STRUCTURE AND FUNCTION OF THE TOOTH PLATES OF THE DEVONIAN LUNGFISH DIPTERUS VALENCIENNESI FROM CAITHNESS AND THE ORKNEY ISLANDS

2006·10.5 MB·English

by  J A N L De Blaauwen

Recordsofthe WesternAustralian Museum23: 91-113(2005).
Structure and function of the tooth plates of the Devonian lungfish
Dipterus valenciennesi from Caithness and the Orkney Islands
JanL. denBlaauwen^, RichardE.Barwick^andKentonS.W.CampbelF
'SwammerdamInstituteforLifeSciences,UniversityofAmsterdam,Kruislaan406, 10985m,Amsterdam,
TheNetherlands,[email protected]
^SchoolofEarthandMarineSciences,AustralianNationalUniversity,Canberra,ACT0200,Australia,
[email protected],[email protected]
Abstract-TheteethoftheMiddleDevonianDipnoanDipterusvalenciennesi
are described from new material from Caithness and the Orkney Islands,
Scotland.ThebiostratigraphyoftheOldRedSandstoneinthesetwoareas is
described on thebasisofnew information.Thepallialdentineis madeupof
groups of hard clusters of material. The core dentine in the tooth plates is
nowunderstood intermsofthedevelopmentofindividualelementsmaking
up the structure of the dentine. The first deposited material is interstitial
dentine, and the second is transparent dentine which is deposited from the
pulp canals against the interstitial dentine. All the core dentine is perforate.
Denteons continue to the tip of the tooth, and dentine tubules run from the
pulp canals through the transparent dentine to the pallial dentine. The
structure is not thatof petrodentine. The difficulties ofusing living material
for the understanding of dentine in remote structures in time are outlined.
Therelationshipsoforganismsafterthedevelopmentofnewpalatalbitingin
gnathostomesisdiscussed.
INTRODUCTION Following White (1965) we consider Dipterus
DipterusvalenciennesiSedgwickand Murchison, valenciennesiasavalidname.
1829 from the Middle Old Red Sandstone of
Scotland was studied by White (1965). References STRATIGRAPHY
to previous work can be obtained from his paper.
Later work by Schultze (1975) and Ahlberg and A stratigraphic table showing the distribution of
Trewin(1995)isavailable. the Middle Old Red Sandstone is attached (Figure
The solid-snouted, cosmine-coated specimens 1)-
from the Thurso Flagstones, described by Agassiz D. valenciennesi is well known from Eifelian or
in 1844 as Polyphractusplatycephalus, was one of Givetian cyclic sequences in the Orcadian Basin.
the reasons for Pander (1858) and Watson and Day Thespeciesiscommoninthefish-bearinglaminites
(1916) to use the specific name Dipterus of Achanarras (Forster-Cooper 1937; Trewin 1986)
platycephalus. More recently Westoll (1949) and the equivalent laminites on Orkney, the
described theskull roofpatternsofspecimensfrom Sandwick fishbed (Trewin 1976). These laminites
Banniskirk (Caithness) and found them sufficiently were deposited in deep water in an extended lake
aberrant to separate them into a new species, in the Orcadian Basin. Small specimens lack
Dipterus braebypygopterus, and he revived cosmine on the scales and dermal plates, but
Agassiz's specific nameplatycephalus for all other specimens20cmoroverinlength,havecosmineon
Scottish specimens of Dipterus. He advocated the partofthescalesontheventralsideandpartofthe
abandonment of the name Dipterus valenciennesi. dermal bones. Fully grown ones have a complete
White (1965) concluded that the braebypygopterus cosminecover. Dipterusis also found inthecalcitic
pattern was a variation on other specimens that nodules from the Moray Firth area where the
occurred at Banniskirk and elsewhere. The only sedimentsshow fluvial domination in a southward
other genus comparable with Dipterus is a new extension of the Achanarras fishbed (Trewin and
genus to be described by Newman and den Thirlwall2002).
Blaauwen from the Middle Old Red Sandstone of Research in museum collections in theU.K. has
Caithness and Sutherland, formerly included in shown that it is not possible to identify D.
either Pentlandia or Dipterus. It has a different valenciennesi positively in sediments older than
postcranial morphology and skull-roof pattern. the Achanarras-Sandwick fishbed horizon.
92 ].L.denBlaauwen,R.E.Barwick,K.S.W.Campbell
CAITHNESS/ Fauna ORKNEY Fauna
G SUTHERLAND ost—arthr—dipn. ost—arthr—dipn.
