Records of the Western Allstralian Mllsellm Supplement No. 57: 207-218 (1999).

Cretaceous ichthyosaurs from Western Australia

Brian Choo

Department of Anatomy and Human Biology, University of Western Australia,Nedlands, WA 6907; email: bchoo@cyllene.uwa.edu.au

Abstract Outcrops of probable Birdrong Sandstone (late Hauterivian-midBarremian) at Cardabia Station, Giralia Anticline, Carnarvon Basin, WesternAustralia, have yielded numerous ichthyosaurian remains in recent years.Two fragmentary skeletons from the area are referred to Platyptcrygills sp.II1det. A proximal humerus from one of these skeletons bears a dorsaltrochanter that is morphologically distinct from that of P. longmani from theAlbian of Queensland and more closely resembles forms of Platypterygillsfrom Europe and Russia.

Briefly reviewed is additional indeterminate ichthyosaur material fromCardabia Station, as well as fossils from the Birdrong Sandstone and AlingaFormation (early Cenomanian) from just north of Kalbarri.

INTRODUCTION

All known Australian ichthyosaur material isof Cretaceous age and, when of determinatenature, represents the cosmopolitan genusPlatypterygius von Huene, 1922, the solerecognized ichthyosaur genus from this period(McGowan 1972a, 1972b). Discoveries of P.longrnani in Queensland have been welldocumented by Wade (1984, 1990) whilefragmentary remains are known from theNorthern Territory (Murray 1985, 1989), SouthAustralia (Wade 1990) and Western Australia.

The earliest discovery of ichthyosaurs in WesternAustralia consists of eight centra and other elementsrecovered from phosphate nodules excavated atDandaragan in December 1943 (Teichert andMatheson 1944). These, along with plesiosaurianremains (Long and Cruickshank 1998) wereextracted from an exploratory sample for acommercial mining operation and the originaldisposition of the specimens remains unclear.Claims of the Santonian age of the material, whichwould make these the latest known ichthyosaurremains (McGowan 1972b; Wade 1990; Long 1993),cannot be substantiated owing to their mode ofrecovery. The youngest undisputed ichthyosaurianrecord consists of fragments attributed toPlatypterygills sp. from the latest Cenomanian ofBavaria (Bardet et al. 1994).

In 1993, personnel from the Department ofGeology and Geophysics of the University ofWestern Australia visited an outcrop of glauconiticsandstone at Cardabia Station in the central part ofthe Giralia Anticline (McLoughlin et al. 1995). Fossilmaterial discovered at the site included at least sixichthyosaurian vertebrae as well as possible

sauropterygian limb elements. A team from theWestern Australian Museum visited the same sitein June 1994 and recovered more ichthyosaurianmaterial. In addition to isolated centra, twofragmentary skeletons were discovered by KristineBrimmel and John Long. John Long recoveredfurther material from the site in 1996 and 1997.Isolated centra are known to have been collected bystudents during excursions conducted by theDepartment of Geology and Geophysics of theUniversity of Western Australia.

Other recently discovered ichthyosaur materialincludes centra from outcrops of the BirdrongSandstone at Murchison House Station recoveredby J.A. Long in 1994 and 1997. In late 1994, M.Siverson (Geology Department, University of Lund)recovered several bones from an outcrop of theAlinga Formation (early Cenomanian) at ThyridinePoint, Murchison House Station. Among these werea phalanx and a worn centrum which appear to beichthyosaurian.

ICHTHYOSAUR LOCALITIES AND AGES

Scattered outcrops of glauconitic sandstone onCardabia Station (Figure 1) are considered to belongprobably to the Birdrong Sandstone of theMuderongia allstralis Zone of late Hauterivian­Barremian age (Helby et a/. 1987; Helby andMcMirU1 1992; McLoughlin et al. 1995). Reptilianbones were found weathered out on the surface ofthese exposures, both in situ and in scree material.Apart from ichthyosaurs, plesiosaur remains havebeen recovered from the area (J.A. Long pers.comm. 1997). Other fossils from the outcropsinclude partial external moulds of ammonites which

208 B. Choo

Murchison House Station XKalbarriGeraldton

Dandaraga

u

t1I)

500 km

Figure 1 Locality map showing where the remains of ichthyosaurs have been found in Western Australia.

are problematic in resembling typically Aptianforms (McLoughlin et al. 1995), and abundant fossilconifer wood which often bears Teredolites boringsand saprophytic fungal hyphae. Nostratigraphically useful microfossils have beenidentified. It has been suggested that the beds maybe better placed within the Mardie Greensand(McLoughlin et al. 1995). However, until furtherwork is done on the area, it is most appropriate toconsider the outcrop as probable BirdrongSandstone. It has been suggested recently (D.W.Haig pers. comm. 1998) that the exposures mayrepresent the base of the Windalia Radiolarite(latest Aptian-Albian).

