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Harris et al., eds., 2006, The Triassic-Jurassic Terrestrial Transition. New Mexico Museum of Natural History and Science Bulletin 37.
THE EARLY JURASSIC CLEVOSAURS FROM CHINA
(DIAPSIDA: LEPIDOSAURIA)
MARC E. H. JONES
Evolutionary Anatomy Unit, Department of Anatomy and Developmental Biology, University College London, London, UK, WCIE 6BT,
E-mail: marc.jones@ucl.ac.uk
Abstract—The Lufeng Formation of Yunnan Province, China has provided an important contribution to the
understanding of Early Jurassic terrestrial vertebrate faunas. Here, previously described rhynchocephalian skull
material is reassessed and new information is provided regarding the dentition. Unfortunately, poor preservation
obscures a number of morphological features and is, in places, misleading. No significant characters can be found
to warrant prior taxonomic separations. Affinity to Clevosaurus is supported by the presence of a lateral
ectopterygoid-palatine contact that excludes the maxilla from the suborbital fenestra and a jugal with a long dorsal
process that extends posteriorly. As in other clevosaurs, the snout is short and rounded, and all specimens
demonstrate a large and steeply inclined coronoid process of the dentary. The taxon possesses a greater number of
teeth than the type species Clevosaurus hudsoni and in this respect more closely resembles C. bairdi, C. convalis,
or C. minor. Flanges, if at all present on the dentary teeth, are small. Differences from other described species of
Clevosaurus include a palatine tooth row that is strongly curved rather than straight, and there is evidence of an
additional row of teeth on the pterygoid, making three in all. Due to the lack of reliable autapomorphies the material
is probably best treated as Clevosaurus sp. but further material may provide enough evidence to resurrect
“Clevosaurus petilus” or the generic name “Dianosaurus.” Nevertheless, the Lufeng material represents the
earliest known lepidosaur material from Asia and confirms the presence of the Rhynchocephalia in China during
the Jurassic. The latter is significant because they are notably absent from productive younger localities.
INTRODUCTION
The Early Jurassic section of the Lufeng Formation in Yunnan
Province, China, has yielded a range of fossil vertebrate taxa (Luo and
Wu, 1994), including crocodylomorphs (Wu and Sues, 1996; Harris et
al., 2000), prosauropods (Young, 1941; Simmons, 1965; Evans and Milner,
1989; Barrett and Xing, 2005; Barrett et al., 2005), a sauropod (Barrett,
1999), non-avian theropods (Hu et al., 1993; Zhao and Xu, 1998, Xu et
al., 2001; Irmis, 2004), ornithischians (Lucas, 1996; Dong, 2001),
tritylodontids (Luo and Wu, 1994) and mammaliaformes (Patterson and
Olsen, 1961; Luo et al., 2001).
The Lufeng Formation also provides the only existing record of
material referred to as the Rhynchocephalia (sensu Gauthier, et al., 1988)
from Asia (note that India was not part of Asia until the Miocene [Smith
et al., 1994; Evans et al., 2001]). This material is of biogeographic signifi-
cance because it demonstrates that rhynchocephalians attained a global
distribution in the Early Mesozoic (Sues and Reisz, 1995; Evans et al.,
2001). More specifically, the attribution of the Lufeng material to
Clevosaurus by Wu (1994) allowed Sues and Reisz (1995) to assert that
the genus itself had attained a global distribution. Clevosaurus was first
described from the Late Triassic of the UK (Swinton, 1939; Halstead
and Nicoll, 1971; Robinson, 1973; Marshall and Whiteside, 1980;
Whiteside and Robinson, 1983; Fraser, 1988, 1993, 1994; Benton and
Spencer, 1995), but has since been described from the Early Jurassic of
North America (Sues et al., 1994), South Africa (Sues and Reisz, 1995)
and the UK (Pacey, 1978; Crush, 1984; Evans and Kermack, 1994; Säilä,
2005). Less complete remains have also been attributed to Clevosaurus
from the Late Triassic of North America, (Fraser, 1993; Heckert, 2004),
Belgium (Duffin, 1995), and Early Jurassic of Zimbabwe (Gow and
Raath, 1977) and Mexico (Reynoso, 1993; Fastovsky et al., 1998). In
total, eight species of Clevosaurus have been named: C. hudsoni (the
type species), C. bairdi, C. convalis, C. latidens, C. minor, C. mcgilli, C.
petilus, and “C. wangi” (Swinton, 1939; Robinson, 1973; Fraser, 1988,
1993; Wu, 1994; Säilä, 2005). In addition, the larger taxonomic grouping
of “clevosaurs” includes Clevosaurus as well as Polysphenodon and
Brachyrhinodon, from the Triassic of Germany and the UK, respec-
tively (Fraser and Benton, 1989; Wu, 1994; Reynoso and Clark, 1998).
Despite the apparent success of clevosaurs in the early Mesozoic, the
Lufeng specimens are some of the last known records of Clevosaurus
(Table 1).
No other lepidosaurs are known from Lufeng (Evans and Milner,
1989; Evans, 2003) and the oldest known squamates from China are part
of the Early Cretaceous Jehol Biota: Dalinghosaurus, Jeholacaerta,
Liaoningolacerta, Yabeinosaurus (Endo and Shikama, 1942; Ji and Ren,
1999; Evans, 2003; Evans et al., 2004; Evans and Wang, 2005a, b), and
the contemporaneous Mimobecklesisaurus (Li, 1985; S.E. Evans, per-
sonal commun., 2006; J.D. Harris, personal commun., 2006). Similarly,
no squamates are known from the Triassic or Early Jurassic of Asia.
Earliest examples include Changetisaurus and other material from the
Middle Jurassic of Kirghizia/Kyrgyzstan (Nessov, 1985; Fedorov and
Nessov, 1992), and the presumed paramacellodid Sharovisaurus from
the Late Jurassic of Kazakhstan (Hecht and Hecht, 1984). However
there is a high degree of lizard diversity in the Late Cretaceous of east
Asia (Alifanov, 1993, 2000; Evans, 1998; Evans, et al., 2001). Conse-
quently, in Asia, as elsewhere, there is little evidence for large scale
coexistence of rhynchocephalians and squamates.
In terms of global faunas, while Triassic squamates remain un-
known, rhynchocephalian material of this age is widespread (Evans et
al., 2001; Evans, 2003). Jurassic localities seem to be divided between
those that provide many specimens of rhynchocephalians and few liz-
ards (e.g., Cerin, Morrison, Solnhofen) or many lizards and few rhyn-
chocephalians (e.g., Uña, Las Hoyas, Purbeck, Kirtlington, Guimarota)
(Evans, 1995, 1996, 2003; Evans and Chure, 1999; Evans and Waldman,
1996). This suggests either that the two groups preferred different envi-
ronments (Evans, 1995) or that the two groups were in direct competi-
tion (Milner et al., 2000) with each other for resources such as food or
living space. This, coupled with the somewhat dramatic, mid Jurassic-
Late Cretaceous decline of the Rhynchocephalia, has prompted hypoth-
eses that rhynchocephalians were out-competed and eventually replaced
by squamates in most parts of the world (Milner et al., 2000; Evans et
al., 2001; Apesteguía, 2005).
With this replacement hypothesis in mind, the number of Early
549
Jurassic rhynchocephalian species in east Asia becomes important. The
greater the number of species, the greater the diversity and, correspond-
ingly, the more dramatic and severe a local Mid- to Late Jurassic extinc-
tion appears (Evans et al., 2001). On the basis of the Lufeng material, Wu
(1994) diagnosed three new species of Clevosaurus. Direct examination
of the Lufeng lepidosaur material by the present author led to somewhat
different interpretations to that of Wu (1994) and a more conservative
estimate for the number of species represented.
