All rights reserved. agrees well with with well agrees is considered. A median basihyal is likely a primitive isaprimitive basihyallikely A median isconsidered. Journal ofMorphology John Wiley&Sons Pseudopetalichthys Paraplesiobatis heinrichsi Paraplesiobatis from the samedeposit, the from Paraplesiobatis Broili, from from Broili, and rza 2 Brazeau Page 2of67

Page 3of67

Research Highlights Research

• • •

jawed vertebrates. jawed fish. fish. placoderm 405millionyearolda fromdescribed is gnathostome stemgroup of askeleton arch gill preserved, articulated threedimensionally first The respiratory mechanics in early jawed vertebrates. inearly jawed mechanics respiratory inand feeding systemskeletalessential of a diversity known adds to fossil The Accepted Article theearliest patterns in primitive archgill of hypotheses informdata new These This article isprotected by copyright. All rights reserved. Journal ofMorphology John Wiley&Sons rza 3 Brazeau

jaws and is a key system in understanding the early diversification of feeding and ofand feeding theearly understandingdiversification system key isain and jaws p pharynx (throat). Each arch consists of a chain of elements extending from a dorsal extending a from of aofelements consists Eachchain arch (throat). pharynx pharyngeal arch segments, particularly in the ventral elements. Both chondrichthyans chondrichthyans Both ventral elements. in particularly the segments, arch pharyngeal respiratory systems in jawed vertebrates (gnathostomes). (gnathostomes). vertebrates injawed systems respiratory The pharyngeal skeleton has long been implicated in theories of the origin oforigin of theoriesthe implicated in been longskeletonhas pharyngeal The INTRODUCTION o complete gill complete comprises a jointed network of bones and cartilages surrounding the mouththeand surrounding bonescartilages andofnetwork a jointed comprises (Nelson, 1969; Wiley, 1979; Pradel et al., 2014). Unfortunately, fossil examples of examples fossil Unfortunately, 2014). Pradeletal., 1979; 1969;Wiley, (Nelson, uncertainty about uncertainty leaves considerable gnathostomes stemgroup offrom A lackinformation study. to theminaccessible makesthat often position anatomicaldeepand mineralization weak The two main divisions of the gnathostome crown group (Osteichthyes and (Osteichthyes groupcrown gnathostome of the maindivisions two The of their relationships topological thesignificantlypattern of in differ Chondrichthyes) usefulness. connect one or more arches.orone more connect may paired)corpuses (oror moremedialone where midline, ventral atthe meeting thethroatand around extendingand orbraincasevertebrae, the either on origin 2013; Pradel et al., 2014). By contrast, in osteichthyans, the ceratohyals attach to a attach theceratohyals osteichthyans, in contrast,By2014). Pradeletal., 2013; al.,1992; Carvalho et Shirai, 1923; 1922; Allis, (Garman, 1913; element hypohyal amedian todirectly of attaching ceratohyals archesconsist hyoid Chondrichthyan elements. basibranchial medianmoreor one possess osteichthyans and rovided a rich source of character data for studies of gnathostome interrelationships interrelationships of gnathostome studiesfor data character of rich source a rovided f mandibular and hyoid arches; and the branchial skeleton, or gill arches. Itgill or arches. branchial skeleton, theand hyoid andarches; mandibular f

Accepted gill The Article

skeletons from early gnathostomes are rare owing to rareowing are gnathostomes early skeletons from

skeleton pharyngeal pharyngeal This article isprotected by copyright. All rights reserved.

, in particular, as well as wellas in particular, ,

skeleton character polarities, limiting theirphylog limitingpolarities, skeleton character Journal ofMorphology John Wiley&Sons its musculature have classically musculature its This skeletal system consists skeletalsystem This theirtypically rza 4 Brazeau enetic enetic Page 4of67

Page 5of67 preserved endoskeletons—are extremely rare. extremely endoskeletons—are preserved with fossils—particularly placoderm articulated Complete, preserved. poorly placoderms: an assemblage of Paleozoic jawbearing stemgroup gnathostomes. stemgroup Paleozoic jawbearing of assemblage an placoderms: be ‘anteriorly directed’ and at least one anterior branchial arch pair usually joins the the pairusually joinsarch branchial anterior one least at and directed’ ‘anteriorly be to considered are thehypobranchials osteichthyans, In or cartilage. bone basibranchial Unfortunately, these gill skeletons are weakly mineralized and therefore tend to be to tend therefore and mineralized weakly are gill skeletons these Unfortunately, Garman, 1913). Garman, (seee.g.basihyal of the angle theposterolateral to connected directed and anteriorly often hypobranchial is first copula. The toorabasibranchial midline anatomical the either at directed, join and (usually)posteriorly arehypobranchials first theall chondrichthyans,but Inelasmobranch thehyoid arch. as basibranchial same Morris and Caron, 2014). However, partially ossified examples exist in thein ossifiedexist examples partially However, 2014). Caron, and Morris 2007; Conway Arsenault, Janvierand2006; etal.,(Janvier outgroups gnathostome 2014). al.,(Pradel conditions et arch branchial primitive reconstruct to attempting mappingexercises inhibitedcharacter has gnathostomes group stem from outgroupTheof information lack an remains. uncertainty considerable 2014), etal., (Pradel derived conditions and primitive of theseparation aids fossils of consideration 2014).Although etal., Pradel 2014; Friedman, and (Brazeau cartilage, which may connect either at the midline to its antimere or to a ventralora to itsantimere to atthe midline either connect may which cartilage, or bone by hypobranchial medially anda terminatesarchventrally branchial each osteichthyans, andIn both chondrichthyans inchondrichthyans. absent considered usuallywhichare of the latter 1998) Bemis,and Grande 1972; 1954; Jarvik, 1897;1922; (Allis, via ahypohyals, termedbasibranchial) (usually bone median

All of these contrasts are potentially phylogenetically informative variables informative phylogenetically arepotentially contrastsof these All Accepted jawless knownfrom poorly skeletons gillextremely are Fossilized Article This article isprotected by copyright. All rights reserved. Journal ofMorphology John Wiley&Sons However, multiple However, examples are known are examples rza 5 Brazeau

branchial arch patterns. patterns. arch branchial phylogenetically coherent. Nevertheless, these taxa are known from complete and complete and fromtaxaknownare these Nevertheless, coherent. phylogenetically MATERIALS AND METHODS AND MATERIALS Geological context context Geological (1962).by Gross and (1933) by Broili described beenpreviouslyhas It squamation. trunk and armor dermal a Thearticulated iscomplete, 1986). specimen byWuttke, (assigned 1983/294 KGM Kreuznach Bad (KarlGeibMuseum), Schlossparkmusuem the from Broili(1933) of onthespecimen type based investigationis This Specimen in early and modern gnathostomes is here used to infer some aspects of primitive of primitive some aspects to infer used ishere gnathostomes modern and early in gillelementsbasal of arch analysis A comparative skeletons. branchial osteichthyan and in elements some chondrichthyan theofhomology aboutquestions raise that peculiaritiespresents itHowever, also examples.less in complete observed anatomy from arches gill placoderm of onthemorphologydetails further providespaper This of CT analysis synchrotron a through investigations. (CT) tomographyto computed amenable therefore are and (Gross, 1962) Xray contrast these fossils exhibit Furthermore, fossils. articulated be toisunlikely thatthegroup however,diverse, morphologically so is Stensioella including “stensioellids”, enigmatic phylogenetically anatomicallyand the are these from the exceptional Early Devonian Hunsrück Slate Hunsrück Early Devonian the exceptional from

Accepted Article Paraplesiobatis

, Pseudopetalichthys This article isprotected by copyright. All rights reserved. confirm some generalized aspects of placoderm branchial archbranchial aspectsplacoderm of generalized some confirm , , Journal ofMorphology Nessariostoma

John Wiley&Sons Paraplesiobatis heinrichsi Paraplesiobatis and Paraplesiobatis heinrichsi Paraplesiobatis Paraplesiobatis Lagerstätte Broili (1933). Data(1933). Broili of Germany. Among Among Germany. of . This assemblage assemblage This . rza 6 Brazeau Page 6of67

Page 7of67 Paraplesiobatis Paraplesiobatis paleontological and geological literature. Bartels et al. (1998) suggest that that suggestthe (1998) al.et Bartels literature. geologicaland paleontological projected pixel size of 12.6 micron at the sample. The tomographic 3d imageswere 3d tomographic sample. The atthe of micron12.6size pixel projected lithostratigraphic nomenclature. The exact collection horizonfor collection The exact nomenclature. lithostratigraphic in formation, thangroup,ratherto a iscomparable Slateeffectively Hunsrück usage in the despitecommon status stratigraphic lacksaformal but 2002), etal., 1998;Schindler al., (Bartels Germanyet of southeastern Mountains Rhenish theinDevonianageof Early muddy facies isoffshore, Slatean Hunsrück The into the into extends Bundenbach the of at thetopwhileformation 2005), et al., Ma(Kaufmann near the base of the Kaub Formation is radiometrically dated as 407.7 as dated isradiometrically Formation theKaub of thebase near layerAnash 1962). locality(Gross, theBundenbach Formation at Kaub midbasinal the clayrich, derives itfrom likely unclear,but issuccession Hunsrück the within Zone lies within the within lies Zone I12 at the radiationXraymicrotomography synchrotron scanned usingwas specimen The tomography Synchrotron splinedated to 397.68 to splinedated optics onto the detector of PCO4000 CMOS camera (PCOAG, Germany), with a with Germany), (PCOAG, CMOS camera PCO4000 ofdetector onto the optics bymicroscopeimaged was which scintillator (CdWO4) Tungstate Cadmium 0.9mm a illuminating , Xrays monochromatic (100keV) lambda=.0124nm using spacing 2 reconstructed using filtered back projection and ring suppression ring suppression and projection back filtered using reconstructed 2015) 011). The resulting voxel size was 12.7 µm. Because of the size of the specimen,of the thesizeof Because wasµm. 12.7 size voxel resulting The 011). JEEP

AcceptedXrayradiog acquiring bywas performed Tomography . Article Nowakia elegans elegans Nowakia beamline of the Diamond Light Source, Didcot,(DUK Light Source, Diamond of the beamline can be roughly constrained to between 398408 Ma. Ma. 398408 between to roughlybeconstrained can This article isprotected by copyright. All rights reserved. Polygnathus inversusPolygnathus ± 2.144 Ma (Becker et al., 2012). Thus the of Thusthe age 2012). (Becker et Maal., 2.144 Dacryoconarid Zone (De Baets et al., 2013). The2013). (Deal., Zoneet Baets Dacryoconarid Journal ofMorphology John Wiley&Sons Conodont Zone, the top of whichbeen has of the top Zone, Conodont raphs at 0.1 deg angular 0.1 deg at raphs Paraplesiobatis (Titarenko et al., (Titarenko et rakopoulos et al., etal., rakopoulos ± 0.7 rza 7 Brazeau N. elegans

perichondrally ossified bones (Figs. 1, 2). The skeleton is mostly intact and nearlyintact skeletonandismostly The 2).1,(Figs. bones ossified perichondrally pyrite crystals (Supporting Information Fig. 1). Furthermore, the discontinuous thediscontinuous Fig.1).Furthermore, Information (Supporting crystals pyrite branchial) elements are preserved. Thegillskeleton preserved. areelements pharyngobranchial) complete ventral gill basket spanning the entire breadth of the skull. No dorsal (epi ordorsal (epi No theskull. breadthof theentire basketspanning gillventral complete in postprocessing. in together later“stitched” were These stage. rotation thetomography supporting stages translation vertical theautomated using generated scans overlappingwere seven DESCRIPTION DESCRIPTION https://dx.doi.org/10.6084/m9.figshare.4555462 at freely areavailable study thisusedin models Surface Booleanoperations. usingunited laterwere that masks multiple from bonesformed were theindividual of Therefore, most values. threshold consistent selecting difficulties in caused Fig.1) Information (Supporting volume thetotal scanseriescomprising each separate normalization between grayscale

of a pair of heavy ring artefacts and the ‘brightness artefacts’ caused by highlydenseby ‘brightnesscaused artefacts’ the and heavyartefacts pairofring a of thetoinfluence wastakenavoid Particular care versions. some earlier 18and version in Software) completed and (Materialise Mimics loaded in wasvolume resultant The modeling virtual and Segmentation the ventral midline), and a lateral segment. The fifth arch consists ofvisible single a The fifth segment.consists arch a andlateralmidline), ventral the itsantimere across (that joins segment medial atwosegments: of archesconsist four Thefirst below). (explained arches segmented tofour five set of basihyal and median Tomography data can be accessed at: https://figshare be at: accessed can data Tomography

Acceptedofnetwork segmented a ispreservedas 1983/294 KGM skeletonof gill The Article This article isprotected by copyright. All rights reserved. Journal ofMorphology John Wiley&Sons .com/s/8bdd8e20f76de18febf9 .com/s/8bdd8e20f76de18febf9 comprises asingle, comprises rza 8 Brazeau Page 8of67

Page 9of67 been pushed posteriorly from its original life position. The anterolateral corners are The anterolateral position.original life its from posteriorly pushed been thatit has suggest These angles horizontal. 30 degrees from byabout upwards pitched longitudinal keel with a convex profile. Similar toSimilar profile. witha convex keel longitudinal small fragment of it may be preserved on the left). This isproblematic the most theleft). This on preserved it ofmay be fragment small only on the medial elements of each arch.of elements each themedial on only descriptionfocuses remaining Theridge.ventral alongitudinal show toenough well resolvehoweversome quality, poor scan to the owing featureless Most appear 2). arch elements. elements. arch other with articulations forthe positionsto possiblycorresponding mineralization, incomplete suggesting thescans, in indistinct are thebone of boundaries posterior The of thebone. margin the meet anterior to upwards anteriorly tapers andposterior its deeply notched. As in the phyllolepid placoderm placoderm thephyllolepid in Asnotched. deeply displaced taphonomically: rotated clockwise about ten degrees from the midline, andthe tenmidline, from degrees about clockwise rotated taphonomically: displaced thearches. of order theanteroposterior onlyto refer and therefore other gnathostomes with identity indicate exact tointended necessarily not arehere assigned numbersofarch this, the Because gnathostomes. other inidentitiesserial with their to respect numbers arch the in interpreting uncertainty issome thereshow, willdescription this Asthe mouth. to intrusions or other sediment bydislodged possibly displaced, disruptedandare bones left, anterior the However, preserved. bonesunpaired nomedian areadditional There its antimere. meeting than rather arch, theof fourth facet posterolateral to connectsthe that segment

