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New and Unusual Plio-Pleistocene Lizard (Reptilia: Scincidae) from
Wellington Caves, New South Wales, Australia
MARK N. HUTCHINSON
1
AND JOHN D. SCANLON
2
South Australian Museum, North Terrace, Adelaide, South Australia 5000, and School of Earth and Environmental
Sciences, University of Adelaide, South Australia 5005, Australia
ABSTRACT.—A new genus and species of extinct lizard is described from the Early Pliocene to Early
Pleistocene deposits of Wellington Caves, New South Wales, Australia. The description is based on the
anterior half of a left mandibular ramus that shows a suite of unusual characteristics. The fossil is referred to
the Scincidae, based on its combination of a distinct coronoid process of the dentary and completely fused
Meckelian groove, but it differs significantly from living scincids in several respects. The dental sulcus
disappears posterior to the symphysis. The dentition shows slight enlargement of the teeth posteriorly, with
the terminal tooth the largest. The new taxon has an exceptionally massive jaw, with a hypertrophied
symphysis and coronoid region and the angle at the symphysis suggests a short, deep snout. The new species
is not obviously related to any of the major extant scincid lineages.
Our knowledge of the fossil record of
Australia’s extensive modern lizard fauna is
sketchy. Apart from a probable scincid humerus
from the Eocene (Hocknull, 2000), remains of
lizards are limited to beds of Late Oligocene age
or younger, with relatively few taxa reported.
Estes (1984) and Martin et al. (2004) have
recorded skinks in the Late Oligocene Etadunna
Formation of South Australia, attributing them
to Egernia or a related genus, and there are also
indeterminate remains of agamids and varanids
from these deposits (Estes, 1984). The Late
Oligocene to Middle Miocene faunas from the
Riversleigh area of Queensland have yielded
the most diverse fossil lizard faunas (Covace-
vich et al., 1990; Shea and Hutchinson, 1992;
Hutchinson, 1992, 1997). Pliocene sites have
yielded scanty fossil material of several families
(Pledge, 1992; Mackness and Hutchinson, 2000)
as have Pleistocene cave deposits in South
Australia (Smith, 1974), New South Wales
(Dawson and Augee, 1997; Morris et al., 1997),
Western Australia (Prideaux et al., 2007), and
Queensland (Bartholomai, 1977; Molnar and
Kurz, 1997).
A feature of the relatively small number of
Australian fossil lizard taxa known to date is the
relatively minor degree of evolutionary diver-
gence evident compared with the living fauna
(e.g., Hutchinson, 1992). Indeed, their very
similarity necessitates a laborious comparative
search through the morphologies of the living
fauna to establish identity. Most fossil speci-
mens can be allocated to living genera and
species groups, with only a few weakly differ-
entiated extinct genera described so far (e.g.,
Megalania, Varanidae, Hecht, 1975; Molnar,
1990; Sulcatidens, Agamidae, Covacevich et al.,
1990; Proegernia, Scincidae, Martin et al., 2004).
In this paper, we describe a very distinctive
skink based on a partial mandible. We cannot
readily place this new form close to any living
taxon, not least because the scincid lizards have
yet to be subjected to a comprehensive mor-
phological phylogenetic analysis. It is notewor-
thy that the specimen is Plio-Pleistocene, the
best indication yet that there have been recent
extinctions of lizard taxa that differed markedly
from living Australian lizards.
MATERIALS AND METHODS
J. D. Scanlon collected the partial mandible in
December 1995, from a pile of excavated cave
earth and limestone rubble that resulted from
cave access work in or adjacent to the Phosphate
Mine (Osborne, 1997). Reference material is in
the South Australian Museum Herpetology
collection. Terminology for osteological anato-
my is mostly from Estes et al. (1988). Following
Schwenck (2000) ‘‘intermandibularis’’ is used in
preference to ‘‘mylohyoid’’ for the nerve and
associated foramina on the lingual surface of the
mandible. The large lingual opening of the
inferior alveolar canal is usually called the
anterior inferior alveolar foramen. Because there
is no discrete posterior foramen, we use the
marginally shorter term, inferior alveolar fora-
men.