Previous Taxonomy and Diagnoses
The Lufeng material consists of four small, partial skulls (Table
1). The first of these (Institute of Vertebrate Paleontology and
Paleoanthropology [IVPP] V.4007) was described by Young (1982) and
published posthumously as Dianosaurus petilus, a member of the
“Protorosauria.” The assessment was made prior to final preparation
and Young was unsatisfied with his phylogenetic conclusion (Wu, 1994).
Wu (1994) subsequently redescribed the skull in detail along with three
additional skulls (IVPP V.8271, IVPP V.8272, IVPP V.8273) and attrib-
uted them to the rhynchocephalian genus Clevosaurus as three separate
species: Clevosaurus petilus, “C. wangi,” and C. mcgilli.
Clevosaurus petilus (IVPP V.4007) was diagnosed by Wu (1994)
as possessing:
1. Supratemporal fenestra oval and oriented diagonally.
2. Parietal narrow anteriorly.
3. Maxilla with a dorsal margin that slopes upward toward its
contact with the jugal.
4. Jugal with a short anterior process.
5. Very slender basipterygoid process.
6. Prearticular that extends anteriorly beyond the ventral edge of
the coronoid.
“C. wangi” (IVPP V.8271) was diagnosed by Wu (1994) as pos-
sessing:
1. Relatively small supratemporal fenestrae.
2. Parietal width between the supratemporal fenestrae broader
than the interorbital width.
3. Paroccipital process fitting into a fossa on the underside of the
squamosal.
4. Supratemporal underlying the posteromedial margin of the
squamosal.
5. Dorsal process of the jugal sloping backward to overlap the
squamosal at a point beyond the midpoint of the supratempo-
ral bar.
6. Pterygoid with an elongate central region between three rami.
7. Epipterygoid broad dorsally but narrow ventrally.
C. mcgilli (IVPP V.8272, V.8273) was diagnosed by Wu (1994) as
TABLE 1. Known material with possible clevosaur affinities. Note the material referred to by Flynn et al. (1997) is in fact juvenile rhynchosaur material
(R. Whatley, personal commun., 2005). Pamizinsaurus (Reynoso, 1997) and Tingitana (Evans and Sigogneau-Russell, 1997) are not included.
550
possessing:
1. A large row of palatine teeth that is subparallel to the marginal
teeth of the maxilla.
2. Palatine becoming broad posteriorly, resulting in an L-shaped
suborbital fenestra.
3. Jugal with a long anterior process that meets the ventral pro-
cess of the prefrontal at the anteroventral corner of the orbit
and a dorsal process that is expanded laterally at its extremity.
4. Postorbital strongly curved ventrally, showing a T-shaped lat-
eral outline.
5. Supratemporal asymmetrically V-shaped.
6. Very short snout (less than a quarter of the skull length).
MATERIAL AND METHODS
The material consists of four partial skulls that were preserved in
ferruginous nodules and subjected to varying degrees of diagenetic crush-
ing (Wu, 1994). As a result, most bones are fractured or displaced to
some degree. Furthermore, the surfaces bear a colorful, venous, mottled
appearance that often renders the distinction between matrix and bone
unclear. All of these factors obscure sutures, teeth, and foramina and
encourage subjectivity. The specimens certainly do not demonstrate the
detail or preservation quality exhibited by microvertebrate material from
England and Wales (Evans, 1980; Fraser, 1982, 1986, 1988; Fraser and
Walkden, 1983; Whiteside, 1986).
The fossil material was examined using a Wild Stereo Microscope,
and impressions of the teeth were made using Speedex light body dental
putty (polysiloxane). The teeth were subsequently cast using epoxy
resin. The resulting casts were then sputter coated and examined under
the JEOL JSM-5410LV Scanning Electron Microscope in the Depart-
ment of Anatomy and Developmental Biology at University College
London. Drawings were made using a camera lucida and images were
produced using a EPSON GT-7300U flat bed scanner at high resolution.
DESCRIPTION
The uncertain taxonomic status of the Lufeng specimen warrants
individual description of the specimens. This is not intended to replace
the descriptions of Wu (1994), as it is merely an alternative interpreta-
tion. However, it does allow this paper to be read independently, with-
out relying on a referral to the previous publication.
IVPP V.4007
As mentioned above, this specimen, the largest of the Lufeng
specimens, was originally described by Young (1982) but subsequently
redescribed by Wu (1994). It consists of the posterior half of a crushed
skull with parts of both lower jaws preserved in a closed position. No
information regarding the premaxillae, nasals, or vomers is available. The
skull is widest at the posterior corners and tapers anteriorly, suggesting
the skull was triangular in dorsal view, although this may have been
exaggerated by lateral crushing (Figs. 1A-D). Its estimated length (from
the tip of the rostrum to the back of the jaw joint) is 31-34 mm; its
estimated width at the jaw articulation is 25-26 mm.
The posterior end of the right maxilla is preserved, but the surface
is badly damaged. The ventral margin bears an acrodont dentition with
basally ovoid teeth, four of which are preserved posteriorly. They have
also been badly abraded, which precludes meaningful comment regarding
the shape of their cusps, although the best preserved (fourth from rear)
exhibits ridges around its base that may be evidence of enamel ornamen-
tation or food-on-tooth wear (Figs. 2A, 2B). As described by Wu (1994),
the dorsal margin of the maxilla appears to curve upward along the orbital
margin to meet the jugal, although this is only preserved on one side (Fig.
1C). The posterior extent of the right postorbital can be seen as a faint,
rounded outline and is situated more posteriorly than figured by Wu
(1994). There is no posterior process on the right jugal of IVPP V.4007
(left not preserved), but the smooth posterior edge may be the result of
postmortem polishing or overpreparation. The anterior tip of the jugal
fits into a notch on the medial surface of the maxilla (Fig. 1A) and would
not have reached the prefrontal.
In dorsal view, large, oval, supratemporal fenestrae are seen on
both sides. The anterior portions of the frontals are not preserved, but
the section available demonstrates that the frontals were paired and that
the external seam of the intervening suture is straight. At the frontopari-
etal joint, the dorsal surface of neither bone is preserved but the internal,
interdigitated suture is visible The medial edge of the left parietal has
been rotated ventromedially so that only the lateral adductor surface is
visible; the true transverse width of the parietal table therefore cannot be
estimated with certainty (contra Wu [1994] who described the parietal
as narrower than the orbits). There are also no natural edges of the
presumed parietal foramen preserved. On both sides there are faint seams
between the postorbital and the squamosal. The dorsal process of the
jugal is poorly preserved, but it probably extends posteriorly to contact
the squamosal halfway along the upper temporal bar.
The lateral processes of the ectopterygoid and palatine clearly
meet, excluding the maxilla from contributing to the suborbital fenestra
(Fig. 1B). This can be viewed not only in ventral aspect but also in lateral
and dorsal aspects because the right maxilla is absent. The pterygoid is
FIGURE 1. Specimen IVPP V.4007. A, Dorsal view. B, Ventral view. C,
Lateral view of the right side. D, Occipital view. Scale bars equal 5 mm.
551
also excluded from the suborbital fenestra by the palatine and
ectopterygoid. The enlarged palatine tooth row is visible on both sides
and is curved. The medial portion of the palate is heavily damaged,
possibly during preparation, and there is no evidence of an inter-ptery-
goid joint. The anteromedial parts of both pterygoids are absent. The
basipterygoid processes are strangely elongate, but this may again be
because of overpreparation.