The first arch in the series is preserved only on the right side (however, a (however, onsidethe right only series ispreserved the in arch first The Each of the distal arch elements are short, roughly rectangular bony rods (Fig. bonyrods(Fig. rectangular roughly short,areelements archthedistal of Each Accepted ArticlebeenhasIt dorsoventral inaspect. istrapezoidal roughly basihyal The 2).(Fig.position life preserved in nearly completely isside right The This article isprotected by copyright. All rights reserved. Journal ofMorphology John Wiley&Sons Cowralepis Cowralepis (Ritchie, 2005) there isathere 2005) (Ritchie, , the keel is deepest atisdeepest thekeel , rza 9 Brazeau

placoderms in Stensiö’s (1969) terminology or the basibranchials of other authors basibranchials the terminologyor Stensiö’s(1969)in placoderms Onthe featureless. mainlysurfaceandis flat Therod.dorsal angled posterolaterally brought into close proximity when the pharynx was disrupted and cannot be resolved resolved becannot and disrupted waspharynx thewhen proximity close into brought rectangular profile. rectangular roughlyamedial giving areathe themargin,posterior with parallelsided roughly is of archthe third region By same flange. contrast, the rodlikeits lateral into narrow inhalfmedial margin its anterior along a arched stronglyhas arch second The backwards to turning sharply before anterolaterally, arcs 2).It (Fig. view dorsoventral basibranchial elements. andhypo, tocerato, fused these correspond whether unclear therefore is2).It projection(Fig. rodlike lateral withthe continuous completely these1983/294are KGM that notableIt 2009). is in al., 2005; Carr et (Ritchie, of hypobranchials thethepositionof to corresponding extremity, medial their at tumidity deep ventral a haveHowever,they side.dorsal ontheir featureless relatively and flat, are elementsmedial 2).The series(Fig. of itsmembers following or precedingwith the of articulation broadareashave toregion expanded appear of faces anterior posterior and tumidity. The ‘basibranchial’ bears a side,thesurface ventral abruptly, at about midlength along the anterior margin to form a narrow,aformmargin to theanterior along atmidlength about abruptly, regionthattapers broadmedial aof outlineconsists their aspect, dorsoventral in thescan. in were arch—that branchial firstand ceratohyal bones—a separateof two composite isathatit it possible consider weHowever, here. structure single aas described This (Fig.is 3). regionelement rodlike a dorsal ‘blade’, flattened and ventral roughlyoval broad, of a consistingmorphology, unusualhas bone an The artifacts. bynumberof severelya isdataafflicted tomographic becausethe todescribe element

Accepted ArticleIn (Fig.bone2). sweptrodlike aposterolaterally of 4to 2 consist Arches This article isprotected by copyright. All rights reserved. Journal ofMorphology John Wiley&Sons rza 10 Brazeau Page 10of67

Page 11of67 Paraplesiobatis Paraplesiobatis points towards) the crux of the fourth arch medial element (Fig.2). medial element arch thefourthcrux the oftowards) points generated in generated pattern beHowever,cansimilar a the‘ceratobranchials’. and ‘basibranchials’ crescentshaped bone, opening posterolaterally. The fifth arch articulates (orat least articulates archfifth The posterolaterally. bone,opening crescentshaped a Theisresult width. longthebone’s nearly asas processas a posteriorly extends Thomas. It shares in common with with inItcommon shares Thomas. of specimen onlyandtype 1986) (Wuttke, lost thenowbelongs to skeleton known branchial placoderm complete most The additional details provided by provided details additional of the gill skeleton ofskeleton gill theof interpretation reviseda attempted (2009) etal. Carr Recently, examples. comparative few are there though placoderms, isunusual among 4).This(Fig. “basibranchials” A key difference in the gill skeletons of skeletons gill in differencethe key A isquiteaccurate. reconstructions Alternative interpretation of interpretation Alternative DISCUSSION ofthebone. on theanterolateral face deepfossa a bulge accommodates This thebone. widthof the bulgespanning to keel a out flares ventral theDistally, edge. bladed a to dorsallymargin thinning theposterior theanterior margin; along keeled isdeeplyit two thirds, its anterior Inprofile. dorsoventral in rectangular roughly

The fourth arch differs from the preceding arches in that the tumid portion portion thatthe tumid arches in thepreceding differs from arch fourth The Accepted Articleisrobustand bone The bone. observed asingle of consists arch fifth The

Paraplesiobatis is that the gill skeleton of the former appears segmented between the between segmented appears of the formerskeleton gill thatthe is This article isprotected by copyright. All rights reserved. Pseudopetalichthys by embedding the reconstructed arches in a plane (Fig.plane a in arches thereconstructed by embedding Paraplesiobatis Pseudopetalichthys Journal ofMorphology

John Wiley&Sons Paraplesiobatis in light ofin Pseudopetalichthys problematicus Pseudopetalichthys reveals that neither of their their ofneither revealsthat Pseudopetalichthys Pseudopetalichthys

posteriorly extended posterior extended posteriorly Cowralepis . However, theHowever, . and and rza 11 Brazeau Moy

partial burial ofskeleton in thegill burial partial Pseudopetalichthys inobserved similararepositionin abroad Unusual plates basihyal. Pseudopetalichthys both direct examinations and radiographs of radiographs and directexaminations both placoderms (Fig. 5). This structure is observedin is clearlystructure 5).This(Fig. placoderms KGM 1983/294 exhibits a broad, thin, spatulate ossification flanking the the ossificationspatulateflanking thin, broad, aexhibits 1983/294 KGM 4). The differences could therefore reflect differences in the degree of ossification or ofdegreeossification the indifferences reflect therefore differences could The 4). The resulting interpretation brings the gill skeletons ofgill skeletons thebrings interpretation resulting The ceratohyals. in expanded thesefact, are, that argue it to reasonable consider we 2009) absent in in absent However, in comparison with KGM 1983/294 and1983/294 KGM comparison with in However, Tapinosteus Tapinosteus the arthrodires materialinclude arch preservingbranchial placoderms Other otherplacoderms with Comparison Cowralepis Cowralepis morphologyof the resembles 1983/294of KGM Thebasihyal bone. basihyalalso a is itthat to reasonableconclude it is elements, otherpharyngeal to relative the bone this Gemuendina Gemuendina Basihyal. Basihyal. elsewhere. treatedbe will “stensioellids” remaining The below. subsection Forey and Gardiner, 1986; Long, 1997) and the socalled “stensioellids” socalled“stensioellids” theand 1997)Long, 1986; Gardiner, and Forey and

Accepted Pseudopetalichthys Article

Tapinosteus Tapinosteus A single median basihyal is common (possibly universal) among(possiblyuniversal) is basihyalcommon median A single

, and and , in the structure of its longitudinal ventral keel. Such a keel appears to be to appears Suchakeel keel. ventral itslongitudinal ofthestructure in (Stensiö, 1969) and 1969)and (Stensiö, (Gross, 1963) and 1963)and (Gross, Pseudopetalichthys This article isprotected by copyright. All rights reserved. and interpreted by Gross (1962) as mandibular elements. as elements. (1962)mandibular Gross byinterpreted and into close agreement. agreement. into close (Stensiö, 1969).(Stensiö, (Gross, 1962), the latter will be treated in a separate in treateda be latter will the(Gross,1962), Jagorina Journal ofMorphology Cowralepis John Wiley&Sons Pseudopetalichthys . Gross (1963) describes a “copula element” in in a“copula element” (1963)describes Gross . (Stensiö, 1969); pytctodontids (Miles, 1967; 1967; (Miles, pytctodontids 1969); (Stensiö, (Ritchie, 2005); the rhenanids2005); the(Ritchie, Gemuendina Cowralepis . Paraplesiobatis Tapinosteus . Based on the position of onposition Basedthe . (based on Carr et al., on Carr et (based (Stensiö, 1969), (Stensiö, and and Stensioella rza 12 Brazeau

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Page 13of67 placoderms, and here further corroborated by KGM 1983/294, thebasihyalis KGM1983/294, by corroborated further here and placoderms, processes that would themselves correspond to either hypobranchials or hypobranchials either to correspond wouldthemselves that processes proximal end of the first arch bears a spatulate expansion (shown bothin Gross’s (shown expansion spatulate bears a the of arch first end proximal followed by a paired series of basibranchiallike ossifications. Inossifications. basibranchiallike seriesof apaired by followed Stensiö, 1969)and Stensiö, the basihyal. the ofposteriorto the very orclosely apposed iswith articulates either ‘basibranchials’ The number and structure of branchial arches in placoderms. placoderms. arches branchialin andof structure number The (‘hypobranchials’ of Stensiö) in other placoderms are joined to extended lateral to extended otherare placoderms joined in of Stensiö) (‘hypobranchials’ ‘basibranchials’ the to corresponding one. The area lateraland amedial segments: corresponding to at least four individual pharyngeal arches. What remains unclear is unclear remains What arches. pharyngeal leastindividual four to at corresponding ‘basibranchial’elements, least atand afour median basibranchial possess generally a beas ceratohyal. interpreted reasonably could and cartilage arch mandibular thebehind isnestled expansion spatulate This plate). photographic and illustration (fourth) arch. The ‘basibranchial’ series of ‘basibranchial’series The arch. (fourth) preceding rather the region,joins but ‘basibranchial’ itsown nothave does arch theidentityfifthand orhyoid branchial uncertain isof arch Thefirst ceratobranchials. However, an indistinct fifth arch can be observed in his plate 8, fig B. Notably, the Notably,plateB. 8, his be fig observed in can indistinct arch fifth an However, model. hexanchiform—interpretive specifically, more and onachondrichthyan— based these bones arches joining reconstructs multiple Stensiö inpairs three are there while al.,2009), et

The branchial bones of KGM 1983/294 consist of arches comprising only two only comprising of arches consist 1983/294of KGMbones branchial The Based on these details, it seems reasonable to conclude that placoderms thatto conclude reasonable it seems details, on these Based AcceptedIn Article

Gemuendina This article isprotected by copyright. All rights reserved. Cowralepis , Gross (Gross, 1963) illustrates up to four separate arches. separate up to four illustrates (Gross,1963) Gross , (Fig. 5; Carr et al., 2009), the first pair ofpairfirst the al.,2009),5; Carr et (Fig. Journal ofMorphology John Wiley&Sons Tapinosteus Cowralepis (Stensiö, 1969). However,1969). (Stensiö, numbers four elements (Carr elements four numbers Tapinosteus Tapinosteus In all examples ofall In examples rza 13 Brazeau (Fig. 5;(Fig.

penultimate arch. Nothing in the arches of KGM 1983/294 or any other placoderm or any 1983/294 KGM of thearches in Nothing arch. penultimate Paraplesiobatis Paraplesiobatis possibly accommodating articulation with the hyoid arch (Fig. 5).(Fig.thehyoid archwith articulation accommodating possibly Paraplesiobatis Paraplesiobatis Interpretation and reconstructionand Interpretation hypohyal. posteriorlydirected aas interpretedbe here can considered example the theseries join in last arch the having osteichthyans in resembles further 1983/294 5).KGM (Fig. ceratohyals havinginenlarged/differentiated examples osteichthyan osteichthyans. with Similarities Similarities with chondrichthyans. chondrichthyans. with Similarities gnathostomes crown-group with Comparison gnathostomes. other of tohypobranchials correspond realistically more they that,whether or as interpreted befact, should, in elements the‘basibranchial’ whether together when the front of the gill skeleton was dislodged. The ovate,bladelike The dislodged. was skeleton thegill offront when the together pushedthatwere elements separateof two a in composite fact, is, arch the first of themodel Alternatively, arches. branchial four consistof therefore would arches subsequent Thebasihyal). the with ofarticulating aceratohyals pair (comprising arch isaarchhyoid preservedthefirst isthat interpretation first5).The (Fig. gnathostomes othertheof toinarchesrelation interpretations competingtwo offerwe Here (Grogan and Lund, 2000) in being roughly trapezoidal with anterolateral ‘notches’, ‘notches’, with anterolateral roughlybeing trapezoidal 2000) in Lund, and (Grogan

Accepted Articleholocephalan theCarboniferousof similarto that is 1983/294 KGM thebasihyal in of outline The 2013). et 5;al., Carvalho e.g.(Fig. see chondrichthyans specimen KGM 1983/294 preserves at least five pharyngeal arches. pharyngeal at least preserves five 1983/294 KGM specimen coupled with no apparent hypohyals compares well with modernwithwell hypohyals compares no apparent with coupled This article isprotected by copyright. All rights reserved. Journal ofMorphology Placoderm pharyngeal skeletons agree withagree skeletons pharyngeal Placoderm John Wiley&Sons The presence of a median basihyal in basihyal amedian of Thepresence Debeerius rza 14 Brazeau

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Page 15of67 p branchial arches only, numbering 15. As in osteichthyans, arch 5 articulates with articulates 5archosteichthyans, in As 15. numbering only, arches branchial branchial basket appears to have met the lateral margins of the braincase directly, braincasedirectly, the marginsoflateral met the have to basket appears branchial arch 4, but is highly differentiated. ishighlydifferentiated. but 4, arch to thecorrespond this In1.archarches branchialcase, of element medial the be would upper rodshaped region the toceratohyal, adisplaced would correspond element A median basihyal is apparently universal among placoderms, it is common to to common it amongis universalplacoderms, basihyalis apparently median A pair state—a The alternative chondrichthyans. stemgroup putative some and crown placoderms. of paraphyly bothormonophyly with offerconsistent interpretations we will indicated, otherwise Unless monophyly. placoderm about assumptions prior to no make elect therefore Wemethods. under modified analytical 2013) et al., (Zhu monophyletic as of placoderms majority arecover and result with this problems demonstrate recently (2016)al. King however et paraphyly, favorMostplacoderm analyses groups. crownosteichthyan and chondrichthyan tomonophyletic assumedbe are There inferences. phylogenetic numberof a make can5),we (Fig. gnathostomes group Furthermore there are no evident epi or pharyngobranchial ossifications. Theossifications. or pharyngobranchial epi noevident are there Furthermore arches. branchial of gnathostome conventions to nomenclatural equivocally conforms of skeleton the branchial aspect Thetoventral apply. difficultare terms nomenclatural standard theof basihyal,the exception and, with gnathostomes other Under the assumption that placoderms (including (including thatplacoderms theassumption Under P without any intervening ossifications. intervening ossifications. any without ossibly unossified, and therefore unpreserved. therefore and unossified, ossibly hylogenetic distributions hylogenetic

Accepted Articleof architecture branchial The This article isprotected by copyright. All rights reserved.