1
Corresponding Author. E-mail: hutchinson.
mark@saugov.sa.gov.au
2
Present address: RiversleighFossils Centre, Outback
at Isa, 19 Marian Street, Mount Isa, Queensland 4825,
Australia; E-mail: riversleigh@outbackatisa.com.au
Journal of Herpetology, Vol. 43, No. 1, pp. 139–147, 2009
Copyright 2009 Society for the Study of Amphibians and Reptiles
Description
Family Scincidae
Aethesia n. gen.
Type Species.—Aethesia frangens n. sp.
Diagnosis.—Description and diagnosis as for
the sole included species.
Locality and Stratigraphy.—As for the sole
included species.
Etymology.—From Greek ae
¨thes (¸
ag
´hgz), odd,
unusual.
Aethesia frangens n. sp.
Figures 1–2
Diagnosis.—Very large skink (estimated basi-
cranial length 70 mm) with a massive mandible
showing hypertrophy of the mandibular sym-
physis and coronoid process, the dentary broad
and almost planar ventrally; dental sulcus
absent except for the symphysial region; Meck-
el’s groove obliterated by dentary overgrowth;
scar for the jaw musculature (adductor mandib-
ulae externus superficialis,a.m.e.s.) forming a
slightly raised arcuate platform lying ventral
to the coronoid process. Fifteen teeth, those
remaining intact (posterior seven) almost iso-
dont, with slight anteroposterior enlargement of
successive teeth. Last tooth the largest. Tooth
implantation pleurodont anteriorly, but in the
absence of a dental sulcus posterior to the
seventh tooth position, attachment becomes
pleuroacrodont posteriorly, with replacement
pits adjacent to the bases of existing teeth. Each
tooth with an almost symmetrical domed crown
tipped by an obtusely pointed cusp. Splenial
shortened anteriorly, terminating at the poste-
rior edge of the inferior alveolar foramen. The
shape of the head implied by the restored angle
at the symphysis and the dentary proportions is
unusually short and deep compared with all
other skinks.
Holotype.—P43196 in the Palaeontology col-
lection of the South Australian Museum, Ade-
laide.
Locality and Stratigraphy.—Collected from
spoil heaps following excavations of the Phos-
phate Mine-Bone Cave complex, Wellington
Caves, New South Wales.
The Wellington Caves are about 8 km south
of the town of Wellington in the Great Dividing
Range west of Sydney and comprise five major
caves plus other smaller caves and sinkholes
(Dawson, 1985). Additional underground cham-
bers were created during 1915–1917 when the
New South Wales Phosphate Company mined
breccia-filled passages adjacent to the Big Sink
and Bone Caves for phosphate fertilizer (Os-
borne, 1983). Excavations carried out in 1995–
1996 comprised ‘‘removal of fallen mullock
FIG.1. Aethesia frangens n. sp. holotype partial
mandible in (A) labial view, (B) lingual view, and (C)
occlusal view. Scale bar equals 10 mm.
FIG.2. Aethesia frangens n. sp. holotype partial
mandible indicating major structural features. Abbre-
viations: ames, scar for the external jaw adductor
(adductor mandibulae externus superficialis); cor, coro-
noid; d, dentary; ds, dental sulcus; imf, intermandibu-
laris foramen; iaf, inferior alveolar foramen; mf,
mental foramina; pr cor, coronoid process of the
dentary; rp, replacement pits for new teeth; spl,
splenial; sym, symphysis.
