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Reappraisal Of The Early Cretaceous Sauropod Dinosaur Amargatitanis Macni (Apesteguía, 2007), From Northwestern Patagonia, Argentina
... Historically, the worldwide dicraeosaurid record was scarce with less than a handful known-taxa (Janensch, 1914;Salgado and Bonaparte, 1991). However, in the last two decades the family diversity incremented significantly (Harris and Dodson, 2004;Rauhut et al., 2005;Gallina, 2016;McPhee et al., 2016;Xu et al., 2018;Coria et al., 2019;Gallina et al., 2019). The Gondwanan dicraeosaurid record represents the majority of the diversity of the group Dicraeosauridae. ...
... The Gondwanan dicraeosaurid record represents the majority of the diversity of the group Dicraeosauridae. Especially in the Lower Cretaceous, this diversity is exclusively composed of Argentinian taxa and some fragmentary materials from Africa (Salgado and Bonaparte, 1991;Rauhut, 1999;Gallina, 2016;McPhee et al., 2016;Coria et al., 2019;Gallina et al., 2019). In this sense, the fossil record shows that the dicraeosaurids have been an important component in the ecosystem of La Amarga Formation in terms of diversity and abundance (Salgado and Bonaparte, 1991;Gallina, 2016;Salgado et al., 2006). ...
... Especially in the Lower Cretaceous, this diversity is exclusively composed of Argentinian taxa and some fragmentary materials from Africa (Salgado and Bonaparte, 1991;Rauhut, 1999;Gallina, 2016;McPhee et al., 2016;Coria et al., 2019;Gallina et al., 2019). In this sense, the fossil record shows that the dicraeosaurids have been an important component in the ecosystem of La Amarga Formation in terms of diversity and abundance (Salgado and Bonaparte, 1991;Gallina, 2016;Salgado et al., 2006). ...
Dicraeosauridae is a family of small body-sized sauropod dinosaurs that diversified from the Middle Jurassic to the Lower Cretaceous, whose distinctive feature is a long dorsally projected, bifid neural spines in most of the presacral vertebrae. The dicraeosaurid fossil record is limited to few taxa, therefore each new finding, however fragmentary, allows to improve the knowledge about this group. Here, we report new dicraeosaurid remains, consisting of two associated anterior dorsal vertebrae (MOZ-Pv 6126-1; MOZ-Pv 6126-2) collected from the La Amarga Formation (Barremian–Aptian, Lower Cretaceous). MOZ-Pv 6126-1 is represented by an almost complete anterior dorsal vertebra, while MOZ-Pv 6126-2 is an anterior dorsal vertebral centrum with a portion of the neural arch. The morphological features of these axial elements, as well as the absence of lateral fossae, the orientation of the transverse processes and an elongated bifid neural spine, allow us to refer them to the dicraeosaurid sauropods (Janensch, 1929; Salgado y Bonaparte, 1991; Rauhut et al., 2005; Coria et al., 2019; Gallina et al., 2019). However, due to the lack of more diagnostic features, we prefer to consider MOZ-Pv 6126-1 and MOZ-Pv 6126-2 as Dicraeosauridae indet. The new materials increase the fossil record of dicraeosaurid sauropods from La Amarga Formation and enrich the poor worldwide fossil record of the Dicraeosauridae.
... The majority are Jurassic taxa that comprise Dicraeosaurus hansemanni and D. sattleri from the Tendaguru Formation (Kimmeridgian) from Tanzania (Janensch, 1914); Dyslocosaurus polyonychius and Suuwassea emilieae from the Morrison Formation (Upper Kimmeridgian) of the United States of America (McIntosh et al., 1992;Harris and Dodson, 2004;Tschopp et al., 2015); and Brachytrachelopan mesai from the Cañad on Calc areo Formation (Tithonian) from Chubut Province, Argentina (Rauhut et al., 2005). The Lower Cretaceous Patagonian record consists of Amargasaurus cazaui (Salgado and Bonaparte, 1991) and Amargatitanis macni (Apesteguía, 2007;Gallina, 2016), both from the La Amarga Formation (Barremian-Aptian), Neuqu en Province, Argentina. ...
... The centrum has a concave anterior articular surface with a subcircular outline, is slightly wider than tall, and has a concave dorsal edge (Fig. 11A). In contrast, the posterior dorsal edge is rather flat (Fig. 11B) as in the previously described vertebra and other Flagellicaudata (Janensch, 1929;Harris, 2006;Gallina, 2016). In anterior view (Fig. 11A) the articular facets of the prezygapophyses face inward. ...
... However, because both specimens cannot be assigned to a single individual, the relative positions of these elements remain uncertain. The centrum is taller than long, as in other dicraeosaurids (Janensch, 1929;Salgado and Bonaparte, 1991;Harris, 2006;Apesteguía, 2007;Tschopp et al., 2015;Gallina, 2016) and the lateral surface is dorsoventrally convex. The preserved transverse process is small and robust. ...
A new dicraeosaurid sauropod, Pilmatueia faundezi gen. et sp. nov. from the Mulichinco Formation (Valanginian, Lower Cretaceous, Neuquén Basin, Argentina) is based on isolated skeletal remains collected from a single stratigraphic level, relatively close to each other, with unquestionable dicraeosaurid features in the axial elements. Pilmatueia faundezi is diagnosed by a unique combination of several features that include cervico-dorsal vertebrae with dorsoventrally oriented ridges on the anterior surfaces of the anterior centrodiapophyseal laminae, and posterior dorsal vertebrae with deep fossae at the bases of the bifid neural spines separated by a thick, low, sagittal lamina. Pilmatueia is recovered as the sister taxon of the late Early Cretaceous Amargasaurus cazaui. Pilmatueia increases our knowledge about the record of sauropods during the Valanginian, a period in which dinosaur diversity worldwide is poorly known.
... The analysis retrieved 820 most parsimonious trees of a length of 1114 steps. The strict consensus tree shows a large polytomy at the base of Neosauropoda, which can be resolved if two unstable taxa (Amargatitanis macni 11,12 and Erketu ellisoni 35 ) are pruned from the MPTs (see Supplementary Information). A reduced strict consensus tree recovered Bajadasaurus well nested within the family Dicraeosauridae (Fig. 3, Supplementary Fig. 12), sharing six synapomorphies with all dicraeosaurids, plus five synapomorphies shared with Lingwulong, Pilmatueia, Brachytrachelopan, Dicraeosaurus and Amargasaurus. ...
