Dalinghosaurus longidigitus Ji, 1998

Evans, Susan E. & Wang, Yuan, 2005, The Early Cretaceous lizard Dalinghosaurus from China, Acta Palaeontologica Polonica 50 (4), pp. 725-742 : 725-736

Dalinghosaurus longidigitus Ji, 1998

Figs. 1–9 .

Holotype: GMV2127 .

Type locality: Sihetun Village, Beipiao City, western Liaoning Province, China.

Type horizon: Early Cretaceous Yixian Formation Jianshangou Bed.

Referred specimens.—IG−02−7−16−2 (nearly complete postcranial skeleton, Ji and Ji, 2004); IVPP V12345 (part and counterpart of associated skeleton); IVPP V12586 (posterior skeleton with skin traces); IVPP V12643 (part and counterpart of poorly preserved associated skeleton); IVPP V13281 (associated skeleton, immature/subadult); IVPP V13282 (skull, adult); IVPP V13864 (part and counterpart of associated skeleton); IVPP V13865 (part and counterpart of associated skeleton); IVPP V14069 (immature skull); IVPP V14234 (block with at least ten associated skeletons); IVPP V14262 (poorly preserved associated skeleton; and IVPP V14295 (posterior half of postcranial skeleton).

Distristribution.—Lower Cretaceous Yixian Formation of north−eastern China from the Lujiatun Bed (c. 128–132 Ma), to the Dawangzhangzi Bed (c. 122 Ma) (Wang and Zhou 2003).

Revised diagnosis.—A lizard with small adult size (c. 150 mm snout−pelvis length) distinguished from most Mesozoic lizards but resembling carusioids (sensu Gao and Norell 1998) in the following combination of derived characters: pustulate sculpture on dermal skull bones (mature adult); maxillary facial process narrow dorsally and inturned medially; frontals fused, with deep cristae cranii and orbital constriction; parietal foramen within parietal but close to anterior margin; jugal large with tall postorbital ramus that meets squamosal and bears pustulate sculpture. Dalinghosaurus resembles the Late Cretaceous Carusia ( Borsuk−Białynicka 1985; Gao and Norell 1998) in the strong development and pattern of the skull ornamentation (double interorbital row of large pustules that diverge posteriorly along the orbital margin), the loss/fusion of the lacrimal, and the presence of a small coronoid notch on the rear of the dentary, but differs in dental structure (tightly packed teeth in Carusia , fewer conical teeth in Dalinghosaurus ) and in having a longer snout; it resembles Shinisaurus , but differs from Carusia and Xenosaurus , in having an anteriorly extended prefrontal that separates the maxilla from the nasal, and differs from all three in the posterior extension of the nares and the possession of a strongly flared angular flange on the lower jaw. The postcranial skeleton of Carusia is unknown, but Dalinghosaurus differs from both Xenosaurus and Shinisaurus (and from most Mesozoic lizards except the Upper Jurassic Bavarisaurus, Evans 1984a ) in having a pes that is equal in length to the femur and tibia combined.

Specimens used in the description.— IVPP V13282 is an almost complete, fully articulated skull ( Figs. 1 , 2 ) that provides the basis for the description of cranial anatomy, with additional information from IVPP V13281 (an immature specimen of roughly 70–80% of the size of IVPP V13282, Figs. 3–5 ), IVPP V13864 (a complete skeleton with a disarticulated and incomplete skull), and two individuals on IVPP V14234 (V14234.1, V14234.2). Postcranial information comes mainly from IVPP V13281 ( Figs. 5 , 7 ), with additional information from IVPP V14234.1 ( Fig. 6 ), IVPP V14234.2, and IVPP V14295 ( Fig. 8 ).

Skull.—The skull of IVPP V13282 is 28 mm long and preserves most of the dorsal and lateral surfaces, the braincase, the lower jaws and part of the palate ( Figs. 1 , 2 ). In general, the skull is characterised by its large narial openings and its robust jaws and dentition. The dorsal surface of the adult skull bears distinctive pustulate sculpture, but this is less developed on anterolateral elements. The sculpture appears to be derived from the interaction of the dermal bone and the skin; there is no evidence that this results from the attachment of separate osteoderms. The skull of IVPP V13281 ( Fig. 3 ) is smaller, with only weak development of the sculpture, unfused premaxillae, and more gracile circumorbital and postorbital bones.

