Phylogenetic status of the Irrawaddy Dolphin Orcaella brevirostris (Owen in Gray) : a cladistic analysis

64 Pages·1996·27.1 MB·

by  Peter W Arnold

PHYLOGENETIC STATUS OFTHEIRRAWADDY DOLPHIN ORCAELLA
BREV1ROSTR1S(OWEN IN GRAY): A CLADISTIC ANALYSIS
PETERW. ARNOLD ANDGEORGEE. HEINSOHN
Arnold, P.W. &Heinsohn, G.E. 199607 20: Phylogcnetic status ofthe Irrawaddy Dolphin
Orcaella brevirostris (Owen in Gray): a cladistic analysis. Memoirs ofthe Queensland
Museum39(2): 141-204. Brisbane. ISSN0079-8835.
Examination ofOrcaella brevirostris from Queensland has provided new information on
colourpattern,externalmorphometries,skull morphology,variationinthetympanoperiotic
bones and postcranial skeleton. Facial anatomy isdescribed forthe firsttime,
Cladisticanalyses,incorporatingthenewinformation,investigatedthephylogeneticposition
ofOrcaella. Our results provide no support for the separation ofbeluga and narwhal into
twodifferentfamilies(Kasuya,1973)norfortheproposalthatOrcaellaandDelphinapterus
areclosely related (Kasuya,1973; Pilleri elal.,1989).Thepositionofdelphinoid families in
our cladograms is consistent with previous synoptic classifications (Slijper,1962, fig.36;
Heyning,1989; Barnes,1990). Ourresultsofferno support forclassifications which widely
separatedelphinids and phocoenids(Shimura& Numachi,1987; Lintet al., 1990; Pilleri et
al.,1989).
We suggest that Orcaella is a delphinid sensu law. Comparison ofcharacters in the two
nearestoutgroups(phocoenidsandmonodontids)suggestOrcaella(andother'blunt-headed'
genera)representthemostprimitive Delphinidae. However, wecannotruleoutthealterna-
tive that extensive convergence occurred. Extensive neoteny of the skull in Orcaella
suggests one means by which the many apparently primitive features could occur.
Cetacea, Orcaella,perioticbone, tympanicbone,facialanatomy, neoteny, cladistics.
Peter W. Arnold, Museum of Tropical Queensland, 70-84 Flinders Street, Townsville,
Queensland4810; GeorgeE. Heinsohn, DepartmentofZoology, JamesCookUniversityof
North Queensland, Townsville, Queensland4811; received8November1995.
The phylogenetic status of the Irrawaddy dol- anatomicalsystem(Fraser&Purves,1962;Mead,
phin Orcaella brevirostris (Owen in Gray,1866) 1975; Kasuya,1973; Pilleri et al.,1989) and have
remains in doubt (Marsh et al.,1989). At least produced partially conflicting classifications,
eight taxonomic hypotheses are implied in Only Heyning (1989) used computerized
various proposed classifications (Fig.l). Orcael- phylogenetic analysis on a range of characters.
la was initially classified as a porpoise in Although he argued for a phocoenid-delphinid
Phocoena. It has also been placed in a more clade, his cladograms left relationships of the
strictly defined Delphinidae (dolphins), Del- Monodontidae, Phocoenidae and Delphinidae
phinapteridae (with beluga Delphinapterus unresolved. Gretarsdottir& Arnason (1992) also
leucas (Pallas,1776)), Monodontidae (with left the relationship of these 3 families un-
beluga and narwhal Monodon monoceros Lin- resolved. deMuizon (1988)examinedextantand
naeus,1758) orin the monotypic Orcellidae. fossil taxa, using acomprehensive rangeofchar-
ThispaperaddressesclassificationofOrcw//^. acters to produce 4 arrangements of the
We re-describe the skull, emphasizing neotenic Monodontidae, Phocoenidae & Albireonidae,
characterswhichhaveconfoundedpreviouscom- Kentriodontidae and Delphinidae, which were
We
parisons between Orcaella and other odon- still only a subset ofthe possibilities. present
tocetes. We re-examine the tympanoperiotic a cladistic analysis of the Monodontidae,
boneswhichwerepoorlyknown anddescribethe Phocoenidae and Delphinidae s. I. Within this
facial anatomy which was unknown. We assess context we discuss affinities ofOrcaella.
colour patterns for possible taxonomic charac-
ters.Newdataonexternalmorphometriesandthe MATERIALS
post-cranial skeleton are presented.