140 M. N. HUTCHINSON AND J. D. SCANLON
from the mine passages, reopening of the tunnel
between the [Phosphate Mine] and Bone Cave
… and excavation of a new entrance tunnel,’’
and trenching for new concrete paths (Osborne,
1997). Osborne (1997) states that ‘‘Spoil from
these operations, which contains significant
amounts of out-of-context bone fragments, has
been stockpiled in labelled dumps which can be
identified with the part of the mine from which
they were extracted.’’ However, the label (if
any) associated with the specimen described
here was not observed at the time of collection
(some restriction on the source may be provided
by the date of collection in December 1995,
whereas development work on the Phosphate
Mine continued until April 1996). Moreover, it
is known that sediments from various parts of
the system did become mixed, such that
identification of stockpiled material is unreli-
able (M. Augee and M. Archer, pers. comm.),
and in any case the complex stratigraphy of the
fossiliferous sediments within the caves (Os-
borne, 1983, 1997) makes the ‘‘part of the mine’’
a poor guide to the identity of the enclosing
sediment. The sediments from which the holo-
type specimen was obtained, therefore, are from
the Phosphate Mine-Bone Cave complex but
cannot be confidently associated with a partic-
ular stratum or locality within this large system
at this time.
Osborne (1997) concluded that the oldest
bone-bearing bed of the Wellington Caves
system is the upper graded-bedded unit of the
Phosphate Mine beds. The Phosphate Mine
beds yielded specimens of a peramelid marsu-
pial that Muirhead et al. (1997) referred to the
early Pliocene species Perameles bowensis. The
next oldest deposits are those of Big Sink, which
Hand et al. (1988) concluded were early to mid-
Pliocene in age. These are overlain unconform-
ably by the Quaternary Mitchell Cave beds
(Osborne, 1983, 1997). Thus, A. frangens could be
Pleistocene or as old as early Pliocene.
Description.—The specimen is the anterior
half of a left mandibular ramus, including most
of the dentary and splenial and fragments of the
coronoid and surangular bones (Figs. 1–2). The
dentary lacks the tip of the coronoid process
and most of the angular process, as well as the
crowns of the first eight teeth. The splenial lacks
only its posterior apex and suture with a
presumed angular. The other two bones are
very incomplete, the coronoid being limited to
just the anterolingual, dentary process and a
small broken piece of the ascending process,
whereas the surangular is present only as the
anterior extremity, broken off inside the ramus.
Total length, from the anteriormost point of
the symphysis to the remaining tip of the
coronoid process, 39.1 mm. Distance from an-
terior point of symphysis to apex of the splenial
notch 21.2 mm. Length of tooth row 25.7 mm.
Depth at level of last (15th) tooth (excluding
tooth), 10.2 mm. Maximum depth of jaw,
measured vertically down from the apex of the
coronoid process, 14.3 mm. Maximum width
measured in occlusal view at the level of the
15th tooth, 6.8 mm. Longest dimension of
symphysis 7.8 mm; width of symphysis, taken
normal to the longest dimension, 4.4 mm.
The jaw has an exceptionally robust appear-
ance. The ramus has a pronounced inflection
toward the symphysis, the tooth row curving
medially at about the level of the eighth tooth. A
well-developed crest runs from the symphysis
along the ventrolingual margin of the medially
inflected portion of the jaw. The ventral surface
of the dentary is broad and flattened, meeting
the lingual face of the mandible at a sharp angle,
and merging with the labial face more gradu-
ally, although still forming a longitudinal ridge
at the line of transition.
The labial surface of the dentary is unusually
highly pitted anteriorly, implying considerable
neural (inferior alveolar nerve) and vascular
(mandibular artery and vein) supply to the
dermis in this region. The pitting is an elabora-
tion of the series of eight mental foramina, of
which the three posteriormost openings are the
largest. The posteriormost mental foramen lies
below the position of the 11th tooth, and all of
the foramina are irregular in shape, with bony
outgrowths or other obscuring sculpturing. The
coronoid process of the dentary is very well
developed, 3.2 mm thick (in occlusal view) just
anterior to where it has broken. Below the
coronoid process is a pronounced, arcuate
adductor muscle scar (for the a.m.e.s.) that has
its apex about 5 mm posterior to the level of the
last tooth. The trailing edge of the dentary is
mostly broken, but a short concave region of
apparently unbroken, free edge can be observed
below the broken apex of the coronoid process.
