Search

RHOMALEOPAKHUS, gen. nov. Diagnosis —As for type species., Published as part of Upchurch, Paul, Mannion, Philip D., Xu, Xing & Barrett, Paul M., 2021, Re-assessment of the Late Jurassic eusauropod dinosaur Hudiesaurus sinojapanorum Dong, 1997, from the Turpan Basin, China, and the evolution of hyper-robust antebrachia in sauropods, pp. 1-31 in Journal of Vertebrate Paleontology (e 1994414) (e 1994414) 41 (4) on page 12, DOI: 10.1080/02724634.2021.1994414, http://zenodo.org/record/5839134

RHOMALEOPAKHUS TURPANENSIS, sp. nov. (Figs. 6–10; Tables 3 and 4) Nomenclatural Acts —The electronic edition of this article conforms to the requirements of the amended International Code of Zoological Nomenclature, and hence the new names contained herein are available under that Code from the electronic edition of this article. This published work and the nomenclatural acts it contains have been registered in ZooBank, the online registration system for the ICZN. The ZooBank LSIDs (Life Science Identifiers) can be resolved and the associated information viewed through any standard web browser by appending the LSID to the prefix ‘http://zoobank.org/.’ The LSID for this publication is: urn:lsid:zoobank.org:pub:A42348FE-ECE6-4524-B536- 857AFFD22DB2. The electronic edition of this work was published in a journal with an ISSN, and has been archived and is available from the following digital repositories: CLOCKSS. Species Diagnosis — Rhomaleopakhus turpanensis is diagnosed on the basis of three autapomorphies: (1) humeral deltopectoral crest terminates distally in a transversely narrow ridge that is separated from the main body of the crest by distinct lateral and medial grooves; (2) prominent (100 mm long) ridge, projecting posteromedially, on posterior surface of radial shaft, a short distance below the proximal end; and (3) radial distal articular surface markedly concave in central and medial portions. In addition, Rhomaleopakhus turpanensis possesses one of the most robust ulnae of any known sauropod (maximum proximal end width to proximodistal length ratio is 0.50; Table S2 in Supplemental Data 1), and is currently the only known non-somphospondylan eusauropod with the long-axes of the proximal and distal surfaces of the radius twisted through ∼90° with respect to each other. Holotype —A right forelimb, IVPP V11121-1 (Figs. 6–10; Tables 3 and 4), consisting of the humerus, ulna, radius, one carpal, and virtually complete manus of a single individual. Etymology — Rhomaleos (ancient Greek, masculine) equals ‘robust’ (pertaining to the body), and pakhus (ancient Greek, masculine) equals ‘forearm.’ The species name refers to the Turpan Basin, China, where the holotype was found. Locality and Horizon — Lower part of the Kalazha Formation (Upper Jurassic: upper Kimmeridgian–Tithonian) of Qiketai, Shanshan County, Turpan Basin, Xinjiang Uyghur Autonomous Region, China (Dong, 1997; Deng et al., 2015; Fang et al., 2016). Description and Comparisons Humerus — The right humerus is nearly complete, apart from a portion of the proximomedial expansion (Dong, 1997) and a small part of the proximolateral corner (Figs. 6, 7A, 8A). The posterior surface of this element could not be examined fully due to its large size and storage within a protective cradle. It is a relatively robust element, with an estimated Humeral Robusticity Index (sensu Wilson and Upchurch, 2003) of 0.35, similar to those of other heavily built taxa such as Mamenchisaurus youngi, Apatosaurus, dicraeosaurids, and Opisthocoelicaudia (Upchurch et al., 2015:table 2). Proximally, the humerus expands laterally relative to the shaft, giving it an hourglass-shaped outline in anterior view; this is the plesiomorphic sauropod condition, contrasting with the more asymmetrical humeri of most titanosauriforms and turiasaurians (Tschopp et al., 2015a; Poropat et al., 2016). The anterior surface of the humerus is too damaged proximally to determine whether a tuberosity for the attachment of the M. coracobrachialis was present. The deltopectoral crest of Rhomaleopakhus is more prominent than those of most sauropods and is similar to those in Turiasaurus (Royo-Torres et al., 2006) and brachiosaurids (Wilson and Sereno, 1998). The crest lies entirely on the anterolateral margin of the humeral shaft: it does not expand or project medially across the anterior surface (Fig. 7A), unlike those in many titanosauriforms (Wilson, 2002; Mannion et al., 2013). It terminates at ∼44% of humerus length from the proximal end: by comparison, values among other sauropods range between 35–50% (Upchurch et al., 2015:table 2). In this respect, Rhomaleopakhus is almost identical to several other CMTs: for example, these values are 44% in Anhuilong and Omeisaurus tianfuensis, and 43% in Huangshanlong (Ren et al., 2018). In anterior view, the anterolateral margin of the deltopectoral crest has a sigmoid profile and is relatively narrow throughout its length. One unusual feature of the deltopectoral crest is that its distal terminus forms a narrow ridge that is offset medially and laterally from the rest of the crest surface by deep, dorsoventrally oriented grooves or breaks-in-slope: this is provisionally regarded as autapomorphic. Rhomaleopakhus lacks prominent ridges or bulges on the posterolateral surface of the shaft, at the level of the deltopectoral crest. Such projections occur in many titanosaurs, including Alamosaurus, Opisthocoelicaudia, Patagotitan, and Saltasaurus, and have been interpreted as the insertion sites of a number of muscles, including the M. latissimus dorsi, M. scapulohumeralis anterior, and M. deltoideus