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• W2894494577 abstract "•A new species of Early Jurassic South African sauropodomorph weighed 12 metric tons•Proportional limb robusticity is useful for inferring posture in extinct tetrapods•Many early-branching sauropodomorphs were quadrupeds with flexed limbs•Quadrupedality evolves at low body mass but facilitates larger body masses Sauropod dinosaurs were dominant, bulk-browsing herbivores for 130 million years of the Mesozoic, attaining gigantic body masses in excess of 60 metric tons [1Benson R.B.J. Campione N.E. Carrano M.T. Mannion P.D. Sullivan C. Upchurch P. Evans D.C. Rates of dinosaur body mass evolution indicate 170 million years of sustained ecological innovation on the avian stem lineage.PLoS Biol. 2014; 12: e1001853Crossref PubMed Scopus (0) Google Scholar, 2Benson R.B. Hunt G. Carrano M.T. Campione N. Cope’s rule and the adaptive landscape of dinosaur body size evolution.Palaeontology. 2017; 61: 13-48Crossref Scopus (97) Google Scholar]. A columnar-limbed, quadrupedal posture enabled these giant body sizes [3Sander P.M. Christian A. Clauss M. Fechner R. Gee C.T. Griebeler E.-M. Gunga H.-C. Hummel J. Mallison H. Perry S.F. et al.Biology of the sauropod dinosaurs: the evolution of gigantism.Biol. Rev. Camb. Philos. Soc. 2011; 86: 117-155Crossref PubMed Scopus (244) Google Scholar], but the nature of the transition from bipedal sauropodomorph ancestors to derived quadrupeds remains contentious [4Yates A.M. A definite prosauropod dinosaur from the Lower Elliot Formation (Norian: Upper Triassic) of South Africa.Palaeontologia Africana. 2003; 39: 63-68Google Scholar, 5Otero A. Allen V. Pol D. Hutchinson J.R. Forelimb muscle and joint actions in Archosauria: insights from Crocodylus johnstoni (Pseudosuchia) and Mussaurus patagonicus (Sauropodomorpha).PeerJ. 2017; 5: e3976Crossref PubMed Scopus (35) Google Scholar, 6Carrano M.T. Rogers C. Wilson J. The evolution of sauropod locomotion.in: Curry Rogers K.A. Wilson J.A. The Sauropods: Evolution and Paleobiology. University of California Press, 2005: 229-249Google Scholar]. We describe a gigantic, new sauropodomorph from the earliest Jurassic of South Africa weighing 12 metric tons and representing a phylogenetically independent origin of sauropod-like body size in a non-sauropod. Osteohistological evidence shows that this specimen was an adult of maximum size and approximately 14 years old at death. Ledumahadi mafube gen. et sp. nov. shows that gigantic body sizes were possible in early sauropodomorphs, which were habitual quadrupeds but lacked the derived, columnar limb postures of sauropods. We use data from this new taxon and a discriminant analysis of tetrapod limb measurements to study postural evolution in sauropodomorphs. Our results show that quadrupedality appeared by the mid-Late Triassic (Norian), well outside of Sauropoda. Secondary reversion to bipedality occurred in some lineages phylogenetically close to Sauropoda, indicating early experimentation in locomotory styles. Morphofunctional observations support the hypothesis that partially flexed (rather than columnar) limbs characterized Ledumahadi and other early-branching quadrupedal sauropodomorphs. Patterns of locomotory and body-size evolution show that quadrupedality allowed Triassic sauropodomorphs to achieve body sizes of at least 3.8 metric tons. Ledumahadi’s Early Jurassic age shows that maximum body mass in sauropodomorph dinosaurs was either unaffected or rapidly rebounded after the end-Triassic extinction event. Sauropod dinosaurs were dominant, bulk-browsing herbivores for 130 million years of the Mesozoic, attaining gigantic body masses in excess of 60 metric tons [1Benson R.B.J. Campione N.E. Carrano M.T. Mannion P.D. Sullivan C. Upchurch P. Evans D.C. Rates of dinosaur body mass evolution indicate 170 million years of sustained ecological innovation on the avian stem lineage.PLoS Biol. 2014; 12: e1001853Crossref PubMed Scopus (0) Google Scholar, 2Benson R.B. Hunt G. Carrano M.T. Campione N. Cope’s rule and the adaptive landscape of dinosaur body size evolution.Palaeontology. 