The premaxilla is single in the adult, but fusion occurred late in ontogeny (as shown by IVPP V13281). The alveolar portion is “U”−shaped but without a strong palatal flange. It bears seven small teeth. The ventral aspect of the bone is obscured by the dentary symphysis, so that the presence or absence of an incisive process cannot be confirmed. Dorsally, the nasal process is quite short, overlying the tips of the nasals but barely separating them; there are no conspicuous perforating foramina on the dorsolateral margins. The premaxilla is clasped firmly on each side by the maxillae.

The maxillae are triradiate bones that extend back just beyond the midpoint of the orbit, but are excluded from the ventral orbital margin by the jugal and prefrontal. The premaxillary process is relatively long, contributing to a large narial opening. The process bifurcates anteromedially where it clasps the premaxilla, the posterior limb extending medially behind the premaxilla but not reaching the midline. Behind the nares, the maxilla ascends more steeply to form a tall facial process, the narrow apex of which curves over onto the dorsal surface of the skull. Here it meets the prefrontal rather than the nasal (see below). Medially, the facial process has a strong overlapping suture with the prefrontal and then decreases in height gradually to its meeting with the jugal. It bears around 16–18 large conical teeth. Laterally, a series of neurovascular foramina open from the superior alveolar canal; these carried branches of the maxillary nerve and blood vessels. The main canal has its exit foramen at the medial junction of the facial process with the premaxillary process. The medial surface of the bone is preserved in IVPP V13281, showing an unexpanded medial palatal shelf and a concavity for the nasal region.

The nasals are small and subrectangular, with an anteromedian premaxillary process and an oblique (and slightly curved) anterolateral narial margin. Laterally, the nasal appears to have been separated from the maxilla by the enlarged prefrontal. Medially, the two nasals meet along the entirety of their suture, the two bones overlapping the frontal without the intervention of an anteromedian frontal process. The posterior ends of the nasals are partially obscured by overlaps in IVPP V13282, but the isolated right nasal of IVPP V13281 shows the edge to have been bifurcated into a short lateral and longer medial process.

The frontal is single and probably became so at an early stage of development since the smallest skull (IVPP V14069) already lacks a median suture. In IVPP V13282 ( Figs. 1 , 2 ), the frontal bears heavy pustulate sculpture that is particularly well developed on the posterior part, with the “pustules” forming an inverted “V” (a small central interorbital boss with further “pustules” running down each edge but an unsculptured area in the centre). In the smaller IVPP V13281 ( Fig. 3 ) the pustules are not developed. Instead the bone bears weak sculpture but the “V” pattern is still present with a central depressed and unsculptured area. This feature helps to link the two skulls despite the ontogenetic differences between them. The frontal is long and slender, with a sharp orbital constriction. The anterior edge of the bone is covered by the nasals in IVPP V13282, but in IVPP V13281, the nasals have disarticulated. Anteriorly, the frontal appears bifurcate, with paired lateral facets separated by a central recess. Judging from the morphology of the adjacent nasal in IVPP V13281, these frontal facets accommodated the posterolateral and posteromedial ends of the nasals. Anterolaterally, the frontal has a long contact with the prefrontal. Posterior to the orbit, the frontal expands again into its suture with the parietal (roughly twice the width of the frontonasal suture). Here the frontal bears a lateral facet for the postfrontal or postorbitofrontal, this bone clasping the lateral frontoparietal angle. The posterior border is almost straight (but slightly irregular) in the adult, and more “U”−shaped in the subadult (as is usually the case, the thickened lateral margins ossifying first). Ventrally, the bone bears strong cristae cranii (partially visible in the lateral views, Fig. 2C, D ) but these do not approach in the midline or form strong descending orbitonasal processes. They rather reinforce the orbital rim.

