Lufengosaurus huenei Young 1941

Lufengosaurus huenei Young 1941 ( Figs 1–18 View Figure 1 View Figure 2 View Figure 3 View Figure 4 View Figure 5 View Figure 6 View Figure 7 View Figure 8 View Figure 9 View Figure 10 View Figure 11 View Figure 12 View Figure 13 View Figure 14 View Figure 15 View Figure 16 View Figure 17 View Figure 18 )

Synonym

‘ Gyposaurus ’ sinensis Young 1941 .

Holotype

IVPP V15 View Materials , an almost complete skeleton.

Referred specimens

GMC V00636 (formerly V27 of ‘ Gyposaurus ’ sinensis ), almost complete postcranial skeleton, consisting of eight cervical vertebrae, 13 dorsal vertebrae, three sacral vertebrae, four caudal vertebrae, almost complete pectoral girdle, forelimb, pelvic girdle, and hindlimb elements. IVPP V26 (formerly V26 of ‘ Gyposaurus ’ sinensis ), incomplete postcranial skeleton including nine cervical vertebrae, 13 dorsal vertebrae, pectoral girdle, both humeri, both ulnae, both radii, left femur, left tibia, and partial pedal elements.

Locality and horizon

Shawan village, Lufeng City, Yunnan Province, People’s Republic of China. The Shawan Member of the Lower Jurassic Lufeng Formation.

Previous work

Rozhdestvensky (1965) suggested that all the non-sauropodan sauropodomorphs, including ‘ Gyposaurus ’ sinensis , from the Lufeng Formation were junior synonyms of Lufengosaurus huenei . Galton (1990) retained both Lufengosaurus and Yunnanosaurus as valid genera but regarded ‘ Gyposaurus ’ sinensis as a junior synonym of Lufengosaurus huenei . Sereno (1997, 1999), however, accepted ‘ Gyposaurus ’ sinensis as a distinct taxon and considered it to be basal to Lufengosaurus and Yunnanosaurus . Yates (2003) demonstrated that the morphology of the syntypes of ‘ Gyposaurus ’ sinensis is similar to that of Lufengosaurus and treated ‘ Gyposaurus ’ sinensis as a junior synonym of Lufengosaurus huenei in his phylogenetic analysis. He also proposed the autapomorphies of Lufengosaurus huenei and ‘ Gyposaurus ’ sinensis , including ‘a strongly arched dorsal margin of the ilium and an exceptionally large manual digit I relative to the other manual digits’. Galton and Upchurch (2004) reconsidered ‘ Gyposaurus ’ sinensis as a putative distinct species from Lufengosaurus huenei . Barrett et al. (2003) suggested a referred specimen of ‘ Gyposaurus ’ sinensis (NGMJ V 108, former V43) as a distinct taxon. Furthermore, Smith and Pol (2007) and Pol et al. (2011) recovered V43 as a distinct taxon in their phylogenetic analysis.

Here, we provide the first comprehensive and detailed redescription of the two syntype specimens (V26 and V27) of ‘ Gyposaurus ’ sinensis originally described by Young (1941b).

Revised diagnosis

The cranial autapomorphies of Lufengosaurus huenei are herein listed from Barrett et al. (2005): distinct tuberosity on lateral surface of ascending process of maxilla; low boss on central portion of jugal at junction of the three jugal processes; prominent boss on dorsal surface of rostrolateral process of parietal; and presence of ridge on posterior part of lateral surface of maxilla. The postcranial diagnosis of Lufengosaurus huenei , which is only tentatively put forward in this study, includes the following combination of characters and an autapomorphy (indicated by an asterisk): a gracile scapula with dorsal end weakly expanded and almost symmetrical, without a well-developed posterodorsal corner; ilium with dorsoventrally high main body and strongly arched dorsal margin; pendant-shaped distal termination of fourth trochanter of femur; and length of tibia being ~0.65 times the length of femur*. Further research on the postcranial skeleton of the holotype of Lufengosaurus huenei will be addressed elsewhere.

Description

The comparisons with specific taxa mentioned in the description are based on the personal observations and references listed in Table 1 View Table 1 . The measurements of all the bones are provided in the Supporting Information (Appendix S2).

Vertebral column

Cervical vertebrae: According to the description by Young (1941b), nine cervical vertebrae are preserved in V26 (IVPP V26), probably representing Cv3–Cv10 based on their morphology. Among them, the centrum of Cv3 lacks the posterior end, and Cv4 lacks the anterior end of the right region. Other cervical vertebrae preserve almost complete centra, and most of them retain at least part of the neural arches ( Fig. 1A View Figure 1 ). The preservation of the cervical vertebrae of V27 (GMC V00636) is more complicated than that of V26. Young (1941b) described how nine cervical vertebrae are assignable to V27. However, after careful comparison, the last two cervicals described by Young (1941b) are interpreted herein as the anterior dorsal vertebrae, because the parapophysis has shifted from the middle of the lateral surface of the centrum to the neurocentral juncture. Furthermore, the centrum of one dorsal vertebra in V27 described by Young (1941b) bears a keel on its ventral surface and appears to possess a trace of the development of a parapophysis on its anteroventral corner of the lateral surface. Here, it is tentatively assigned to Cv10 on account of its shorter length than that of the ninth cervical. Therefore, V27 preserves eight cervical vertebrae, which possibly represent Cv3–Cv10 ( Fig. 1B–D View Figure 1 ). Cv3 preserves only the posterior half of the centrum. Except for Cv3, Cv8, and Cv10, which retain only the centrum, other cervicals preserve at least parts of the neural arches, and Cv9 represents the bestpreserved element among them.

In general, the cervical centra are dorsoventrally low, anteroposteriorly elongated, and constricted mediolaterally. As in other non-sauropodan sauropodomorphs, the centra are both amphicoelous and acamerate. In V26, the centra of Cv5 and Cv6 have almost the same length, and they are the longest centra among all the cervical vertebrae, although it is possible that the length of Cv6 was artificially exaggerated owing to poor preservation of the posterior end ( Fig. 1A View Figure 1 ). The centrum of Cv5 is 2.56 times longer than it is high anteriorly, whereas the anterior surface of the centrum of Cv6 is so distorted that this ratio cannot be measured. This ratio is similar to that of the centrum of Cv5 of Lufengosaurus , although in Lufengosaurus the centrum of Cv6 is the longest, with a length-to-height ratio of 2.2. In V27, the centrum of Cv5 is the longest, and it is 2.8 times longer than it is high anteriorly. The centrum of Cv6 is 2.3 times longer than its anterior height, resembling that of Lufengosaurus . A ventral keel is only weakly developed on the ventral surface of the centrum from Cv4 to Cv8 and is more prominent on the anterior half than on the posterior half, whereas Cv9 has a well-developed keel that extends along its entire length. The condition wherein the ventral keel is weakly developed in the anterior and middle cervicals and becomes more prominent in the posterior cervicals is similar to that of Lufengosaurus , Yunnanosaurus , and Xingoiulong. In the anterior cervical vertebrae, the parapophyses are developed as small projections located close to the anterior and ventral margins of the centra. Moving posteriorly, the parapophyses gradually increase in size and are located more dorsally and posteriorly. In lateral view, the ventral margin of the cervical centra of V27 appears less concave than those of Lufengosaurus (possibly owing to differential preservation).