Journal ofMorphology John Wiley&Sons Paraplesiobatis Alternatively, these elements were small,were elements these Alternatively,

Paraplesiobatis is not easily compared with with isnot easily compared ) comprise stem comprise ) rza 15 Brazeau

parsimonious distribution for these structures could be arrived at by placing by arrivedbeat structurescould these distribution for parsimonious but their phylogenetic significance is somewhat more ambiguous (Fig. 5). Hypohyals (Fig.5). Hypohyals more somewhat significanceambiguous is theirphylogenetic but gained in symmoriiforms, osteichthyans, and osteichthyans, insymmoriiforms, gained weretheyAlternatively, threesteps). (minimum twicechondrichthyans in least) (at lostcrown originand thegnathostome the to ofgainedprior been in have may They also observed in the stemholocephalanin theobserved also (along with other symmoriiforms) on the holocephalan stem (Fig. 5), as has been has 5),as been (Fig. stemholocephalan on the symmoriiforms) other with (along among extant gnathostomes. extant among osteichthyansto uniquebe to basihyal—appears median to a connecting hypohyals of symmoriiforms more generally. Paired hypohyals in in Pairedhypohyals generally. more symmoriiforms thatortaxonof state,derived either abe considered canand anomalous subdivided visceral and branchial series ofseries branchial visceral and subdivided heavily the However, theof ceratohyal. subdivision aas hypohyal osteichthyan ofthe interpretation nothing precludes Furthermore, andhypohyal. a ceratohyal aor ceratohyal asubdivided either as interpreted Thisbecould ossifications. al., 2015; Burrow et al., 2015). Burrow et al., 2015; al., Blaiset2012; Brazeau, 2010; Hanke Wilson, and 2001; et al., (Hanke acanthodians othernonacanthodiform patternin ossification of thistypeof no evidence is ceratohyal of ceratohyal The competing)interpretations. necessarily (not multiple with segmentation of pharyngeal pattern it presentsabut2015), etal., Giles2015; deWinter, and al.,(Zhu2013; Brazeau et chondrichthyan stemgroupa considered increasingly now istaxon This hypohyals in chondrichthyans. ofor absence thepresence to respect When extinct gnathostomes are considered, considered, are gnathostomes extinct When Accepted in of basihyal a median absence The Article

Acanthodes This article isprotected by copyright. All rights reserved. , according to Gardiner (1984) is composed of two discreteof two iscomposed (1984) Gardiner to according , Journal ofMorphology John Wiley&Sons Debeeriusellefseni Acanthodes Ozarcus Debeerius Acanthodes (Pradel et al., 2014) is 2014) et al., (Pradel Ozarcus may be apomorphic, as there as apomorphic, maybe (also three steps). A more steps).more Athree (also (Grogan and Lund, 2000).Lund,and (Grogan resemble osteichthyans, resembleosteichthyans, presents a caveat with with caveat a presents rza 16 Brazeau Ozarcus

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Page 17of67 been identified been Median, unpaired basibranchials are absent in placoderms. No examples have placoderms. inNo examples absent are basibranchials unpaired Median, 2017). etal., 2015;Coates Giles etal., 2001; Sequeira, (Coates and of otherlinesof evidence thebasis onelsewhere suggested the RheinlandPalatinate). We gratefully acknowledge Diamond Light Source, UK forUK Source, Light Diamond gratefully acknowledge We RheinlandPalatinate). the of Heritage Cultural Directorate forGeneral (then Dr. Wuttke Michael andstudy for theUK transported to be toit for allowingandspecimen to forthe access Kreuznach) Bad (Schloßparkmuseum, NestlerZappAngela Dr.thank to wouldlike Accepted authors The ACKNOWLEDGMENTS the figures. composedAJ and MDB MDB.MF and from with assistance reconstructions tomography and scanning synchrotron the conducted RA segmentation. performedthe AJ MDB and MF. from input with manuscript the MDB study;wrote theoriginal MFdesigned and MDB CONTRIBUTIONS AUTHOR in elasmobranchs. foreshortened become buthas ofchondrichthyans, thebasihyal to ishomologous osteichthyans basibranchialof Alternatively,the separate. arechondrichthyans and osteichthyans Article in theirorigins that primitive and thebasihyalis to posterior mineralisations unpaired median of theabsence that argue provisionally, we However, this. help will London)clarify College (Imperial RPDearden andauthors the byunderway is currently other species ofacanthodian two investigations tomography Computed 1984). (Gardiner, Gardinerand (1973) byMiles disputed are (1968) identifiedby Nelson basibranchials median ofchain known. are The ossifications

in

canthodes A This article isprotected by copyright. All rights reserved.

, the only acanthodian for which substantial gill skeleton skeleton gill which substantial acanthodian thefor only , Journal ofMorphology John Wiley&Sons rza 17 Brazeau

Accepted Article themanuscript. improvehelped referees twoanonymous from Comments Oxford. University ofFell theJohn Fund, fromsupport acknowledges MF number 311092. GrantAgreement (FP/2007–2013)/ERC Programme Framework SeventhUnion’sEuropean under the Council Research European thefromsupport generous acknowledges MDBbeamline. ontheI12 time supplying This article isprotected by copyright. All rights reserved. Journal ofMorphology John Wiley&Sons rza 18 Brazeau Page 18of67

Page 19of67 be misleading ( misleading be Pseudopetalichthys

correspondence with correspondence to show highlighted arch pharyngealelements 1962) Gross,with from (modified KGM 1983/294 1983/294 KGM skeletonof gill articulated of illustrations interpretive and renderings Virtual 2. Fig. Fig. 3. Basihyal and first arch elements. Dorsal view ( viewDorsal elements. archfirst and 3.Basihyal Fig. = 1cm. bar Scale gnathostomes. to other homologies direct not thebuttext,innecessarily to referredorders archindividual indicate condition ( condition life to restoredapproximate elements posterior basihyal andand mirrored elements resulting in apparent segmented pattern ( patternsegmented in apparent resulting views (upper left) with branchial arches ( branchial arches with left) (upper views transparent andright) (lower solidshowing tomography light computed synchrotron view ( view Fig. 1. Fig. FIGURES Fig. 4. Alternative reconstructions of reconstructions Alternative 4. Fig. C

Accepted ArticleParaplesiobatis ). Anterior view( ).Anterior

A

). Reconstruction in panel A partially embedded inplane virtual a partiallyembedded inA panel ). Reconstruction C Paraplesiobatis ). Not to scale. scale. Not to ). This article isprotected by copyright. All rights reserved. . Partially reconstructed gill skeleton with left and right first arch right arch firstand withleft gill skeleton reconstructed Partially . Paraplesiobatis specimen KGM 1983/294 ( 1983/294 KGM specimen D ). Scale bar = 1= cm.bar Scale ). . Dorsal view ( view Dorsal . Journal ofMorphology John Wiley&Sons suggesting that the segmented appearance may appearance thesegmented that suggesting Paraplesiobatis B B ). Reconstruction of ).Reconstruction ). Scale bar = 1 cm.bar ).Scale A , B A ). ventral view ( view ventral ). ) and virtual renderings of virtualrenderings and ) and comparison with comparison and A ). Ventral view ( view ).Ventral Pseudopetalichthys C , D ). Numbers B rza 19 Brazeau ).Posterior

Not to scale. scale. to Not Pradel et al. (2014).( et al. Pradel Garman (1913). ( (1913). Garman (right). ( (right). Jarvik (1972). Jarvik

Accepted Article ( vertebrates. earlyjawed patterns in gillventral of arch comparison Phylogenetic 5. Fig. H)

Cowralepis

A

( ) Two possible interpretations of interpretations possible Two ) C ) E This article isprotected by copyright. All rights reserved. Mimipiscis Mimipiscis ) Debeerius G) after Carr et al. (2009).( etal. Carr after Acanthodes

after Gardiner (1984). ( (1984).Gardiner after after Grogan(2000).( Lund and after Journal ofMorphology John Wiley&Sons after Miles (1973) (left), and Gardiner (1984) Gardiner and (1973) (left), Miles after Paraplesiobatis I ) Tapinosteus D ) Scapanorhynchus after Stensiö (1969).Stensiö after F . ( . ) Ozarcus B ) Glyptolepis after rza 20 Brazeau after after after after Page 20of67

Page 21of67 Brazeau MD, de Winter V. 2015. The hyoid arch and braincase anatomy of anatomy hyoidbraincase andarch The 2015. V.deWinter MD, Brazeau Burrow CJ, Davidson RG, Blaauwen den JL, Newman MJ. 2015. Revision ofRevision 2015. Newman MJ. JL, den Blaauwen Davidson RG, CJ, Burrow Broili F. 1933. Weitere Fischreste aus den Hunsrückschiefern. Sber Bayer Ak Wiss,AkSber Bayer Hunsrückschiefern. den aus Fischreste 1933. Weitere F. Broili Brazeau MD, Friedman M. 2014. The characters of Palaeozoic jawed vertebrates. vertebrates. Palaeozoicjawed of characters The2014. FriedmanM. MD, Brazeau Brazeau MD. 2012. A revision of the anatomy of the Early Devonian jawed vertebrate vertebrate Devonian jawed Early theof the anatomy of Arevision2012. MD. Brazeau Allis EP. 1923. The cranial anatomy of anatomy Thecranial 1923. EP. Allis Allis E. 1897. The cranial muscles and cranial and first spinal nerves in spinal andfirst cranial and musclesThe 1897. E. cranial Allis CITED LITERATURE Allis EP. 1922. The cranial anatomy of anatomy The cranial 1922.EP. Allis Blais SA, Hermus CR, Wilson MVH. 2015. Four new Early Devonian ischnacanthid ischnacanthid Early Devonian newFour 2015. MVH. CR, SA,Wilson Hermus Blais Becker RT, Gradstein FM, Hammer O. 2012. The Devonian Period. In: The Geologic In:Period. DevonianO.The 2012. FM, Hammer Gradstein RT, Becker Slate: Marine theHunsrück of The Fossils 1998. G. Brassel DEG, Briggs C, Bartels Acanthodes Ptomacanthus anglicus Ptomacanthus Polypterus bichir Polypterus Climatius reticulatus Climatius MathNaturw Abt 2:269–313. Abt2:269–313. MathNaturw Zool J Linn Soc 170:779–821. 170:779–821. Soc Linn J Zool 282:20152210. 282:20152210. Morphol 11:487–808. 11:487–808. Morphol early experiment in dental diversity. J Vertebr Paleontol e948546. PaleontolVertebrJe948546. diversity.dental in experiment early an Canada: NorthwestTerritories, Mountains, Mackenzie the from acanthodians Time Scale Elsevier. p. 559–601.p. Elsevier.Scale Time 309p. University Cambridge Press. Cambridge: Devonian. in the Life Accepted Article 4:123–221.

support chondrichthyan affinity of “acanthodians.” Proc BiolSci of “acanthodians.” affinity chondrichthyan support This article isprotected by copyright. All rights reserved. . J Anat 190–294. 190–294. AnatJ .

Agassiz, 1844 (Acanthodii, Climatiidae), from the Lower from Climatiidae), 1844Agassiz,(Acanthodii, Miles. Palaeontology 55:355–367. Palaeontology55:355–367. Miles. Journal ofMorphology John Wiley&Sons Polypterus Chlamydoselachus anguineus Chlamydoselachus , with special reference to to reference special with , . ActaZoologica . Amia Amia calva rza 21 Brazeau . J .