clavicularis, although these interpretations are debated (e.g., Borsuk-Białynicka, 1977; Otero, 2010, 2018; Upchurch et al., 2015; Moore et al., 2020; Otero et al., 2020; Voegele et al., 2020). In Rhomaleopakhus, as in most sauropods (Wilson, 2002; Mannion et al., 2013; Upchurch et al., 2015), the humeral shaft is wider transversely than anteroposteriorly, producing an elliptical horizontal cross-section at midlength. The transverse width of the shaft at midlength to proximodistal length ratio is estimated at 0.17–0.18. There is a small amount of torsion in the shaft, such that the long-axes of the proximal and distal end surfaces are slightly rotated relative to each other, but Rhomaleopakhus lacks the marked torsion (c. 40°) seen in many diplodocids (Tschopp et al., 2015a) and some CMTs (e.g., at least 30° in Klamelisaurus [Moore et al., 2020] and 25° in Huangshanlong [Huang et al., 2014] and Anhuilong (Ren et al., 2018]). Huang et al. (2014) regarded such humeral torsion as a synapomorphy of Mamenchisauridae, but there is clearly some variation among CMTs and homoplasy within Sauropoda, especially given that a strong degree of torsion of the humeral shaft is the plesiomorphic sauropodomorph condition that is lost in early sauropods (e.g., Yates, 2007; McPhee et al., 2014). The distal end of the humerus is relatively wide transversely compared with the width of the shaft at midlength, largely because it projects a considerable distance medially (Fig. 7A). The ratio of distal end transverse width to humerus proximodistal length is 0.38, which is equaled or exceeded only by Apatosaurus and a few titanosaurs (Poropat et al., 2016; Table S2 in Supplemental Data 1). Distally, the anterior surface of the humerus is flat, apart from the relatively large lateral and medial anterodistal processes (sensu Upchurch et al., 2015) (Fig. 8B). Although the relative size of these anterodistal processes is difficult to quantify, they are very reduced or absent in Chubutisaurus and titanosaurs (D’ Emic, 2012), and are particularly large in several CMTs (Remes, 2008), such as Chuanjiesaurus (Sekiya, 2011) and Huangshanlong (Huang et al., 2014). Enlarged (Huang et al., 2014) and/or anteriorly directed (Ren et al., 2018) anterodistal processes have been regarded as a synapomorphy of Mamenchisauridae: however, reduction and loss of these processes appears to be the derived state (D’ Emic, 2012), and increased process size requires quantification and more comparative work before it can provide support for mamenchisaurid affinities. In Rhomaleopakhus, the distal articular surface is rugose and does not expand up onto the anterior face of the shaft, unlike the humeri of some titanosaurs (Wilson and Carrano, 1999; Wilson, 2002). The ulnar and radial condyles are not strongly divided from each other, and the former is somewhat larger than the latter. Remes (2008) suggested that mamenchisaurids possess a unique distal humeral configuration. In Klamelisaurus, Omeisaurus tianfuensis, and Mamenchisaurus youngi, the lateral condyle (which Remes [2008] termed the ‘radial’ condyle, but which has become the ulnar condyle in sauropods because of the rotation of the antebrachium [Bonnan, 2003]), is larger than the radial one. Moreover, the ulnar and radial condylar surfaces have long axes that are at ∼90° to each other in distal end view, with the former directed anterolaterally. This results in the lateral part of the distal end having a distinct subtriangular profile, formed by fairly straight anterolateral and posterolateral margins that meet each other at an acute angle (e.g., He et al., 1988:fig. 44B; Ouyang and Ye, 2002:fig. 35F; Sekiya, 2011:figs. 38C, 39C). In many other sauropods, this lateral portion is more semicircular or subquadrate in distal view (see Upchurch et al., 2015:fig. 4; N.B., Upchurch et al.’s fig. 4A shows the distal end profile of the right humerus of Mamenchisaurus youngi incorrectly labelled as the left). Rhomaleopakhus possesses the same distal end profile seen in other CMTs (Fig. 8B): however, several non-CMTs also possess this state and, in any case, it is potentially the plesiomorphic eusauropod condition (Mannion et al., 2019a). In Rhomaleopakhus, the lateral third of the flat distal end surface is quite strongly beveled (∼30° relative to the plane lying perpendicular to the proximodistal long-axis of the humerus) (Fig. 7A): as a result, it faces laterodistally. This feature, however, does not seem to have a clear phylogenetic significance; it occurs sporadically in distantly related taxa such as Amargasaurus, Anhuilong, Haestasaurus, Limaysaurus, Mamenchisaurus youngi, and Saltasaurus (Ouyang and Ye, 2002; Upchurch et al., 2015; Ren et al., 2018; Mannion et al., 2019a). The supracondylar (= olecranon or cuboid) fossa, and the medial and lateral ridges that bound it on the distal part of the posterior surface of the shaft, are partially obscured by the packing material upon which the humerus rests (Fig. 8B). However, this fossa is not deep, unlike those of Giraffatitan and several somphospondylans (Upchurch et al., 2004 a, 2015; D’ Emic, 2012), and the associated ridges are broadly rounded transversely rather than acute. Ulna —The ulna is complete apart from a small amount of material missing from the proximal end (Figs. 6, 9A–F). It is extremely robust, with one of the highest proximal end maximum width to proximodistal length ratios (0.50) of any sauropod, although Opisthocoelicaudia has a ratio of 0.51 (Table S2 in Supplemental Data 1). The expanded proximal end is triradiate because of the presence of well-developed