The neural arches become higher from the anterior to posterior cervical vertebrae. The suture dividing the centrum from the neural arch is clearly visible in most cervicals that preserve the neural arches. The diapophyses are poorly developed in the anterior cervicals. In Cv6–Cv8, the diapophyses are short and placed anteriorly; they are almost ventrally directed and close to the parapophyses, becoming more developed from Cv6 to Cv8. The diapophysis of Cv9 is more prominent, almost horizontally oriented, and separated from the parapophysis. The preserved prezygapophyses of Cv 7 in V26 extend anterodorsally beyond the anterior margin of the neural arch and centrum. In V27, the prezygapophyses of Cv9 are upturned and have dorsomedially facing articular facets. The postzygapophyses are relatively short with respect to the prezygapophyses; they are projected posteriorly only slightly beyond the posterior margin of the centrum. Cervical lamination is only weakly developed in Cv9, including the prezygodiapophyseal and posterior centrodiapophyseal laminae ( Fig. 1B View Figure 1 ). On the dorsal surface of the postzygapophysis of Cv 5 in V26, the epipophysis is well developed and appears to extend posteriorly to overhang the rear margin of the postzygapophysis. However, the epipophyses of Cv 6 in V26 and all the cervicals in V27 are less developed and do not extend as posteriorly as in Cv5 of V26.

The neural spines of Cv5, Cv6, and Cv 8 in V26, in addition to Cv5–Cv7 and Cv 9 in V27, are preserved ( Fig. 1C View Figure 1 ). Although most of the neural spines are not complete, they are probably anteroposteriorly longer than they are dorsoventrally high. Based on the length of its base, the neural spine of Cv5 is the longest of all; its anteroposterior length is ~5.4 times its dorsoventral height. The neural spine becomes shorter along the posterior cervical vertebrae. In lateral view, the preserved posterior portion of the dorsal margin of the neural spines is straight to slightly convex, similar to that of most non-sauropodan sauropodomorphs, but differs from that of Leyesaurus Apaldetti et al. 2011 , in which the posterior half of the dorsal margin of the neural spines of the anterior to mid-cervicals is slightly concave ( Apaldetti et al. 2011). The neural spine of Cv 9 in V27 is the only one that is completely preserved. As in most non-sauropodan sauropodomorphs, its dorsal end is laterally expanded, forming a neural spine table.

Dorsal vertebrae: Most of the disarticulated dorsal vertebrae are represented by only the centra and lack the neural arches. Young (1941b) described that there were 10 dorsal vertebrae preserved in V26 and 15 dorsal vertebrae in V27. Furthermore, as described above, two cervical vertebrae stated by Young (1941b) are hereby regarded as anterior dorsals of V27, and one dorsal described by Young (1941b) is assigned as a cervical. Therefore, based on the relative size (especially the size of the articular surfaces of the centra), the position of the parapophysis, the presence or absence of a ventral keel, and the vertebral count present in other non-sauropodan sauropodomorphs, we suggest that V26 preserves 13 dorsals and that V27 preserves 13 dorsals. The 13 dorsals of V26 possibly represent five anterior-most and eight middle-posterior dorsals, although it is difficult to estimate whether the latter elements are articulated or isolated owing to the lack of enough morphological features. The 13 dorsals preserved in V27 are tentatively referred to as D1, D2, and D4–D14 (D4 is herein supported by the higher placement of its respective parapophysis; Fig. 2 View Figure 2 ). Owing to the non-articulation, the precise position of the elements within the dorsal series cannot be established with certainty; therefore, their positional assignment is treated as tentative here.

The dorsal vertebrae are relatively short compared with the cervical vertebrae ( Fig. 2 View Figure 2 ). All the dorsal centra are amphicoelous and concave both laterally and ventrally. The first dorsal can be distinguished from others by its sharp keel present on the ventral surface of the centrum ( Fig. 2C View Figure 2 ). This ventral keel is gently developed in the second dorsal and absent from the fourth dorsal. The anteroposterior length of the dorsal centrum is slightly longer than the dorsoventral height of the posterior surfaces, with a length-to-height ratio of 1.25, roughly resembling that of Lufengosaurus (~1.1, IVPP V15), but shorter than those in Adeopapposaurus Martínez 2009 ( Martínez 2009), Massospondylus Owen 1854 ( Barrett et al. 2019) and Seitaad Sertich and Loewen 2010 ( Sertich and Loewen 2010), in which this ratio is 1.5.

The parapophysis of the dorsal vertebrae is large and has a sub-elliptical outline. In D1 and D2, the parapophysis is present below the neurocentral suture and close to the mid-length of the centrum. In D4, the parapophysis has migrated higher and thus is located mainly at the neural arch, although this could be exaggerated by preparation. The majority of the parapophysis of D5 is located at the neural arch. From D6, the parapophysis appears to have migrated entirely to the neural arch. In D7, the region that bears the parapophysis has been broken. In D8 and D9, it is positioned on the ventrolateral corner of the neural arch ( Fig. 2A, B View Figure 2 ).

The diapophyseal laminae can be observed in D6–D9, which, among all the dorsal elements, preserve partly complete neural arches. The prezygodiapophyseal lamina is developed in D6 and appears to be absent in D8 and D9. Owing to poor preservation, it is difficult to determine whether the anterior centrodiapophyseal lamina is developed. Paradiapophyseal, postzygadiapophyseal, and posterior centrodiapophyseal laminae are moderately developed in D8 and D9 ( Fig. 2E, F View Figure 2 ).

Among all the dorsal vertebrae, only D8 and D9 preserve relatively complete diapophyses. In dorsal view, they are rounded trapezoid in shape, with a kidney-shaped articular facet. In D8, the diapophysis is directed laterally and raised dorsally in lateral view, whereas in D9 it projects more posteriorly, which could havebeenaffectedbypostmortemdistortion.Themorphologyof the prezygapophysis is difficult to assess fully in most dorsals, although the right prezygapophysis in D8 is completely preserved. It is an elongated process with rounded ends and an oval, subhorizontal facet. There is no evidence of spinoprezygapophyseal laminae in any of the preserved material. In D7 and D9, the postzygapophyses are short and stout, with the articular facets facing ventrolaterally. The spinopostzygapophyseal laminae are weakly developed in D7. A thin, plate-like hyposphene appears to be present on the posterior midline in D6 and D7, immediately ventral to the postzygapophyses.

The dorsal neural spine is completely preserved in D7 ( Fig. 2A, D View Figure 2 ). It is subrectangular in lateral view, being dorsoventrally low and anteroposteriorly elongated, as in most non-sauropodan sauropodomorphs. Its posterior margin is straight.

Sacrum: There are three sacral vertebrae preserved in V27 (GMC V00636); the first one is represented by a centrum, the second one is composed of an isolated centrum and two sacral ribs that probably belong to this vertebra, as described by Young (1941b: plate I, fig. 6), and the third one is represented by a centrum connected with the right sacral rib ( Fig. 3 View Figure 3 ). No other elements could be assigned to the sacrum. Therefore, the sacrum of V27 is probably composed of three vertebrae, as in most non-sauropodan sauropodomorphs. Their positional assignment mainly follows Young’s description. Both the second and third sacral ribs have anterior and posterior surfaces that contact the ilium ( Young 1941b: plate I, fig. 6), which is a particular morphology that is present only in primordial sacrals ( Pol et al. 2011). Therefore, a dorsosacral (S1) and two primordial sacrals (S2 and S3) are tentatively adopted here.

