THE LEPTOLEPID FISH CAVENDERICHTHYS TALKBRAGARENSIS (WOODWARD, 1895) FROM THE TALBRAGAR FISH BED (LATE JURASSIC) NEAR GULGONG, NEW SOUTH WALES

2006·14.5 MB·English

by  L B Bean

Recordsofthe WesternAustralianMuseum23: 43-76(2006).
The leptolepid fish Cavenderichthys talbragarensis (Woodward, 1895) from
the Talbragar Fish Bed (Late Jurassic) near Gulgong, New South Wales
L. B.Bean
DeptofEarthandMarineSciences,TheAustralianNationalUniversity,
Canberra,ACT0200,Australia
e-mail: [email protected]
Abstract- "Leptolepis"talbragarensisWoodward, 1895,isthemostcommon
fish species in the Talbragar Fish Bed near Gulgong, New South Wales. The
genus CavenderichthysArratia, 1997, has this species as its type. The three
speciesoriginallyproposedbyWoodward(1895)for"Leptolepis"areasingle
species.AdetailedcomparisonofCavenderichthystalbragarensiswithmembers
ofthegenus Leptolepis, and alsowiththeLateJurassicforms Tharsisdubius
andLeptolepidessprattiformis,indicatesthatCavenderichthystalbragarensisis
most closely related to LateJurassicmembers of the Family Leptolepididae.
Analysis of zircons for geochronology showed that the sedimentjust below
the richest fish layer has a youngest component of 151.55 ± 4.27 Ma,
corresponding to the Kimmeridgian Stage ofthe LateJurassic. Thin sections
of the upper prolific fish layer show preservation in tuffaceous sediments,
indicating that the fish population was killed by ash falls of felsic tuff that
filledthepondtheyinhabited.
INTRODUCTION partly on his own observations, but also on the
Fossil fishes were first discovered at Talbragar work of Cavender (1970) who compared
about30 km northeast ofGulgongby Arthur Lowe coregonines and other salmonids with some of the
of Wilbertree, NSW in 1889 (Woodward 1895). earliest known teleosts, including L. talbragarensis.
Later, many specimens were collected by Charles Arratia(1997)erectedanewgenus, Cavenderichthys,
Cullen, the collector of fossils for the NSW Mines with talbragarensisasthetypespecies, on the basis
Department. This material is now in the Australian of material from the Natural History Museum,
Museum, Sydney, and the NSW Department of London, the Field Museum of Natural History,
Mineral Resources. Associated with the fishes is Chicago, and the Swedish Museum of Natural
abundantplantmaterial, firstdescribed by Walkom History, but she did not have access to the vast
(1921), then re-examined and classified by White amountofmaterialavailableinAustralia.
(1981). Some undescribed insect remains are also TheTalbragarsitehasrevealedthebest-preserved
housed intheAustralianMuseum,Sydney. Jurassic fish in Australia. The outcrop now is very
Woodward (1895) described a representative poor, as somuch material has been removed in the
selection ofdifferentfossil fishesthathadbeen sent past and it is now in a paddock used for grazing.
to London in 1890. He considered that the Theage has been difficult to confirm because there
assemblagewas ofJurassic age, despite an original is no control of stratigraphy as the relationship to
field assessment oftheage as Triassic, made by W. surrounding rocks is unclear. Previously, no
Anderson of the Geological Survey of NSW. The volcanic rocks had been identified to be dated, and
vast majority ofthe fishes in the material belong to palynology is impossible because of the highly
LeptolepistalbragarensisWoodward,1895,whichwas oxidisednatureoftherocks.
