Anshunsaurus (Muller, 2002)

LIU, JUN & RIEPPEL, OLIVIER, 2005, Restudy of Anshunsaurus huangguoshuensis (Reptilia: Thalattosauria) from the Middle Triassic of Guizhou, China, American Museum Novitates 3488, pp. 1-35 : 11-25

Anshunsaurus bears at least 38 presacral,

2 sacral, and more than 50 caudal vertebrae

(figs. 3–7). The 35th presacral vertebra is represented by part of the neural spine only in the holotype (fig. 5), and it is separated from the succeeding one by a narrow gap,

such that the number of presacral vertebrae might be 39. The cervical vertebrae are exposed in both specimens, but the dorsal vertebrae are completely concealed by the gastral ribs in IVPP V 11834 , and only a few caudal vertebrae are observed in the holotype .

CERVICAL REGION

Müller (2002, in press) used the morphology of the ribs to demarcate the cervical from the dorsal region in Askeptosaurus , and the same method also is used here. The number of the cervical vertebrae is at least 15,

because the 15th vertebra still is articulated with a double­headed rib in the holotype. It is difficult to assess whether the 16th vertebra, located immediately in front of the clavicle, is the last cervical or first dorsal because it is incompletely preserved in the holotype and concealed in specimen IVPP V 11834 . The length of the cervical region is 49 cm in the holotype. Almost all the cervical vertebrae in the holotype are exposed in dorsal view, but the atlas, axis, and the 3rd and 14th to 16th vertebrae are also prepared in ventral view; in IVPP V 11834 the cervical vertebrae are exposed in right lateral view .

The relationship of the various components of the atlas–axis complex can be observed in ventral view in the holotype. The atlas is ring shaped to match the outline of the occipital condyle. A pair of cervical ribs articulates with the lateral aspect of the atlas. The intercentrum is of roughly rectangular shape in ventral view. The morphology of the atlas neural arch remains uncertain. A vertebral element that lies posterior to the intercentrum, and appears to project dorsal beyond the latter, is identified as the first (atlas) centrum. It is a half­saddle­shaped bone with clear margins setting it off from neighboring anterior and posterior elements. This bone seems not to be preserved in Askeptosaurus . Kuhn (1952) noted a possible centrum lying anteriorly to the atlas neural arches, but it is

1 for anatomical abbreviations.

1 for anatomical abbreviations.

determined to be a broken part of the braincase ( Müller, 2002). The proatlas, which was reported in Askeptosaurus ( Müller, 2002, in press), cannot be identified in Anshunsaurus .

The axis is a prominent, elongated element. The axis centrum is longer than high, and shows a distinctly longitudinal keel extending along the midline of its ventral surface. A pair of double­headed ribs articulates laterally. The neural arch of the axis shows weakly developed pre­ and postzygapophysis. The neural spine is low and distinctly elongated; its dorsal margin is straight.

The remaining cervical vertebrae are rath­ er small elements carrying a relatively low neural spine. They slightly increase in size in an anteroposterior direction. The centrum is slightly constricted in its central part and generally longer than high. It may show a semilunar depression on its ventrolateral aspect that faces ventrally. A distinct ventral keel is present on the third centrum, which in the last few cervicals is reduced to a faint ridge. The remaining lateral part of the centrum consists of a concave curvature.

The base of the neural arch of the cervical vertebrae forms relatively stout pre­ and postzygapophyses. The prezygapophyses are somewhat more prominently developed, and cover the postzygapophyses in lateral view (fig. 4). They show a broad base, and whereas the prezygapophyses face dorsomedially, the postzygapophyses taper only slightly in a posterior direction and are nearly horizontally orientated. The neural spine is of roughly rectangular shape. The length and the height of the neural spine show some increase from the 3rd to the 16th vertebra.

Müller (2002, in press) identified paired rib articulations on the cervical vertebrae of Askeptosaurus , comprising a diapophysis for the tuberculum and a parapophysis for the capitulum. The diapophysis lies directly below the neural arch on the dorsalmost part of the centrum, more or less in the middle of the vertebra, and it consists of an irregularly rounded or rectangular depression. The parapophysis is located on the central aspect of the centrum and is somewhat more posteriorly directed than the diapophysis. In Anshunsaurus , only a diapophysis with the same shape and position as seen in Askeptosaurus can be identified on the cervicals, but no parapophysis (fig. 4). The capitulum articulated with the anteroventral aspect of the centrum. This position is close to the original position of the intercentrum, which may be the reason why Kuhn (1952) suggested that the capitulum articulated with a cartilaginous intercentrum in Askeptosaurus .