The Cretaceous stratigraphy of the MurchisonHouse Station area near Kalbarri has been dealt

with in Clarke and Teichert (1948) and Johnstone etal. (1958). Reptilian fossils were found weatheringout of the Birdrong Sandstone outcrops includeichthyosaur vertebrae, the pliosauroid Leptocleidusclemai (Cruickshank and Long 1997) and the mid­caudal vertebra of a theropod dinosaur (Long andCruickshank 1996). Also from this area are isolatedichthyosaurian elements from the Alinga Formationoutcrop at Thyridine Point. Complete details of allthe sites are held by the Western AustralianMuseum.

Abbreviations used in this paper are: QM =Queensland Museum, Brisbane; UWA = E. de C. ClarkeMuseum, Department of Geology and Geophysics,University of Western Australia, Nedlands; WAMWestern Australian Museum, Perth.

Western Australian Cretaceous ichthyosaurs

SYSTEMATIC PALAEONTOLOGY

Class Reptilia Laurenti, 1768

Order Ichthyosauria de Blainville, 1835

Family Leptopterygiidae Kuhn, 1934

Genus Platypterygius von Huene, 1922

Species indeterminate

Material Examined

Referred Material

WAM 94.7.3. Cardabia Station, northwesternAustralia, approximately 500 m west of CardabiaCreek; (upper) glauconitic facies of the BirdrongSandstone, Carnarvon Basin; collected 26 June 1994by J.A. Long et al.; vertebrate palaeontologicalcollection of the Western Australian Museum.

WAM 94.7.2. Cardabia Station, northwesternAustralia, approximately 800 m west of CardabiaCreek; (upper) glauconitic facies of the BirdrongSandstone, Carnarvon Basin; collected 26 June 1994by K.M. Brimmell et al.; vertebrate palaeontologicalcollection of the Western Australian Museum.

Other Material

UWA 120176A-F. Cardabia Station, northwesternAustralia; (upper) glauconitic facies of the BirdrongSandstone, Carnarvon Basin; E. de C. ClarkeMuseum.

WAM 94.7.7. Murchison House Station, central westcoast of Australia; Birdrong Sandstone, CarnarvonBasin; collected 22 June 1994 by J. Clema et al.;vertebrate palaeontological collection of theWestern Australian Museum.

WAM 99.1.4, phalanx. Murchison House Station,central west coast of Australia; Alinga Formation,Carnarvon Basin; collected in 1994 by M. Siverson;vertebrate palaeontological collection of theWestern Australian Museum.

209

WAM 99.1.6, vertebra. Murchison House Station,central west coast of Australia; Alinga Formation,Carnarvon Basin; collected in 1994 by M. Siverson,vertebrate palaeontological collection of theWestern Australian Museum.

WAM94.7.3The specimen (Figures 2-8, 12A) consists of a

partial array of articulated caudal vertebrae foundin si tu, along with disarticulated fragmentsrecovered from scree material scatteredimmediately below the exposure. These includeadditional vertebrae, rib fragments and partialforelimb elements. In all likelihood, a far greaterproportion of the fossil skeleton was once in anarticulated state, but most of it had weathered outand disintegrated, leaving only the posterior part ofthe spinal column in the original disposition.

VertebraeIn general, the vertebral centra are in a poor state

of preservation due to physical erosion and fungalgrowth after exposure. They range from amorphousfragments of bone to centra that are roughly two­thirds complete. All specimens display signs ofdeformation resulting from compression. In nospecimen has the left one third of the centrum beenpreserved, indicating that the animal was lying onits right side, the leftmost portion of the vertebraebeing weathered away. Although none of thepreserved centra retains a neural arch, twofragments of neural spines were identified.

The articulated series, WAM 94.7.3.1-.20 (Figure2), consists of at least 19 individual centra, the exactnumber being uncertain due to the highlyfragmentary nature of some specimens. The arraytapers significantly in one direction (away from thescree zone) and no rib apophyses are present,suggesting that they are caudal vertebrae locatedshortly anterior to the tail fin. The disarticulatedmaterial (Figures 4, 5) represents more than 20individual centra, and some fragments display freshbreakage indicating recent disarticulation andbreakdown. Several fragments display partiallypreserved rib facets (Figure 5) indicating that atleast part of the dorsal column is represented.