cited by Long (1991) as "the firstappearanceofthe The assemblage of fossil fishes has been thought
teleosteans in the Australian fossil record". Other to indicate an Upper Jurassic age (Long 1991), but
fishesincludeonespeciesofpalaeoniscid, Coccolepis early workers suggested a Middle Jurassic age, for
australis (Woodward, 1895), and the holosteans example Hind and Helby (1969) who suggested
Archaeomaene tenuiWoodward, 1895, Madariscus EarlytoMiddleJurassicbasedonpalynologyofthe
robustus Wade, 1941, Aphnelepis australis Purlawaugh Formation, within which the Fossil
Woodward, 1895,AetheolepismirabilisYloodward, Fish Bed occurs. The site is interpreted as a mass
1895,and UarbryichthyslatusWade, 1941.Interestin kill site with a longitudinal extent of possibly 200
Leptolepis talbragarensis is due largely to its early metres. The upper layer contains a high
teleosteanfeatures.Nybelin(1974)suggestedthat L. concentration of extremely well preserved fossil
talbragarensis should be excluded from the family fish, while the layer below, probably less that one
Leptolepididae Agassiz, 1833-44. This was based metre thick, has scattered fish throughout.
L.B. Bean
44
indicating a lacustrine environment. Until now sedimentary history (Dr 1 Williams, personal
evidence for the cause of death has been sparse, communication).
although Percival (1979), and White (1981), have Dulhunty and Eadie (1969) described the "Fish
madesuggestions. Bed Chert" as a hard, fine limonitic cherty-shale,
The purpose of this paper is to reassess the and Pogson and Cameron (1999) stated "In thin
description and classification of Cavenderichthys section the unit is a red-brown silty mudstonewith
talbragarensis, and to discuss the environment of compaction bedding features and chips of
deposition, theageofthe fossil bed, and thenature ?tuffaceous quartz, clayey patches after feldspar
of preservation. To do this the type material in the and/or lithicfragments, magnetite, ankeriticcement
Australian Museum, as well as about 250 other and manganese oxide dendrites." Thin section and
specimensfrom theAustralianMuseum, theN.S.W. chemical analysis shows that the fossil-bearing
Geological Survey and the Australian National rocks are largely tuff and sediments derived from
University have been examined. The sediment has the underlying sandstones, some of the tuffs
beenstudied inthinsection,ashasitsgeochemistry, representingoneormorevery fine-grainedash falls
and plant content. Zircon dating was carried out (Prof. R. Arculus, personal communication). EDXA
usingtheSHRIMPmethod. (Energy Dispersive X-ray Analysis) has not shown
any evidence of carbonate or calcium ions being
present,excludinganankerite[FeCa(CO,), cement
]
GEOLOGY (Dr A Christy, personal communication). There is
The Talbragar Fossil Fish Bed is the informal evidence of hne bedding and subsequent
name given by Dulhunty and Eadie (1969) to the compaction. The red-brown colour is post
outcrop found on the northeastern side of Farrs depositional because each block has concentric
Hill, about 5 km south of the Talbragar River. The bands of varying intensity of colour as the iron
location is GR 753090 6437910, Dubbo 1:250 000 oxide has penetrated from the joint block
Geological Sheet (Pogson and Cameron 1999). The boundaries. Manganese dioxide is often found
siteisnowa geological reserveadministered by the infillingthefossil fish cavitiesand isgenerallyclose
National Parks and Wildlife Service, Mudgee to the edge of a block, forming dendrites. Many of
Office. The strike is generally north-south, and the the fish and most of the plant fossils are white,
dipofadjacentbedsisabout10°west.TheFishBed having not taken up the red iron oxides. EDXA
is thin, formingpartofa non-marinesequence,just showsthecomposition oftheinfillingofplants and
below the fossil bed are layers that contain animals is not the same. The plants have been
tuffaceoussections.Unweathered samplesaregrey, replaced by very fine-grained opalised quartz,
very finegrained, andcontainangular fragmentsof whereas kaolin is present with the opalised quartz
minerals such as quartz, some of which is detrital in the infilling of the fish (Dr A Christy, personal
and someofwhich appears tobe igneous in origin. communication).