I
V
John o' Groat Eday Flags
E
A
T Subgr. -1 Ta '"]
1
I
A Mey Subgr. Rousay Flags
N 1
Mm. Mm.
1 1
Latheron Subgr./ Tp. 1 UpperStromness Tp 1
"
Ham-Scarfsk.Subg. Flags
E
1
I Dt. Gm Dt.
F Achanarras Horizon Gm. Sandwick Fishbed
E 1
1
L
Robbery Head Oni. Dv. Lower Stromness Ga.=
I Om. Dv.
A Subgr. Flags
N Pt
Lybster Subgr. Cc. ost. Cc.
Tni.
Figure1 Biostratigraphic table of Caithness, Sutherland and Orkney indicating faunal elements which are of
importance for correlation. Bars indicate the approximate range. Abbrcv.: arthr. arthrodire; Cc. Coccosteus
cuspidatus; dipn. dipnoan; Dt. Dickosteus threiplandi; Dv. Dipterus valenciennesi; Ga. Gvroptychius
agassizi;Gm. Gvroptychiusmilleri; Mm. Millerosteusminor, Pm. Pentlandiamacroptera; Ps. New Dipnoan
Genus; Om. Osteolepismacrolepidotus', Osteolepispanderi; ost. osteolepid;Ta. Tristichopterusalatus; Tm.
Thursiusmacrolepidotus',Wf. IVafsonosfeus.
Specimens from the Lybster Subgroup which the dried up lake floors (Astin and Rogers 1991;
belong to the osteolepid Thursius Rogers and Astin 1991). Sediments indicatingvery
macrolepidotus are often misidentified as D. shallow lake deposits produce only disarticulated
valenciennesi. The specimens from the Robbery fish remains, sometimes locally concentrated in
Head Subgroup include a new genus being 'bonebeds'.
described by Newman and den Blaauwen, and From extensive field work and mapping of fish
thosefrom theJohn o' GroatSubgroup belongto remains a biostratigraphic pattern has been
Pentlandiamacroptera. distilled. Naturally there are some difficulties in
The lacustrine sediments above the Achanarras- correlationoffresh wafersequencesin theOrcadian
Sandwick fishbed show climatically controlled Basin, where drying of parts of the lake and the
cyclesresultingfrom long-term riseand falloflake prevalenceof desiccation features occur in contrast
levels in an enclosed basin (Crampton and withwidespreadlakeextensionconditionsinwhich
Carruthers 1914; Donovan et al. 1974; Donovan laminites were deposited. Details of the issues will
1980;TrewinandThirlwall2002).Thesebedsshow be discussed elsewherebydenBlaauwen etal.,but
playa-lake conditions, though in places the water from the point of view of the dipnoans, D.
may have been sufficiently deep to allow valenciennesi has been identified from the base of
articulated fish skeletons to accumulate. The the Achanarras Horizon to the top of the Mey
cyclicity of the sediments probably results from Subgroup on the mainland, and the equivalent
Milankovitch periodicities. Some of the sediments Sandwick fishbed to the top of theRousay Flags in
deposited in shallow water have polygonal Orkney.
mudcracksand shrinkagecracks. Many secliments Specimensused inthisstudycomefrom theunits
show structures the shape of gypsum crystals or indicated intheFigure1, abovetheAchanarrasand
pseudomorphs showing gypsum crystal solution. Sandwick fishbeds. They are common in the
These sedimentary structures are often preserved Latheron Subgroup and the Mey Subgroup in
bysandinfill, introducedbywind transportacross Caithness and in the Upper Stromness Flags and
ToothplatesofDevonianlungfish Dipterus 93
the Rousay Flags of Orkney. Also specimens from and part of the original median row resorbed. The
Tynet Burn, one of the fishbeds from the nodule same specimen shows gaps for the occlusion with
localitiesintheMorayFirtharea,havebeenstudied. themandibularteeth. Irregularityofrowsisshown
Specimens of D. valenciennesi sampled in byG2004.10.5 which leavesspaces forthe insertion
sediments indicating shallow lake conditions, are ofnew rows on the mediolateral parts ofthe teeth.
disarticulated and are mostly mature or even fully Obviously the new rows were formed wherever a
grown. Most specimens possess a well developed space exists because of irregular growth in old
cosminecoating. rows, and we conclude that genetic control on the
precise position of new teeth was limited. New
rows occupy only a small part of the length of the
SPECIMENSEXAMINED head.