Figure 2 WAM 94.7.3, articulated caudal vertebral array from 94.7.3.1 (left) to 94.7.3.20 (right).which are probably worn fragments of adjacently numbered specimens, are not10 cm.

210

D

B. Choo

Figure 3 Platypterygius sp., WAM 94.7.3. A-B, caudal vertebra 93.7.3.13 from articulated array, seen in posterior (A)and lateral (B) views. C-O, disarticulated caudal vertebra in posterior (C) and lateral (0) views. E-F,fragment of disarticulated dorsal vertebra in posterior (E) and lateral (F) views. Scale bar = 2 cm.

Western Australian Cretaceous ichthyosaurs 211

I

c

E

B

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... . :',:

.,(..\. .. .-',' .1

,.

o

G

Figure 4 Platypterygills sp., individual caudal centra of WAM 94.7.3. A-C, 93.7.3.13 from articulated array seen inposterior (A), lateral (B) and dorsal views (C). D-F, uncatalogued disarticulated centrum from scree materialin posterior (D), lateral (E) and dorsal views (F). G-I, uncatalogued disarticulated centrum from screematerial in posterior (G), lateral (H) and dorsal (J) views. Scale bar 5 cm.

212 B. Choo

Table 1 Some measurements (mm) of the centra of Platypterygills sp. WAM 94.7.3.

69.972.4

88.094.292.795.596.196.6105.9

95.9100.7103.2

Uncatalogued disarticulated centra(Figures 3C-D, 4D-F 105.8(Figure 4G-I) 109.1(Figures 3E-F, 5)

53.654.347.555.454.150.5

42.043.2

Length41.436.436.4

Diameter92.9

98.5

Cat. No.94.7.3.1594.7.3.1694.7.3.1794.7.3.1894.7.3.1994.7.3.20

27.030.235.4

38.636.037.240.340.943.242.344.344.1

LengthCat. No. DiameterArticulated caudal array94.7.3.194.7.3.294.7.3.394.7.3.494.7.3.594.7.3.694.7.3.794.7.3.894.7.3.994.7.3.1094.7.3.1194.7.3.1294.7.3.1394.7.3.14

Figure 5 PlatypterygillS sp., WAM 94.7.3. Fragment ofdorsal vertebra in lateral (A) and posterior (B)views, Arrows point to partially preserved ribfacet. Scale bar = 5 cm.

In form, the centra are compressed amphicoelousdiscs displaying a distinct biconcave appearance inlateral cross section. Measurements of thearticulated series and selected disarticulatedspecimens are listed in Table 1. The posteriormostcaudal vertebrae in the articulated segment are toopoorly preserved for accurate measurement. Most

Adisarticulated centra (from the scree material) aretoo fragmentary to reveal diameter except forseveral fairly well preserved specimens, allapparently of caudal origin.

HumeriProximal fragments of both humeri were

recovered from scree material. The left specimen(Figure 6), which is missing it's trailing edge,measures 6.7 cm in breadth from the leading edgeand 5.7 cm in height from the tip of the dorsaltrochanter. There are trochanters on both the dorsaland ventral surfaces, both of which decrease inheight and width distally. The dorsal trochanter iswell preserved and forms a rounded triangularcrest in distal view while the ventral one has beenbadly weathered.

The right proximal fragment (Figures 78, 8C) ismore heavily compressed dorsoventrally than theleft and is lacking both lateral edges. It measures 7.2cm in breadth and 5.5 cm in height. The ventraltrochanter is better preserved and forms a low,rounded ridge-like structure. Much of the dorsal

A

Figure 6 Platypterygills sp., WAM 94.7.3. Proximal fragment of left humerus in dorsal (A) and distal (B) views. Scalebar =5 cm. Abbreviations: dt =dorsal trochanter; vt =ventral trochanter.

Western Australian Cretaceous ichthyosaurs

/I

I\

A "\

\\J

/I

II

/I,

...... - .....,.

,\I

II

IIIII\\,,

\

8

dt

/

213

Figure 7 Platypterygius sp., A, restored right humerus of WAM 94.7.3 in dorsal view. It is uncertain as to whether thedistal fragment represents the dorsal or ventral surface. B, proximal fragment of right humerus in distalview. Scale bar =5 cm. Abbreviations: dt =dorsal trochanter; vt =ventral trochanter.