The cervical ribs articulate with vertebrae beginning with the atlas. It remains unknown whether the ribs articulating with the atlas are dichocephalous or holoceophalous. They form a small and slender rod of bone with a slightly expanded anterior head, tapering in a posterior direction and terminating in a sharp tip. Dichocephalous cervical ribs are preserved in articulation with the axis and the 3rd and 15th cervical in the holotype, and from the 3rd to the 10th cervical in V 11834 . The dorsal tuberculum is broader than the ventral capitulum. The cervical ribs become increasingly more elongated posteriorly. The posterior ends of the third, the fourth, and the fifth ribs do not project beyond the posterior margin of the respective centrum, whereas more posterior ribs overlap with the anterior margin of the succeeding centrum .

DORSAL REGION

In specimen V 11834 , the vertebrae of the dorsal region are almost completely concealed by the ribs and gastralia, such that the following description is mainly based on the holotype. The vertebrae expose their dorsal to lateral side from anterior to posterior. The number of dorsals is minimally 23. No intercentra are identified in the dorsal region .

The length of the centra is fairly constant throughout the dorsal region, with just the anteriormost vertebrae being slightly smaller. The length of the centrum ranges from 33 mm to 36 mm (with an average of about 35 mm). All dorsal vertebrae are larger than any of the cervicals, mainly as a result of the dorsal extension of the neural spine. The synapophysis is anteroventrally directed, originating in the midventral region of the neural arch and then extending down to near the anterior margin of the centrum (figs. 5, 6). The attachment site develops into a prominent process anteriorly, and posteriorly is reduced to a small knob. The centrum is generally longer than high, its middle part being slightly constricted.

The neural arch is relatively long and fully fused with the centrum. The prezygapophyses are anteromedially directed. Their dorsal edge is unusually straight, whereas the distalmost margin is slightly recurved dorsally. The postzygapophyses are distinctly shorter and not as broad as the prezygapophyses, but the dorsal recurvation of the distalmost tip is distinct as well. Below the zygapophyseal articulation between the succeeding vertebrae lie the distinct intervertebral foramens with distinct triangular outline. The neural spines are broad and trapeziform in shape, expanded in the dorsal direction. They are more or less vertically oriented. The last few neural spines are relatively narrow and higher than the preceding ones.

All the dorsal vertebrae bear ribs, including the vertebrae immediately preceding the sacrum; there is no true lumbar vertebra. The morphology of the dorsal ribs differs distinctly from that of the cervical ribs. The proximal head of the dorsal ribs is holocephalous and slightly expanded. With the exception of the posteriormost ribs, all dorsal ribs are similar in size (about 16 cm in length) and notably longer than the cervical ones. All ribs are strongly curved and show a slight distal expansion. The last four dorsal ribs decrease abruptly in size, with the last two dorsal ribs being the shortest; they are slender and point almost straight laterally.

A series of gastralia is partially exposed below ribs in the holotype, whereas they are well exposed in IVPP V 11834 in ventral view, in the area between the pectoral and pelvic girdle. Gastralia can only be observed behind the 24th vertebra in the holotype and behind the posterior tip of the interclavicle in IVPP V 11834 . They appear to be slender elements, being slightly expanded medially and tapering laterally. Both halves overlap each other in the ventral midline of the body. More than 35 and 50 pairs of gastralia are preserved in the holotype and IVPP V 11834 , respectively, indicating the presence of one pair of gastral ribs per body segment .

SACRAL REGION

Two sacral vertebrae are present in Anshunsaurus (fig. 6). There is no sign of any fusion between the vertebrae, nor do the sacral ribs fuse to the centra or the neural arches. The sacral vertebrae are similar in shape to the preceding dorsals, but the length of the centrum of the sacral vertebrae is somewhat longer than that of the dorsal vertebrae, and the neural spines are reduce in height. The sacral rib meets the vertebra in the lower half of the centrum.

The sacral ribs are not fused to the sacral vertebra. They are expanded, especially the distal portion, and fan shaped, contacting the ilium with their distal margin. The left sacral ribs measure 57 mm (anterior) and 59 mm (posterior) in length, 32 mm (anterior) and 35 mm (posterior) in width of the distal end, and 12 mm (anterior) and 23 mm (posterior) in width of the proximal end.

