HERPETOLOGICAL JOURNAL Vol 15 pp 15-20 (2005)

THE COMPLEX VOMERONASAL STRUCTURE OF DIPSOCHELYS GIANTTORTOISES AND ITS IDENTIFICATION AS A TRUE JACOBSONrsquoS ORGAN

J GERLACH

University Museum of Zoology Department of Zoology Cambridge UK

The nasal structure of the western Indian Ocean Dipsochelys giant tortoises is describedThese tortoises are known to possess structures facilitating lsquonasal drinkingrsquo Additional uniquenasal features include the processus dorsalis vomerinus supporting an enlarged medial nasalgland and a lsquotuberculum palatinumrsquoThe medial nasal gland can be considered homologous to thevomeronasal organ (Jacobsonrsquos organ) and is connected directly to the tuberculum palatinum inthe buccal cavity through the foramina praepalatina An homologous vomeronasal organ witha direct buccal connection is also identified in existing literature accounts of the leatherbackturtle Dermochelys coriacea and may have been overlooked in other Chelonia

Key words Chelonia olfaction tortoise palatine gland pheromones

INTRODUCTION

The nasal region is of great significance in individualinteractions in many tetrapod groups because of the roleof the vomeronasal organ (sometimes referred to asJacobsonrsquos organ) in pheromone detection This struc-ture is well developed in many reptile groups mostnotably the lizards and snakes but its presence in theChelonia has been disputed over many years (Parsons1970) Tissue layers in the nasal region of several turtleshave been associated with the vomeronasal organ al-though no discrete structure comparable to the complexJacobsonrsquos organ of many mammals and squamate rep-tiles is apparent in most species examined The view thatchelonian nasal structures are highly conservative com-pared to other classes of tetrapods (Parsons 1970) is notsupported by some recent studies (Saito et al 2000Murphy et al 2001) Discussion of the apparent vome-ronasal structures in chelonians date from 1895 whenSeydel concluded that a Jacobsonrsquos organ was presenton the grounds that the vomeronasal epithelium devel-ops ventrally and medially (as opposed to the dorsalolfactory epithelium) with innervation of the vomero-nasal nerve from the accessory olfactory bulb and noBowmanrsquos glands This contrasts with more recent stud-ies that have not accepted the chelonian structure as atrue Jacobsonrsquos organ on the basis of not forming a dis-tinct evaginated structure (Parsons 1959) The presenceof vomeronasal epithelium in pockets of the nasal cavityin some chelonians has obscured such classification(Parsons 1970) and the vomeronasal epithelium is nowgenerally referred to as a vomeronasal organ despite theabsence of discrete physical structures (Murphy et al2001)

Some of the most complex chelonian nasal structureshave been described from the western Indian Ocean gi-ant tortoise genus Dipsochelys (Bour 1982 Arnold

1979 Gerlach amp Canning 1998) The raised nasalopening and the structures within the nasal chamberhave been interpreted as adaptations to facilitate draw-ing water up through the nasal passages during drinkingthrough the nose (Arnold 1979) This behaviour hasbeen reported in wild D dussumieri (also referred to asGeochelone gigantea or D elephantina) on Aldabra(Arnold 1979) Further discussion of the structures ofthe Dipsochelys nasal region has considered the possi-bility of this genus having an enhanced olfactorycapability a suggestion following from the descriptionof a bony support for a lsquovomeronasal organrsquo (Gerlach ampCanning 1998) The palate has also been noted as beingunusual in possessing a tuberculum palatinum as de-scribed by Fritsch (1870)

ldquoIn Testudo elephantina [=Dipsochelys dussumieri]an oval whitish body 3 mm long is located ventral to thehard palate in the anterior of the upper jaw its preciseoutline is obscured by the enclosing membrane Undercloser examination this body appears as only an appar-ent swelling in the membrane covering the partition thatseparates the choanae from one another as the section isnot distinguished in coloration or structure whichwould allow the so called Tuberculum palatinum to berecognised as a separate organrdquo

The published interpretations of the nasal structureshave relied on comparative osteology and dissectionThese provide structural information but there havebeen no published accounts of the detailed morphologyof the lsquoflap-like ridgersquo (Arnold 1979) or the lsquovomerona-sal organrsquo (Gerlach amp Canning 1998) to supportfunctional interpretations In order to investigate thesestructures in more detail available dissections and mi-croscopic preparations were examined to providemorphological and histological data on the unique fea-tures of Dipsochelys The availability of freshlypreserved material allowed new dissections to be pre-pared The results are described below identifying thestructure as a true vomeronasal organ with a level ofcomplexity comparable to the Jacobsonrsquos organ ofmammals or squamates

Correspondence J Gerlach University Museum of ZoologyDepartment of Zoology Downing Street Cambridge CB23EJ UK E-mail jstgerlachaolcom

MATERIAL AND METHODS

During a taxonomic revision a detailed osteologicalstudy was made on 118 specimens of all species of thegenus (Gerlach amp Canning 1998) During this studycareful attention was paid to the ridges and bony proc-esses within the nasal chamber following observationthat there were differences in these structures betweenD dussumieri and D grandidieri A dissection of anadult female head of a Dipsochelys dussumieri fromAldabra (preserved in 70 ethanol since 1971) has pre-viously been figured and described (Arnold 1979) thepreserved dissection (BM(NH) R1978772) was re-ex-amined Recent material of one adult D dussumieri onAldabra atoll was examined Previously undescribedmaterial was available in the form of serial transversesections of a D dussumieri late embryo The 10 micro sec-tions stained with Massonrsquos trichrome had beenprepared by A drsquoA Bellairs and are stored in the BritishMuseum (Natural History) In 2003 five full-term em-bryos of D hololissa were preserved and stored by theNature Protection Trust of Seychelles These were pre-served in 4 paraformaldehyde enabling newdissections and microscope preparations to be made Allsectioned material was prepared by cutting 5 micro paraffinembedded sections followed by staining with cresyl vio-let

Comparison was made with lsquoGeochelonersquo(Stigmochelys) pardalis which may be the closest livingrelative of Dipsochelys (Gerlach 2001 Palkovaks etal 2002) and with published accounts of the nasalanatomy of Testudo (Parsons 1970) and other turtles(Bellairs amp Kamal 1981 Nick 1912)

Due to the large size of these tortoises it is possible toobserve structures in the palate when the mouth is openOne adult female Dipsochelys hololissa and one adultfemale D arnoldi in the captive groups of the NatureProtection Trust of Seychelles on Silhouette island Sey-chelles responded to scratching of the neck by standingupright and stretching the neck and head upwards Inthis pose the lower jaw would open and could be gentlylevered open further to expose the palate

RESULTS

OSTEOLOGY

The soft-tissue structure suggested to be a vomerona-sal organ is supported by the processus vomerinusdorsalis positioned on the dorsum of the vomer betweenthe foramina praepalatina anterior to the sulcusvomerinus (Figs 1 2) This bony process is a uniquefeature of Dipsochelys (Gerlach amp Canning 1998) notrace of any similar structure has been found in any othertortoise genus The processus vomerinus dorsalis is aslightly elevated piece of bone on the dorsum of the pre-maxillae In adult tortoises (straight carapace lengthover 45cm) it measures 2-6 mm diameter and is raised05-6 mm The height of the processus vomerinus dorsa-lis varies with different species being low (05 mm) inD hololissa moderately elevated in D dussumieri (05-2 mm) and D arnoldi (1-2 mm) and high (6 mm) in the

extinct Malagasy species D grandidieri In Dgrandidieri the exceptionally large process bears two15 mm diameter pits in the anterior surface (Fig 2)

SOFT-TISSUE ANATOMY

The nasal passage in Dipsochelys is exceptional intortoises in rising steeply above a vertical cartilaginousprocess on the floor of the nasal passage supported bythe processus vomerinus dorsalis This elongate processcontains a deep pocket directed posteriorly (Fig 1a)No distinctive features are apparent within the pocketexcept for a very narrow duct passing into the foramenpraepalatinumThe tissues lining the processusvomerinus dorsalis are innervated by both the olfactorynerve and the accessory olfactory bulb the nervus septinarium and the vomeronasal nerve respectively

The nasal passage descends vertically behind thecartilaginous process before dividing into the postero-ventral nasopharyngeal duct and the postero-dorsalcavum nasi proprium The opening to the latter is par-

J GERLACH

FIG 1 Nasal structures of Dipsochelys dussumieri andlsquoGeochelonersquo pardalis (a) medial view of right nasal passageand nasal chamber of D dussumieri (b) medial view of rightnasal passage and nasal chamber of lsquoGrsquo pardalis (c) Detailof the vomeronasal structures of D dussumieri in medialview d ndash duct from the tuberculum palatinum e ndash externalnaris i ndash internal naris fndashnasal flap pv ndash processusvomerinus dorsalis tp ndash tuberculum palatinum

FIG 2 Anterior view of skull of Dipsochelys grandidierishowing the exceptionally large processus vomerinus dorsalis(marked by arrow)

16

tially covered by a flap of soft tissue projecting from theseptum No muscular areas are apparent in associationwith the flap Two low ridges lie along the nasopharyn-geal duct one is on the medial and one on theventro-medial wall