Thereisnoevidenceofsedimentary flow structure. TlieTalbragarFossilFishBed isprobablynomore
Stratigraphically below this unit are quartz than 60 cm thick (Percival 1979). The current state
sandstones of the Purlawaugh Formation, which of the outcrop is poor as the bed occurs as small
showsedimentarystructuressuchascross-bedding, blocks of fossil-bearing rock scattered through the
pebble layers and washouts. This sandstone unit is soil of a paddock. It is impossible to measure the
comparable to thenearest units of the Purlawaugh precise thickness or the boundaries of the bed
Formationthatoutcropabout50kmaway.TheFish withoutexcavation.Thelayersoffossil-bearingrock
Bed is probably the upper unit of the Purlawaugh vary from about 2 cm to 4 cm thick, but within
Formation, but no equivalent outcrop to the Fish these layers the fish are scattered in overlapping
BedsisexposedinNewSouthWales. layers, rather than all being at the top or all at the
SHRIMP (Sensitive High mass Resolution Ion bottom of the layer. The exception is some large
MicroProbe) analysis of zircons was carried out blocks covered with vast numbers of small fish,
using the SHRIMP RG machine in the ANU someavailable in part and counterpart. Tliere is no
Research School of Earth Sciences. The age of the evidenceoftheoriginallocationoftheseblocks,but
youngest population was 151.55 ± 4.27 Ma, it isassumed that thisvery fossiliferous layer is the
corresponding to the Late Jurassic (Veevers 2000), upper layer ofthe deposit, and thus represents one
indicating that the sediment must be this age, or mass-kill event. There is no evidence ofdesiccation
younger if the zircons were all of sedimentary in the sediment, such as mud cracks or aerially
origin.Themorphologyoftheyoungestgrainsdoes exposed surfaces, so this is not a mound spring
not show any evidence of transportation by water. deposit. It is not an overbank deposit either, as
Examination of the zircons shows that the rock theseusuallyhavecycliclayersincludingsandsand
contains a small tuffaceous component. The range coarse-grained layers from flooding, interspersed
of different types of zircons was quite large, and with soil developments from dry times. The layers
many of them showed clear evidence of a that contain an abundance of small fish, which are
LateJurassicleptolepidfish Cavenderichthystalbragarcnsis 45
thought to occurat thetop ofthebed, arevery fine Materials
grained and represent a period ofslow deposition, Thespecimensdescribed in thisstudycomefrom
or a time when the pond was still and suddenly three sources; Australian Museum, Sydney, prefix
became anoxic. Lower layers have occasional AMF (30 specimens); NSW Geological Survey,
scattered fish that have been deposited along with Sydney, prefix MMF (107 specimens); Australian
sediment. Percival (1979) recorded that "it is now National University, Canberra, prefix ANU (106
thought to represent the erosional remnant of the specimens).
margin ofa freshwater lakebed deposit". Evidence Where more than one fossil appears on a
now points to thedestructionofthelakeby several numbered specimen, the individual fossils have
eruptionsofvolcanicash. beenallocatedalettersuffixtodistinguish them, eg
The fossils show no preferred orientation, MMF36743b.
although most are laterally flattened. Only one of Some material mentioned in text and figures
several hundred specimens is dorso-ventrally relates to specimens in the Natural History
flattened. Some of the smaller individuals show Museum,London,prefixBMNH.
dorsal flexion. This flexion of the spine could
represent greater flexibility of the juvenile
individuals, or could possibly be a result of them SYSTEMATICS
dying in suddenly anoxic water as the result of an
ash fall. The dorsal flexion of the small specimens SubclassTeleosteiMuller,1844
was also commented upon by Waldman (1971) in FamilyLeptolepididae(Agassiz,1833-44)
his description of the fish in the Cretaceous
Koonwarra beds in Victoria. He considered that Genus CavenderichthysArratia,1997
particular assemblage, which includes a large
number of the closely related species, Leptolepis Synonymy
koonwarriWaldman, 1971,wasduetowinterkilland SeeArratia (1997:19).