De Baets K, Klug C, Korn D, Bartels C, Poschmann M. 2013. Emsian Ammonoidea Ammonoidea Emsian 2013.M. Poschmann Bartels KornC, D,K, Klug C, Baets De Carr RK, Johanson Z, Ritchie A. 2009. The phyllolepid placoderm placoderm Thephyllolepid 2009.A. Z, Ritchie Johanson RK, Carr Conway Morris S, Caron JB. 2014. A primitive fish from the Cambrian of the Cambrian North fromA primitive 2014.fish JB.S, Caron Morris Conway symmoriiform A 2017.K. Tietjen KE, CriswellRW,Finarelli JA, Gess MI, Coates theLower from stethacanthid chondrichthyan Anew2001. S. Sequeira M, Coates Carvalho M, Bockmann FA, de Carvalho MR. 2013. Homology of the fifththeofHomology 2013.MR. deCarvalho FA, M, Bockmann Carvalho Drakopoulos M, Connolley T, Reinhard C, Atwood R, Magdysyuk O, Vo N, Hart M, Hart Magdysyuk VoN,R, O, Atwood C, T, Reinhard M, Connolley Drakopoulos Forey PL, Gardiner BG. 1986. Observations on Observations BG. Gardiner1986. PL, Forey America. Nature 512:419–422. Nature America. Nature. fishes. chimaeroid oftheorigin andbraincase chondrichthyan 21:438–459.Paleontol Vertebr J Scotland. Bearsden,of Carboniferous mclachlani Vertebr Paleontol 35:e913421. Paleontol Vertebr J data. morphological histological and basedonnew Scotland, of Devonian 8:e62389. 8:e62389. PLoSONE ostariophysans. of development the insightsfrom gnathostomes: among the ceratobranchials of accessoryandelements epibranchial vertebrates. J Morphol 270:775–804. 270:775–804. MorpholJ vertebrates. Palaeontographica, Abt 299:1–113. A Palaeontographica, Germany). Western (Rhenish Mountains, Hunsrück Slate the of the age and Source. J Synchrotron Rad 22:828–838. 22:828–838. Rad Synchrotron J Source. Light Diamond beamline at (JEEP) Processing Environmentand Engineering, the JointI12: 2015. K. F,Wanelik Yuan M, MaioBasham N, DeA, Foster G, Pedersen U, T,Wilkin S,Davies Hill G, Howell Humphreys B, L, Connor classification of placoderm fishes. Zool J Linn SocLinnJ86:43–74. Zool of fishes. placoderm classification Accepted Article

: insights into the evolution of feeding mechanisms in jawed injawed feeding ofmechanisms evolution into the insights : This article isprotected by copyright. All rights reserved. Journal ofMorphology John Wiley&Sons Ctenurella (Ptyctodontida) and the (Ptyctodontida)and Cowralepis Cowralepis rza 22 Brazeau Page 22of67

Page 23of67 Giles S, Friedman M, Brazeau MD. 2015. Osteichthyanlike cranial conditions in in an conditions cranialOsteichthyanlike2015. MD. Brazeau M, S,Friedman Giles Garman S. 1913. The Plagiostomia (sharks, skates, and rays). Mem Mus Comp ZoolComp MusMem rays). skates, and (sharks,The Plagiostomia 1913. S. Garman Gardiner BG. 1984. The relationships of the palaeoniscid fishes, a review based on basedreview a fishes, palaeoniscid of the The relationships 1984.BG. Gardiner Grogan E, Lund R. 2000.R.Lund E, Grogan amiid fishes of study phylogenetic Acomprehensive 1998. L, Bemis WE. Grande Gross W. 1962. Neuuntersuchung der Stensiöellida (Arthrodira, Unterdevon). Notizbl Unterdevon). (Arthrodira, Stensiöellida der Neuuntersuchung 1962. W. Gross Gross W. 1963. W. Gross Hanke GF, Davis SP, Wilson M. 2001. New species of the acanthodian genus theacanthodian ofNew 2001. species M. SP,Wilson Davis GF, Hanke Hanke GF, Wilson MV. 2010. The putative stemgroup chondrichthyans stemgroupputative chondrichthyans The MV.2010. GF, Wilson Hanke Kathemacanthus Harvard Coll 36:1–528. 36:1–528. Coll Harvard Australia. Bull Br Mus nat Hist (Geol) 37:173–428. 37:173–428. (Geol) Hist MusnatBr Bull Australia. new specimens of specimens new interconnected patterns of natural history. J Vertebr Paleontol 18:1–696. Paleontol VertebrJhistory. of patternsnatural interconnected for searchempirical An anatomy. skeletal on basedcomparative (Amiidae) Early Devonian stem gnathostome. Nature 520:82–85. 520:82–85. Nature gnathostome. stemDevonian Early gnathostome evolution. J Morphol 243:219–245. 243:219–245. MorpholJ evolution. gnathostome on comments theChondrichthyes,and of therelationships (USA), Montana of LimestoneGulch Bear theMississippian from chondrichthyan autodiastylic Hess Landesamt Bodenforsch Wiesbaden 90:48–86. Wiesbaden Bodenforsch Landesamt Hess of Fossil Fishes Eds. D.K. Elliott, J.G. Maisey, X. Yu, and D. Miao, VerlagMiao, D. Dr. X.and Yu, J.G. Elliott,Maisey, D.K.Eds. Fishes Fossil of Paleobiogeography Phylogenyand Morphology, Canada.Mountains, Mackenzie Tetanopsyrus Landesamt Bodenforsch Wiesbaden 91:36–73. 91:36–73. Wiesbaden Bodenforsch Landesamt Accepted 21:740–753. Paleontol Article

Gemuendina stuertziGemuendina from northern Canada, and comments on related taxa.VertebrJonrelated comments and northern Canada, from This article isprotected by copyright. All rights reserved. and and Mimia Seretolepis Debeeriusellefseni and and Journal ofMorphology Moythomasia John Wiley&Sons from the Lower Devonian MOTH locality,MOTH Lower Devonian the from Traquair. Neuuntersuchung. Notizbl HessNotizbl Neuuntersuchung. Traquair. (fam. nov., gen. nov., spec. nov.), an nov.),spec. nov., gen. nov., (fam. from Upper Devonian of Western of Western Devonian Upper from rza 23 Brazeau

Miles RS. 1973. Relationships of acanthodians. In: Greenwood PH,RS, Miles Greenwood In: of acanthodians. RS.Relationships 1973. Miles Miles R. 1967. Observations on the ptyctodont fish, onfish, theptyctodont Observations 1967.R. Miles Long JA. 1997. Ptyctodontid fishes (Vertebrata, Placodermi) from the Late Devonian LateDevonian the Placodermi) from (Vertebrata, fishes Ptyctodontid 1997. JA. Long King B, Qiao T, Lee M, Zhu M. 2016. Bayesian Morphological Clock Methods Methods Clock Morphological Bayesian 2016. M. LeeM,Zhu T, Qiao B, King Kaufmann B, Trapp E, Mezger K, Weddige K. 2005. Two new Emsian (EarlyEmsian Two2005. new K. Weddige K, E,MezgerTrapp B, Kaufmann Jarvik E. 1972. Middle and Upper Devonian porolepiformes from east Greenlandwith east fromporolepiformes Devonian Upper and Middle E.1972. Jarvik Jarvik E. 1954. On the visceral skeleton inskeleton On thevisceral E.1954. Jarvik Janvier P, Arsenault M. 2007. The anatomy ofThe anatomy 2007.M. P, Arsenault Janvier Janvier P, Desbiens S, Willett JA, Arsenault M. 2006. Lampreylike gills gills inaLampreylike 2006. M. JA,Arsenault S, WillettP, Desbiens Janvier parasphenoid and palatoquadrate in fishes. K Sven Vetenskapsakad Handl 4:1– Handl Vetenskapsakad Sven inK palatoquadratefishes. and parasphenoid Soc (Zool) 47:99–120. 47:99–120. (Zool) Soc Ctenurella genus theEuropean withofarevision Australia, Western Formation, Gogo Vertebrates. SystBiol. Vertebrates. Jawedin Early Evolution RapidReveal and Monophyly Placoderm Resurrect 162:363–371. 162:363–371. Soc London Geol Jscale. Devonian time the implications for (Germany): Massif Rhenish theofvolcanic rocks zirconfrom U–Pbages Devonian) structure of the head in porolepiformes. Medd Grønl 187:1–307. 187:1–307. Grønl Medd porolepiformes. in thehead of structure special reference reference to special 104. 104. Friedrich Pfeil, München, Germany:159–182. Germany:159–182. Pfeil,München, Friedrich gnathostomerelated Devonian jawless vertebrate. Nature 440:1183–1185. 440:1183–1185. Naturevertebrate. jawless Devonian gnathostomerelated Accepted Article 29:143–216. Geodiversitas Canada. Quebec, Miguasha,of Devonian Upper the vertebrate from anaspidlike jawless an1900,

. Geodiversitas 19:515–555. 19:515–555. Geodiversitas . This article isprotected by copyright. All rights reserved. Glyptolepis groelandica Glyptolepis Journal ofMorphology John Wiley&Sons Eusthenopteron Euphanerops longaevus Euphanerops n. sp. and a discussion onthe adiscussion sp.n.and Rhamphodopsis with a discussion of theof discussion with a Watson. J LinnJ Watson. Woodward, Woodward, rza 24 Brazeau Page 24of67

Page 25of67 Nelson GJ. 1969. Gill arches and the phylogeny of fishes, with notes onthenotes with phylogenyfishes, of the and Gill arches 1969.GJ. Nelson Nelson GJ. 1968. Gill arch structure in structure Gill arch 1968.GJ. Nelson Wiley EO. 1979. Ventral gill arch muscles and the interrelationships of gnathostomes, gnathostomes, of theinterrelationships and muscles arch gillVentral 1979. EO. Wiley Titarenko S, Titarenko V, Kyrieleis A, Withers P, De Carlo F. 2011. Suppression of F. Suppression 2011.Carlo A,P, De Kyrieleis Withers V, S,Titarenko Titarenko JPiveteau In: Arthrodires. Placodermata Elasmobranchiomorphi 1969.EA. Stensiö Shirai S. 1992. Identity of extra branchial arches in Hexanchiformes (Pisces, Hexanchiformes arches inbranchialof extraIdentity 1992. S. Shirai Schindler T, Sutcliffe OE, Bartels C, Poschmann M, Wuttke M.2002. Wuttke Poschmann M, BartelsOE,C, Sutcliffe T, Schindler Ritchie A. 2005.A. Ritchie Palaeozoicshark A J.2014.Mallatt RH, P,Mapes JG, TafforeauMaisey A, Pradel

NSW 126:215–259. 126:215–259. NSW with a new classification of the Vertebrata. Zool J Linn Soc 67:149–179. J67:149–179. Soc LinnZoolthe Vertebrata. newof classification a with Synchrotron Rad 18:427–435. Rad Synchrotron J samples. attenuating tomographingwhenanisotropically artefacts ring 71–692. p.4 Paris. vol dePaléontologie, Traité editor. Elasmobranchii). Bull Fac Fish Hokkaido Univ 43:24–32. UnivHokkaido Fish BullFac Elasmobranchii). (Hunsrück, SW Germany). Metalla 9:73–88. 9:73–88. Metalla SWGermany). (Hunsrück, area Bundenbach of Devonian)the Lower Emsian, (Lower Formation Kaub of the middle position chronostratigraphical and subdivision Lithostratigraphical 129–143. 129–143. p. Wiksell. & Almqvist Stockholm: Phylogeny Vertebrate of Lower Problems 103. 103. 63– p.London.Press Academicof Fishes Interrelationships Ceditors. Patterson with osteichthyanlike branchial arches. Nature 509:608–611. 509:608–611. Nature branchial arches. osteichthyanlike with 141:475–552. MusHistNat Am ofBull vertebrates. classification

Accepted Linn ProcSoc Australia. New South Wales, of Devonian LateMiddle the from Article Cowralepis This article isprotected by copyright. All rights reserved. , a new genus of phyllolepid fish (Pisces, Placodermi) Placodermi) (Pisces, fish phyllolepid of genus new a , Journal ofMorphology John Wiley&Sons Acanthodes . In: Ørvig T editor. Currenteditor.In: ØrvigT. rza 25 Brazeau

Zhu M, Yu X, Ahlberg PE, Choo B, Lu J, Qiao T, Qu Q, Zhao W, Jia L, Blom H, ZhuH, Blom Jia L, Zhao T,LuQiaoW, QuQ, B, J, Choo PE, X, Ahlberg Yu M, Zhu Wuttke M. 1986. Katalog der Typen und Belegstücke zurHunsrückschiefer Typenund Belegstücke der Katalog M.1986. Wuttke

Nature 502:188–193. 502:188–193. Nature YA. 2013. A Silurian placoderm with osteichthyanlike marginal jaw bones. jaw marginal osteichthyanlike placoderm with ASilurian 2013. YA.

Accepted Article 24:87–117. Archiv Naturw Mainzer (BRD). Kreuznach Bad in Schloßparkmuseum im Schiefergebirge) (Rheinisches Sammlung This article isprotected by copyright. All rights reserved. Journal ofMorphology John Wiley&Sons rza 26 Brazeau Page 26of67

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tomography showing solid tomography Scaleviews right)(lower transparent (B). (upper witharches branchial and left)

Accepted Paraplesiobatis specimenFig.1. 1983/294 and KGM (A) lightvirtual renderings computed synchrotron of Article This article isprotected by copyright. All rights reserved. 109x59mm (300109x59mm 300DPI) x Journal ofMorphology John Wiley&Sons bar = 1 cm. cm. 1 = bar

Paraplesiobatis. Dorsal view (A, B). ventral B). view Dorsal viewParaplesiobatis. (A, D). (C, Numbersindicateorders individual arch referred to Fig. 2. Virtual renderings Virtual Fig.2. interpretive and illustrationsarticulated gillof 1983/294 KGM of skeleton

Acceptednecessarily not but intext, = the bar homologies Scale direct gnathostomes. cm. 1 other to Article This article isprotected by copyright. All rights reserved. 149x140mm(300 300DPI) x Journal ofMorphology John Wiley&Sons

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Fig. 3. Fig.3.

Accepted Articlefirst Basihyalarch and elements.view view PosteriorDorsal (A). Ventral (B). viewAnterior view (C). This article isprotected by copyright. All rights reserved. 86x38mm (300 x 300 DPI) (300 30086x38mm DPI) x (D). Scale bar = 1 cm. Scale cm. 1 (D). = bar Journal ofMorphology John Wiley&Sons

highlightedwith Paraplesiobat correspondence show to elementslife restored partially planeconditionapproximate resulting to embedded in Reconstruction (A). a in apparent segmented inapparent pattern Reconstruction of (B). Pseudopetalichthys elements arch with pharyngeal Fig. 4. AlternativeParaplesiobatis reconstructions of Fig.4. and Partially withcomparison Pseudopetalichthys.

Accepted Articlereconstructedright leftgill mirrored posterior firstand skeleton elements and with basihyal arch and This article isprotected by copyright. All rights reserved. misleading (C). Not to scale. misleading scale. to Not (C). 70x23mm (300 x 300 DPI) (300 30070x23mm DPI) x Journal ofMorphology John Wiley&Sons

is suggesting that the segmented the issuggesting may that be appearance

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Accepted Article This article isprotected by copyright. All rights reserved. 125x127mm(300 300DPI) x Journal ofMorphology John Wiley&Sons

Accepted Article This article isprotected by copyright. All rights reserved. 33x33mm (300 x 300 DPI) (300 30033x33mm DPI) x Graphical Abstract GraphicalImage Abstract Journal ofMorphology John Wiley&Sons

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Page 33of67 placoderm fish is described. This adds to the diversity of feeding and respiratory and of feeding thediversity adds to This isdescribed. fish placoderm

Accepted Article vertebrates. the jawed first in gillofevolution arch hypotheses informingand animals vertebrate in jawed structures 410-million-year-old skeletona of arch gill articulated three-dimensional A Text Abstract – Graphical Brazeau This article isprotected by copyright. All rights reserved. Journal ofMorphology John Wiley&Sons

Date Submitted Date Author: the by Complete List of Authors: of CompleteList Wileytype: - Manuscript A three

Accepted Articlepharyngeal skeleton and its implications for primitive Manuscript Manuscript ID

Keywords:

- Journal: dimensional pl

gnathostome gnathostome pharyngeal architecture This article isprotected by copyright. All rights reserved.