anterolateral, anteromedial, and posteromedial processes. As in other sauropods, the anterolateral and anteromedial processes define a deep concavity that receives the proximal end of the radius (Wilson and Sereno, 1998). In proximal view (Fig. 9E), the ulna of Rhomaleopakhus has a ‘V’-shaped profile, rather than the ‘T’-shape seen in several somphospondylans (Upchurch et al., 2015). The angle between the anteromedial and anterolateral processes is ∼70°, which is the derived state (i.e., less than 80°) that occurs in most sauropods (including Chuanjiesaurus, Mamenchisaurus youngi, and Klamelisaurus), except some nonneosauropods, such as Shunosaurus, Omeisaurus tianfuensis, Anhuilong, Huangshanlong, Bellusaurus, and Cetiosaurus, as well as several titanosaurs, in which this angle is greater than 80° and often approaches 90° (Huang et al., 2014; Tschopp et al., 2015a; Poropat et al., 2016; Ren et al., 2018; Moore et al., 2020). In Rhomaleopakhus, the anteromedial to anterolateral process length ratio (sensu Upchurch et al., 2015) is 1.72 (N.B., the measurements in Table 3 give a ratio of 1.25, but these are the maximum lengths of the processes, not their lengths measured to the intersection of process long-axes, as defined by Upchurch et al. [2015:fig. 13A]). This ratio typically ranges between 1.6–1.8 in non-neosauropod eusauropods (e.g., Vulcanodon, Cetiosauriscus, Ferganasaurus), 1.0–1.3 in most diplodocoids and non-titanosauriform macronarians, and>1.5 in titanosauriforms (with values>1.6 in titanosaurs such as Opisthocoelicaudia and ≥2.0 in Epachthosaurus and Cedarosaurus) (Upchurch et al., 2015:table 2). The anteromedial process of the proximal end of the Rhomaleopakhus ulna has a strongly concave articular surface (Fig. 9A–D), as also occurs in many titanosaurs (Upchurch, 1995, 1998), several non-neosauropod eusauropods such as Janenschia and Haestasaurus (Bonaparte et al., 2000; Upchurch et al., 2015; Mannion et al., 2019a), and in a more shallowly concave form in Chuanjiesaurus (Sekiya, 2011). Dong (1997) stated that the olecranon process is relatively low in Rhomaleopakhus, although this region is moderately projected, which is emphasized by the concave proximal surface of the anteromedial process. Similarly developed olecranon processes are seen in Mamenchisaurus youngi (Ouyang and Ye, 2002:fig. 36), Chuanjiesaurus (Sekiya, 2011:fig. 40), Haestasaurus (Upchurch et al., 2015), Janenschia (Bonaparte et al., 2000; Mannion et al., 2019a), and several titanosaurs (Upchurch, 1995; Wilson and Carrano, 1999; Upchurch et al., 2004a). In Rhomaleopakhus, the posteromedially directed process of the proximal end creates a concavity on the posteromedial surface that does not fade out until approximately the midlength of the element, whereas the lateral surface is flat or slightly convex anteroposteriorly. In horizontal cross-section, the proximal portion of the ulna retains the triradiate configuration, but by midlength it is elliptical, with the long-axis of this ellipse oriented anteromedially. There is a prominent ridge for a ligamentous attachment to the radius, located on the anteromedial surface of the shaft at ∼100 mm above the distal end. The distal end of the ulna is expanded both anteroposteriorly and transversely relative to the shaft. In distal view (Fig. 9F), the margins of this surface are strongly convex laterally and posteriorly, but slightly concave anteromedially, resulting in a comma-shaped distal profile, as is typical for most non-titanosaurian sauropods (Upchurch et al., 2015). The distal articular surface is mildly convex anteroposteriorly and transversely. Radius —The radius is complete and is 63% of the length of the humerus. This is broadly similar to the condition in many other sauropods, which tend to have values ≥65% (Yates and Kitching, 2003; Mannion et al., 2013). For example, this value is ∼66% in Mamenchisaurus youngi (Ouyang and Ye, 2002) and ranges from 65–76% in specimens referred to Omeisaurus (He et al., 1988; Ren et al., 2018). By contrast, this ratio is reduced in titanosauriforms (Mannion et al., 2013) and many CMTs (Ren et al., 2018), with particularly low values of 58% and 50% in Huangshanlong and Anhuilong, respectively (Huang et al., 2014; Ren et al., 2018). The radius of Rhomaleopakhus is a robust element with expanded proximal and distal ends relative to the shaft (Dong, 1997) (Fig. 9G–J). The maximum widths of the proximal and distal ends are subequal, the proximal end transverse width to radius proximodistal length ratio is 0.31, and the distal end is ∼1.3 times as wide as the shaft at its midlength (Table 3). The proximal end surface is flat, with a central shallow concavity and a slightly convex portion around both its anterior and lateral margins. In proximal view (Fig. 9K), the radius has a ‘D’-shaped profile, comprising a straight posterior margin (that becomes mildly concave towards the medial corner), and strongly convex anterior and lateral margins. This proximal profile appears to be plesiomorphic for sauropods, contrasting with the derived subtriangular profile with pointed medial process seen in many titanosauriforms (Upchurch et al., 2015:fig. 9), and the anteroposteriorly narrow morphology that characterizes some turiasaurians (Mateus et al., 2014). Approximately 100 mm below the mildly concave posteromedial margin of the proximal end, on the posterior surface, there is a prominent 100 mm long ridge that projects posteromedially. Titanosaurs, such as Epachthosaurus, Rapetosaurus, and Saltasaurus, usually have a ridge on the posterior surface of the radius that extends along much of the