claimed the flexion is due to asphyxia of the
individuals when thepond was covered by ice. As Diagnosis
is noted later in this paper, many of the fish are Small teleostsranging from about4cm to 12 cm;
preserved with their mouths open, which could head with short snout; lower jaw projecting
supporttheideaofanoxia. anteriorly; fusiform body. Frontal bone short
Plant fossils are commonly associated with the anteriorly. Suborbital bone absent. Quadrate-
fish. Noneoftheserepresentplantsgrowinginsitu, mandibular articulation below anterior half of
and there is no evidence for any water dwelling orbit. Elongatedsymplecticandhyomandibular, as
plants. The plant material consists of twigs, well as ventral limb of preoperculum. Lower jaw
individual leaves, occasional cones, and very small with deep coronoid process and wide leptolepid
fragments. Some beds have masses of very finely notch. Hyomandibular with a preopercular
shreddedplantmaterial. process. No suprapreopercular bone. Infraorbital
The area surrounding the lake was heavily sensory canal with very few tubules; generally
forested with an araucarian pine, Agathisjurassica four broad tubules on lower limb of
(White 1981). The fine detail of plants and fishes preoperculum, one at the angle, and one on
preservedimpliesananaerobicburial environment. vertical limb. Anterior ceratohyal short and
Most of the fish are intact with very few examples usually not fenestrate; with six thin arcinaciform
of disarticulated bones, indicating a lack of post- branchiostegal rays, and three or four spathiform
mortem turbulence, predationand decay.Theplant branchiostegal rays associated with the posterior
fragments show venation and coll structure, thus ceratohyal. 35-45 vertebrae with autogenous
showingnosignsofdecayortransportation. neural arches in abdominal region and fused
Etheridgeand Olliff(1890) described one example neural and haemal arches in caudal region, with
of a cicada named Cicada? lowei found in the fish 20-26 pairs of ribs. Midcaudal autocentra thin,
beds,andfurtherexamplesofinsectshavesincebeen ring-like, with or without a longitudinal crest on
found. The Australian Museum houses a collection lateral surface. 12 pectoral rays, 12 pelvic rays, 12
of Talbragar insects that has not been studied in dorsal rays+ 3 procurrent dorsal rays, and 10 anal
detail. Theseinsectsare theonly preserved evidence rays. Pelvic, dorsal and anal rays branching
of a food source for the fish. The insects are distally into4 lepidotrichs. Preural centrum 1 with
apparently found in the upper layer where the fish short neural spine. Three or rarely four epurals;
fossils are most concentrated (R. Beattie, personal seven hypurals and fiveuroneurals; 10+9 principal
communication). Sincenone havebeen found in the caudal rays. Well-developed dorsal processes on
lowerlayerswherethefisharemorescattered itmay bases of innermost principal caudal rays of dorsal
indicatethatthe insects were trapped by theash fall lobe of caudal fin absent. Two "urodermals". Six
thatfinallyfilled inthepond. basal fulcra on upper lobeofcaudal fin.
46 L.B. Bean
Remarks Australian Museum, Sydney, are paratypes,
This diagnosis is based on Arratia (1997:19). described by Woodward (1895). The old numbers
However changes have been made where have prefix MF, and have been replaced by new
examinationofnewmaterialhasaddedinformation numbers with prefix AMF. AMF120525 (MF276),
thatcontradictstheoriginaldiagnosis.Forexample, AMF120509 (MF276), AMF120505 (MF276),
Arratia cited a deep body, the hyomandibular AMF120498 (MF276), AMF120512 (MF276),
lacking a preopercular process, the lower jaw AMF120497 (MF276).
lacking a leptolepid notch, 12 or 13 branchiostegal
rays, 43-45 vertebrae, 25-27 ribs, nine hypurals, Othermaterial
seven uroneurals, and a lack of epipleural bones. The following specimens have been examined,
Thesefeaturesarediscussed later. provided latex casts in most cases, and are quoted
asexamplesinthetext.
