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Reconstruction of Eucnemesaurus entaxonis. Illustrated bones are those preserved in the holotype BP/1/6234. Scale bar equals 50 cm.

Reconstruction of Eucnemesaurus entaxonis. Illustrated bones are those preserved in the holotype BP/1/6234. Scale bar equals 50 cm.

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The Late Triassic-Early Jurassic Elliot Formation of South Africa is one of the most important geological formations worldwide for understanding the early evolution of sauropodomorph dinosaurs. However, many of the taxa currently recognized as valid within its lower strata remain either poorly understood, vaguely diagnosed, or both. The recent disc...

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... of a medium-sized sauropodomorph dinosaur. It consists of an articulated vertebral column composed of the pos- terior-most dorsal vertebrae, sacral vertebrae, and the anterior portion of the tail; partial right ilium; partial pubic apron; left ischium; right femur and fragments of the left; distal epipodium (crus); and almost complete right pes (Fig. 1). McPhee et al.-A second species of Eucnemesaurus (e980504-2) FIGURE 2. Stratigraphic section of the Cannon Rock site. Arrow on map indicates excavation site of BP/1/6234. The large-bod- ied sauropodomorph is of indeterminate tax- onomy and cataloged within the ESI collections as BP/1/7408. The section spans most of lower Elliot and may ...
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... tibia of E. entaxonis is incompletely represented. The distal end of the right tibia is preserved in articulation with distal limb elements (Fig. 10). A partial proximal end is pre- served, but because the anterior portion is missing (including the cnemial crest), it is impossible to say with confidence whether it is of the right or left side. However, one side of the proximal sur- face is expanded in such a manner that it roofs a shallow depres- sion on the proximal surface of the ...
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... Antetonitrus, and Sauropoda (e.g., Yates and Kitching, 2003;Yates, 2004). This morphology also distinguishes E. entaxonis from TM 119 (E. fortis), which preserves a mediolaterally expan- sive posterodistal end in which the ascending and descending dis- tal processes are essentially level with each other (Van Hoepen, 1920;Yates, 2007a: fig. 1). Although the relationship of the distal to the proximal end of the bone is unknown in BP/1/6234, and it is possible that the reduced lateral expansion of the descending process may have been taphonomically exaggerated by an abstruse angle of preservation, the possibility remains that this feature has a more varied distribution than ...
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... facets that divide the distal edge of the posterior surfaces of the tibia: in E. fortis this surface is divided into two broad, subequal facets that are separated by a subtle, centrally located ridge, whereas in E. entaxonis this same ridge is located medially, resulting in a con- siderably reduced medial facet and a greatly expanded lateral one (Fig. ...
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... distal fibula is a morphologically simple element that in cross-section has a subcircular shaft and an anteroposter- iorly expanded distal end (Fig. 10). There is a distinct swelling evident on the posterodistal corner of the bone, and this connects to a ridge that runs dorsomedially along the anterior face of the shaft about 15 mm from the distal end. However, these latter two features are interpreted as either taphonomic or diagenetic ...
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... the astragalus was clearly articulated with the epipodium at death, most of its cortical bone has not been preserved, with only the ascending process visible beneath the ascending process of the tibia (D facet for reception of the ascending process of the astragalus) (Fig. 10). Given that the ascending process occupies an anterior position upon the astrag- alus in sauropodomorph dinosaurs, the absence of any bone pos- terior to this process in E. entaxonis is illustrative of the amount of diagenetic attrition experienced by this element. The ascend- ing process appears to have been transversely flat in ...
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... almost complete and articulated right foot is pre- served (Fig. 11). However, although each digit can be readily dis- tinguished, it is clear that some of the bones have experienced the same distorting process evident in other parts of the skeleton of E. entaxonis, resulting in the 'withered' appearance of pedal digits III and ...
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... making it difficult to substantiate whether or not the proximal surface of metatarsal II in E. entaxonis con- formed to the biconcave (hourglass) morphology generally found in basal Sauropodomorpha. It appears, however, that the lateral margin was distinctly less concave than the medial, as is generally observed in most basal sauropodomorphs (Fig. 11). The ventral margin of the proximal end is less symmetrical than the dorsal margin, possessing a large flange of bone that extends medially and thus cradles the ventral margin of metatarsal I. A similar medially directed flange can be seen in the proximal second metatarsals of a number of non-massospondylid sauropodo- morphs (e.g., ...
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... phylogenetic analysis returned eight most parsimonious trees (MPTs) of length 1244, consistency index (CI) D 0.34, and rescaled consistency index (RCI) D 0.7 (Fig. 12). Overall, the topologies of these trees do not differ greatly from previous cla- distic analyses of basal sauropodomorphs (e.g., Yates, 2007aYates, , 2007bYates et al., 2010;Otero and Pol, 2013;McPhee et al., 2014). The genus Eucnemesaurus is monophyletic, with the sis- ter-taxon relationship between E. entaxonis and E. fortis sup- ...
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... near the base of Sauropoda, a somewhat more derived position than in previous analyses Otero and Pol, 2013) (see below for further discussion). It should also be noted that, congruent with the results of Mart ınez et al. (2012), the problematic basal saurischian Eoraptor was resolved as one of the basal-most sauropodomorphs currently known (Fig. ...
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... to be non-monophyletic results in 65 MPTs with a best score only a single step longer than in the initial analysis (1245). The majority of the fundamental MPTs in that analysis place Eucnemesaurus in a position at the base of Sauropodiformes, a position consis- tent with the relatively derived condition of several characters within E. entaxonis (Fig. 12B) (see below for further discussion). It should also be noted that in the constrained analysis the mono- phyly of Eucnemesaurus is not supported in a number of funda- mental MPTs, with E. fortis considerably more basal with respect to E. entaxonis in these instances. Accordingly, the strict consensus tree places both taxa in a sizeable ...

