Middle Caudal Vertebrae Research Articles

Unraveling sauropod diversity in the Portezuelo Formation of Patagonia through a comprehensive analysis of new and existing material

The Portezuelo Formation preserves an outstanding record of the upper Turonian – lower Coniacian. Despite the discovery of a significant quantity of sauropod fossil material from the formation, only two species have been formally described to date: Malarguesaurus florenciae and Futalognkosaurus dukei. Here we present new sauropod material mostly composed of non-articulated caudal vertebrae (MCF-PVPH 916 and 917) that belong to two titanosauriforms on the basis of the following features: anterior caudal vertebrae with procoelous-opisthoplatyan articulations, transverse processes that reach the posterior articular face of the centrum and neural spines with a transverse width of around 50% of their anteroposterior length; anterior and middle caudal vertebrae with the neural arch restricted to the anterior half of the centrum; middle caudal centra with circular cross-section. Phylogenetic analysis recovers the new material in close relation to Malarguesaurus within a monophyletic clade at the base of Somphospondyli. This clade shares large pedicel height with a vertical anterior border on the middle caudal vertebrae, a vertical orientation of the neural spines on the distalmost middle caudal vertebrae and proximalmost posterior caudal vertebrae, and subequal relative lengths of the proximal ulnar condylar processes. The specimens presented here are distinct not only from Futalognkosaurus, but also from other indeterminate titanosaurian remains from the same formation. However, there are no significant differences between the specimen MCF-PVPH 917 and Malarguesaurus, but there are differences between the posterior caudal vertebrae of MCF-PVPH 916 and Malarguesaurus, so they could be considered different species. Whilst we err on the side of caution in not naming new taxa here, the two specimens significantly expand what we know about sauropods in the Turonian–Coniacian ecosystems of Patagonia, which will continue to do so as more material is discovered.

A new sauropod species from north-western Brazil: biomechanics and the radiation of Titanosauria (Sauropoda: Somphospondyli)

Abstract Titanosaurs were the most diverse sauropod group during the Cretaceous period, with most of its diversity being found during the Late Cretaceous. In this work, Tiamat valdecii, gen. et sp. nov. is described, a new species of basal titanosaur prospected from the Açu Formation (Albian–Cenomanian), Potiguar Basin, Ceará state, north-east Brazil. The new taxon is composed by an associated sequence of anterior to middle caudal vertebrae, being diagnosed by four diagnostic features: a marked accessory tuberosity dorsoventrally developed, located on the prezygapophyses; deeply medioventral excavated articulation facets of prezygapophysis and post-zygapophyses articular facets; presence of developed hypantrum–hyposphene articulations; and short middle centra with a well-marked articular facet for the haemal arch. The phylogenetic analysis reveals that Tiamat valdecii was a basal member of Titanosauria. Tiamat is the first species of Early Cretaceous titanosaur known for the Açu Formation. Biomechanical analysis shows that the tuberosity and excavation of the zygapophyses of the middle caudal vertebrae of Tiamat provide greater stability against shear loads in the amphicoelous vertebrae presented; in addition, they allow greater range of lateral movements without affecting the integrity of the joints. These features may have been an evolutionary alternative for the stability of the middle of the caudal vertebral column. The discovery of T. valdecii in the Açu Formation not only increases the known dinosaur diversity for this unit, but also helps us elucidate part of the first titanosaur radiation.

Dinosaur remains from the Upper Cretaceous (Campanian) of the Western Desert, Egypt