Journal of Morphology Journalof tomography tomography Devonian, hyoid Slate, skeleton, arch,branchial Hunsrück synchrotron Robert; Light Ltd Atwood, Diamond Source Jerve,College Imperial Anna; SciencesLife London, University of Matt; Museum Frieman, Paleontology Michigan, of Martin; Brazeau, SciencesLife College Imperial London, 22-Apr-2017 ResearchArticle JMOR-17-0039.R1 Journal ofMorphology Journal ofMorphology acoderm (stem John Wiley&Sons John Wiley&Sons

- group gnathostome)group

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Page 1of333567 K Buckhurst Road, SL5 7PY, United Kingdom United7PY,SL5Road, Buckhurst University of Michigan, 1109 Geddes Ave, Ann Arbor, MI Arbor,48109-1079 Ann Ave, Geddes 1109 ofMichigan, University M architecturepharyngeal Phone: +44 (0)20 7594 2254 7594+44(0)20 Phone: 3 2 2 4 1 pha three-dimensionalA placoderm(stem-group gnathostome) Email: Email: Kingdom. SL5 United 7PY, Road, Buckhurst Park Campus, Silwood London, College Imperial Sciences, Lifeof Department D. Brazeau,Martin to: *Correspondence Kingdom United0DE, OX11 Oxfordshire,

iamond Light Source, Harwell Science and Innovation Campus, Didcot,Campus, andScienceInnovation Light Source,Harwell iamond Sciences, andEnvironmental Earth of andDepartment ofPaleontology useum Campus, ParkSilwood London, Imperial College LifeSciences, of epartment

Department of Earth Sciences, Natural History Museum, London SW7 5BD, United United 5BD,London SW7 History NaturalMuseum, Earthof Sciences, Department M D D ingdom ingdom artin D. Brazeau D. artin

Accepted Article ryngealandforskeletonits implications primitive gnathostome [email protected]

This article isprotected by copyright. All rights reserved. 1,2 *, Matt Friedman Matt*,

Journal ofMorphology John Wiley&Sons

3 , Anna Jerve Anna , 1 , Robert Atwood Robert , 4 rza 1 Brazeau

ABSTRACT— poorly known. Here we describe an articulated, nearly complete pharyngeal skeleton pharyngealnearly complete describean articulated, we Here known. poorly remain stemgroupgnathostomes from skeletons pharyngeal of examples preserved Paraplesiobatis pharyngobranchial) elements are observed. The structure of the pharyngealskeleton ofstructure the The observed. areelements pharyngobranchial) or (epibranchial Nodorsal inchondrichthyans. present as is basihyal branchial arch pair. Unpaired basibranchial bones may be independently derived in in derived bones independently be may Unpaired basibranchial pair. arch branchial reconstruct the threedimensional gill arch architecture of architecture arch gill thethreedimensional reconstruct resolveand we tomography, light synchrotron Using ofGermany.Slate Hunsrück in an Early Devonian placoderm fish, placoderm Devonian Early an in Well data. phylogenetic of a source potential as considerable it offers Furthermore, feeding. vertebrate)(jawed gnathostome ofand theorigin jaws on debates The final and penultimate arches are connected as in osteichthyans. A single median median Asingle in osteichthyans. as archesconnected are penultimate and final The present. archesare branchial least fourat However, preserved. archesnumberof exact the interpreting in uncertainty some scan causes the tomography inresolution Limited arches. branchial seriesof anda ceratohyal) (probable thehyoidarch of elements comprises skeleton pharyngeal Thepreserved othergnathostomes. with it compare

KEY WORDS: Branchial skeleton, Hunsrück Slate, Devonian, hyoid Slate,hyoid arch, Devonian,Hunsrück skeleton, Branchial WORDS: KEY osteichthyans. and chondrichthyans hyoidthefirstand boththeto connection some withprobably character, gnathostome significance of significance phylogenetictaxon. The of thelatter interpretation analternative allowing of AcceptedParaplesiobatis Article

The pharyngeal skeleton is a key vertebrate anatomical system in anatomical isvertebrate key a skeleton pharyngeal The

Paraplesiobatis Paraplesiobatis , synchrotron tomography synchrotron ,

This article isprotected by copyright. All rights reserved. agrees well with with well agrees is considered. A median basihyal is likely a primitive isaprimitive basihyallikely A median isconsidered. Journal ofMorphology John Wiley&Sons Pseudopetalichthys Paraplesiobatis heinrichsi Paraplesiobatis from the samedeposit, the from Paraplesiobatis Broili, from from Broili, and rza 2 Brazeau Page 36of67 Page 2of33

Page 3of333767 Research Highlights Research

• • •

jawed vertebrates. jawed fish. fish. placoderm 405millionyearolda fromdescribed is gnathostome stemgroup of askeleton arch gill preserved, articulated threedimensionally first The respiratory mechanics in early jawed vertebrates. inearly jawed mechanics respiratory inand feeding systemskeletalessential of a diversity known adds to fossil The Accepted Article theearliest patterns in primitive archgill of hypotheses informdata new These

This article isprotected by copyright. All rights reserved. Journal ofMorphology John Wiley&Sons rza 3 Brazeau

jaws and is a key system in understanding the early diversification of feeding and ofand feeding theearly understandingdiversification system key isain and jaws pharynx (throat). Each arch consists of a chain of elements extending from a dorsal extending a from of aofelements consists Eachchain arch (throat). pharynx pr pharyngeal arch segments, particularly in the ventral elements. Both chondrichthyans chondrichthyans Both ventral elements. in particularly the segments, arch pharyngeal respiratory systems in jawed vertebrates (gnathostomes). (gnathostomes). vertebrates injawed systems respiratory The pharyngeal skeleton has long been implicated in theories of the origin oforigin of theoriesthe implicated in been longskeletonhas pharyngeal The INTRODUCTION of comprises a jointed network of bones and cartilages surrounding the mouththeand surrounding bonescartilages andofnetwork a jointed comprises complete gill complete of examples fossil Unfortunately, 2014). Pradeletal., 1979; 1969;Wiley, (Nelson, connect one or more arches.orone more connect may paired)corpuses (oror moremedialone where midline, ventral atthe meeting thethroatand around extendingand orbraincasevertebrae, the either on origin The two main divisions of the gnathostome crown group (Osteichthyes and (Osteichthyes groupcrown gnathostome of the maindivisions two The of their relationships topological thesignificantlypattern of in differ Chondrichthyes) usefulness. uncertainty about uncertainty leaves considerable gnathostomes stemgroup offrom A lackinformation study. to theminaccessible makesthat often position anatomicaldeepand mineralization weak 2013; Pradel et al., 2014). By contrast, in osteichthyans, the ceratohyals attach to a attach theceratohyals osteichthyans, in contrast,By2014). Pradeletal., 2013; al.,1992; Carvalho et Shirai, 1923; 1922; Allis, (Garman, 1913; element hypohyal amedian todirectly of attaching ceratohyals archesconsist hyoid Chondrichthyan elements. basibranchial medianmoreor one possess osteichthyans and o

mandibular and hyoid arches; and the branchial skeleton, or gill arches. Itgill or arches. branchial skeleton, theand hyoid andarches; mandibular vided a rich source of character data for studies of gnathostome interrelationships interrelationships of gnathostome studiesfor data character of rich source a vided

Accepted gill The Article

skeletons from early gnathostomes are rare owing torareowing are gnathostomes early skeletons from

skeleton

pharyngeal pharyngeal This article isprotected by copyright. All rights reserved.

, in particular, as well as wellas in particular, ,

skeleton character polarities, limiting theirphyloge limitingpolarities, skeleton character Journal ofMorphology John Wiley&Sons its musculature have classically musculature its This skeletal system consists skeletalsystem This t heirtypically rza 4 Brazeau n etic etic Page 38of67 Page 4of33

Page 5of333967 preserved endoskeletons—are extremely rare. extremely endoskeletons—are preserved with fossils—particularly placoderm articulated Complete, preserved. poorly placoderms: an assemblage of Paleozoic jawbearing stemgroup gnathostomes. stemgroup Paleozoic jawbearing of assemblage an placoderms: be ‘anteriorly directed’ and at least one anterior branchial arch pair usually joins the the pairusually joinsarch branchial anterior one least at and directed’ ‘anteriorly be to considered are thehypobranchials osteichthyans, In or cartilage. bone basibranchial Unfortunately, these gill skeletons are weakly mineralized and therefore tend to be to tend therefore and mineralized weakly are gill skeletons these Unfortunately, Garman, 1913). Garman, (seee.g.basihyal of the angle theposterolateral to connected directed and anteriorly often hypobranchial is first copula. The toorabasibranchial midline anatomical the either at directed, join and (usually)posteriorly arehypobranchials first theall chondrichthyans,but Inelasmobranch thehyoid arch. as basibranchial same Morris and Caron, 2014). However, partially ossified examples exist in thein ossifiedexist examples partially However, 2014). Caron, and Morris 2007; Conway Arsenault, Janvierand2006; etal.,(Janvier outgroups gnathostome 2014). al.,(Pradel conditions et arch branchial primitive reconstruct to attempting mappingexercises inhibitedcharacter has gnathostomes group stem from outgroupTheof information lack an remains. uncertainty considerable 2014), etal., (Pradel derived conditions and primitive of theseparation aids fossils of consideration 2014).Although etal., Pradel 2014; Friedman, and (Brazeau cartilage, which may connect either at the midline to its antimere or to a ventralora to itsantimere to atthe midline either connect may which cartilage, or bone by hypobranchial medially anda terminatesarchventrally branchial each osteichthyans, andIn both chondrichthyans inchondrichthyans. absent considered usuallywhichare of the latter 1998) Bemis,and Grande 1972; 1954; Jarvik, 1897;1922; (Allis, via ahypohyals, termedbasibranchial) (usually bone median

All of these contrasts are potentially phylogenetically informative variables informative phylogenetically arepotentially contrastsof these All Accepted jawless knownfrom poorly skeletons gillextremely are Fossilized Article

This article isprotected by copyright. All rights reserved. Journal ofMorphology John Wiley&Sons However, multiple However, examples are known are examples rza 5 Brazeau

branchial arch patterns. patterns. arch branchial phylogenetically coherent. Nevertheless, these taxa are known from complete and complete and fromtaxaknownare these Nevertheless, coherent. phylogenetically Stensioella including “stensioellids”, enigmatic phylogenetically anatomicallyand the are these Geological context context Geological (1962).by Gross and (1933) by Broili described beenpreviouslyhas It squamation. trunk and armor dermal a Thearticulated iscomplete, 1986). specimen byWuttke, (assigned 1983/294 KGM Kreuznach Bad (KarlGeibMuseum), Schlossparkmusuem the from Broili(1933) of onthespecimen type based investigationis This Specimen METHODS AND MATERIALS of primitive some aspects to infer used ishere gnathostomes modern and early in gillelementsbasal of arch analysis A comparative skeletons. branchial osteichthyan and in elements some chondrichthyan theofhomology aboutquestions raise that peculiaritiespresents itHowever, also examples.less in complete observed anatomy from arches gill placoderm of onthemorphologydetails further providespaper This of CT analysis synchrotron a through investigations. (CT) tomographyto computed amenable therefore are and (Gross, 1962) Xray contrast these fossils exhibit Furthermore, fossils. articulated be toisunlikely thatthegroup however,diverse, morphologically so is from the exceptional Early Devonian Hunsrück Slate Hunsrück Early Devonian the exceptional from

Accepted Article Paraplesiobatis

,

Pseudopetalichthys

This article isprotected by copyright. All rights reserved. confirm some generalized aspects of placoderm branchial archbranchial aspectsplacoderm of generalized some confirm , , Journal ofMorphology Nessariostoma

John Wiley&Sons Paraplesiobatis heinrichsi Paraplesiobatis and Paraplesiobatis heinrichsi Paraplesiobatis Paraplesiobatis Lagerstätte Broili (1933). Data(1933). Broili of Germany. Among Among Germany. of . This assemblage assemblage This . rza 6 Brazeau Page 40of67 Page 6of33

Page 7of334167 paleontological and geological literature. Bartels et al. (1998) suggest that that suggestthe (1998) al.et Bartels literature. geologicaland paleontological Paraplesiobatis Paraplesiobatis projected pixel size of 12.6 micron at the sample. The tomographic 3d imageswere 3d tomographic sample. The atthe of micron12.6size pixel projected lithostratigraphic nomenclature. The exact collection horizonfor collection The exact nomenclature. lithostratigraphic in formation, thangroup,ratherto a iscomparable Slateeffectively Hunsrück usage in the despitecommon status stratigraphic lacksaformal but 2002), etal., 1998;Schindler al., (Bartels Germanyet of southeastern Mountains Rhenish theinDevonianageof Early muddy facies isoffshore, Slatean Hunsrück The near the base of the Kaub Formation is radiometrically dated as 407.7 as dated isradiometrically Formation theKaub of thebase near layerAnash 1962). locality(Gross, theBundenbach Formation at Kaub midbasinal the clayrich, derives itfrom likely unclear,but issuccession Hunsrück the within Zone lies within the within lies Zone into the into extends Bundenbach the of at thetopwhileformation 2005), et al., Ma(Kaufmann splinedated to 397.68 to splinedated I12 at the radiationXraymicrotomography synchrotron scanned usingwas specimen The tomography Synchrotron optics onto the detector of PCO4000 CMOS camera (PCOAG, Germany), with a with Germany), (PCOAG, CMOS camera PCO4000 ofdetector onto the optics bymicroscopeimaged was which scintillator (CdWO4) Tungstate Cadmium 0.9mm a illuminating , Xrays monochromatic (100keV) lambda=.0124nm using spacing 2015) 20 ring suppression and projection back filtered using reconstructed 1 JEEP 1). The resulting voxel size was 12.7 µm. Because of the size of the specimen,of the thesizeof Because wasµm. 12.7 size voxel resulting The 1).