This short curve suggests that the angular
process of the dentary began high on the
dentary and ran posteroventrally from about
the level of the tooth row.
The symphysis of the jaw is well preserved
and very massive. The articulating surface of a
typical scincid left dentary symphysis is shaped
like a numeral 7, with the angle pointing
anteriorly. The upper, nearly horizontal surface
lies below the anterior two teeth, and the angle
is formed by an indentation in which the
anterior tip of Meckel’s cartilage lies. In skinks
with a fused Meckelian groove, this indentation
has a foramen for the emerging cartilage. In
Aethesia, the dorsal and ventral areas of the
symphysis are very greatly expanded posteri-
orly and ventrally. The angle containing the
AUSTRALIAN FOSSIL LIZARD 141
Meckelian foramen has become constricted into
a very narrow channel running posteriorly from
the foramen. Dorsal to this, the upper portion of
the symphysis expands upward, its dorsal
margin forming the medial wall delimiting the
anterior part of the dental sulcus. The ante-
roventral portion of the symphysis is greatly
expanded into an inverted triangular surface
that extends ventrally to form a large crest
below the ‘‘chin.’’ The symphysis also shows
that the mandibular rami met at an unusually
wide angle in Aethesia. Mirroring the specimen
to re-create this angle shows that the linear,
posterior portions of the tooth row on each side
lay at about 50uto one another. The large angle
between the rami in Aethesia extrapolates to an
exceptionally blunt, short muzzle. The skull
length can be estimated from the restored angle
at the chin, assuming that the jaw ramus is
broken close to its midpoint. This gives an
estimated basicranial length of about 70 mm,
equivalent to the longest skull of any living
skink (Tiliqua spp.). Compared to Tiliqua,
however, Aethesia was much more robust, with
a shorter muzzle and possibly broader and
deeper skull.
On the lingual surface, the Meckelian groove
is closed by dentary overgrowth, with no trace
of a suture. The apex of the splenial notch (i.e.,
the anterior extremity of the inferior alveolar
foramen) lies below the level of the rear of the
tooth row, at about the level of the 13th tooth.
The ventral suture between the splenial and
dentary runs directly posteroventrally from the
posterior edge of the inferior alveolar foramen,
producing a significant lingual exposure of the
angular process of the dentary. The dental
sulcus is well defined only in the symphysial
region. Progressing posteriorly, once the sym-
physis has curved back to the main body of the
jaw, the medial wall of the dental sulcus and
then the sulcus itself disappear, no trace of the
sulcus being evident beyond the level of the
eighth tooth locus. The lingual face of the
dentary below the tooth row forms a continuous
sheet of bone with only a weakly defined
concave surface to indicate the position of the
dental lamina.
The tooth row, in occlusal view, is straight
posteriorly, curving medially anterior to the
level of the 10th tooth. Dentition is pleurodont
but is evidently different to that of any other
skink. The first seven of 15 teeth are broken off,
the eighth is a broken stump, and the ninth to
15th are present and well preserved. The teeth
vary only slightly in size, becoming larger
posteriorly with the posteriormost the largest.
Unlike all other skinks examined, there are no
smaller teeth forming a termination of the tooth
row posterior to the ‘‘cheek’’ teeth. Instead a
bare area of the dentary bearing rugosities
follows the terminal tooth.
The condition of the cheek teeth is like that
seen in acrodont lizards such as agamids and
some teiids in that the dental sulcus is absent
and the posteriormost tooth is the largest.
Nevertheless, the teeth are clearly implanted
on the lingual face of the dentary, and the
presence of deep pits below the teeth implies
that tooth loci had cycles of replacement. Where
the dental sulcus is absent, the pits for replace-
ment teeth are entirely confined to the bone of
attachment below the tooth; there is relatively
little evidence of significant erosion into the
dentine of the tooth itself. Anteriorly, where the
dental sulcus persists, the bases of the teeth
show the usual excavation. Cycles of tooth
replacement must have been slow in this
species. More or less comparable skinks, such
as Tiliqua species, show clear erosion of the
bases of every second to fourth tooth along the
tooth row, whereas none of the posterior teeth
of Aethesia show tooth erosion. There is weak
evidence for two alternating tooth generations,
because the teeth alternate slightly in size
(Table 1), and the replacement tooth pits are
alternately larger and smaller (or absent).