... The phylogenetic position of Bajadasaurus pronuspinax was tested through an equally weighted parsimony analysis in TNT v.1.1 47 . The data matrix used was based on a previously published phylogeny which included a wide array of sauropodomorph taxa 7 , with the addition of Amargatitanis macni 11,12 , Pilmatueia faundezi 10 , and Bajadasaurus pronuspinax. This dataset included 375 characters and 76 taxa (Supplementary Information). ...
Dicraeosaurids are a group of sauropod dinosaurs characterized by a distinctive vertebral column with paired, long, neural spines, present in an extreme fashion in the South American form Amargasaurus cazaui. This distinctive morphology has been interpreted as a support structure for a thermoregulatory sail, a padded crest for display, a dorsal hump acting as fat reservoir, and even as inner cores for dorsal horns. Other inferred functions (if any) of this structure were related to sexual display and/or defense strategies. Here we describe a new dicraeosaurid sauropod, Bajadasaurus pronuspinax gen. et sp. nov., from Patagonia which preserves the most complete skull of the group and has extremely elongate bifid cervical neural spines that point permanently forward, irrespective of the neck position. Although much shorter versions of this neural spine configuration were already recorded for other dicraeosaurid taxa, the long, anteriorly bent spines of this new dinosaur support the hypothesis that these elongate spines of dicraeosaurid sauropods served as passive defense structures.
... Several teeth from the Barremian-lower Aptian La Amarga Formation of Neuquén, Argentina have been assigned to Titanosauria (Apesteguía 2007). However, this interpretation has been questioned (Zaher et al. 2011), with some workers explicitly removing them from Titanosauria (D'Emic 2012) and others hesitating to classify them beyond Titanosauriformes (Gallina 2016). Amargatitanis macni, a sauropod also derived from the La Amarga Formation, was originally described as a titanosaur (Apesteguía 2007); however, a full reappraisal of the type specimen has revealed it to be a chimaera, as suggested by D'Emic (2012), with the majority of the remains actually pertaining to a dicraeosaurid diplodocoid (Gallina 2016). ...
... However, this interpretation has been questioned (Zaher et al. 2011), with some workers explicitly removing them from Titanosauria (D'Emic 2012) and others hesitating to classify them beyond Titanosauriformes (Gallina 2016). Amargatitanis macni, a sauropod also derived from the La Amarga Formation, was originally described as a titanosaur (Apesteguía 2007); however, a full reappraisal of the type specimen has revealed it to be a chimaera, as suggested by D'Emic (2012), with the majority of the remains actually pertaining to a dicraeosaurid diplodocoid (Gallina 2016). ...
Poropat, S.F., Nair, J.P., Syme, C.E., Mannion, P.D., Upchurch, P., Hocknull, S.A., Cook, A.G., Tischler, T.R. & Holland, T. XX.XXXX. 2017. Reappraisal of Austrosaurus mckillopi Longman, 1933 Longman, H.A., 1933. A new dinosaur from the Queensland Cretaceous. Memoirs of the Queensland Museum 10, 131–144. [Google Scholar] from the Allaru Mudstone of Queensland, Australia’s first named Cretaceous sauropod dinosaur. Alcheringa XX, XX–XX. ISSN 0311-5518
Austrosaurus mckillopi was the first Cretaceous sauropod reported from Australia, and the first Cretaceous dinosaur reported from Queensland (northeast Australia). This sauropod taxon was established on the basis of several fragmentary presacral vertebrae (QM F2316) derived from the uppermost Lower Cretaceous (upper Albian) Allaru Mudstone, at a locality situated 77 km west-northwest of Richmond, Queensland. Prior to its rediscovery in 2014, the type site was considered lost after failed attempts to relocate it in the 1970s. Excavations at the site in 2014 and 2015 led to the recovery of several partial dorsal ribs and fragments of presacral vertebrae, all of which clearly pertained to a single sauropod dinosaur. The discovery of new material of the type individual of Austrosaurus mckillopi, in tandem with a reassessment of the material collected in the 1930s, has facilitated the rearticulation of the specimen. The resultant vertebral series comprises six presacral vertebrae—the posteriormost cervical and five anteriormost dorsals—in association with five left dorsal ribs and one right one. The fragmentary nature of the type specimen has historically hindered assessments of the phylogenetic affinities of Austrosaurus, as has the fact that these evaluations were often based on a subset of the type material. The reappraisal of the type series of Austrosaurus presented herein, on the basis of both external morphology and internal morphology visualized through CT data, validates it as a diagnostic titanosauriform taxon, tentatively placed in Somphospondyli, and characterized by the possession of an accessory lateral pneumatic foramen on dorsal vertebra I (a feature that appears to be autapomorphic) and by the presence of a robust ventral mid-line ridge on the centra of dorsal vertebrae I and II. The interpretation of the anteriormost preserved vertebra in Austrosaurus as a posterior cervical has also prompted the re-evaluation of an isolated, partial, posterior cervical vertebra (QM F6142, the ‘Hughenden sauropod’) from the upper Albian Toolebuc Formation (which underlies the Allaru Mudstone). Although this vertebra preserves an apparent unique character of its own (a spinopostzygapophyseal lamina fossa), it is not able to be referred unequivocally to Austrosaurus and is retained as Titanosauriformes indet. Austrosaurus mckillopi is one of the oldest known sauropods from the Australian Cretaceous based on skeletal remains and potentially provides phylogenetic and/or palaeobiogeographic context for later taxa such as Wintonotitan wattsi, Diamantinasaurus matildae and Savannasaurus elliottorum.
Stephen F. Poropat* [sporopat@swin.edu.au; stephenfporopat@gmail.com] Department of Chemistry and Biotechnology, Swinburne University of Technology, John St, Hawthorn, Victoria 3122, Australia; Jay P. Nair [j.nair@uq.edu.au; jayraptor@gmail.com] School of Biological Sciences, The University of Queensland, St Lucia, Queensland 4072, Australia; Caitlin E. Syme [caitlin.syme@uqconnect.edu.au] School of Biological Sciences, The University of Queensland, St Lucia, Queensland 4072, Australia; Philip D. Mannion [philipdmannion@gmail.com] Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK; Paul Upchurch [p.upchurch@ucl.ac.uk] Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK; Scott A. Hocknull [scott.hocknull@qm.qld.gov.au] Geosciences, Queensland Museum, 122 Gerler Rd, Hendra, Queensland 4011, Australia; Alex G. Cook [alex.cook@y7mail.com] School of Earth Sciences, The University of Queensland, St Lucia, Queensland 4072, Australia; Travis R. Tischler [travisr.tischler@outlook.com] Australian Age of Dinosaurs Museum of Natural History, Lot 1 Dinosaur Drive, PO Box 408, Winton, Queensland 4735, Australia; Timothy Holland [drtimothyholland@gmail.com] Kronosaurus Korner, 91 Goldring St, Richmond, Queensland 4822, Australia. *Also affiliated with: Australian Age of Dinosaurs Museum of Natural History, Lot 1 Dinosaur Drive, PO Box 408, Winton, Queensland 4735, Australia.