Upper Cretaceous dinosaur remains from Afro-Arabia are rare and mainly restricted to pre-Turonian horizons. Consequently, the discovery of new fossils from Upper Cretaceous deposits in the Western Desert, central Egypt is significant because it adds to the meager record of dinosaurs described from this landmass. The oases of Kharga and Dakhla, Western Desert, Egypt, expose the Quseir Formation (Campanian), with the titanosaurian sauropod Mansourasaurus shahinae as the only currently named dinosaur from strata of this age in the entire region. Numerous (~80) other non-avian dinosaur fossils have also been collected from the Quseir Formation, including material that can be referred to Somphospondyli, Titanosauriformes/Titanosauria, and non-avian Theropoda. Among the discoveries from the Dakhla Oasis are the proximal ends of an associated sauropod tibia and fibula and several sauropod caudal vertebrae representing both sub-adult and adult individuals. Middle caudal vertebrae can be referred to Titanosauria on the basis of procoelous centra and anteriorly displaced neural arches. One caudal vertebra even exhibits pneumatic internal structures rarely observed outside of the Upper Cretaceous South American saltasaurines. Dinosaur fossils recovered from the Kharga Oasis include a partial femur and partial cervical vertebra of a sauropod dinosaur and an isolated proximal fibula of a non-avian theropod dinosaur. Taken together, these findings indicate that Late Cretaceous North African ecosystems supported a diversity of non-avian dinosaurs, some demonstrating affinities with South American forms and others (e.g., Mansourasaurus) with Eurasian groups. Additional exploration of the uppermost Cretaceous units in southern Egypt offers promise for the discovery of important fossils to better characterize Afro-Arabian biotas generally while also providing important perspectives on non-avian dinosaur faunas near the close of the Mesozoic Era.

Re-description of the sauropod dinosaur Amanzia (\u201cOrnithopsis/Cetiosauriscus\u201d) greppini n. gen. and other vertebrate remains from the Kimmeridgian (Late Jurassic) Reuchenette Formation of Moutier, Switzerland

Dinosaur remains were discovered in the 1860’s in the Kimmeridgian (Late Jurassic) Reuchenette Formation of Moutier, northwestern Switzerland. In the 1920’s, these were identified as a new species of sauropod, Ornithopsis greppini, before being reclassified as a species of Cetiosauriscus (C. greppini), otherwise known from the type species (C. stewarti) from the late Middle Jurassic (Callovian) of the UK. The syntype of “C. greppini” consists of skeletal elements from all body regions, and at least four individuals of different sizes can be distinguished. Here we fully re-describe this material, and re-evaluate its taxonomy and systematic placement. The Moutier locality also yielded a theropod tooth, and fragmentary cranial and vertebral remains of a crocodylomorph, also re-described here. “C.” greppini is a small-sized (not more than 10 m long) non-neosauropod eusauropod. Cetiosauriscus stewarti and “C.” greppini differ from each other in: (1) size; (2) the neural spine morphology and diapophyseal laminae of the anterior caudal vertebrae; (3) the length-to-height proportion in the middle caudal vertebrae; (4) the presence or absence of ridges and crests on the middle caudal centra; and (5) the shape and proportions of the coracoid, humerus, and femur. These anatomical differences, combined with their discrepancy in stratigraphic age, make it unlikely that C. stewarti and “C.” greppini belong to the same genus, as also supported through our phylogenetic analysis. “C.” greppini cannot be assigned to any other contemporaneous sauropod taxon from Europe, but is diagnosed by an autapomorphic rugosity on the posteromedial margin of the humerus, as well as a unique combination of features. As such, we erect the new genus name Amanzia for the Swiss taxon “Ornithopsis” greppini, augmenting the growing diversity of Late Jurassic European sauropods. Our phylogenetic analysis places it outside of Neosauropoda, either as the sister taxon to that clade, or as a member of Turiasauria.

An unusual new sauropod dinosaur from the Late Cretaceous of Mongolia

A new sauropod, Abdarainurus barsboldi gen. et sp. nov., is described based on several anterior and one middle caudal vertebrae and chevrons from the Late Cretaceous Alagteeg Formation at Abdrant Nuru, northern Gobi Desert, Mongolia. The new taxon is characterized by 16 unique or rare characters of the caudal skeleton, including opisthocoelous centra, longitudinal ridges on the neural canal walls, postprezygapophyseal processes, a hypertrophied postspinal fossa, mediolaterally constricted neural spines, and a deep pocket-like spinodiapophyseal fossa covered laterally by high postzygodiapophyseal lamina. Our preferred phylogenetic analysis places Abdarainurus as a basal titanosaurian sauropod, but this result could be affected by inadequate knowledge of basal titanosaurs. The new taxon likely represents a highly specialized lineage of Asian macronarian sauropods that was unknown previously.http://zoobank.org/urn:lsid:zoobank.org:pub::87174FD4-0616-4BD6-9209-C40C0455D2DA

Caudal vertebrae of titanosaurian sauropod dinosaurs from the Lower Cretaceous Ilek Formation in Western Siberia, Russia