The crown of each tooth is obtusely pointed
in profile, the outlines curving ventrally from
the apex to be parallel sided where the tooth
meets the dentary. In mesial view, the tooth
crowns have a curved outline labially and
lingually, with only weak expression of the
anterior and posterior ridges that typically
demarcate the lingual and labial faces of scincid
tooth crowns. All intact teeth are similar in
morphology.
The splenial tapers to a point anteriorly, the
apex forming the posterior edge of the inferior
alveolar foramen; there is no superficial exten-
sion of the splenial either above or below the
foramen. The splenial is pierced by two small
TABLE 1. Measurements of the teeth of Aethesia frangens. Length is measured mesiodistally along the trend of
the tooth row. Width is measured linguo-labially normal to the trend of the tooth row.
Locus 9 10 11 12 13 14 15
Length (mm) 1.30 1.40 1.36 1.48 1.44 1.52 1.64
Width (mm) 1.10 1.20 1.32 1.36 1.40 1.28 1.42
L/W 1.18 1.17 1.03 1.09 1.03 1.19 1.15
142 M. N. HUTCHINSON AND J. D. SCANLON
foramina, one close to its ventral margin in the
expected topographic position of the anterior
intermandibularis (5mylohyoid; Schwenk,
2000) foramen, the other lying directly behind
the inferior alveolar foramen. Another possible
interpretation is that the bone represents a fused
splenial +angular. At present, we favor the first
interpretation (splenial only) mainly because
the most common lizard condition is for a
distinct splenial and angular, and the normal
proportions of these bones in scincoid lizards
would have only the splenial visible in the
section of mandible that was recovered (anterior
to the midpoint of the coronoid).
The anterolingual (dentary) process of the
coronoid forms a triangular wedge lying dorsal
to the splenial. Its suture with the dentary is
flush with the surface of the bone, unlike the
case in other skinks where the dorsal surface of
this process forms a posterior extension of the
dental sulcus. In Aethesia, the coronoid termi-
nates posterior to the level of the posteriormost
tooth, although its topographic position with
respect to the dentary as a whole is about the
same as in other skinks.
Etymology.—The Latin frangens means ‘‘break-
ing into pieces,’’ ‘‘smashing,’’ alluding to the
probable effect of the massive jaws of this
species.
DISCUSSION
Aethesia has so many specialized features that
its affinities with living families are not imme-
diately obvious. Of the areas of the mandible
preserved, several attributes combine to suggest
that this is a scincid.
Coronoid Process of the Dentary.—In most
lizards, the base of the dorsal process of the
coronoid bone overlaps the dentary externally.
A minority of lizard taxa show the reverse
situation of a posterodorsally directed finger or
flange of the dentary running back over the
anterolabial part of the coronoid. This character
state is the normal state for all species of
Scincidae, Cordylidae, and Gerrhosauridae (cor-
dyliforms sensu Lang, 1991), Xantusiidae, Xe-
nosauridae, and Anguidae (Estes et al., 1988;
Lee, 1998). Dentary overlap of the coronoid as
defined here is an occasional variant within
some clades (e.g., Brachylophus within Iguanids,
REF), and two limbless burrowing clades,
dibamids and amphisbaenians (Gans, 1960;
Rieppel, 1984) have an even more expansive
coronoid process of the dentary covering most
of the labial face of the coronoid bone. The
dentary of Aethesia has a coronoid process that
would have overlapped the coronoid anterola-
bially.