... Although sauropods are primarily known from postcranial remains, diplodocoid and particularly dicraeosaurid diplodocoid taxa are known from an atypically high degree of cranial elements. Seven of 10 dicraeosaurid species are known from cranial remains; only Brahytrachelopan (Rauhut et al. 2005), Amargatitanis (Gallina 2016) and Pilmatueia (Coria et al. 2019) are known exclusively from postcrania. Of these seven taxa, only Amargasaurus (Salgado & Bonaparte 1991) and Smitanosaurus (Whitlock & Wilson Mantilla 2020) preserve only the braincase and periorbital elements. ...
... Brachytrachelopan mesai is a sauropod dinosaur from Cañadón Calcáreo Formation, Upper Jurassic of Patagonia (Argentina), characterised by having a particularly short neck (Rauhut et al. 2005). The phylogenetic hypotheses show certain consensus in recovering it as well nested within Dicraeosauridae, close to Amargasaurus and Dicraeosaurus (Rauhut et al. 2005;Whitlock 2011;Gallina 2016;Tschopp and Mateus 2017;Xu et al. 2018;Coria et al. 2019;Gallina et al. 2019;Whitlock and Wilson Mantilla 2020;Windholz et al. in press.). Brachytrachelopan represents the only Jurassic record of Dicraeosauridae in South America and, therefore, it is the oldest in this geographic area. ...
Brachytrachelopan is a dicraeosaurid sauropod that comes from the Jurassic of Argentine Patagonia. With the purpose to infer different palaeobiological traits (e.g., ontogenetic stage, growth dynamics, temporal correlation between morphological and anatomical parameters of maturation), we perform an osteohisto-logical study on different postcranial elements from the holotype individual, including axial (i.e., cervical hemispinous process, dorsal ribs) and appendicular (i.e., femur) bones. The absence of a distinct external fundamental system indicates that the individual died before full body size achievement (i.e., somatic maturity). Furthermore, although not conclusive, the histological data suggest that despite its body size, which is comparable with fully grown individuals of other dicraeosaurid taxa, the individual also corresponds to a sexually immature specimen. Predominance of highly vascularised fibrolamelar with only a cyclical growth mark (CGM) in the outer cortex of the femur reveals a sustained, accelerated growth, typical feature of neosauropod dinosaurs. The external anatomy (i.e., neurocentral sutures are visible in presacral vertebrae) is consistent with histological data, since both indicate some degree of immaturity. Dorsal ribs are best elements to estimate age. The new evidence reinforces the hypothesis that mechanical forces were higher in the anterior edge of cervical hemispinous processes, although, these findings do not support the presence of horn cores or interspinous ligament system in the neck of Brachytrachelopan. ARTICLE HISTORY
... Berriasian-Hauterivian deposits in Brazil have also yielded putative titanosaurs, including Triunfosaurus [151,152], although these have more recently been regarded as non-titanosaurian somphospondylans [17,131]. In Argentina, Hauterivian-Barremian deposits have produced remains of titanosauriforms [153,154], but dicraeosaurids dominate the Barremian deposits [155][156][157][158][159][160][161]. Terminal Barremian deposits in Colombia have produced the titanosauriform Padillasaurus, originally described as a brachiosaurid by Carballido et al. [162] but reinterpreted as a somphospondylan by Mannion et al. [71], whereas upper Barremian-lower Aptian deposits in Argentina host rebbachisaurids [163]. ...
The Upper Cretaceous Winton Formation of Queensland, Australia, has produced several partial sauropod skeletons, but cranial remains—including teeth—remain rare. Herein, we present the first description of sauropod teeth from this formation, based on specimens from three separate sites. An isolated tooth and a dentary fragment from the Diamantinasaurus matildae type locality are considered to be referable to that titanosaurian taxon. A single tooth from the D. matildae referred specimen site is similarly regarded as being part of that individual. Seventeen teeth from a new site that are morphologically uniform, and similar to the teeth from the two Diamantinasaurus sites, are assigned to Diamantinasauria. All sauropod teeth recovered from the Winton Formation to date are compressed-cone-chisel-shaped, have low slenderness index values (2.00–2.88), are lingually curved at their apices, mesiodistally convex on their lingual surfaces, and lack prominent carinae and denticles. They are markedly different from the chisel-like teeth of derived titanosaurs, more closely resembling the teeth of early branching members of the titanosauriform radiation. This provides further support for a ‘basal’ titanosaurian position for Diamantinasauria. Scanning electron microscope microwear analysis of the wear facets of several teeth reveals more scratches than pits, implying that diamantinasaurians were mid-height (1–10 m) feeders. With a view to assessing the spatio-temporal distribution of sauropod tooth morphotypes before and after deposition of the Winton Formation, we provide a comprehensive continent-by-continent review of the early titanosauriform global record (Early to early Late Cretaceous). This indicates that throughout the Early–early Late Cretaceous, sauropod faunas transitioned from being quite diverse at higher phylogenetic levels and encompassing a range of tooth morphologies at the start of the Berriasian, to faunas comprising solely titanosaurs with limited dental variability by the end-Turonian. Furthermore, this review highlights the different ways in which this transition unfolded on each continent, including the earliest records of titanosaurs with narrow-crowned teeth on each continent.
... quadrupedal stance with small heads, long necks and long tails), sauropods showed a highly morphological variation in the skeleton, particularly in the vertebrae, which exhibit a strong degree of anatomical disparity amongst the different lineages (Salgado & Powell, 2010;Wilson, 1999). Perhaps one of the most extreme examples of vertebral disparity is found in Dicraeosauridae, a clade of diplodocoid sauropods, whose fossil record comes from Argentina, Tanzania, United States and China (Bonaparte, 1986;Bonaparte, 1996;Coria et al., 2019;Gallina, 2016;Gallina et al., 2019;Harris & Dodson, 2004;Janensch, 1929;Rauhut et al., 2005;Salgado & Bonaparte, 1991;Upchurch et al., 2004;Windholz et al., 2021;Xu et al., 2018). Presacral vertebrae of dicraeosaurid sauropods are characterized by the presence of elongate bifid neural spines, which are therefore composed by two hemispinous processes (following Harris [2006] and referring to one half of a bifurcated spine. ...