The parietal of IVPP V13282 has a small anteriorlyshifted parietal foramen that lies just behind the frontoparietal suture and is surrounded by a raised edge. The dorsal sculpture is more developed anteriorly than posteriorly. The ventral surface is not exposed in any specimen, but none shows any evidence of a descending process for the epipterygoid. The parietal is short anteroposteriorly, with shallow embayed lateral margins, no major adductor crests, and long divergent postparietal processes that become blade−like towards their tips. The anterior parietal margin meets the frontal as described above. The presence or absence of ventral tabs extended forward under the frontal cannot be determined. The posterior margin is a wide open “U” shape between the postparietal processes, with recesses to either side of the midline for epaxial neck muscles. In cross−section, the postparietal processes are triangular, the apex formed by a sharp dorsal crest that separates the lateral surface from the posteromedial surface. The end of the lateral face bears a facet for the supratemporal. In IVPP V13282, the squamosals are missing and only a fragment of the left supratemporal is preserved. In IVPP V13281, the squamosal is also preserved although the bones are disarticulated backward.

The prefrontal is a large bone with a long narrow frontal process and a broad main body. It meets the frontal posteromedially, and the nasal anteromedially, and the maxilla anterolaterally. Somewhat unusually, it seems to be fully interposed between the maxilla and nasal and enters the dorsal narial margin for a short distance.The orbitonasal flange is broad dorsally but narrows ventrally. It meets the palatine and is embayed laterally for the lacrimal canal, the lateral border being provided by the maxilla. There is no trace of a lacrimal and no specimen shows any indication of the presence of a palpebral (none in situ, and no suggestion of a notch or tubercle on the prefrontal to which it might have been attached).

The jugal is preserved in several specimens. It is roughly L−shaped, but with both limbs approximately the same length and enclosing an angle of c. 120 degrees. The ventral ramus extends along the dorsal margin of the maxilla up to the lacrimal opening, thus excluding the maxilla from the orbital margin. The dorsal ramus bears pustulate sculpture like that on the skull roof and appears to have formed much of the posterior orbital margin. Even allowing for some displacement, the dorsal tip of the jugal reaches a level well behind the anterior margin of the parietal. Given the length of the displaced squamosal in IVPP V13281, it is likely that the jugal and squamosal met. At the ventral junction of the dorsal and ventral jugal rami, there is a small posterior tubercle but no strong quadratojugal process. Together, the maxilla and jugal provided a surface of articulation for the ectopterygoid, although the position of the facet is not clear on existing specimens.

The area between the jugal and skull roof in IVPP V13282 is damaged on both sides. The postorbital/postfrontal complex has been lost on the left, but on the right is displaced under the parietal as a single mass. The postorbital component is triangular, with a slender posterior process that bears a ventrolateral facet for the jugal and, presumably, a dorsal one for the squamosal, although this is obscured. In IVPP V13281, the postfrontal and postorbital bones are preserved on both sides as separate elements. The postfrontal in this specimen is triradiate, with a strongly bifurcated medial margin that clasped the frontoparietal suture and a short ventrolateral process that met the postorbital. The postorbital has been rotated anticlockwise, but shows a short thickened orbital margin and a longer, relatively broad posterior process. Its contribution to the posterior orbital margin thus seems to have been small, with most of this margin being formed by the jugal.

The squamosal is preserved in IVPP V13281 but not IVPP V13282. It is a long slender bone without a dorsal process and only a slight ventral hook, although these features may have been more pronounced in the adult. The bone tapers anteriorly where it met the postobital and probably the jugal.

On all of our specimens, the palate is more poorly preserved than the rest of the skull and cannot be clearly figured. The anterior region is largely obscured by the mandibles in IVPP V13282, but some of this is exposed in IVPP V14234.1 and IVPP V14234.2. The vomer is visible in one of the latter animals as a short bone fully separated from the maxilla by the elongate choana. In this individual, at least, there is no division of the choana into anterior (vomeronasal) and posterior (choanal) parts, although this may have changed in a fully mature animal. The palatines are quite large (IVPP V13865A) and retained at least some teeth (IVPP V13282). IVPP V14234.2 shows that they were fully, or almost fully, separated in the midline by the interpterygoid vacuities and had short deep choanal grooves. The pterygoids are also large and bore a long cluster of teeth along the pterygoid plate (IVPP V13282, IVPP V13865A, IVPP V14234.1). There is a long, narrow palatal process, and a short pterygopalatine suture. The posterior process is long and slender, tapering towards its meeting with the quadrate. The medial recess for the basipterygoid process of the sphenoid is deep and bordered ventrolaterally by a crest. It seems to have formed an open surface for sliding rather than a distinct fossa (IVPP V13282, IVPP V14234.1). The right ectopterygoid is preserved in IVPP V13282 but has been rotated so that its lateral head faces posteromedially. It has a typical lepidosaurian configuration, with a small concave lateral head that probably met both jugal and maxilla, and a bifurcate medial head that clasped, and interlocked with, the pterygoid flange.