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... Brief reviews of the taxonomic history of Melanorosaurus can be found in Van Heerden (1979), Galton et al. (2005), Yates (2007a), McPhee et al. (2015bMcPhee et al. ( , 2017, and Peyre de Fabrègues and Allain (2016), but a more comprehensive account is provided below. Melanorosaurus readi was named by Haughton (1924) in his magisterial review of the geology and paleontology of the Stormberg Group. ...
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... Among the first attempts to assess Plateosaurus interrelationships was the phylogenetic analysis done by Yates [15], where Plateosaurus was recovered at the base of Plateosauria, defined as the least inclusive clade containing Plateosaurus and Sauropoda (sensu [15]). The clade that includes species closer to Plateosaurus trossingensis than to Sauropoda was referred to as Plateosauridae in the same work [15] and is recovered in most cladistic analyses with Unaysaurus tolentinoi [20] as the sister taxon to Plateosaurus [11,12,15,18,21]. However, this comes as no surprise as the dataset used to assess non-sauropod sauropodomorphs usually derives from the work of Yates [15]. ...
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... The South American record of these times includes representatives of multiple lineages, most of which have adaptations to omnivory or herbivory (Barrett, 2000(Barrett, , 2014Button et al., 2017) and others show the earliest acquisition of quadrupedality (e.g., Bonaparte, 1972;McPhee et al., 2018). Some of these lineages share striking similarities with taxa recorded in southern Africa (e.g., Yates, 2006;2007;Apaldetti et al., 2012;McPhee et al., 2015a), such as lessemsaurids that show the earliest steps towards gigantism and are regarded as the earliest sauropods in some studies (Yates, 2007;Apaldetti et al., 2018;see below). ...
... Its holotype is a relatively complete postcranium ( Fig. 1; Bonaparte, 1967Bonaparte, , 1972 and multiple referred specimens include postcranial materials (Bonaparte, 1972) and a subadult specimen with a complete cranium ( Fig. 5I; Bonaparte and Pumares, 1995). Riojasaurus was allied with the two species of the genus Eucnemesaurus from the lower Elliot Formation of South Africa (Yates, 2007;McPhee et al., 2015a). Their affinities have been confirmed in most phylogenetic analyses and this clade has been referred as Riojasauridae (Yates, 2006). ...
... Fortunately, some areas of agreement have now been reached that define basic patterns of the evolution of sauropodomorphs. This agreement is the result of an intensification of studies on early sauropodomorph phylogenetics, largely prompted by discoveries and description of specimens from South America and South Africa (e.g., Leal et al., 2004;Yates, 2006Yates, , 2007Martinez and Alcober, 2009;Yates et al., 2010;Ezcurra, 2010;Knoll, 2010;Apaldetti et al., 2011Apaldetti et al., , 2012Apaldetti et al., , 2018Cabreira et al., 2011Cabreira et al., , 2016Pol et al., 2011;Otero and Pol, 2013;Martinez et al., 2013b;McPhee et al., 2015aMcPhee et al., ,b, 2017McPhee et al., , 2018McPhee et al., , 2019Otero et al., 2015;Allain, 2016, 2020;Chapelle and Choiniere, 2018;Müller et al., 2018a, b;Pretto et al., 2018;Bronzati et al., 2018aBronzati et al., , 2019Langer et al., 2019;Chapelle et al., 2019;Müller, 2020). There are five points of agreement reached in recent years that are most relevant to Triassic taxa: 1) the paraphyletic nature of Prosauropoda with respect to sauropods; 2) the placement of small bodied Carnian taxa at the base of Sauropodomorpha (outside Plateosauria); 3) the monophyly of four family-level clades: Plateosauridae, Riojasauridae, Massospondylidae, and Lessemsauridae; 4) the basal position of Plateosauridae relative to other three families; 5) the position of Lessemsauridae as closer to eusauropods than the other three families; Fig. 6). ...
Article
Sauropodomorpha is the first major dinosaurian group that radiated during the Triassic. During this time the group underwent major changes in body plan, including the acquisition of features related to herbivory, large body size, and quadrupedality. By the end of the Late Triassic, approximately 30 million years after the origin of dinosaurs, sauropodomorphs predominated the niches of large herbivores in continental ecosystems throughout the world. The Triassic sauropodomorph diversity includes diverse lineages with great disparity in body size, feeding biomechanics, and locomotion types, ranging from small (∼10 kg) bipedal taxa to the large (>5 tons) quadrupedal lessemsaurids. The South American record has provided key information to understand certain stages of this evolutionary radiation. We review here the diversity and composition of sauropodomorph faunas throughout the Late Triassic of South America and highlight their contribution for understanding the evolution of this group.