B

Figure 8 Platypterygius sp., WAM 94.7.3. A-B, proximal fragment of left humerus seen in dorsal (A) and posterior (B)views. C-D, proximal fragment of right humerus seen in dorsal (C) and distal (D) views. Scale bar =2 cm.

214

A

8

8. Choo

Figure 9 Platypterygius sp., WAM 94.7.2. Fragments of left (A) and right (8) jugals in lateral view. Scale bar = 5 cm.

trochanter has been worn away, thus bothtrochanters appear to be of roughly the same size.One flattened element (Figure 7A) is interpreted aspart of either the dorsal or ventral surface of thedistal two-thirds of the right humerus bearing theremnants of the ulnar and radial facets.

Other ElementsMany flattened rib fragments were recovered

ranging from 1 to 2.5 cm in thickness. Broad, flatpieces of bone might represent worn fragments ofeither the coracoid or the scapula. Along withnumerous small flakes of bone, several large piecescould not be positively identified.

WAM94.7.2This specimen (Figures 9-11) comprises a

completely disarticulated collection of fragmentarybones found partially weathered out within a 3 x 2 marea of the outcrop surface. Bony remnants consist ofpieces of the skull, partial vertebral centra and ribs.Most of the material consists of small «2 cm) flakesof bone which cannot be identified with certainty.

Skull FragmentsPortions of the jaw are readily distinguished from

rib fragments due to their more robust appearanceand the presence of a distinct longitudinal grooveon the lateral surface. No teeth were preservedalthough one jaw fragment may display a partialtooth socket.

Two elongated elements measuring 14 and 16.5cm in length, represent portions of the left and rightjugals respectively (Figures 9, 11A,B). Bothspecimens comprise portions of the horizontalramus consisting of a dorsoventrally flattenedposterior and laterally compressed anterior part.Miscellaneous compressed fragments foundassociated with these fossils could be pieces of theascending vertical ramus and anterior horizontalramus but are too badly weathered to be associatedto the figured specimens.

A large, flat bone is tentatively identified as afragment of the nasal (Figures 10, !le,D). Thethickness of the presumed posterior part of thespecimen suggests a much larger complete unit. Arobust element remains indeterminate but probablyoriginated at the back of the skull.

VertebraeSeven identifiable fragments of centra are present.

They are typically ichthyosaurian with a deeplybiconcave articular surface and a shallow flutedcircumferance. No rib or neural arch facets arepreserved but otherwise they are similar in form tothose of WAM 94.7.3.

RibsNumerous rib fragments consist of broad

flattened elements and narrow, compressedsegments that appear almost reniform in crosssection. Rib fragments of Platypterygius sp.described by Bardet et al. (1994) are similar in form.They are of little further diagnostic value other thantheir relatively large size.

Figure 10 Platypterygius sp., WAM 94.7.2. Probablefragment of nasal in dorsal (A) and lateral(8) views. Scale bar =5 cm.

Western Australian Cretaceous ichthyosaurs

B

215

Figure 11 Platypterygius sp., WAM 94.7.2. A, left jugal in lateral view. S, right j~gal ~ ~ateral view. C-D, probablefragment of nasal in dorsal (C) and lateral (D) views (catalogue no. on speamen IS mcorrect. Scale bar =2 cm.

Other Western Australian Ichthyosaur Fossils

Isolated Vertebrae from Cardabia StationNumerous isolated ichthyosaur vertebrae have

been collected from Cardabia Station and arehoused in the Western Australian Museum, theUniversity of Western Australia and in private fossilcollections. At least six partial centra (UWA120176A-F) from the material initially recoveredfrom the site are ichthyosaurian (McLoughlin et al.1995). UWA 120176A is fairly complete and is 10.1cm in diameter and 4.4 cm long. Neither rib norneural arch facets are preserved. UWA 120176B islarger (11.2 cm diameter, 4.6 cm long) and bearsclosely spaced rib apophyses. Aside from being ofgreater diameter, in overall appearance the centraclosely resemble those of WAM 94.7.3 in form.