Incorporating this data we evaluate characters Specimens of Orcaella were either found
that have been used in odontocete classification, stranded and dead, or recovered after drowning
Most classifications have been based on one in shark nets near Townsville. Skeletal material
142 MEMOIRS OFTHEQUEENSLANDMUSEUM
Phocoena OtherDelphinidae
Orcuella (includingDelphinapterus Phocoenidae Monodontidae Ziphiidae Physeteridae Delphinidae
Monodon)
Monodon
Delphinapterus
A
Owen, 1866
Delphinapterinae Orcaellinae £ L\meial., 1990
Ddphimpierus *Orcaella
Monodontidae Delphinidae Phocoenidae Delphinapteridae Ziphiidae Monodontidae Stenidae Phocoenidae
(Monodon)
Monodon Sousa
Delphinapterus Solatia
Stem)
p FraserandPurves. 1962
Monodontinac Delphinapterinae Orcaellinae Phocoenidae Delphinidae*
Monodon Delphinapterus & *Orcaella Monodontidae Globicephalidae
+Denebola Monodon Orcaellidae Grampidac
Delphinapterus *Orcaella Grampus
Phocoenidae Delphinidae
Monodontidae
+eilmct
* includesSlenidaeofFraser&Purves,1962
C Barnes. 1984.Gaskin. 1982,Evans.1989
Q
Nishiwaki, 1963.1966
Delphinidae Phocoenidae
Monodontidae Phocoenidae Delphinidae
Monodontidae Delphinapteridae Iniidae Pontoporidae Platanistidae Monodon *Orcaella
'OnaeSa Delphinapterus
Mpkmpiew
hllm,GihrandKraus, 1989 H Heyninu, 1989;deMuizon, 1988;GretarsdottirandArnoson. 199:
FIG. 1.TaxonomichypothesesofphylogeneticrelationshipofOrcaellatoothertoothedwhales.Aindicatesthat
OrcaellawasplacedwithinPhocoena,which wasmorebroadlydefinedthan atpresent. TheDelphinidaewas
alsomoreinclusive,containingboththebelugaDelphinapterusand narwhalMonodon. Thedashed linesin D
separatedifferentlineages as envisionedby Pilleri etal. (1989). Thetaxonomic relationships in Farederived
from the table in Fraser & Purves (1962); the most generalized taxon is Ziphiidae on the left, and increasing
specialization is inferred as one moves to the right. The dashed lines indicate a separation of taxa: the
Physeteroidea (Physeter, Kogia) and Platanistoidea (Platanisla, Inia, Ponloporia, Lipotes) were interspersed
betweentheMonodontidaeand Stenidae. Thereferences indicatedinHare only afewofthemorerecentones
supporting placementofOrcaellain the Delphinidae.
PHYLOGENY OFTHEIRRAWADDY DOLPHIN, ORCAELLA 143
is deposited in the Queensland Museum (Pater- Delphinidae
son, 1986, 1994) (QMJ or QMJM). Most are Delphinus delphis Linnaeus, 1758
currently held at the Museum of Tropical *QMJM2033, Gold Coast; *QMJM2776,
Queensland, Townsville; those held in Brisbane Moreton Bay.
are indicatedbyan asterisk. Specimenscollected Feresa attenuata Gray, 1874 *QMJM825,
MbyMJames Cook University staff are registered Kingscliff, NSW.
or CET, which numbers have been quoted Globicephala macrorhynchus Gray, 1846
in the literature; these numbers are used par- *QMJM5354; CET1001, Mackay.
ticularlywhendiscussinganatomical material. If Globicephala melas (Traill, 1809)
skeletal material from these specimens has been *QMJM4480, PointLookout; *QMJ15.2104.