All three sacral centra bear a low longitudinal ridge on the ventral surface; the ridge of S1 is more developed and acute than those of S2 and S3 (contra Young 1941b), although this is probably attributable to deformation ( Fig. 3B View Figure 3 ). The morphology of the ventral surface of the sacral centra is highly variable in early-branching sauropodomorphs. This surface is smooth in most early-branching sauropodomorphs (e.g. Yunnanosaurus, Xingoiulong , Adeopapposaurus , and Leonerosaurus Pol et al. 2011; Martínez, 2009; Pol et al. 2011). In Lufengosaurus and Mussaurus Bonaparte and Vince 1979 ( Otero and Pol 2013), only the third sacral possesses this ventral ridge. The first two sacral centra of Massospondylus , however, bear grooves on the ventral surface (BP/1/4934; Barrett et al. 2019). The origin of the transverse process on the lateral surface of the sacral centrum is sub-oval and large, occupying approximately one-quarter of the area of the lateral surface of the centrum.

Generally, the sacral ribs are similar in morphology to other non-sauropodan sauropodomorphs in which these elements are well preserved (e.g. Lufengosaurus , Yunnanosaurus , Adeopapposaurus , and Massospondylus ; Martínez, 2009; Barrett et al. 2019). In dorsal view, the sacral ribs of S2 exhibit a T-shaped outline, consisting of a stout, twisted shaft and a lateral expansion ( Fig. 3C View Figure 3 ). The lateral expansion, which is sub-rectangular in shape and anteroposteriorly much longer than it is dorsoventrally high, probably contacts the medial surface of the ilium. Both the anterior and posterior ends of the lateral articular surface are slightly convex, whereas its middle region is occupied by an inclined and elongated depression. The dorsomedial region of the sacral rib of S3 is reconstructed with plaster. In dorsal view, the sacral rib of S3 attaches to nearly two-thirds of the lateral surface of the centrum of S3. The medial expansion is constricted to a shaft that expands laterally to form an extensive and oblique articular surface to contact the ilium. In posterior view, S3 displays a butterfly-shaped outline also seen in the second primordial sacral of Lufengosaurus and Massospondylus ( Barrett et al. 2019) , which suggests that S3 of V27 could also be referred to as the second primordial.

Caudal vertebrae: There are four caudal vertebrae preserved in GMC V00636, which are all referred to V27 ( Fig. 4 View Figure 4 ). Young (1941b) described how the first three caudals are probably in natural connection and represent the anterior caudals, although they are missing the neural arches. The first two caudal centra are dorsoventrally taller than they are anteroposteriorly long at the anterior articular facet, with length-to-height ratios of 0.91 and 0.97, respectively. The third caudal centrum, however, is 1.11 times longer than dorsoventrally tall. These ratios, which are higher than those of the anterior-most five caudals of Lufengosaurus (0.6–0.8), Yunnanosaurus (0.7–0.9), and Jingshanosaurus (0.6–0.8), indicate that the first three caudals could have been positioned slightly behind the anterior-most region of the tail and possibly represent the sixth to eighth caudals. Another preserved caudal vertebra probably derives from the middle part of the caudal series, as evidenced by its greater elongation of anteroposterior length than the first three elements ( Young 1941b; Fig. 4C, D View Figure 4 ). The caudal centra are amphicoelous, with a relatively flat lateral surface. A shallow ventral sulcus is absent on the ventral surface of the first three caudal centra but is developed on the ventral surface of the middle caudal.

Pectoral girdle

Scapula: Both scapulae are represented in V27 (GMC V00636) and V26 (IVPP V26). The scapulae of V26 are somewhat distorted and damaged, and the elements are better preserved in V27 ( Fig. 5 View Figure 5 ), hence the latter form the focus of the following description ( Fig. 5A, B View Figure 5 ).

The ventral end of the scapula comprises the acromion process anteriorly and the glenoid region posteriorly. The dorsal margin at its steepest point of the acromion process forms an angle of 50° relative to the long axis of the scapular blade, differing from the angle of 60° in Lufengosaurus , but this is probably attributable to deformation and breakage. Viewed laterally, the acromion fossa is roughly triangular and extends from the anterior margin of the glenoid to the anterior apex of the acromion process. The glenoid region faces posteroventrally and represents the lateromedially thickest part of the scapula. Ventrally, the glenoid articular facet of the proximal end is concave and subcircular in shape. The anteroposterior length of the ventral end is 0.42 times the total length of the scapula, as in other non-sauropodan sauropodomorphs (e.g. Lufengosaurus , Jingshanosaurus , Plateosaurus Meyer 1837 , Massospondylus , Coloradisaurus Bonaparte 1978 , and Unaysaurus Leal et al. 2004 ), but contrasts with Xingoiulong, in which this ratio is 0.56.

The scapular shaft is gracile, with its minimum anteroposterior length 0.15 times the total scapular length, resembling that of Lufengosaurus and Yunnanosaurus , but differing from Jingshanosaurus and Xingoiulong, in which this proportion is 0.2. On the medial surface of the scapular shaft, a gently convex ridge runs from the dorsal region of the posterior margin of the glenoid to a position about midway along the bone, as in most sauropodomorph taxa ( McPhee et al. 2014, Otero et al. 2015).

The dorsal end of the scapula is expanded anteroposteriorly. A weakly developed posterodorsal corner of the dorsal end is present in the right scapula of V27, making the dorsal end slightly asymmetrical. However, the completely preserved dorsal end of the left scapula of V26 is almost symmetrical and lacks a well-developed, projecting posterodorsal corner, and although incomplete, a projecting posterodorsal corner appears absent in the left scapula of V27; the differences observed in this condition are indicative of the slight morphological variations that could occur even within single individuals. The scapula with a symmetrical dorsal end that lacks a distinct posterodorsal corner is also present in Lufengosaurus . In Yunnanosaurus , Jingshanosaurus , and Xingoiulong, the dorsal end of the scapula is highly asymmetrical, with a well-developed posterodorsal corner. The anteroposterior length of the dorsal end is 0.26–0.32 times the scapular length, as also occurs in Lufengosaurus , Coloradisaurus , Plateosaurus , Massospondylus , and Adeopapposaurus . In contrast, the dorsal expansion is more developed in Yunnanosaurus (ratio = 0.45) and Jingshanosaurus (ratio = 0.49).

Coracoid: Both the coracoids are partly preserved in V27 (GMC V00636) and V26 (IVPP V26). Some parts of the elements have been lost, in contrast to the substantially complete coracoids at the time of Young’s (1941b) description. In V27, both coracoids retain the posterior region. In V26, the left coracoid preserves its anterior portion, and the right element retains its posterior part. The posterior end is much thicker mediolaterally than the remaining coracoid and forms the glenoid region ( Fig. 5 View Figure 5 ). The glenoid facet is lateromedially wide and faces posteroventrally. A well-developed coracoid tubercle is placed anterodorsally to the glenoid region. It projects laterally and further anteroventrally, forming a ventral process that is also present in other early-branching sauropodomorphs. No coracoid foramen is observed in any of the elements (contra Young 1941b); this foramen was probably present on the parts of the coracoids that have been lost. The anterior region of the coracoid is lateromedially thin, flat laterally, and concave medially.

Forelimb

Humerus: V27 (GMC V00636) and V26 (IVPP V26) both preserve the left and right humeri. However, the left humerus of V26 has been compressed proximodistally. Therefore, the following description is based mostly on the elements of V27.