A large coronoid process of the dentary (CPD) can be found on
both sides (Fig. 1C). This is approximately equal in height to the dentary
immediately in front of the coronoid process. A small, rounded coronoid
bone is exposed above the CPD on the right. Anterior to the coronoid
process, the left lower jaw is either hidden from view by the maxilla or
not preserved. Two or three triangular or conical teeth can just be seen in
lingual view at an oblique angle. The anterior extent of the prearticular is
unclear, but it may have reached beyond the CPD (Wu, 1994). On the
right side, the tooth row is almost entirely absent except for the
posteriormost few millimetres. Just below this, there is a slight rim that
probably represents the edge of a secondary bone skirt (“longitudinal
lip” of Whiteside [1986], “ridge” of Säilä [2005], “ledge” of Fraser and
Benton [1989]). The dentary extends posteriorly past a point level with
the anterior margin of the jaw joint, but the posteriormost tip is damaged
on both sides. The posterior ends of the articulars and prearticulars are
not preserved.
In rhynchocephalians, the quadrate and quadratojugals often form
a single fused element with the lateral part representing the quadratojugal
and the medial part representing the quadrate. In Sphenodon, a portion of
suture is occasionally visible at the dorsal margins of the bones. In oc-
cipital view (Fig. 1D), the quadrate-quadratojugals are tall and narrow
dorsally; they have a height over twice the width at the base. There is a
small depression on the right quadratojugal that might be evidence of a
small facet for the posterior process of the jugal. The quadrate wing of
the right pterygoid is relatively well preserved. Posterior to this lies an
elongate element that may be a stapes, although it is uncharacteristically
thick. The anterior portion of the basioccipital is preserved and exhibits
a semicircular depression on its ventral surface (Wu, 1994).
IVPP V.8271
This specimen was named “C. wangi” by Wu (1994) but
synonymized with C. petilus by Sues et al. (1994). The specimen con-
sists of a crushed partial skull primarily preserving the left lateral face of
the skull, left lower jaw, and part of the right lower jaw and maxilla. Part
of the palate, nasals and left frontal are also preserved (Figs. 3A-D, 5A-
C). Its estimated length is 27 mm; its estimated width at the jaw articu-
lation is 20-24 mm.
In lateral view, the outline of the left maxilla is discernable, and
although the surface is cracked, a damaged band of secondary bone (lip of
Sues et al. [1994]) is visible (Fig. 3A). The ascending process (facial
process in Säilä [2005]) is slightly shorter in length than the suborbital
section. The anteroventral corner of the maxilla is not available but the
premaxillary process of the maxilla is either short or absent. Anterior to
the maxilla, the premaxilla is partially preserved; its lateral process cer-
tainly extends above the base of the naris, but the full dorsal extent is
unknown. Therefore, although the process is dorsally expanded, it is
possible that the maxilla was not excluded from the dorsal half of the
naris. Nevertheless, IVPP V.8271 probably possessed a short, rounded
snout with a vertically oriented naris as found in other species of
Clevosaurus. The dentition and nasal process of the premaxilla is un-
known and the internal structure of the premaxilla–maxilla joint is hidden
from view.
Above the maxilla, part of the prefrontal structure is preserved; it
precludes the presence of a lacrimal bone on the margin of the orbit. The
dentition on the maxilla is poorly preserved but certainly appears to be
acrodont. The occlusal view suggests the presence of at least seven teeth;
there is room for 12 in all. The two small posterior teeth may represent
part of the successional dentition (Fig. 2C) but are reminiscent of the
anterior teeth found in Rebbanasaurus (Evans et al., 2001, figs. 3B-D).
They are conical with a apicobasal dimension greater than their mesiodis-
tal dimension. Obvious flanges are not evident on any of the teeth and the
tooth bases appear generally ovoid (Fig. 4).
The posterior end of the maxilla has a broad contact with the jugal,
but the posterior end of the jugal is unknown. The posterior orbital
margin is also absent. Part of the dorsal process remains; it meets the
postorbital and squamosal halfway along the upper temporal bar. Before
meeting the squamosal, the jugal constitutes 33% of the bar’s height,
whereas the postorbital constitutes 66%. The descending process of the
squamosal extends at least halfway down the lateral edge of the quadrate-
quadratojugal. The right quadratojugal is not preserved and the left shows
no sign of contact with the posterior of a lower temporal bar. In posterior
view, the quadrate-quadratojugal is broadly triangular with a height over
twice the width at its base.
A secondary bone skirt is present on the left dentary (Fig. 3B).
The dentary itself extends posteriorly past a point level with the anterior
margin of the jaw joint. The CPD is well preserved and approximately
equal in height to the dentary in front of the coronoid, about 20% the
length of the tooth row. A small coronoid bone may also be present above
the tip of the CPD.
Evidence of the nasal is mainly preserved as an internal cast with
only a small portion of the left bone preserved posteriorly (Fig. 3D). The
latter meets the frontal with a “V”-shaped seam, but the medial part of
this seam is more anteriorly positioned than drawn by Wu (1994, fig.
3.7A). A dorsal view of IVPP V.8271 clearly demonstrates the lateral
FIGURE 2. Scanning electron microscope images of the dentition. A, Part
of the left maxilla of IVPP V.4007 in ventral view. B, Enlargement of
fourth maxillary tooth from rear. C, Posterior teeth on the left maxilla of
IVPP V.8271 in lateral view. D, Left maxilla of IVPP P.8273 in lateral view.
E, Right maxilla of IVPP P.8273 in lateral view. F, Premaxillary chisel
dentition of IVPP V.8273 in anterior view. G, Posteriormost teeth from
the left dentary of IVPP V.8273. Dark patches are artifacts of the casting
process. All scale bars equal 1 mm.
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crushing. The frontals are paired with a straight seam. The supratempo-
ral fenestra is badly distorted and damaged, precluding a reliable estimate
of its former shape and size. Only a small sliver of parietal survives and
the existence of a parietal foramen is completely unknown. The presence
of supratemporal bones is also uncertain. Only one suture is clear that
could represent contact between the parietal and squamosal.
In ventral view, the enlarged palatine tooth rows and suborbital
fenestrae are visible on both the left and right sides (Fig. 5A-C). The
ectopterygoid and palatine can clearly be seen to meet and therefore
would have excluded the maxilla from contributing to the rim of the
suborbital fenestra. In addition, the pterygoid is excluded from the sub-
orbital fenestra by the same two bones. The palatine tooth rows are very
curved, as in IVPP V.4007. On the pterygoid, pale dots are visible within
darker colouration where teeth might be expected. However, similar pale,
ovoid features appear on the pterygoid flange and on the base of the
quadrate-pterygoid wing (not figured by Wu [1994]) (Fig. 5A). This
suggests that not all the pale dots are necessarily teeth. Some of the
“teeth” on the pterygoid (not figured by Wu [1994]) could represent a
posterior continuation of the enlarged palatine tooth row. In addition,
providing that the portion of pterygoid preserved on the right is indeed
all part of the right pterygoid, there are also two rows of sagittally
aligned teeth. The interpterygoid joint is not preserved. The medial por-
tions of both paired vomers are preserved and they too bear ovoid fea-
tures suggesting the presence of at least one row of teeth (not figured by
Wu [1994]). The central region of the pterygoid, which unites the ante-
rior, posterior and lateral processes, is elongate (sensu Wu, 1994). How-
ever, the exact length and shape of this region in Sphenodon varies
intraspecifically (personal obs.).
Some braincase structure can be discerned. The basipterygoid
rami appear to be relatively long but the possibility of damage cannot be
excluded (Fig. 5). Also, a semicircular depression is present on the ven-
tral surface of the basioccipital (Wu, 1994). In posterior view, on the left
side, there is a bone that could be a stapes. It is in the correct position for
a stapes but it is strangely robust and might therefore be a displaced
epipterygoid or hyoid element (S.E. Evans, personal commun., 2005;
N.C. Fraser, personal commun., 2006).