Three sauropod middle caudal vertebrae are described from the three different localities within the Lower Cretaceous (Barremian-Aptian) Ilek Formation in Krasnoyarsk Territory, Western Siberia, Russia. All vertebrae are strongly procoelous and can be referred to Lithostrotia indet. LMCCE 005/40 from Bol'shoi Kemchug 3 locality has a ventral groove on centrum and a very large neural spine that projects posteriorly far beyond the centrum. This specimen also lacks postzygapophyses and bears a heavily sculptured neural spine suggesting high degree of development of the interosseous ligaments. The structure of the neural spine LMCCE 005/40 is similar to that of the saltasaurine Neuquensaurus from the Late Cretaceous of South America. However, the Siberian specimen lacks camellate bone texture characteristic for the caudal vertebrae of Saltasaurinae and its similarity with Neuquensaurus in development of the neural spine likely was independently acquired. These new findings increase the known diversity of sauropod dinosaurs in the Early Cretaceous of Siberia, which includes three taxa of Lithostrotia indet. described herein, lithostrotian Tengrisaurus, and titanosauriform Sibirotitan.

New data on the tyrannosauroid dinosaur Kileskus from the Middle Jurassic of Siberia, Russia

ABSTRACT New postcranial bones (cervical and caudal vertebrae, chevron, fibula) of the proceratosaurid tyrannosauroid Kileskus aristotocus from the Middle Jurassic (Bathonian) Itat Formation at Berezovsk coal mine, Krasnoyarsk Territory, Western Siberia, Russia, reveal three possible autapomorphies of Kileskus: a deep anterior recess between the neural canal and prezygapophysis; a distinct pit at the base of the neural spine on the middle cervical vertebrae; and a ventral groove on the middle caudal vertebrae. Phylogenetic analysis recovered a nearly horizontal posterior centrodiapophyseal lamina in the anterior-middle cervicals with the infrapostzygapophyseal fossa located primarily dorsally to the lamina as a new synapomorphy for the Proceratosauridae. The deep oval fossa on the medial surface of the fibula with well-defined margins is a tyrannosauroid synapomorphy of Kileskus. In other Proceratosauridae the fibula is either absent or not described in detail. The longitudinal and reticular vascularization of the primary cortex in the Kileskus tibia suggests a slower growth rate compared with large-bodied tyrannosaurids.

Titanosaur dinosaurs from the Upper Cretaceous of La Rioja province, NW Argentina

Our current knowledge of Argentinean titanosaurs outside Patagonia has been effectively limited to the province of Salta (e.g., Saltasaurus). However, several skeletal remains of titanosaurian sauropod dinosaurs have been discovered in the Cretaceous strata of La Rioja Province, northwest Argentina. Herein we describe new titanosaur material from two Upper Cretaceous localities from La Rioja. The first record corresponds to two caudal vertebrae found in the exposures of the Ciénaga del Río Huaco Formation, in the Quebrada de Santo Domingo locality. The largest sample, which includes fragmentary postcranial material of five individuals, was recovered from the Los Llanos Formation, in the Tama locality. The comparative analyses conducted here suggest that most of the specimens should be referred to as Lithostrotia non Saltasaurinae. However, differences between the middle caudal vertebrae from Tama and Quebrada de Santo Domingo suggest that the taxa at each locality are distinct.

The oldest titanosaurian sauropod of the Northern Hemisphere

Volgatitan simbirskiensis, gen. et sp. nov., is described based on a series of anterior and middle caudal vertebrae from a single individual discovered in the Lower Cretaceous (upper Hauterivian, Speetoniceras versicolor ammonite Zone) marine deposits at Slantsevy Rudnik vertebrate locality near Ulyanovsk City, Russia. The new taxon is characterized by strongly procoelous anterior and middle caudal vertebrae, a long centrum of the first caudal vertebra, a strong ventral ridge in the anterior and middle caudal vertebrae, a neural arch positioned at the anterior half of the centrum, hyposphene-hypantrum articulation in the anterior caudal vertebrae, and somphospondylous bone texture. Phylogenetic analysis places the new taxon as a lithostrotian titanosaur, a basal member of the lineage leading to the Lognkosauria. This lineage previously contained only South American taxa with body mass reaching 60–70 tons. Volgatitan gen. nov. is the first European and the geologically oldest representative of this lineage. Its body mass is estimated as 17.3 tons. Discovery of Volgatitan gen. nov. suggests that the lithostrotian lineage leading to the Lognkosauria had a wider distribution in the Early Cretaceous and became extinct everywhere except South America by the end of the Early Cretaceous.