Overall, the morphology of the humerus is congruent with the generalized condition of most non-sauropodan sauropodomorphs ( Fig. 6 View Figure 6 ). The humerus is gracile, with a slender midshaft. The proximal end of the humerus is expanded lateromedially and convex proximally. It is rotated at an angle of 40° relative to the transverse axis of the distal end. The mediolateral width of the proximal end is 0.41 (right) to 0.47 (left) times the humeral length, resembling that of Lufengosaurus (~0.48) but differing from Yunnanosaurus and Jingshanosaurus , in which this ratio is 0.6 and 0.55, respectively. A well-developed internal tuberosity is present medially at the proximal end of the humerus, projected both medially and posteriorly. In anterior view, the humeral head is moderately convex proximally, with an elliptical outline, distinguished from the nearly straight proximal margin of the humerus in Yunnanosaurus .

The deltopectoral crest extends distally for 0.5 times the total humeral length, similar to that of most non-sauropodan sauropodomorphs (e.g. Lufengosaurus , Adeopapposaurus , and Coloradisaurus ). In anterior and lateral views, the lateral margin of the deltopectoral crest exhibits a sinuosity that occurs approximately one-third of the distance from its dorsal margin; the degree of this sinuosity resembles that of Lufengosaurus but is more pronounced than those of Yunannosaurus and Jingshanosaurus .

The humeral shaft is notably slender, with a subcircular cross-section. The minimum width of the shaft is 0.14 times the humeral length, similar to the condition present in Lufengosaurus and Yunannosaurus but contrasting with the more robust elements of Jingshanosaurus (0.19) and Xingoiulong (0.16). The distal end of the humerus is 0.36 times the length of the humerus, contrary to Yunnanosaurus , in which the distal condyles are widened, with a width-to-humeral length ratio of 0.43 ( Young 1942). The distal condyles are well developed and delimit a deep cuboid fossa on the anterior surface, although this has probably been exaggerated by the distortion. The medial condyle is more expanded than the lateral one. Proximal to the medial condyle, the entepicondylar surface faces ventromedially. A shallow olecranon fossa is developed on the posterior surface of the distal end.

Radius: Two radii are completely preserved in GMC V00636, which have different lengths, and the proximal end of the left radius is preserved in IVPP V26. The shorter and more slender right and left radii are therefore referred to V26, and the longer left radius is referred to V27.

The radius is a slender element, with expanded proximal and distal ends ( Fig. 7 View Figure 7 ). The length of the radius is 0.56 (V26) and 0.63 (V27) times the length of the humerus, which is a fairly typical ratio for early-branching sauropodomorphs (e.g. Lufengosaurus, Xingoiulong , and Adeopapposaurus ).

The shaft bows slightly medially. It has a mediolaterally compressed, elliptical cross-section at midlength, with the long axis oriented anteroposteriorly. The distal end of the radius is almost as wide mediolaterally as the proximal end but has a more circular outline than the proximal end, although it is still sub-elliptical, with its long axis extending anteroposteriorly, as in Lufengosaurus and Massospondylus . The distal articular surface is flat and oriented at an angle of 80° to the shaft of the radius.

Ulna: Two ulnae are almost completely preserved in GMC V00636, and two ulnae are partly preserved in IVPP V26. In GMC V00636, the left ulna is remarkably longer than the right ulna. Based on the relative length and width of all the preserved elements, the complete right ulna of GMC V00636 and the left ulna of IVPP V26 are referred to V26, and the complete left ulna of GMC V00636 and the proximal half of the right ulna of IVPP V26 are referred to V27 ( Fig. 7 View Figure 7 ).

The right ulna of V26 is 0.68 times the length of the humerus, and the left ulna of V27 is 0.71 times the length of the humerus. This ratio resembles those of Lufengosaurus (0.68), Yunnanosaurus (0.68), Adeopapposaurus (0.72; Martínez 2009), and Unaysaurus (0.72; McPhee et al. 2020), but differs from those of Xingoiulong (LFGT-D0003; 0.61) and Massopondylus (0.6; Barrett et al. 2019). The proximal end of the ulna is expanded both mediolaterally and anteroposteriorly relative to the shaft owing to the development of the anterolateral process and the anteromedial process. The anterolateral process is enlarged and rounded distally, whereas the anteromedial process is less developed and tapers distally, both of which delimit a shallow radial fossa, as in other non-sauropodan sauropodomorphs. The olecranon process is well developed; proximally, it is rounded and extends above the proximal articular surface of the ulna.

The ulnar shaft is slender. It tapers from the proximal end and becomes anteroposteriorly restricted and medially bowed towards the distal end. At midlength, the shaft is convex laterally and flat to shallowly concave medially, forming a D-shaped transverse cross-section. The distal end of the ulna is much more expanded, mediolaterally wider than anteroposteriorly long, with a width-to-length ratio of 1.8. The distal articular surface is convex and sub-oval in shape.

Carpus: Three distal carpals are completely preserved in V27. These carpal elements are tentatively interpreted as the left distal carpal I and the right distal carpals I and III based on their morphology and position relative to the metacarpals. The left distal carpal I and the right distal carpal III are still articulated with metacarpal I and metacarpal III, respectively.

Distal carpal I is discoidal in shape ( Fig. 8A View Figure 8 ), and its overall morphology resembles that of Lufengosaurus , Adeopapposaurus , and Massospondylus . It is transversely wide, although narrower than the proximal width of metacarpal I, and proximodistally flattened. Nearly two-thirds of the distal surface is articulated with the proximal surface of metacarpal I. The proximal surface is smooth, convex, and sub-trapezoidal in proximal view, similar to that of Lufengosaurus . The distal surface is slightly concave.

Distal carpal III is considerably smaller than distal carpal I ( Fig. 8C View Figure 8 ). Most of the distal surface is in articulation with the dorsomedial side of the proximal surface of metacarpal III. The proximal surface is slightly convex and subtriangular in proximal view, with three round margins. The distal surface appears flat.

Manus: The manus is preserved only in GMC V00636. All the elements are disarticulated. After a thorough observation and comparison, most of the manual elements are tentatively assigned to V27 based on Young’s description and their relatively large size, and two smaller elements, including putative right metacarpals III and IV, are tentatively assigned to V26. Therefore, the following description is based on the better-preserved manus of V27 ( Fig. 8 View Figure 8 ).

V27 preserves the right metacarpals I, III, IV, and V and the left metacarpals I, V, and a putative metacarpal III. The isolated phalanges could not be referred confidently to any digit. Based on their relative size and the description and illustration by Young (1941a: plate IV, figs 1, 2), the manual phalanges are tentatively referred to as digits I–IV of the right hand and digits I, III, and IV of the left hand.

Metacarpal I is mediolaterally broader and proximodistally shorter than metacarpals III and IV ( Fig. 8A, B View Figure 8 ). The proximal maximum width of the left and right metacarpal I is 0.93 and 0.79 times the proximodistal maximum length, respectively. This is similar to those of most early-branching sauropodomorphs, which typically display a ratio of 0.7–0.9 (e.g. Massospondylus , Adeopapposaurus , Plateosaurus , and Unaysausus), but lower than Lufengosaurus and Jingshanosaurus , in which metacarpal I is proximally wider than proximodistally long, with a width-to-length ratio of 1.1. The proximal articular surface is concave and has a subtriangular outline, with a dorsoventrally deep lateral end and a dorsoventrally shallower medial end. The dorsal margin of the proximal surface is almost straight, and the palmar margin is slightly concave. The medial end terminates in a round, convex medial margin. The lateral margin is slightly concave, probably to fit with metacarpal II. The lateropalmar and laterodorsal corners of the proximal surface are elevated both proximally and laterally, forming a proximal concavity on the lateral surface of metacarpal I. The shaft of metacarpal I is transversely wide and dorsopalmarly flat. The minimum transverse width is 0.57 times the proximodistal length of metacarpal I. The lateral margin of the shaft is more concave than the medial margin. The distal articular condyles are highly asymmetrical. The lateral condyle is transversely wider in distal view and projected more dorsally and distally than the medial condyle. In palmar view, the medial condyle is palmarly elevated, forming a pronounced palmar tubercle. Collateral ligament pits are well developed on both distal condyles. The lateral collateral ligament pit is elliptical, deep, and marked by well-defined margins, whereas the medial collateral ligament pit is rounded, shallow, and lacks well-defined margins.