All the specimens examined have come from The parasphenoid is well defined, is up to three
Caithness and the Orkneys. They have been taken times thelengthofthetooth plates, andhasa well-
from the collections of den Blaauwen, Michael defined buccohyphophysial foramen. The nasal
Newman and Jack Saxon, and they have been capsules occupy about two thirds of the length of
placed in the National Museum ofScotland (NMS) the plates. Most of the posterior buccal cavity is
collections.Thenewnumbersareasfollows: thereforenotroofedbythedentalplates.This point
G2004.10.1 From Clardon Haven, Caithness. is emphasized bythemandiblein which the dental
Latheron Subgroup. Posterior end eroded in situ. plates are relatively small in relation to the whole
Palataltoothplateswelldeveloped. structure.
G2004.10.2 From Clardon Haven, Caithness.
Latheron Subgroup. Palate sectioned to show the StructureoftheMandible
'cosmine'betweentheteeth. The best specimens we have are of individuals
G2004.10.3 From Clardon Haven, Caithness. which are a little above half grown, and show
LatheronSubgroup.Mandiblewithtoothplates. features which we consider significant. The tooth
G2004.10.4 From Thurso East, (the slates), platesare0.33-0.40thelengthofthejaw(Figures3
Caithness. Latheron Subgroup. Mandible with left A,B), and the distance between the two tooth
toothplatelost. plates is large in comparison with the Early
G2004.10.5 From Thurso East, Caithness. Latheron Devonian genera Dipnorhynchus and
Subgroup. Right palatal tooth plate. Sectioned Speonesydrion (Campbell and Barwick 1984). The
horizontally,andvertically. ratioofthemedian lengthtothetotal lengthofthe
G2004.10.6 From Clardon Haven, Caithness. mandible, is only about one third. Note also that
LatheronSubgroup.Pectoralgirdle. the mandibular dental plates have a short median
G2004. 10.7 From Thurso East, Caithness, Latheron length in comparison with the posterior length.
Subgroup. This is different from the shape of the palatal
G2004.10.8 From Clardon Haven, Caithness, dental plates, suggesting that the contactbetween
LatheronSubgroup. the mandibular and palatal plates was not one-to-
G2004.10.9 From Buckquoy west of Aikerness, one. This interpretation is supported by the fact
MainlandOrkney,RousayFlags. that the inner face of the mandibular plate is
G2004.10.10Sameas2004.10.9. turned ventrally, and could not have met the
G2004.10.il From Thurso East, Caithness, Latheron palatal plate on full closure of the jaw. This is
Subgroup. standard for the assembled Late Devonian species
G2004.10.12 to G2004.10.16 From Clardon Haven, (Barwick and Campbell 1996; Campbell and
Caithness, LatheronSubgroup. Barwick 1998).
A second point is that the anterior gap between
the two mandibular plates is very large, and the
GROSSFEATURESOFTHEDENTALSYSTEM unencumbered space for the tongue pad would be
not only widebutalso long and deep.The point of
ThePalatalToothPlates originofthetoothrowshavebeen resorbed,andon
New rows of teeth are introduced between the G2004.10.3 restorative dentine has been added to
anterior sets of rows as spaces become available the anteromedian side ofthe tooth plate.Thetooth
(Figures2, 8A). Somespecimensshow symmetrical plates of Dipterus platycephalus from a Scottish
insertionsofthetwoplatesoftheonespecimen,but specimen in the Manchester Museum, and figured
others do not. The specimen figured by White byWatsonandGill (1923,figure34),alsoshowsthe
(1965, plate 1, figure 1) shows small teeth inserted reduced tooth plates similar to those described
between the first and second rows, and in places above. The cavities for the cartilage forming the
these teeth are more closely spaced. Specimen articulationwith thequadratearedeepand slightly
G2004.10.8(Figure2A) isremarkablein thatithasa doubled (Figure 3C), thus limiting the lateral
new irregularrow ofteeth anteromedially inserted. movementofthemandible.
94 J.L.denBlaauwen,R.E.Barwick,K.S.W.Campbell
10mm
Figure2 A, palateofG4004.10.8. Specimen antero-posteriorlycompressed, 'cosminc' removed;boneon theposterior
ofthetooth plates. B,G2004.10.], 'cosmine' on the palate; first rowofteeth partly covered by'cosmine'. C,
palatal view ofthespecimenG2004.10.2; 'cosmine'scctioned from right palatal tooth plate. D, thespecimen
fromwhichFigure2Bwasprepared;squashedantero-posteriorly.Scale=10mm.