element’ s length (Curry Rogers, 2005, 2009; Mannion et al., 2013), and Ren et al. (2018: fig. 4C) described a ‘lateral ridge’ (‘lr’) on the proximal part of the Anhuilong radius. However, the morphology and position of the short, prominent and posteromedially directed ridge seen in Rhomaleopakhus appears to be unique and is provisionally regarded as an autapomorphy. The radius is twisted along its length such that the long-axis of the proximal articular surface is set at about 90° to that of the distal end. As a result, the posterior surface of the shaft turns to face laterally as it approaches the distal end. Such torsion of the radius is rare among sauropods (Mannion et al., 2013), although it has also been observed in the somphospondylan Huabeisaurus (D’ Emic et al., 2013) and a few titanosaurs (e.g., Epachthosaurus – Poropat et al., 2016; Malawisaurus – Gomani, 2005; Rapetosaurus – Curry Rogers, 2009). At midlength, the cross-section through the shaft is elliptical in Rhomaleopakhus, with the radius being wider transversely than anteroposteriorly. There is a prominent vertical ridge on the posterolateral surface, located at approximately onefifth of element length from the distal end. This matches the prominent ridge on the anteromedial surface of the shaft of the ulna, close to the distal end, suggesting that these two ridges marked the location of a strong interosseous ligament (Upchurch et al., 2004a). In medial view (Fig. 9J), the distal end surface is set at an oblique angle to the long axis of the shaft such that it slopes anteroproximally (N.B., this would be proximolateral beveling of the distal end, in anterior view, if the radius was not twisted through 90° along its length). As a result, the distal end surface is set at ∼15° to the plane perpendicular to the proximodistal longaxis of the radius. Non-neosauropod eusauropods (such as Shunosaurus and Mamenchisaurus), and at least some rebbachisaurids, display no such beveling of the distal radius, whereas turiasaurians and several titanosaurs have angles of ∼25° or higher (Wilson, 2002; Mannion et al., 2019a). The degree of distal radial beveling in Rhomaleopakhus is similar to that seen in several nonneosauropod eusauropods, including Omeisaurus tianfuensis, Chuanjiesaurus, and Jobaria, as well as some neosauropods such as Diplodocus and Giraff

(?) MAMENCHISAURIDAE Young and Chao, 1972 GEN. ET SP. INDET. (Fig. 5) Material —Four teeth, IVPP V11121-2 (Fig. 5; Table 2). Locality and Horizon —Lower part of the Kalazha Formation (Upper Jurassic: upper Kimmeridgian–Tithonian) of Qiketai, Shanshan County, Turpan Basin, Xinjiang Uyghur Autonomous Region, China (Dong, 1997; Deng et al., 2015; Fang et al., 2016) (Fig. 1). Exact locality unknown (see Introduction, above). Description The four teeth are not labelled with unique specimen numbers and so are referred to as specimens 1–4 herein. Two of the teeth (identified as premaxillary teeth by Dong [1997]) are embedded in a fragment of very worn, indeterminate bone, and the other two teeth are loose and were interpreted by Dong (1997) as maxillary teeth. It is not possible to determine which elements yielded these teeth, but it seems likely that the three smaller, low-crowned teeth were from the posterior part of the tooth row, whereas the single larger, higher-crowned tooth would have been more anteriorly positioned. No useful morphology can be gleaned from the bone fragment, although it is unlikely to have been the premaxilla on the basis of tooth size. Two of the teeth are quite similar in morphology: these are the larger tooth in the bone fragment (tooth 2) and the smaller of the two loose teeth (tooth 3). These specimens resemble the low broad teeth of Jobaria (Sereno et al., 1999; Chure et al., 2010), Turiasaurus (Royo-Torres and Upchurch, 2012), and Zby (Mateus et al., 2014), whereas the other two teeth (teeth 1 and 4) are more slender (Table 2). Tooth 1 (smaller tooth in bone fragment: Fig. 5A–D) has been badly damaged and is missing most of the original surface, so its true shape cannot be determined. No informative character states can be observed. Tooth 2 (larger tooth in bone fragment: Fig. 5A–D) lacks denticles and wear facets. There is no sign of wrinkled enamel texture on either the labial or lingual surface, suggesting some general surficial wear either during life or after the tooth was shed. The apex of the tooth is pointed and is deflected distally: this suggests that it is either an upper right or lower left tooth. The labial surface is gently convex mesiodistally and apicobasally, with the part of the crown mesial to the apex more strongly convex than that section distal to it, creating an asymmetrical ‘D’-shaped cross-section. Mesial and distal grooves appear to be absent on the labial surface. The crown is mesiodistally expanded with respect to the tooth base, but the crown–root junction cannot be precisely determined because most of the tooth below this expansion is obscured by bone. The mesial margin is smoothly convex from apex to base, whereas the distal margin is first concave, then convex, producing a mildly sinuous profile in labial and lingual views (Fig. 5A, B). Most of the lingual surface of the crown is concave mesiodistally and apicobasally: the base of this concavity lies at a point approximately level with the maximum mesiodistal width of the tooth. Basal to this point, the lingual crown surface is swollen and mesiodistally convex. The crown margins are both slightly swollen, with the distal margin possessing a small, low, and elliptical boss that is level with the point of greatest mesiodistal