2017; 61: 13-48Crossref Scopus (97) Google Scholar]. A columnar-limbed, quadrupedal posture enabled these giant body sizes [3Sander P.M. Christian A. Clauss M. Fechner R. Gee C.T. Griebeler E.-M. Gunga H.-C. Hummel J. Mallison H. Perry S.F. et al.Biology of the sauropod dinosaurs: the evolution of gigantism.Biol. Rev. Camb. Philos. Soc. 2011; 86: 117-155Crossref PubMed Scopus (244) Google Scholar], but the nature of the transition from bipedal sauropodomorph ancestors to derived quadrupeds remains contentious [4Yates A.M. A definite prosauropod dinosaur from the Lower Elliot Formation (Norian: Upper Triassic) of South Africa.Palaeontologia Africana. 2003; 39: 63-68Google Scholar, 5Otero A. Allen V. Pol D. Hutchinson J.R. Forelimb muscle and joint actions in Archosauria: insights from Crocodylus johnstoni (Pseudosuchia) and Mussaurus patagonicus (Sauropodomorpha).PeerJ. 2017; 5: e3976Crossref PubMed Scopus (35) Google Scholar, 6Carrano M.T. Rogers C. Wilson J. The evolution of sauropod locomotion.in: Curry Rogers K.A. Wilson J.A. The Sauropods: Evolution and Paleobiology. University of California Press, 2005: 229-249Google Scholar]. We describe a gigantic, new sauropodomorph from the earliest Jurassic of South Africa weighing 12 metric tons and representing a phylogenetically independent origin of sauropod-like body size in a non-sauropod. Osteohistological evidence shows that this specimen was an adult of maximum size and approximately 14 years old at death. Ledumahadi mafube gen. et sp. nov. shows that gigantic body sizes were possible in early sauropodomorphs, which were habitual quadrupeds but lacked the derived, columnar limb postures of sauropods. We use data from this new taxon and a discriminant analysis of tetrapod limb measurements to study postural evolution in sauropodomorphs. Our results show that quadrupedality appeared by the mid-Late Triassic (Norian), well outside of Sauropoda. Secondary reversion to bipedality occurred in some lineages phylogenetically close to Sauropoda, indicating early experimentation in locomotory styles. Morphofunctional observations support the hypothesis that partially flexed (rather than columnar) limbs characterized Ledumahadi and other early-branching quadrupedal sauropodomorphs. Patterns of locomotory and body-size evolution show that quadrupedality allowed Triassic sauropodomorphs to achieve body sizes of at least 3.8 metric tons. Ledumahadi’s Early Jurassic age shows that maximum body mass in sauropodomorph dinosaurs was either unaffected or rapidly rebounded after the end-Triassic extinction event. Saurischia Seeley 1888. Sauropodomorpha von Huene 1932. Sauropodiformes Sereno 2007. Ledumahadi mafube gen. et sp. nov. Southern Sotho. “Ledumahadi,” a giant thunderclap—in recognition of the tremendous size of this taxon; and “mafube,” dawn—in the sense of the stratigraphically early position of this taxon. BP/1/7120, a disarticulated assemblage of associated postcranial material comprising a partial cervical neural arch; several dorsal vertebrae; partial, conjoined primordial sacral vertebrae; anterior and middle caudal vertebrae; an anterior chevron; a right ulna; a first metacarpal; a left metacarpal, probably III or IV; distal third of the right femur; and a pedal ungual (Figures 1 and 4). Beginsel farm, 25 km southeast of the town of Clarens, Free State Province, on the border of South Africa and Lesotho (Figures 1 and S1). The in situ material was found within mudrocks diagnostic