On the ventral surface of the palate situated betweenthe foramina praepalatina is a hemispherical structureprojecting into the buccal cavity this has previouslybeen referred to as the lsquotuberculum palatinumrsquo (Bojanus1819-21 Fritsch 1870) This structure is oval 3 mmwide and 4 mm long in the adult tortoise 1 times 2 mm in thefull-term embryo In live and in preserved material it isdetectable as a pale bulge in the anterior of the palate (itsexact extent is indistinct in the older preserved bleachedmaterial) It is partially enclosed by the cartilage aroundthe foramina praepalatina and the outline is indistinct

The nasal branches of the palatine arteries pass throughthe foramina praepalatina and lie on either side of thetuberculum palatinum Capillaries from the nasal arter-ies pass through the foramina praepalatina and enter thetuberculum palatinum no major nerves enter the tuber-culum On either side of the tuberculum palatinum thereis a duct passing from the buccal cavity into the proces-sus vomerinus dorsalis

HISTOLOGY

The available microscope preparations are of embry-onic tortoises and the palatal region has beenextensively fragmented during preparation of most sec-tions Consequently the description below andaccompanying figures (Fig 4-5) are based on a compos-ite of the slides (Fig 3)

Throughout the anterior sections the nasal passages(cavi nasi) are clearly visible as dense ovals beingclosed anteriorly by the hypertrophied epithelial liningA short distance from the external nares the nasal pas-sages are open and the anterior portion of thecartilaginous septum is visible At the position of theprocessus vomerinus dorsalis the nasal passages aredorso-ventrally elongate broadened dorsally and with amedial fold forming a ventro-medial pocket Below thenasal passages the tuberculum palatinum is visiblecomposed of large open cells

The nasal passages themselves form two distinct re-gions the anterior (vestibular) part and the cavum nasiproprium The vestibulum is lined with darkly stainedcuboid epithelial cells with large nuclei a darker basallayer is also apparent The cavum nasi proprium is linedwith distinctive columnar epithelial cells above the ba-sal layer The medial wall is heavily stained in mostsections No elastic fibres could be detected in the basallayer

DIPSOCHELYS TORTOISE NASAL STRUCTURES

FIG 3 Photomicrographs of the cavi nasum propium ofDipsochelys embryos (Scale bar 500 micro ) (a) sectioned at pointb on Fig 4 (b) section posterior to point b on Fig 4 (c)respiratory epithelium of the intermediate region showing theabsence of ciliated cells (d) vomeronasal epithelium of themedial nasal gland showing columnar cells with cilia andthickened basal connective tissue (e) tuberculum palatinum

FIG 4 Transverse sections through the nasal passages ofDipsochelys (a) medial view of the skull showing thelocation of the sections (b) section though the processusvomerinus (c) section through the nasal flap f ndash nasal flapmgndash medial nasal glandondasholfactory chamber pvndashprocessusvomerinus dorsalis s ndash septum tp ndash tuberculum palatinum 1ndash nervus septi narium 2- vomeronasal nerve

FIG 5 Transverse section through the vomeronasal organ ofDipsochelys section taken between lines b and c in Fig 4 dndash duct from the tuberculum palatinum to the vomeronasalorgan oe ndash olfactory epithelium s ndash septum tp ndash tuberculumpalatinum v ndash vomer ve ndash vomeronasal epithelium

17

Throughout the anterior sections the nasal passages(cavi nasi) are clearly visible as dense ovals beingclosed anteriorly by the hypertrophied epithelial liningA short distance from the external nares the nasal pas-sages are open and the anterior portion of thecartilaginous septum is visible At the position of theprocessus vomerinus dorsalis the nasal passages aredorso-ventrally elongate broadened dorsally and with amedial fold forming a ventro-medial pocket Below thenasal passages the tuberculum palatinum is visiblecomposed of large open cells

The nasal passages themselves form two distinct re-gions the anterior (vestibular) part and the cavum nasiproprium The vestibulum is lined with darkly stainedcuboid epithelial cells with large nuclei a darker basallayer is also apparent The cavum nasi proprium is linedwith distinctive columnar epithelial cells above the ba-sal layer The medial wall is heavily stained in mostsections No elastic fibres could be detected in the basallayer

Within the cavum nasi proprium the broad dorsal ol-factory region and the more compressed intermediateregion are distinctive The olfactory region is character-ised by the presence of olfactory epithelium withBowmanrsquos glands The olfactory epithelium is distinc-tive in its high columnar shape and the presence of longcilia projecting into the lumen The intermediate regionis covered with respiratory epithelium (lacking the ciliaof the sensory olfactory cells) with the exception of themedial pocket (the medial nasal gland) that is lined bysensory epithelium Bowmanrsquos glands were not de-tected (and are absent from this region in othervertebrates) The nervous evaginations of the basallayer reported for Testudo (Parsons 1970) were not ob-served

The sections show a large area of thickened basalconnective tissue on the medial wall of the nasal cham-ber The cells present are typical basal cells with aconical form and could be interpreted as an area of erec-tile connective tissue as conjectured by Arnold (1979)In conjunction with this a dense network of capillariesare present between the connective tissue and theseptum but the connective tissue does not surround ve-nous spaces or contain detectable elastic tissue as wouldbe expected in an erectile tissue In the central and pos-terior sections the connective tissue is generallyreduced and the medial fold absent as is the medialpocket The posterior portion of the nasal chamber is anelongate dorsally broadened lumen lined by a narrowborder of sensory epithelium with only a very narrowbasal layer

PALATE OBSERVATIONS

When the mouths of the tortoises are opened the tu-berculum palatinum is visible as an oval yellowish areaof the palate (Fig 6)

DISCUSSION

The present study confirms earlier reports (Arnold1979 Gerlach amp Canning 1998) of the complexity of

the nasal passages of Dipsochelys The largest structurein the nasal region is the flap of soft tissue projectingfrom the septum across the opening to the nasal cham-ber This is lined with respiratory epithelium andsupported by connective tissue suggesting that it doesnot have a sensory function but may serve to partiallyclose off the nasal chamber as suggested by Arnold(1979) However the interpretation of the thickenedarea of connective tissue as an erectile tissue is madedoubtful by the apparent absence of venous spaces orelastic tissue and it may be a passive inhibitor to waterflow permitting lsquonasal drinkingrsquo but in a less specialisedform than the valve proposed by Arnold (1979)

The cartilage and soft tissue structure resting on theprocessus vomerinus dorsalis is lined with sensory epi-thelium of the chelonian vomeronasal type(non-glandular) The position of the ventro-medialpocket identifiable as the medial nasal gland where themedial sulcus would be in other testudinids and its sen-sory development support the suggestion that theprocessus vomerinus dorsalis encloses a vomeronasalorgan (Gerlach amp Canning 1998) This putative vome-ronasal organ is connected to the tuberculum palatinumby the open lateral ducts opening directly into the buccalcavity In other testudinids such as Testudo andGeochelone pardalis vomeronasal-like structures areless developed lacking extensive cartilage (theparaseptal process of the septal cartilage only partly cov-ers the duct) are not supported by a bony process of thevomer and lack a connection to the buccal cavity Thebony support and extensive cartilaginous encapsulationin Dipsochelys is more reminiscent of the vomeronasalorgan of mammals (Rasmussen amp Hultgren 1990)

In all testudinids examined the gland is innervated bythe nervus septi narium a branch of the opthalmic divi-sion of the trigeminal nerve This is the case with the

J GERLACH

FIG 6 Anterior view of palate of Dipsochelys hololissashowing the location of the tuberculum palatinum (marked byarrow)

18

vomeronasal organ of other reptiles supporting the iden-tification of the intermediate region of the cheloniannose as a vomeronasal organ (Tucker 1963 Graziadeiamp Tucker 1970 Parsons 1970) There is also innerva-tion from the accessory olfactory bulb where this hasbeen studied (Dipsochelys pers obs Caretta Saito etal 2000) as in a true vomeronasal organ (Doslashving ampTrotier 1998) contrary to Gauthier et alrsquos (1990)analysis The pars anterior of the vomeronasal organ(equivalent to the anterior sulcus containing the medialnasal gland) is normally described as supporting sensoryepithelium without Bowmanrsquos glands (olfactory regionssupport olfactory epithelium and Bowmanrsquos glands Par-sons 1970) In Testudo the ventral lateral walls andventral surfaces of the olfactory ridges are non-sensorysupporting respiratory epithelium only without Bow-manrsquos glands The medial nasal gland duct enters theintermediate region in Testudo (Parsons 1970) throughthe ventral surface of the medial ridge These featuresare all in accordance with the observations ofDipsochelys A distinct vomeronasal organ was de-scribed in the lateral wall of the nasal septum ofGopherus polyphemus (Tucker 1963) but this was sub-sequently noted to be the duct of the medial nasal gland(Graziadei amp Tucker 1970) and as with Testudo thegeneral region of the anterior sulcus can be considered apoorly defined vomeronasal organ