Systematic review of Late Jurassic sauropods from the Museu Geológico collections (Lisboa, Portugal)

The Museu Geologico collections house some of the first sauropod references of the Lusitanian Basin Upper Jurassic record, including the Lourinhasaurus alenquerensis and Lusotitan atalaiensis lectotypes, previously considered as new species of the Apatosaurus and Brachiosaurus genera, respectively. Several fragmentary specimens have been classical referred to those taxa, but the most part of these systematic attributions are not supported herein, excluding a caudal vertebra from Maceira (MG 8804) considered as cf. Lusotitan atalaiensis . From the material housed in the Museu Geologico were identified basal eusauropods (indeterminate eusauropods and turiasaurs) and neosauropods (indeterminate neosauropods, diplodods and camarasaurids and basal titanosauriforms). Middle caudal vertebrae with lateral fossae, ventral hollow border by pronounced ventrolateral crests and quadrangular cross-section suggest for the presence of diplodocine diplodocids in north area of the Lusitanian Basin Central Sector during the Late Jurassic. A humerus collected from Praia dos Frades (MG 4976) is attributed to cf. Duriatitan humerocristatus suggesting the presence of shared sauropod forms between the Portugal and United Kingdom during the Late Jurassic. Duriatitan is an indeterminate member of Eusauropoda and the discovery of new material in both territories is necessary to confirm this systematic approach. The studied material is in according with the previous recorded paleobiodiversity for the sauropod clade during the Portuguese Late Jurassic, which includes basal eusauropods (including turiasaurs), diplodocids and macronarians (including camarasaurids and basal titanosauriforms).

Postcranial anatomy of Bonitasaura salgadoi (Sauropoda, Titanosauria) from the Late Cretaceous of Patagonia

ABSTRACTBonitasaura salgadoi, from the Bajo de la Carpa Formation (Santonian), Río Negro, Argentina, is a well-preserved titanosaur. Previously described cranial material of Bonitasaura demonstrated the presence of square jaws in titanosaurs, but the nearly complete postcranium of the holotype specimen remains mostly undescribed. We present an osteological description of this material, which includes cervical, dorsal, and caudal vertebrae, elements of the pectoral and pelvic girdles, as well as forelimbs and hind limbs. Characteristics of the axial skeleton suggest that the holotype represents an immature individual. The base of the neck was likely robust, based on the broad, rhomboidal neural spines in the vertebrae across the cervicodorsal transition. Bonitasaura is assigned to Titanosauria based on lateral constriction of the neural canal in the anterior cervical vertebrae, presence of anterior and posterior spinodiapophyseal laminae in the middle to posterior dorsal vertebrae, distolateral expansions of the middle dorsal vertebral neural spines, absence of hyposphene-hypantrum articulations in posterior dorsal vertebrae, anterior and middle caudal vertebrae with strongly procoelous centra, anterior caudal vertebrae with transverse processes extending beyond the posterior margin of the centrum, and other axial features. The appendicular anatomy of Bonitasaura also supports referral to Titanosauria based on characters such as the semilunar sternal plates, flat and rugose distal surfaces of the metacarpals, medial curvature of the proximal femur, posterior shallow fossa of the astagalus undivided, and mediolaterally expanded distal tibia. The gracile long bones further support placement within non-saltasaurine titanosaurs. Bonitasaura provides additional osteological data that will contribute to a better resolution of titanosaur phylogeny.

The basal titanosaurian Rukwatitan bisepultus (Dinosauria, Sauropoda) from the middle Cretaceous Galula Formation, Rukwa Rift Basin, southwestern Tanzania