Dentary-Surangular Relationship.—Of the above
five families, there is a dichotomy in the manner
in which the surangular contacts the dentary. In
scincids, xantusiids, and cordyliforms, the trail-
ing edge of the dentary below the coronoid forms
a single forward-curving embayment that expo-
ses the front of the surangular, including the
anterior surangular foramen. In xenosaurs and
anguids, the trailing edge of the dentary is split
into two embayments or notches, a posterodorsal
coronoid notch and a posterolateral surangular
notch (Estes, 1983). Dibamus has a distinctive
posteroventrally angled and almost straight
posterior margin to the dentary (Rieppel, 1984)
that is arguably most like the single-embayment
condition. Although the surviving section of
dentaryedgeontheAethesia holotype is small,
it shows the apex of the dentary embayment and
reveals a relatively broad angle, more consistent
with the open, single embayment seen in the first
three families.
Pattern of Tooth Replacement.—Although the
posterior teeth of Aethesia show an aberrant
pattern of tooth replacement, the anterior teeth
show that new teeth developed in the eroded
bases of existing teeth. This mode of tooth
replacement is consistent with scincids and
many other lizards but excludes the angui-
morphs, in which replacement teeth lie beside
the emplaced tooth and there is no erosion of
the tooth base (Estes et al., 1988).
Meckelian Groove.—The closed Meckelian
groove of Aethesia, completely overgrown by
the dentary, is characteristic of some or all of
several lizard families (all gekkonoids and
xantusiids, some scincids, gymnophthalmids,
iguanids and amphisbaenians; Estes et al.,
1988).
Splenial, Anterior Extent.—The splenial of
Aethesia has its anterior limit at the inferior
alveolar foramen, for which it forms the
posterior margin. The splenial completely en-
closes the inferior alveolar foramen in some
lizard families. In anguids, xenosaurids, cordy-
liforms, and teiids, the splenial extends much
further forward, even approaching the symphy-
sis. In skinks with a patent Meckelian groove,
the splenial sends a process ventral to and
anterior to the inferior alveolar foramen, but in
those with a closed Meckelian groove, the
splenial extends no further forward than the
region of the inferior alveolar foramen, as in
Aethesia. In xantusiids, the splenial is fused to
the dentary. In other squamate lineages, the
splenial is greatly reduced, lying entirely pos-
terior to the inferior alveolar foramen, or is
completely absent.
The only major lineage of lizards that matches
Aethesia in all of the above respects is the
scincids.
AUSTRALIAN FOSSIL LIZARD 143
Possible Relationships.—The partial jaw has too
few characters, and too many these are appar-
ently unique, at least in their degree of
development, to justify a formal phylogenetic
analysis. Some of the characteristics, and possi-
ble implications for relationships, are discussed
below to indicate the problematic nature of the
possible relationships of this peculiar lizard.
Aethesia has a suite of features that correlate
with durophagy (Estes and Williams, 1984),
with a massive dentary, reduced numbers of
teeth with obtusely pointed crowns and an
enlarged coronoid region. Alternatively, its
characteristics also accord with patterns seen
in fossorial skinks that use the head for
burrowing (Rieppel, 1981). Such species typi-
cally have shortened tooth rows, with relatively
large teeth, and shorter, more stoutly built
mandibles. If the anatomy is interpreted as
adaptive for durophagy, this, together with its
absolute size and robustness and its relatively
recent Australian occurrence, suggest a possible
relationship with the species of the Tiliqua
lineage (Shea, 1990).
Species of Tiliqua have powerful jaws, but
even these lizards have more gracile jaws than
Aethesia (Fig. 3A). The teeth of Aethesia are
relatively robust in form but are not especially
large given the size of the jaw. The isodont
condition in Aethesia contrasts strongly with the
condition in the Tiliqua lineage (Shea, 1990), in
which several of the more posterior cheek teeth
are markedly larger than the others in the tooth
row. Although the dental sulcus becomes less
pronounced posteriorly in Tiliqua, it is never lost
as in Aethesia. The adductor muscles (a.m.e.s.)
leave an arcuate scar on the labial surface of the
dentary in Tiliqua, the scar forming a depressed
region relative to the surrounding dentary
surface, as it does in other skinks. In Aethesia,
the muscle scar has the contrasting condition of
being slightly raised compared to the dentary.