ToothplatesofDevonianlungfishDipterus 95
the reality of Westoll lines will be considered later
inthispaper.Thepresenceofenamelonthesurface
of this tissue is the most important point to be
consideredhere.
SignificanceofTheseGrossFeatures
The functional significance of these features is
largely related to air breathing. We consider these
points under the following headings; extant air
breathers; palatal plates and parasphenoid; tongue
padspace;andbrachiallaminae
Extantairbreathers
Extant dipnoans fall into two groups -
Lepidosiren and Protopteruswhich areobligate air
breathers, and Neoceratoduswhich is a facultative
airbreather.Thesetwogroupshavebeendiscussed
by Thomson (1969), who has also compared them
withtheMiddleDevonianDipterus.
In Lepidosiren and Protopterus (Bishop and
Foxon 1968) the tongue fits between the pterygoid
tooth plates and makes a closing valve when air is
depressed into the lungs. This is done by the
anterior rotation of both the ceratohyal and the
pectoral girdles. The air is stored in the
parabranchial cavity partly roofed by the elongate
parasphenoid, the teeth are small with respect to
thesizeoftheheadand theyareseparated to leave
a space for thetonguetocloseoffthebuccal cavity
when air is forced into the lungs. Associated with
this procedure is the increase in spacebetw^een the
mandibular tooth plates which allows the tongue
pad to expand forwards.Theventral surface ofthe
head is also able to expand the buccal cavity to
permit more space for the retention of air.
Neoceratodushasadifferentarrangementbasedon
an opercular pump, and Thomson (1969, figure 5)
showsthemovementoftheopercularfold duringa
breathing phase. In addition Neoceratodus has a
massive ceratohyal which takes part in breathing
Figure3 A-C, two small mandibles G2004.10.3 and
G2004.10.4; A and B are dorsal views show- movements.
ingtooth-plates.Cisamoreposteriorviewof
B showing the articulation cavities and the PalatalPlatesandParasphenoid
positionoftheadductorfossae. D, G2004.10.7 The palatal plates in Dipterus are situated well
showingbothtoothplates. anterior in the mouth, and they are well separated
from each other. In comparison with such Early
Devonian genera as Dipnorhynchus or the Late
Devonian Chirodipterus the plates are very short.
'Cosmine'ontheMedialPartsofthePalatal
The parasphenoid has a long posterior projection,
Tooth
White (1965, plate2) and Denison (1974, figure4) aptnedryegxotiednsd.s bBaoctkhotvheersea fleoantgurdeisstamnackeebefhoirndlotnhge
figured a thin layer of tissue occupying the space
between thetwo palatal tooth plates. Itwas termed orobranchialandparabranchialcavities.
'cosmine' by both the above authors, because this
layer has a shiny surface, it often contains a large SpacefortheTonguePad
number of pores, and superficially it has a The gap left for the tongue between the
resemblance to cosmine. But pores are not always prearticulars is large and deep in comparison with
present, and where pores are present, no pore that of Early Devonian genera Dipnorhynchus and
canals can be found beneath them. This point and Speonesydrion. The gap between the palatal tooth
96 J.L.denBlaauwen,R.E.Barwick,K.S.W.Campbell
plates is covered with 'cosmine', and this shows morphological features which would indicate that
that the large tongue pad had ample room to lie theywereairbreathers.
betweentheseplateswhenthemouthisclosed.The
enamel surface on the 'cosmine' shows that the
epidermis was in contact with this surface. This is DESCRIBEDHISTOLOGYOFTHETOOTH
the ideal arrangement for the stop valve when the PLATES
air was being forced into the lungs from the ThehistologicalstructureofD. valenciennesiwas
orobranchialandparabranchialcavities. not described from Scottish material until recently,
because like all the bones at the fossiliferous
PectoralGirdleofD.valenciennesi localities, the teeth were deeply stained by organic
We have access to several specimens of D. carbon. White (1966, plate 1, figure 2) published a
valenciennesiwhich arebetter preserved than any figureofasection ofa tooth plate inwhich theend
specimens previously described. The four tooth was sectioned medially and showed a
specimens are now labeled G2004.10.6, translucent core. The figured adjacent teeth
G2004.10.13,G2004.10.14andG2004.10.15. Wewill apparently showed a bony core, presumably
describe this material in a separate paper. The because they were from marginal sections of the
pattern of the branchial laminae and the teeth. Denison (1974: 39) commented on these
scapulocoracoid are very similar to those on structures,buthisworkhasnotbeenconfirmed.
