ORIGINAL PAPER

A long-bodied centriscoid fish from the basal Eoceneof Kabardino-Balkaria, northern Caucasus, Russia

Alexandre F. Bannikov & Giorgio Carnevale

Received: 18 February 2012 /Revised: 23 March 2012 /Accepted: 26 March 2012 /Published online: 17 April 2012# Springer-Verlag 2012

Abstract The Paleocene–Eocene transition is of crucialinterest for interpreting the Cenozoic evolutionary radiationof vertebrates. A substantial increase of the number ofvertebrate families occurred between the Late Paleoceneand Early Eocene, with the appearance of most of therepresentatives of extant lineages. Basal Eocene marine fishdiversity is currently poorly known, exclusively restricted totwo assemblages from Denmark and Turkmenistan, respec-tively. Exceptionally well-preserved articulated skeletalremains of fishes have recently been discovered from a basalEocene sapropelitic layer exposed along the Kheu River inthe Republic of Kabardino-Balkaria, northern Caucasus,Russia. Here, we report on Gerpegezhus paviai gen. et sp.nov., a new peculiar syngnathoid fish from this new Ciscau-casian locality. The morphological structure of the singleavailable specimen suggests that it is the first long-bodiedmember of the superfamily Centriscoidea, representing thesole member of the new family Gerpegezhidae, which formsa sister pair with the extant family Centriscidae.

Keywords Teleostei . Centriscoidea . Gerpegezhidae fam.nov. .Gerpegezhus paviai gen. et sp. nov. . Eocene .

Kabardino-Balkaria . Relationships

Introduction

Based on graphic correlation of horizons of exceptionalpreservation of fishes in different sectors of the world,Retallack (2011) recently evidenced that exceptional fossilpreservation may be correlated over wide areas. Such anal-ysis clearly indicates that certain time intervals in the geo-logical history were conducive to exceptional preservationof fossils and that the origin of Konservat Lagerstätten mayhave been promoted in coincidence with global environ-mental changes, such as mass extinctions, stage boundaries,oceanic anoxic events, carbon isotopic anomalies and highconcentrations of atmospheric carbon dioxide. In summary,the greenhouse preservation hypothesis proposed byRetallack (2011) postulates that spikes in atmosphericcarbon dioxide coincide with widespread exceptional pres-ervation, and that both are consequences of transient globalperturbations (see also, Retallack 2001).

The Early Paleogene experienced one of the most pro-nounced global environmental perturbations of the CenozoicEra. At the Paleocene–Eocene epoch boundary, both marineand continental records show an abrupt negative shift incarbon isotopic values (see Pagani et al. 2006), the carbonisotopic excursion (CIE), resulted from the release of a mas-sive amount of isotopically light carbon into the atmosphereand associated with a dramatic rise in global temperaturesknown as the Paleocene–Eocene thermal maximum (PETM).Both the CIE and PETM seem to be related in different waysto mobilization of marinemethane clathrates that were respon-sible for a natural greenhouse climate event (see, e.g., Dickenset al. 1995; Schmidt and Schindell 2003).

At least two fossil fish localities characterized by excep-tional preservation originated during the anoxic event asso-ciated to the PETM, one in Denmark (Mo-Clay, FurFormation) and the other in Turkmenistan (Danata

Communicated by: Sven Thatje

A. F. BannikovBorisyak Paleontological Institute, Russian Academy of Sciences,Profsoyuznaya 123,Moscow 117997, Russia

G. Carnevale (*)Dipartimento di Scienze della Terra, Università degli Studi diTorino,Via Valperga Caluso, 35,10125 Torino, Italye-mail: giorgio.carnevale@unito.it

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Formation). These localities have provided most of avail-able data about the structure and composition of the basalYpresian marine fish communities. The fish assemblagefrom the Fur Formation was cursorily described by Bonde(1966, 1987, 1997), with only few taxa properly documented(Kühne 1941; Nielsen 1960; Tyler and Santini 2002; Baciuet al. 2005; Bonde 2008) while the Turkmenian assemblageincludes about 38 taxa of teleost fishes (Danilchenko 1968;Bannikov and Parin 1997; Bannikov 2010).

Recent excavations in Paleogene deposits outcroppingalong the Kheu River in the Republic of Kabardino-Balkaria(Fig. 1), northern Caucasus, led to the discovery of a newbasal Eocene fish assemblage from a sapropelitic layer depos-ited in response to the greenhouse conditions associated to thePETM. The goal of this paper is to describe a well-preservedarticulated fish skeleton collected from the sapropelitic layerexposed along the Kheu River. A detailed systematic analysisof this fossil unequivocally indicates that it is a very peculiarmember of the syngnathoid superfamily Centriscoidea.