AcceptedXrayacquiringradiogra bywas performed Tomography . Article Nowakia elegans elegans Nowakia beamline of the Diamond Light Source, Didcot,(DrUK Light Source, Diamond of the beamline

can be roughly constrained to between 398408 Ma. Ma. 398408 between to roughlybeconstrained can This article isprotected by copyright. All rights reserved. Polygnathus inversusPolygnathus ± 2.144 Ma (Becker et al., 2012). Thus the of Thusthe age 2012). (Becker et Maal., 2.144 Dacryoconarid Zone (De Baets et al., 2013). The2013). (Deal., Zoneet Baets Dacryoconarid Journal ofMorphology John Wiley&Sons Conodont Zone, the top of whichbeen has of the top Zone, Conodont phs at 0.1 deg angular 0.1 deg at phs Paraplesiobatis (Titarenko et al., (Titarenko et a kopoulos et al., etal., kopoulos ± 0.7 rza 7 Brazeau N. elegans

perichondrally ossified bones (Figs. 1, 2). The skeleton is mostly intact and nearlyintact skeletonandismostly The 2).1,(Figs. bones ossified perichondrally pyrite crystals (Supporting Information Fig. 1). Furthermore, the discontinuous thediscontinuous Fig.1).Furthermore, Information (Supporting crystals pyrite branchial) elements are preserved. Thegill skeleton preserved. areelements pharyngobranchial) postprocessing. in together later“stitched” were These stage. rotation thetomography supporting stages translation vertical theautomated using generated scans overlappingwere seven complete ventral gill basket spanning the entire breadth of the skull. No dorsal (epi ordorsal (epi No theskull. breadthof theentire basketspanning gillventral complete DESCRIPTION DESCRIPTION https://dx.doi.org/10.6084/m9.figshare.4555462 at freely areavailable study thisusedin models Surface Booleanoperations. usingunited laterwere that masks multiple from bonesformed were theindividual of Therefore, most values. threshold consistent selecting difficulties in caused Fig.1) Information (Supporting volume thetotal scanseriescomprising each separate normalization between grayscale of a pair of heavy ring artefacts and the ‘brightness artefacts’ caused by highlydenseby ‘brightnesscaused artefacts’ the and heavyartefacts pairofring a of thetoinfluence wastakenavoid Particular care versions. some earlier 18and version in Software) completed and (Materialise Mimics loaded in wasvolume resultant The modeling virtual and Segmentation the ventral midline), and a lateral segment. The fifth arch consists ofvisible single a The fifth segment.consists arch a andlateralmidline), ventral the itsantimere across (that joins segment medial atwosegments: of archesconsist four Thefirst below). (explained arches segmented tofour five set of basihyal and median Tomography data can be accessed at: https://figshare. be at: accessed can data Tomography

Acceptedofnetwork segmented a ispreservedas 1983/294 KGM skeletonof gill The Article

This article isprotected by copyright. All rights reserved. Journal ofMorphology John Wiley&Sons c om/s/8bdd8e20f76de18febf9 om/s/8bdd8e20f76de18febf9 c omprises asingle, omprises rza 8 Brazeau Page 42of67 Page 8of33

Page 9of334367 been pushed posteriorly from its original life position. The anterolateral corners are The anterolateral position.original life its from posteriorly pushed been thatit has suggest These angles horizontal. 30 degrees from byabout upwards pitched longitudinal keel with a convex profile. Similar toSimilar profile. witha convex keel longitudinal deeply notched. As in the phyllolepid placoderm placoderm thephyllolepid in Asnotched. deeply small fragment of it may be preserved on the left). This isproblematic the most theleft). This on preserved it ofmay be fragment small arch.of elements each themedial on only descriptionfocuses remaining Theridge.ventral alongitudinal show toenough well resolvehoweversome quality, poor scan to the owing featureless Most appear 2). elements. arch other with articulations forthe positionsto possiblycorresponding mineralization, incomplete suggesting thescans, in indistinct are thebone of boundaries posterior The of thebone. margin the meet anterior to upwards anteriorly tapers andposterior its displaced taphonomically: rotated clockwise about ten degrees from the midline, andthe tenmidline, from degrees about clockwise rotated taphonomically: displaced thearches. of order theanteroposterior onlyto refer and therefore other gnathostomes with identity indicate exact tointended necessarily not arehere assigned numbersofarch this, the Because gnathostomes. other inidentitiesserial with their to respect numbers arch the in interpreting uncertainty issome thereshow, willdescription this Asthe mouth. to intrusions or other sediment bydislodged possibly displaced, disruptedandare bones left, anterior the However, preserved. bonesunpaired nomedian areadditional There its antimere. meeting than rather arch, theof fourth facet posterolateral to connectsthe that segment

The first arch in the series is preserved only on the right side (however, a (however, onsidethe right only series ispreserved the in arch first The bonyrods(Fig. rectangular roughly short,areelements archthedistal of Each Accepted ArticlebeenhasIt dorsoventral inaspect. istrapezoidal roughly basihyal The 2).(Fig.position life preserved in nearly completely isside right The

This article isprotected by copyright. All rights reserved. Journal ofMorphology John Wiley&Sons Cowralepis Cowralepis (Ritchie, 2005) there isathere 2005) (Ritchie, , the keel is deepest atisdeepest thekeel , rza 9 Brazeau

placoderms in Stensiö’s (1969) terminology or the basibranchials of other authors basibranchials the terminologyor Stensiö’s(1969)in placoderms Onthe featureless. mainlysurfaceandis flat Therod.dorsal angled posterolaterally brought into close proximity when the pharynx was disrupted and cannot be resolved resolved becannot and disrupted waspharynx thewhen proximity close into brought rectangular profile. rectangular roughlyamedial giving areathe themargin,posterior with parallelsided roughly is of archthe third region By same flange. contrast, the rodlikeits lateral into narrow inhalfmedial margin its anterior along a arched stronglyhas arch second The backwards to turning sharply before anterolaterally, arcs 2).It (Fig. view dorsoventral basibranchial elements. andhypo, tocerato, fused these correspond whether unclear therefore is2).It projection(Fig. rodlike lateral withthe continuous completely these1983/294are KGM that notableIt 2009). is in al., 2005; Carr et (Ritchie, of hypobranchials thethepositionof to corresponding extremity, medial their at tumidity deep ventral a haveHowever,they side.dorsal ontheir featureless relatively and flat, are elementsmedial 2).The series(Fig. of itsmembers following or precedingwith the of articulation broadareashave toregion expanded appear of faces anterior posterior and tumidity. The ‘basibranchial’ bears a side,thesurface ventral abruptly, at about midlength along the anterior margin to form a narrow,aformmargin to theanterior along atmidlength about abruptly, regionthattapers broadmedial aof outlineconsists their aspect, dorsoventral thescan. in were arch—that branchial firstand ceratohyal bones—a separateof two composite isathatit it possible consider weHowever, here. structure single aas described This (Fig.is 3). regionelement rodlike a dorsal ‘blade’, flattened and ventral roughlyoval broad, of a consistingmorphology, unusualhas bone an The artifacts. bynumberof severelya isdataafflicted tomographic becausethe todescribe element

Accepted ArticleIn (Fig.bone2). sweptrodlike aposterolaterally of 4to 2 consist Arches

This article isprotected by copyright. All rights reserved. Journal ofMorphology John Wiley&Sons rza 10 Brazeau Page 10of334467

Page 11of334567 Paraplesiobatis Paraplesiobatis points towards) the crux of the fourth arch medial element (Fig.2). medial element arch thefourthcrux the oftowards) points generated in generated pattern beHowever,cansimilar a the‘ceratobranchials’. and ‘basibranchials’ A key difference in the gill skeletons of skeletons gill in differencethe key A isquiteaccurate. reconstructions additional details provided by provided details additional crescentshaped bone, opening posterolaterally. The fifth arch articulates (orat least articulates archfifth The posterolaterally. bone,opening crescentshaped a Theisresult width. longthebone’s nearly asas processas a posteriorly extends of the gill skeleton ofskeleton gill theof interpretation reviseda attempted (2009) etal. Carr Recently, examples. comparative few are there though placoderms, isunusual among 4).This(Fig. “basibranchials” with inItcommon shares Thomas. of specimen onlyandtype 1986) (Wuttke, lost thenowbelongs to skeleton known branchial placoderm complete most The Alternative interpretation of interpretation Alternative DISCUSSION ofthebone. on theanterolateral face deepfossa a bulge accommodates This thebone. widthof the bulgespanning to keel a out flares ventral theDistally, edge. bladed a to dorsallymargin thinning theposterior theanterior margin; along keeled isdeeplyit two thirds, its anterior Inprofile. dorsoventral in rectangular roughly

The fourth arch differs from the preceding arches in that the tumid portion portion thatthe tumid arches in thepreceding differs from arch fourth The Accepted Articleisrobustand bone The bone. observed asingle of consists arch fifth The

Paraplesiobatis

is that the gill skeleton of the former appears segmented between the between segmented appears of the formerskeleton gill thatthe is This article isprotected by copyright. All rights reserved. Pseudopetalichthys by embedding the reconstructed arches in a plane (Fig.plane a in arches thereconstructed by embedding Paraplesiobatis Pseudopetalichthys Journal ofMorphology

John Wiley&Sons Paraplesiobatis in light ofin Pseudopetalichthys problematicus Pseudopetalichthys reveals that neither of their their ofneither revealsthat Pseudopetalichthys Pseudopetalichthys

posteriorly extended posterior extended posteriorly Cowralepis . However, theHowever, . and and rza 11 Brazeau Moy

partial burial ofskeleton in thegill burial partial Pseudopetalichthys inobserved similararepositionin abroad Unusual plates basihyal. placoderms (Fig. 5). This structure is observedin is clearlystructure 5).This(Fig. placoderms Pseudopetalichthys both direct examinations and radiographs of radiographs and directexaminations both KGM 1983/294 exhibits a broad, thin, spatulate ossification flanking the the ossificationspatulateflanking thin, broad, aexhibits 1983/294 KGM 4). The differences could therefore reflect differences in the degree of ossification or ofdegreeossification the indifferences reflect therefore differences could The 4). However, in comparison with KGM 1983/294 and1983/294 KGM comparison with in However, The resulting interpretation brings the gill skeletons ofgill skeletons thebrings interpretation resulting The ceratohyals. in expanded thesefact, are, that argue it to reasonable consider we 2009) Basihyal. Basihyal. elsewhere. treatedbe will “stensioellids” remaining The below. subsection Cowralepis absent in in absent Cowralepis morphologyof the resembles 1983/294of KGM Thebasihyal bone. basihyalalso a is itthat to reasonableconclude it is elements, otherpharyngeal to relative the bone this Tapinosteus Tapinosteus the arthrodires materialinclude arch preservingbranchial placoderms Other otherplacoderms with Comparison Gemuendina Gemuendina and Forey and Gardiner, 1986; Long, 1997) and the socalled “stensioellids” socalled“stensioellids” theand 1997)Long, 1986; Gardiner, and Forey

Accepted Pseudopetalichthys Article

Tapinosteus Tapinosteus A single median basihyal is common (possibly universal) among(possiblyuniversal) is basihyalcommon median A single

, and and , in the structure of its longitudinal ventral keel. Such a keel appears to be to appears Suchakeel keel. ventral itslongitudinal ofthestructure in (Stensiö, 1969) and 1969)and (Stensiö, (Gross, 1963) and 1963)and (Gross,

Pseudopetalichthys This article isprotected by copyright. All rights reserved. and interpreted by Gross (1962) as mandibular elements. as elements. (1962)mandibular Gross byinterpreted and into close agreement. agreement. into close (Stensiö, 1969).(Stensiö, (Gross, 1962), the latter will be treated in a separate in treateda be latter will the(Gross,1962), Jagorina Journal ofMorphology Cowralepis John Wiley&Sons Pseudopetalichthys . Gross (1963) describes a “copula element” in in a“copula element” (1963)describes Gross . (Stensiö, 1969); pytctodontids (Miles, 1967; 1967; (Miles, pytctodontids 1969); (Stensiö, (Ritchie, 2005); the rhenanids2005); the(Ritchie, Gemuendina Cowralepis . Paraplesiobatis Tapinosteus . Based on the position of onposition Basedthe . (based on Carr et al., on Carr et (based (Stensiö, 1969), (Stensiö, and and Stensioella rza 12 Brazeau

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Page 13of334767 placoderms, and here further corroborated by KGM 1983/294, thebasihyalis KGM1983/294, by corroborated further here and placoderms, processes that would themselves correspond to either hypobranchials or hypobranchials either to correspond wouldthemselves that processes proximal end of the first arch bears a spatulate expansion (shown bothin Gross’s (shown expansion spatulate bears a the of arch first end proximal followed by a paired series of basibranchiallike ossifications. Inossifications. basibranchiallike seriesof apaired by followed Stensiö, 1969)and Stensiö, the basihyal. the ofposteriorto the very orclosely apposed iswith articulates either ‘basibranchials’ The number and structure of branchial arches in placoderms. placoderms. arches branchialin andof structure number The (‘hypobranchials’ of Stensiö) in other placoderms are joined to extended lateral to extended otherare placoderms joined in of Stensiö) (‘hypobranchials’ ‘basibranchials’ the to corresponding one. The area lateraland amedial segments: (fourth) arch. The ‘basibranchial’ series of ‘basibranchial’series The arch. (fourth) preceding rather the region,joins but ‘basibranchial’ itsown nothave does arch theidentityfifthand orhyoid branchial uncertain isof arch Thefirst ceratobranchials. corresponding to at least four individual pharyngeal arches. What remains unclear is unclear remains What arches. pharyngeal leastindividual four to at corresponding ‘basibranchial’elements, least atand afour median basibranchial possess generally a beas ceratohyal. interpreted reasonably could and cartilage arch mandibular thebehind isnestled expansion spatulate This plate). photographic and illustration and more specifically, hexanchiform—interpretive model. hexanchiform—interpretive specifically, more and onachondrichthyan— based these bones arches joining reconstructs multiple Stensiö inpairs three are there while al.,2009), et However, an indistinct fifth arch can be observed in his plate 8, fig B. Notably, the Notably,plateB. 8, his be fig observed in can indistinct arch fifth an However,

The branchial bones of KGM 1983/294 consist of arches comprising only two only comprising of arches consist 1983/294of KGMbones branchial The Based on these details, it seems reasonable to conclude that placoderms thatto conclude reasonable it seems details, on these Based AcceptedIn Article Gemuendina

This article isprotected by copyright. All rights reserved. Cowralepis , Gross (Gross, 1963) illustrates up to four separate arches. separate up to four illustrates (Gross,1963) Gross , (Fig. 5; Carr et al., 2009), the first pair ofpairfirst the al.,2009),5; Carr et (Fig. Journal ofMorphology John Wiley&Sons Tapinosteus Cowralepis (Stensiö, 1969). However,1969). (Stensiö, numbers four elements (Carr elements four numbers Tapinosteus Tapinosteus In all examples ofall In examples rza 13 Brazeau (Fig. 5;(Fig.