AMF27069, AMF4133, AMF51899, ANU54916,
Cavenderichthystalbragarensis(Woodward,1895) ANU54940, ANU54946, ANU54956, ANU54962,
Figures1-22 ANU54968, ANU54970, ANU54975, ANU54976,
Leptolepis talbragarensis Woodward, 1895: pp. 21, ANU54977, ANU54980, ANU54982, ANU54983,
22, pi.6, figs1-8. MMF13555, MMF13561a, MMF13564, MMF13569,
MMF13599b, MMF13603k, MMF13606a,
LeptolepisloweiWoodward, 1895: pp. 22, 23, pi. 6, MMF13734a, MMF36716, MMF36718, MMF36721,
figs9, 10. MMF36728, MMF36729, MMF36730, MMF36732,
Leptolepisgregarius'Woodward, 1895:pp23-24,pi. MMF36732a, MMF36733, MMF36735, MMF36737,
4,figs8-10, pi.5, fig.5, pi. 6, figs11, 12. MMF36743, MMF36743a, MMF36743b, MMF36746,
MMF36753a, MMF36758a, MMF36759,
Material Examined MMF36761b, MMF36773, MMF36778.
Holotype
MMF81. This specimen has been examined, but Description
notusedinthecurrentdescription. Itwasnamedas Olfactoryregion
the type specimen by Woodward (1895) and The rostral is evident on several specimens,
appearedasPlate6,figure4. including ANU54956 (Figure 2A) and MMF13555
(Figure 2B), and is small and almost shaped like an
Paratypes isosceles triangle, with the apex anterior. The two
The following specimens, housed in the lateral marginsareslightlyconcave,and theposterior
extrascapulars
parietal
frontal ,dermosphenotic
supraorbital
,pterotic
nasal
supracleithrum
rostral
supraethmoid,
lachrymal
(infraorbital 1)
premaxilla infraorbital5
parasphenoid
maxilla infraorbital4
dentary 4 infraorbital3
supramaxilla1 operculum
supramaxilla2
infraorbital2
preoperculum
gularplate
quadrate
hypohyal 1
hypohyal2 suboperculum
retroarticular
ceratohyal cleithrum
branchiostegal rays urohyal interoperculum
Figure1 Cavenderichthystalbragarensis.Reconstructionofhead, lateralview,basedonMMF36716.
LateJurassicleptolepidfish Cavenderichthystalbragarensis 47
supraorbital
sclerotic ring
rostral
supraethmoid parasphenoid
premaxilla
supramaxilla 2
A
1mm
nasal (R?) infraorbital 4
supraethmoid preoperculum
premaxilla
infraorbital 3
? nasal L
(seetext) infraorbital 2
lachrymal
quadrate
supramaxilla 2
ceratohyal
maxilla
with teeth
hypohyal 1
dentary
hypohyal 2
Figure2 Cavenderichthystalbragarensis. Detailsofanteriorhead. A, thisview ofthefrontofthehead ofANU54956
shows unusual detail of the anterior bones. B, the anterior of MMF13555 shows the premaxilla and nasal
bones.Onthesupermaxilla2itispossibletoseetracesofthepathofnerves.Thepreservationofteethonthe
maxillaisunusuallyclear.Theposterioroftheparasphenoidcanbeseetobeenlarged.
margin is crenulated where it articulates with the under the anterior part of the frontal-rostral and
frontal. In ANU54956 it is disarticulated from the probably is the ossified covering of the ethmoid
frontal, but the posterior margin is clear (Figure 2A). cartilage. Two specimens, ANU54956 (Figure 2A)
This bonearticulates with themaxillaand premaxilla and MMF1355 (Figure2B), show the supraethmoid
andpresumablywiththesupraethmoid,althoughthis to be roughly Y-shaped, with the two branches
articulation has not been observed. The ethmoid has being posterior. The articulation of these branches
notbeenobservedinthismaterial. with other bones cannot be determined in these
The supraethmoid is a small median bone that is specimens.