The superfamily Centriscoidea includes a small group offishes characterized by extremely compressed and relativelydeep bodies some of which usually swim in vertical positionwith the snout down. As other syngnathoids, members of thissuperfamily exhibit small mouths placed at the end of tube-shaped snouts and adapted for suction feeding and head and

trunk encased, at least in part, in solid body plates. These fishesare today restricted to the tropical and subtropical waters of theAtlantic, Indian and Pacific oceans (Nelson 2006).

Locality and stratigraphy

The Kheu River stratigraphic section (43°22′31.22′′N; longi-tude, 43°39′22.20′′E) crops out close to the Gerpegezh village,about 10 km southeast of the city of Nalchik, in the south-eastern part of the Kabardino-Balkarian Republic (Fig. 1).This Ciscaucasian section has been investigated in great detailbecause of its excellent record of the CIE and events related tothe PETM in the northeastern Peri-Tethys epicontinental basin(Gavrilov and Muzylev 1991; Gavrilov et al. 1997, 2000,2003). Fossil fishes are relatively abundant in a 0.5-m thickdark brown laminated sapropelitic layer located in the upperpart of a monotonous marly clays sequence belonging to theAbazinka (0Nalchik) Formation. The sapropelitic layer ischaracterized by a poorly diverse nannoflora sharply domi-nated by species of the genus Toweius, a relatively highplanktic/benthic foramiferal ratio (Stupin and Muzylov2001), abundant organic-walled plankton remains and a veryhigh total organic content. Organic walled dinocysts are wellpreserved without evidence of reworking within the saprope-litic layer, documenting the Apectodinium acme that occurred

Fig. 1 Satellite view of Caucasus region showing (A) the location of Kabardino-Balkarian Republic and (B) fossiliferous locality of Gerpegezh

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at the base of the PETM (Crouch et al. 2001). The benthicbiota is primarily represented by dysoxic species of benthicforaminifera, suggesting varying degrees of dysoxia/anoxia inthe depositional basin. The organic matter of the sapropeliticlayer appears to be mainly derived from marine plankton.Gavrilov et al. (2003) hypothesized that the sapropelitic layeroriginated in response to increased primary productivity, trig-gered by a massive influx of nutrients that reached the basinwhen phosphorous- and organic-rich sediments in low-lyingcoastal areas were flooded during a rapid transgressive event.

The age of the sapropelitic layer was estimated based on itsmicrofossil content and geochemical data. Considering thatthe base of the global CIE is currently interpreted ascorresponding to the Paleocene–Eocene boundary (e.g., Stottet al. 1996; Dupuis et al. 2003; Aubry et al. 2007), the base ofthe sapropelitic layer in the Kheu River section seems to fall atthis boundary (Gavrilov et al. 2003), which also correspondsto the NP9/NP10 zonal boundary (see Martini 1971). ThePaleocene–Eocene boundary has been recently constrainedby combining radioisotopic dating and cyclostratigraphicanalysis, resulting in an age ranging from 55.964 to55.728 Ma (Charles et al. 2011). The sapropelitic layer ofthe Kheu River section seems to have accumulated in a fewthousands of years (between 10 and 60 ky; Gavrilov et al.2003), thereby implying that the fossil fish described hereindates back to the basal Eocene, around 55.8 Ma.

The ichthyofauna associated to the specimen documentedherein has not been investigated in detail. However, a cur-sory survey of the material collected from the Kheu Riversapropelitic layer revealed the presence of anguilliforms,clupeiforms and several percomorphs, many of which rep-resented by larval or juvenile individuals.

Materials and methods

The fossil was collected during the 2008 excavation carried outalong the right bank of the Kheu River, in the nearby of theGerpegezh village and is deposited in the paleoichthyologicalcollection of the Borisyak Paleontological Institute of the Rus-sian Academy of Sciences, Moscow (PIN). It consists of anearly complete articulated skeleton preserved on a laminatedsapropelite. The specimen required matrix removal before ex-amination and was prepared using thin entomological needles.It was examined using a WILD 104710 stereomicroscopeequipped with a camera lucida drawing arm. Measurementswere taken with a dial calliper, to the nearest 0.1 mm. Com-parative information was derived mainly from the literature.

Systematics

Subdivision Teleostei sensu Patterson and Rosen (1977)Order Gasterosteiformes Goodrich (1909)

Suborder Syngnathoidei Regan (1909)Infraorder Macroramphosa Pietsch (1978)Superfamily Centriscoidea Rafinesque (1810)Family Gerpegezhidae fam. nov.