Dicraeosaurid sauropods are iconically characterized by the presence of elongate hemispinous processes in presacral vertebrae. These hemispinous processes can show an extreme degree of elongation, such as in the Argentinean forms Amargasaurus cazaui, Pilmatueia faundezi and Bajadasaurus pronuspinax. These hyperelongated hemispinous processes have been variably interpreted as a support structure for a padded crest/sail as a display, a bison‐like hump or as the internal osseous cores of cervical horns. With the purpose to test these hypotheses, here we analyze, for the first time, the external morphology, internal microanatomy and bone microstructure of the hemispinous processes from the holotype of Amargasaurus, in addition to a second dicraeosaurid indet. (also from the La Amarga Formatin; Lower Cretaceous, Argentina). Transverse thin‐sections sampled from the proximal, mid and distal portions of both cervical and dorsal hemispinous processes reveal that the cortical bone is formed by highly vascularized fibrolamellar bone interrupted with cyclical growth marks. Obliquely oriented Sharpey's fibres are mostly located in the medial and lateral portions of the cortex. Secondary remodelling is evidenced by the presence of abundant secondary osteons irregularly distributed within the cortex. Both anatomical and histological evidence does not support the presence of a keratinized sheath (i.e. horn) covering the hyperelongated hemispinous processes of Amargasaurus, and either, using a parsimonious criterium, in other dicraeosaurids with similar vertebral morphology. The spatial distribution and relative orientation of the Sharpey's fibres suggest the presence of an important system of interspinous ligaments that possibly connect successive hemispinous processes in Amargasaurus. These ligaments were distributed along the entirety of the hemispinous processes. The differential distribution of secondary osteons indicates that the cervical hemispinous processes of Amargasaurus were subjected to mechanical forces that generated higher compression strain on the anterior side of the elements. Current data support the hypothesis for the presence of a ‘cervical sail’ in Amargasaurus and other dicraeosaurids. Life restoration of Amargasaurus cazaui. Current data support the hypothesis for the presence of a ‘cervical sail’ in Amargasaurus and other dicraeosaurids. Illustration made by Gabriel Lio.
... Amargasaurus cazaui MACN PV N15 preserves the posterior region of the skull, the complete presacral series, a sacrum composed of five vertebrae, some caudal vertebrae, fragments of cervical and dorsal ribs, three haemal arches, a right scapulo-coracoid, a left humerus, an ulna and radius, a left ilium, a femur, a tibia, a fibula, an astragalus, and two metatarsals (Salgado and Bonaparte, 1991). Amargatitanis macni MACN PV N53, is composed of two caudal vertebrae, a right ischium, a femur, a tibia, a fibula, an astragalus and metatarsal I (Apesteguia, 2007;Gallina, 2016). In A. cazaui MACN PV N15, the proximal end of a dorsal rib, the anterior and posterior regions (including the perimedullary cortex) of the humerus diaphysis, and the anterior surface of the femoral diaphysis (only the outer half of the cortex) were sampled. ...
Despite the large number of paleohistological studies carried out on sauropodomorph dinosaurs, some particular groups, such as dicraeosaurids, have been little explored. The current knowledge about the osteological microanatomy of this family is limited to that from specimens of Dicraeosaurus spp. and the holotype specimen of Suuwassea emiliae. We have examined the bone microstructure of the femur, humerus, and dorsal rib of the holotype of Amargasaurus cazaui and the femur of the holotype of Amargatitanis macni. The main purpose of this study is to obtain information regarding the ontogenetic stages of these individuals and, in a more general sense, to increase our understanding about the growth dynamics of dicraeosaurid sauropods. We interpret that Amargatitanis represents a more maturational stage than Amargasaurus, due to its high degree of bone remodeling and to the greatest number of lines of arrested growth (LAGs). Sexual maturity, mainly evidenced by the relative abundance of LAGs in the outer cortex of stylopodial bones, appears to have been reached by both individuals prior to death. Nevertheless, only Amargatitanis shows somatic maturation, evidenced by the presence of an External Fundamental System (EFS). In Amargasaurus, the dorsal rib preserved more LAGs than the long bones, supporting previous hypotheses that the dorsal ribs are good elements for making age estimates.
... During the Cretaceous, dicraeosaurids and diplodocids become extinct all over the world but southern Gondwana, with most complete records coming from Patagonia, with four dicraeosaurids named (Amargasaurus, Amargatitanis, Pilmatueia, and Bajadasaurus; Salgado & Bonaparte, 1991;Gallina, 2016;Coria et al., 2019;Gallina et al., 2019a) and, so far, only one diplodocid (Leinkupal Gallina et al., 2014). By contrast, Cretaceous sauropod faunas are mainly dominated by somphospondylans, a lineage not represented during the Jurassic (except probably for Australodocus and Oceanotitan; Mocho et al., 2019). ...
The titanosaur sauropod record of Patagonia, mainly recovered from Upper Cretaceous strata, is probably the richest worldwide. Here
we present a new sauropod dinosaur, Ninjatitan zapatai gen. et sp. nov., from the Lower Cretaceous Bajada Colorada Formation (Berriasian–
Valanginian) of north Patagonia (Neuquén Province, Argentina), from which postcranial remains are preserved. The anatomical analysis and com-
parisons performed in this specimen evidence strong affinity with titanosaur sauropods. This assumption is corroborated with the inclusion of
the new taxon in an updated phylogenetic data matrix. The cladistic analyses indicate that Ninjatitan could be considered the earliest known
titanosaur sauropod. The combination of features such as the presence of procoelous anterior caudal centra, the pneumatized neural arch of
anterior caudal vertebrae, and the posterodorsal border of the scapular acromion near the glenoid level supports its titanosaur affinities. The
presence of a basal titanosaurian sauropod in the lowermost Cretaceous of Patagonia supports the hypothesis that the group was established
in the Southern Hemisphere and reinforces the idea of a Gondwanan origin for Titanosauria. The Bajada Colorada sauropod fauna represents
one of the most diverse and unique associations from the lowermost Cretaceous worldwide recorded.