of the upper Elliot Formation, one of the lowermost Jurassic continental successions (Hettangian-Sinemurian, ∼200–195 mya; Figures 1 and S1). Ledumahadi mafube possesses several autapomorphies not observed in any other sauropodomorph: (1) medial edge of the proximal surface of the first metacarpal sharply tapering and curved, giving it a sublacriform outline and differing from the typical “keyhole” shape of the proximal first metacarpals of, e.g., Aardonyx, Ingentia, and Antetonitrus (Figure 1G); (2) anterior articular facet of the anterior caudal vertebra deeply concave, being set back from the anterolateral margin of the centrum 4.5 cm at its deepest; and (3) preserved forelimb elements extremely robust, with the minimum shaft circumference of the ulna 0.57 times the total length of the bone (cf. 0.46 in Antetonitrus). Ledumahadi is known from an incomplete postcranial skeleton that preserves several autapomorphies and generally lacks synapomorphies of Sauropoda, indicating a basal (non-sauropodan) phylogenetic position. The postzygapophysis of the single partial cervical neural arch is not elevated relative to the coronal plane, unlike in Pulanesaura and more derived sauropods (Figure 1A) [7McPhee B.W. Bonnan M.F. Yates A.M. Neveling J. Choiniere J.N. A new basal sauropod from the pre-Toarcian Jurassic of South Africa: evidence of niche-partitioning at the sauropodomorph-sauropod boundary?.Sci. Rep. 2015; 5: 13224Crossref PubMed Scopus (46) Google Scholar]. The neural spine of the anteriormost dorsal vertebra is anteroposteriorly short and expands transversely toward its dorsal apex (Figure 1B). The more posterior dorsal neural spines are proportionately tall for non-sauropodan Sauropodomorpha, with the dorsoventral height approximately twice that of the anteroposterior length of their bases (Figure 1C). They are therefore proportionally taller than those of the large-bodied non-sauropodan sauropodomorph Antetonitrus, which are 1.5 times as tall as they are long [8McPhee B.W. Yates A.M. Choiniere J.N. Abdala F. The complete anatomy and phylogenetic relationships of Antetonitrus ingenipes (Sauropodiformes, Dinosauria): implications for the origins of Sauropoda.Zool. J. Linn. Soc. 2014; 171: 151-205Crossref Scopus (66) Google Scholar]. The dorsal neural arches (including spine) are roughly twice the dorsoventral height of their associated centra. The dorsoventral height of the anterior caudal vertebral centrum is 1.7 times its anteroposterior length (Figure 1E). Its anterior face is deeply concave, and its posterior face is shallowly convex. The proximal articular surface of the ulna bears a large olecranon process and a shallow radial fossa, similar to other non-sauropodan sauropodiforms (e.g., Aardonyx, Antetonitrus, and Lessemsaurus) (Figure 1F) [8McPhee B.W. Yates A.M. Choiniere J.N. Abdala F. The complete anatomy and phylogenetic relationships of Antetonitrus ingenipes (Sauropodiformes, Dinosauria): implications for the origins of Sauropoda.Zool. J. Linn. Soc. 2014; 171: 151-205Crossref Scopus (66) Google Scholar, 9Yates A.M. Bonnan M.F. Neveling J. Chinsamy A. Blackbeard M.G. A new transitional sauropodomorph dinosaur from the Early Jurassic of South Africa and the evolution of sauropod feeding and quadrupedalism.Proc. Biol. Sci. 2010; 277: 787-794Crossref PubMed Scopus (111) Google Scholar, 10Bonnan M.F. Yates A.M. A new description of the forelimb of the basal sauropodomorph Melanorosaurus: implications for the evolution of pronation, manus shape and quadrupedalism in sauropod dinosaurs.Special Papers in Palaeontology. 2007; 77: 157-168Google Scholar, 11Pol D. Powell J. New information on Lessemsaurus sauropoides (Dinosauria: Sauropodomorpha) from the Upper Triassic of Argentina.Special Papers in Palaeontology. 