Diagnosis. A centriscoid family unique in having bodyelongate and slender, with maximum depth contained aboutten times in SL; head elongate, anteriorly tubular, its lengthcontained slightly less than four times in SL; 34 (13+21)vertebrae; elongate and slender ossified myoseptal tendonspresent epaxially and hypaxially with longitudinal arrange-ment throughout the caudal portion of the vertebral column;eight (or nine) principal caudal-fin rays; procurrent caudal-fin rays absent; dorsal-fin spines absent; dorsal- and anal-finrays eight and 17, respectively; pelvic fin and girdle absent;anterior part of the body encased by strong bony plates withfinely ornamented outer surface; dorsal component of thebony armour comprises two bilateral series of plates of 21narrow and 22 subrectangular plates, respectively; ventralcomponent of the body armour reduced to a short series of atleast six unpaired, flat rectangular plates; posterior part ofthe body naked.

Type genus. Gerpegezhus gen. nov., sole genus of thefamily.

Genus Gerpegezhus gen. nov.

Diagnosis. That of the family.Type species. Gerpegezhus paviai sp. nov., by monotypy

and designation herein.Etymology. Generic epithet refers to the type locality,

Gerpegezh village, Republic of Kabardino-Balkaria; gendermasculine.

Composition. Type species only.

Gerpegezhus paviai sp. nov.

Diagnosis. As for the genus.Holotype. PIN 5314/1, complete part and partially com-

plete counterpart, articulated skeleton, 139-mm standardlength (SL). Only known specimen (Fig. 2a).

Etymology. It is our pleasure to name this species inhonour to our friend and colleague Prof. Giulio Pavia inrecognition of his outstanding contribution to the Mesozoicand Cenozoic paleontology of the Tethyan realm.

Type locality and horizon. Gerpegezh village, rightbank of the Kheu River, Republic of Kabardino-Balkaria, southwestern Russia; basal Eocene, lowermostYpresian, base of NP 10 (in the sense of Gavrilov et al.2003).

Measurements (as percentage of SL). Head length, 28.2;maximum body depth, 9.9; caudal peduncle depth, 2.6;predorsal length, 89.7; preanal length, 79.5; distance

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between pectoral and anal fins, 44.4; dorsal-fin base length,2.6; anal-fin base length, 11.4; preorbital length, 18.7; orbitdiameter, 2.7; lower jaw length, 3.7; maximum depth ofbody armour, 7.5; length of the longest dorsal-fin ray, 4.8;length of the longest anal-fin ray, 5.2.

Description

The body is elongate, slender and laterally compressed(Fig. 2a). The maximum body depth (measured just behindthe head) is contained about ten times in SL. The caudal

Fig. 2 Gerpegezhus paviai gen. et sp. nov., from the basal Eocene ofGerpegezh, Republic of Kabadino-Balkaria, Russia. A Holotype, PIN5314/1, left side, lateral view, specimen coated with ammonium chlo-ride (scale bar, 20 mm); B reconstruction of the head, left side, lateralview (scale bar, 5 mm); C median fins and associated axial skeleton,left side, lateral view, specimen coated with ammonium chloride (scalebar, 4 mm); and D pectoral fin and girdle, left side, lateral view,

specimen coated with ammonium chloride (scale bar, 2 mm). Abbre-viations: aa anguloarticular, d dentary, f frontal, h hyomandibula, laclachrymal, le lateral ethmoid, me mesethmoid, mtp metapterygoid, mxmaxilla, na nasal, pas parasphenoid, pmx premaxilla, pto pterotic, pttposttemporal, op opercle, pa parietal, pop preopercle, q quadrate, socsupraoccipital, sop subopercle, spo sphenotic, sym symplectic, v vomer

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peduncle is slender and relatively short. The caudal pedun-cle depth is contained slightly less than four times in max-imum body depth. The head is elongate, contained slightlyless than four times in SL. The orbit is rounded and placedin the upper half of the posterior third of the head; itsdiameter is contained more than ten times in head length.The snout is tubular and greatly elongate; its length iscontained more than seven times in SL. The mouth is small,terminal in position and evidently toothless. Overall, themorphology of the head of Gerpegezhus paviai greatlyresembles that of the members of the family Centriscidae.