MregMistaenrdedQiMnJthMe QnuuemebnesrlsanardeMliussteedubme,lobwo.thAtbh-e N.GSrtarmapdbursogkrei1s;eu*sQ(MCJuMvi3e8r.581,81M2)or*eQtMoJnMI.9542,
breviations for other collections are: CMN: Lagenodelphis hosei Fraser, 1956 *QMJM
Canadian Museum of Nature, Ottawa, Ontario, 2749,FraserI.
CNaatnuardaal;HiNsStoMryN,HH:aliNfoaxv,aN.SSc.o,tiCaanMaudsa;euUmBCo:f Lagenorhynchusacutus(Gray, 1828)NSMNH
unregistered.
Dept. Zoology, University of British Columbia, Lagenorhxnchus albirostris (Gray, 1846)
Vancouver, B.C., Canada; VA: Vancouver NSMNH
72.2.343.8.
Aquarium, Vancouver, B.C., Canada. Measure- Peponocephala electra (Gray, 846)
mentsofbelugaand narwhal areofcondylobasal *QMJM2144, Moreton I; *QMJM6577I, N.
length and are approximate. Stradbroke I; *QMJM7854; QMJM4702, Mis-
Orcaella brevirostris (Owen in Gray,1866) sion Beach; QMJM4730, Crystal Creek, N of
Queensland: QMJM4740; QMJM4735
Townsville.
(MM1004); QMJM4700(MM006): QMJM4704 Pseudorca crassidens (Owen, 846)
(MM012); QMJM4708 (MM021); QMJM4709 *QMJM14210; *QMJM937, Townsv1ille;
(MM025); QMJM4712 (MM030); QMJM4714
MM1028.
(MM032); QMJM4721 (MM 061); QMJM4725 Sousa chinensis (Osbeck, 1765) QMJM4701,
(MM081); QMJM4726 (MM082); QMJM4727 Magnetic QMJM4703, Magnetic
(MM088); MM092; MM1003; QMJM11342, QMJM47 IT;ownsville;QMJM4717,MagnetiIc;
QMJM1 1343; MM1015; MM016. I; QMJM4171,28; QMJM4731, Pallarenda,
Townsville; QMJM4737, Rowes Bay,
Phocoenidae Townsville.
Neophocaena phocaenoides (Cuvier,1829) Stenella attenuata (Gray, 1846) *QMJM6433,
Saudi Arabia: A. Preen,privatecollection. Moreton
I.
Phocoena phocoena (Linnaeus, 1758) Nova Stenella coeruleoalba (Meyen, 1833)
Scotia, Canada: NSMNH973.Z.309.1; NSMNH *QMJM3859.
unregistered, Oct. 26, 1982; NSMNH971.- Stenellalongirostris(Gray, 1828)QMJM4716,
NSMNH
Z.300.1; unregistered, Crescent Beach QMJM4718, QMJM4719, all from offMichael-
1977;NSMNH973.Z.310.1. mas Cay, nearCairns.
Tursiops truncatus (Montagu, 1821)
Monodontidae *QMJM8859;QMJM4713Juvenile,MagneLicI;
Delphinapterus leucas (Pallas,1776) Quebec, QMJM4715, Magnetic I; QMJM4724,Magnetic
Canada: Trois Pistoiles, May 1 1, 1983, 573 mm; I;MM91A,PalmI;MM1018.
DL4.85, 400 mm; DL2.86, 468 mm; Northwest
CMN METHODS
Territories,Canada: 19556,CollinsonInlet;
CMN29997, 548 mm; CMN29998-30000, Bel-
cherI,HudsonBay,505,549and552mmrespec- Colour pattern is described from photographs
tively; one unregistered. ofacaptivefromCairns(Dawbin,1972;Leather-
Monodonmonoceros(Linnaeus,1758)Canada: wood & Reeves,1983; Mitchell,1975:91 1 ); a
CMN32278-32280, Baffin I, latter 508 mm; 1.86m 9(MM334)and2.19m 9 (MM335) from
Arctic Biological Station MM65(at CMN); Cairns; a 2.15m 9 (MM30), 1.87m 5 (MM21)
Arctic Biological Station MM66, 580 mm (at and 2.2 m 9 (MM25) from near Townsville
CMN); Koluktoo Bay, Baffin I: UBC 9467, 285 (Talbot & Steene,1984; unpubl. photographs).
mm; Holman I, Northwest Territories: VA, un- Based on dentinal layers in teeth, MM25 was
registered; VA, unregistered (nodata). estimated at 9 years and MM30 an estimated 8
MEMOIRS OFTHEQUEENSLANDMUSEUM
144
FIG. 2. Colourpattern ofMM30, a2.15 m long 9 fromTownsville.