IVPP V.8272
Named “C. mcgilli” by Wu (1994), IVPP V.8272 is the posterior
half of a small skull with parts of both jaws preserved in a closed posi-
tion. The skull has been crushed both dorsally and laterally; the premax-
illa and anterior tip of the maxilla are not preserved. Meaningful features
of the braincase are obscure at best and the palate is also poorly pre-
served (Fig. 6A-D). Its estimated length is 22-24 mm; the estimated
width at the jaw articulation is 16-18 mm.
On the lateral surface of the left maxilla there is evidence of both a
band of secondary bone and an acrodont dentition, but the presence of
flanges is unclear (Fig. 6A). In the section preserved, there are perhaps
eight teeth, all of which possess ovoid bases (Fig. 7). The two
posteriormost teeth are about half the size of the preceding six and
resemble those of IVPP V.8271. Posteriorly, the maxilla demonstrates a
broad contact with the jugal. The jugal appears to have a broken surface
at the base of its posterior surface, suggesting the presence of a thin
lower temporal bar that is broken. The dorsal process of the jugal is also
broken but it is possible that it extended posteriorly. Much of the afore-
mentioned breakage may be due to the lateral crushing that has also
pushed the maxilla and jugal dorsolaterally and reduced the apparent size
of the orbits (Fig. 6B).
FIGURE 3. Specimen IVPP V.8271. A, Lateral view of left side. B, Ventrolateral view of left side. C, Lateral view. D, Dorsolateral view of the left side.
Scale bars equal 10 mm.
553
The left postfrontal is present but has been displaced so that its
lateral, faceted edge faces anteriorly (contra Wu, 1994). A small portion
of the postorbital’s medial process is preserved posterior to this. The
right postorbital is more complete and is somewhat “T-shaped” (Wu,
1994) (Fig. 6C). The left squamosal bears a faint, lanceolate facet for the
postorbital, suggesting a similar squamosal-postorbital-jugal arrangement
to that of Clevosaurus hudsoni. The descending process of the squamo-
sal extends at least halfway down the lateral edge of the quadrate-
quadratojugal but the ventral tip is not preserved with certainty. The
lateral surface of the quadrate-quadratojugal is damaged but appears
smooth. The right quadratojugal foramen cannot be seen (contra Wu,
1994) and, on the left, the relevant area is damaged.
The right dentary bears a well defined, secondary bone skirt and a
large CPD approximately equal in height to the dentary in front of the
coronoid process (Figs. 6C, 8A). Posteriorly, below the tooth row, there
is also some indication of crescent-shaped wear facets like those found in
Clevosaurus convalis (Säilä, 2005). The anterior portion of the dentary
tooth row is not preserved. Approximately seven tooth bases are present
on the remaining section, probably constituting half the entire length
(Fig. 8A). The two posteriormost bases are small and no crowns are
preserved; hence, they are not visible in lateral view (Fig. 8B). The
preceding five bases are larger and possess crowns that seem to be ob-
tusely conical (Fig. 8C). The posterior end of the dentary extends to at
least the level of the jaw joint. It seems to taper abruptly (Wu, 1994), but
this could be the result of damage and abrasion. The prearticular is cer-
tainly damaged so that its posterior shape is unknown.
Matrix separates the paired frontals from the portion of left pari-
etal. Wu (1994) perceived the parietal table as narrowing in IVPP V.8272,
but the full lateral extent of the frontals is not preserved and the parietal
has shifted from its original position, making the proportions difficult to
assess with any confidence. The presence of supratemporal bones is not
obvious. The lateral suture labelled by Wu (1994) is here interpreted as
a line of coloration, not a joint in the skull, suggesting the medial suture
instead joins the parietal and squamosal. If the Lufeng taxon does pos-
sess supratemporal bones, they are not clearly delimited.
The palate is poorly preserved, but an enlarged palatine tooth row
might be present. The pterygoid is probably excluded from the subor-
bital fenestra by the ectopterygoid and palatine, but it is questionable
whether the maxilla is excluded from the suborbital fenestra by the pa-
latine and ectopterygoid. Viewed dorsally, within the orbit, the structure
is difficult to assess and remains inconclusive (contra Wu, 1994). The
palate of IVPP V.8272 also exhibits some ovoid, tooth-like features on
the left and right pterygoids, but both bones are damaged medially and
therefore do not permit assessment of the exact arrangement. The brain-
case of IVPP V.8272 is severely damaged.
IVPP V.8273
Attributed to “C. mcgilli” by Wu (1994), this is perhaps the best
preserved Lufeng specimen. However, it is also very incomplete, com-
prising only the anterior portion of a small skull including the premaxil-
lae, a partial right maxilla, a partial right prefrontal, and reasonably well-
preserved maxillary and dentary dentitions (Figs. 2E-G). The frontals,
postfrontals, postorbitals, squamosals, parietal, quadrate-quadratojugal,
and braincase are completely absent (Figs. 9A-D). It has an estimated
FIGURE 4. Tooth row on the left maxilla of specimen IVPP V.8271 in
ventral view with schematic interpretation. Scale bar equals 10 mm.
FIGURE 5. Palate of specimen IVPP V.8271. A, Ventrolateral view. B-C,
Ventral view. Scale bars equal 5 mm.
FIGURE 6. Specimen IVPP V.8272. A, Ventrolateral view of the left side. B,
Dorsal view. C, Lateral view of the right side. D, Ventral view. Scale bars
equal 5 mm.
554
length of 21-26 mm and an estimated width at the jaw articulation of 15-
19 mm.
The anterior, chisel-like dentition suggests the presence of two or
three cusps (Figs. 2F, 9A). On both sides, the dorsally expanded lateral
process of each premaxilla extends above the base of the naris, but the
dorsal portions of the premaxillae are damaged so the full dorsal extent is
unknown. Therefore, although the process is dorsally expanded, it is
possible that the maxilla was not excluded from the dorsal half of the
naris. The right maxilla is well preserved and demonstrates a secondary
bone band running above the tooth row. The ascending process has a
similar rounded dorsal margin to that of IVPP V.8271, but its longitudinal
dimension is smaller, only about one-third the length of the suborbital
section. The premaxillary process of the maxilla was either very short or
completely absent. A band of secondary bone can clearly be seen on both
the left and right maxillae (Figs. 2D, 2E, 9B). The maxillary dentition is
clearly acrodont. On the right maxilla there are around seven teeth present,
with space anteriorly for three more (Fig. 10A). The posteriormost
tooth is small and the preceding five are large. A large posterior flange is
visible on the third tooth from the rear on the right maxilla. Flange-like
structures are also exhibited by the second, fourth and six teeth from the
rear of the row (Fig. 2E). On the left maxilla there are three small teeth
anteriorly followed by five larger teeth (one of which is shattered) and,
lastly, a small conical tooth (Figs. 2D, 10B). The second-to-last tooth
exhibits a depression posteriorly; this may be a flange but could also
conceivably be a chipped section. The right prefrontal is preserved and
forms the anterior border of the orbital rim. The posterior end of the jugal
is unknown.
FIGURE 7. Tooth row on the left maxilla of specimen IVPP V.8272 in
ventral view with schematic interpretation. Scale bar equals 5 mm.
FIGURE 8. Dentary dentition of IVPP V.8272. A, Right lower jaw in lateral
view. B, Close up of dentition. C, Dorsal view with schematic interpretation.
Scale bars equal 5 mm.