2007; 77: 223-243Google Scholar]. In contrast, sauropods display a highly reduced olecranon process and much deeper radial fossa (e.g., Vulcanodon and Camarasaurus) [10Bonnan M.F. Yates A.M. A new description of the forelimb of the basal sauropodomorph Melanorosaurus: implications for the evolution of pronation, manus shape and quadrupedalism in sauropod dinosaurs.Special Papers in Palaeontology. 2007; 77: 157-168Google Scholar]. The anterior tip of the anterior process is deflected medially, similar to the condition seen in Antetonitrus [8McPhee B.W. Yates A.M. Choiniere J.N. Abdala F. The complete anatomy and phylogenetic relationships of Antetonitrus ingenipes (Sauropodiformes, Dinosauria): implications for the origins of Sauropoda.Zool. J. Linn. Soc. 2014; 171: 151-205Crossref Scopus (66) Google Scholar]. The ulnar shaft is markedly robust (Figures 1 and 4). The first metacarpal is extremely stout, with the mediolateral breadth of the proximal articular surface ∼1.1 times the overall length (Figure 1G). This ratio is similar to that of metacarpal I in Aardonyx and Antetonitrus. However, the proximal outline of metacarpal I is considerably different from those taxa, bearing a sublacriform, rather than keyhole shape, and a proportionally longer shaft. The other preserved metacarpal is similarly stout (Figure 1H). Only the distal third of the femur is preserved (Figure 1K). In cross-section, the shaft is circular, differing from the elliptical (but possibly distorted) cross-section of the femur of Antetonitrus. The distal condyles are anteroposteriorly expansive and strongly concave ventrally, differing from the anteroposteriorly shortened and flatter distal condyles of sauropod femora (e.g., Tazoudasaurus [12Allain R. Aquesbi N. Anatomy and phylogenetic relationships of Tazoudasaurus naimi (Dinosauria, Sauropoda) from the late Early Jurassic of Morocco.Geodiversitas. 2008; 30: 345-424Google Scholar]). The single large pedal ungual is most likely from the first or second digit (Figure 1I). It has a subcircular proximal outline, similar to the condition of the first and second digits in other late-branching non-sauropodan sauropodomorph taxa such as Blikanasaurus. Osteohistological evidence shows that the holotype of Ledumahadi had reached maximum size and was an adult of approximately 14 years of age at its time of death (Figure S2; STAR Methods). Ledumahadi exhibited high growth rates during early ontogeny, annual temporary decreases in growth from mid-ontogeny, and a gradual transition to parallel-fibered bone and closely spaced growth marks near the periphery representing an external fundamental system (Figure S2; STAR Methods). The closely related sauropodiforms Lessemsaurus [13Klein N. Sander M. Ontogenetic stages in the long bone histology of sauropod dinosaurs.Paleobiology. 2008; 34: 247-263Crossref Scopus (175) Google Scholar] and Antetonitrus [14Krupandan E. Chinsamy-Turan A. The long bone histology of the sauropodomorph, Antetonitrus ingenipes.Anat. Rec. 2018; https://doi.org/10.1002/ar.23898Crossref Scopus (8) Google Scholar] also exhibit rapid, but cyclical, growth throughout ontogeny. Given that Ledumahadi presents growth marks from at least mid-ontogeny (early growth destroyed by secondary remodeling), it is likely that it grew similarly to these other sauropodiforms. It therefore did not exhibit the sustained growth typical of Sauropoda [13Klein N. Sander M. Ontogenetic stages in the long bone histology of sauropod dinosaurs.Paleobiology. 