FIG. 3. Lateral colourpattern ofMM25, a 2.2 m long 9fromTownsville.
Fig4. VentralcolourpatternofMM25, a2.2 m long 9fromTownsville.
PHYLOGENY OFTHE IRRAWADDY DOLPHIN. ORCAELLA 145
years in age (Heinsohn,1979). Lengths of both In this analysis, only extant families ofodon-
animals exceeded the minimum length of con- tocetes were considered as outgroups, although
firmed sexually mature 9 9 in the Queensland character states in fossil taxa have been con-
population (Marsh et a!.,1989); MM335 was sidered in certain cases. We have not examined
pregnant. fossil material, and many features used have not
Qualitativefeaturesoftheskullwerecompared beendescribedintheliteratureavailabletous.To
with Tursiops (Rommel,1990). Standard skull include them would result in many missing
measurements are as in Perrin (1975). values, which can cause problems. The
The angle of the posterior process of the tym- Kentriodontidae, which has been considered a
panic was determined by temporarily fixing the potential sister group to delphinids, phocoenids
bulla ventral sideupwardson a desk. One armof and monodontids, cannot be clearly defined (de
acompass wasalignedalongthemeridional axis; Muizon,1988) and may be polyphyletic. de
the second arm was swung to lie over the lateral Muizon (1993) considered the peculiar
edge of the process. The angle so formed was Odobenocetopsidae the sister group to the
tracedontopaperandmeasuredwithaprotractor. Monodontidae, butitissohighly modified that it
The periotics were temporarily fixed dorsal is not relevant to ourdiscussion.
sainddetuhpe oponsitthieonsstaogfetohfeathcroemepcoouchnldeamricapreorstcuorpees PlaAlmanoinstga,exLtiapnotteos,doInmtaocaetneds,Potnhteopriovreiradaorlepchoinn-s
drawn using a camera lucida. Care was taken to sidered the closest living relatives of the
orient thebulla in the same waytoavoidparallex Monodontidae-Phocoenidae-Delphinidae (de
problems. The periotic triangle of Pilleri et al. Muizon,1988;Heyning,1989; Barnes,1990).The
(1989) was created by drawing lines between firsttwoauthorsalsodemonstratedthatPlatanis-
outlines ofthe apertures on the drawing. Angles ta is separate from the other genera; de Muizon
and lengths of sides of the triangles were deter- (1990) placed it in a separate superfamily. In the
mined from the drawings. presentcomparisons, the taxonomic status ofthe
river dolphins can be left unresolved, but
Three specimens ofOrcaella (MM333, 1.34m
Platanista was considered separately from Inia
9 from Mackay, MM334, MM335, 9 9 from
and Pontoporia, and was used as the outgroup.
Ellis Beach, Cairns) were dissected to examine
the upperrespiratory tract and facial region. The Characterstatesoffeaturesusedinthisanalysis
frozen head of MM334 was sectioned lon- were also determined for Berardius, a primitive
ziphiid(Moore,1968)andPhyseter,todetermine
gitudinally on a band saw. The blowhole was set
polarityofcharacters. In cases where the charac-
well to the left so the first cut wasjust to the left ter was not present in either physeterids or
ofthe median line, and the second c.2cm further
ziphiids, the character state in the fossil taxon
left. The latter section passed through the tym- Eurhinodelphoideawasconsidered tohelpdeter-
panoperiotic bones and pterygoid region. Facial
mine the polarity, de Muizon (1990) considered
musculature was not examined, but the relative
the Eurhinodelphoidea as the sistertaxon toDel-
proportions of muscle, connective tissue and
4melon* were assessed. The 'melon* was dif- phinida(histaxon,whichencompassesallgenera
consideredhere,exceptPlatanista).Reasoningin
ferentiated from connective tissue by its lesser
vascularisation (Mead,1975) and the more fatty these cases is therefore not that the character is
appearance relative to muscle and connective primitive because it occurs in a fossil taxon but
because it occurs in a putative sister group, the
tissue. members of which happen to be all extinct.