The quadrate is present in several specimens, and is most clearly seen on the left side of IVPP V13282. It has a relatively small ventral joint surface for the articular and a slightly larger, elongated, dorsal head with no obvious trace or either a foramen or notch. The lateral conch is narrow, and there is a distinct medial pterygoid lappet (out of view in Fig. 2C ). Epipterygoids were present, but their dorsal and ventral articulations cannot be reconstructed with any confidence.

IVPP V13282 preserves the braincase in three−dimensions: sphenoid, basioccipital, prootic and opisthotic, and the ventral elements are also visible in IVPP V14234.1. Only the supraoccipital is obscured. The sphenoid has short basipterygoid processes that project laterally and slightly anteriorly. Their distal ends are strongly expanded. Between them is a deep dorsum sellae, perforated bilaterally by abducens foramina that open into large recesses for eye muscle origin. Ventrally, the parasphenoid rostrum is either broken or unossified, probably the latter since the same condition is seen in several individuals. The anterior and posterior openings of the vidian canals are obscured, but there are no accessory cristae ventrolaterales and the body of the sphenoid is quite narrow. The spheno−occipital suture is fully closed in IVPP V13282, but is visible on IVPP V14234.1. The sphenoid has a triradiate posterior margin. A small triangular flange overlaps the basioccipital in the midline while longer lateral processes contribute to the well−developed basal tubera. The basioccipital is short with a single occipital condyle. Dorsally, the basal tubera contribute to large occipital recesses. The prootic is obscured by the medially displaced postorbital elements but a well−developed alary process projects anteriorly. IVPP V13282 also shows a distinct medial recess for the floccular lobe of the cerebellum. The opisthotic is well−preserved and has a long, slender paroccipital process. The fenestra vestibuli is large and is separated from the more posterior vagus foramen by a weak interfenestral crest. The lateral opening of the recessus scala tympani is extended ventrally and posteriorly by a well−developed occipital recess and a strong crista tuberalis. The braincase is also partially preserved in IVPP V13281, disarticulated backwards from the rear of the skull and so exposing a wide supraoccipital.

The mandible is represented by the dentary, splenial, coronoid, surangular, angular and articular−prearticular. The dentary is laterally quite shallow, but the surface is damaged in IVPP V13282 and the teeth are hidden. The following description is therefore based mostly on IVPP V13281, IVPP V13864A and IVPP V13865A. The dentary has 16–19 tooth positions. It bifurcates posteriorly into a short posterodorsal process that meets the small lateral flange of the coronoid, and a small ventral process that extends below the anterior tip of the angular, with the angular and surangular wedging into the triangular gap between. This surangular notch is deep, so that the angular extends forward (IVPP V13281) to the level of the last preserved tooth. Above the surangular notch, however, IVPP V13281 shows a very small additional notch. A small line of neurovascular foramina runs along the lateral surface of the bone. No specimen shows a clear medial view of the dentary, partly because a large splenial covers the surface from the symphysial region to the level of the coronoid process (IVPP V13282). The coronoid is tall, with a small lateral flange, and a strong dorsal process. Medially it is bifurcate, with a smaller anterior ramus and a longer posterior ramus. Seen from above, the medial surface of the coronoid is strongly concave, due mainly to a posteromedially directed ridge along the margin of the posterior ramus. The surangular forms most of the lateral and ventrolateral faces of the postdentary region, extending forward to a level in front of the coronoid eminence, and has a large lateral foramen anterodorsally. Medially the bone contributes to the lateral wall of the adductor fossa. The angular makes a narrow contribution to the ventral margin of the jaw. It meets the splenial anteromedially but its posterior extension is unclear because the suture with the surangular is indistinct. The articular−prearticular is robust. The surface for the quadrate (IVPP V13282) is anteroposteriorly short but broad, with a small anterior boss to prevent forward slippage of the quadrate condyle. Medially, a strong angular process is embedded in a broad prearticular flange. Posteriorly, there is a short, posteromedially directed retroarticular process (broken in IVPP V13282). The prearticular component is mostly obscured by overlying bones.