Metacarpal III is slender and slightly longer than metacarpal I ( Fig. 8C View Figure 8 ). The right element shares nearly the same length and proximal width as the left element; however, it is distally narrower than the left element, and no trace of compression could be observed. We hence assign this element to the right metacarpal III tentatively, owing to possible allometric growth. The maximum proximal breadth of metacarpal III is 0.54 times the total proximodistal length. The proximal articular surface is triangular in outline, with its apex pointing mediodorsally. A crest is present on the proximal surface, extending in a dorsopalmar direction from the apex to the mediopalmar corner. The mediodorsal corner of the proximal surface forms a right angle, and the mediopalmar corner is rounded. A shallow and sub-elliptical fossa is developed on the dorsal surface of the proximal end. The shaft of metacarpal III is constricted. The distal end is less mediolaterally expanded than the proximal end and lacks an intercondylar groove, giving it a convex, sub-trapezoid outline. The medial margin is concave, and the lateral margin is almost straight. The medial collateral ligament pit is better developed than the lateral pit.

Metacarpal IV is shorter than metacarpals I, II, and III ( Fig.8D View Figure 8 ). The proximal articular surface is convex and triangular, with three almost straight margins. The longest margin contacts metacarpal III and is oriented dorsomedially. The lateropalmar corner forms a right angle, whereas the mediodorsal and mediopalmar corners are more acute. The shaft is straight and becomes constricted towards the distal end, with flat medial and palmar surfaces. The distal end lacks distinct condyles or an intercondylar groove. The distal articular surface is convex, sub-rectangular, and more expanded lateromedially than dorsopalmarly. The collateral ligament pits are moderately developed.

Metacarpal V is a stout element ( Fig. 8E View Figure 8 ). It is robust and the shortest element of the metacarpus. The proximal end is expanded mediolaterally and dorsopalmarly relative to both the shaft and the distal end, with a mediolateral width being 0.76 times the proximodistal length of the bone. The proximal articular surface is subtriangular in outline, with a mediodorsally oriented apex. There is a proximomedially facing flat surface present on the proximal articular surface of metacarpal V, which probably contacts metacarpal IV. The shaft is short and constricted. The distal end is a sub-globular structure that lacks differentiated condyles. The collateral ligament pits are absent.

A non-terminal phalanx is significantly larger and more robust than other elements, and its proximal articular area is compatible with the distal articular area of metacarpal I; consequently, it could be assigned confidently to the first phalanx of digit I ( Fig. 9 View Figure 9 ). Phalanx I.1 is almost as long as the respective metacarpal I. The proximal articular surface is highly asymmetrical and subdivided into medial and lateral cotyles by an oblique ridge that expands dorsally to form a proximodorsally projected tubercle. The medial cotyle is small and subtriangular in outline, with its medioventral corner strongly projected palmarly.The lateral cotyle is semicircular and larger and more concave than the medial cotyle. The distal articular surface is twisted 45° relative to the proximal end, similar to most non-sauropodomorphs, in which this metric is 45°–60° (e.g. Lufengosaurus , Adeopapposaurus , and Mussaurus ; Martínez 2009, Otero and Pol 2013, McPhee et al. 2020). The medial collateral ligament pit is larger and deeper than the lateral one.

Five manual ungual phalanges are preserved in V27. Four of them are tentatively assigned to right digits I–IV, respectively ( Fig. 9 View Figure 9 ), and another one is possibly associated with left digit I. The ungual that is referred to as phalanx I.2 is the largest ungual in all dimensions. It is strongly recurved and mediolaterally compressed. The proximal articular surface is elliptical in outline and taller dorsoventrally than transversely wide. It is also concave and seems to lack a ridge that defines two articular facets, probably owing to compression. The dorsal extensor process is well developed on the dorsal margin of the proximal surface. The flexor tubercle is mildly developed on the palmar margin. The medial and lateral claw sheath grooves are prominent and extend in a nearly parallel manner to the dorsal margin of the ungual from the proximal end to the distal tip.

Two of the non-terminal phalanges are much shorter than phalanx I.1 but longer and more robust than other preserved elements, probably referable to digit II. The shorter phalanges possibly belong to digits III and IV. These phalanges are longer than wide ( Fig. 9 View Figure 9 ). Their shafts are constricted relative to the expanded proximal and distal ends. The distal end has two defined condyles separated by an intercondylar groove. Collateral ligament pits are developed and well defined.

The ungual phalanges of digits II–IV are much smaller and less recurved than the ungual of digit I ( Fig. 9 View Figure 9 ). Their proximal articular surfaces are separated by a low ridge, forming two distinct concave articular facets to receive the distal condyles of the corresponding phalanx. The dorsal extensor process is more poorly developed than that of the ungual of digit I, whereas the flexor tubercle is more prominent. The claw sheath grooves are present on both the medial and lateral surfaces of the ungual of digit II and become faint on the surfaces of the unguals of digits III and IV. The palmar surface of the three unguals is slightly concave to almost flat.

Pelvic girdle

The elements of the pelvic girdle are preserved only in GMC V00636, including both ilia, pubes, and ischia, all of which are assigned to V27 according to Young (1941b).

Ilium: Both ilia are incompletely preserved ( Fig. 10 View Figure 10 ). The left ilium is missing the preacetabular process and a small dorsal portion of the iliac blade. The right ilium lacks most of the dorsal and posterior region of the main body of the ilium and the postacetabular process.

The preacetabular process is triangular and tapers to a blunt point anteriorly. It appears slightly anteroposteriorly longer than it is dorsoventrally high and does not extend as far anteriorly as the anterior margin of the pubic peduncle, as in other non-sauropodan sauropodomorphs except for Anchisaurus , in which the preacetabular process is at least twice as long as high ( Yates 2004). The lateral surface of the preacetabular process is slightly convex. The medial surface is separated by a low and stout ridge that extends anteroposteriorly, forming a laterally oriented dorsal surface and a medioventrally oriented ventral surface, resembling that of Lufengosaurus , whereas in Yunannosaurus and Adeopapposaurus this ridge is more prominent and mediolaterally higher.The main body of the ilium above the acetabulum is dorsoventrally high. Although the middle region is broken, the dorsal margin of the ilium is probably strongly arched owing to the preserved raised anterior and posterior portions of the dorsal margin, similar to that of Lufengosaurus , but unlike the condition seen in Jingshanosaurus , Yunnanosaurus , and Xingoiulong, in which the ilium displays a lower main body and nearly straight dorsal margin. The lateral surface of the iliac body is relatively smooth and flat, whereas the medial surface possesses a rugose scar posterior to the anteroposterior midline, which would have received the sacral rib.

In lateral view, the postacetabular process is sub-rounded, in contrast to the bluntly pointed postacetabular process of Lufengosaurus , Adeopapposaurus , and Massospondylus ( Martínez 2009, Barrett et al. 2019) or sub-square elements of Jingshanosaurus , Yunnanosaurus , and Xingoiulong. In medial view, a shallow brevis fossa, which is bounded by a low brevis shelf, is developed on only the medioventral surface of the postacetabular process, as also occurs in Lufengosaurus, Xingoiulong , and Massospondylus ( Barrett et al. 2019) ; however, in Yunnanosaurus , Jingshanosaurus , and Adeopapposaurus the brevis fossa projects ventrally and is also developed on the lateral surface of the ilium, forming a centrally convex outline of the posterior iliac margin between the postacetabular process and the ischial peduncle.