... Given that dicraeosaurids and diplodocids were both thriving in eastern Africa (Janensch, 1914(Janensch, , 1929(Janensch, , 1935(Janensch, -1936(Janensch, , 1961Remes, 2006Remes, , 2009Schwarz-Wings & Böhm, 2014) and Patagonia (Rauhut et al., 2005(Rauhut et al., , 2015Salgado et al., 2015b) during the latest Jurassic and persisted into the earliest Cretaceous of southern Africa (McPhee et al., 2016) and Patagonia (Gallina et al., 2014(Gallina et al., , 2019Paulina Carabajal et al., 2018;Coria et al., 2019;Windholz et al., 2020), they would have had ample opportunity to enter Australia at this time. However, by the end of the Barremian, both diplodocids and dicraeosaurids appear to have gone extinct worldwide; the dicraeosaurids of the La Amarga Formation are the geologically youngest flagellicaudatans known (Salgado & Bonaparte, 1991;Salgado & Calvo, 1992;Apesteguía, 2007;Gallina, 2016;Windholz et al., 2021). Thus, even if flagellicaudatans occupied Australia, they might not have persisted until the mid-Cretaceous. ...
The titanosaurian sauropod dinosaur Diamantinasaurus matildae is represented by two individuals from the Cenomanian-lower Turonian 'upper' Winton Formation of central Queensland, northeastern Australia. The type specimen has been described in detail, whereas the referred specimen, which includes several elements not present in the type series (partial skull, atlas, axis and postaxial cervical vertebrae), has only been described briefly. Herein, we provide a comprehensive description of this referred specimen, including a thorough assessment of the external and internal anatomy of the braincase, and identify several new autapomorphies of D. matildae. Via an expanded data matrix consisting of 125 taxa scored for 552 characters, we recover a close, well-supported relationship between Diamantinasaurus and its contemporary, Savannasaurus elliottorum. Unlike previous iterations of this data matrix, under a parsimony framework we consistently recover Diamantinasaurus and Savannasaurus as early-diverging members of Titanosauria using both equal weighting and extended implied weighting, with the overall topology largely consistent between analyses. We erect a new clade, named Diamantinasauria herein, that also includes the contemporaneous Sarmientosaurus musacchioi from southern Argentina, which shares several cranial features with the referred Diamantinasaurus specimen. Thus, Diamantinasauria is represented in the mid-Cretaceous of both South America and Australia, supporting the hypothesis that some titanosaurians, in addition to megaraptoran theropods and possibly some ornithopods, were able to disperse between these two continents via Antarctica. Conversely, there is no evidence for rebbachisaurids in Australia, which might indicate that they were unable to expand into high latitudes before their extinction in the Cenomanian-Turonian. Likewise, there is no evidence for titanosaurs with procoelous caudal vertebrae in the mid-Cretaceous Australian record, despite scarce but compelling evidence for their presence in both Antarctica and New Zealand during the Campanian-Maastrichtian. These later titanosaurs presumably dispersed into these landmasses from South America before the Campanian (~85 Mya), when seafloor spreading between Zealandia and Australia commenced. Although Australian mid-Cretaceous dinosaur faunas appear to be cosmopolitan at higher taxonomic levels, closer affinities with South America at finer scales are becoming better supported for sauropods, theropods and ornithopods.
... The phylogenetic position of Agustinia is debated and its inclusion within Titanosauria has been questioned in recent studies (see Salgado et al., 2006;Mannion and Calvo, 2011 ). Amargatitanis, originally described as a titanosaur from the La Amarga Formation (Barremian; Apesteguía, 2007) was recently interpreted as a dicraeosaurid sauropod (Gallina, 2016). Therefore, the Late Aptian-Late Albian age herein obtained for the Cerro Barcino sauropods reinforces the hypotheses that nontitanosaur titanosauriforms dominated the sauropod fauna of Patagonia until the Cenomanian. ...
The Cretaceous Cerro Barcino Formation (Chubut Group) of Central Patagonia, Argentina has yielded a remarkable fossil vertebrate fauna, which form important components of the South American “mid-Cretaceous” fauna, including titanosauriform sauropod dinosaurs, theropod dinosaurs, crocodyliforms, turtles, and lepidosauromorphs. However, a lack of robust chronostratigraphic framework for its fossil occurrences has so far hampered a full realization of their paleobiologic significance. This contribution presents new stratigraphic, sedimentologic, and U-Pb isotopic age data from 11 localities throughout the Patagonian Somuncurá-Canadón Asfalto Basin and analyzes the evolutionary characteristics of the Cerro Barcino fauna within the biostratigraphic context of the Cretaceous of Gondwana.
Four new high-precision ²⁰⁶Pb/²³⁸U zircon dates by the CA-ID-TIMS method range from 118.497 ± 0.063 Ma to 98.466 ± 0.048 Ma (2σ internal errors) and limits the Puesto La Paloma, Cerro Castaño and Las Plumas members of the Cerro Barcino Formation largely to the Aptian, Albian and Cenomanian stages of the Cretaceous, respectively. Accordingly, the majority of the Cerro Barcino vertebrates fall within a ~118–110 Ma time interval in the latest Early Cretaceous, which makes them the oldest documented component of the “mid-Cretaceous” faunal assemblage of Gondwana. Paleobiologic analyses of the latter assemblage suggests a ~10 m.y. period of faunistic stability characterized by only minor evolutionary novelties or faunal turnovers.
The Early Jurassic and Cretaceous deposits of India are known for their diverse sauropod fauna, while little is known from the Middle and Late Jurassic. Here we report the first ever remains of a dicraeosaurid sauropod from India, Tharosaurus indicus gen. et sp. nov., from the Middle Jurassic (early–middle Bathonian) strata of Jaisalmer Basin, western India. Known from elements of the axial skeleton, the new taxon is phylogenetically among the earlier-diverging dicraeosaurids,
and its stratigraphic age makes it the earliest known diplodocoid globally. Palaeobiogeographic considerations of Tharosaurus, seen in conjunction with the other Indian Jurassic sauropods, suggest that the new Indian taxon is a relic of a lineage that originated in India and underwent rapid dispersal across the rest of Pangaea. Here we emphasize the importance of Gondwanan India in tracing the
origin and early evolutionary history of neosauropod dinosaurs.
En esta publicación se listan los libros, capítulos de libros, tesis, artículos especializados y de divulgación, que han sido producto del trabajo de los investigadores de la Fundación Azara a lo largo de dos décadas, en no pocos casos, en coautoría con colegas de otras instituciones de diversas partes del mundo.