The mandibular symphysis in the Tiliqua
lineage is considerably expanded relative to
other skinks and is most extensive in the highly
specialized snail eater, Cyclodomorphus gerrardii.
Even so, relative size of the joint surface of the
symphysis is greater in Aethesia than any Tiliqua
or Cyclodomorphus species (Fig. 3A). In species
of Tiliqua and Cyclodomorphus (based on maxil-
lary tooth rows), the angle between the tooth
rows is much less than in Aethesia, ranging
between 30uand 40u(Tiliqua multifasciata). The
angle in other skinks is similar to that seen in
Tiliqua, mostly around 30ubut with some of the
shorter-snouted forms opening out to close to
40u. The broadest angle was observed in another
member of the Egernia Group, Corucia (Fig. 3B),
with the tooth rows angled at 45u.
In summary, Aethesia at first glance shares
several broad similarities with the Tiliqua
lineage, but they do not match once examined
in detail. Other members of the Egernia group
reach a large size, and some also have relatively
short, deep faces. Members of the Egernia
inornata species group have especially short
snouts, and one, E. kintorei reaches a large size
(206 mm SVL, McAlpin 1997). The cheek teeth
diverge at a greater angle than usual (38u) but
still well short of the 50useen in Aethesia, and E.
kintorei has a conventional morphology in other
respects. The short snout and widely angled
tooth rows of Corucia have already been
mentioned. This large member of the Egernia
Group also has relatively heavy dentaries that
show some flattening of the ventral surface
suggestive of the condition in Aethesia. Howev-
er, the proportions of the splenial are far
different. The morphology in Corucia (Fig. 3B)
is similar to that in Egernia, except that the
inferior alveolar foramen is unusually far
FIG. 3. Mandibles in lingual view of representative
scincid genera, showing some of the major patterns of
variation. (A) Tiliqua multifasciata (Lygosominae,
Egernia Group), (B) Corucia zebrata (Lygosominae,
Egernia Group). (C) Eugongylus albofasciolatus (Lygo-
sominae, Eugongylus Group). (D) Acontias plumbeus
(Acontinae). The vertical line on each indicates the
approximate comparable point to the break in the
fossil specimen. Abbreviations as in Figure 2, with the
addition of the following: ang, angular; art, articular;
san, surangular. Scale bar in each equals 10 mm.
144 M. N. HUTCHINSON AND J. D. SCANLON
forward relative to the tooth row. This suggests
that the short face has been achieved by
truncation of the anterior portion of the dentary,
in contrast to the situation in Aethesia in which
the splenial and inferior alveolar foramen have
retreated posteriorly, and the mandible has
greatly expanded dorsoventrally.
If Aethesia is not a member of the Egernia
Group, are there other possible relationships
that might be proposed? The dentary over-
growth of the Meckelian groove is a character
state that tends to be restricted to certain
lineages, with only minor exceptions. Two other
skink lineages show complete obliteration of the
Meckelian groove by the dentary, the Eugongy-
lus Group (Lygosominae; Fig. 3C) and the
Acontinae (Fig. 3D).
Three lineages of the subfamily Lygosominae
are recognized in Australia, the Egernia Group
(Fig. 3A,B), the Eugongylus Group (Fig. 3C), and
the Sphenomorphus Group (Greer, 1979; Honda
et al., 2000). Members of first two groups all
show closure of the Meckelian groove by
dentary overgrowth, whereas the members of
the last group, as well as the stem group skinks
in the grade subfamily ‘‘Scincinae,’’ almost all
have the Meckelian groove completely open.