48 L.B.Bean
Oticregion suture between them is straight in the narrow
Thegenerallypoorpreservationoftheoticregion region, and then bends back and forth in the wider
results from it overlying the back of the braincase region. The frontals carry the sensory canal, with
causingit tobeusuallycrushed, and isonly known pores occurringatthe front, above thecentreofthe
from one specimen (Figure 7A). The pterotic is supraorbitalbone,andattheend ofabranchwhere
roughly rectangular, and located dorsal to the thecanal curves down around the eye. Thecanal is
preoperculumandposteriortothedermosphenotic. close to the surfaceofthe boneand is coveredby a
It carries thesensory canal where it branches offto ridgeinsomespecimensintheanteriornarrowpart
the preoperculum. Tire parietals are medial to the of thefrontal, e.g., MMF13564 (Figure 3B). In other
pterotic. Only one specimen has an identifiable cases the delicate ridge has been removed and a
pterotic(Figure7A). canal is visible, e.g., ANU54916, MMF36781,
MMF36735, MMF36753a (not figured). About two
Dorsalroofingbones thirds of the distance from the anterior of the
A small cylindrical bone on MMF13555 (Figure frontals is a prominent pore, behind which the
2B), just ventral to the supraethmoid, has unclear sensory canal branches, with one branch leading
relationshipswithotherbones.Itappearstocarrva into the parietals where it terminates at a pore
sensory canal, and in the flattened fossil it appears (MMF36753a, Figure 6A). The other branch turns
to be adjacent to the anterior end of the ventrally and passes into the dermosphenotic.
parasphenoid. Thisbonemay be the left nasal. The Wherethefrontal broadensout, itformsthemargin
right nasal is well exposed on MMF13555 (Figure of the orbit between the supraorbital and the
2B), havingbeen detached during fossilization. It is dermosphenotic.
identified on its tubular form and containing the The parietals are generally rectangular in form
supraorbital sensory canal. It sits adjacent to the and meet medially by an irregular suture. The
anteriorpartofthefrontal,wherethesensorycanal sensory canal crosses them from the frontals, but
emerges from under the ridge of covering that does not emerge posteriorly. The parietals occur
protectsitintheregionabovethesupraorbital. directly behind the frontals and anterior to the
Frontals are the largest skull roof bones, almost extrascapulars.
thesamesizeasthedentarybones.Theyarenarrow The extrascapulars (Figure 6A) are smaller than
at the front and becomewiderbehind the eye. The theparietalsandareposteriortothem.Theycarrya
supraorbital
covering
ridges
frontals
dermosphenotic
parietals
A B
Figure3 Cavenderichthystalbragarensis.Skullroofs. A,thisphotographofalatexpeeloftheskullroofofMMF36728
isarareexampleofthisview.B,onthispeelofMMF13564itispossibletoseeevenmoredetailincludingthe
mid-linesutureandseveralporesfortheemergenceofnerves.
LateJurassicleptolepid fish Cavenderichthystalbragarensis 49
ANU54916
Figure4 Cavenderichthys talbragarensis. A, sketches of the differences in arrangements ofbones in the upperjaw.
Thisisnatural intra-speciesvariation, and isasmuch a functionofdifferencesin preservationasdifferences
between individuals. B, sketches of the variations in arrangement of the preopercular canal on the
preoperculum.Scalebars=1 mm.
so L.B. Bean
sensory canal with several pores. They are the body of the posterior supramaxilla has a radiating
posteriorbonesoftheroofoftheskull, but in many pattern of grooves and small ridges, which appear
specimens they are crushed and difficult to to represent a point of ligament attachment. The
interpret.Figures3A and 3B arephotos oftheskull maxilla and the two supramaxillae move as a unit
roofsofMMF36728and MMF13564respectively. and are generally found joined together. Figures 5,
6and 7illustratethevariousstructuresoftheupper
Lateralskullbones andlowerjaws.