It appears that Dipsochelys possesses an unusuallywell developed vomeronasal organ for a chelonian Thishas an olfactory role and is generally associated withpheromone detection Nose touching has been observedin genera other than Dipsochelys Gopherus agassizii(Camp 1916) and Homopus areolatus (Carpenter ampFerguson 1977) Although it appears to be an infrequentaction it has been used to suggest that olfaction andpheromones are important in species recognition(Legler 1960 Carpenter amp Ferguson 1977) Despitethis few secretory glands have been identified in tor-toises the axillary and inguinal pores of the Rathkersquosglands found in many chelonians are not present in theTestudinidae (Loveridge ampWilliams 1957) and mentalglands (Rathke 1848 Winokur amp Legler 1975) are onlyfound in Gopherus and Manouria Although it has beensuggested that lsquocloacal discharge of female turtles at-tracts or stimulates males to court during the breedingseasonrsquo (Manton 1979) only one glandular tissue hasbeen described from this region (in Clemmysmarmoratus Disselhorst 1904 Whiting 1969) None ofthese glands has been identified in Dipsochleys and thelsquoscent-glandrsquo described by Owen (1866) in a lsquoTestudoindica of two feet longrsquo could not be located by dissec-tion (Gerlach 2004) and appears to be the mental glandof a Gopherus specimen and not a gland of any of thegiant tortoise species frequently referred to lsquoT indicarsquo inthe 19th century

In the case of Dipsochelys the contact between thebuccal region and the olfactory region provided by theducts between the tuberculum palatinum and the medialnasal gland means that the vomeronasal organ closelyresembles the Jacobsonrsquos organ of squamates and mam-

mals The lack of previous reports of such organs inchelonians may be due to the scarcity of dissections ofthis region in many chelonians A review of the litera-ture and of skull material identifies one additionaltaxon with a structure resembling a Jacobsonrsquos organthe leatherback turtle Dermochelys coriacea possessesa direct connection between the intermediate nasal re-gion (lined with vomeronasal epithelium Parsons1970) and buccal cavities through the foraminapraepalatina a connection figured as long ago as 1912(Nick 1912) This connection differs from that foundin Dipsochleys in that there is a single opening into thebuccal cavity this is through an opening between thepremaxillae (Fig 4) this may be due to modificationfrom a common arrangement reflecting structural dif-ferences in the rostral region of these species As withDipsochelys the duct into the buccal cavity lies next toan area of loose connective tissue resembling the tuber-culum palatinum The function of this tissue remainsobscure in Dipsochelys it could act as a pad of tissuethat would be pressed against the ducts into the medialnasal gland during chewing effectively closing themand preventing food passing into the gland InDermochelys it appears to be positioned too farposteriorly for such a function Similarly in Emyswhere the tuberculum palatinum was first described(Bojanus 1819-21) no connection between the buccaland nasal cavities has been reported The vomeronasalorgan in Dermochelys may be associated with the loca-tion of natal nesting beaches rather than socialinteractions as in Dipsochelys In this case a buccalconnection would facilitate sensory detection under-water without flooding the nasal cavity Other marineturtles with similar homing behaviours may also havewell developed vomeronasal organs although the possi-bility of buccal connections is very limited due to theextensive development of the secondary palateThesefindings in Dipsochelys and the identification of similarstructures in Dermochelys demonstrates that much re-mains to be discovered in the sensory capabilities ofchelonians Although there have been detailed investi-gations of the anatomy and neurobiology of olfaction insome freshwater taxa (eg Geoclemys reevesiiGraziadei amp Tucker 1970 Taniguchi et al 19951996 Sternotherus odoratus Murphy et al 2001Fadool et al 2001) the Chelonia are an ecologicallydiverse group and there is a need for more through ex-amination of the histology and function of this region

ACKNOWLEDGEMENTS

I am grateful to E N Arnold and S Chapman forenabling me to examine material at the British Museum(Natural History) and to R Gerlach for careful preser-vation of the Dipsochelys hololissa embryos

REFERENCES

Arnold E N (1979) Indian Ocean giant tortoises theirsystematics and island adaptations PhilosophicalTransactions of the Royal Society of London B 286127-145

DIPSOCHELYS TORTOISE NASAL STRUCTURES 19

MATERIAL AND METHODS

During a taxonomic revision a detailed osteologicalstudy was made on 118 specimens of all species of thegenus (Gerlach amp Canning 1998) During this studycareful attention was paid to the ridges and bony proc-esses within the nasal chamber following observationthat there were differences in these structures betweenD dussumieri and D grandidieri A dissection of anadult female head of a Dipsochelys dussumieri fromAldabra (preserved in 70 ethanol since 1971) has pre-viously been figured and described (Arnold 1979) thepreserved dissection (BM(NH) R1978772) was re-ex-amined Recent material of one adult D dussumieri onAldabra atoll was examined Previously undescribedmaterial was available in the form of serial transversesections of a D dussumieri late embryo The 10 micro sec-tions stained with Massonrsquos trichrome had beenprepared by A drsquoA Bellairs and are stored in the BritishMuseum (Natural History) In 2003 five full-term em-bryos of D hololissa were preserved and stored by theNature Protection Trust of Seychelles These were pre-served in 4 paraformaldehyde enabling newdissections and microscope preparations to be made Allsectioned material was prepared by cutting 5 micro paraffinembedded sections followed by staining with cresyl vio-let

Comparison was made with lsquoGeochelonersquo(Stigmochelys) pardalis which may be the closest livingrelative of Dipsochelys (Gerlach 2001 Palkovaks etal 2002) and with published accounts of the nasalanatomy of Testudo (Parsons 1970) and other turtles(Bellairs amp Kamal 1981 Nick 1912)

Due to the large size of these tortoises it is possible toobserve structures in the palate when the mouth is openOne adult female Dipsochelys hololissa and one adultfemale D arnoldi in the captive groups of the NatureProtection Trust of Seychelles on Silhouette island Sey-chelles responded to scratching of the neck by standingupright and stretching the neck and head upwards Inthis pose the lower jaw would open and could be gentlylevered open further to expose the palate

RESULTS

OSTEOLOGY

The soft-tissue structure suggested to be a vomerona-sal organ is supported by the processus vomerinusdorsalis positioned on the dorsum of the vomer betweenthe foramina praepalatina anterior to the sulcusvomerinus (Figs 1 2) This bony process is a uniquefeature of Dipsochelys (Gerlach amp Canning 1998) notrace of any similar structure has been found in any othertortoise genus The processus vomerinus dorsalis is aslightly elevated piece of bone on the dorsum of the pre-maxillae In adult tortoises (straight carapace lengthover 45cm) it measures 2-6 mm diameter and is raised05-6 mm The height of the processus vomerinus dorsa-lis varies with different species being low (05 mm) inD hololissa moderately elevated in D dussumieri (05-2 mm) and D arnoldi (1-2 mm) and high (6 mm) in the

extinct Malagasy species D grandidieri In Dgrandidieri the exceptionally large process bears two15 mm diameter pits in the anterior surface (Fig 2)

SOFT-TISSUE ANATOMY

The nasal passage in Dipsochelys is exceptional intortoises in rising steeply above a vertical cartilaginousprocess on the floor of the nasal passage supported bythe processus vomerinus dorsalis This elongate processcontains a deep pocket directed posteriorly (Fig 1a)No distinctive features are apparent within the pocketexcept for a very narrow duct passing into the foramenpraepalatinumThe tissues lining the processusvomerinus dorsalis are innervated by both the olfactorynerve and the accessory olfactory bulb the nervus septinarium and the vomeronasal nerve respectively

The nasal passage descends vertically behind thecartilaginous process before dividing into the postero-ventral nasopharyngeal duct and the postero-dorsalcavum nasi proprium The opening to the latter is par-

J GERLACH

FIG 1 Nasal structures of Dipsochelys dussumieri andlsquoGeochelonersquo pardalis (a) medial view of right nasal passageand nasal chamber of D dussumieri (b) medial view of rightnasal passage and nasal chamber of lsquoGrsquo pardalis (c) Detailof the vomeronasal structures of D dussumieri in medialview d ndash duct from the tuberculum palatinum e ndash externalnaris i ndash internal naris fndashnasal flap pv ndash processusvomerinus dorsalis tp ndash tuberculum palatinum

FIG 2 Anterior view of skull of Dipsochelys grandidierishowing the exceptionally large processus vomerinus dorsalis(marked by arrow)

16

tially covered by a flap of soft tissue projecting from theseptum No muscular areas are apparent in associationwith the flap Two low ridges lie along the nasopharyn-geal duct one is on the medial and one on theventro-medial wall

On the ventral surface of the palate situated betweenthe foramina praepalatina is a hemispherical structureprojecting into the buccal cavity this has previouslybeen referred to as the lsquotuberculum palatinumrsquo (Bojanus1819-21 Fritsch 1870) This structure is oval 3 mmwide and 4 mm long in the adult tortoise 1 times 2 mm in thefull-term embryo In live and in preserved material it isdetectable as a pale bulge in the anterior of the palate (itsexact extent is indistinct in the older preserved bleachedmaterial) It is partially enclosed by the cartilage aroundthe foramina praepalatina and the outline is indistinct

The nasal branches of the palatine arteries pass throughthe foramina praepalatina and lie on either side of thetuberculum palatinum Capillaries from the nasal arter-ies pass through the foramina praepalatina and enter thetuberculum palatinum no major nerves enter the tuber-culum On either side of the tuberculum palatinum thereis a duct passing from the buccal cavity into the proces-sus vomerinus dorsalis

HISTOLOGY

The available microscope preparations are of embry-onic tortoises and the palatal region has beenextensively fragmented during preparation of most sec-tions Consequently the description below andaccompanying figures (Fig 4-5) are based on a compos-ite of the slides (Fig 3)