FIGURE 9. Specimen IVPP V.8273. A, Ventrolateral view of the left side. B,
Lateral view of the left side C, Ventral view. D, Lateral view of the right
side. Scale bars equal 5 mm.
555
The palate is poorly preserved. Wu (1994 p. 52) described an
“L”-shaped suborbital fenestra in IVPP V.8273 “very similar to that of
Sphenodon.” Although a ridge of bone is present in the correct location to
represent such a palatine tooth row, it is surrounded by matrix and
isolated (contra Wu, 1994). Its position is therefore not reliable. It is also
not possible to determine whether or not the pterygoids and/or the
maxillae are excluded from the suborbital fenestra (contra Wu, 1994, fig.
3.14C). Posteriorly, the palatal area of IVPP V.8273 bears three or four
raised ridges that may represent the posterior ends of paired pterygoids,
each with two medial rows of teeth.
The anterior edge of the lower jaw is preserved only in IVPP
V.8273 and it is almost upright, unlike those of Palaeopleurosaurus or
Pamizinsaurus (Reynoso, 1997). It also exhibits a small ventral projec-
tion similar to those of other derived rhynchocephalians (Reynoso, 1997,
p. 56; Fraser, 1982). The ventral edge of the lower jaw is damaged for
most of its length. The dentary again possess a large CPD and there is
also evidence of a secondary bone skirt on the dentary (Fig. 9A). The
anterior of the prearticular is obscured. Two of the three well-preserved
posterior teeth on the left dentary seem to bear small posterior flanges
that are approximately 25% the length of the rest of the tooth (Figs. 2G,
10C). The most anterior tooth preserved bears a large depression along
its posterior edge that may be a facet produced by precise orthal wear.
DISCUSSION
Rhynchocephalian CharacterS
The Lufeng material can confidently be referred to the
Rhynchocephalia on the basis of the following characters:
- Acrodont or slowly replaced dentition (Whiteside, 1986):
present in all four specimens.
- Dentary extends posteriorly past a point level with the ante-
rior margin of the jaw joint (Whiteside, 1986): present in three specimens
but unknown in IVPP V.8273.
- Enlarged palatine tooth row (Whiteside, 1986): certainly
present in IVPP V.4007 and IVPP V.8271 and less certainly present in
IVPP V.8272 and IVPP V.8273 because of poor preservation.
The prefrontal structure of two of the specimens (IVPP V.8273
and IVPP V.8271) precludes the presence of a large lacrimal. Further-
more, small suborbital fenestrae and large supratemporal fenestrae are
visible where preservation permits (IVPP V.4007, IVPP V.8271 and IVPP
V.8272).
There are also a number of characters that suggest the Lufeng
material represents a taxon more derived than the two most phylogeneti-
cally basal rhynchocephalian taxa, Diphydontosaurus and Gephyrosaurus
(Evans, 1980; Whiteside, 1986; Reynoso, 1996):
- Secondary bone (referred to as “secondary dentine” by Fraser
FIGURE 10. Dentition of specimen IVPP V.8273. A, Right maxilla in lateral and ventrolateral view. B, Left maxilla in lateral and ventrolateral view. C,
Teeth from the left dentary in lateral and occlusal views. Scale bars for A and B equal 5 mm, scale bar for C equals 1 mm.
1986, 1988) (Harrison, 1901; Fraser 1986, 1988, p. 143; Fraser and
Benton, 1989; Sues et al., 1994; Evans et al., 2001, p. 315; Säilä, 2005):
present in all specimens.
- Stout teeth with broad bases (Whiteside, 1986; Evans et al.,
2001; Jones, 2006): present in all specimens.
- Chisel-like premaxillary dentition (Whiteside, 1986; Fraser,
1988): IVPP V.8273.
- A ventral projection at the anterior end of the dentary (Fraser,
1982; Reynoso, 1997): IVPP V.8273.
- Postorbital length equal to or greater than the orbit length
(Whiteside, 1986; Wu, 1994): IVPP V.8271, although the orbital margin
is damaged.
- Pterygoid excluded from the suborbital fenestra by the pa-
latine and ectopterygoid (Wu, 1994): IVPP V.4007, IVPP V.8271, and
possibly IVPP V.8272.
Derived rhynchocephalians can primarily be divided into five main groups
all of which are supposedly monophyletic. The clevosaurs (discussed
below), pleurosaurs (long bodied aquatic forms [Cocude-Michel, 1963;
Carroll, 1985; Carroll and Wild, 1994; Rothery, 2002; Dupret, 2004]),
sapheosaurs (short bodied aquatic forms [Cocude-Michel, 1963; Renesto
and Viohl, 1997; Reynoso, 2000; Reynoso and Gómez-Bonilla, 2000]),
sphenodontines (which contains the only extant genus, Sphenodon
[Günther, 1867; Reynoso, 1996; Reynoso, 2003]) and eilenodontines
(large, derived, terrestrial herbivores [Rasmussen and Callison, 1981;
Throckmorton et al., 1981; Apesteguía and Novas, 2003; Foster, 2003]).
Relationships between these five groups remain uncertain, although a
sister group relationship between the eilenodontines and sphenodontines
has been supported (Reynoso, 1996, 1997; Evans et al., 2001).
Planocephalosaurus is more derived than Gephyrosaurus and
Diphydontosaurus but it positions below all the five derived groups
(Fraser, 1982; Reynoso, 1996). There are also a number of taxa of uncer-
tain affinity, such as Homoeosaurus, Opisthias, Pamizinsaurus,
Rebbanasaurus and Tingitana (Reynoso, 1997; Evans and Sigogneau
Russell, 1997; Fraser and Wu, 1998; Evans et al., 2001; Evans and Searle,
2002).
Clevosaur Characters
As described by Wu (1994), the Lufeng material does possess
characters that suggest affinity with Clevosaurus. However, recent fos-
sil discoveries suggest some of the characters may be more widely dis-
tributed within the Rhynchocephalia.
A dorsally expanded lateral process (posterodorsal process of Wu
[1994]) of the premaxilla that may exclude the maxilla from the external
naris is present in IVPP V.8271 and probably also in IVPP V.8273 (al-
though it cannot be assessed in IVPP V.4007 or IVPP V.8273). This was
considered an important diagnostic character of Clevosaurus (Fraser,
556
1988, 1993; Wu, 1994; Sues et al., 1994; Sues and Reisz, 1995; Säilä,
2005): for example, material from Canada and South Africa was referred
to Clevosaurus primarily on the basis of this character (Sues et al., 1994,
p. 336; Sues and Reisz, 1995, p. 124). However, as more recently pointed
out, its presence is not restricted to Clevosaurus (Evans et al., 2001;
Säilä, 2005); it is also found in the Early Cretaceous Godavarisaurus
(Evans, 2001) and the eilenodontine Priosphenodon (Apesteguía and
Novas, 2003). A dorsally expanded lateral process of the premaxilla may
also exist in Pamizinsaurus (Reynoso, 1997) and the sapheosaur
Ankylosphenodon (Reynoso, 2000, personal commun., 2006). A more
widespread distribution of this character is perhaps not unsurprising
since its probable function, to strengthen the snout, induced its conver-
gent evolution in many archosauromorphs as well as the lepidosauromoph
Kuehneosaurus (e.g., Robinson, 1962).
The premaxillary process of the maxilla is known to be very short
or absent in Clevosaurus bairdi, C. hudsoni, and C. minor (Fraser, 1988;
Sues et al., 1994) whereas it is long in most other well known rhyn-
chocephalians apart from the eilenodontine Priosphenodon (Apesteguía
and Novas, 2003). The process is certainly short in IVPP V.8273, prob-
ably short in IVPP V.8271, but not preserved in IVPP V.8272 or IVPP
V.4007. However, the size of the process on the maxilla is, in part, related
to the structure of the lateral process of the premaxilla. Both IVPP
V.8271 and IVPP V.8273 probably possessed short, rounded snouts
with near vertically oriented nares like those seen in Brachyrhinodon,
Clevosaurus bairdi, and C. hudsoni (Fraser, 1988; Fraser and Benton,
1989; Sues et al., 1994).