The acetabulum is completely open, as in other sauropodomorphs. The supracetabular crest is sharp and has a curved lateral margin, which projects from the distal end of the pubic peduncle up to the anteroposterior midpoint of the acetabulum. The anterior and dorsal surfaces of the acetabulum are broad and concave, whereas the posterior surface is flat.

The pubic peduncle extends anteroventrally. The pubic peduncle of the left ilium is slightly curved ventrally along its length. However, given that the pubic peduncle of the right ilium is almost straight, it is possible that the curved left pubic peduncle might have been augmented by artificial exaggeration. The anterior surface of the pubic peduncle is broad and convex, and the posterior surface is concave, forming the anterior surface of the acetabulum. The lateral margin forms the supracetabular crest that encloses the anterior part of the dorsal margin of the acetabulum. The pubic peduncle is subtriangular in cross-section and has a semicircular distal articular surface.

The ischial peduncle is shorter than the pubic peduncle and projects ventroposteriorly. It has a subtriangular transverse cross-section. The distal end of the ischial peduncle is slightly expanded, with a subtriangular distal articular surface. A posterior heel is developed on the posteroventral corner of the ischial peduncle of the right ilium, which is also present in Lufengosaurus , Plateosaurus , and Adeopapposaurus .

Pubis: Both pubes are preserved, with the right element being the better preserved of the two, although they are both missing the posterior part of the pubic plate. The majority of the following description focuses on the right pubis ( Fig. 11 View Figure 11 ).

The total length of the pubis is 0.71 times the length of the femur. The distal part of the pubic plate is damaged, hence it is difficult to determine the ratio of its length to the total pubic length, although it appears that the pubic plate is short, as in most early-branching sauropodomorphs, but contrasts with the elongated pubic plate of Xingoiulong. The obturator foramen preserves only its dorsal margin, and therefore its size and shape remain unclear.

The pubic apron is long and transversely oriented, with its minimum width being 0.58 times the distance between the iliac peduncles. In contrast, the pubic apron of Anchisaurus is narrower and no more than 0.4 times the distance between the iliac peduncles ( Yates 2004). In anterior and posterior views, the lateral margin of the pubic apron is concave, resembling that of most early-branching sauropodomorphs (e.g. Lufengosaurus , Jingshanosaurus , and Adeopapposaurus ). The distal end of the pubis is expanded both mediolaterally and anteroposteriorly. Its anteroposterior depth is 0.14 times the length of the pubis. The mediolateral width of the distal end is 1.2 times the minimum width of the pubic apron, similar to that of Lufengosaurus and Adeopapposaurus but differing from that of Jingshanosaurus (~1.5) and Coloradisaurus (~2.0: Apaldetti et al. 2013). The distal surface of the pubic expansion is smooth, slightly convex, and has a sub-ovoid outline, with a slightly convex anterior margin and a strongly convex posterior margin.

Ischium: Both ischia are almost completely preserved ( Fig. 12 View Figure 12 ). The ischium is composed of an expanded proximal plate and an elongated, thin ischial shaft. The proximal plate is slightly convex laterally and concave medially. Proximally, the articular surface of the pubic peduncle is sub-elliptical in outline, with its long axis being much longer than the transverse axis. Along the proximal margin of the proximal plate, the pubic peduncle and the iliac peduncle are separated by a concavity that contributes to the posteroventral corner of the acetabulum. The articular surface of the iliac peduncle is subtriangular, with a concave medial margin. The distal end of the proximal plate is broken in both ischia, hence it cannot be determined whether a notch was present between the ventrodistal corner of the proximal plate and the ischial shaft, which is absent in Lufengosaurus .

The shaft of the ischium is thin and subtriangular in cross-section. Unlike the more rod-like ischial shaft in some non-sauropodan sauropodomorphs (e.g. Coloradisaurus , Jingshanosaurus , and Mussaurus ), in which the dorsoventral depth of the shaft is subequal to the mediolateral width, the shaft of V27 is wider, with a ratio of dorsoventral depth to mediolateral width of ~0.67, similar to that of Lufengosaurus , Yunnanosaurus , Adeopapposaurus , and some specimens of Massospondylus (e.g. QG1159; Cooper 1981). However, the ischial shafts of Anchisaurus and sauropods are flattened, blade-like, and much wider than they are deep ( Yates 2004: fig. 2). A moderately developed longitudinal groove extends along the proximal third of the ischial length on the dorsolateral surface. The distal end of the ischium is expanded both dorsoventrally and mediolaterally, with a subtriangular distal surface. The expansion of the distal ischium is not developed like that of Lufengosaurus ( Fig. 12E View Figure 12 ), probably owing to the ontogenetic variation that is also present in individuals of different ontogenetic stages of Mussaurus ( Otero and Pol 2021) .

Hindlimb

Only a left femur, partial left tibia, left fibula, and some elements of the pes are present in IVPP V26. The hindlimb elements are almost completely preserved in GMC V00636. Based on the relative size and the description by Young (1941b), the elements of IVPP V26 are assigned to V26, and the elements of GMC V00636 are assigned to V27, on which the following description is mainly based.

Femur: Both femora are almost complete in V27. However, the left element has suffered mediolateral deformation, and the right element is better preserved.

The femur is a gracile element, and its overall morphology is similar to that of other non-sauropodan sauropodomorphs ( Fig. 13 View Figure 13 ). It is 1.5 times as long as the humerus. This compares with a ratio of 1.75 in Lufengosaurus , which is probably an ontogenetic difference that is also present in Mussaurus ( Otero and Pol 2021) . In anterior view the femur is relatively straight, but it is sigmoidal in lateral view, as in other non-sauropodan sauropodomorphs. The femoral head is well developed and oriented subparallel to the transverse axis of the distal end of the femur.

The lesser trochanter is an elongated and low ridge that is present on the anterior surface and close to the lateral margin. Its proximal tip is placed almost level to the distal margin of the femoral head; this condition is similar to that of Lufengosaurus , Coloradisaurus , Yunnanosaurus , and Jingshanosaurus , whereas in Xingoiulong the proximal tip of the lesser trochanter is located distally to the distal femoral head.

The fourth trochanter is developed as a proximoposteriorly elongated, anteroposteriorly tall crest on the proximal half of the femoral shaft and close to the medial margin of the femur. It is pendant shaped, with a notch and a distal termination, as in Lufengosaurus and some specimens of Massospondylus (QG1159; Cooper 1981), but contrasts with the subrectangular-shaped fourth trochanter of most non-sauropodan sauropodomorphs (e.g. Adeopapposaurus , Coloradisaurus , Yunnanosaurus , Jingshanosaurus, Xingoiulong , and Anchisaurus ), which might represent a potential diagnostic feature of Lufengosaurus that differs from other sauropodomorph taxa from Lufeng.

The femoral shaft is slender and subcircular in cross-section. The distal end of the femur is expanded both anteroposteriorly and mediolaterally. Anteriorly, a shallow extensor depression is located at the central region of the distal femur. Both the medial and lateral condyles are well developed and posteriorly exposed. On the posterior surface of the distal femur, a deep and narrow popliteal fossa is defined by the two condyles. The tibiofibular crest is robust and separated from the lateral condyle by a shallow sulcus.