Throughout the anterior sections the nasal passages(cavi nasi) are clearly visible as dense ovals beingclosed anteriorly by the hypertrophied epithelial liningA short distance from the external nares the nasal pas-sages are open and the anterior portion of thecartilaginous septum is visible At the position of theprocessus vomerinus dorsalis the nasal passages aredorso-ventrally elongate broadened dorsally and with amedial fold forming a ventro-medial pocket Below thenasal passages the tuberculum palatinum is visiblecomposed of large open cells

The nasal passages themselves form two distinct re-gions the anterior (vestibular) part and the cavum nasiproprium The vestibulum is lined with darkly stainedcuboid epithelial cells with large nuclei a darker basallayer is also apparent The cavum nasi proprium is linedwith distinctive columnar epithelial cells above the ba-sal layer The medial wall is heavily stained in mostsections No elastic fibres could be detected in the basallayer

DIPSOCHELYS TORTOISE NASAL STRUCTURES

FIG 3 Photomicrographs of the cavi nasum propium ofDipsochelys embryos (Scale bar 500 micro ) (a) sectioned at pointb on Fig 4 (b) section posterior to point b on Fig 4 (c)respiratory epithelium of the intermediate region showing theabsence of ciliated cells (d) vomeronasal epithelium of themedial nasal gland showing columnar cells with cilia andthickened basal connective tissue (e) tuberculum palatinum

FIG 4 Transverse sections through the nasal passages ofDipsochelys (a) medial view of the skull showing thelocation of the sections (b) section though the processusvomerinus (c) section through the nasal flap f ndash nasal flapmgndash medial nasal glandondasholfactory chamber pvndashprocessusvomerinus dorsalis s ndash septum tp ndash tuberculum palatinum 1ndash nervus septi narium 2- vomeronasal nerve

FIG 5 Transverse section through the vomeronasal organ ofDipsochelys section taken between lines b and c in Fig 4 dndash duct from the tuberculum palatinum to the vomeronasalorgan oe ndash olfactory epithelium s ndash septum tp ndash tuberculumpalatinum v ndash vomer ve ndash vomeronasal epithelium

17

Throughout the anterior sections the nasal passages(cavi nasi) are clearly visible as dense ovals beingclosed anteriorly by the hypertrophied epithelial liningA short distance from the external nares the nasal pas-sages are open and the anterior portion of thecartilaginous septum is visible At the position of theprocessus vomerinus dorsalis the nasal passages aredorso-ventrally elongate broadened dorsally and with amedial fold forming a ventro-medial pocket Below thenasal passages the tuberculum palatinum is visiblecomposed of large open cells

The nasal passages themselves form two distinct re-gions the anterior (vestibular) part and the cavum nasiproprium The vestibulum is lined with darkly stainedcuboid epithelial cells with large nuclei a darker basallayer is also apparent The cavum nasi proprium is linedwith distinctive columnar epithelial cells above the ba-sal layer The medial wall is heavily stained in mostsections No elastic fibres could be detected in the basallayer

Within the cavum nasi proprium the broad dorsal ol-factory region and the more compressed intermediateregion are distinctive The olfactory region is character-ised by the presence of olfactory epithelium withBowmanrsquos glands The olfactory epithelium is distinc-tive in its high columnar shape and the presence of longcilia projecting into the lumen The intermediate regionis covered with respiratory epithelium (lacking the ciliaof the sensory olfactory cells) with the exception of themedial pocket (the medial nasal gland) that is lined bysensory epithelium Bowmanrsquos glands were not de-tected (and are absent from this region in othervertebrates) The nervous evaginations of the basallayer reported for Testudo (Parsons 1970) were not ob-served

The sections show a large area of thickened basalconnective tissue on the medial wall of the nasal cham-ber The cells present are typical basal cells with aconical form and could be interpreted as an area of erec-tile connective tissue as conjectured by Arnold (1979)In conjunction with this a dense network of capillariesare present between the connective tissue and theseptum but the connective tissue does not surround ve-nous spaces or contain detectable elastic tissue as wouldbe expected in an erectile tissue In the central and pos-terior sections the connective tissue is generallyreduced and the medial fold absent as is the medialpocket The posterior portion of the nasal chamber is anelongate dorsally broadened lumen lined by a narrowborder of sensory epithelium with only a very narrowbasal layer

PALATE OBSERVATIONS

When the mouths of the tortoises are opened the tu-berculum palatinum is visible as an oval yellowish areaof the palate (Fig 6)

DISCUSSION

The present study confirms earlier reports (Arnold1979 Gerlach amp Canning 1998) of the complexity of

the nasal passages of Dipsochelys The largest structurein the nasal region is the flap of soft tissue projectingfrom the septum across the opening to the nasal cham-ber This is lined with respiratory epithelium andsupported by connective tissue suggesting that it doesnot have a sensory function but may serve to partiallyclose off the nasal chamber as suggested by Arnold(1979) However the interpretation of the thickenedarea of connective tissue as an erectile tissue is madedoubtful by the apparent absence of venous spaces orelastic tissue and it may be a passive inhibitor to waterflow permitting lsquonasal drinkingrsquo but in a less specialisedform than the valve proposed by Arnold (1979)

The cartilage and soft tissue structure resting on theprocessus vomerinus dorsalis is lined with sensory epi-thelium of the chelonian vomeronasal type(non-glandular) The position of the ventro-medialpocket identifiable as the medial nasal gland where themedial sulcus would be in other testudinids and its sen-sory development support the suggestion that theprocessus vomerinus dorsalis encloses a vomeronasalorgan (Gerlach amp Canning 1998) This putative vome-ronasal organ is connected to the tuberculum palatinumby the open lateral ducts opening directly into the buccalcavity In other testudinids such as Testudo andGeochelone pardalis vomeronasal-like structures areless developed lacking extensive cartilage (theparaseptal process of the septal cartilage only partly cov-ers the duct) are not supported by a bony process of thevomer and lack a connection to the buccal cavity Thebony support and extensive cartilaginous encapsulationin Dipsochelys is more reminiscent of the vomeronasalorgan of mammals (Rasmussen amp Hultgren 1990)

In all testudinids examined the gland is innervated bythe nervus septi narium a branch of the opthalmic divi-sion of the trigeminal nerve This is the case with the

J GERLACH

FIG 6 Anterior view of palate of Dipsochelys hololissashowing the location of the tuberculum palatinum (marked byarrow)

18

vomeronasal organ of other reptiles supporting the iden-tification of the intermediate region of the cheloniannose as a vomeronasal organ (Tucker 1963 Graziadeiamp Tucker 1970 Parsons 1970) There is also innerva-tion from the accessory olfactory bulb where this hasbeen studied (Dipsochelys pers obs Caretta Saito etal 2000) as in a true vomeronasal organ (Doslashving ampTrotier 1998) contrary to Gauthier et alrsquos (1990)analysis The pars anterior of the vomeronasal organ(equivalent to the anterior sulcus containing the medialnasal gland) is normally described as supporting sensoryepithelium without Bowmanrsquos glands (olfactory regionssupport olfactory epithelium and Bowmanrsquos glands Par-sons 1970) In Testudo the ventral lateral walls andventral surfaces of the olfactory ridges are non-sensorysupporting respiratory epithelium only without Bow-manrsquos glands The medial nasal gland duct enters theintermediate region in Testudo (Parsons 1970) throughthe ventral surface of the medial ridge These featuresare all in accordance with the observations ofDipsochelys A distinct vomeronasal organ was de-scribed in the lateral wall of the nasal septum ofGopherus polyphemus (Tucker 1963) but this was sub-sequently noted to be the duct of the medial nasal gland(Graziadei amp Tucker 1970) and as with Testudo thegeneral region of the anterior sulcus can be considered apoorly defined vomeronasal organ

It appears that Dipsochelys possesses an unusuallywell developed vomeronasal organ for a chelonian Thishas an olfactory role and is generally associated withpheromone detection Nose touching has been observedin genera other than Dipsochelys Gopherus agassizii(Camp 1916) and Homopus areolatus (Carpenter ampFerguson 1977) Although it appears to be an infrequentaction it has been used to suggest that olfaction andpheromones are important in species recognition(Legler 1960 Carpenter amp Ferguson 1977) Despitethis few secretory glands have been identified in tor-toises the axillary and inguinal pores of the Rathkersquosglands found in many chelonians are not present in theTestudinidae (Loveridge ampWilliams 1957) and mentalglands (Rathke 1848 Winokur amp Legler 1975) are onlyfound in Gopherus and Manouria Although it has beensuggested that lsquocloacal discharge of female turtles at-tracts or stimulates males to court during the breedingseasonrsquo (Manton 1979) only one glandular tissue hasbeen described from this region (in Clemmysmarmoratus Disselhorst 1904 Whiting 1969) None ofthese glands has been identified in Dipsochleys and thelsquoscent-glandrsquo described by Owen (1866) in a lsquoTestudoindica of two feet longrsquo could not be located by dissec-tion (Gerlach 2004) and appears to be the mental glandof a Gopherus specimen and not a gland of any of thegiant tortoise species frequently referred to lsquoT indicarsquo inthe 19th century