The neurocranium is greatly elongate, narrow and com-pressed (Fig. 2b). The dorsal margin of the neurocranium isnearly linear for most of its length becoming gently convexin the orbital sector. The precise configuration of its osteo-logical architecture is not completely clear due to the prob-lematic evaluation of the limits of certain of its constitutivebony elements. The neurocranial bones are superficial inposition and ornamented by shallow longitudinal grooves.The frontals are elongate and narrow bones that taper ante-riorly to a point and are laterally expanded behind the orbit.These bones articulate anteriorly with the mesethmoid, ante-rolaterally with the nasal, lachrymal and lateral ethmoid,posterolaterally with sphenotic and pterotic and posterome-dially with the parietal and supraoccipital. The mesethmoidis slender and dorsally flattened; it articulates anteriorly withthe vomer, laterally with the nasals, and posteriorly with thefrontals. The vomer is a narrow bone that is clearly exposedsuperficially, at least for its anterior portion; this bone artic-ulates posteriorly with the mesethmoid and posterolaterallywith the nasals. The lateral ethmoid forms the anteriormargin of the orbit together with an anteroventral laminarexpansion of the frontal and the posterior sector of thelachrymal. The nasal is a strongly elongate and laminarbone, extending for most of the length of the snout. Itarticulates anteromedially with mesethmoid and vomer,posterolaterally with the lachrymal and posteromediallyand posteriorly with the frontal. What appears to be a smalland narrow parietal articulates medially with the supraoccipitaland anterolaterally and (possibly) posterolaterally with thefrontal. The supraoccipital is a large bone that occupies arelevant portion of the postorbital skull roof; this bone articu-lates anteriorly with frontal and laterally with the (presumed)parietal. A short and robust occipital spine is clearly evident onthe specimen. The structure and limits of the pterotic aredifficult to define because of inadequate preservation; anterior-ly, this bone articulates with the sphenotic while posteriorly itembraces the posttemporal; the dorsal border of this boneseems to articulate with the frontal, even though a contact withthe parietal cannot be excluded. The sphenotic is a roughlytriangular, massive bone that forms most of the posterior mar-gin of the orbit; it bears a short and pointed ventral process thatwas possibly connected with the hyomandibula in origin; the

sphenotic articulates with the frontal anteromedially and withthe pterotic posteriorly. The prootic is partially exposed justbehind the sphenotic. There is no trace of the dermosphenotic.The parasphenoid is partially exposed along the lower marginof the orbit and the lower border of the lateral ethmoid. Thelachrymal is a laminar, elongate bone that articulates with thenasal and mesethmoid anteriorly and the lateral ethmoid poste-riorly and the preopercle and quadrate laterally; together withthe frontal, lateral ethmoid and nasal, it forms the external wallsof what can be interpreted as an olfactory cavity, which possiblyallocated the nasal capsule in origin. The basicranial structurecannot be detected thereby preventing the description of theelements of this portion of the neurocranium.

Both the upper and lower jaws are badly damaged anddifficult to interpret (Fig. 2b). The toothless premaxillaappears to be a rod-like bone with highly reduced to nearlyabsent ascending and articular processes; the postmaxillaryprocess is absent. The morphology of the maxilla is com-pletely unclear due to inadequate preservation. The dentaryis toothless and roughly triangular in outline, characterizedby a large coronoid process; the lower margin of this bone isnearly straight except for a gentle medial curvature near thesymphysis. The angulo-articular also exhibits a well-developed coronoid process; posteriorly, this bone formsthe articular facet to receive the articular head of the quad-rate. The retroarticular cannot be observed.

The suspensorium, palato-pterygoid arch and opercularbones (Fig. 2b) appear to be slightly shifted backwards withrespect to the original configuration of the head skeleton.

The hyomandibula is poorly preserved, underlying thepointed ventral process of the sphenotic. The metapterygoidis a thin laminar bone approximately triangular in shape.The symplectic articulates anteriorly with the quadrate,anterodorsally with the metapterygoid and ventrally withthe preopercle. The quadrate is the largest element of thesuspensorium; this bone is rather thick and laminar with auniform depth throughout its development; anteroventrally,it bears a robust articular head for the mandible with arounded profile. Highly fragmented ectopterygoid andendopterygoid appear to be present anteriorly along thedorsal margin of the quadrate. The palatine, which wascertainly present in origin, is not recognizable on thespecimen.

The preopercle is an enormous, laterally flattened andposteroventrally expanded bone characterized by a greatlyelongate and deep lamina that extends ventrally throughoutthe length of its horizontal and vertical arms; the horizontaland vertical arms form an angle of 135° at their confluencealong the dorsal border of the bone where a small triangularflange can be observed; the lateral surface of the preopercleis not ornamented, except for a prominent furrow along thedorsal border of its horizontal arm; the horizontal arm of thepreopercle apparently articulates with the ventral margin of

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the quadrate. The opercle is a thin bone with a remarkablyrounded ventral profile and a slightly concave dorsal mar-gin; a relatively small condyle emerges anteriorly from itsdorsal margin; similar to the preopercle, the lateral surfaceof this bone is not ornamented. An elongate, thin andlaminar bone that extends horizontally under the operclepossibly represents the subopercle.