expansion. This boss is in the same position as similar structures in Euhelopus (Wilson and Upchurch, 2009). There is no true lingual ridge, but a slight eminence extends from the tooth apex for a very short distance basally, before merging into the surface of the lingual concavity. Tooth 3 (the smaller of the isolated teeth: Fig. 5E–H) has the same morphology, in most respects, as tooth 2. The enamel surface is better preserved and has a wrinkled texture. The lingual ‘boss’ is less distinct and is a simple swelling of the distal margin, situated at a point level with the greatest mesiodistal expansion. As in tooth 2, there are no true mesial or distal grooves on the labial surface, but a distinct change in slope distal to the apical swelling does create the impression of a groove in the distal position (the cross-sectional asymmetry mentioned above). The root–crown junction cannot be observed because of breakage. Neither ‘shoulder-like’ nor apical macrowear are present. Tooth 4 (largest tooth: Fig. 5I–L) is badly abraded and the enamel surface texture cannot be observed. There is also some damage to the crown margins. No wear facets or serrations can be identified. This tooth is much longer than the others, with a maximum length of 40 mm (Table 2): however, it is not possible to judge the position of the root–crown boundary because of the absence of enamel. It appears to be much slenderer than the other teeth, with a maximum mesiodistal width of 11 mm, and thus a Slenderness Index (SI: sensu Upchurch, 1998; Chure et al., 2010) that is potentially>3, but the true value cannot be determined because of the lack of accurate information on the location of the crown–root junction. The crown has a ‘D’- shaped cross-section but has only a very shallow lingual concavity. There is no sign of a lingual ridge, lingual bosses, or labial grooves, but these absences could be the result of poor preservation. Comparisons and Identification The teeth are too incomplete to be usefully incorporated into a formal phylogenetic analysis. Instead, we assess their affinities by evaluating the potential significance of the putative synapomorphies and symplesiomorphies that they display. Possession of crowns that are basally constricted mesiodistally is a derived state characteristic of Sauropodomorpha (Yates, 2007; McPhee et al., 2014; Peyre de Fabrègues et al., 2015; Apaldetti et al., 2018; Chapelle and Choiniere, 2018), although this is lost in the elongated ‘pencil-like’ teeth of most diplodocoids and derived somphospondylans (Upchurch, 1998; Upchurch et al., 2004a). The labial profile of the IVPP V11121-2 teeth, with convex mesial and sigmoid distal margins, is characteristic of most spatulate sauropod teeth (Carballido and Pol, 2010). Only tooth 3 confirms the presence of wrinkled tooth enamel, but its absence on the other three crowns appears to be the result of poor preservation. Such enamel texturing is absent in the earliest branching sauropodomorphs (e.g., Efraasia), occurs in small patches of fine wrinkles in more derived non-sauropods (such as massospondylids, Melanorosaurus), and occurs over the entire crown as coarse anastamosing ridges and grooves in ‘true’ sauropods (e.g., Pulanesaura, Gongxianosaurus, Tazoudasaurus, and eusauropods) (Yates, 2007; Carballido and Pol, 2010; McPhee et al., 2015; Apaldetti et al., 2018; Chapelle and Choiniere, 2018). The presence of a lingual concavity on tooth crowns is generally regarded as a synapomorphy pertaining to a node between Sauropoda and Eusauropoda (Upchurch, 1995; Yates, 2007; Peyre de Fabrègues et al., 2015; Apaldetti et al., 2018; Chapelle and Choiniere, 2018). For example, this feature occurs in the teeth of all eusauropods (except diplodocoids and those somphospondylans with ‘pencil-like’ teeth), as well as some non-eusauropod sauropods such as Gongxianosaurus and Tazoudasaurus, but is rudimentary in Chinshakiangosaurus and Pulanesaura (Barrett et al., 2002; Upchurch et al., 2007a; Mannion et al., 2013; McPhee et al. 2015). Labial grooves are a synapomorphy of Eusauropoda, being present in Shunosaurus, Barapasaurus, Omeisaurus, Patagosaurus, and many other forms, including most neosauropods (except some diplodocoids and titanosaurs with cylindrical teeth). By contrast, with the exception of Pulanesaura (McPhee et al., 2015), such grooves are absent in non-eusauropod sauropods (e.g., Tazoudasaurus) and non-sauropod sauropodomorphs such as Plateosaurus and Anchisaurus (Upchurch, 1995; Yates, 2007; Peyre de Fabrègues et al., 2015; Apaldetti et al., 2018; Chapelle and Choiniere, 2018). There is some evidence that the distal labial groove evolved before the mesial one, since the teeth of Chinshakiangosaurus and Amygdalodon either possess only the latter, or the distal groove is more marked than the mesial one (Upchurch et al., 2007a; Carballido and Pol, 2010). This character state distribution could be taken as evidence that the IVPP V11121-2 teeth did not belong to a eusauropod: however, Mamenchisaurus sinocanadorum (IVPP V10603) also lacks both mesial and distal grooves (PMB and PU pers. observ., 2010), and this feature might sometimes reflect individual variation and/or position in the jaws (Holwerda et al., 2015). Non-sauropod sauropodomorphs typically have SI values in the range of 1.5–2.0, with some taxa (such as Thecodontosaurus and Anchisaurus) having SIs around 2.2 (Chure et al., 2010). Most sauropods, except diplodocoids and titanosaurs, have SI values between 2.0–2.5, although a few forms (such as Amygdalodon, Patagosaurus, Jobaria, and turiasaurians) have unusually low SIs in the range of 