In Clevosaurus bairdi, C. hudsoni, and C. minor, the maxilla is
excluded from the suborbital fenestra by a contact between the lateral
processes of the ectopterygoid and palatine (Fraser, 1988; Sues et al.,
1994). By contrast, the lateral processes of the ectopterygoid and pa-
latine do not meet in Diphydontosaurus, Gephyrosaurus, Kallimodon,
Planocephalosaurus, Priosphenodon, Palaeopleurosaurus, or Spheno-
don (Cocude-Michel, 1963; Fraser, 1982, personal commun., 2005; Sues
et al., 1994; Apesteguía and Novas, 2003). This character cannot be
evaluated in Ankylosphenodon, Brachyrhinodon, Polysphenodon,
Sapheosaurus, or Zapatadon (Sues et al., 1994; Apesteguía and Novas,
2003) and therefore is currently considered exclusive to Clevosaurus. It
is found in both IVPP V.8271 and V.4007 (not preserved in IVPP V.8272
or V.8273).
A broad contact between the maxillary and jugal (approximately
33% the height of the orbit) is found in all clevosaurs, but is also present
in other derived taxa such as Priosphenodon and Godavarisaurus (Evans
et al., 2001). This character is directly affected by orbit size and there-
fore, to some extent, skull size. It is not usually found in small taxa like
Diphydontosaurus, Gephyrosaurus, Planocephalosaurus, and
Rebbanasaurus (Evans, 1980; Fraser, 1982; Whiteside, 1986 ; Evans et
al., 2001). Neither is it supposedly found in the aquatic pleurosaurus
with their streamlined skulls (Carroll, 1985; Carroll and Wild, 1994; Wu,
1994, character 2; Reynoso, 1996, character 6). All the Lufeng material
possesses broad contacts.
In Brachyrhinodon, Clevosaurus bairdi, C. hudsoni, and
Polysphenodon, the long, thin dorsal process of the jugal extends poste-
riorly to meet the squamosal approximately halfway along the upper
temporal bar (Fraser, 1988; Wu, 1994; Reynoso and Clark, 1998, charac-
ter 7). The jugal does not extend as far as the posterior process of the
postorbital and is not as thick. As a result, the anterior portion of the
upper temporal bar comprises 66% postorbital and 33% jugal. This
character is present in both IVPP V.8271 and IVPP V.4007, and nothing
precludes its presence in the remaining specimens. The posterior pro-
cess of the jugal also meets the squamosal in basal rhynchocephalians,
but here the process is not long and meets the squamosal at a more
anterior position. The difference between the clevosaur and basal condi-
tions may be a symptom of the larger postorbital area of the former, but
the postorbital area is also large in Sphenodon in which the jugal does not
extend posteriorly to meet the squamosal.
Supratemporal bones are seemingly absent from phylogenetically
basal rhynchocephalians (Evans, 2003). By contrast they have been
reported in both Clevosaurus bairdi and C. hudsoni (Robinson, 1973;
Fraser, 1988; Wu, 1994; Sues et al., 1994), and Wu (1994) was confident
that supratemporal bones were present in the Lufeng specimens. As a
result, the presence of supratemporal bones helped to group Clevosaurus
in phylogenetic analyses (Sues et al., 1994, character 9; Reynoso, 1997,
character 45). However the presence of supratemporal bones in the
Lufeng material is open to interpretation. Also, supratemporal bones
have now been reported in Priosphenodon (Apesteguía and Novas, 2003)
and Zapatadon (Reynoso and Clark, 1998). Similarly, Pamizinsaurus
may also possess supratemporal bones but this remains uncertain
(Reynoso, 1997, personal commun., 2006). Rieppel (1992) reported
evidence for a small supratemporal bone in a hatchling Sphenodon skull
although in phylogenetic analyses it is generally coded as being absent
(e.g. Reynoso, 1997, character 45; Apesteguía and Novas, 2003, charac-
ter 31; Dupret, 2004, character 14).
Previously, the nature of the lower temporal bar was considered
very important for reptilian systematics (e.g., Romer, 1956). It is now
clear that considerable variation exists within Rhynchocephalia and it is
not always phylogenetically informative. Some taxa possess a complete
bar (Clevosaurus hudsoni) or a robustly sutured bar (e.g., Sphenodon),
whereas others possess a shorter posterior process on their jugal
(Diphydontosaurus, Gephyrosaurus, Palaeopleurosaurus and
Planocephalosaurus) or lack either a bar or a process (e.g., Pleurosaurus
and Priosphenodon). The lower temporal bar was interpreted as com-
plete in both C. hudsoni and C. minor based on the length of the jugal
posterior process and a “small boss” on the quadratojugal (Fraser, 1988).
The interpretation of a complete bar in C. bairdi is based on a small
depression on the quadratojugal (Sues et al., 1994). Such a depression
could, however, represent a site of ligament attachment. None of the
Lufeng specimens demonstrate clear evidence of a complete lower tem-
poral bar.
Tooth structure in the Rhynchocephalia is very diverse (e.g.,
Günther, 1867; Harrison, 1901; Howes and Swinnerton, 1901; Robinson,
1976; Evans, 1980; Rasmussen and Callison, 1981; Throckmorton et al.,
1981; Fraser, 1982, 1986; Fraser and Walkden, 1984; Fraser and Shelton,
1988; Reynoso, 1996, 1997, 2000; Evans and Sigogneau-Russell, 1997;
Renesto and Viohl, 1997; Evans et al., 2001; Foster, 2003; Dupret, 2004;
Heckert, 2004; Säilä, 2005; Jones, 2006) and therefore provides several
characters for both differentiating and characterizing taxa. Unfortunately,
because teeth in rhynchocephalians are generally acrodont, they can be
heavily worn, and the extent of wear is not thought to correlate simply
with age or skull size (Robinson, 1976; Fraser and Walkden, 1982).
Furthermore, in rhynchocephalian taxa, tooth structure and tooth ar-
rangement varies during ontogeny. In particular, the number of additional
and successional teeth varies with age and occasionally even between left
and right sides (Robinson, 1976; Fraser, 1986, 1988). Therefore, al-
though rhynchocephalian dentition provides a great deal of morphology
for phylogenetic characters, comparisons are greatly limited without
large sample sizes of each taxon in question. The tooth structure of some
sapheosaurus also remains poorly described (Cocude-Michel, 1963).
Clevosaurus hudsoni has a very characteristic dentition that clearly
distinguishes it from phylogenetically basal taxa (Diphydontosaurus,
Gephyrosaurus, Planocephalosaurus), sphenodontines, and
eilenodontines. The maxillary teeth are half cones with large posterior
flanges, whereas the dentary teeth are obtusely conical with large ante-
rior flanges, and small posterior flanges (Fraser, 1988). The dentary teeth
are arranged so that the anterior flange of each tooth extends anterolaterally
beyond the posterior flange of the preceding tooth. Similarly, the maxil-
lary teeth are arranged so that the posterior flange extends posterolingually
beyond the anterior margin of the more posterior tooth. There is an
increase in size posteriorly of the additional dentition and generally no
more than four additional teeth are present on both the maxilla and
dentary (Fraser, 1988). As stated above, all four Lufeng specimens pos-
557
sess fragments of acrodont dentition but dentition is best preserved in
IVPP V.8273 (Figs. 2D-G, 10A-C ). The maxillary dentition seems to
have been composed of about five or six large teeth with one or two
smaller teeth anteriorly and posteriorly. The larger teeth were not exactly
equal in size, but neither do they exhibit the drastic posterior increase in
size found in C. hudsoni (Fraser, 1988). A hatchling series (sensu Robinson,
1976) is either absent, fully replaced, or not preserved (Fig. 6). Teeth on
the maxilla are half cones and may bear flanges that can be up to 50% the
length of the entire tooth (Fig. 2E).