In the case of Dipsochelys the contact between thebuccal region and the olfactory region provided by theducts between the tuberculum palatinum and the medialnasal gland means that the vomeronasal organ closelyresembles the Jacobsonrsquos organ of squamates and mam-

mals The lack of previous reports of such organs inchelonians may be due to the scarcity of dissections ofthis region in many chelonians A review of the litera-ture and of skull material identifies one additionaltaxon with a structure resembling a Jacobsonrsquos organthe leatherback turtle Dermochelys coriacea possessesa direct connection between the intermediate nasal re-gion (lined with vomeronasal epithelium Parsons1970) and buccal cavities through the foraminapraepalatina a connection figured as long ago as 1912(Nick 1912) This connection differs from that foundin Dipsochleys in that there is a single opening into thebuccal cavity this is through an opening between thepremaxillae (Fig 4) this may be due to modificationfrom a common arrangement reflecting structural dif-ferences in the rostral region of these species As withDipsochelys the duct into the buccal cavity lies next toan area of loose connective tissue resembling the tuber-culum palatinum The function of this tissue remainsobscure in Dipsochelys it could act as a pad of tissuethat would be pressed against the ducts into the medialnasal gland during chewing effectively closing themand preventing food passing into the gland InDermochelys it appears to be positioned too farposteriorly for such a function Similarly in Emyswhere the tuberculum palatinum was first described(Bojanus 1819-21) no connection between the buccaland nasal cavities has been reported The vomeronasalorgan in Dermochelys may be associated with the loca-tion of natal nesting beaches rather than socialinteractions as in Dipsochelys In this case a buccalconnection would facilitate sensory detection under-water without flooding the nasal cavity Other marineturtles with similar homing behaviours may also havewell developed vomeronasal organs although the possi-bility of buccal connections is very limited due to theextensive development of the secondary palateThesefindings in Dipsochelys and the identification of similarstructures in Dermochelys demonstrates that much re-mains to be discovered in the sensory capabilities ofchelonians Although there have been detailed investi-gations of the anatomy and neurobiology of olfaction insome freshwater taxa (eg Geoclemys reevesiiGraziadei amp Tucker 1970 Taniguchi et al 19951996 Sternotherus odoratus Murphy et al 2001Fadool et al 2001) the Chelonia are an ecologicallydiverse group and there is a need for more through ex-amination of the histology and function of this region

ACKNOWLEDGEMENTS

I am grateful to E N Arnold and S Chapman forenabling me to examine material at the British Museum(Natural History) and to R Gerlach for careful preser-vation of the Dipsochelys hololissa embryos

REFERENCES

Arnold E N (1979) Indian Ocean giant tortoises theirsystematics and island adaptations PhilosophicalTransactions of the Royal Society of London B 286127-145

DIPSOCHELYS TORTOISE NASAL STRUCTURES 19

tially covered by a flap of soft tissue projecting from theseptum No muscular areas are apparent in associationwith the flap Two low ridges lie along the nasopharyn-geal duct one is on the medial and one on theventro-medial wall

On the ventral surface of the palate situated betweenthe foramina praepalatina is a hemispherical structureprojecting into the buccal cavity this has previouslybeen referred to as the lsquotuberculum palatinumrsquo (Bojanus1819-21 Fritsch 1870) This structure is oval 3 mmwide and 4 mm long in the adult tortoise 1 times 2 mm in thefull-term embryo In live and in preserved material it isdetectable as a pale bulge in the anterior of the palate (itsexact extent is indistinct in the older preserved bleachedmaterial) It is partially enclosed by the cartilage aroundthe foramina praepalatina and the outline is indistinct

The nasal branches of the palatine arteries pass throughthe foramina praepalatina and lie on either side of thetuberculum palatinum Capillaries from the nasal arter-ies pass through the foramina praepalatina and enter thetuberculum palatinum no major nerves enter the tuber-culum On either side of the tuberculum palatinum thereis a duct passing from the buccal cavity into the proces-sus vomerinus dorsalis

HISTOLOGY

The available microscope preparations are of embry-onic tortoises and the palatal region has beenextensively fragmented during preparation of most sec-tions Consequently the description below andaccompanying figures (Fig 4-5) are based on a compos-ite of the slides (Fig 3)

Throughout the anterior sections the nasal passages(cavi nasi) are clearly visible as dense ovals beingclosed anteriorly by the hypertrophied epithelial liningA short distance from the external nares the nasal pas-sages are open and the anterior portion of thecartilaginous septum is visible At the position of theprocessus vomerinus dorsalis the nasal passages aredorso-ventrally elongate broadened dorsally and with amedial fold forming a ventro-medial pocket Below thenasal passages the tuberculum palatinum is visiblecomposed of large open cells

The nasal passages themselves form two distinct re-gions the anterior (vestibular) part and the cavum nasiproprium The vestibulum is lined with darkly stainedcuboid epithelial cells with large nuclei a darker basallayer is also apparent The cavum nasi proprium is linedwith distinctive columnar epithelial cells above the ba-sal layer The medial wall is heavily stained in mostsections No elastic fibres could be detected in the basallayer

DIPSOCHELYS TORTOISE NASAL STRUCTURES

FIG 3 Photomicrographs of the cavi nasum propium ofDipsochelys embryos (Scale bar 500 micro ) (a) sectioned at pointb on Fig 4 (b) section posterior to point b on Fig 4 (c)respiratory epithelium of the intermediate region showing theabsence of ciliated cells (d) vomeronasal epithelium of themedial nasal gland showing columnar cells with cilia andthickened basal connective tissue (e) tuberculum palatinum

FIG 4 Transverse sections through the nasal passages ofDipsochelys (a) medial view of the skull showing thelocation of the sections (b) section though the processusvomerinus (c) section through the nasal flap f ndash nasal flapmgndash medial nasal glandondasholfactory chamber pvndashprocessusvomerinus dorsalis s ndash septum tp ndash tuberculum palatinum 1ndash nervus septi narium 2- vomeronasal nerve

FIG 5 Transverse section through the vomeronasal organ ofDipsochelys section taken between lines b and c in Fig 4 dndash duct from the tuberculum palatinum to the vomeronasalorgan oe ndash olfactory epithelium s ndash septum tp ndash tuberculumpalatinum v ndash vomer ve ndash vomeronasal epithelium

17

Throughout the anterior sections the nasal passages(cavi nasi) are clearly visible as dense ovals beingclosed anteriorly by the hypertrophied epithelial liningA short distance from the external nares the nasal pas-sages are open and the anterior portion of thecartilaginous septum is visible At the position of theprocessus vomerinus dorsalis the nasal passages aredorso-ventrally elongate broadened dorsally and with amedial fold forming a ventro-medial pocket Below thenasal passages the tuberculum palatinum is visiblecomposed of large open cells

The nasal passages themselves form two distinct re-gions the anterior (vestibular) part and the cavum nasiproprium The vestibulum is lined with darkly stainedcuboid epithelial cells with large nuclei a darker basallayer is also apparent The cavum nasi proprium is linedwith distinctive columnar epithelial cells above the ba-sal layer The medial wall is heavily stained in mostsections No elastic fibres could be detected in the basallayer

Within the cavum nasi proprium the broad dorsal ol-factory region and the more compressed intermediateregion are distinctive The olfactory region is character-ised by the presence of olfactory epithelium withBowmanrsquos glands The olfactory epithelium is distinc-tive in its high columnar shape and the presence of longcilia projecting into the lumen The intermediate regionis covered with respiratory epithelium (lacking the ciliaof the sensory olfactory cells) with the exception of themedial pocket (the medial nasal gland) that is lined bysensory epithelium Bowmanrsquos glands were not de-tected (and are absent from this region in othervertebrates) The nervous evaginations of the basallayer reported for Testudo (Parsons 1970) were not ob-served

The sections show a large area of thickened basalconnective tissue on the medial wall of the nasal cham-ber The cells present are typical basal cells with aconical form and could be interpreted as an area of erec-tile connective tissue as conjectured by Arnold (1979)In conjunction with this a dense network of capillariesare present between the connective tissue and theseptum but the connective tissue does not surround ve-nous spaces or contain detectable elastic tissue as wouldbe expected in an erectile tissue In the central and pos-terior sections the connective tissue is generallyreduced and the medial fold absent as is the medialpocket The posterior portion of the nasal chamber is anelongate dorsally broadened lumen lined by a narrowborder of sensory epithelium with only a very narrowbasal layer

PALATE OBSERVATIONS

When the mouths of the tortoises are opened the tu-berculum palatinum is visible as an oval yellowish areaof the palate (Fig 6)

DISCUSSION

The present study confirms earlier reports (Arnold1979 Gerlach amp Canning 1998) of the complexity of

the nasal passages of Dipsochelys The largest structurein the nasal region is the flap of soft tissue projectingfrom the septum across the opening to the nasal cham-ber This is lined with respiratory epithelium andsupported by connective tissue suggesting that it doesnot have a sensory function but may serve to partiallyclose off the nasal chamber as suggested by Arnold(1979) However the interpretation of the thickenedarea of connective tissue as an erectile tissue is madedoubtful by the apparent absence of venous spaces orelastic tissue and it may be a passive inhibitor to waterflow permitting lsquonasal drinkingrsquo but in a less specialisedform than the valve proposed by Arnold (1979)