Members of the Sphenomorphus Group and the
Egernia Group show a consistent condition for
the splenial, which has its ventral margin
reaching almost to the bottom edge of the
mandible, its anterior extremity curving up to
margin the anterior inferior alveolar foramen
both posteriorly and ventrally. This morpholo-
gy is also seen in stem group skinks, such as
Eumeces, implying that it is plesiomorphic for
lygosomine skinks (Estes et al., 1988). By
contrast, in the Eugongylus Group, the anterior
portion of the splenial is remote from the
bottom edge of the mandible because of
posterior expansion of the lingual surface of
the denary (Fig. 3C). This expansion creates a
triangular wedge of the dentary tapering pos-
teroventrally and underlying both the inferior
alveolar foramen and the splenial. In this group,
the anterior tip of the splenial contacts the
posterior and dorsal margins of the inferior
alveolar foramen (Hutchinson, 1992). The rela-
tionship of the splenial to the dentary and the
inferior alveolar foramen in Aethesia most nearly
matches the condition in the Eugongylus Group,
with a posteroventral lingual wedge of the
dentary underlying the splenial, which in turn
contacts only the rear of the inferior alveolar
foramen. Unlike the condition in the Eugongylus
Group skinks, the splenial has no process lying
along the dorsal margin of the inferior alveolar
foramen and none of the extant genera (over
30 distributed across Australia, New Guinea,
New Caledonia, and New Zealand) approaches
Aethesia in size or robustness. The very few
fossorial species in this group, such as Nanno-
scincus (Sadlier, 1990), do not show the adapta-
tions for head-first burrowing seen in limb-
reduced skinks of other lineages.
Besides the lygosomines, the other major
skink lineage with uniform loss of the Meck-
elian groove is the subfamily Acontinae (Greer,
1970; Rieppel, 1981). Acontines are an entirely
southern African group of limbless burrowers.
Most species are small, but one, Acontias
plumbeus, reaches a considerable size (snout–
vent length to 490 mm; Branch, 1998). Acontines
have a splenial reduced in size such that, as in
Aethesia, it contacts only the posterior extremity
of the inferior alveolar foramen (Fig. 3D).
Unlike Aethesia, the splenial is also reduced in
size ventrally and posteriorly and, in the two
specimens examined, is either distinct (Aethesia
meleagris) or fused with the angular (Aethesia
plumbeus). As highly developed head-first bur-
rowers, acontines show the usual morphological
correlates of a stout mandible and relatively
few, large teeth. The dentary of Acontias has an
acutely pointed, posteroventrally directed me-
dial projection extending the symphysis as in
Aethesia, although unlike it in detailed shape.
However, some dissimilarity may be no more
than the scaling effect of the much larger
Aethesia. At present a significant objection to
thinking of Aethesia as related to acontines is the
lack of evidence that this lineage has ever lived
anywhere but Africa.
Preliminary searching of available lizard
material from Wellington Caves by M. Augee
has yielded a small sample of lizard remains
from early Pleistocene layers. Almost all are
partial dentaries and maxillae that appear to be
assignable to Egernia (MNH, pers. obs.), most
probably E. cunninghami based on the close-
packed, sharp-edged tooth crowns (Mackness
and Hutchinson, 2000). No other material
assignable to Aethesia is known at present.
Discovery of a lizard as divergent in form as
Aethesia is unexpected. Fossil evidence so far
available suggests that Australian lizard evolu-
tion over the Neogene has consisted of fine
tuning of morphologies that diverged in the
Mesozoic or early Tertiary (Estes, 1983). The
discovery of Aethesia in Australia’s recent past
suggests that the modern fauna represents only
part of the morphological diversity that evolved
here during the Tertiary.
Acknowledgments.—We thank M. Lee and
anonymous reviewers for their comments on
an earlier draft of the manuscript. M. Augee,
University of New South Wales, and P. Willis
provided us with other samples of reptile
remains from the Wellington Caves system,
AUSTRALIAN FOSSIL LIZARD 145
and M. Augee and M. Archer provided infor-
mation and comments on the question of
provenance. Digital images of Aethesia (Figs. 1–
2) prepared by R. Hamilton-Bruce.
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