2008; 34: 247-263Crossref Scopus (175) Google Scholar], in spite of its sauropod-like adult body size. Phylogenetic analysis recovers Ledumahadi as a sister taxon of another large-bodied upper Elliot Formation taxon, Antetonitrus ingenipes (Figures 2 and S4; STAR Methods). This is consistent with the general similarities observed between the two taxa. Nevertheless, the presence of several autapomorphies shows that Ledumahadi is distinct from Antetonitrus (see Diagnosis). Together with the South American taxon Lessemsaurus (known from very large, but most likely skeletally immature, material [11Pol D. Powell J. New information on Lessemsaurus sauropoides (Dinosauria: Sauropodomorpha) from the Upper Triassic of Argentina.Special Papers in Palaeontology. 2007; 77: 223-243Google Scholar]), these three genera form a monophyletic Lessemsauridae (a fourth member, Ingentia, was too recently described [15Apaldetti C. Martínez R.N. Cerda I.A. Pol D. Alcober O. An early trend towards gigantism in Triassic sauropodomorph dinosaurs.Nat. Ecol. Evol. 2018; 2: 1227-1232Crossref PubMed Scopus (48) Google Scholar] to be included in our analysis). Lessemsauridae is within a pectinate grade of non-sauropodan sauropodiforms sensu [8McPhee B.W. Yates A.M. Choiniere J.N. Abdala F. The complete anatomy and phylogenetic relationships of Antetonitrus ingenipes (Sauropodiformes, Dinosauria): implications for the origins of Sauropoda.Zool. J. Linn. Soc. 2014; 171: 151-205Crossref Scopus (66) Google Scholar], basal to Leonerasaurus, Gongxianosaurus, Pulanesaura, and the columnar-limbed quadrupeds known as Sauropoda sensu [16McPhee B.W. Choiniere J.N. The osteology of Pulanesaura eocollum: implications for the inclusivity of Sauropoda (Dinosauria).Zool. J. Linn. Soc. 2017; 182: 830-861Crossref Scopus (21) Google Scholar] (Figures 2 and S4). The minimum circumferences of limb bone shafts provide information about weight-bearing capacity in tetrapods [17Campione N.E. Evans D.C. A universal scaling relationship between body mass and proximal limb bone dimensions in quadrupedal terrestrial tetrapods.BMC Biol. 2012; 10: 60Crossref PubMed Scopus (236) Google Scholar]. Using this relationship for quadrupedal tetrapods [17Campione N.E. Evans D.C. A universal scaling relationship between body mass and proximal limb bone dimensions in quadrupedal terrestrial tetrapods.BMC Biol. 2012; 10: 60Crossref PubMed Scopus (236) Google Scholar], the preserved limb elements of BP/1/7120 provide a mass estimate of 12 metric tons for Ledumahadi mafube (Figures 2 and S3; STAR Methods). Furthermore, skeletal dimensions of Ledumahadi mafube are similar to those of geologically younger sauropods, including Jainosaurus and Tornieria. This confidently indicates sauropod-like body size in L. mafube, unlike the smaller-bodied sauropodomorphs that have hitherto been known from the earliest Jurassic. Ledumahadi mafube is thus the largest animal currently known to have lived on Earth at its time. It is more than three times the size of the largest confidently estimated Late Triassic sauropodomorph (Camelotia, 3.8 metric tons; but see [15Apaldetti C. Martínez R.N. Cerda I.A. Pol D. Alcober O. An early trend towards gigantism in Triassic sauropodomorph dinosaurs.Nat. Ecol. Evol. 2018; 2: 1227-1232Crossref PubMed Scopus (48) Google Scholar] for a 7-metric-ton estimate for Lessemsaurus) and considerably larger than the Early Jurassic sauropodomorphs Antetonitrus (5.6 metric tons; osteologically immature), and Vulcanodon (a sauropod; 10.3 metric tons; ?Sinemurian–Pliensbachian). Ledumahadi also extends the total known size range for Early Jurassic Sauropodomorpha, which now spans almost two orders of magnitude, down to a minimum of 0.26 metric tons in Anchisaurus (STAR Methods). To quantify quadrupedality, we used a dataset of humeral and femoral circumferences of 81 dinosaur specimens and hundreds of mammals plus several large-bodied reptiles that are confidently known to have been bipedal or quadrupedal. We used a classification of the predominant mode of locomotion during travel, rather than during slow-speed foraging. For