Phylogcnetic analyses used Hennig86, version
Polarity decisions for all characters arejustified
1.5 (Farris,1988). The implicit enumeration op- in Appendix 2.
tion was chosen to find all of the most par-
simonious trees. The implicit enumeration COLOUR PATTERN
method istime consuming forlargedatasetssoa
subsetofdelphinidgenerawereanalysed. Repre-
sentatives of most delphinid genera were ex- RESULTS. A broad grey or blue-grey cape
amined; character states within the genera used ('spinal field' ofMitchell,1970)extendsfromthe
to generate the cladograms cover the range of top ofthe head and back downwards about half
variation within the Delphinidae. Whereverpos- the distance to the level of the eye, continuing
sible,characterswerereduced tobinaryvaluesto posteriorly tojust behind the base of the dorsal
avoid someofthe problems with multistatechar- fin, from which it tapers as a wedge along the
acters. All characters were set tonon-additive. upperhalfofthetail stock(captiveanimal: Daw-
146 MEMOIRS OFTHEQUEENSLANDMUSEUM
FIG. 5. Dorsal view of QMJM4721, wilh 312.8 mm FIG. 6. Dorsal view of QMJM4740. Note triangular
condylobasal length and 11.5 dentinal layers. Note area of spongy bone at base of rostrum, extending
broad transverse width of neurocranium; super- forward to just in front of spina mesethmoidalis;
numerary bone ( triangle) infilling the postnarial nodular nasal bones (open arrow); supernumerary
fossa; conspicuous triangular interparietal bone bone; poor development of mesethmoid plate
(arrow); dorsal extension of parietal bones, (posteriormarginindicatedbyarrow)andconsequent
posterolateral to the interparietal bone; wide separa- exposure of frontal bones anterior to nasal bones;
tion of exoccipital and frontal bones; weakly ex- wideexposureoffrontalbone (triangle)betweenthe
pressed telescoping (wide expanse of frontal bone interparietal andmaxillary bones.
exposed); prominent spina mesethmoidalis (open
arrow); poorly developed nuchalcrest. &
grey (Talbot Steene,1984; Figs 2,3); the light
bin,1972; MM30: Fig. 2; Talbot & Steene, grey extends onto the tail stock.
1984:300; MM25: Fig.3). The dark grey is more MM334 has the subtle 3-tone pattern, but the
extensive on the melon of MM25 than MM30 dorsal fin on both sides is lighter than the back.
(Figs 2,3). Grey extends onto the lowerjaw and This does not appearto be a post-mortem effect.
throatregion inthecaptiveanimal (Leatherwood
&Reeves,1983:154)andMM25(Fig.4)butinthe
DISCUSSION. Underwater photographs of O.
latter, a lighter grey throat patch extends as far
baabcdkomiasnatlhefiaexlidllfaroomf tthhee fflliippppeerrsre(Fgiigo.n4).toTthhee b(rTeavsi'raonst&riLsefartohmertwhoeoMda,h1a98k4a;nunRipvuebrl,.Ipnhdootnoessbiya
genital region in MM25 and MM30 (Figs 2,4) is Dr. A. Preen) do not show the three tone colour.
white. The flanks between the dark cape and This may be a real difference, or simply reflect
whiteabdominalfield arelightgreytobrownish- the difficulty in differentiating subtle shading
with the rapid lossofcontrast underwater.
PHYLOGENY OFTHEIRRAWADDY DOLPHIN, ORCAELLA 147
Anderson (1879, pis 25, 25a) described O. cranialasymmetryasisgeneralindelphinids;this
brevirostrisas 'darkslaty-blue,nearly black, and will beconsidered indetail in aseparatepublica-
very little paler on the ventral surface'. It is un- tion.