Dentition.—The dentition consists of robust homodont teeth with labiolingually compressed tips. The tooth count varies between specimens but there are around 16–18 maxillary teeth, 16–19 dentary teeth, and 7 premaxillary teeth. The implantation is strongly pleurodont and tooth replacement occurs from the lingual surface by erosion of the tooth base.

Postcranial skeleton.—Of the IVPP specimens, the postcranial skeleton is best preserved in IVPP V13281 ( Figs. 4 , 5 , 7 ), IVPP V14234.1 ( Fig. 6 ), IVPP V14234.2, and IVPP V14295 ( Fig. 8 ). The skeleton of IVPP V13281 broke into three pieces post mortem. The first section includes the skull, the first twelve presacral vertebrae and their ribs, and the pectoral girdle and forelimbs; the second part consists of nine dorsal vertebrae and their ribs; and the third part consists of the last five presacrals, the sacrals, the caudal series (only partially visible), the pelvic girdle and the hind limbs. IVPP V14234.1 and IVPP V14234.2 provide supplementary information on ventral anatomy (most notably of the vertebral structure, pectoral girdle, and pelvis), whereas IVPP V14295 shows details of the pelvic girdle and tail. All the complete specimens of Dalinghosaurus show the same basic features and proportions, but the robusticity of the bones varies with ontogenetic age, and many individuals are young (as demonstrated by the lack of fusion of long bone epiphyses).

Vertebral column.—In IVPP V13281 there are five or six cervical vertebrae (CV), 19–20 dorsals (DV), two sacrals and an unspecified number of caudals. A similar count can be made on IVPP V14234.1 and IVPP V14234.2, but there is uncertaintly as to the total presacral number (at least 27, Ji and Ji 2004; 26 this paper). The tail is composed of around 10 anterior caudals and a long series of autotomous posterior caudals. In his short nomenclatural paper, Ji (1998) gave a count of 55 for the caudal series. All vertebrae are procoelous with rounded condyles that are slightly oblique (larger dorsally than ventrally). There are no free intercentra in the trunk region, but IVPP V14234.1 and IVPP V14234.2 have small intercentral hypapophyses between the cervicals ( Fig. 6 ). These may have been larger in adults.

IVPP V13281 preserves the left atlantal arch behind and to the side of the braincase. The axis lies immediately behind the skull, rotated slightly so that it is seen in left lateral view. The spine of the axis is large and is longer than the centrum. Posteriorly, it is drawn into a hook−like posterior process with a curved posteroventral margin. The axis is also preserved associated with the skull in IVPP V13282 and is seen to have attached anterior and posterior hypapophyses (c 2 –c 3 hypapophyses, Fig. 2B ). The bodies of the cervical vertebrae are shorter than those of the dorsal series (IVPP V14234.1, Fig. 6 ); the neural spines are not well preserved but they were clearly taller in the anterior part of the series. The dorsal vertebrae show little or no development of neural spines. In IVPP V13281, most dorsals are preserved in lateral view and show elongated posterior zygapophyses, suggesting strong contacts between adjacent elements. Only one vertebra (presacral 10) is preserved in dorsal view on IVPP V13281 and this has no trace of a zygosphene−zygantral accessory articulation. In IVPP V14234.1 and IVPP V14234.2, the dorsal centra are preserved in ventral view. They taper anteroposteriorly towards the small posterior condyle. The sacral ribs are quite gracile with little expansion, and no bifurcation in the second sacral rib. There is, however, a groove in the distal part of the second sacral rib that opens from a small more proximal foramen (not figured). The caudal vertebrae of IVPP V13281 are mostly covered by matrix, but at least eleven anterior caudals are preserved, of which nine have long, posterolaterally directed transverse processes. The processes are also visible in IVPP V13865, and are well−preserved in IVPP V14295 ( Fig. 8 ). They do not taper and are rather blunt−ended. Anteriorly, each caudal neural arch bears a low mid−dorsal ridge that extends posteriorly as a small median process. Further posteriorly, the spine becomes more pronounced as the transverse processes decrease in length. These posterior spines are more clearly seen in IVPP V14295. They form long, low dorsal blades with rounded dorsal margins ( Fig. 8 ). Ji (1998) and Ji and Ji (2004) record the caudal vertebrae as being autotomous from about caudal 11 or 12 backwards, and our specimens show a similar morphology. Haemal arches are present and attach to the posterior end of the centrum.