Tibia: Both tibiae have suffered breakage and deformation. The left element is better preserved and forms the main focus of the following description ( Fig. 14A–F View Figure 14 ).

The length of the tibia is nearly 0.88 times the length of the femur. This ratio differs from that of Lufengosaurus , in which the tibia is much shorter and ~0.65 times the femoral length (see Discussion). The proximal end of the tibia is expanded, with a subtriangular-shaped articular surface. The anteroposterior length of the proximal expansion is 0.24 times the proximodistal length of the tibia, similar to that seen in the immature skeletons of Mussaurus ( Otero and Pol 2021) , but compares with a ratio of 0.43 in Lufengosaurus . Most early-branching sauropodomorph taxa display ratios that vary between 0.3 and 0.4 (e.g. Yunnanosaurus, Xingoiulong , Jingshanosaurus , Coloradisaurus , Adeopapposaurus , and mature specimens of Mussaurus ). The relatively high ratio of Lufengosaurus resembles those of some robust sauropodiforms, such as Antetonitrus Yates and Kitching 2003 (0.46; McPhee et al. 2014) and Blikanasaurus Galton and van Heerden 1985 (0.5; Apaldetti et al. 2013). The cnemial crest is a distinct projection that is oriented anterolaterally, as in other non-sauropodan sauropodomorphs. The posterior margin of the proximal articular surface is approximately as long as the lateral margin and bears two well-defined condyles that are separated from each other by a notch. In proximal view, the lateral condyle extends more posteriorly than the medial condyle. The proximal articular surface of the lateral condyle is slightly convex, whereas the medial condyle has a flat proximal surface.

The shaft of the tibia is straight and sub-oval in cross-section. The distal end of the tibia is expanded and transversely wider than anteroposteriorly long. It is difficult to determine the relative anteroposterior length between the medial margin and the lateral margin owing to the breakage and deformation of the distal tibia. The lateral margin bears a notch that is bounded by the anterolateral and posterolateral processes. The posterolateral process is much narrower anteroposteriorly and appears to be projected more laterally and distally than the anterolateral process, but this has probably been accentuated by deformation of the anterolateral process.

Fibula: The right fibula retains the proximal and distal ends, and the left fibula has suffered severe deformation ( Fig. 14G–L View Figure 14 ). The proximal end of the fibula is anteroposteriorly expanded, with its lateral surface convex and its medial surface concave; therefore, the proximal articular surface is crescent shaped in outline. The poorly preserved shaft of the fibula is relatively straight and subcircular in cross-section. The distal end is less expanded anteroposteriorly than the proximal end. The distal articular surface is slightly convex and sub-ovoid in outline. In lateral view, the distal margin of the fibula is oblique to the long axis of the shaft.

Astragalus: Both astragali are preserved in V27. The general morphology of the astragalus is similar to that of other non-sauropodan sauropodomorphs ( Fig. 15 View Figure 15 ). In proximal view, the main body of the astragalus has a subrectangular profile. The anterior margin of the astragalus is slightly concave in proximal view. The posterior margin, although lacking a small portion, bears a gently developed pyramidal process, as in Lufengosaurus , Massospondylus , and Coloradisaurus . A posterior bulge, which is present close to the mid-line of the posterior margin of the astragalus in Xingoiulong and Mussaurus ( Otero and Pol 2013) , is absent in V27. The lateral margin is anteroposteriorly shorter than the medial margin. The lateral surface is slightly concave, thereby forming the fibular facet, and the medial surface is convex. A well-developed and proximally projected ascending process occupies the anterolateral corner of the astragalus. It is sub-rectangular in proximal view, mediolaterally wide, and proximodistally high. In anterior or posterior view, the ascending process is triangular, with the lateral margin much steeper than the medial margin. A deep fossa is notably developed at the base of the anterior surface of the ascending process, which is a common condition in early-branching sauropodomorphs (e.g. Lufengosaurus , Yunnanosaurus , and Coloradisaurus ). The posterior surface of the ascending process displays a large, shallow, and subtriangular fossa that is bounded dorsally and medially by a sharp ridge. The vascular foramen, which is present in this posterior fossa in Glacialisaurus Smith and Pol 2007 ( Smith and Pol 2007) and Coloradisaurus (Apaldetti et al. 2013) , is absent in V26 and V27, although this might have been augmented owing to preservation. The distal surface of the astragalus is relatively flat along the medial region and becomes convex towards the lateral end.

Tarsals: There is one distal tarsal element adhered to the dorsal surface of the left astragalus in V27 ( Fig. 15G View Figure 15 ). Based on its morphology and relative size, this element is tentatively interpreted as the left distal tarsal IV. It is subtriangular in outline, and its maximum mediolateral length is subequal to the mediolateral length of the proximal end of metatarsal IV.

Pes: In V27, the left pes is represented by the proximal and distal ends of metatarsal I, nearly complete metatarsals II, III, and V, and nearly complete pedal phalanges; the unguals of pedal digits II and IV are missing. The right pes is represented by a distal fragment of metatarsal I, nearly complete metatarsals II, IV, and V, and nearly complete pedal phalanges; the first phalanx of digit III is missing. The distal end of right metatarsal III illustrated by Young (1941a: plate VIII, fig. 3) is herein referred to V26 owing to its slenderness when compared with other metatarsus of V27.

The proximal end of metatarsal I is still in natural articulation with metatarsal II ( Fig. 16A, B View Figure 16 ). Its proximal articular surface is dorsoplantarly higher than mediolaterally wide. The dorsal and plantar borders are both convex. The distal end of metatarsal I is highly asymmetrical, with the lateral condyle extending more distally and dorsoplantarly higher than the medial condyle.

Metatarsal II is 0.87 times the proximodistal length of metatarsal III ( Figs 16 View Figure 16 , 17B View Figure 17 ). In proximal view, the proximal end is hourglass shaped, with concave medial and lateral margins, as in Lufengosaurus , Jingshanosaurus , Coloradisaurus , Glacialisaurus , and Mussaurus ( Smith and Pol 2007, Apaldetti et al. 2013, Otero and Pol 2013). The dorsal margin of the proximal end is straight, whereas the plantar margin is slightly concave. The ventrolateral corner is projected lateroventrally, forming a flange that underlies the proximal end of metatarsal III, which is also present in other massospondylids, including Lufengosaurus , Coloradisaurus , and Glacialisaurus . The dorsoplantar axis of the proximal end is set at an angle of 60° with respect to the mediolateral axis of the distal end. The articular surface of the proximal end for metatarsal I is more concave than the articular surface for metatarsal III. The shaft of metatarsal II is robust and mediolaterally wider than dorsoplantarly high. Although crushed, the distal condyles of metatarsal II appear roughly symmetrical and are separated by a shallow groove that is more pronounced plantarly. The plantar margin of the medial condyle is subtriangular, with a plantarly pointed apex, and extends more plantarly than the lateral condyle, which has a rounded plantar margin; this condition resembles that of Lufengosaurus . The medial collateral ligament pit is deeper than the lateral pit, although this has probably been accentuated by deformation and breakage.