1.3–1.6 (Barrett et al., 2002; Chure et al., 2010). Thus, although caution is warranted given their incomplete preservation, the SI of 1.5 (tooth 2) to ∼3.0 (tooth 4) estimated for the IVPP V11121-2 teeth (Table 2) is consistent with a phylogenetic position anywhere within Sauropodomorpha apart from Diplodocoidea and Somphospondyli. Dong (1997) stated that the teeth of Hudiesaurus are serrated, but we found no such structures on any of the four crowns. Virtually all non-sauropod sauropodomorphs, and many non-eusauropod sauropods, have relatively large serrations on both the mesial and distal margins of their tooth crowns (Upchurch, 1998; Wilson and Sereno, 1998; Upchurch et al., 2004a, 2007a, b; Yates, 2007; Apaldetti et al., 2018; Chapelle and Choiniere, 2018). Well-developed serrations are also present on both mesial and distal crown margins in some non-neosauropod eusauropods, such as the CMT Klamelisaurus (Moore et al., 2020). In a few early-branching eusauropods (e.g., Barapasaurus, Omeisaurus tianfuensis, a referred specimen of Mamenchisaurus hochuanensis), serrations are retained on the mesial margins and lost on the distal margins (Ye et al., 2001; Yates, 2007; Moore et al., 2020). Variation can even occur along the length of the jaw of a single individual: for example, the anterior dentary teeth of Mamenchisaurus sinocanadorum lack serrations, whereas they are present as relatively small projections on just the mesial/apical margins of the posterior teeth (Moore et al., 2020). Thus, the absence of serrations in the IVPP V11121-2 teeth is more typical of a neosauropod (or close relative such as a turiasaurian) (Upchurch et al., 2004a; Royo-Torres and Upchurch, 2012), though this is also seen in Amygdalodon, Shunosaurus, and teeth referred to Kotasaurus (Carballido and Pol, 2010). Given this variation, however, the absence/presence of serrations probably provides only weak evidence of phylogenetic affinities (Upchurch, 1998; Barrett and Upchurch, 2005; Upchurch et al., 2007b; Carballido and Pol, 2010). An apicobasally oriented ridge within the lingual concavity is present in nearly all known spatulate sauropod teeth (Barrett et al., 2002; Mannion et al., 2013), and might be homologous with the mesiodistally convex lingual surface of the crowns of many diplodocoids and somphospondylans (Upchurch et al., 2004 a, 2011). The absence of this ridge in the IVPP V11121-2 teeth is shared with just three other taxa with spatulate teeth: Oplosaurus armatus from the Early Cretaceous of England (Upchurch et al., 2004 a, 2011), Jobaria from the Middle Jurassic of Niger (Mannion et al., 2017), and Klamelisaurus gobiensis from the Middle Jurassic of China (Zhao, 1993; Moore et al., 2020). However, in most other respects the teeth of the former two taxa are very different from those of IVPP V11121-2 (Upchurch et al., 2011; Mannion et al., 2017). In particular, the lingual surfaces of the IVPP V11121-2 crowns are nearly flat mesiodistally, whereas this surface is concave in Oplosaurus and Jobaria. Perhaps the most informative character state in the IVPP V11121-2 teeth is the presence of a boss on the distal margin of the crown. These resemble those seen in Euhelopus (Wilson and Sereno, 1998; Wilson and Upchurch, 2009). Over the past decade, nearly all studies have recovered Euhelopus within Macronaria, usually as an early-branching somphospondylan (e.g., Wilson and Sereno, 1998; Wilson, 2002; Wilson and Upchurch, 2009; D’ Emic, 2012; Mannion et al., 2013; Gorscak and O’ Connor, 2019; Carballido et al., 2020). Consequently, the presence of these bosses in IVPP V11121-2 specimens 2 and 3 would previously have been interpreted as indicative of macronarian affinities and potential membership of an Early Cretaceous somphospondylan euhelopodid radiation (sensu D’ Emic, 2012; see also Canudo et al. [2002] and Barrett and Wang [2007]). However, Moore et al. (2020) found that most of their phylogenetic analyses placed Euhelopus within CMTs, well outside Neosauropoda. Moreover, the distolingual boss is also present on the dentary teeth of Mamenchisaurus sinocanadorum (Suteethorn et al., 2013; Moore et al., 2020), although it also characterizes the teeth of the Early Cretaceous Chinese taxon Yongjinglong, which has been recovered as a somphospondylan in previous studies (Li et al., 2014; Mannion et al., 2019b). In summary, the character states present in the teeth of IVPP V11121-2 support their identification as those of a non-neosauropod eusauropod (though somphospondylan affinities cannot be ruled out) and are consistent with Dong’ s (1997) suggestion that they belonged to a mamenchisaurid. Indeed, apart from the absence of the lingual apicobasal ridge in IVPP V11121-2, these teeth most closely resemble those of Mamenchisaurus sinocanadorum. IVPP V11121-2 lacks any true autapomorphies but does possess a unique combination of features: it is the only taxon currently known that lacks both the apicobasal lingual ridge and clear labial grooves, while also possessing a distolingual boss. Given the inadvisability of naming new taxa on such scant material (e.g., the danger of historical obsolescence described by Wilson and Upchurch [2003]), we refrain from erecting a new genus or species at this time, pending further discoveries., Published as part of Upchurch, Paul, Mannion, Philip D., Xu, Xing & Barrett, Paul M., 2021, Re-assessment of the Late Jurassic eusauropod dinosaur Hudiesaurus sinojapanorum Dong, 1997, from the Turpan Basin, China, and the evolution of hyper-robust antebrachia in sauropods, pp. 1-31 in Journal of Vertebrate Paleontology (e 1994414) (e 