The cartilage and soft tissue structure resting on theprocessus vomerinus dorsalis is lined with sensory epi-thelium of the chelonian vomeronasal type(non-glandular) The position of the ventro-medialpocket identifiable as the medial nasal gland where themedial sulcus would be in other testudinids and its sen-sory development support the suggestion that theprocessus vomerinus dorsalis encloses a vomeronasalorgan (Gerlach amp Canning 1998) This putative vome-ronasal organ is connected to the tuberculum palatinumby the open lateral ducts opening directly into the buccalcavity In other testudinids such as Testudo andGeochelone pardalis vomeronasal-like structures areless developed lacking extensive cartilage (theparaseptal process of the septal cartilage only partly cov-ers the duct) are not supported by a bony process of thevomer and lack a connection to the buccal cavity Thebony support and extensive cartilaginous encapsulationin Dipsochelys is more reminiscent of the vomeronasalorgan of mammals (Rasmussen amp Hultgren 1990)

In all testudinids examined the gland is innervated bythe nervus septi narium a branch of the opthalmic divi-sion of the trigeminal nerve This is the case with the

J GERLACH

FIG 6 Anterior view of palate of Dipsochelys hololissashowing the location of the tuberculum palatinum (marked byarrow)

18

vomeronasal organ of other reptiles supporting the iden-tification of the intermediate region of the cheloniannose as a vomeronasal organ (Tucker 1963 Graziadeiamp Tucker 1970 Parsons 1970) There is also innerva-tion from the accessory olfactory bulb where this hasbeen studied (Dipsochelys pers obs Caretta Saito etal 2000) as in a true vomeronasal organ (Doslashving ampTrotier 1998) contrary to Gauthier et alrsquos (1990)analysis The pars anterior of the vomeronasal organ(equivalent to the anterior sulcus containing the medialnasal gland) is normally described as supporting sensoryepithelium without Bowmanrsquos glands (olfactory regionssupport olfactory epithelium and Bowmanrsquos glands Par-sons 1970) In Testudo the ventral lateral walls andventral surfaces of the olfactory ridges are non-sensorysupporting respiratory epithelium only without Bow-manrsquos glands The medial nasal gland duct enters theintermediate region in Testudo (Parsons 1970) throughthe ventral surface of the medial ridge These featuresare all in accordance with the observations ofDipsochelys A distinct vomeronasal organ was de-scribed in the lateral wall of the nasal septum ofGopherus polyphemus (Tucker 1963) but this was sub-sequently noted to be the duct of the medial nasal gland(Graziadei amp Tucker 1970) and as with Testudo thegeneral region of the anterior sulcus can be considered apoorly defined vomeronasal organ

It appears that Dipsochelys possesses an unusuallywell developed vomeronasal organ for a chelonian Thishas an olfactory role and is generally associated withpheromone detection Nose touching has been observedin genera other than Dipsochelys Gopherus agassizii(Camp 1916) and Homopus areolatus (Carpenter ampFerguson 1977) Although it appears to be an infrequentaction it has been used to suggest that olfaction andpheromones are important in species recognition(Legler 1960 Carpenter amp Ferguson 1977) Despitethis few secretory glands have been identified in tor-toises the axillary and inguinal pores of the Rathkersquosglands found in many chelonians are not present in theTestudinidae (Loveridge ampWilliams 1957) and mentalglands (Rathke 1848 Winokur amp Legler 1975) are onlyfound in Gopherus and Manouria Although it has beensuggested that lsquocloacal discharge of female turtles at-tracts or stimulates males to court during the breedingseasonrsquo (Manton 1979) only one glandular tissue hasbeen described from this region (in Clemmysmarmoratus Disselhorst 1904 Whiting 1969) None ofthese glands has been identified in Dipsochleys and thelsquoscent-glandrsquo described by Owen (1866) in a lsquoTestudoindica of two feet longrsquo could not be located by dissec-tion (Gerlach 2004) and appears to be the mental glandof a Gopherus specimen and not a gland of any of thegiant tortoise species frequently referred to lsquoT indicarsquo inthe 19th century

In the case of Dipsochelys the contact between thebuccal region and the olfactory region provided by theducts between the tuberculum palatinum and the medialnasal gland means that the vomeronasal organ closelyresembles the Jacobsonrsquos organ of squamates and mam-

mals The lack of previous reports of such organs inchelonians may be due to the scarcity of dissections ofthis region in many chelonians A review of the litera-ture and of skull material identifies one additionaltaxon with a structure resembling a Jacobsonrsquos organthe leatherback turtle Dermochelys coriacea possessesa direct connection between the intermediate nasal re-gion (lined with vomeronasal epithelium Parsons1970) and buccal cavities through the foraminapraepalatina a connection figured as long ago as 1912(Nick 1912) This connection differs from that foundin Dipsochleys in that there is a single opening into thebuccal cavity this is through an opening between thepremaxillae (Fig 4) this may be due to modificationfrom a common arrangement reflecting structural dif-ferences in the rostral region of these species As withDipsochelys the duct into the buccal cavity lies next toan area of loose connective tissue resembling the tuber-culum palatinum The function of this tissue remainsobscure in Dipsochelys it could act as a pad of tissuethat would be pressed against the ducts into the medialnasal gland during chewing effectively closing themand preventing food passing into the gland InDermochelys it appears to be positioned too farposteriorly for such a function Similarly in Emyswhere the tuberculum palatinum was first described(Bojanus 1819-21) no connection between the buccaland nasal cavities has been reported The vomeronasalorgan in Dermochelys may be associated with the loca-tion of natal nesting beaches rather than socialinteractions as in Dipsochelys In this case a buccalconnection would facilitate sensory detection under-water without flooding the nasal cavity Other marineturtles with similar homing behaviours may also havewell developed vomeronasal organs although the possi-bility of buccal connections is very limited due to theextensive development of the secondary palateThesefindings in Dipsochelys and the identification of similarstructures in Dermochelys demonstrates that much re-mains to be discovered in the sensory capabilities ofchelonians Although there have been detailed investi-gations of the anatomy and neurobiology of olfaction insome freshwater taxa (eg Geoclemys reevesiiGraziadei amp Tucker 1970 Taniguchi et al 19951996 Sternotherus odoratus Murphy et al 2001Fadool et al 2001) the Chelonia are an ecologicallydiverse group and there is a need for more through ex-amination of the histology and function of this region

ACKNOWLEDGEMENTS

I am grateful to E N Arnold and S Chapman forenabling me to examine material at the British Museum(Natural History) and to R Gerlach for careful preser-vation of the Dipsochelys hololissa embryos

REFERENCES

Arnold E N (1979) Indian Ocean giant tortoises theirsystematics and island adaptations PhilosophicalTransactions of the Royal Society of London B 286127-145

DIPSOCHELYS TORTOISE NASAL STRUCTURES 19

Throughout the anterior sections the nasal passages(cavi nasi) are clearly visible as dense ovals beingclosed anteriorly by the hypertrophied epithelial liningA short distance from the external nares the nasal pas-sages are open and the anterior portion of thecartilaginous septum is visible At the position of theprocessus vomerinus dorsalis the nasal passages aredorso-ventrally elongate broadened dorsally and with amedial fold forming a ventro-medial pocket Below thenasal passages the tuberculum palatinum is visiblecomposed of large open cells

The nasal passages themselves form two distinct re-gions the anterior (vestibular) part and the cavum nasiproprium The vestibulum is lined with darkly stainedcuboid epithelial cells with large nuclei a darker basallayer is also apparent The cavum nasi proprium is linedwith distinctive columnar epithelial cells above the ba-sal layer The medial wall is heavily stained in mostsections No elastic fibres could be detected in the basallayer

Within the cavum nasi proprium the broad dorsal ol-factory region and the more compressed intermediateregion are distinctive The olfactory region is character-ised by the presence of olfactory epithelium withBowmanrsquos glands The olfactory epithelium is distinc-tive in its high columnar shape and the presence of longcilia projecting into the lumen The intermediate regionis covered with respiratory epithelium (lacking the ciliaof the sensory olfactory cells) with the exception of themedial pocket (the medial nasal gland) that is lined bysensory epithelium Bowmanrsquos glands were not de-tected (and are absent from this region in othervertebrates) The nervous evaginations of the basallayer reported for Testudo (Parsons 1970) were not ob-served

The sections show a large area of thickened basalconnective tissue on the medial wall of the nasal cham-ber The cells present are typical basal cells with aconical form and could be interpreted as an area of erec-tile connective tissue as conjectured by Arnold (1979)In conjunction with this a dense network of capillariesare present between the connective tissue and theseptum but the connective tissue does not surround ve-nous spaces or contain detectable elastic tissue as wouldbe expected in an erectile tissue In the central and pos-terior sections the connective tissue is generallyreduced and the medial fold absent as is the medialpocket The posterior portion of the nasal chamber is anelongate dorsally broadened lumen lined by a narrowborder of sensory epithelium with only a very narrowbasal layer

PALATE OBSERVATIONS

When the mouths of the tortoises are opened the tu-berculum palatinum is visible as an oval yellowish areaof the palate (Fig 6)