CAUDAL REGION

Only the anteriormost six caudal vertebrae are preserved in the holotype (fig. 7), whereas 50 are exposed in lateral view in IVPP V 11834 (fig. 3). The anterior caudal vertebrae bear ribs, which do not fuse with the vertebra in the anterior six caudals. The articular facet for the ribs represents a halfrounded lateral depression on the centrum. Where the ribs are fused with the vertebrae, they appear like transverse processes; more posteriorly, the causal ribs abruptly reduce to a small knob and completely disappear from the 12th caudal onward. In more posterior caudals, where no ribs attach, the centra show a vertical depression in the mid region, running from the ventrolateral margin up to the dorsal edge, in an otherwise smooth lateral surface .

The length of all centra is relatively constant within the caudal region, around 32 mm in IVPP V11834 . However, the height of the centra gradually decreases in an anteroposterior direction. In the anterior caudals, the centrum appears square in lateral view, as its length approximates its height. More posteriorly, the centra become relatively slender as their height decreases.

The neural arches in the anterior caudals are relatively similar to the condition of the dorsals. They are comparatively high and with stout pre­ and small postzygapophyses. The neural arches of the more posterior caudals differ in many respects. The ventral base is not that high, and almost directly above the contact to the centrum the prominent prezygapophysis originates. It is distinctly more elongated than in the anterior portion of the tail and is anterodorsally directed. Conversely, the postzygapophysis remains very small, representing only a small, posterolaterally projecting triangle.

The neural spines are not as broad as the dorsal neural spines; rather they only reach two­thirds of the width of the latter at maximum. The neural spine becomes increasingly shorter in the middle and posterior portion of the tail. Furthermore, they become more slender and the orientation changes from more or less dorsal to posterodorsal.

Beginning with the fourth caudal (figs. 3, 7), haemal arches are present between vertebrae. No haemal arch contacts with the centra behind of the 13th caudal, and most haemal arches are not preserved in IVPP V11834 . The haemal arch contacts both centra but only articulates with the posteroventral margin of the preceding centrum. The haemal arches are posteroventrally directed and V shaped, with the dorsal end being distinctly expanded. The two dorsal knoblike tips show small articulation surfaces, whereas the ventral tip of the arch is elongated and rectangular in shape.

At least six pairs of caudal rib are present in Anshunsaurus . The border between the ribs and the vertebrae is clear even if some ribs seem to fuse to the vertebrae. The first two pairs of ribs in the proximal caudal region are short and broad, but taper distally, showing a posterior recurvation. The ribs decrease in size from front to back. In the holotype, the following ribs are more tapering into the distal direction, and their straight margins form a triangular shape in dorsal view. In IVPP V 11834 , all these caudal ribs show more or less recurvation and less tapering. They are generally slender. All caudal ribs point anterolaterally .

PECTORAL GIRDLE

The elements of the pectoral girdle are prepared mainly from the ventral (lateral) side. The shoulder girdle is preserved in situ in the holotype but is slightly dislocated in IVPP V 11834 . It consists of interclavicle, clavicles, coracoids, and scapulae. In the holotype, the interclavicle is almost complete other than the left side of the crossbar; two incomplete clavicles are exposed in dorsal view; two nearly complete coracoids are preserved in situ; scapulae are fragmentary (fig. 8). In IVPP V 11834 , all elements of the girdle except the left clavicle are completely preserved and close to their original position, and the left scapula is exposed in dorsomedial view (fig. 9) .

INTERCLAVICLE

The interclavicle is a T­shaped, elongated element of flattened appearance. Its crossbar is crescent shaped; the anterior tip is rounded and rostrally directed; the lateral processes taper into the posterolateral direction. Two lateral processes are not symmetric. These lateral processes are stronger than those in Askeptosaurus . Their anterior margin is slightly depressed for the contact with the back edge of the clavicles. The posterior process is the main body of the interclavicle; its caudal elongation is about two times as long as the crossbar. There is no tapering into the posterior direction until the distal tip ends in a sharp angle in the holotype. The distal tip in IVPP V11834 is broken and partly covered by ribs. In contrast, the distal tip appears to be broad and rounded in Askeptosaurus .

CLAVICLE

The clavicle is a thin, slender, rodlike element, which is significantly recurved into an anterolateral direction. It can be divided into two parts: the anterior part that articulates with the interclavicle and the posterior part that does not. The proximal and the distal portions enclose an angle of about 1208, which is more pronounced than that in Xinpusaurus (Liu, 2001) . The anterior part is slightly narrower than the posterior part in ventral view, whereas the width of the entire posterior part is nearly the same. This is different from the thinning backward in the posterior part of this bone in Askeptosaurus . The anterior part is markedly shorter than the posterior one.