Chirodipterus australis (Campbell and Barwick, Smith (1984) described teeth from the specimens
1987)a marineform from theLateDevonianGogo described by White (BMNH P44691), and later
Formation, Western Australia. The branchial another specimen, BMNH P53537, from Caithness
laminae would have operated in the same way in (Smith 1989). These papers give no details of the
thetwospecies. pallial dentine,and their structureofthetooth core
is obscure. Comments will be made on this work
Summary laterinthispaper.
Dipterus has a large opercular plate as well as Kemp (2001) in her paper on petrodentine does
smallsuboperculars,themovementofwhichwould not describe the histological structure of D.
haveproducedalargeexpansionandcontractionof valenciennesi, and most ancient forms dealt with
theparabranchial chamberasdetailed byThomson are of Carboniferous age. Because of this lack of
(1969). Wenotethat Neoceratodususesa opercular direct analysis of Dipterus valenciennesi tooth
parabranchial pump when breathing air, and uses plates, the discovery of well-preserved specimens
the very large ceratohyals to push the air from the nowgivesusanopportunitytoplacetheseplatesin
orobranchial and parabranchial chambers into the the primitive position which their stratigraphic
lung. On the other hand, thebranchial laminae are positionaccordsthem.
so large and the ceratohyal so short, that Dipterus
could not have used the methods of breathing
adopted by Lepidosiren and Protopterus. We have INTERPRETATION OFDENTINEINNEW
concluded that Dipterus was a facultative air MATERIAL
breather,thoughthestructurescouldnothavebeen
asefficientasthoseofNeoceratodus. There is nothing more contentious than the
WenotethatSchultzeand Chorn (1997) consider terminology of dentine in dipnoan teeth. For
thatlungswereafeatureofprimitiveosteichthyans, present purposes Smith (1984, 1985, Table 1) has
provided the basis on which subsequent work has
quoting the fact that lungs are present in primitive
developed.Furtherworkon thistopiccanbe found
actinopterygians (e.g., Polypterus), actinistians,
lungfish, and tetrapods. Campbell and Barwick in Lison(1941), Barwicketal. (1997),Campbell and
(1999: 137-138) have commented on their Smith (1987), Lund et al. (1992), Kemp (2001) and
arguments, and these will not be repeated here. Reiszetal. (2004).
Incidentally they offer no mechanism supporting
theirviews.Neoceratodusisalsogillbreathing, and VerticalSectionsofTeeth
spendsmostofitslifesubmerged.Comparisonwith The considerable advantage we have is the
Dipterus valenciennesisuggests that this Devonian availabilityofgrowthstagesoftheteeth.Growthof
form alsohad thecapacity tousegill respiration as the layers in the dentine can be outlined by a
wellasaerialrespiration. number of specimens. In the first instance we
Our arguments are based on morphology of describeanumberofteethfromasinglesection.
Dipterus and the extant dipnoans, and not on
cladistics or the range of air breathing in some Sectionsthroughsedhnentwithplacodermplates
extant animals. Contrary to the argument of Some specimens have structures sufficiently well
Schultze and Chorn (1997), we still maintain the preserved to show histological detail throughout
marine Devonian dipnoans lacked the theteeth.SectionG2004.10.9showsthebestvertical
ToothplatesofDevonianlungfishDipterus 97
towardsthebase.Theedgescontainsomebranched
tubules which arise directly from the pulp canals,
and these areeither simpleor branched. At higher
magnifications, the tubules subdivide extensively
towards their outer edges (Figure 5A) making a
meshwork-like pattern. In the lower half of the
tooth the pallial dentine shows very fine tubules,
butatthebaseofthetooth,thepallialdentineturns
inwards(Figure5B)andhascrenellateddendriform
pattern. This is best known as pedestal dentine.
Pallial dentine is well shown on the lateral tooth
and the tangential tooth (Figure 6). It forms a dark
layerwhich isalsopenetratedbytubules. In places
the boundary between the pallial dentine and the
core dentine is sharp, but in other areas the
boundaryisgradational.