example, kangaroos were classified as bipeds, although they can forage as quadrupeds, and non-human apes were classified as terrestrial quadrupeds (they also use four limbs for arboreal locomotion). Linear discriminant analysis of these data demonstrates that the relationship between the forelimb and hindlimb shaft circumferences can be used to make robust inferences of quadrupedality: a linear discriminant function calibrated using dinosaurs predicts the stances of mammals with a high degree of accuracy, indicating that the method can reliably predict novel datapoints (Figure 3; 90% accuracy; Tables S2 and S3). By contrast, lengths of forelimb bones, which have previously been used as evidence of sauropodomorph quadrupedality [9Yates A.M. Bonnan M.F. Neveling J. Chinsamy A. Blackbeard M.G. A new transitional sauropodomorph dinosaur from the Early Jurassic of South Africa and the evolution of sauropod feeding and quadrupedalism.Proc. Biol. Sci. 2010; 277: 787-794Crossref PubMed Scopus (111) Google Scholar], are unreliable (STAR Methods). We confidently classify Ledumahadi and numerous other sauropodiforms as quadrupeds based on their proportionally robust forelimbs (Figures 1, 2, 3, and S3; STAR Methods). Phylogenetic optimization indicates that the transition to quadrupedality occurred during the origins of the clade uniting Jingshanosaurus and Xingxiulong with more derived sauropodomorphs and had evolved at least by the mid-Norian, signaled by the occurrence of Riojasaurus. Quadrupedal sauropodomorphs have greater maximum body sizes than those of bipeds (1.5 metric tons in bipeds versus ∼4 metric tons, or up to 7 metric tons [15Apaldetti C. Martínez R.N. Cerda I.A. Pol D. Alcober O. An early trend towards gigantism in Triassic sauropodomorph dinosaurs.Nat. Ecol. Evol. 2018; 2: 1227-1232Crossref PubMed Scopus (48) Google Scholar] in Triassic quadrupeds). Nonetheless, Anchisaurus (0.26 metric tons) indicates that the smallest quadrupedal sauropodomorphs were similar in mass to the smallest post-Carnian bipeds (Sarahasaurus, 0.17 metric tons; see also Leonerasaurus). The current phylogenetic position of the inferred bipeds Mussaurus and Yunnanosaurus suggests the occurrence of at least one reversal back to bipedality. A more detailed understanding of the distribution and evolutionary pattern of quadrupedality is precluded by the lack of reliable appendicular measurements for several taxa, especially some of the closest relatives of Sauropoda (e.g., Lessemsaurus, Ingentia, Leonerasaurus, and Pulanesaura), as well as a continued lack of consensus on phylogenetic relationships among non-sauropodan sauropodiforms. Quadrupedality has been viewed as a key adaptation of Sauropoda, allowing for larger body masses and hence increased gut retention times required for processing low-quality, fibrous vegetable matter (e.g., [18Rauhut O. Fechner R. Remes K. Reis K. How to get big in the Mesozoic: the evolution of the sauropodomorph body plan.in: Klein N. Remes K. Gee C.T. Sander P.M. Biology of the Sauropod Dinosaurs: Understanding the Life of Giants. Indiana University Press, 2011: 119-149Google Scholar]). Sauropods were unique among quadrupedal dinosaurs in having a columnar stance with erect, parasagittal limbs, allowing efficient, graviportal support of body mass [7McPhee B.W. Bonnan M.F. Yates A.M. Neveling J. Choiniere J.N. A new basal sauropod from the pre-Toarcian Jurassic of South Africa: evidence of niche-partitioning at the sauropodomorph-sauropod boundary?.Sci. Rep. 2015; 5: 13224Crossref PubMed Scopus (46) Google Scholar, 12Allain R. Aquesbi N. Anatomy and phylogenetic relationships of Tazoudasaurus naimi (Dinosauria, Sauropoda) from the late Early Jurassic of Morocco.Geodiversitas. 