The concave edge of the clavicle, rather than the convex edge, articulates with the interclavicle (fig. 9). The same should be true for the articulation with the scapula. In the reconstruction of the pectoral girdle in Askeptosaurus ( Müller, 2002: fig 18), the author followed Kuhn­Schnyder (1952, 1960) to position the clavicles curving to the posterior; as a result the convex edge of the clavicle contacts the interclavicle. If this is the right reconstruction, these two animals are quite different in this structure. However, the similar situation as in Anshunsaurus also is observed in specimen PIMUZ T4842 of Askeptosaurus , so the relationship of the interclavicle and the clavicle in Askeptosaurus could be the same as described here in Anshunsaurus . The contact area for the interclavicle looks fixed in Anshunsaurus .

SCAPULA

The scapular blade is a broad, low structure, as is the case in Askeptosaurus . Its anterior margin is narrow and convex. Its dorsal margin is broad and only slightly convex. The clavicle perhaps contacts only the dorsal margin of the scapula, not the anterior margin as in Askeptosaurus . Its posterior margin is strongly concave. The posteroventral portion of the bone is thickened and forms the dorsal part of the glenoid region. The ventral margin is slightly convex, corresponding to the morphology of the dorsal edge of the coracoid, to which it is sutured.

As mentioned by Liu (2001), there are two different types of scapulae in Thalattosauria : one type that is seen in Thalattosaurus , Nectosaurus , and Xinpusaurus and another type characteristic of Askeptosaurus , Clarazia , Hescheleria , and Anshunaurus. These two types can also be found in the Ichthyopterygia ( Motani, 1999). The function of these shape types is still unknown.

CORACOID

The coracoid is a broad and somewhat parallelogram­shaped bone. The left coracoid is incomplete in the holotype. Its lateral (dorsal) margin is slightly convex and loosely articulated with the scapula with a pointed anterolateral (anterodorsal) corner. The medial (ventral) margin is covered by the interclavicle, so its exact shape is unclear. The posteroventral part extends posteriorly to the glenoid cavity. The coracoid foramen cannot be observed in the position as in Askeptosaurus ; it is perhaps obscured due to crushing.

It is difficult to reconstruct the original po­

11835­4). See appendix 1 for anatomical abbreviations.

sition of coracoids in IVPP V 11834 . If the right coracoid is thought to be preserved in articulation with the right scapula, then the side with a straight margin is ventral and contacts the interclavicle; nevertheless the shape of the coracoids is quite different from that of the holotype. If we accepted that shape should be at least similar in two specimens, then the axial/anteroposterior direction of two coracoids should be reversed. This is less possible than the previous hypothesis .

PELVIC GIRDLE

The pelvis consists of three elements, ilium, ischium, and pubis. It is completely preserved in articulation in the holotype. In the holotype (figs. 6, 10), only the ilia can be seen in dorsal view; the ischiums and pubes are covered by the vertebrae and ribs dorsally, but they are completely exposed ventrally. A vein of calcite splits the sacral rib and also goes across the right pubis and right ischium. The bones are displaced along this vein. The pelvic girdle is exposed in ventral view in IVPP V11834 . The following description is mainly based on the holotype. No thyroid fenestra presents in Anshunsaurus , it shows a weak notch in the ventral margin of the pubo­ischiadic plate where the two bones meet. This is similar to Hescheleria ( Rieppel, 1987) , corroborating the conclusion that the thyroid fenestra is absent in Askeptosaurus ( Müller, 2002) .

ILIUM

The ilium is similar to that of Askeptosaurus in shape and mainly exposed in medial view (fig. 6). It forms the dorsal part of the acetabulum and contacts the sacral ribs at its medial side. The ilium does not fuse with the ribs. The dorsal part of the ilium consists of an elongated process that is directed strongly posterodorsally. Posterodorsally, the process becomes increasingly flattened but slightly narrowing into the distal direction, with a sharp dorsal and ventral edge. The dorsal edge of the ilium is rugose, which may have served for muscle attachment, that is, iliofemoralis and iliofibularis muscles. There is no development of a preacetabular process. The posterodorsal wing of the ilium spans about two vertebral centra. The basal part of the ilium, sutured to the ischium and pubis and contributing to the formation of the acetabulum, is distinctly expanded and presents a convex ventral margin.