Neither the gill arches nor the bones of the hyoid appa-ratus are exposed on the specimen. Overall, the length of theabdominal portion of the vertebral column is about 1.4 timesgreater than that of the caudal portion (Fig. 2a). Most of thevertebral column is hidden by the armour of bony plates; theposteriormost 12 vertebral centra are clearly visible, in ad-dition to nine haemal spines that project below the armouranterior to the clearly exposed vertebrae; therefore, thenumber of caudal vertebrae is most likely equal to 21. Theposterior bony plates of the armour appear to be character-ized by a one-to-one relationship with the vertebrae; thishypothesis is consistent with the condition observed inextant centriscids in which the second to posteriormostabdominal vertebrae are firmly attached to lateral bonyplates via parapophyses with a one-to-one relationship (seeJurgensen 1908). Thus, considering such a mutual anatom-ical association, we hypothesize that the vertebral column ofG. paviai consists of 13 abdominal vertebrae, resulting inthe total number of 34 (13+21) vertebral elements. Thecentra gradually decrease in length posteriorly in the series,with the 12 posterior elements that are subrectangular inshape. Vertebral spines are short and slender with the neuralspines of the vertebrae in the middle of the caudal series thatare remarkably inclined with respect to the correspondinghaemal spines. Elongate and slender ossified myoseptaltendons are present epaxially and hypaxially with longitu-dinal arrangement (at least) throughout the caudal portion of

the vertebral column (Fig. 2c). Pleural ribs and epineuralbones are absent.

The caudal skeleton is moderately well-preserved(Fig. 3). The terminal centrum more likely consists of thefusion of the first preural centrum with two ural centra. Thehypurals are fused with the terminal centrum into a nearlysymmetrical fan, possibly characterized by a superficialmedian furrow. The structure and anatomical relationshipsof the parhypural are difficult to interpret. The neural spineof the second preural centrum is fully developed while thecorresponding haemal spine is thickened, anteroposteriorlyexpanded and fused to the centrum. A single epural appearsto be present. The caudal fin seems to be of reduced size,with eight or nine unbranched principal rays; procurrent raysappear to be absent.

The short-based dorsal fin originates at the level of theposterior end of the 11th caudal vertebra (Fig. 2c). Dorsal-finspines are absent and the fin consists of eight unbranched rayssupported by nine pterygiophores, the first of which is rayless;the longest dorsal-fin rays are longer than the dorsal-fin base;the dorsal-fin pterygiophores are laterally compressed anddecrease in length posteriorly in the series. The neural spinesof the vertebrae directly underlying the dorsal fin are remark-ably shortened, resulting in a reduced interdigitation with thedorsal-fin pterygiophores.

The anal fin (Fig. 2c) inserts well anterior to the dorsal-finoriginwith its end located slightly behind the dorsal-fin origin;it contains 17 unbranched rays supported by 17 pterygio-phores. The base length of the dorsal fin is contained morethan four times in the base length of the anal fin. The first twoanal-fin pterygiophores interdigitate with the haemal spines ofthe fourth and fifth caudal vertebrae, with the subsequentelements that gradually decrease in size posteriorly.

The posttemporal is deeply integrated to the posteriorportion of the neurocranium, where it is articulated anteri-orly with the pterotic (Fig. 2b). The supracleithrum is notclearly recognizable, possibly hidden by the armour of bonyplates. The vertical process of the cleithrum is clearly visiblejust behind the posterior margin of the opercle (Fig. 2d); it issuperficial in position and consists of an elongate and robustpiece of bone characterized by a relatively large thickeningalong its posterior margin; the ventral portion of the verticalprocess of the cleithrum articulates with the slender andgently arcuate anteroventral extension of the coracoid. Theelongate anteroventral process of the coracoid is not super-ficial while the thickened ascending process arising from itsposterior sector appears to be superficially exposed. Thescapula is badly preserved. A narrow postcleithrum is visi-ble just behind the pectoral-fin base. The pectoral fin isrelatively small and contains about ten unbranched rays;the pectoral-fin rays become gradually shorter downwardin the series; the pectoral fin inserts in the lower half of thebody, just below the second element of the lower series of

Fig. 3 Gerpegezhus paviai gen. et sp. nov., from the basal Eocene ofGerpegezh, Republic of Kabardino-Balkaria, Russia. Reconstruction ofthe caudal skeleton, left side, lateral view. Scale bar, 2 mm

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the dorsal body armour (Fig. 2d). Pelvic fin and girdleappear to be absent.