2008; 30: 345-424Google Scholar, 19Cooper M.R. A reassessment of Vulcanodon karibaensis Raath (Dinosauria:Saurischia) and the origin of the Sauropoda.Palaeontologia Africana. 1984; 25: 203-231Google Scholar], similar to that in large mammals [20Biewener A.A. Scaling body support in mammals: limb posture and muscle mechanics.Science. 1989; 245: 45-48Crossref PubMed Scopus (601) Google Scholar]. This is indicated by a set of derived morphological features of sauropod forelimbs, including reduction of the deltopectoral crest; straightening of the humeral and femoral shafts; lengthening of the antebrachium and modification of the proximal ulna to a triradiate shape; modification of the metacarpus into a U-shaped support structure; loss of the lesser trochanter, migration of the fourth trochanter distally and medially, increase in fibular robustness; and many others [16McPhee B.W. Choiniere J.N. The osteology of Pulanesaura eocollum: implications for the inclusivity of Sauropoda (Dinosauria).Zool. J. Linn. Soc. 2017; 182: 830-861Crossref Scopus (21) Google Scholar, 18Rauhut O. Fechner R. Remes K. Reis K. How to get big in the Mesozoic: the evolution of the sauropodomorph body plan.in: Klein N. Remes K. Gee C.T. Sander P.M. Biology of the Sauropod Dinosaurs: Understanding the Life of Giants. Indiana University Press, 2011: 119-149Google Scholar]. These features evolved, at least in incipient forms, by the middle of the Early Jurassic and are exemplified by the early sauropod Vulcanodon [19Cooper M.R. A reassessment of Vulcanodon karibaensis Raath (Dinosauria:Saurischia) and the origin of the Sauropoda.Palaeontologia Africana. 1984; 25: 203-231Google Scholar, 21Viglietti P.A. Barrett P.M. Broderick T. Munyikwa D. MacNiven R. Broderick L. Chapelle K. Glynn D. Edwards S. Zondo M. et al.Stratigraphy of the Vulcanodon type locality and its implications for regional correlations within the Karoo Supergroup.J. Afr. Earth Sci. 2018; 137: 149-156Crossref Scopus (11) Google Scholar] (see also Pulanesaura [16McPhee B.W. Choiniere J.N. The osteology of Pulanesaura eocollum: implications for the inclusivity of Sauropoda (Dinosauria).Zool. J. Linn. Soc. 2017; 182: 830-861Crossref Scopus (21) Google Scholar]). Unlike sauropods, Ledumahadi retains plesiomorphic features of the ulna (i.e., short, robust shaft and a large olecranon process) and femur (i.e., circular shaft and expansive distal condyles). These features are present to some degree in all non-sauropodan sauropodomorphs and are generally thought to indicate flexed limb postures [6Carrano M.T. Rogers C. Wilson J. The evolution of sauropod locomotion.in: Curry Rogers K.A. Wilson J.A. The Sauropods: Evolution and Paleobiology. University of California Press, 2005: 229-249Google Scholar, 7McPhee B.W. Bonnan M.F. Yates A.M. Neveling J. Choiniere J.N. A new basal sauropod from the pre-Toarcian Jurassic of South Africa: evidence of niche-partitioning at the sauropodomorph-sauropod boundary?.Sci. Rep. 2015; 5: 13224Crossref PubMed Scopus (46) Google Scholar, 8McPhee B.W. Yates A.M. Choiniere J.N. Abdala F. The complete anatomy and phylogenetic relationships of Antetonitrus ingenipes (Sauropodiformes, Dinosauria): implications for the origins of Sauropoda.Zool. J. Linn. Soc. 2014; 171: 151-205Crossref Scopus (66) Google Scholar, 10Bonnan M.F. Yates A.M. A new description of the forelimb of the basal sauropodomorph Melanorosaurus: implications for the evolution of pronation, manus shape and quadrupedalism in sauropod dinosaurs.Special Papers in Palaeontology. 