PUBIS

The pubis is the most expanded element of the pelvic girdle. It is a broad plate of bone with an enlarged ventral portion. The posterodorsal part of the pubis contributes to the formation of the acetabulum. The small, oval obturator foramen is positioned anteroventrally to the contact with the ilium. The ventral margin of the bone is convex, and the dorsal margin is nearly triangular. Its posterior margin, shorter than the anterior one, meets the ilium along its complete extension. The anterior margin of the pubis is strongly concave, whereas the outline of the posterior edge is only slightly concave. The right pubis seems to be wider than the left one in ventral view; this is caused by the offset along the calcite vein.

ISCHIUM

The ischium is a more or less semicircular plate of bone. Its narrow anterodorsal portion forms the posteroventral portion of the acetabulum. Its anterodorsal margin is slightly concave, the posterodorsal margin is strongly concave, and the ventral margin is convex. The outline of the anterior and posterior margins is not so obvious, but it seems that the anterior one is slightly convex, corresponding to the posterior margin of the pubis, whereas the posterior margin is concave as in IVPP V11834 . The ischium is thickened on the anterodorsal area; the bone becomes increasingly flattened into the ventral direction.

LIMBS

Anshunsaurus bears well­developed fore­ and hindlimbs, although both are relatively short in relation to the length of the trunk. The forelimb is shorter than the hindlimb. In contrast to the terrestrial reptiles generally, several details of the extremities such as muscle scars, processes and epiphyses are not present or at least very difficult to detect.

FORELIMB

Preservation allows both the flexor (dorsal) and the extensor (ventral) side of the forelimb to be described. The forelimb is nearly complete in IVPP V 11834 (fig. 9), whereas most of the hand is lost in the holotype (fig. 5) .

HUMERUS

The humerus (fig. 11) is the most robust and longest element of the forelimb skeleton. There is a notable torsion in the bone so that both heads are twisted to one another. The proximal and distal articular surfaces are strongly rounded. The proximal head pinches to a narrow shaft and the shaft rapidly expands to the distal side, forming a broad, convex end. A prominent crest, the deltopectoral crest, originates near the head and mainly lies in the middle of the ventral surface. The crest is most distinct on its central part, fading away in the distal and proximal direction, but the crest is more slender proximally than distally. There is no significant development of a supinator process, ectepicondyle, or entepicondyle, nor is there any trace of a respective foramen. Radial and ulnar condyles are not well developed either.

RADIUS

The radius is a relatively stout bone. It is stouter and broader than the ulna. The radius is characterized by a slight proximal expansion and marked distal expansion. The proximal margin is almost straight whereas the distal one is convex. The medial margin is more concave than the lateral one.

ULNA

The ulna is slightly shorter than the radius and lacks an ossified olecranon. The widest part of the distal portion is nearly the same as that of the proximal one. The proximal head varies in shape in the two specimens: The margin is round and slightly convex in the holotype but is nearly straight or even slightly concave in IVPP V 11834 . A different degree of ossification may be the cause. The distal articular surface shows a convex margin. The ulna is significantly constricted in the shaft area, and shows concave lateral and medial margins. The ulna encloses a pronounced interosseal space with the radius .

MANUS

Seven rounded ossified elements are present in the left carpus of the holotype whereas only four and half elements are preserved in the right carpus; six and five, respectively, are present in IVPP V11834 . Two proximal elements are present, ulnare and intermedium. A small element, the centrale, is situated between the intermedium and the distal carpals 2 and 3 in the holotype. Four distal carpals, distal carpals 1 to 4, which are adjacent to the metacarpals, form a distally arched carpus. The intermedium is the largest element of the carpus, and of rectangular shape with rounded edges. The ulnare, contacting the intermedium and distal carpal 4, is generally smaller than distal carpal 4, but it is slightly larger than the latter in the right hand of IVPP V11834 . The centrale is approximately half as large as the intermedium in Askeptosaurus , but it is much smaller than the intermedium and is the smallest bone in the carpus here. Distal carpal 4 is the largest of all distal carpals. Distal carpal 3 is similar to the centrale in size in the holotype, but it is notably bigger than distal carpals 1 and 2 in IVPP V11834 . These kinds of variation also are observed in Askeptosaurus .

Five metacarpals are shown in Anshunsaurus as is general in tetrapods. Metacarpal 1 is the shortest bone, being prominently widened both on its two ends and in the shaft area. The proximal articular surface is the most expanded part. The remaining metacarpals are relatively slender. All are nearly equal in size; only metacarpal 2 is slightly shorter.