Only the posterior half of the dentary dentition can be assessed
because in all specimens the anterior half is either not preserved or
obscured. This space is normally occupied by the heavily worn hatchling
series in derived rhynchocephalians (Robinson, 1976). Posteriorly, the
dentary of IVPP V.8272 indicates that there were at least five additional
teeth on the dentary and possibly two small successional teeth posterior
to these. The two well preserved teeth (on the left dentary of IVPP
V.8273) have small posterior flanges that are approximately 25% the
length of the entire tooth. They lack the long anterior flanges present in
C. hudsoni and, as a result, the tooth row would have had space for a
greater number of teeth, provided the jaw was of the same length. As
noted by previous authors, this arrangement more closely resembles C.
bairdi, C. convalis, or C. minor (Fraser, 1993; Wu, 1994; Sues et al.,
1994; Säilä, 2005). The only available premaxillary dentition (IVPP
V.8273) is chisel-like, which is characteristic for derived members of the
Rhynchocephalia. It bears two or three cusps, but the significance of this
is uncertain. The number of cusps on the premaxillary chisel has been
noted in species diagnoses: for example, C. bairdi possesses one (e.g.,
Sues et al., 1994). However, the number of cusps visible in Sphenodon
can vary between one and three depending on age, wear, and secondary
bone deposition (Howes and Swinnerton, 1901; Robinson, 1976; per-
sonal obs.). Similar variation is found in large samples of Clevosaurus
hudsoni (Fraser, 1988).
All Lufeng specimens exhibit a large, steeply inclined CPD that is
approximately equal in height to the dentary in front of the coronoid and
about 20% the length of the tooth row. The steep inclination is much like
that in other clevosaurs where the CPD is known, e.g., Clevosaurus
hudsoni and C. bairdi. A tall, steep CPD is also found in Sigmala (Fraser,
1986) and Palaeopleurosaurus, although the latter possesses a relatively
long tooth row (Carroll, 1985; Carroll and Wild, 1994) and the former a
distinct, sigmoid jaw (Fraser, 1986).
Within the Rhynchocephalia, there is a general decrease in ptery-
goid tooth number. Gephyrosaurus possesses four tooth rows (Evans,
1980) whereas sphenodontines and eilenodontines possess no pterygoid
teeth at all (Apesteguía and Novas, 2003). Clevosaurs posses two rows
of parasagittally aligned pterygoid teeth (Fraser, 1988; Fraser and Benton,
1989; Wu, 1994). None of the Lufeng specimens possess a complete
pterygoid bone or easily discernable pterygoid teeth. Some evidence of
two parasagittal rows is present, but there is also some indication of a
third that was continuous with the palatine tooth row.
Number of Taxa
There are no adequate characters available that indicate the Lufeng
material represents more than one taxon. Wu (1994) provided a list of
characters to justify the erection of three new taxa but these are rendered
questionable by preservation quality, crushing, and the possibilities of
ontogenetic or other intraspecific variation (Table 2). The main factors
used to separate the specimens taxonomically were small differences in
skull proportions (Wu, 1994; Sues et al., 1994). Sues et al. (1994) con-
sidered the difference between C. petilus and “C. wangi” to have been
exaggerated by crushing and thus inconsequential. Similarly, the sup-
posed differences found in C. mcgilli (Wu, 1994; Sues et al., 1994) are
derived from a reconstruction that used the posterior end of IVPP V.8272
and anterior end of IVPP V.8273. As described above, the posterior end
of IVPP V.8272 is crushed and distorted.
One possible reason for retaining separate species is stratigraphic
differentiation. Specimen IVPP V.4007 was recovered from the Lower
Lufeng’s Dull Purplish Beds, whereas all others (IVPP V.8271, IVPP
V.8272, IVPP V.8273) were recovered from the overlying, slightly younger
Dark Red Beds (Wu, 1994). Based on biostratigraphic comparisons, Luo
and Wu (1994, p. 268) estimated the former to be Hettangian in age and
the latter to be Sinemurian in age. Sues et al. (1994) did not consider the
age difference to be a problem when they asserted that “C. wangi” (IVPP
V.8271) was a junior synonym of C. petilus (IVPP V.4007). In agreement
with Sues et al. (1994), stratigraphic level is here not considered a valid
criterion for separation of taxa that are otherwise based on morphological
characters. Otherwise, one risks circularity when assessing species di-
versity over time.
Potential autapomorphies for a single Lufeng taxon are largely
ambiguous. A semicircular depression on the ventral surface of the basio-
ccipital is preserved in two of the specimens (IVPP V.4007, IVPP V.8271).
However, braincase characters within the Rhynchocephalia are currently
not well surveyed and Sphenodon itself demonstrates notable variation
in braincase structure (D. Gower [NHM], personal commun., 2004;
personal obs.). A highly curved palatine tooth row is also present in the
same two specimens, as is the robust stapes-like element. Nevertheless
TABLE 2. Characters previously used to separate the Lufeng material. Note
that none of the characters used by Wu (1994) to define C. mcgilli are found
in both specimens so presumably they were grouped on the basis of size.
558
the Lufeng material is probably best considered as Clevosaurus sp. until
additional data demonstrate otherwise. Alternatively, for the purposes
of a cladistic analysis, the material could be considered as separate speci-
mens. Material is still being collected from the Lufeng (J. Li and Y. Wang,
personal commun., 2005) and further rhynchocephalian specimens may
be available in the future to shed light on several phylogenetically impor-
tant, but currently uncertain, characters. They may provide
autapomorphies allowing a revised diagnosis of Clevosaurus petilus.
Alternatively new material may reveal sufficient differences from
Clevosaurus to warrant resurrection of the name “Dianosaurus” (Young,
1982). Cranial characters of prime interest include adult and juvenile
tooth morphology and arrangement, the precise nature of the pterygoid
tooth rows, the presence or absence of the lower temporal bar, presence
or absence of the supratemporal bones, parietal structure, and the total
height and structure of the lateral premaxillary processes. These may
fully resolve the issue of whether or not the four currently available
skulls belong to a single taxon. Furthermore, the recovery of phyloge-
netically informative postcranial material, such as the sacrum, would
permit a more detailed discussion of the generic status of the Lufeng
rhynchocephalians.
Implications for Local and Global Mesozoic Diversity
On current evidence there is no support for more than one species
of rhynchocephalian from the Lufeng. This reduces the known diversity
of Clevosaurus (and Rhynchocephalia) in Asia during the Early Jurassic
and therefore the magnitude of a more recent extinction. In addition,
without species distinctions, the material no longer supports the hy-
pothesis of Luo and Wu (1994, p. 253) that there was an increase in
rhynchocephalian diversity within the Lufeng. Without more material,
our assessment of local fauna through time is greatly limited. Material
recovered from new Triassic and Middle Jurassic localities in China (e.g.,
Lucas, 2001) should provide a fuller picture. Nevertheless the Lufeng
material remains important because it represents the earliest known record
lepidosaurs from Asia (Evans and Milner, 1989; Evans, 2003), and the
only record of Rhynchocephalia from Asia, and because it supports the
view that that Clevosaurus (and Rhynchocephalia) were globally dis-
tributed during the early Mesozoic (Sues and Reisz, 1995).