ABSTRACTWhereas titanosaurians represent the most diverse and cosmopolitan clade of Cretaceous sauropod dinosaurs, they remain rare components of Cretaceous African faunas. Currently recognized continental African titanosaurians include Aegyptosaurus baharijensis and Paralititan stromeri from early Upper Cretaceous deposits near Bahariya Oasis, Egypt, and Malawisaurus dixeyi and Karongasaurus gittelmani from the Lower Cretaceous (∼Aptian) Dinosaur Beds of Malawi, in addition to several undesignated and fragmentary forms across the continent. Here, we describe a new titanosaurian taxon, Rukwatitan bisepultus, on the basis of a partial, semiarticulated postcranial skeleton recovered from the middle Cretaceous Galula Formation in southwestern Tanzania. Unique to Rukwatitan are carotid processes on posterior cervical vertebrae, a deep coracobrachialis fossa and subquadrangular cross-section of the humerus, and a slender, curved, teardrop-shaped pubic peduncle on the ilium. Parsimony and Bayesian phylogenetic analyses of 35 sauropod taxa congruently place Rukwatitan as a non-lithostrotian titanosaurian, a relationship supported by cervical vertebrae with undivided pleurocoels and strongly procoelous anterior caudal vertebrae. Rukwatitan differs from the potentially penecontemporaneous and geographically proximate Malawisaurus by exhibiting weakly developed chevron articulations and posteriorly inclined neural spines on the middle caudal vertebrae, a proximally robust and distally unexpanded humerus, and an anteroventrally elongated coracoid. Similar to biogeographic patterns identified in certain crocodyliform clades (e.g., small-bodied notosuchians), titanosaurians on continental Africa appear to exhibit a regional (e.g., southern versus northern Africa), rather than a continental- or supercontinental-level signal.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

Evidence of titanosauriforms and rebbachisaurids (Dinosauria: Sauropoda) from the Early Cretaceous of Tunisia

Isolated sauropod remains including vertebrae and a humerus from the Aïn El Guettar Formation (Albian, Early Cretaceous) of Tunisia are described. Vertebrae include a slightly procoelous anterior caudal vertebra, amphicoelous middle caudal vertebrae, and strongly procoelous distal caudal vertebrae. The humerus has an anteroposteriorly compressed shaft, robust deltopectoral crest restricted laterally and prominent condyles bounding a distinct distal fossa. The morphological characters present in the specimens suggests that isolated remains can be referred to at least two distinct sauropod taxa.The anterior caudal vertebra is referred to Rebbachisauridae, whereas remaining caudal vertebrae show titanosauriform and titanosaurian derived features (anteriorly placed neural arches and, in the posterior vertebrae, distincly procoelous centra); finally, the humerus may pertain to a somphospondylian titanosauriform, perhaps the same taxon represented by the middle and posterior caudal vertebrae. This study introduces some of the oldest titanosauriform remains from Northern Africa and provides additional data on the stratigraphic and geographic distribution of this clade during the Early Cretaceous.

New information on a juvenile sauropod specimen from the Morrison Formation and the reassessment of its systematic position

Abstract: Morphological changes in the ontogeny of sauropods are poorly known, making difficult to establish the systematic affinities of very young individuals. New information on an almost complete juvenile sauropod (SMA 0009) with an estimated total length of about 2 m is here presented. The specimen was described as a diplodocid owing to the presence of some putative synapomorphies of this group. However, recent further preparation revealed the absence of diplodocid characters and the presence of macronarian derived characters. To test the affinities of this specimen, a phylogenetic analysis was conducted. The strict consensus tree recovers the specimen as a basal titanosauriform, in an unresolved relation with Brachiosaurus and Giraffatitan. Nevertheless, a brachiosaurid assignment is here suggested in base of the widely accepted monophyly of this group (only recovered when SMA 0009 is placed within this group). Although the existence of a new taxon cannot be completely ruled out, the combination of derived and plesiomorphic characters in the specimen suggests its assignment to Brachiosaurus. Sixteen extra steps are needed to place this specimen within Diplodocidae. The high cost to place this specimen within this group is owing to the fact that several diplodocid characters are absent in SMA 0009, such as the absence of divided centroprezygapophyseal lamina in cervical vertebrae, procoelous anterior caudal centra, composed lateral lamina in anterior caudal vertebrae, elongated middle caudal vertebrae, short cervical ribs and caudolateral projection of distal condyle of metatarsal I. Finally, the systematic position reveals few major ontogenetic transformations. These affect the pneumatic structures (e.g. change from simple pleurocoels in the cervical vertebrae to complex pleurocoels and the development of lateral excavations in the dorsal vertebrae) but also include unrecorded transformations of the neural spine (e.g. the development of the spinodiapophyseal lamina, the widening of the neural spines in the dorsal vertebrae) and allometric growth in some limb bones.