DISCUSSION

The present study confirms earlier reports (Arnold1979 Gerlach amp Canning 1998) of the complexity of

the nasal passages of Dipsochelys The largest structurein the nasal region is the flap of soft tissue projectingfrom the septum across the opening to the nasal cham-ber This is lined with respiratory epithelium andsupported by connective tissue suggesting that it doesnot have a sensory function but may serve to partiallyclose off the nasal chamber as suggested by Arnold(1979) However the interpretation of the thickenedarea of connective tissue as an erectile tissue is madedoubtful by the apparent absence of venous spaces orelastic tissue and it may be a passive inhibitor to waterflow permitting lsquonasal drinkingrsquo but in a less specialisedform than the valve proposed by Arnold (1979)

The cartilage and soft tissue structure resting on theprocessus vomerinus dorsalis is lined with sensory epi-thelium of the chelonian vomeronasal type(non-glandular) The position of the ventro-medialpocket identifiable as the medial nasal gland where themedial sulcus would be in other testudinids and its sen-sory development support the suggestion that theprocessus vomerinus dorsalis encloses a vomeronasalorgan (Gerlach amp Canning 1998) This putative vome-ronasal organ is connected to the tuberculum palatinumby the open lateral ducts opening directly into the buccalcavity In other testudinids such as Testudo andGeochelone pardalis vomeronasal-like structures areless developed lacking extensive cartilage (theparaseptal process of the septal cartilage only partly cov-ers the duct) are not supported by a bony process of thevomer and lack a connection to the buccal cavity Thebony support and extensive cartilaginous encapsulationin Dipsochelys is more reminiscent of the vomeronasalorgan of mammals (Rasmussen amp Hultgren 1990)

In all testudinids examined the gland is innervated bythe nervus septi narium a branch of the opthalmic divi-sion of the trigeminal nerve This is the case with the

J GERLACH

FIG 6 Anterior view of palate of Dipsochelys hololissashowing the location of the tuberculum palatinum (marked byarrow)

18

vomeronasal organ of other reptiles supporting the iden-tification of the intermediate region of the cheloniannose as a vomeronasal organ (Tucker 1963 Graziadeiamp Tucker 1970 Parsons 1970) There is also innerva-tion from the accessory olfactory bulb where this hasbeen studied (Dipsochelys pers obs Caretta Saito etal 2000) as in a true vomeronasal organ (Doslashving ampTrotier 1998) contrary to Gauthier et alrsquos (1990)analysis The pars anterior of the vomeronasal organ(equivalent to the anterior sulcus containing the medialnasal gland) is normally described as supporting sensoryepithelium without Bowmanrsquos glands (olfactory regionssupport olfactory epithelium and Bowmanrsquos glands Par-sons 1970) In Testudo the ventral lateral walls andventral surfaces of the olfactory ridges are non-sensorysupporting respiratory epithelium only without Bow-manrsquos glands The medial nasal gland duct enters theintermediate region in Testudo (Parsons 1970) throughthe ventral surface of the medial ridge These featuresare all in accordance with the observations ofDipsochelys A distinct vomeronasal organ was de-scribed in the lateral wall of the nasal septum ofGopherus polyphemus (Tucker 1963) but this was sub-sequently noted to be the duct of the medial nasal gland(Graziadei amp Tucker 1970) and as with Testudo thegeneral region of the anterior sulcus can be considered apoorly defined vomeronasal organ

It appears that Dipsochelys possesses an unusuallywell developed vomeronasal organ for a chelonian Thishas an olfactory role and is generally associated withpheromone detection Nose touching has been observedin genera other than Dipsochelys Gopherus agassizii(Camp 1916) and Homopus areolatus (Carpenter ampFerguson 1977) Although it appears to be an infrequentaction it has been used to suggest that olfaction andpheromones are important in species recognition(Legler 1960 Carpenter amp Ferguson 1977) Despitethis few secretory glands have been identified in tor-toises the axillary and inguinal pores of the Rathkersquosglands found in many chelonians are not present in theTestudinidae (Loveridge ampWilliams 1957) and mentalglands (Rathke 1848 Winokur amp Legler 1975) are onlyfound in Gopherus and Manouria Although it has beensuggested that lsquocloacal discharge of female turtles at-tracts or stimulates males to court during the breedingseasonrsquo (Manton 1979) only one glandular tissue hasbeen described from this region (in Clemmysmarmoratus Disselhorst 1904 Whiting 1969) None ofthese glands has been identified in Dipsochleys and thelsquoscent-glandrsquo described by Owen (1866) in a lsquoTestudoindica of two feet longrsquo could not be located by dissec-tion (Gerlach 2004) and appears to be the mental glandof a Gopherus specimen and not a gland of any of thegiant tortoise species frequently referred to lsquoT indicarsquo inthe 19th century

In the case of Dipsochelys the contact between thebuccal region and the olfactory region provided by theducts between the tuberculum palatinum and the medialnasal gland means that the vomeronasal organ closelyresembles the Jacobsonrsquos organ of squamates and mam-

mals The lack of previous reports of such organs inchelonians may be due to the scarcity of dissections ofthis region in many chelonians A review of the litera-ture and of skull material identifies one additionaltaxon with a structure resembling a Jacobsonrsquos organthe leatherback turtle Dermochelys coriacea possessesa direct connection between the intermediate nasal re-gion (lined with vomeronasal epithelium Parsons1970) and buccal cavities through the foraminapraepalatina a connection figured as long ago as 1912(Nick 1912) This connection differs from that foundin Dipsochleys in that there is a single opening into thebuccal cavity this is through an opening between thepremaxillae (Fig 4) this may be due to modificationfrom a common arrangement reflecting structural dif-ferences in the rostral region of these species As withDipsochelys the duct into the buccal cavity lies next toan area of loose connective tissue resembling the tuber-culum palatinum The function of this tissue remainsobscure in Dipsochelys it could act as a pad of tissuethat would be pressed against the ducts into the medialnasal gland during chewing effectively closing themand preventing food passing into the gland InDermochelys it appears to be positioned too farposteriorly for such a function Similarly in Emyswhere the tuberculum palatinum was first described(Bojanus 1819-21) no connection between the buccaland nasal cavities has been reported The vomeronasalorgan in Dermochelys may be associated with the loca-tion of natal nesting beaches rather than socialinteractions as in Dipsochelys In this case a buccalconnection would facilitate sensory detection under-water without flooding the nasal cavity Other marineturtles with similar homing behaviours may also havewell developed vomeronasal organs although the possi-bility of buccal connections is very limited due to theextensive development of the secondary palateThesefindings in Dipsochelys and the identification of similarstructures in Dermochelys demonstrates that much re-mains to be discovered in the sensory capabilities ofchelonians Although there have been detailed investi-gations of the anatomy and neurobiology of olfaction insome freshwater taxa (eg Geoclemys reevesiiGraziadei amp Tucker 1970 Taniguchi et al 19951996 Sternotherus odoratus Murphy et al 2001Fadool et al 2001) the Chelonia are an ecologicallydiverse group and there is a need for more through ex-amination of the histology and function of this region

ACKNOWLEDGEMENTS

I am grateful to E N Arnold and S Chapman forenabling me to examine material at the British Museum(Natural History) and to R Gerlach for careful preser-vation of the Dipsochelys hololissa embryos

REFERENCES

Arnold E N (1979) Indian Ocean giant tortoises theirsystematics and island adaptations PhilosophicalTransactions of the Royal Society of London B 286127-145

DIPSOCHELYS TORTOISE NASAL STRUCTURES 19

vomeronasal organ of other reptiles supporting the iden-tification of the intermediate region of the cheloniannose as a vomeronasal organ (Tucker 1963 Graziadeiamp Tucker 1970 Parsons 1970) There is also innerva-tion from the accessory olfactory bulb where this hasbeen studied (Dipsochelys pers obs Caretta Saito etal 2000) as in a true vomeronasal organ (Doslashving ampTrotier 1998) contrary to Gauthier et alrsquos (1990)analysis The pars anterior of the vomeronasal organ(equivalent to the anterior sulcus containing the medialnasal gland) is normally described as supporting sensoryepithelium without Bowmanrsquos glands (olfactory regionssupport olfactory epithelium and Bowmanrsquos glands Par-sons 1970) In Testudo the ventral lateral walls andventral surfaces of the olfactory ridges are non-sensorysupporting respiratory epithelium only without Bow-manrsquos glands The medial nasal gland duct enters theintermediate region in Testudo (Parsons 1970) throughthe ventral surface of the medial ridge These featuresare all in accordance with the observations ofDipsochelys A distinct vomeronasal organ was de-scribed in the lateral wall of the nasal septum ofGopherus polyphemus (Tucker 1963) but this was sub-sequently noted to be the duct of the medial nasal gland(Graziadei amp Tucker 1970) and as with Testudo thegeneral region of the anterior sulcus can be considered apoorly defined vomeronasal organ