The Lufeng material also represent one of the last known occur-
rences of Clevosaurus globally. As the age of the La Boca Formation is
now considered to be latest Early Jurassic (Reynoso, 1993; Fastovsky et
al., 1998, 2005), there is no longer any record of clevosaurs from the
Middle Jurassic or later in marked contrast to the Early Jurassic. Al-
though, the affinities of Pamizinsaurus and Tingitana remain enigmatic
(Evans and Sigogneau-Russell, 1997; Reynoso, 2000) and the Middle
Jurassic record is poor for many terrestrial vertebrate groups. As a result,
the current faunal picture may alter rapidly with the discovery of new
fossil localities and material.
The apparent disappearance of clevosaurs (or other
Rhynchocephalia) from Asia coincides with the appearance of squamates
(Nessov, 1985; Fedovrov and Nessov, 1992; Hecht and Hecht, 1984).
This is consistent with evidence from other localities suggesting that
rhynchocephalians and squamates rarely coexisted in the early Meso-
zoic (Evans, 1995, 1996, 2003; Evans and Waldman, 1996; Evans and
Chure, 1999). This may indicate either that the two groups exhibited
different environmental preferences (Evans, 1995) or that the two groups
were in direct competition with each other (Milner et al., 2000; Evans et
al., 2001; Apesteguía, 2005).
Correspondingly, the loss of a preferred environment or competi-
tion with lizards provides two possible causes for rhynchocephalian
extinction (Milner et al., 2000; Evans et al., 2001; Apesteguía, 2005).
However, given the diversity of the group it is unlikely that a single
factor can explain the extinction or decline of all members (e.g. Evans,
1980; Fraser and Walkden, 1983; Carroll and Wild, 1984; Fraser, 1988;
Reynoso, 2000; Apesteguía and Novas, 2003; Jones, 2006).
A more detailed picture of global Mesozoic fauna is required in
order to assess rhynchocephalian extinction with more confidence (e.g.,
Benton, 1987, 1991). This maybe achieved through more detailed de-
scription of previously reported lepidosaur material (e.g., Nessov, 1985;
Meszoely, 1987; Fedorov, and Nessov, 1992; Ferigolo, 1999), a greater
understanding of early lepidosaur paleoecology, improved dating of lo-
calities (independent of the fauna themselves), and greater efforts to
survey new and old localities for three-dimensional disarticulated
microvertebrate material (e.g., Ward, 1984). The latter has the potential
of providing large sample sizes of informative material (e.g., Evans, 1980;
Fraser, 1982, 1986, 1988; Whiteside, 1986) which is essential for supple-
menting data obtained from articulated specimens (Evans, 2003).
CONCLUSION
Recent fossil discoveries demonstrate that several characters pre-
viously thought to diagnose clevosaurs and Clevosaurus are in fact more
widely distributed within the Rhynchocephalia, e.g., “a dorsal expansion
of the premaxilla lateral process.” The nature of the characters them-
selves need to be investigated further as this may provide more precise
definitions that may help distinguish between instances of convergence
(e.g., Reynoso, 2003). The presence of a second contact between the
palatine and ectopterygoid lateral to the suborbital fenestra appears to
be a reliable character for diagnosing Clevosaurus however its state is
unknown in several taxa including Pamizinsaurus (Reynoso, 1997) and
Tingitana (Evans and Sigogneau-Russell, 1997).
The material described here is not well preserved and is either
misleading or inadequate for the assessment of several important fea-
tures. There are no unambiguous characters that preclude the material
from belonging to a single taxon. This taxon shares derived characters
with Clevosaurus, including a suborbital fenestra bounded solely by the
ectopterygoid and palatine, and a jugal with a long dorsal process that
extends far enough backward to contact the squamosal. The taxon also
possesses a dorsally expanded lateral process of the premaxilla, a short
snout, a high, steeply inclined coronoid process of the dentary, flanged
teeth, and a broad maxillary-jugal contact; characters found in, but not
restricted to, clevosaurs. The presence of supratemporal bones, an ap-
parent characteristic of Clevosaurus, cannot be confirmed. Some dentary
and maxillary teeth may possess small flanges, but not to the extent of
those found in Clevosaurus hudsoni. There seem to be five additional
teeth on the maxilla and at least five on the dentary, in both cases more
than is usually found in Clevosaurus hudsoni (Fraser, 1988). The teeth
are not wide as in C. latidens (Fraser, 1993), a poorly known taxon that
may not actually be Clevosaurus. The Lufeng skulls do not seem to be as
robust as C. bairdi (Sues et al., 1994). The palatal tooth row is curved
unlike that of C. convalis, C. hudsoni, and C. minor. The Lufeng taxon
also possesses some plesiomorphic characters that distinguish it from
other Clevosaurus species. For example, there may have been up to
three rows of teeth on the pterygoid instead of the two found in other
species of Clevosaurus. The additional row seems to be a posterior
continuation of the palatal tooth row, similar to those in basal rhyn-
chocephalians (Evans, 1980; Whiteside, 1986). A greater number of teeth
may also be present on the vomer than was previously appreciated (Wu,
1994). On the balance of current evidence, the Lufeng material is prob-
ably best treated as Clevosaurus sp., although future material may pro-
vide enough unambiguous characters to resurrect Clevosaurus petilus or
the generic name “Dianosaurus” (Young, 1982).
The uncertain phylogentic identity of the Lufeng material reduces
the current known diversity of Clevosaurus (and that of Rhynchocephalia)
in Asia during the Early Jurassic and therefore the magnitude of a subse-
quent extinction. However the Lufeng material does at least confirm the
presence of the Rhynchocephalia in Asia during the Early Jurassic de-
spite their absence from, younger Asian localities (some of which are
highly productive), where they have been seemingly replaced by squamates
559
(Hecht and Hecht, 1984; Nessov, 1985; Fedovrov and Nessov, 1992;
Alifanov, 1993, 2000; Evans, 1998; Evans et al., 2001). This may corre-
spond to a larger scale and long term global trend (Milner et al., 2000;
Evans, et al., 2001; Apesteguía and Novas, 2003; Apesteguía, 2005) but
whether a replacement was competitive or noncompetitive remains largely
speculative.
ACKNOWLEDGMENTS
I thank Professor Lin Jin Li for allowing me to study this material
and all the IVPP staff, particularly Lin Jin Li and Yuan Wang, for their
hospitality and assistance. I am grateful to Professor M. Chris Dean
(UCL) who provided valuable advice for taking the impressions of the
teeth and helped with the subsequent casting and also to Mark Turmaine
(UCL) for assistance using the SEM. Thanks is also extended to Nick C.
Fraser (Virginia Museum of Natural History) for swift replies to ques-
tions (regarding both Clevosaurus and Planocephalosaurus) and Susan
E. Evans (UCL) for a second opinion on many aspects of the specimens
discussed above. Access to comparative material at University Museum
of Zoology Cambridge (Professor Jennifer A. Clack, Mr. Ray J. Symonds)
and the Natural History Museum (Sandra D. Chapman, Dr. Angela C.
Milner) is also greatly appreciated. My visit to China was funded by a
Royal Society Chinese Academy of Sciences Joint project grant to Susan
E. Evans and Yuan Wang. Last but not least I thank Susan E. Evans
(UCL), Nick C Fraser (VMNH), Jerry D. Harris (Dixie State College)
and Gwilym H. Jones for editing, constructive comments, and sugges-
tions regarding this work.
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APPENDIX 1. Abbreviations for figures. Note capital letters are used for elements and lowercase for features.