The phalanges are not so well preserved, but a least formula of 2­3­4­4­4 can be counted. Compared to the general formula of 2­3­4­5­3, it is notable that the fifth digit possesses one additional element. The phalanges are generally smaller than the metacarpals. The proximal phalanges of the first and the fifth digits are slightly longer than that of the second and the third, and the first two are slender whereas the last two are stout. The state of the phalanges in the fourth is unclear. The phalanges tend to become somewhat smaller distally. The ungual phalanges are triangular in shape with a sharp distal tip.

HINDLIMB

The hindlimb is completely preserved in IVPP V 11834 (fig. 12), whereas only parts of the femur and the fibula are present in the holotype (figs. 6, 10). The left hindlimb of IVPP V 11834 is exposed in dorsal (anterior) view, whereas the right limb is observed in medial view .

FEMUR

The incomplete femora in the holotype are mainly observed in ventral view whereas their dorsal sides are partly covered by the ilium. The right femur in IVPP V 11834 is broken and exposed in medial view; the left femur is mainly exposed in dorsal view with the head partially covered by the pelvic girdle .

The femur is an elongated bone of cylindrical shape that is longer than the humerus. The femoral heads are not so well preserved, but it is clear that they are rounded, weakly convex, and at least about the same width as the distal end. A well­developed internal trochanter is shifted somewhat posteriorly (laterally) on the ventral aspect of the bone. This crest can also be observed in IVPP V11834 , developed as a modest expansion at the medial edge of the proximal articular surface. This suggests that the two heads were affected by a slight torsion. There is little evidence of a fourth trochanter, and the adductor crest is absent. The intertrochanteric fossa is reduced. The anterior edge of the femur is smoothly concave; the posterior edge is straight to form a pronounced angulation. The femoral distal end shows two facets: a medial major one, which is slightly concave, for receiving the convex head of the tibia and a lateral small one, which is angled with the major one, for articulating to the fibula.

TIBIA

The tibia is a cylindrical bone like the femur. The proximal end, clearly expanding, is wider than the little­expanded distal end. The proximal end is slightly convex, but the distal end is flat. The shaft does not significantly constrict, and shows slight curvatures both in mediolateral and dorsoventral views.

FIBULA

The fibula is roughly as long as the tibia, but shows a distinctly different shape. The proximal head shows torsion related to other parts, and is only slightly broader than the shaft. The bone becomes more flattened toward the distal end, and bears a greatly expanded distal head. The latter is fan shaped and nearly three times as broad as the shaft, with the medial edge being slightly sharper than the external one. The margin of the distal articular surface is convex.

PES

The tarsus presents six bones, two proximal and four distal elements. The proximal bones are interpreted as astragalus and calcaneum; the distal elements represent distal tarsals 1–4. The astragalus is the most prominent element, being approximately the size of the calcaneum plus the fourth distal tarsal. It is broad and roughly kidney shaped, its proximolateral facet articulating with the fibula, and the proximomedial edge contacting the tibia. Laterally, the astragalus meets the calcaneum; distally, it articulates with all four tarsals with a convex margin. The calcaneum is a rounded bone, with the proximal side articulating with the fibula, the lateral side with the astragalus, and the distal side with the fourth distal tarsal. A notch for the perforating artery cannot be observed. The distal tarsals vary in size. Distal tarsals 1–3 are more or less equally large, although the first distal tarsal is sometimes slightly more expanded. Distal tarsal 4 is the largest element. The distal tarsals all contact their neighboring elements and meet their respective metatarsal, although the fourth also perhaps articulate with metatarsal 5.

The five metatarsals are longer and relatively more slender than the complementary elements in the manus. The first metatarsal is shorter and stouter than the remaining elements and shows a distinct proximal expansion. The fifth metatarsal is only slightly longer than the first one, expanded at least at its proximal end. It is partially concealed by the haemal arch. Metatarsals 2–4 are similar in size and shape. They are slender, elongated elements with slightly expanded heads; the proximal heads are slightly wider than the distal ones.

The phalangeal formula of the pes is 2­3­ 4­5­4, as is the general pattern of reptiles. The proximal phalange of the first digit is the longest, the remaining proximal phalanges are shorter and stouter, and that of the fifth digit is the shortest. All phalanges decrease in size toward the distal direction. The ungual phalanges are of the same shape as in the manus.