The premaxilla (Figures 2A, 2B, 4A and 5A) is
smalland mobile,and becauseofthis itisoften lost Circumorbitalseries
due to poor preservation. It fits intoa concavity on Thesystem ofnamingall lowercircumorbitalsas
thefrontofthemaxilla(seebelow).Thereareabout infraorbitals, as used by Cavender (1970), Nybelin
6small teeth on thepremaxilla, which lies adjacent (1974), Patterson (1977) and Arratia (1997)hasbeen
to the rostral bone and the supraethmoid, used here. Confusion can arise when some bones
(ANU54956, Figure 2A) but this region is not are not preserved, e.g., infraorbital 1 or lachrymal,
usually seen clearly. Other non-figured specimens and the terminology used by Norden (1961), based
showing the premaxilla include MMF36732a, on living fish, which clearly identifies specific
MMF36778, MMF13555, ANU54916, and bones, was used initially by the author to establish
ANU54968. relationships. However, the modern terminology
Themaxilla hasalong itsventral margina row of has been used to be consistent with contemporary
small, even teeth, which can be seen on specimens publications.
ANU54956 (Figure 4A), ANU54976 (Figure 5A), A single supraorbital bone is the anterodorsal
and MMF36729 (not figured). This margin is a bone of the circumorbital series. It is a long thin
smoothgentle convex curveventrally, with a small oval with a slight upwards curve to follow the
arcuate toothless concavity at the front to dorsal margin of the eye. The ends of thebone are
accommodate the premaxilla. The maxilla and the rounded and there is nosensory canal. It forms the
premaxilla are certainly not fused in any way, as anterodorsalmarginoftheorbit(ANU54956,Figure
the premaxilla is often detached from the maxilla, 2Aand MMF36728,Figure3A).
but their articulation is not obvious. The posterior The infraorbital 1, also called the lachrymal,
end of the maxilla is a smooth semicircular curve (MMF13555 Figure 2B) is small, forming the lower
and is connected to the coronoid process of the anteriorrim oftheorbit, and contains the terminus
mandible by a flat maxillomandibular ligament of the infraorbital canals (Norden 1961). It is a
(Lauder 1980). The anterior end of the bone has a dermal bone external to the ectopterygoid, fitting
peg-like process, which enables it to articulate into the series around the eye. It is narrow
probablywiththevomer, ethmoid andpalatineina anteriorly and broadens posteriorly and is almost
similar mannerto Amia (Lauder 1980). This means triangularinnaturewiththeapextowardsthefront.
the maxilla is fixed at the anterior end and free to It carries the sensory canal, but due to the state of
swing forward and backward from the posterior. preservation itis impossibletodetermine ifitisthe
When the mouth is agape, the maxilla swings siteoftheterminusoftheinfraorbitalcanal.
forward, and is often found preserved in this Specimens MMF36728 (Figure 5C), AMF51899
position. Teeth form the margin of the gape when (Figure 7A) and MMF36735 (not figured) show the
the maxilla is fully protracted. When the mouth is continuation of the infraorbital series. There are
closed the maxilla is pulled backward, and passes four bones all about the same size and depth
outsidethedentary, coming to reston the ridgeon around the ventral and posterior part of the eye.
the dentary formed by the heavy ossification Theyall carrythesensorycanal. The firstoneisthe
aroundtheMeckeliancartilage.Theoutsidesurface infraorbital2.InCavenderichthystalbragarensisithas
ofthemaxilla hasaridgerunningalongthemiddle aroughlytrapezoidshape. Abranchoffthecanalis
from theanteriorend. Of142specimens inwhichit directed ventrally. The infraorbital 2 is not as deep
ispossibleto distinguish thestateofthemaxilla, 83 as the subsequent ifraorbitals. Its ventral margin is
havethemaxillawideopen. levelwiththeventral marginofthe infraorbital 1 in
Therearetwosupramaxillae, theanteriorbeinga front, but at theback it is about halfas deep as the
small smooth oval bone that on-laps the anterior infraorbital3.