Specimens from Near KalbarriThese specimens come from outcrops of the

Birdrong Sandstone exposed to the north ofKalbarri on Murchison House Station. WAM 94.7.7consists of an articulated array of at least threefragmentary centra. The most complete specimen is12.4 cm across and over 6.0 cm thick making it thelargest ichthyosaur vertebra known from WesternAustralia. The preserved dorsoventral and lateralsurfaces have been obscured by crystalline deposits,hiding any trace of rib and neural arch facets andmaking comparisons with the other materialdifficult. In 1997 I.A. Long recovered additionalichthyosaur vertebrae from the area, including anarticulated array of at least 10 caudal centra. Thismaterial has yet to be prepared.

216

Murchison House Station Material from the AlingaFormation

A single phalanx (WAM 99.1.4),2.8 cm across, isa flattened oblong element that is broadenedlaterally, typical of a proximal phalanx of alongipinnate ichthyosaur (McGowan 1972a).Elasmosaurid plesiosauroid proximal phalanges arealso oblong but are broadened dorsoventrally. Asingle, tiny centrum (WAM 99.1.6), 2.3 cm indiameter, displays amphicoelous curvature.

SYSTEMATIC DETERMINATION ANDCOMPARISONS

Size of the Cardabia Station IchthyosaursFew well preserved skeletons of Platypterygius

are known, making comparisons difficult. Thealmost complete holotype of P. longmani, QM F2453(Wade 1984, 1990) with an estimated total length of5.6 m, has a humerus over 16.5 cm in length. Thefragments of the humeri of WAM 94.7.3 aresufficient to determine rough lengths of over 13cm and widths of over 9 cm for the completebones. This, along with the relative size of thevertebrae suggests a medium-sized individual ofPlatypterygius 4-5 m in length. As little of WAM94.7.2 has been preserved intact, the size of thatindividual is difficult to determine. The skullfragments are relatively thick and robust, while thepreserved lengths of the jugals sug?e.st.co~pl~teelements of over 30 cm in length. ThIS IS mdlcatlveof a much larger individual than WAM 94.7.3.

ComparisonsOf the available material from the Giralia Anticline,

the humeri are of the greatest diagnostic importance, asthey have been prominently figured in the literature(Broili 1907; Kiprijanoff 1881; McGowan 1972b; Wade1984) and, within the genus Platypterygius, display fairlyconsistent variation between individuals of differentspecies. While of limited value by themselves, the jugalsand centra can, with some subjectivity, be comparedwith other material to provide an overall picture ofsimilarity or dissimilarity with other ichthyosaurspecimens. It should be noted that near-eompleteskeletons of Cretaceous ichthyosaurs are very rare, theonly two that have been fully described are theholotypes of P. platydactylus (Broili 1907) and P.longnumi (Wade 1984, 1990). .

Although numerous species of PlatypteryglUs havebeen named (McGowan 1972b) only four are widelyrecognized as valid: P. campylodon (Carter, 1846)from Western Europe, P. kiprijanoffi (Romer, 1968)from Russia, P. americanus (Nace, 1939) from NorthAmerica and P. longnlani Wade, 1990 from theQueensland Artesian Basin, Australia. Complete,well preserved humeri have been described for allfour species.

B.Choo

Vertebral CentraThe centra of the Giralia Anticline ichthyosaurs

are large, robust elements that in generalappearance and range of sizes, resemble those ofPlatypterygius vertebrae from Australia (Wade 1984,1990) and Europe (Kuhn 1946; Bardet et al. 1994) aswell as specimens probably referrable to the genusfrom New Zealand (Fleming et al. 1971). However,the centra also bear a likeness to the similar-sizedJurassic form Temnodontosaurus platyodon(McGowan 1974), suggesting that their robustnessis mainly a reflection of the large sizes of theanimals.

JugalsThe preserved portions of the jugals of WAM 94.7.2

suggest long but robust elements over 30 cm in length,that display relatively little curvature in lateral profile.They closely resemble, in size and shape, a jugal of aEuropean Platypterygius sp. illustrated in Bardet et al.(1994). They are also similar to the jugals present oncomplete skulls of P. longnumi (Wade 1984) and P.americanus (McGowan 1972b).

HumeriCaution must be exercised in using ichthyosaur

humeri for diagnostic purposes, as compression canradically alter the appearance of the bones(McGowan 1972b), while weathering can obscurethe height and shape of the trochanters. Fortunately,despite their incompleteness, the left proximalhumerus fragment of WAM 94.7.3 bears a wellpreserved dorsal trochanter while the rightfragment retains much of the ventral one. Asmorphology of the humerus varies intraspecificallyin Platypterygius, it is useful to provide acomparison of the humeral trochanters of thedifferent species of this genus with WAM 94.7.3.While distal humeral morphology has also beenused to distinguish between different species ofPlatypterygius (Wade 1990), this part of the boneremains imperfectly known for the Cardabia Stationichthyosaurs.