Most of the abdominal portion of the body is covered bystrong interconnected bony plates characterized by a finelyornamented outer surface (Figs. 2d and 4). Such a body armourconsists of dorsal and ventral components (Fig. 4). The dorsalcomponent comprises two bilateral series of plates; the 21narrow plates of the dorsal series appear to be sutured withtheir opposite counterparts; this series terminates posteriorlyjust in front of the unpaired rayless pterygiophore of the dorsalfin; the 22 plates of the ventral series are large and subrectan-gular in outline, with a gently rounded ventral profile; thesecontact dorsally the anterior 15 plates of the dorsal series; theseven posterior elements of the two series are separated fromeach other by a moderately developed gap, which begins justposterior to the origin of the caudal portion of the vertebralcolumn; the plates of the ventral series are characterized by acouple of thick transversal bony crests and diffuse ornamenta-tion of tiny irregular subvertical ridges and grooves; overall, theventral series reaches its maximum depth approximately at thelevel of the centre of the abdominal portion of the vertebralcolumn, becoming narrower posteriorly; the nine posteriorplates of the ventral series cover the anterior nine caudal verte-brae and contact each other through an oblique suture. Theventral component of the body armour consists of a short seriesof at least six (possibly) paired, flat rectangular plates thatoriginate at the level of the posterior margin of the verticalarm of the preopercle and run posteriorly along the ventralborder of the body up to the pectoral-fin origin.

Discussion

The gasterosteiform suborder Syngnathoidei includes some ofthe most morphologically derived and bizarre of all acantho-morph fishes, characterized by a unique set of peculiar mor-phological, reproductive and locomotory adaptations. Mostmembers of this heterogeneous and predominantly marinegroup exhibit a body rigidly armoured by bony plates and atubular snout adapted for suction feeding. The known diversityof this group comprises seven extant families (Aulostomidae,Centriscidae, Fistulariidae, Macroramphosidae, Pegasidae,Solenostomidae and Syngnathidae), plus at least six Eocenefamilies (Aulorhamphidae, Fistularioididae, Paraeoliscidae,

Parasynarcualidae, Rhamphosidae and Urosphenidae; see Blot1980) and the problematic Cretaceous species Gasterorham-phosus zuppichinii Sorbini 1981 (see Sorbini 1981; Patterson1993).

The interrelationships of the syngnathoid families havebeen discussed by several authors in the last decades who,with the exception of a few cases (Springer and Orrell 2004;Dettai and Lecointre 2005; Li et al. 2009), evidenced themonophyly of this suborder based on morphological andmolecular features (e.g. Pietsch 1978; Johnson and Patter-son 1993; Britz and Johnson 2002; Keivany and Nelson2006; Kawahara et al. 2008; Wilson and Orr 2011). Acomprehensive morphological and phylogenetic survey ofthe group, primarily based on osteology was conducted byOrr (1995) in a sadly underused thesis of considerableinsight and breadth. Orr (1995) discussed 16 apomorphiesdefining the Syngnathoidei. Unfortunately, some of theseare uninformative for the interpretation of the taxonomicstatus of Gerpegezhus because they refer to characters poor-ly preserved or inaccessible in the single available speci-men, such as the pterotic, hyoid apparatus or abdominalvertebrae. Nevertheless, the holotypic specimen of Gerpe-gezhus clearly exhibits a set of apomorphic features thatunambiguously support its placement within the Syngna-thoidei (Orr 1995), including the reduced ascending processof the premaxilla, metapterygoid placed anterior to the orbit,coracoid bearing rod-like anteroventral process andabsence of anal-fin spines, pleural ribs and epineural bones.

Within the Syngnathoidei, Orr (1995) established twoinfraorders, the Aulostoma (aulostomids and fistulariids)and Macroramphosa (centriscids, macroramphosids, pega-sids, solenostomids and syngnathids). Gerpegezhus showsthree of the characters of the Macroramphosa identified byOrr (1995), absence of premaxillary and dentary teeth(Fig. 2b), posttemporal firmly sutured to the cranium(Fig. 2b) and possession of unbranched caudal-fin rays.The six remaining characters of the Macroramphosa in thelist assembled by Orr (1995) concern larval features orregions inaccessible in the fossil. According to Orr (1995),the Macroramphosa includes a pair of sister groups, theCentriscoidea (centriscids and macroramphosids) and Syn-gnathoidea (pegasids, solenostomids and syngnathids). Heproposed 13 unique centriscoid characters, of which three(sphenotic articulating with hyomandibula through a ventral

Fig. 4 Comparison of bodyarmour arrangement in (A)Gerpegezhus paviai gen. et sp.nov., (B) centriscids and (C)macroramphosids. B, CModified from Britz andJohnson (2002)