On G2004.10.9, interstitial dentine is clearly
exposed (Figures 4, 6). Dark columns of interstitial
dentine extend into the basal pulp cavity where
their outlines are clear. In the basal pulp cavity at
highmagnification theinterstitialdentineshowsan
open-work structure, which is seen on all three
teeth (Figures 5B; 6B; 14E). The implication is that
the growing edge of the material in the basal pulp
cavity is made of crenellated dendriform material,
which has the same appearance as the pedestal
dentine, and laterally this material joins the pallial
dentine (Figure 5B). In the central part ofFigure 4,
and the distal parts ofFigures 6A,C, the interstitial
dentinebecomes vaguely outlined, notbecause the
section is marginal to the dentine layer but the
dentine is partly transformed into translucent
dentine.
The marginal tooth is very informative with
respect to the formation of the interstitial dentine.
Figure4 G2004.10.9. Vertical section in single AsshownonFigure6A, inthecoreofthe tooththe
polarized light; specimen was incompletely interstitial dentine becomes rough in its outline
grown; enamel is largely destroyed; towards the basal pulp cavity. On the left
interstitial dentinegrey in colour; translucent ventrolateral margin the interstitial dentine grades
dentinearoundpulpcanals. into the pallial dentine and ventrally into the
pedestal dentine as shown on Figure 6B. The
toothsections wehaveseen (Figures4-6; 14E). The tangential tooth (Figure 6C) also shows the
largest tooth in the section has a large basal pulp interstitial dentine extending to the basal pulp
cavity, and the smaller teeth are in process of cavity.
formation. These show the development of the The translucent columns are the most striking
histologicalstructures. part of the core, and show up in plain light as a
Thelargesttoothhaslostitsapex,butonthesame clear translucent structure. Near the crest of the
sectiontwoothersmallteeth,oneatthelateraledge largetooththestructureisclear(Figure5A)andthe
of the plate (referred to as the lateral tooth below) translucent layer carries many tubules which are
and the other being cut tangentially to the axis of derived from the pulp canals, and in places these
thetooth (referred toasthetangential toothbelow. run through the layer into the pallial dentine. This
Figures 6; 14E). The enamel is present around the is in an early stage of the tooth formation. In the
marginofthelateraltooth,butitispartlydestroyed central part of the tooth, the fine structure of the
by decomposition on all sides of the larger tooth. translucent layers is not clear, but it does contain
The core dentine consists of two different types of small openings and vague lines. The mode of
structure, clear translucent columns, and formation of this tissue is clearly demonstrated by
interstitialdentinecolumns(Figure14E). this section (Figures 4; 5B; 14E). It was deposited
As Figure 4 shows, the pallial dentine is thickest against the interstitial dentine by cells in the pulp
towards the apex but fades away somewhat canals. Thebase ofthe large tooth shows a layer of
98 J.L.denBlaauwen,R.E. Barwick,K.S.W.Campbell
pulpcanals
pallial
dentine interstitial
dentine
tubules
translucent
dentine
translucent
dentine
interstitial
dentine
crenellated
dendriform
dentine
pedestal
dentine
Figxu-e5 A, apex of Figure 4; tubules penetrating the translucent dentine and connecting with the pallial dentine;
translucentdentinehasreplacedmostoftheinterstitialdentine.B,enlargementofthebottomrightofFigure
4; interstitialdentinearoundthepulp canalsandtranslucentdentinedeposited fromthepulp canalsonthe
interstitial dentine;crenellatededgeofthepallialdentinejoined by acolumnofverticalinterstitialdentine,
andbasallyjoiningthepedestaldentine.
ToothplatesofDevonianlungfishDipterus 99
Figure6 G2004.10.9asonFigure14E.A,thelateraltoothrotated;interstitialdentinerunsfrompulptopallialdentine;
pallial dentinewithtubules;translucentdentinearound pulp canals. B,bottom leftofFigure6A with pallial
dentinejoiningwiththepedestal dentine.C,thetangentialtooth. Figure14E;contactbetweeninterstitialand
translucentdentineintergrading;translucentdentineoftenbulbous.
100 J.L.denBlaauwen,R.E.Barwick,K.S.W.Campbell
10mm
dentine
mm
0.1mm-- •interstitwi 0.1
.*j .'I .V i
dentinl
carbonate
gulp
I in pulp
canals
' canals.
V
w.
Figure7 A,G2004.10.5C,slightlyetched inaceticacid;coreofeachtoothextendsintothebasalbone.BandC,optical
sections cut from the opposite face of Figure 7A; baseof pulp canals with CaCOj; interstitial dentine near
margins but replaced medially by translucent dentine. D, enlargement of the area outlined in A; pallial
dentineonleftjoinedwithpedestaldentineofrighttooth.