Metatarsal III is the longest element of the metatarsus ( Figs 16 View Figure 16 , 17C View Figure 17 ). The proximal end is sub-trapezoidal in proximal view, with a broad and slightly concave dorsal margin and a narrower plantar edge that is exposed in plantar view, as in other massospondylids (e.g. Lufengosaurus , Glacialisaurus , and Coloradisaurus ). The lateral margin is gently concave, and the medial margin is also concave, differing from the convex medial margin in other non-sauropodan sauropodomorphs, although this might be attributable to breakage on the medial surface of the proximal end. The dorsoplantar axis of the proximal end is twisted by an angle of 60° with respect to the mediolateral axis of the distal end. The shaft of metatarsal III is dorsoventrally compressed and mediolaterally narrower than that of metatarsal II. The distal condyles of metatarsal III are almost symmetrical in mediolateral width, but the lateral condyle projects more distally than the medial condyle, forming a medially deflected distal margin. The intercondylar groove is less developed than that of metatarsal II. A deep collateral ligament pit is present on both the medial and lateral surfaces of the distal condyles.

Metatarsal IV is subequal in length to metatarsal II ( Figs 16 View Figure 16 , 17D View Figure 17 ). TheproximalendofmetatarsalIVismediolaterally broader than the distal end. In proximal view, the proximal articular surface is triangular in outline, with a mediodorsally oriented apex, and it is almost three times mediolaterally broader than dorsoplantarly high. The dorsal margin of the proximal end is long and straight, forming an obtuse angle with the medial margin, similar to that of other early-branching sauropodomorphs (e.g. Lufengosaurus , Jingshanosaurus, Xingoiulong , and Coloradisaurus ). The medial margin is short and concave, thereby fitting with the lateral surface of the proximal end of metacarpal III. The plantar margin is gently concave. There is a subtly developed ridge extending mediodistally along the dorsal surface of metacarpal III from the apex of the proximal articular surface to the halfway point of the medial margin of the shaft, delimiting a concave medial surface overlapped by metatarsal III and a flat lateral surface. The shaft of metatarsal IV is dorsoplantarly flattened and mediolaterally wide. The distal condyles are highly asymmetrical. The medial condyle is dorsoplantarly high, whereas the lateral condyle is not as high as the medial condyle and possesses a prominent lateral flange. The medial collateral ligament pit is shallow and faces medially. The lateral collateral ligament pit, however, is deep and faces dorsolaterally.

Metatarsal V is the shortest element of the metatarsus ( Figs 16 View Figure 16 , 17E View Figure 17 ). It is flat and funnel shaped, as in other non-sauropodan sauropodomorphs. The right element is preserved in articulation with metatarsal IV ( Fig. 16D, E View Figure 16 ). The proximal end is mediolaterally much broader than the distal end, with a transverse proximal width of 0.57 times the total length of metatarsal V, which is consistent with most non-sauropodiform sauropodomorphs (e.g. Coloradisaurus , 0.47, Apaldetti et al. 2013; Massospondylus , 0.53, McPhee et al. 2015). In contrast, Lufengosaurus displays a higher ratio of 0.69, which could represent an ontogenetic change or intraspecific variation. This ratio exceeds 0.7 in sauropodiforms (e.g. Xingoiulong, Jingshanosaurus , and Blikanasaurus ). In proximal view, the proximal end is higher laterally than medially, forming a triangular proximal articular surface. A moderately developed crest extends distally along the dorsolateral surface of the proximal end, delimiting a concave medial surface that is overlapped by metatarsal IV. The plantar surface of the proximal end is concave, whereas the plantar surface of the distal end is convex. Metatarsal V tapers distally and ends in a simple rounded articular surface.

All pedal phalanges are disarticulated, and their positional assignment is considered herein as tentative ( Fig. 18 View Figure 18 ). The phalangeal formula of the pes is probably 2-3-4-5-1. All pedal phalanges are proximodistally longer than transversely wide and constricted at the midshaft, with expanded proximal and distal ends. The distal end has two well-developed and almost symmetrical condyles separated by a shallow intercondylar groove. The collateral ligament pits are well developed on the medial and lateral surfaces on the distal end. They are deep, sub-rounded in outline, and facing dorsomedially or dorsolaterally owing to transverse expansion of the plantar surface at the distal end. Phalanx I.1 is the longest of all the non-terminal pedal phalanges. The proximal articular surfaces of phalanx I.1, phalanx II.1, phalanx II.2, and phalanx III.1 are undivided and concave, with poorly developed dorsal processes. The proximal surface of the two distal non-terminal phalanges of digit III and all the non-terminal phalanges of digit IV displays two well-defined articular facets that are defined by the longitudinal intercondylar ridge and a dorsoproximally extended, acute dorsal process. The phalanges of digit IV are remarkably shorter than those of other pedal digits. The phalanx of digit V is highly reduced and the smallest phalanx of the pes. Its proximal articular surface is nearly flat, and the distal articular surface is rounded. The dorsal and ventral surfaces are both concave.

The proximal articular surface of all the unguals of the pedal digits is concave and dorsoventrally deeper than transversely wide. The longitudinal intercondylar ridge is only weakly developed. The dorsal process is moderately developed and projected proximally. The ventral flexor tubercle is weakly developed. The lateral nail groove is deep, narrow, and developed on both the medial and lateral surfaces. There is a sharp ventral margin present on the medial surface, which is absent on the lateral surface. The ungual of pedal digit I is the most robust element of all the unguals. It is slightly recurved ventrally, although lacking its distal end. The ungual of pedal digit II is slender, long, and lacks the distal apex. The ungual of pedal digit III is shorter and more slender than that of digit II. The ungual of pedal digit IV is the shortest of all unguals.

Osteohistology

Thin sections of the midshaft of the femur and fibula of V26 and a small portion of the putative fibula of V27 were obtained to evaluate their ontogenetic stage. The sample of the fibula of V26 had suffered severe damage and was poorly preserved, whereas the thin sections of the femur of V26 and the putative fibula of V27 were better preserved ( Fig. 19 View Figure 19 ).

Both samples exhibit a large medullary cavity and a narrow cortex. No endosteal bone is found in the medullary cavity. The cortex is composed of a woven–parallel complex with weakly developed primary osteons ( de Buffrénil et al. 2021). The wovenfibred bone, which is monorefringent under crossed polarized light and represents the earliest stage of woven–parallel bone formation, is commonly found in immature animals with high growth rates ( Chinsamy-Turan 2005, Padian and Lamm 2013). Primary osteons are composed of only a few layers of lamellar bone, also indicating an early ontogenetic stage. The bone tissue is highly vascularized, with a large number of longitudinal vascular canals that are elongate and arranged in a laminar pattern, implying a fast growth rate ( Francillon-Vieillot et al. 1990, Sander 2000, Chinsamy-Turan 2005, Pretto et al. 2016). The density of vascular canals and osteocyte lacunae has no decline through the cortex. Globular and flattened osteocyte lacunae are randomly distributed. Lines of arrested growth (LAGs) are absent in all three samples.

Phylogenetic analysis

The phylogenetic analysis recovered 500 most parsimonious trees, with a tree length of1695 steps (consistency index = 0.288, retention index = 0.654). The strict consensus was fairly well resolved, although with two small polytomies that unresolved the relationships of some early-branching sauropodomorphs ( Fig. 20 View Figure 20 ). However, the clade of Massospondylidae was well resolved, in which V26 and V27 were placed as a member of a polytomy with Lufengosaurus and Glaciasaurus, indicating the close relationship among them. This clade was supported by the following unambiguous synapomorphies: lengths of the anterior cervical centra (cervicals 3–5) are 2.5–4 times the height of their anterior faces (character 131.1); notch separating posteroventral end of the ischial obturator plate from the ischial shaft is absent (character 268.1); transverse width of the conjoined distal ischial expansions is greater than their sagittal depth (character 278.0); and proximal width of the first metatarsal is at least as great as the proximal width of the second metatarsal (character 331.1).