clear how long his specimens had been dead;
postmortem darkening ofcetaceans can be sub- DORSAL ASPECT. The neurocranium is broad
stantial (Pilleri,1976). Anderson (1879) noted (Fig.5), 65.6% (62.6-68.0%) at the postorbital
that living O. fluminalis (=brevirostris) were processofthefrontal which is usually the widest
more lightly coloured . The dark grey to black point of the skull. Zygomatic width is 65.4%
colourationofOrcaellaneedstobeconfirmedon (63.2-68.3%).The lacrymal bones extend for-
living animals. wardfromthemaxillarybonestoformthelateral
The subtle 3-tone colouration of Queensland border of prominent antorbital notches, 4.0%
Orcaella may be found in juveniles of several (2.8^t.5%)deep.
dolphingenera,becomingfainterorlostinadults. The rostrum is 44.4% (43.2-45.5%)long and
eHxoawmeivneerd,,gtihveecnotlhoeursipzaetstearnndsawgeesdeosfcrthiebeaanipmpaelasr l3a7r.ie6s%as(3a4p.e4r-c3e9n.t8a%g)eowfidreosattrtuhmewbiadsteh. aPrreem5a0x.i5l%-
to becharacteristic ofadult animals. (47.0-57.6%)atthebase,62.8% (60.0-65.9%)at
Mitchell (1970) considered the three-tone pat- 0.25 length, 61.2% (58.1-65.1%) at 0.5 length
tern as the 'common baseline from which to and 65.0% (56.0-73.1%) at 0.75 length. The
interpret most of the patterns found within the spongy, triangular area of the rostrum, bounded
Delphinidae'. ItsoccurrenceinOrcaellathuscan laterallyby2obliqueridges, extendsjustbeyond
not be used as evidence for relationship to other the proximal quarterofthe rostrum (Fig.6).
delphinidgenera. Theextension ofgrey onto the
The premaxillaries continue onto the cranial
lowerjaw and throat in Orcaella is similarto the vault, showingdistinctasymmetry atthepointof
pcaetpthearlnaianndGGlorbaimcpeupsh.alNao,nePsoefudthoercOar,caePlelpaonhoa-d maximum width: the left premaxillary is 4.3%
(2.4-5.7%) wide and the right 8.5% (7.6-9.1)%
a throat chevron, midventral stripe or genital
wide at this point. There is aprominentexposure
p1a9t8c7h;aMsiotccchuelrls i1n9t7h0o)s,eagletnheoruagh(MiMnMas2i5anheatdal.a, ofthe frontalsbetween and behind theascending
processes ofthe maxillaries (Fig. 5).
vague light grey throat patch similar to a throat
chevron. The throat chevron is not restricted to The vertex is composed mainly ofthe frontals,
with a median suturedeflected totheleft (Fig.5).
the 'blunt-headed* whales; Tursiopstruncatascf
aduncus may have a distinct throat chevron It forms an ill-defined ridge running along the
bodyaxisbetweentheascendingprocessesofthe
(GJ.B. Ross pers. comm.). The photographs of
maxillaries.Thenasalbonesarepeculiarnodules,
Orcaella are not of sufficient quality to show
unequivocally more specialised features such as often twooneachsideofthevertex (Fig.6), from
7.3-15.6mm long by 6.4-14.0mm wide. The
spinalblaze,bridlesorflipperstripe. In thiscase,
nasal bones sometimes coalesce, but always
colour pattern is oflittle taxonomic use. retain their nodular appearance (Fig. 7). The
SKULL postero-medial pair of nasal nodules are at the
apex of the vertex while the anterolateral nasal
nodulesareontheanteriorfaceofthevertex.The
RESULTS
anterior face of vertex has a shallow postnarial
pit, usually filled in by a supernumerary bone
REDESCR1PTION OF SKULL. Values 6.0-22.0mm long by 5.4-17.8mm wide (Figs 5-
presented below are based on 14 animals from 7).
central Queensland, Australia with condylobasal The mesethmoid plate is generally poorly
lengths from 297.7-334.8mm and an estimated developed (Figs 5-8), leaving much of the
age (based on dentinal layers) of3-28 years. An anteriorfaceofthevertex exposed(Figs6,8). An
additional skull of a newborn, 232.1mm con- elongate, shallow fossa occurs laterally in this
dylobasal length, was examined for non-men- space, between the apical nasals and the meseth-
sural characters, but measurements of this moidplate(Fig.8).Whenthemesethmoidplateis
specimen were excluded from the descriptive more extensive, the fossa excavates its postero-
statistics. lateral margin, leaving amedianextension ofthe
Unlessotherwiseindicated,valuesarepercent- plate which reaches back to the supernumery
ages ofcondylobasal length, based on measure- bone on the vertex (Fig.7).