part of the dorsal margin of the maxilla Infraorbitals 3-5, which are all about the same
(MMF36732a, Figure 6B). The posterior depth, form the posterior rim of the eye. A suture
supramaxilla has a generally oval shaped base on- between infraorbitals 3 and 4 always appears in
lapping the maxilla, but it also has a long thin compressed forms to be adjacent to the posterior
slightly curved process extending anteriorly under end of the parasphenoid. In all the specimens
and above the anterior supramaxilla. This process illustrated in this articlethere is an easily identified
hasathinridgeandgroovethatextendfrom thetip bone, infraorbital 3, which occurs anterior to the
down into thebody ofthebone. Thesurface of the bend of the preoperculum. Dorsal to this bone is
LateJurassicleptolepidfish Cavenderichthyslalbragarensis 51
premaxilla
maxilla
supramaAiiici
i
lateral dentary
medial dentary
displaced
supramaxilla2
ectopterygoid
suboperculum
maxillaopen
interoperculum
medial preopercularcanal
angular
ceratohyal (not
fenestrate)
B
urohyal
supramaxilla 1
lachrymal ?
infraorbital 2
infraorbital 3
preoperculum
infraorbital 2
ceratohyal interoperculum
hypohyal cleithrum
acinacifori
branchiosLc^di
0 spathiform
rays
branchiostegal rays
Figure5 Cavenderichthystalbragarensis. A, detailofthejawsofANU54976. Leftand rightdentariesarebothvisible,
and well preserved teeth on the maxilla. Supramaxilla 2 has been displaced but its medial ridge is clear. B,
medial view of MMF36732a, showing the ectopterygoid and bones of the circumorbital series. In this
specimen the ceratohyal is clearly not fenestrate, and the delicate nature of the urohyal is obvious. C,
MMF36728 has well preserved bonesofthecircumorbitalseries, including the lachrymal. D, inthisdetailof
theposteriorventral regionofthehead ofMMF13555, theceratohyal ispartlycoveredbythepreoperculum,
but the relationship of the two forms ofbranchiostegal rays to the ceratohyal is clear. Two hypohyals are
visibleattheanterioroftheceratohyal.
52 L.B. Bean
extrascapular
parietal with terminating end of soc
supracleithrum
hyomandibular
frontal with pores on
supraorbital canal
maxilla
supramaxilla 2
angular
ral fin
quadrate cleithrum
Imm suboperculum
ceratohyal interoperculum
urohyal branchiostegal rays
ectopterygoid
angular
quadrate
supramaxilla 2
Meckelian
groove
maxilla with
teeth angular
dentary
gular plate
1mm
Figure6 Cavendehchthys talbragarensis. Heads showing the maxilla in the forward open position. A, this photo-
graph of a peel of MMF36753a includes a ceratohyal that is not fenestrate, and very clear pores on the
supraorbital canal. The characteristic position of the parasphenoid appearing to bisect the orbit is well
demonstrated.B,thedetailofthejawsofMMF36732aistakendirectlyfromthespecimen.Thelocationofthe
Meckeliancartilagepresentalongtheinteriorsurfaceofthedentaryisobvious.
infraorbital 4, a squarish bone that in Dorsal to infraorbital 5 is the dermosphenotic, or
Cavenderichthysisasdeepasinfraorbital3.Themost infraorbital 6 (AMF51899, Figure 7A). Norden
dorsal infraorbital 5 (Figures 7A, 7B, 8A) is not classifies the dermosphenotic as a "small, dermal
squarish but roughly triangular with rounded postorbital bone, which bears a triradiate sensory
corners, theapex pointingdorsally.Thesebones lie canal." In manyspecimens thisboneiscrushedand
anteriortothepreoperculumandoverlapitslightly. difficult to identify, but it is possible to see in
Infraorbitals 3 and 4 have approximately several specimens that it carries a junction of the
rectangular shapes with curved margins. There are sensory canal where it descends from the frontal,
no branches of the sensory canal in infraorbitals 4 continuesintothehighestinfraorbital,andbranches
and 5 (see MMF36761b, Figure 7B, and posteriorly towards the pterotic. It makes part of
MMF13599b, Figure8A). theposteriorrim oftheorbit.