Comparison of Humeral TrochantersPlatypterygius campylodon: the humerus figured in

Broili (1907, as P. platydactylus) appears to have anegligible ventral trochanter while the dorsal one isprominent but flattened and rounded. Photogr~phsof humeri figured in Kuhn (1946, as P. hercymcus)possess a similar dorsal appearance and seem toshow a low ridge-like ventral trochanter.

Platypterygius kiprijanoffi: The proximal humerusbears extremely prominent trochanters on bothdorsal and ventral surfaces (Kiprijanoff 1881). Thedorsal trochanter (which Kiprijanoff figured as theventral one) forms a narrow, curve-shaped crestwhile it's ventral counterpart is also rounded butmuch broader.

Western Australian Cretaceous ichthyosaurs 217

Figure 12 Outlines of restored left humeri in proximal view of (A) WAM 94.7.3, compared with (8) Platypterygillslongmani (QM F2573, after Wade 1984). Not shown to scale. Arrows point to dorsal trochanters.

Platypterygius americanus: The dorsal trochanter isextremely high forming a tapering crest-likestructure. The ventral trochanter is a much smaller,broadly rounded triangular structure (McGowan1972b).

Platypterygius longmani: Trochanters appear verysimilar to P. americanus with the dorsal tapering intoa pointed crest. Distinguished from P. americanus inalways possessing a distinct socket for the pisiformbone adjacent to the ulna (Wade 1984, 1990). Aproximal humerus from the Northern Territory(Murray 1989) resembles that of P. americanus andP. longmani.

WAM 94.7.3: Dorsal trochanter forms aprominent, rounded structure that does not taper.Ventral trochanter is low and broadly rounded.

CONCLUSIONSOf probable late-Hauterivian-Barremian age (or

possibly latest Aptian), the Giralia Anticline fossilsare considerably older than the Late Albian materialfrom Queensland and the Northern Territory.WAM 94.7.3 possesses a humerus bearing arounded dorsal trochanter, distinct from thetapering crest-like structure found in P. longmani(Figure 12). In this feature, WAM 94.7.3 resemblesEurasian forms of Platypterygius from the Albian­Cenomanian (P. campylodon and P. kiprijanoffi).

The morphology of the proximal humeri of WAM94.7.3, combined with the overall size, robustnessand Cretaceous provenance of the material enablesWAM 94.7.3 to be placed within the genusPlatypterygius with some confidence.

Most of WAM 94.7.2 is too fragmentary for usefulcomparisons, however on the basis of the size androbustness of the jugals and centra, it also is

tentatively referred to Platypterygius. The remainingichthyosaur fossils from the the area consist solelyof incomplete centra and are regarded asindeterminate as to genus and species.

While clearly a distinct form from P. longmani, theCardabia Station ichthyosaurs are referred toPlatypterygius sp. indet. Despite WAM 94.7.3 beingthe most complete ichthyosaur skeleton yet knownfrom Western Australia, it is still extremelyfragmentary and the humeri are too incomplete forthe species to be accurately determined.

The Birdrong Sandstone material from theMurchison House Station area consists solely ofvertebrae which resemble those from CardabiaStation in form and preservation. As it has beenestablished that these outcrops do indeed belong tothe Birdrong Sandstone, the presence of largeichthyosaurs in the Hauterivian-Barremian ofWestern Australia is confirmed. The AlingaFormation material is of little diagnostic valuebeyond "typically ichthyosaurian". It does,however, establish the presence of the group inWestern Australia during the Cenomanian.

ACKNOWLEDGEMENTS

Elements of this study formed part of a MSc.(prelim.) course undertaken in 1996. My sincerethanks to my supervisors Or John Long and OrDavid Haig. 1 am indebted to the staff and studentsof the Geology and Geophysics Department of theUniversity of Western Australia for invaluableassistance. Thanks also to Prof. Charles Oxnard, OrMikael Siverson, Ms Kristine Brimmel and MrGeorge Kendrick for their helpful comments. Muchgratitude goes to Mr Laszlo Bubrik for hisoutstanding photography.

218

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Manuscript received 17 March 1998; accepted 13 January1999.