Flagellicaudatan diplodocoids include the two families Dicraeosauridae and Diplodocidae. Although different in sizes and relative proportions (e.g. neural arches height, neck length, tail length), they share several features, both cranial and postcranial, that recover them as a monophyletic group in updated phylogenies. The record of the group in South America was particularly scarce during the twentieth century, but their number and taxonomical diversity noticeably increased in the last decade. Up to now, five dicraeosaurid taxa (Amargasaurus cazaui, Amargatitanis macni, Bajadasaurus pronuspinax, Brachytrachelopan mesai, and Pilmatueia faundezi) and one diplodocid (Leinkupal laticauda) were recognized. Additionally, two presumably dicraeosaurid and three diplodocid records are known from fragmentary materials. Jurassic strata have provided both Brachytrachelopan and two of the indeterminate diplodocids, whereas the remaining five taxa, the third indeterminate diplodocid and the indeterminate dicraeosaurids come from the Early Cretaceous. Curiously, they are the only Cretaceous flagellicaudatan diplodocoids in the world, together with fragmentary records from South Africa, since the Jurassic–Cretaceous boundary marks a global extinction event for numerous species within the group. All these occurrences come from the only two countries of Patagonia: Argentina and Chile. The currently rich record of South American flagellicaudatans demonstrates that they were a key component of the Late Jurassic to the earliest Cretaceous sauropod fauna, the Bajadan tetrapod assemblage, occupying the niches of narrow-crowned megaherbivores by a time when macronarian neosauropods only attained broad-crown forms.
One of the diagnostic characters of dicraeosaurid sauropods is a reduction of pneumatization of dorsal and caudal vertebrae relative to their Flagellicaudata sister taxon, Diplodocidae. Here, we analyse pneumatic structures in the dicraeosaurid sauropod Pilmatueia faundezi, compare them to those of diplodocoids and report the first record of camerate chambers in a dicraeosaurid. The pneumatic structures are in a posterior cervical centrum (MLL‐Pv‐002) and consist of lateral pneumatic fossae on the centrum that communicate internally with large camerae. By contrast, Pilmatueia's dorsal and caudal vertebrae (MLL‐Pv‐005‐016) lack pneumatic fossae on the centra, which is consistent with the previously reported reduced pneumaticity in dicraeosaurids. Nevertheless, the base of the neural arch and possibly the base of the bifid neural spines of a posterior dorsal vertebra (MLL‐Pv‐005) show pneumatic internal chambers. The pneumatic features of the Pilmatueia cervical centrum and dorsal neural arch we describe indicate that the degree of pneumatization is variable within dicraeosaurids.
The Late Jurassic Tendaguru Formation of Tanzania, southeastern Africa, records a rich sauropod fauna, including the diplodocoids Dicraeosaurus and Tornieria, and the brachiosaurid titanosauriform Giraffatitan. However, the taxonomic affinities of other sympatric sauropod taxa are poorly understood. Here, we critically reassess and redescribe these problematic taxa, and present the largest phylogenetic analysis for sauropods (117 taxa scored for 542 characters) to explore their placement in Eusauropoda. Janenschia robusta has played a prominent role in discussions of titanosaur origins, with various authors referring at least some remains to Titanosauria, a clade otherwise known only from the Cretaceous. Redescription of the holotype of Janenschia, and all referable remains, supports its validity and placement as a nonneosauropod eusauropod. It forms a clade with Haestasaurus from the earliest Cretaceous of the UK, and the Middle/Late Jurassic Chinese sauropod Bellusaurus. Phylogenetic analysis and CT scans of the internal pneumatic tissue structure of Australodocus bohetii tentatively support a non-titanosaurian somphospondylan identification, making it the only known pre-Cretaceous representative of that clade. New information on the internal pneumatic tissue structure of the dorsal vertebrae of the enigmatic Tendaguria tanzaniensis, coupled with a full redescription, results in its novel placement as a turiasaur. Tendaguria is the sister taxon of Moabosaurus, from the Early Cretaceous of North America, and is the first turiasaur recognized from Gondwana. A previously referred caudal sequence cannot be assigned to Janenschia and displays several features that indicate a close relationship with Middle–Late Jurassic East Asian mamenchisaurids. It can be diagnosed by six autapomorphies, so we erect the new taxon Wamweracaudia keranjei gen. et sp. nov. The presence of a mamenchisaurid in the Late Jurassic of southern Gondwana indicates an earlier and more widespread diversification of this clade than previously realized, prior to the geographic isolation of East Asia. Our revised phylogenetic dataset sheds light on the evolutionary history of Eusauropoda, including supporting a basal diplodocoid placement for Haplocanthosaurus, and elucidating the interrelationships of rebbachisaurids. The Tendaguru Formation shares representatives of nearly all sauropod lineages with Middle Jurassic–earliest Cretaceous global faunas, but displays a greater range of diversity than any of those faunas considered individually. Biogeographic analysis indicates that the Tendaguru sauropod fauna was assembled as a result of three main phenomena during the late Early and/or Middle Jurassic: (1) invasions from Euramerica (brachiosaurids, turiasaurs); (2) endemism in west Gondwana (dicraeosaurids, diplodocids); and (3) regional extinctions that restricted the ranges of once widespread groups (mamenchisaurids, the Janenschia lineage). Multiple dispersals across the Central Gondwanan Desert are required to explain the distributions of Jurassic sauropods, suggesting that this geographic feature was at most a filter barrier that became easier to cross during the late Middle Jurassic.
A great amount of the sauropod record is based on caudal vertebrae. Morphological analyses of tail bones until recently were essentially focused on centrum shape, with other anatomical features being poorly studied. A detailed description of anterior caudal transverse processes (ACTP) is presented here in order to improve the scarce knowledge of this tail part. Within Sauropoda there are four different ACTP morphological types; one simple (single element projected on the vertebral side) and three complex (lateral bony laminar plates supported by bony bars). The identity of the ACTP elements includes a rib, a synapophysis and laminar components, which are renamed here. The ventral laminae include the anterior centroparapophyseal lamina (acpl) and the posterior centrodiapophyseal lamina (pcdl), whereas the dorsal ones are the prezygo-diapophyseal lamina (prdl) and the postzygodiapophyseal lamina (podl) when present. ACTP morphology is not informative for higher-level phylogeny, but at lower levels the in-group relationships of Diplodocoidea can be improved through analyzing these structures. ACTP morphological variation between the first and consecutive caudal vertebrae should presumably be interpreted as a consequence of the relative development of the M. caudofetnoralis brevis. The "sacralization" of the ACTP is related to the attachment of soft tissues associated with the tail, among which the Mm. caudofemorales should be the most important muscle group.