Paraplesiobatis Paraplesiobatis other placoderm or any 1983/294 KGM of thearches in Nothing arch. penultimate Paraplesiobatis Paraplesiobatis possibly accommodating articulation with the hyoid arch (Fig. 5).(Fig.thehyoid archwith articulation accommodating possibly Similarities with chondrichthyans. chondrichthyans. with Similarities gnathostomes crown-group with Comparison gnathostomes. other of tohypobranchials correspond realistically more they that,whether or as interpreted befact, should, in elements the‘basibranchial’ whether Interpretation and reconstructionand Interpretation hypohyal. posteriorlydirected aas interpretedbe here can considered example the theseries join in last arch the having osteichthyans in resembles further 1983/294 5).KGM (Fig. ceratohyals havinginenlarged/differentiated examples osteichthyan osteichthyans. with Similarities together when the front of the gill skeleton was dislodged. The ovate,bladelike The dislodged. was skeleton thegill offront when the together pushedthatwere elements separateof two a in composite fact, is, arch the first of themodel Alternatively, arches. branchial four consistof therefore would arches subsequent Thebasihyal). the with ofarticulating aceratohyals pair (comprising arch isaarchhyoid preservedthefirst isthat interpretation first5).The (Fig. gnathostomes othertheof toinarchesrelation interpretations competingtwo offerwe Here (Grogan and Lund, 2000) in being roughly trapezoidal with anterolateral ‘notches’, ‘notches’, with anterolateral roughlybeing trapezoidal 2000) in Lund, and (Grogan

Accepted Articleholocephalan theCarboniferousof similarto that is 1983/294 KGM thebasihyal in of outline The 2013). et 5;al., Carvalho e.g.(Fig. see chondrichthyans

specimen KGM 1983/294 preserves at least five pharyngeal arches. pharyngeal at least preserves five 1983/294 KGM specimen coupled with no apparent hypohyals compares well with modernwithwell hypohyals compares no apparent with coupled This article isprotected by copyright. All rights reserved. Journal ofMorphology Placoderm pharyngeal skeletons agree withagree skeletons pharyngeal Placoderm John Wiley&Sons The presence of a median basihyal in basihyal amedian of Thepresence Debeerius rza 14 Brazeau

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Page 15of334967 po branchial basket appears to have met the lateral margins of the braincase directly, braincasedirectly, the marginsoflateral met the have to basket appears branchial with articulates 5archosteichthyans, in As 15. numbering only, arches branchial Furthermore there are no evident epi or pharyngobranchial ossifications. Theossifications. or pharyngobranchial epi noevident are there Furthermore arches. branchial of gnathostome conventions to nomenclatural equivocally conforms of skeleton the branchial aspect Thetoventral apply. difficultare terms nomenclatural standard theof basihyal,the exception and, with gnathostomes other ishighlydifferentiated. but 4, arch to thecorrespond this In1.archarches branchialcase, of element medial the be would upper rodshaped region the toceratohyal, adisplaced would correspond element without any intervening ossifications. intervening ossifications. any without Ph A median basihyal is apparently universal among placoderms, it is common to to common it amongis universalplacoderms, basihyalis apparently median A pair state—a The alternative chondrichthyans. stemgroup putative some and crown placoderms. of paraphyly bothormonophyly with offerconsistent interpretations we will indicated, otherwise Unless monophyly. placoderm about assumptions prior to no make elect therefore Wemethods. under modified analytical 2013) et al., (Zhu monophyletic as of placoderms majority arecover and result with this problems demonstrate recently (2016)al. King however et paraphyly, favorMostplacoderm analyses groups. crownosteichthyan and chondrichthyan tomonophyletic assumedbe are There inferences. phylogenetic numberof a make can5),we (Fig. gnathostomes group Under the assumption that placoderms (including (including thatplacoderms theassumption Under

s y sibly unossified, and therefore unpreserved. therefore and unossified, sibly logenetic distributions logenetic

Accepted Articleof architecture branchial The

This article isprotected by copyright. All rights reserved.

Journal ofMorphology John Wiley&Sons Paraplesiobatis Alternatively, these elements were small,were elements these Alternatively,

Paraplesiobatis is not easily compared with with isnot easily compared ) comprise stem comprise ) rza 15 Brazeau

parsimonious distribution for these structures could be arrived at by placing by arrivedbeat structurescould these distribution for parsimonious but their phylogenetic significance is somewhat more ambiguous (Fig. 5). Hypohyals (Fig.5). Hypohyals more somewhat significanceambiguous is theirphylogenetic but al., 2015; Burrow et al., 2015). Burrow et al., 2015; al., Blaiset2012; Brazeau, 2010; Hanke Wilson, and 2001; et al., (Hanke acanthodians othernonacanthodiform patternin ossification of thistypeof no evidence is subdivided visceral and branchial series ofseries branchial visceral and subdivided heavily the However, theof ceratohyal. subdivision aas hypohyal osteichthyan ofthe interpretation nothing precludes Furthermore, andhypohyal. a ceratohyal aor ceratohyal asubdivided either as interpreted Thisbecould ossifications. of ceratohyal The competing)interpretations. necessarily (not multiple with segmentation of pharyngeal pattern it presentsabut2015), etal., Giles2015; deWinter, and al.,(Zhu2013; Brazeau et chondrichthyan stemgroupa considered increasingly now istaxon This hypohyals in chondrichthyans. ofor absence thepresence to respect gnathostomes. extant among osteichthyansto uniquebe to basihyal—appears median to a connecting hypohyals of symmoriiforms more generally. Paired hypohyals in in Pairedhypohyals generally. more symmoriiforms thatortaxonof state,derived either abe considered canand anomalous gained in symmoriiforms, osteichthyans, and osteichthyans, insymmoriiforms, gained weretheyAlternatively, threesteps). (minimum twicechondrichthyans in least) (at lostcrown originand thegnathostome the to ofgainedprior been in have may They also observed in the stemholocephalanin theobserved also (along with other symmoriiforms) on the holocephalan stem (Fig. 5), as has been has 5),as been (Fig. stemholocephalan on the symmoriiforms) other with (along The absence of a median basihyal in in of basihyal a median absence The Accepted Article considered, are gnathostomes extinct When

Acanthodes

This article isprotected by copyright. All rights reserved. , according to Gardiner (1984) is composed of two discreteof two iscomposed (1984) Gardiner to according , Journal ofMorphology John Wiley&Sons Debeeriusellefseni Acanthodes Ozarcus Debeerius Acanthodes (Pradel et al., 2014) is 2014) et al., (Pradel Ozarcus may be apomorphic, as there as apomorphic, maybe (also three steps). A more steps).more Athree (also (Grogan and Lund, 2000).Lund,and (Grogan resemble osteichthyans, resembleosteichthyans, presents a caveat with with caveat a presents rza 16 Brazeau Ozarcus

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Page 17of335167 been identified been Median, unpaired basibranchials are absent in placoderms. No examples have placoderms. inNo examples absent are basibranchials unpaired Median, 2017). etal., 2015;Coates Giles etal., 2001; Sequeira, (Coates and of otherlinesof evidence thebasis onelsewhere suggested the RheinlandPalatinate). We gratefully acknowledge Diamond Light Source, UK forUK Source, Light Diamond gratefully acknowledge We RheinlandPalatinate). the of Heritage Cultural Directorate forGeneral (then Dr. Wuttke Michael andstudy for theUK transported to be toit for allowingandspecimen to forthe access Kreuznach) Bad (Schloßparkmuseum, NestlerZappAngela Dr.thank to wouldlike Accepted authors The ACKNOWLEDGMENTS the figures. composedAJ and MDB MDB.MF and from with assistance reconstructions tomography and scanning synchrotron the conducted RA segmentation. performedthe AJ MDB and MF. from input with manuscript the MDB study;wrote theoriginal MFdesigned and MDB CONTRIBUTIONS AUTHOR in elasmobranchs. foreshortened become buthas ofchondrichthyans, thebasihyal to ishomologous osteichthyans basibranchialof Alternatively,the separate. arechondrichthyans and osteichthyans Article in theirorigins that primitive and thebasihyalis to posterior mineralisations unpaired median of theabsence that argue provisionally, we However, this. help will London)clarify College (Imperial RPDearden andauthors the byunderway is currently other species ofacanthodian two investigations tomography Computed 1984). (Gardiner, Gardinerand (1973) byMiles disputed are (1968) identifiedby Nelson basibranchials median ofchain known. are The ossifications

in

Acanthodes This article isprotected by copyright. All rights reserved.

,

the only acanthodian for which substantial gill skeleton skeleton gill which substantial acanthodian thefor only Journal ofMorphology John Wiley&Sons rza 17 Brazeau

Accepted Article themanuscript. improvehelped referees twoanonymous from Comments Oxford. University ofFell theJohn Fund, fromsupport acknowledges MF number 311092. GrantAgreement (FP/2007–2013)/ERC Programme Framework SeventhUnion’sEuropean under the Council Research European thefromsupport generous acknowledges MDBbeamline. ontheI12 time supplying

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Page 19of335367 be misleading ( misleading be Pseudopetalichthys correspondence with correspondence to show highlighted arch pharyngealelements 1962) Gross,with from (modified

Fig. 4. Alternative reconstructions of reconstructions Alternative 4. Fig. view ( view resulting in apparent segmented pattern ( patternsegmented in apparent resulting ( condition life to restoredapproximate elements posterior basihyal andand mirrored elements Fig. 3. Basihyal and first arch elements. Dorsal view ( viewDorsal elements. archfirst and 3.Basihyal Fig. = 1cm. bar Scale gnathostomes. to other homologies direct not thebuttext,innecessarily to referredorders archindividual indicate KGM 1983/294 1983/294 KGM skeletonof gill articulated of illustrations interpretive and renderings Virtual 2. Fig. views (upper left) with branchial arches ( branchial arches with left) (upper views transparent andright) (lower solidshowing tomography light computed synchrotron Fig. 1. Fig. FIGURES C

Accepted ArticleParaplesiobatis ). Anterior view( ).Anterior

A

). Reconstruction in panel A partially embedded inplane virtual a partiallyembedded inA panel ). Reconstruction

C

Paraplesiobatis ). Not to scale. scale. Not to ). This article isprotected by copyright. All rights reserved. . Partially reconstructed gill skeleton with left and right first arch right arch firstand withleft gill skeleton reconstructed Partially . Paraplesiobatis specimen KGM 1983/294 ( 1983/294 KGM specimen D ). Scale bar = 1= cm.bar Scale ). . Dorsal view ( view Dorsal . Journal ofMorphology John Wiley&Sons suggesting that the segmented appearance may appearance thesegmented that suggesting Paraplesiobatis B B ). Reconstruction of ).Reconstruction ). Scale bar = 1 cm.bar ).Scale A , B A ). ventral view ( view ventral ). ) and virtual renderings of virtualrenderings and ) and comparison with comparison and A ). Ventral view ( view ).Ventral Pseudopetalichthys C , D ). Numbers B rza 19 Brazeau ).Posterior

Not to scale. scale. to Not Pradel et al. (2014).( et al. Pradel Jarvik (1972). Jarvik Garman (1913). ( (1913). Garman (right). ( (right).

Accepted Article ( vertebrates. earlyjawed patterns in gillventral of arch comparison Phylogenetic 5. Fig. H)

Cowralepis

A

( ) Two possible interpretations of interpretations possible Two ) C

) E This article isprotected by copyright. All rights reserved. Mimipiscis Mimipiscis ) Debeerius G) after Carr et al. (2009).( etal. Carr after Acanthodes

after Gardiner (1984). ( (1984).Gardiner after after Grogan(2000).( Lund and after Journal ofMorphology John Wiley&Sons after Miles (1973) (left), and Gardiner (1984) Gardiner and (1973) (left), Miles after Paraplesiobatis I ) Tapinosteus D ) Scapanorhynchus after Stensiö (1969).Stensiö after F . ( . ) Ozarcus B ) Glyptolepis after rza 20 Brazeau after after after after Page 20of335467

Page 21of335567 Brazeau MD, de Winter V. 2015. The hyoid arch and braincase anatomy of anatomy hyoidbraincase andarch The 2015. V.deWinter MD, Brazeau Allis EP. 1923. The cranial anatomy of anatomy Thecranial 1923. EP. Allis Burrow CJ, Davidson RG, Blaauwen den JL, Newman MJ. 2015. Revision ofRevision 2015. Newman MJ. JL, den Blaauwen Davidson RG, CJ, Burrow Wiss,AkSber Bayer Hunsrückschiefern. den aus Fischreste 1933. Weitere F. Broili vertebrates. Palaeozoicjawed of characters The2014. FriedmanM. MD, Brazeau Brazeau MD. 2012. A revision of the anatomy of the Early Devonian jawed vertebrate vertebrate Devonian jawed Early theof the anatomy of Arevision2012. MD. Brazeau Allis E. 1897. The cranial muscles and cranial and first spinal nerves in spinal andfirst cranial and musclesThe 1897. E. cranial Allis CITED LITERATURE Allis EP. 1922. The cranial anatomy of anatomy The cranial 1922.EP. Allis Blais SA, Hermus CR, Wilson MVH. 2015. Four new Early Devonian ischnacanthid ischnacanthid Early Devonian newFour 2015. MVH. CR, SA,Wilson Hermus Blais The Geologic In:Period. DevonianO.The 2012. FM, Hammer Gradstein RT, Becker Slate: Marine theHunsrück of The Fossils 1998. G. Brassel DEG, Briggs C, Bartels Acanthodes Ptomacanthus anglicus Ptomacanthus Polypterus bichir Polypterus Climatius reticulatus Climatius Abt2:269–313. MathNaturw 170:779–821. Soc Linn J Zool 282:20152210. Morphol 11:487–808. 11:487–808. Morphol Accepted PaleontolVertebrJe948546. diversity.dental in experiment early an Canada: NorthwestTerritories, Mountains, Mackenzie the from acanthodians 559–601.p. Elsevier.Scale Time Article309p. University Cambridge Press. Cambridge: Devonian. in the Life 4:123–221.

support chondrichthyan affinity of “acanthodians.” Proc BiolSci of “acanthodians.” affinity chondrichthyan support

This article isprotected by copyright. All rights reserved. . J Anat 190–294. 190–294. AnatJ .