2007; 77: 157-168Google Scholar, 22Remes, K. (2008). Evolution of the pectoral girdle and forelimb in Sauropodomorpha (Dinosauria, Saurischia): osteology, myology and function. PhD thesis (Ludwig Maximilian University of Munich).Google Scholar] (Figure 4). Flexed (or “crouched”) limb postures are similar to those of smaller-bodied mammals and are distinct from the laterally sprawling limb postures of extant non-avian reptiles. Although a continuum exists between flexed and columnar limb postures, all extant mammals of >300 kg body mass have fully columnar limbs [20Biewener A.A. Scaling body support in mammals: limb posture and muscle mechanics.Science. 1989; 245: 45-48Crossref PubMed Scopus (601) Google Scholar], and the same seems to have been true in all sauropods. The presence of even partially flexed forelimbs in Ledumahadi, weighing 12 metric tons, is therefore striking and is consistent with interpretations of other lessemsaurids [15Apaldetti C. Martínez R.N. Cerda I.A. Pol D. Alcober O. An early trend towards gigantism in Triassic sauropodomorph dinosaurs.Nat. Ecol. Evol. 2018; 2: 1227-1232Crossref PubMed Scopus (48) Google Scholar]. Our analysis using linear discriminant functions on limb circumferences finds strong support for quadrupedality in non-sauropodan sauropodiforms, although they lack sauropod-like innovations related to columnar limb postures. The phylogenetic lineage leading to Ledumahadi diverged from that of Sauropoda in the Late Triassic (Norian), and its large size (12 metric tons) evolved independently to that of sauropods (Figure 2). The most recent common ancestor of Ledumahadi and Sauropoda has an estimated body mass of 2.2 metric tons (Figure 2), and other lessemsaurids, such as Lessemsaurus (2.1 metric tons as estimated from the most complete specimen; although the adult body mass was most likely much larger [15Apaldetti C. Martínez R.N. Cerda I.A. Pol D. Alcober O. An early trend towards gigantism in Triassic sauropodomorph dinosaurs.Nat. Ecol. Evol. 2018; 2: 1227-1232Crossref PubMed Scopus (48) Google Scholar]) and Antetonitrus (5.6 metric tons) weighed substantially less than Ledumahadi. Ledumahadi shows that quadrupedal sauropodomorphs lacking columnar limbs could attain sauropod-like body sizes. This contradicts hypotheses that columnar limb posture enabled multi-metric-ton masses in sauropods [3Sander P.M. Christian A. Clauss M. Fechner R. Gee C.T. Griebeler E.-M. Gunga H.-C. Hummel J. Mallison H. Perry S.F. et al.Biology of the sauropod dinosaurs: the evolution of gigantism.Biol. Rev. Camb. Philos. Soc. 2011; 86: 117-155Crossref PubMed Scopus (244) Google Scholar, 22Remes, K. (2008). Evolution of the pectoral girdle and forelimb in Sauropodomorpha (Dinosauria, Saurischia): osteology, myology and function. PhD thesis (Ludwig Maximilian University of Munich).Google Scholar]. Ornithischian dinosaurs evolved quadrupedality in several independent lineages, but their osteology shows that none had fully columnar forelimbs [23Barrett P.M. Maidment S.C.R. The evolution of ornithischian quadrupedality.J. Iber. Geol. 2017; 43: 363-377Crossref Scopus (19) Google Scholar]. Our findings suggest that early sauropodiforms followed a similar trajectory in the initial adoption of quadrupedality and that a columnar limb posture evolved only later in one sub-lineage, the sauropods. This columnar limb posture led to a major radiation in Sauropodomorpha. Previous studies of postural evolution in sauropodomorphs have focused on osteological indicators of manual pronation (e.g., [9Yates A.M. Bonnan M.F. Neveling J. Chinsamy A. Blackbeard M.G. A new transitional" @default.
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• W2894494577 date "2018-10-01" @default.
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• W2894494577 title "A Giant Dinosaur from the Earliest Jurassic of South Africa and the Transition to Quadrupedality in Early Sauropodomorphs" @default.
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• W2894494577 doi "https://doi.org/10.1016/j.cub.2018.07.063" @default.
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