The phylogenetic relationships of titanosaurid sauropods are examined by means of a clodistic parsimony analysis based on postcranel features. Eusauropoda (Barapasaurus tagorei + Neosauropoda) have, at least, two synapomorphies. The Camarasauromorpha (Camarasauridae + Titanosauriformes) have five synapomorphies. The Titanosauriformes [Brachiosaurus brancai + (Chubutisaurus insignis + Titanosauria)] share six derived characters (e.g., presence of medial prespinal lamina in posterior trunk vertebrae, neural arches positioned anteriorly in mid and posterior caudal centra, claw on manual digit I reduced or absent). Chubutisaurus insignis Del Corro shares with Titanosauria one apomorphy. Titanosauria is rediagnosed based on five synapomorphies (e.g., eye-shape pleurocoels in trunk vertebrae, anterior caudals procoelous, pubis considerably longer than ischium). Titanosauridae comprises titanosaurids with: absence of hyposphene-hypantrum articulation in posterior trunk vertebrae, six sacral vertebrae, anterior caudals strongly procoelous having "ball and socket" articular faces, mid and posterior caudals strongly procoelous, semilunar sternal plates, claw on manual digit I absent, manual phalanges absent and preacetabular lobe of ilium nearly horizontal, outwardly projected. Titanosaurids more derived than Epachthosaurus sciuttoi Powell and Malawisaurus dixeyi Haughton have medial prespinal lamina formed down to the base of neural spine in posterior trunk vertebrae and quadrangular coracoids. Argentinosaurus huinculensis Bonaparte and Coria, Opisthocoelicaudia skarzynskii Borsuk-Bialynicka and Titanosauridae indet.* (DGM "Serie B") form a monophyletic group characterized by presence of accesory spino-diapophyseal laminae in trunk vertebrae. Aeolnsaurus Powell shares with Alamosaurus sanjuanensis Gilmore and the Saltasaurinae biconvex first caudal and presence of dorsal prominence on inner face of scapula. Alamosaurus sanjuanensis is the sister-taxon of the Saltasaurinae.
The oldest unit present in the studied area is the Mamil Choique Formation (Late Proterozoic-Early Paleozoic). During the Upper Paleozoic (Middle Devonian- Lower Carboniferous), the ectinitic Piedra Santa Formation was deposited, and later, during the Upper Carboniferous-Lower Permian, the Complejo Plutónico del Chachil was intruded. Towards the Late Permian and the Early Triassic , metamorphites as well as plutonites, were unconformably covered by the Choiyoi Forrnation. The sedimentation in the Neuquén Basin truly begins in the Upper Triassic with the deposition of the continental Lapa Formation. Marine sedimentites first appear in the Pliensbachian, and they continue uninterruptedly up to the early Callovian, within the Cuyo Group (Piedra Pintada, Sierra Chacaicó, Lajas, Los Molles y Challacó Formations). During the Middle Callovian, the deposition of the Lotena Formation has occurred, and presumably in part of the Oxfordian, that of the Fortín 1º de Mayo Formation. Towards the end of the Jurassic, a new marine transgression takes place, in this case represented by the Mendoza Group (Quebrada del Sapo, Carrín Curá, Vaca Muerta, Picún Leufú, Bajada Colorada and Agrio Formations) which ranges in age from the Kimmeridgian to the early Hauterivian. In the southeastern part of the studied area the Fortín Nogueira Group (Pichi Picún Leufú, Ortiz and Limay Formations) crops out, which is considered a basin margin equivalent of the Mendoza Group. At the end of the Hauterivian and the beginning of the Barremian , the continental La Amarga Formation was deposited. In the early Aptian, after a period of erosion , the deposition of the continental Lohan Cura Formation has occurred. In the early Cenomanian begins the deposition of the Neuquén Group, which is represented in the studied area by the Candeleros, Huincul, Cerro Lisandro, Portezuelo, Plottier and Bajo de la Carpa Formations, continuing their accumulation up to probably the Santonian. At the beginning of the Cenozoic, the presence of andesites and riodacites (Auca Pan Formation), whose age can be assigned to the Eocene and Oligocene It is recorded. During the late Oligocene/ early Miocene the deposition of the Naupa Huen and Cerro Bandera (nom. nov.) Formations took place. During the Middle Miocene the cyneritic tuffs of the Collón Cura Formation were deposited, whereas in the early Upper Miocene the extrusíon of the Lohan Mahuida Basalt and the intrusion of dikes and necks of the Cerro Horqueta Formation (nom. nov.), were registered. During the late Upper Miocene and Pliocene widespread table lavas identified as Zapala and Santo Tomás Basalts of the Coyocholiten se Cycle, were registered. During the Plio-Pleistocene boundary, an important aggradational event represented by the Pampa Curaco and Bayo Mesa Formations took place. In the early Pleistoceno, fluvioglacial deposits (Las Coloradas Formation) well represented in the Laguna Blanca are a, were recorded In the same region, olivinic laves of the Macho Viejo Basalt (nom. nov.), which belong to the Chapualitense Cycle, are well developed. Subsequently, the First Pediment Level and First Terrace Level deposits of the Lirnay river and Picún Leufú creek were recorded. In the Upper Pleistocene the intrusion of Los Mellizos Basalt, which belong to the Puentelitense Cycle, took place. Following active erosion and sedimentation, with deposits of the Second Pediment Level, the El Trapo Structural Plain and the Old Fans of the China Muerta creek , whereas the Second, Third and Fourth levels of terraces along the Limay and Picún Leufú rivers, were develope.d. During the Holocene, lava flows of the Laguna Blanca Basalt which belong to the lower Tromenlitense Cycle, were recorded. The Holocene stratigraphical picture of the studied arca is completed by MassWasting Deposits, Alluvial and Colluvial Deposits and Recent Fans. The hyclrocarbons constitute the most important economic resource in the region. Three important oil fields, named Cerro Vagón, El Sauce and Sur de la Dorsal (Cerro Lotena area) are briefly described. The most important discovery belongs the Puesto Touquet concession, which possess recoverable gasiferous reserves of the order of 20 million cubic meters, The metalliferous deposits consist in a number of stratabound and vetiform copper occurrences with scarce economic value. The industrial minerals are represented by economic value. The industrial minerals are represented by plastic clays, bentonites, limestones and diatornites. The plastic limestones possess an extrernely important economic value, supplying very active ceramic industries of the Neuquén province. The oil shales may also constitute an important future economic resource in the region. The coal occurrences present in the area do not possess economic value.