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process; neural spine of the second preural centrum fullydeveloped; anterior body encased by interconnected dermalplates; Figs. 2b, 3 and 4) have been observed in Gerpegez-hus. Even in this case, the remaining centriscoid charactersin many cases refer to structures that are inadequately pre-served or not clearly exposed in the fossil. Therefore, thegrounds for considering Gerpegezhus a centriscoid are fea-tures that involve different anatomical complexes of thecranial (sphenotic articulating with hyomandibula througha ventral process), axial (neural spine of the second preuralcentrum fully developed) and dermal (anterior body encasedby interconnected dermal plates) skeleton. The conclusion thatGerpegezhus is a centriscoid is reinforced by the possession ofselected characters that are shared with both centriscids andmacroramphosids, including the laterally compressed body(Fig. 2a), possession of a posteroventrally expanded preop-ercle (Fig. 2b), possession of an anterior rayless dorsal-finpterygiophore (Fig. 2c) and possession of a single postcleith-rum (Fig. 2d; see Orr 1995). Moreover, Gerpegezhus is notknown to possess any of the features listed by Orr (1995) assynapomorphies of the Aulostoma, and, to a less inclusivelevel, it displays only a single reductive feature of the Syn-gnathoidea, absence of procurrent caudal-fin rays, which maybe considered as homoplastic.

The superfamily Centriscoidea includes two extant fam-ilies, the Centriscidae and Macroramphosidae, which arerecognized as subfamilies of the Centriscidae by few authors(e.g. Eschmeyer 1990). The phylogenetic position of theEocene family Paraeoliscidae remains elusive since it hasbeen inadequately defined by plesiomorphic syngnathoidcharacters (see Blot 1980). The Macroramphosidae includes

three genera with about eight extant species (e.g. Duhamel1995) while the Centriscidae includes two extant genera,with four extant (e.g. Mohr 1937) and at least five extinctspecies (Parin and Micklich 1996). A diagnosis of thesefamilies based on apomorphic osteological features is cur-rently not available. However, several aspects of the anato-my of the Centriscidae and Macroramphosidae weredescribed in detail by Jurgensen (1908) based on driedmaterial and subsequently implemented by Banister(1967), Altermatt (1991), Johnson and Patterson (1993)and Orr (1995), providing the basis for a reliable compara-tive analysis of Gerpegezhus.

As discussed above, the overall morphology of the head ofGerpegezhus greatly resembles that of the members of thefamily Centriscidae, to which it appears to be closely related.

Table 1 Synopsis of meristic values of centriscoid fishes

Gerpegezhus Centriscidae Macroramphosidae

Vertebral number 34 20 24

Dorsal-fin formula 8 III+10–12 IV–VIII+9–11

Anal-fin formula 17 11–12 19–20

Principal caudal-finrays

8 (9) 11 11

Upper procurrentcaudal-fin rays

0 0 5

Lower procurrentcaudal-fin rays

0 1 5

Pectoral-fin rays 10 10–12 15

Pelvic-fin rays 0 I+4 I+4

Data from Jurgensen (1908), Mohr (1937) and Orr (1995)

Fig. 5 Cladogram showing the hypothetical relationships of Gerpegezhus within the Centriscoidea. See text for details

386 Naturwissenschaften (2012) 99:379–389

The putative sister-group relationship of Gerpegezhus andCentriscidae is supported by at least five features (see Orr1995): parietal present (Fig. 2b), infraorbital series primitivelyreduced to the lachrymal (Fig. 2b), upper procurrent caudal-fin rays absent (Fig. 2a) and possession of a single bilateralseries of bony plates in the ventral component of the bodyarmour (Figs. 2a and 4). The possession of parietals is crucialto determine the relationships ofGerpegezhus. The absence ofparietals has been traditionally considered as a relevant syn-gnathoid synapomorphy (e.g. Regan 1909; Jurgensen 1910;Johnson and Patterson 1993). Banister (1967) and Orr (1995)recognized the presence of these bones in both centriscidgenera, Aeoliscus and Centriscus. Therefore, the presence ofparietals unquestionably constitutes a synapomorphic featureof the putative sister pair formed by the Centriscidae andGerpegezhidae. Syngnathoids display a highly variable num-ber of elements of the infraorbital series (see Johnson andPatterson 1993). Within centriscoids, Gerpegezhus and thegenera of Centriscidae possess only a lachrymal while macro-ramphosids primitively possess a lachrymal and a secondinfraorbital bone (Orr 1995). As far as the upper procurrentrays are concerned, their absence homoplasiously occurs incentriscids, pegasids, solenostomids and syngnathids apartfromGerpegezhus. Finally,Gerpegezhus and the Centriscidaeshare the possession of a single bilateral series of bony platesin the ventral component of the armour along the ventralmargin of the body (Fig. 4a, b). Such a condition is uniquewithin centriscoids given that macroramphosids possess anadditional series of unpaired ventromedian plates extendingfrom the isthmus to the anus (see Fig. 4c; Jurgensen 1908;Britz and Johnson 2002).