It appears that Dipsochelys possesses an unusuallywell developed vomeronasal organ for a chelonian Thishas an olfactory role and is generally associated withpheromone detection Nose touching has been observedin genera other than Dipsochelys Gopherus agassizii(Camp 1916) and Homopus areolatus (Carpenter ampFerguson 1977) Although it appears to be an infrequentaction it has been used to suggest that olfaction andpheromones are important in species recognition(Legler 1960 Carpenter amp Ferguson 1977) Despitethis few secretory glands have been identified in tor-toises the axillary and inguinal pores of the Rathkersquosglands found in many chelonians are not present in theTestudinidae (Loveridge ampWilliams 1957) and mentalglands (Rathke 1848 Winokur amp Legler 1975) are onlyfound in Gopherus and Manouria Although it has beensuggested that lsquocloacal discharge of female turtles at-tracts or stimulates males to court during the breedingseasonrsquo (Manton 1979) only one glandular tissue hasbeen described from this region (in Clemmysmarmoratus Disselhorst 1904 Whiting 1969) None ofthese glands has been identified in Dipsochleys and thelsquoscent-glandrsquo described by Owen (1866) in a lsquoTestudoindica of two feet longrsquo could not be located by dissec-tion (Gerlach 2004) and appears to be the mental glandof a Gopherus specimen and not a gland of any of thegiant tortoise species frequently referred to lsquoT indicarsquo inthe 19th century

In the case of Dipsochelys the contact between thebuccal region and the olfactory region provided by theducts between the tuberculum palatinum and the medialnasal gland means that the vomeronasal organ closelyresembles the Jacobsonrsquos organ of squamates and mam-

mals The lack of previous reports of such organs inchelonians may be due to the scarcity of dissections ofthis region in many chelonians A review of the litera-ture and of skull material identifies one additionaltaxon with a structure resembling a Jacobsonrsquos organthe leatherback turtle Dermochelys coriacea possessesa direct connection between the intermediate nasal re-gion (lined with vomeronasal epithelium Parsons1970) and buccal cavities through the foraminapraepalatina a connection figured as long ago as 1912(Nick 1912) This connection differs from that foundin Dipsochleys in that there is a single opening into thebuccal cavity this is through an opening between thepremaxillae (Fig 4) this may be due to modificationfrom a common arrangement reflecting structural dif-ferences in the rostral region of these species As withDipsochelys the duct into the buccal cavity lies next toan area of loose connective tissue resembling the tuber-culum palatinum The function of this tissue remainsobscure in Dipsochelys it could act as a pad of tissuethat would be pressed against the ducts into the medialnasal gland during chewing effectively closing themand preventing food passing into the gland InDermochelys it appears to be positioned too farposteriorly for such a function Similarly in Emyswhere the tuberculum palatinum was first described(Bojanus 1819-21) no connection between the buccaland nasal cavities has been reported The vomeronasalorgan in Dermochelys may be associated with the loca-tion of natal nesting beaches rather than socialinteractions as in Dipsochelys In this case a buccalconnection would facilitate sensory detection under-water without flooding the nasal cavity Other marineturtles with similar homing behaviours may also havewell developed vomeronasal organs although the possi-bility of buccal connections is very limited due to theextensive development of the secondary palateThesefindings in Dipsochelys and the identification of similarstructures in Dermochelys demonstrates that much re-mains to be discovered in the sensory capabilities ofchelonians Although there have been detailed investi-gations of the anatomy and neurobiology of olfaction insome freshwater taxa (eg Geoclemys reevesiiGraziadei amp Tucker 1970 Taniguchi et al 19951996 Sternotherus odoratus Murphy et al 2001Fadool et al 2001) the Chelonia are an ecologicallydiverse group and there is a need for more through ex-amination of the histology and function of this region

ACKNOWLEDGEMENTS

I am grateful to E N Arnold and S Chapman forenabling me to examine material at the British Museum(Natural History) and to R Gerlach for careful preser-vation of the Dipsochelys hololissa embryos

REFERENCES

Arnold E N (1979) Indian Ocean giant tortoises theirsystematics and island adaptations PhilosophicalTransactions of the Royal Society of London B 286127-145

DIPSOCHELYS TORTOISE NASAL STRUCTURES 19

Bellairs A drsquoA amp Kamal A M (1981) The chondrocra-nium and the development of the skull in recentreptiles In Biology of the Reptilia Vol 11 1-263Gans C (Ed) London Academic Press

Bojanus L H (1819-21) Anatome TestudinisEuropeaeae Reptinted 1970 SSAR Facsimile Re-prints in Herpetology Athens (Ohio) Society for theStudy of Amphibians and Reptiles

Bour R (1982) Contribution agrave la connaissance desTortues terrestres des Seychelles deacutefinition du genreendeacutemique et description drsquoune espegravece nouvelleprobablement originaire des icircles granitiques et au bordde lrsquoextinction Comptes Rendus Hebdomadaires desSeacuteances de lrsquoAcadeacutemie des Sciences Paris 295 117-122

Camp C L (1916) Notes on the local distribution andhabits of the amphibians and reptiles of south-easternCalifornia University of California Publications inZoology 12 503-544

Carpenter C C amp Ferguson G W (1977) Variation andevolution of stereotyped behaviour in reptiles In TheBiology of the Reptilia Vol 7 335-554 Gans C(Ed) London Academic Press

Disselhorst R (1904) Auffuumlhrapparat und An-hangsdruumlsen der maumlnnlichen Geschlechtorgane InLehrbuch der vergleichende mikroskopischen Anato-mie der Wirbeltiere Vol 4 6-89 Opel A (Ed) JenaGustav Fisher

Doslashving K B amp Trotier D (1998) Structure andfunction of the vomeronasal organ Journal ofExperimental Biology 201 2913-2925

Fadool D A Person D J amp Murphy F A (2000)Sexual dimorphism and developmental expression ofsignal transduction machinery in the vomeronasalorgan Chemical Senses 25 677

Fritsch A (1870) Zur Anatomie der Elephanten-Schild-kroumlte (Testudo elephantina) Abhandlungen derKoumlniglich Boumlhmischen Gesellschaft der Wissenschaf-ten Anatomie (6) 4 un-numbered

Gauthier J Kluge A G amp Rowe T (1988) Amniotephylogeny and the importance of fossils Cladistics 4105-209

Gerlach J (2001) Tortoise phylogeny and the Geoche-lone problem Phelsuma 9A 1-64

Gerlach J (2004) Giant Tortoises of the Indian OceanFrankfurt Chimaira

Gerlach J amp Canning L (1998) Taxonomy of IndianOcean giant tortoises (Dipsochelys) ChelonianConservation amp Biology 3 3-19

Graziadei P P C amp Tucker D (1970) Vomeronasalreceptors in turtles Zoologische Zellforschung 105498-514

Legler J M (1960) Natural history of the ornate boxturtle Terrapene ornata ornata Agassiz Publicationof the Museum of Natural History University ofKansas 11 527-699

Loveridge A amp Williams E E (1957) Revision of theAfrican tortoises and turtles of the suborderCryptodira Bulletin of the Museum of ComparativeZoology Harvard 115 163-557

J GERLACH

Manton M L (1979) Olfaction and behaviour InTurtles Perspectives and Research 289-304 HarlessM amp Marlock H (Eds) New York J Wiley amp Sons

Murphy F A Tucker K amp Fadool D A (2001) Sexualdimorphism and developmental expression of signal-transduction machinery in the vomeronasal organJournal of Comparative Neurology 432 61-74

Nick L (1912) Das Kopfskelet von Dermochelyscoriacea L Zoologische Jahrbuumlcher Abteilung fuumlrAnatomie und Ontogenie der Tiere 33 1-238

Owen R (1866) Anatomy of vertebrates p 562London Longmans Green and Co

Palkovacs E P Gerlach J amp Caccone A (2002) Theevolutionary origin of Indian Ocean tortoises(Dipsochleys) Molecular Phylogenetics and Evolution24 216-227

Parsons T S (1959) Nasal anatomy and phylogeny ofreptiles Evolution 13 175-187

Parsons T S (1970) The nose and Jacobsonrsquos organ InThe Biology of the Reptilia Vol 2 99-191 Gans C(Ed) London Academic Press

Rasmussen L E L amp Hultgren B (1990) Gross andmicroscopical anatomy of the vomeronasal organ in theAsian elephant (Elephas maximus) In ChemicalSignals in Vertebrates Vol 5 154-161 MacDonaldD W Muumlller-Schwarze D amp Natynczuk S E (Eds)Oxford Oxford University Press

Rathke H (1848) Uumlber die Entwicklung derSchildkroumlten Braunschweig FVeiweg

Saito K Shji T Uchida I amp Ueda H (2000)Structure of the olfactory and vomeronasal epithelia inthe loggerhead turtle Caretta caretta FisheriesScience 66 409-411

Seydel O (1895) Uumlber die Nasenhoumlhle und dasJacobsonsche Organ der Amphibien und ReptilienMorphologische Jahrbuumlcher 23 1-53

Taniguchi M Kashiwayanagi M amp Kurihara K (1995)Intracellular injection of inositol 145-triphosphateincreases a conductance in membranes of turtlevomeronasal receptor neurons in the slice preparationNeuroscience Letters 188 5-8

Taniguchi M Kashiwayanagi M amp Kurihara K (1996)Intracellular dialysis of cyclic nucleotides inducesinward currents in turtle vomeronasal receptorneurons Chemical Senses 25 67-76

Tucker D (1963) Olfactory vomeronasal and trigeminalreceptor responses to odorants In Olfaction andTaste pp 45-70 Zotterman Y (Ed) OxfordPergamon Press

Whiting A M(1969) Squamate Cloacal Glands Mor-phology histology and Histochemistry UnpublishedPhD Thesis University Park Pennsylvania State Uni-versity

Winokur R M Legler J M (1975) Chelonian mentalglands Journal of Morphology 147 275-291

Accepted 271103

20