The ribs are single headed throughout, very slender, and without any accessory processes. In IVPP V13281, there is a short rib associated with CV4 (it may be incomplete), but the condition of CV3 is unclear. The anterior dorsal vertebrae bear long slender ribs, but there is a sharp decrease in length from presacral nineteen backward, producing a set of posterior dorsal vertebrae with short “lumbar” ribs, although these are not fused to the centra. Judging from IVPP V13281, IVPP V14234.1, and IVPP V14234.2, all dorsal vertebrae bear ribs.

Forelimbs and pectoral girdle.—The pectoral girdle is rather jumbled in IVPP V13281 ( Fig. 5 ), but is also preserved in IVPP V13865A and is clearest in IVPP V14234.1 ( Fig. 6 ). It is characterised by clavicles that have an expanded, hook−like medial component; a cruciform interclavicle with a small anterior process and a long tapering stem (IVPP V13865A, IVPP V14234.1); and a scapulocoracoid with scapulocoracoid and anterior coracoid fenestrae. The scapular blade is long and slender. Scapula and coracoid are already sutured in IVPP V13281 and in IVPP V14234.1, but the coracoid plate looks unfinished and has a rim of cartilage. Ji and Ji (2004) describe an ossified sternum in their specimen of Dalinghosaurus , but there is no trace of such a structure in any of the IVPP specimens and it is likely to be a misidentification. The sternum is cartilaginous in squamates.

The forelimb is about 50% of the length of the hind limb ( Figs. 4 , 5 ). The humerus is short, with a large proximal head and a slightly narrower distal end containing an ectepicondylar foramen. Ji and Ji (2004) describe an incomplete ectepicondylar foramen in their specimen, a juvenile feature. In IVPP V13281, the epiphyses are not fused to the humeral shaft and they appear to be calcified cartilage rather than bone (lightly coloured, porous). The radius and ulna are shorter than the humerus, and the ulna olecranon is not ossified. The carpus is preserved in several specimens (but not well) and has at least seven separate elements, probably more (i.e., radiale, ulnare, intermedium, centrale, pisiform, and several distal carpals). Ji and Ji (2004) describe (and figure) the same arrangement. All metacarpals are of similar diameter, with the third being longer than the fourth. The hand is relatively long, compared to the humerus and epipodials, but it is small by comparison with the foot. The phalanges are very slender with well−formed joints; in all digits, the penultimate phalanx is the longest. The unguals are long and very pointed, with a distinct flexor tubercle and a pit for muscle or ligament attachment. The phalangeal formula of the manus is 2:3:4:5:4.

Hind limbs and pelvic girdle.—The elements of the pelvic girdle are already conjoined in the immature IVPP V13281, but not in IVPP V14234.2. The ilium has a relatively long, slender blade with a slight anterior tuberosity. It is small in relation to the femoral head. The pubis is slender and elongate, with an anteromedially projecting ramus that has only a short symphysial surface, and a large proximal obturator foramen. The ischium is seen most clearly in IVPP V14234.2 and IVPP V14295 ( Fig. 8 ). It is waisted proximally, but expands distally into a quadrangular plate that has a small posterior angle and a curved anteroventral extension.

The femur is elongate with strong proximal and distal heads. The tibia and fibula are slightly shorter, and lightly built, without any marked proximal or distal expansions. In IVPP V13281, the epiphyses are just fusing to the ends of the long bones so that the epiphysial line is still visible. The tarsus is well preserved in this specimen. There is a broad, but proximo−distally short astragalocalcaneum with a distinct proximal notch between tibial and fibular surfaces. Distally, the recess for distal tarsal 4 (Dt4) is shallow. Dt4 is large but, like the astragalocalcaneum, it is both wide and also proximo−distally short. It meets both metatarsal 4 and metatarsal 5. There is a small Dt3 but no Dt2. Ji and Ji (2004) describe a large Dt5, but from its position and size, this is probably a detached portion of the astragalocalcaneum.