Gerpegezhus exhibits a unique morphological configura-tion, showing a series of derived features that clearly evi-dence its separate status within centriscoids. The moststriking distinctive feature of Gerpegezhus is related to itsoverall axial morphology (Figs. 2a and 4). While centriscidsand macroramphosids are characterized by relatively shortand compact bodies with vertebral numbers ranging from 20(8+12) in centriscids to 24 (9+15) in macroramphosids (seeTable 1), Gerpegezhus has an extremely elongate body witha vertebral column that seems to include 34 (13+21) verte-brae. Taking into account the structure of the vertebralcolumn of extant centriscoids, the axial elongation observedin Gerpegezhus results from substantial additions of bothabdominal and caudal vertebrae. Both the abdominal andcaudal vertebral numbers seem to be controlled by separatedevelopmental modules (e.g. Ward and Metha 2010). Theincrease in both abdominal and caudal number of vertebrae isrelatively uncommon in actinopterygians and may result fromthe synergistic effect of the shifts in Hox expression domainsand the maintaining of the tail organizer with the consequentprolongation of the somitogenesis in the abdominal and caudalregions, respectively (Ward and Brainerd 2007).

It is noteworthy that a large part of the peculiarities ofGerpegezhus refer to reductive features that may be inter-preted as derived, compared with other centriscoids, such as:loss of spinous dorsal fin (Figs. 2a and 4a), loss of lowerprocurrent caudal-fin rays (Fig. 2a), loss of pelvic fin andgirdle (Figs. 2a and 4a), remarkable numerical reduction ofthe plates of the ventral component of the body armour(Fig. 4a) and posterior part of the body naked (Fig. 4a). Ofthese reductive apomorphic features, the loss of the spinyportion of the dorsal fin homoplasiously occurs in fistular-iids, pegasids and syngnathids, whereas the loss of thepelvic fin and girdle also occurs in syngnathids. Both thespiny dorsal fin and the pelvic complex are currentlyregarded as discrete developmental modules and their lossof expression may be produced through different develop-mental mechanisms (e.g. Mabee et al. 2002; Tanaka et al.2005). The reduced extension of the ventral component ofthe body armour, which ends posteriorly at the level ofthe pectoral-fin origin, also represents a clear diagnosticfeature that undoubtedly separates Gerpegezhus fromcentriscids; in both Aeoliscus and Centriscus, the platesof the ventral component extend posteriorly to the anus(see Jurgensen 1908).

Both epaxially and hypaxially, along the caudal portionof the vertebral column of Gerpegezhus there is a series ofslender ossified myoseptal tendons (Fig. 2c). These ossifi-cations are not characteristic of other centriscoids buthomoplasiously occur in aulostomids, fistulariids and fistu-larioidids (see, e.g., Agassiz 1833–1844; Woodward 1901;Jurgensen 1910; Orr 1995), possibly representing a func-tional support for axial undulatory swimming that indepen-dently occurs in fishes characterized by a very elongate andslender body (see Gemballa et al. 2003).

In summary, a detailed comparative analysis of the singleavailable specimen of G. paviai has revealed that it representsthe only member of a new centriscoid family that apparentlyforms a sister pair with the Centriscidae. The separate status ofthis new family of long-bodied centriscoids is supported by aset of unique features (see Fig. 5) that, in a few cases, homo-plasiously occur in other syngnathoid families. However,much new anatomical and comparative information is neededbefore that the interrelationships of the centriscoid familieswill be conclusively demonstrated.

Acknowledgements This study was made possible with the help ofthe financial support provided by the Systematic Association (UK) tomake excavations in Republic Kabardino-Balkaria in 2008. We thankE. Shcherbinina (Geological Institute, Russian Academy of Sciences,Moscow) for information about the Gerpegezh locality, W. Landini(Dipartimento di Scienze della Terra, Università di Pisa, Pisa) and J.W.Orr (Alaska Fisheries Science Center, National Marine Fisheries Ser-vice, NOAA, Seattle) for useful suggestions and critical review of anearly draft of the text, A.V. Mazin (Paleontological Institute, RussianAcademy of Sciences, Moscow) for photographs and B. Villier (Dipar-timento di Scienze della Terra, Università degli Studi di Torino, Torino)

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for technical support. We are much indebted to F. Giudice (Torino) forthe improvement of the English. We thank three anonymous refereesfor careful reviews of the manuscript. The research of A.F.B. wassupported by the Russian Foundation for Basic Research, grants n.09-05-00170 and 12-04-00611. During the preparation of this workG.C. was supported by the MIUR grant 2009 “Paleobiogeografia edinamica di popolazione nel tardo Miocene: nuove evidenze dal Med-iterraneo centrale”. The names of the authors are in alphabetical ordersince each made a substantial contribution to this manuscript.

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