Agassiz, 1844 (Acanthodii, Climatiidae), from the Lower from Climatiidae), 1844Agassiz,(Acanthodii, Miles. Palaeontology 55:355–367. Palaeontology55:355–367. Miles. Journal ofMorphology John Wiley&Sons Polypterus Chlamydoselachus anguineus Chlamydoselachus , with special reference to to reference special with , . ActaZoologica . Amia Amia calva rza 21 Brazeau . J .

Carr RK, Johanson Z, Ritchie A. 2009. The phyllolepid placoderm placoderm Thephyllolepid 2009.A. Z, Ritchie Johanson RK, Carr De Baets K, Klug C, Korn D, Bartels C, Poschmann M. 2013. Emsian Ammonoidea Ammonoidea Emsian 2013.M. Poschmann Bartels KornC, D,K, Klug C, Baets De of the Cambrian North fromA primitive 2014.fish JB.S, Caron Morris Conway symmoriiform A 2017.K. Tietjen KE, CriswellRW,Finarelli JA, Gess MI, Coates theLower from stethacanthid chondrichthyan Anew2001. S. Sequeira M, Coates fifththeofHomology 2013.MR. deCarvalho FA, M, Bockmann Carvalho Drakopoulos M, Connolley T, Reinhard C, Atwood R, Magdysyuk O, Vo N, Hart M, Hart Magdysyuk VoN,R, O, Atwood C, T, Reinhard M, Connolley Drakopoulos Forey PL, Gardiner BG. 1986. Observations on Observations BG. Gardiner1986. PL, Forey Vertebr Paleontol 35:e913421. Paleontol Vertebr J data. morphological histological and basedonnew Scotland, of Devonian America. Nature 512:419–422. Nature America. Nature. fishes. chimaeroid oftheorigin andbraincase chondrichthyan 21:438–459.Paleontol Vertebr J Scotland. Bearsden,of Carboniferous 8:e62389. PLoSONE ostariophysans. of development the insightsfrom gnathostomes: among the ceratobranchials of accessoryandelements epibranchial 270:775–804. MorpholJ vertebrates. mclachlani Palaeontographica, Abt 299:1–113. A Palaeontographica, Germany). Western (Rhenish Mountains, Hunsrück Slate the of the age and Source. J Synchrotron Rad 22:828–838. 22:828–838. Rad Synchrotron J Source. Light Diamond beamline at (JEEP) Processing Environmentand Engineering, the JointI12: 2015. K. F,Wanelik Yuan M, MaioBasham N, DeA, Foster G, Pedersen U, T,Wilkin S,Davies Hill G, Howell Humphreys B, L, Connor classification of placoderm fishes. Zool J Linn SocLinnJ86:43–74. Zool of fishes. placoderm classification Accepted Article

: insights into the evolution of feeding mechanisms in jawed injawed feeding ofmechanisms evolution into the insights :

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Page 23of335767 Giles S, Friedman M, Brazeau MD. 2015. Osteichthyanlike cranial conditions in in an conditions cranialOsteichthyanlike2015. MD. Brazeau M, S,Friedman Giles ZoolComp MusMem rays). skates, and (sharks,The Plagiostomia 1913. S. Garman on basedreview a fishes, palaeoniscid of the The relationships 1984.BG. Gardiner Grogan E, Lund R. 2000.R.Lund E, Grogan amiid fishes of study phylogenetic Acomprehensive 1998. L, Bemis WE. Grande Gross W. 1962. Neuuntersuchung der Stensiöellida (Arthrodira, Unterdevon). Notizbl Unterdevon). (Arthrodira, Stensiöellida der Neuuntersuchung 1962. W. Gross Gross W. 1963. W. Gross Hanke GF, Davis SP, Wilson M. 2001. New species of the acanthodian genus theacanthodian ofNew 2001. species M. SP,Wilson Davis GF, Hanke Hanke GF, Wilson MV. 2010. The putative stemgroup chondrichthyans stemgroupputative chondrichthyans The MV.2010. GF, Wilson Hanke Kathemacanthus Harvard Coll 36:1–528. 36:1–528. Coll Harvard 37:173–428. (Geol) Hist MusnatBr Bull Australia. of specimens new interconnected patterns of natural history. J Vertebr Paleontol 18:1–696. Paleontol VertebrJhistory. of patternsnatural interconnected for searchempirical An anatomy. skeletal on basedcomparative (Amiidae) 520:82–85. Nature gnathostome. stemDevonian Early gnathostome evolution. J Morphol 243:219–245. 243:219–245. MorpholJ evolution. gnathostome on comments theChondrichthyes,and of therelationships (USA), Montana of LimestoneGulch Bear theMississippian from chondrichthyan autodiastylic Hess Landesamt Bodenforsch Wiesbaden 90:48–86. Wiesbaden Bodenforsch Landesamt Hess Tetanopsyrus 91:36–73. Wiesbaden Bodenforsch Landesamt of Fossil Fishes Eds. D.K. Elliott, J.G. Maisey, X. Yu, and D. Miao, VerlagMiao, D. Dr. X.and Yu, J.G. Elliott,Maisey, D.K.Eds. Fishes Fossil of Paleobiogeography Phylogenyand Morphology, Canada.Mountains, Mackenzie Accepted 21:740–753. Paleontol Article

Gemuendina stuertziGemuendina

from northern Canada, and comments on related taxa.VertebrJonrelated comments and northern Canada, from This article isprotected by copyright. All rights reserved. and and Mimia Seretolepis Debeeriusellefseni and and Journal ofMorphology Moythomasia John Wiley&Sons from the Lower Devonian MOTH locality,MOTH Lower Devonian the from Traquair. Neuuntersuchung. Notizbl HessNotizbl Neuuntersuchung. Traquair. (fam. nov., gen. nov., spec. nov.), an nov.),spec. nov., gen. nov., (fam. from Upper Devonian of Western of Western Devonian Upper from rza 23 Brazeau

Miles R. 1967. Observations on the ptyctodont fish, onfish, theptyctodont Observations 1967.R. Miles Long JA. 1997. Ptyctodontid fishes (Vertebrata, Placodermi) from the Late Devonian LateDevonian the Placodermi) from (Vertebrata, fishes Ptyctodontid 1997. JA. Long Methods Clock Morphological Bayesian 2016. M. LeeM,Zhu T, Qiao B, King (EarlyEmsian Two2005. new K. Weddige K, E,MezgerTrapp B, Kaufmann Miles RS. 1973. Relationships of acanthodians. In: Greenwood PH,RS, Miles Greenwood In: of acanthodians. RS.Relationships 1973. Miles Jarvik E. 1972. Middle and Upper Devonian porolepiformes from east Greenlandwith east fromporolepiformes Devonian Upper and Middle E.1972. Jarvik Janvier P, Arsenault M. 2007. The anatomy ofThe anatomy 2007.M. P, Arsenault Janvier Jarvik E. 1954. On the visceral skeleton inskeleton On thevisceral E.1954. Jarvik Janvier P, Desbiens S, Willett JA, Arsenault M. 2006. Lampreylike gills gills inaLampreylike 2006. M. JA,Arsenault S, WillettP, Desbiens Janvier parasphenoid and palatoquadrate in fishes. K Sven Vetenskapsakad Handl 4:1– Handl Vetenskapsakad Sven inK palatoquadratefishes. and parasphenoid Ctenurella genus theEuropean withofarevision Australia, Western Formation, Gogo SystBiol. Vertebrates. Jawedin Early Evolution RapidReveal and Monophyly Placoderm Resurrect 162:363–371. Soc London Geol Jscale. Devonian time the implications for (Germany): Massif Rhenish theofvolcanic rocks zirconfrom U–Pbages Devonian) Soc (Zool) 47:99–120. 47:99–120. (Zool) Soc structure of the head in porolepiformes. Medd Grønl 187:1–307. 187:1–307. Grønl Medd porolepiformes. in thehead of structure reference to special 104. Friedrich Pfeil, München, Germany:159–182. Germany:159–182. Pfeil,München, Friedrich Accepted Article 440:1183–1185. Naturevertebrate. jawless Devonian gnathostomerelated 29:143–216. Geodiversitas Canada. Quebec, Miguasha,of Devonian Upper the vertebrate from anaspidlike jawless an1900,

. Geodiversitas 19:515–555. 19:515–555. Geodiversitas .

This article isprotected by copyright. All rights reserved. Glyptolepis groelandica Glyptolepis Journal ofMorphology John Wiley&Sons Eusthenopteron Euphanerops longaevus Euphanerops n. sp. and a discussion onthe adiscussion sp.n.and Rhamphodopsis with a discussion of theof discussion with a Watson. J LinnJ Watson. Woodward, Woodward, rza 24 Brazeau Page 24of335867

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NSW 126:215–259. 126:215–259. NSW with a new classification of the Vertebrata. Zool J Linn Soc 67:149–179. J67:149–179. Soc LinnZoolthe Vertebrata. newof classification a with 18:427–435. Rad Synchrotron J samples. attenuating tomographingwhenanisotropically artefacts ring 71–692. p.4 Paris. vol dePaléontologie, Traité editor. Elasmobranchii). Bull Fac Fish Hokkaido Univ 43:24–32. UnivHokkaido Fish BullFac Elasmobranchii). 9:73–88. Metalla SWGermany). (Hunsrück, area Bundenbach of Devonian)the Lower Emsian, (Lower Formation Kaub of the middle position chronostratigraphical and subdivision Lithostratigraphical with osteichthyanlike branchial arches. Nature 509:608–611. 509:608–611. Nature branchial arches. osteichthyanlike with 141:475–552. MusHistNat Am ofBull vertebrates. classification 129–143. p. Wiksell. & Almqvist Stockholm: Phylogeny Vertebrate of Lower Problems 103. 103. 63– p.London.Press Academicof Fishes Interrelationships Ceditors. Patterson

Accepted Linn ProcSoc Australia. New South Wales, of Devonian LateMiddle the from Article

Cowralepis This article isprotected by copyright. All rights reserved. , a new genus of phyllolepid fish (Pisces, Placodermi) Placodermi) (Pisces, fish phyllolepid of genus new a , Journal ofMorphology John Wiley&Sons Acanthodes . In: Ørvig T editor. Currenteditor.In: ØrvigT. rza 25 Brazeau

Zhu M, Yu X, Ahlberg PE, Choo B, Lu J, Qiao T, Qu Q, Zhao W, Jia L, Blom H, ZhuH, Blom Jia L, Zhao T,LuQiaoW, QuQ, B, J, Choo PE, X, Ahlberg Yu M, Zhu zurHunsrückschiefer Typenund Belegstücke der Katalog M.1986. Wuttke

Nature 502:188–193. 502:188–193. Nature

Accepted Articlebones. jaw marginal osteichthyanlike placoderm with ASilurian 2013. YA. 24:87–117. Archiv Naturw Mainzer (BRD). Kreuznach Bad in Schloßparkmuseum im Schiefergebirge) (Rheinisches Sammlung

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tomography showing solid tomography Scaleviews right)(lower transparent (B). (upper witharches branchial and left)

Accepted Paraplesiobatis specimenFig.1. 1983/294 and KGM (A) lightvirtual renderings computed synchrotron of Article

This article isprotected by copyright. All rights reserved. 109x59mm (300109x59mm 300DPI) x Journal ofMorphology John Wiley&Sons bar = 1 cm. cm. 1 = bar

Paraplesiobatis. Dorsal view (A, B). ventral B). view Dorsal viewParaplesiobatis. (A, D). (C, Numbersindicateorders individual arch referred to Fig. 2. Virtual renderings Virtual Fig.2. interpretive and illustrationsarticulated gillof 1983/294 KGM of skeleton

Acceptednecessarily not but intext, = the bar homologies Scale direct gnathostomes. cm. 1 other to Article

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Fig. 3. Fig.3.

Accepted Articlefirst Basihyalarch and elements.view view PosteriorDorsal (A). Ventral (B). viewAnterior view (C).

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highlightedwith Paraplesiobat correspondence show to elementslife restored partially planeconditionapproximate resulting to embedded in Reconstruction (A). a in apparent segmented inapparent pattern Reconstruction of (B). Pseudopetalichthys elements arch with pharyngeal Fig. 4. AlternativeParaplesiobatis reconstructions of Fig.4. and Partially withcomparison Pseudopetalichthys.

Accepted Articlereconstructedright leftgill mirrored posterior firstand skeleton elements and with basihyal arch and

This article isprotected by copyright. All rights reserved. misleading (C). Not to scale. misleading scale. to Not (C). 70x23mm (300 x 300 DPI) (300 30070x23mm DPI) x Journal ofMorphology John Wiley&Sons

is suggesting that the segmented the issuggesting may that be appearance

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Accepted Article

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Accepted Article

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Page 33of67 placoderm fish is described. This adds to the diversity of feeding and respiratory and of feeding thediversity adds to This isdescribed. fish placoderm

Accepted Article vertebrates. the jawed first in gillofevolution arch hypotheses informingand animals vertebrate in jawed structures 410-million-year-old skeletona of arch gill articulated three-dimensional A Text Abstract – Graphical Brazeau

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