1994414) 41 (4) on pages 9-12, DOI: 10.1080/02724634.2021.1994414, http://zenodo.org/record/5839134, {"references":["Young, C. C., and X. - J. Chao. 1972. Mamenchisaurus hochuanensis sp. nov. Institute of Vertebrate Paleontology and Paleoanthropology Monographs (Series A) 8: 1 - 30.","Dong, Z. 1997. A gigantic sauropod (Hudiesaurus sinojapanorum, gen. et sp. nov.) from the Turpan Basin, China; pp. 102 - 110 in Z. Dong (ed.), Sino-Japanese Silk Road Dinosaur Expedition. China Ocean Press, Beijing.","Deng, S., S. Wang, Z. Yang, Y. Lu, X. Li, Q. Hu, C. An, D. Xi, and X. Wan. 2015. Comprehensive study of the Middle-Upper Jurassic strata in the Junggar Basin, Xinjiang. Acta Geoscientia Sinica 36: 559 - 574.","Fang, Y., C. Wu, Y. Wang, L. Wang, Z. Guo, and H. Hu. 2016. Stratigraphic and sedimentary characteristics of the Upper Jurassic-Lower Cretaceous strata in the Junggar Basin, Central Asia: tectonic and climate implications. Journal of Asian Earth Sciences 129: 294 - 308.","Upchurch, P. 1998. The phylogenetic relationships of sauropod dinosaurs. Zoological Journal of the Linnean Society 124: 43 - 103.","Sereno, P. C., A. L. Beck, D. B. Dutheil, H. C. E. Larsson, G. H. Lyon, B. Moussa, R. W. Sadleir, C. A. Sidor, D. J. Varricchio, G. P. Wilson, and J. A. Wilson. 1999. Cretaceous sauropods from the Sahara and the uneven rate of skeletal evolution among dinosaurs. Science 286: 1342 - 1347.","Chure, D. J., B. B. Britt, J. A. Whitlock, and J. A. Wilson. 2010. First complete sauropod dinosaur skull from the Cretaceous of the Americas and the evolution of sauropod dentition. Naturwissenschaften 97: 379 - 391.","Royo-Torres, R., and P. Upchurch. 2012. The cranial anatomy of the sauropod Turiasaurus riodevensis and implications for its phylogenetic relationships. Journal of Systematic Palaeontology 10: 553 - 583.","Mateus, O., P. D. Mannion, and P. Upchurch. 2014. Zby atlanticus, a new turiasaurian sauropod (Dinosauria, Eusauropoda) from the Late Jurassic of Portugal. Journal of Vertebrate Paleontology 34: 618 - 634.","Wilson, J. A., and P. Upchurch. 2009. Redescription and reassessment of the phylogenetic affinities of Euhelopus zdanskyi (Dinosauria: Sauropoda) from the Early Cretaceous of China. Journal of Systematic Palaeontology 7: 199 - 239.","Yates, A. M. 2007. The first complete skull of the Triassic dinosaur Melanorosaurus Haughton (Sauropodomorpha: Anchisauria). Special Papers in Palaeontology 77: 9 - 55.","McPhee, B. W., A. M. Yates, J. N. Choiniere, and F. Abdala, 2014. The complete anatomy and phylogenetic relationships of Antetonitrus ingenipes (Sauropodiformes, Dinosauria): implications for the origins of Sauropoda. Zoological Journal of the Linnean Society 171: 151 - 205.","Peyre de Fabregues, C., R. Allain, and V. Barriel. 2015. Root causes of phylogenetic incongruence observed within basal sauropodomorph interrelationships. Zoological Journal of the Linnean Society 175: 569 - 586.","Apaldetti, C., R. N. Martinez, I. A. Cerda, D. Pol, and O. Alcober. 2018. An early trend towards gigantism in Triassic sauropodomorph dinosaurs. Nature Ecology and Evolution 2: 1227 - 1232.","Chapelle, K. E. J., and J. N. Choiniere. 2018. A revised cranial description of Massospondylus carinatus Owen (Dinosauria: Sauropodomorpha) based on computed tomographic scans and a review of cranial characters for basal Sauropodomorpha. PeerJ 6: e 4224. doi. org / 10.7717 / peerj. 4224","Upchurch, P., P. M. Barrett, and P. Dodson. 2004 a. Sauropoda; pp. 259 - 324 in D. B. Weishampel, P. Dodson, and H. Osmolska, (eds.), The Dinosauria (Second Edition). University of California Press, Berkeley.","Carballido, J. L., and D. Pol. 2010. The dentition of Amygdalodon patagonicus (Dinosauria: Sauropoda) and the dental evolution in basal sauropods. Comptes Rendus Palevol 9: 83 - 93.","McPhee, B. W., M. F. Bonnan, A. M. Yates, J. Neveling, and J. N. Choiniere. 2015. A new basal sauropod from the pre-Toarcian Jurassic of South Africa: evidence of niche partitioning at the sauropodomorph - sauropod boundary? Scientific Reports 5: 13224. doi. org / 10.1038 / srep 13224","Upchurch, P. 1995. The evolutionary history of sauropod dinosaurs. Philosophical Transactions of the Royal Society of London, Series B 349: 365 - 390.","Barrett, P. M., Y. Hasegawa, M. Manabe, S. Isaji, and H. Matsouka. 2002. Sauropod dinosaurs from the Lower Cretaceous of Eastern Asia: taxonomic and biogeographic implications. Palaeontology 45: 1197 - 1217.","Upchurch, P., P. M. Barrett, and P. M. Galton. 2007 a. A phylogenetic analysis of basal sauropodomorph relationships: implications for the origin of sauropod dinosaurs. Special Papers in Palaeontology 77: 57 - 90.","Mannion, P. D., P. Upchurch, R. N. Barnes, and O. Mateus. 2013. Osteology of the Late Jurassic Portuguese sauropod dinosaur Lusotitan atalaiensis (Macronaria) and the evolutionary history of basal titanosauriforms. Zoological Journal of the Linnean Society 168: 98 - 206.","Holwerda, F. M., D. Pol, and O. W. M. Rauhut. 2015. Using dental enamel wrinkling to define sauropod tooth morphotypes from the Canadon Asfalto Formation, Patagonia, Argentina. PLoS ONE 10: e 0118100. doi. org / 10.1371 / journal. pone. 0118100","Wilson, J. A., and P. C. Sereno. 1998. Early evolution and higher-level phylogeny of sauropod dinosaurs. Memoir of the Society of Vertebrate Paleontology 5: 1 - 68.","Moore, A. J., P. Upchurch, P. M. Barrett, J. M. Clark, and X. Xu. 2020. Osteology of Klamelisaurus gobiensis (Dinosauria: Eusauropoda) and the evolutionary history of Middle - Late Jurassic Chinese sauropods. Journal of Systematic Palaeontology 18: 1299 - 1393.","Ye, Y., H. Ouyang, and Q. - M. Fu. 2001. New material of Mamenchisaurus hochuanensis from Zigong, Sichuan. Vertebrata PalAsiatica, 39: 266 - 271.","Barrett, P. M., and P. Upchurch. 