The foot is beautifully preserved in IVPP V13281 ( Fig. 7 ). It is very elongate (longer than the femur and tibia together), and strongly asymmetric, with an exceptionally long fourth digit, although digit 5 is quite long. The fourth metatarsal (Mt) has the greatest diameter of the metapodial elements, and, at 10.5 mm, is of similar length to the humerus. Mt3 is narrower, but only slightly shorter (9.5 mm), while Mt2 (8 mm) and then Mt1 (5.2 mm) become both markedly shorter and narrower. Mt5 is the shortest (4 mm) and is clearly hooked, but with little development of the outer process and thus limited proximal expansion. The phalanges of the foot resemble those of the hand in general structure, but become progressively shorter towards the tip of each digit. Like its metatarsal, the proximal phalanx of digit four is very robust. As in the hand, the unguals are long, slender and bear a strongly curved proximal articular surface suggesting they could be strongly flexed to give a firm grip. This is supported by the presence of well−developed extensor and flexor processes. The phalangeal formula of the pes is 2:3:4:5:4.

Soft tissue preservation.—Several IVPP specimens of Dalinghosaurus preserve clear traces of the scales on both the body and the tail, most notably IVPP V13865 ( Fig. 9A ) and IVPP V12586 ( Fig. 9B ). The tail shows a pattern of proximodistally elongated overlapping rectangular scales arranged in distinct transverse rows, or annulae ( Fig. 9A, B ), except on the proximal end where the scales are more granular in appearance. The body scales are also well−preserved ( Fig. 9A, B ). IVPP V12586 shows that there is a distinct difference between dorsal and ventral surfaces. One surface had large rhomboid scales, the other had smaller, rounded granular scales. In IVPP V12585A, the large rhomboid scales seem to lie under the scapulocoracoid, suggesting they are ventral, while the counterpart block looks up into the dorsal surface of the body and seems to have more of the granular scales. Thus Dalinghosaurus appears to have had small rounded granular scales on the dorsum, larger rhomboid scales on the underside, and enlarged caudal scales arranged in transverse rows. This pattern of caudal scalation is found in many scincomorphs and anguimorphs (Autarchoglossa), and a small number of iguanians ( Arnold et al. 2002).

Figures

Fig. 1. Dalinghosaurus longidigitus. IVPP V13282, Hauterivian–Barremian, Lujiatun, China. Skull in dorsal (A), palatal (B), left lateral (C), and right lateral (D) views. See Fig. 2 for explanation.

Fig. 2. Dalinghosaurus longidigitus. IVPP V13282, explanatory drawings for Fig. 1. Skull in dorsal (A), palatal (B), left lateral (C), and right lateral (D) views.

Fig. 3. Dalinghosaurus longidigitus. IVPP V13281, Barremian, Hejiaxin, China, immature specimen, skull in dorsal view.

Fig. 4. Dalinghosaurus longidigitus. IVPP V13281, Barremian, Hejiaxin, China. Complete skeleton, dorsal view.

Fig. 5. Dalinghosaurus longidigitus. IVPP V13281, Barremian, Hejiaxin, China. Anterior skeleton showing right forelimb and part of pectoral girdle.

Fig. 6. Dalinghosaurus longidigitus. IVPP V14234.1, Hauterivian–Barremian, Lujiatun, China. Pectoral girdle in ventral view (A) and explanatory drawing (B), not to scale.

Fig. 7. Dalinghosaurus longidigitus. IVPP V13281, Barremian, Hejiaxin, China. Pelvic girdle, sacrum and right hind limb.

Fig. 8. Dalinghosaurus longidigitus. IVPP V14295, Barremian, Sihetun, Beipiao City, China. Pelvic girdle, hind limbs and tail, mainly dorsal view.

Fig. 9. Dalinghosaurus longidigitus, Barremian, Dawangzhangzi, China. Skin preservation. A. IVPP V13865B, showing body and tail scales. B. IVPP V12586, detail of hind leg and tail with scalation.