ments on the left side of the skull. Orcaella has The frontals are always distinctly separated
MEMOIRS OFTHEQUEENSLANDMUSEUM
148
FIG. 7. Oblique anterodorsal view of vertex, QM FIdGe.vel8.opDmoernstaolfmveiseewthomfoiQdMJplMat4e7(3p5os.terNioortemaprogionr
JM4714. Note nodular, partially coalesced nasal
indicated by arrow); shallow lateral fossa between
bones (open arrow); development of mesethmoid
mesethmoidplateanddepressionsforthenasalbones
plate (posterior margin indicated by triangle); and
(openarrow); prominentinterparietal bone.
maxillaryintrusions(arrow)alonganteriormarginof
superiornares.
(55.3-60.6%) from vertex tothe leftparoccipital
from the supraoccipital by prominent dorsal ex- crest.
tensions of the parietal bone and a triangular The orbit is prominent (Fig. 9), 15.8% (15.0-
interparietal bone (Figs 5,8). 17.1%) between the preorbital and postorbital
Anteromedialborders ofthesuperiornares are processes ofthe frontal bone. Thejugal is stout,
edgedby maxillaryintrusions 8.2% (5.8-10.0%) fitting within a prominent notch on the anterior
longand2.4%(1.3-3.5%)wide(Figs5-8).These face of the zygomatic arch. The maxillary bone
intrusionsareweaklysizedependent(r=0.649for overthe lacrymal and preorbital process offron-
left maxillary intrusion length vs condylobasal tal israised to a variableextent; when itis exten-
length). A very prominent spina mesethmoidalis sively developed it imparts a concave profile to
extends anterior to the bases of the antorbital the supraorbital plate ofthe maxillary bone.
notches and widely separates the premaxillaries The temporal fossa is bounded dorsally and
(Figs 5,6,8). Braincase width is 49.8% (47.0- posteriorlybyaweaklydevelopedtemporalcrest.
54.0%) across the parietals and 51.3% (48.2- Themajority ofthefossaisboundedmedially by
55.2%) across the squamosals. parietal and base of the squamosal (Fig.9). The
zygomatic arch of the squamosal is prominent,
with an extensive mastoid section laterally and a
LATERAL ASPECT. The skull is deep, 57.2% widepost-glenoidspace(Fig.9).Theparoccipital
PHYLOGENYOFTHEIRRAWADDYDOLPHIN, ORCAELLA 149
FIG. 9. Lateral view ofQMJM4721. Note prominent orbit; robustjugal bone (broken); oblique orientation of
occipitalcondyles;poorlydevelopedtemporalcrests;ventralorientationofparoccipitalprocessofexoccipital;
Fissure(triangle)betweenexoccipitalandprominentmastoidportionofzygomaticarch(open arrow).
process of the exoccipital is directed outwards lycoveredbythevomer. Sometimesthevomeris
and ventrally, with minimal intrusion anteriorly visible between the sutures of the palatines and
onto the zygomatic arch. A deep, usually Y- maxillary bones (Fig.12) but in most cases it is
shaped fissure separates the mastoid portion of indicated only by a pit.
the squamosal from the paroccipital process of A medial flange extends from the pterygoid
the exoccipital (Fig. 9). The occipital condyles hamuli (Figs 10-12), bringing them to within
are prominent and directed ventrally at c.45° to 1.0%(0.6-1.5%)ofoneanotherandalmostcom-
the skull axis (Fig.9). Braincase length is 43.1% pletely covering the inferiornares.
(42.0-44.9%). The lacrymal bones are massive (Figs 10,12),
12.4% (10.2-15.0%) long by 14.4% (13.4-
VENTRALASPECT.Theposteriorofthepalate 15.1%)wide.Thefrontalbonesformaprominent
contains triangular lateral lobes of the palatine obliquely transverse ridge (Fig. 11) without an
bones, each with a prominent foramen (Fig.10) optic groove or channel. The optic foramen is
which forms the anteriorend ofa channel exten- incompletelyseparatedfromtheanteriorlacerate
deding dorsally and backwards to the pterygo- foramen by a short vertical bony bridge formed
palatine fossa. by the fused presphenoid-orbitosphenoid bones.