A New Titanosaur Sauropod Dinosaur from the Upper Cretaceous of North Patagonia, Argentina

A new sauropod titanosaur from the Upper Cretaceous Anacleto Formation is described. Narambuenatitan palomoi gen. et sp. nov., is diagnosed by cranial and axial autapomorphies. The holotype, which represent a subadult individual, consists of the left premaxilla and maxilla, braincase, both quadrates, one cervical vertebrae, one dorsal vertebra, fragments of cervical and dorsal ribs, seventeen caudal vertebrae, caudal transverse processes, fragments of haemal arches, left sternal plate, right coracoid, left humerus, left ulnae, both pubes, iliac pedicel, proximal fragment of right ischia, and an incomplete left femur. The phylogenetic analysis indicates that Narambuenatitan is a non-eutitanosaurian lithostrotian, and that it shares with Epachthosaurus a neural spine in middle caudal vertebrae which are laminar and posteriorly elongated.

Anatomy of the basal titanosaur (Dinosauria, Sauropoda) Andesaurus delgadoi from the mid-Cretaceous (Albian-early Cenomanian) Río Limay Formation, Neuquén Province, Argentina: implications for titanosaur systematics

Titanosauria is a taxonomically and morphologically diverse clade of sauropod dinosaurs that appeared in the Middle Jurassic and radiated in the mid–Late Cretaceous; however, its intrarelationships are poorly understood. The mid-Cretaceous Argentinean sauropod Andesaurus delgadoi has repeatedly been recovered at the base of Titanosauria, and thus represents a crucial taxon for determining the evolutionary history of this clade; yet it has only received a brief description. Here, we re-describe the holotype, comprising dorsal, sacral, and caudal vertebrae, as well as limb and pelvic elements. Detailed comparisons are made with a global array of titanosauriforms. Andesaurus is a valid genus and can be diagnosed by five autapomorphies: (1) posterior dorsal neural spine height greater than twice centrum height (autapomorphic within Macronaria); (2) square-shaped anterior–middle caudal centra in lateral view; (3) anteroposteriorly elongate fossa present on the anterodorsal corner of the lateral surface of middle–posterior caudal centra; (4) ridge along the midshaft of the ventral surface of metacarpal I, close to the ventromedial margin; (5) prominent ventromedial ridge along the distal half of metacarpal V. Other remains previously attributed to Andesaurus cannot be referred to this genus. Sixteen putative titanosaur synapomorphies can be recognized in Andesaurus, including: (1) lateral pneumatic foramina in dorsal vertebrae situated within fossae; (2) anterior–middle caudal vertebrae with ventrolateral ridges either side of a ventral midline hollow; and (3) lateral bowing of metacarpal I. This revision provides an important foundation for future phylogenetic analyses of titanosaurs, and adds to our growing understanding of this enigmatic clade. Lastly, we recommend the disuse of the coordinated suprageneric rank taxa of Andesaurus (Andesaurinae, Andesauridae, and Andesauroidea), at least until titanosaur intrarelationships are better elucidated. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011.

Malarguesaurus florenciae gen. et sp. nov., a new titanosauriform (Dinosauria, Sauropoda) from the Upper Cretaceous of Mendoza, Argentina

Malarguesaurus florenciae gen. et sp. nov. is a new and robust somphospondylian titanosauriform (Dinosauria, Sauropoda) from the Neuquén basin, Mendoza Province, Argentina. The specimen comes from Upper Cretaceous strata assigned to the Portezuelo Formation (upper Turonian-lower Coniacian). It includes proximal, middle and distal caudal vertebrae, chevrons, dorsal ribs, and appendicular bones. Malarguesaurus is characterized by the following association of characters: (1) proximal caudal neural spines vertically directed, with a concave caudal border, and a caudodorsal corner forming a right angle; (2) procoelous-opisthoplatyan proximal and middle caudal vertebrae associated with procoelous distal caudal centra; and (3) distal caudal neural spines having a concave and depressed dorsal border. A preliminar cladistic analysis placed ( Ligabuesaurus + ( Malarguesaurus + Phuwiangosaurus)) as a sister taxon of Titanosauria. Unique among the titanosauriforms, Malarguesaurus has procoelous distal caudal centra associated with procoelous-opisthoplatyan proximal caudals. This discovery is a new evidence of the morphologic diversity of the South American sauropods.