2005. Sauropodomorph diversity through time: paleoecological and macroevolutionary implications: pp. 125 - 151 in K. A. Curry Rogers and J. A. Wilson (eds.), The Sauropods: Evolution and Paleobiology. University of California Press, Berkeley.","Upchurch, P., P. M. Barrett, X. - J. Zhao, and X. Xu. 2007 b. A re-evaluation of Chinshakiangosaurus chunghoensis Ye vide Dong 1992 (Dinosauria, Sauropodomorpha): implications for cranial evolution in basal sauropod dinosaurs. Geological Magazine 144: 247 - 262.","Whitlock, J. A. 2011. A phylogenetic analysis of Diplodocoidea (Saurischia: Sauropoda). Zoological Journal of the Linnean Society 161: 872 - 915.","Mannion, P. D., R. Allain, and O. Moine. 2017. The earliest known titanosauriform sauropod dinosaur and the evolution of Brachiosauridae. PeerJ 5: e 3217. doi. org / 10.7717 / peerj. 3217","Zhao, X. - J. 1993. [A new mid-Jurassic sauropod (Klamelisaurus gobiensis gen. et sp. nov.) from Xinjiang, China]. Vertebrata PalAsiatica 31: 132 - 138. [In Chinese with English summary]","Upchurch, P., P. D. Mannion, and P. M. Barrett. 2011. Sauropod dinosaurs; pp. 476 - 525 In D. J. Batten (ed.), English Wealden Fossils. Palaeontology Association Field Guides to Fossils 14, Palaeontological Association, London.","Wilson, J. A. 2002. Sauropod dinosaur phylogeny: critique and cladistic analysis. Zoological Journal of the Linnean Society 136: 217 - 276.","D' Emic, M. D. 2012. The early evolution of titanosauriform sauropod dinosaurs. Zoological Journal of the Linnean Society 166: 624 - 671.","Gorscak, E. and P. M. O' Connor. 2019. A new African Titanosaurian Sauropod Dinosaur from the middle Cretaceous Galula Formation (Mtuka Member), Rukwa Rift Basin, Southwestern Tanzania. PLoS ONE 14: e 0211412.","Carballido, J. L., M. Scheil, N. Knotschke, and P. M. Sander. 2020. The appendicular skeleton of the dwarf macronarian sauropod Europasaurus holgeri from the Late Jurassic of Germany and a re-evaluation of its systematic affinities. Journal of Systematic Palaeontology 18: 739 - 781.","Canudo, J. I., J. I. Ruiz-Omenaca, J. L. Barco, and R. Royo-Torres. 2002. Sauropodos asiaticos en el Barremiense inferior (Cretacico inferior) de Espana. Ameghiniana 39: 443 - 452.","Barrett, P. M., and X. - L. Wang. 2007. Basal titanosauriform (Dinosauria, Sauropoda) teeth from the Lower Cretaceous Yixian Formation of Liaoning Province, China. Palaeoworld 16: 265 - 271.","Suteethorn, S., J. Le Loeuff, E. Buffetaut, V. Suteethorn, and K. Wongko. 2013. First evidence of a mamenchisaurid dinosaur from the Upper Jurassic-Lower Cretaceous Phu Kradung Formation of Thailand. Acta Palaeontologica Polonica 58: 459 - 469.","Li, L. - G., D. - Q. Li, H. - L. You, and P. Dodson. 2014. A new titanosaurian sauropod from the Hekou Group (Lower Cretaceous) of the Lanzhou-Minhe Basin, Gansu Province, China. PLoS ONE 9: e 85979. doi. org / 10.1371 / journal. pone. 0085979","Mannion, P. D., P. Upchurch, X. Jin, and W. Zheng. 2019 b. New information on the Cretaceous sauropod dinosaurs of Zhejiang Province, China: impact on Laurasian titanosauriform phylogeny and biogeography. Royal Society Open Science 6: 191057. doi. org / 10.1098 / rsos. 191057","Wilson, J. A., and P. Upchurch, 2003. A revision of Titanosaurus Lydekker (Dinosauria - Sauropoda), the first dinosaur genus with a \" Gondwanan \" distribution. Journal of Systematic Palaeontology 1: 125 - 160."]}

Upchurch, Paul, Mannion, Philip D., Xu, Xing, Barrett, Paul M. (2021): Re-assessment of the Late Jurassic eusauropod dinosaur Hudiesaurus sinojapanorum Dong, 1997, from the Turpan Basin, China, and the evolution of hyper-robust antebrachia in sauropods. Journal of Vertebrate Paleontology (e1994414) 41 (4): 1-31, DOI: 10.1080/02724634.2021.1994414, URL: http://dx.doi.org/10.1080/02724634.2021.1994414

Poropat, Stephen F, Kundrát, Martin, Mannion, Philip D, Upchurch, Paul, Tischler, Travis R, Elliott, David A (2021): Second specimen of the Late Cretaceous Australian sauropod dinosaur Diamantinasaurus matildae provides new anatomical information on the skull and neck of early titanosaurs. Zoological Journal of the Linnean Society 192 (2): 610, DOI: 10.1093/zoolinnean/zlaa173, URL: https://academic.oup.com/zoolinnean/article/192/2/610/6104802

ARAGOSAURUS SANZ ET AL., 1987 Type species Aragosaurus ischiaticus Sanz et al., 1987. Generic diagnosis – see ‘Revised species diagnosis’., Published as part of Royo-Torres, Rafael, Upchurch, Paul, Mannion, Philip D., Mas, Ramón, Cobos, Alberto, Gascó, Francisco, Alcalá, Luis & Sanz, José Luis, 2014, The anatomy, phylogenetic relationships, and stratigraphic position of the Tithonian-Berriasian Spanish sauropod dinosaur Aragosaurus ischiaticus, pp. 623-655 in Zoological Journal of the Linnean Society 171 (3) on page 630, DOI: 10.1111/zoj.12144, http://zenodo.org/record/5310092, {"references":["Sanz JL, Buscalioni AD, Casanovas ML, Santafe JV. 1987. Dinosaurios del Cretacico Inferior de Galve (Teruel, Espana). Estudios Geologicos Volumen Extraordinario, Galve- Tremp: 45 - 64."]}

Royo-Torres, Rafael, Upchurch, Paul, Mannion, Philip D., Mas, Ramón, Cobos, Alberto, Gascó, Francisco, Alcalá, Luis, Sanz, José Luis (2014): The anatomy, phylogenetic relationships, and stratigraphic position of the Tithonian-Berriasian Spanish sauropod dinosaur Aragosaurus ischiaticus. Zoological Journal of the Linnean Society 171 (3): 623-655, DOI: 10.1111/zoj.12144, URL: http://dx.doi.org/10.1111/zoj.12144