The lateral lobe of the palatines extends The alisphenoid bone is a prominent plate (Fig.
posterolateral^ as a wing-like process (Figs 12), forming the anterior margin ofthe foramen
10,11) 11.0.%(9.3-12.5%)longalongitsanterior ovale (posterior margin offoramen provided by
margin, and underlying an extensive preorbital an extension ofthe basioccipital).
cavity formed between the maxillaries and pres- The zygomatic arch has an extensive tym-
phenoid/frontal bones (Fig.11). This cavity ex- panosquamosal recess (Fig. 12). The falciform
tends dorsally as a lobe, more extensively process is reduced, 3.9% (3.0-5.1%, n=10) long
developed on the rightthan the left side. by 3.7% (2.8-4.9%, n=7) wide. Itrunsparallelto
The pterygoid hamuli are distinctly separated the alisphenoid, rather than ventrally and is not
by triangular medial lobes ofthe palatine bones closely associated with the periotic bone. The
(Figs 10,11). The palatines flank the vomer and postglenoid spacecontains a widegrooveforthe
spinamesethmoidalis,whichisoftenincomplete- auditory meatus and aprominent triangularmas-
50 MEMOIRS OFTHEQUEENSLANDMUSEUM
&
m
FIG. 10. VentralviewofQMJM4708. Notetriangular
anteriorportionoflateral lobeofpalatine,containing
palatine foramen (arrow); posteriorwing-like exten-
sion of lateral lobe of palatine (triangle); complete
separationofmedial andlaterallobesofpalatinesby
phtaemruylgiobiydm(eodpieanl laorbreosw)o;ftsheeppaarlaattiionnes;ofmedpitaelryfgloaind- FIpGo.ste1r1i.oVreenxttreanlsvioinewofolfaQteMraJlMl4ob7e2of1.pNaloatteinwei;nmge-dliiakle
gesonpterygoidhamuli. flangeofpterygoidhamuli(triangle);transversefron-
tal ridge anterior to optic channel; large pre-orbital
toid pad (Figs 11,12), the latter providing ar- spacefordorsalextensionofpre-orbital lobe(curved
ticulation for the tympanoperiotic bones. Be- arrow);mastoidpadofzygomaticarch(broadarrow);
tween the base of the squamosal, just medial to prominent groove forexternal auditory meatus (thin
the mastoid, and a ventral extensionoftheparie- arrow);deeppitmedial tomastoidpad(openarrow).
QM
talisadeeppit(Figs 11,12). In JM4709, this
is one end ofa channel which opens on the back 17 (15-19)/ 17 (16-18) n=13.
ofthe skull in the suture between the squamosal Total alveolar/tooth counts are 66-78. Ap-
and parietal bones. The cranial hiatus is wide in parently the central teeth erupt first; in MM334
young animals, but could be completely infilled theerupted tooth countis only 15/13 11/14.
in olderanimals.
COMPARISON WITH TYPE SPECIMEN.
MANDIBLE (Fig. 13). Mandibles are 76.7% Owen's (1866) description ofthe vertex and the
(75.4-78.6%) long, with coronoid depth 23.6% accuracy of his pl.9, fig.2 are confirmed by the
(22.3-25.1%). The mandibular fossa is 32.8% holotype (R. Sabin pers comm.; Fig.14). The
(29.9-35.4%)long, while the mandibular sym- mostsignificantdifferencesinthevertex,ascom-
physis is 7.7% (5.6-11.4%) long by 8.3% (6.5- paredwithAustralian material,arethe2elongate
9.0%) deep. antero-posteriorly compressed nasal bones (cf
Alveolar/toothcounts(mean,roundedtowhole multiple nodular nasal bones) and well-
number, followed by range in parentheses) are developed mesethmoid plate, abutting on the
18 (17-20)/ 18 (16-20) n=14 nasalbones (cfreducedmesethmoid plate).