Bonitasaura 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.
Diplodocidae are among the best known sauropod dinosaurs. Several species were described in the late 1800s or early 1900s from the Morrison Formation of North America. Since then, numerous additional specimens were recovered in the USA, Tanzania, Portugal, and Argentina, as well as possibly Spain, England, Georgia, Zimbabwe, and Asia. To date, the clade includes about 12 to 15 nominal species, some of them with questionable taxonomic status (e.g., ‘Diplodocus’ hayi or Dyslocosaurus polyonychius), and ranging in age from Late Jurassic to Early Cretaceous. However, intrageneric relationships of the iconic, multi-species genera Apatosaurus and Diplodocus are still poorly known. The way to resolve this issue is a specimen-based phylogenetic analysis, which has been previously implemented for Apatosaurus, but is here performed for the first time for the entire clade of Diplodocidae.
The analysis includes 81 operational taxonomic units, 49 of which belong to Diplodocidae. The set of OTUs includes all name-bearing type specimens previously proposed to belong to Diplodocidae, alongside a set of relatively complete referred specimens, which increase the amount of anatomically overlapping material. Non-diplodocid outgroups were selected to test the affinities of potential diplodocid specimens that have subsequently been suggested to belong outside the clade. The specimens were scored for 477 morphological characters, representing one of the most extensive phylogenetic analyses of sauropod dinosaurs. Character states were figured and tables given in the case of numerical characters.
The resulting cladogram recovers the classical arrangement of diplodocid relationships. Two numerical approaches were used to increase reproducibility in our taxonomic delimitation of species and genera. This resulted in the proposal that some species previously included in well-known genera like Apatosaurus and Diplodocus are generically distinct. Of particular note is that the famous genus Brontosaurus is considered valid by our quantitative approach. Furthermore, “Diplodocus” hayi represents a unique genus, which will herein be called Galeamopus gen. nov. On the other hand, these numerical approaches imply synonymization of “Dinheirosaurus” from the Late Jurassic of Portugal with the Morrison Formation genus Supersaurus. Our use of a specimen-, rather than species-based approach increases knowledge of intraspecific and intrageneric variation in diplodocids, and the study demonstrates how specimen-based phylogenetic analysis is a valuable tool in sauropod taxonomy, and potentially in paleontology and taxonomy as a whole.
Titanosauriforms represent a diverse and globally distributed clade of neosauropod dinosaurs, but their inter‐relationships remain poorly understood. Here we redescribe Lusotitan atalaiensis from the Late Jurassic Lourinhã Formation of Portugal, a taxon previously referred to Brachiosaurus. The lectotype includes cervical, dorsal, and caudal vertebrae, and elements from the forelimb, hindlimb, and pelvic girdle. Lusotitan is a valid taxon and can be diagnosed by six autapomorphies, including the presence of elongate postzygapophyses that project well beyond the posterior margin of the neural arch in anterior‐to‐middle caudal vertebrae. A new phylogenetic analysis, focused on elucidating the evolutionary relationships of basal titanosauriforms, is presented, comprising 63 taxa scored for 279 characters. Many of these characters are heavily revised or novel to our study, and a number of ingroup taxa have never previously been incorporated into a phylogenetic analysis. We treated quantitative characters as discrete and continuous data in two parallel analyses, and explored the effect of implied weighting. Although we recovered monophyletic brachiosaurid and somphospondylan sister clades within Titanosauriformes, their compositions were affected by alternative treatments of quantitative data and, especially, by the weighting of such data. This suggests that the treatment of quantitative data is important and the wrong decisions might lead to incorrect tree topologies. In particular, the diversity of Titanosauria was greatly increased by the use of implied weights. Our results support the generic separation of the contemporaneous taxa Brachiosaurus, Giraffatitan, and Lusotitan, with the latter recovered as either a brachiosaurid or the sister taxon to Titanosauriformes. Although Janenschia was recovered as a basal macronarian, outside Titanosauria, the sympatric Australodocus provides body fossil evidence for the pre‐Cretaceous origin of titanosaurs. We recovered evidence for a sauropod with close affinities to the Chinese taxon Mamenchisaurus in the Late Jurassic Tendaguru beds of Africa, and present new information demonstrating the wider distribution of caudal pneumaticity within Titanosauria. The earliest known titanosauriform body fossils are from the late Oxfordian (Late Jurassic), although trackway evidence indicates a Middle Jurassic origin. Diversity increased throughout the Late Jurassic, and titanosauriforms did not undergo a severe extinction across the Jurassic/Cretaceous boundary, in contrast to diplodocids and non‐neosauropods. Titanosauriform diversity increased in the Barremian and Aptian–Albian as a result of radiations of derived somphospondylans and lithostrotians, respectively, but there was a severe drop (up to 40%) in species numbers at, or near, the Albian/Cenomanian boundary, representing a faunal turnover whereby basal titanosauriforms were replaced by derived titanosaurs, although this transition occurred in a spatiotemporally staggered fashion. © 2013 The Linnean Society of London
Neosauropods are well represented in the Late Jurassic fossil record, both in Laurasia and Gondwana. Among Macronaria, Europasaurus represents one of the most basal forms of this group. In addition to its systematic importance, Europasaurus is also the first unequivocal dwarf sauropod from which adult and juvenile material is available. Despite the abundance of sauropods in the fossil record, early juvenile specimens are rare, limiting knowledge about sauropod ontogeny. Therefore, the great amount of material of Europasaurus provides an excellent opportunity to improve our knowledge on the early evolution of Macronaria, as well as to shed light on some morphological changes through ontogeny. The postcranial axial skeleton of sauropods is extremely modified with respect to the anatomy observed in its ancestors, the ‘prosauropods’, proving to be one of the most informative regions of the body. Here we provide a detailed description of the axial skeleton of Europasaurus, including adult and juvenile elements, discussing its systematic and ontogenetic importance. We also analyse the phylogenetic position of Europasaurus through a cladistic analysis using TNT, which retrieves this taxon in a basal position among Camarasauromorpha. Additionally, the presence/absence of discrete characters and the comparison of juvenile elements with adult specimens allowed us to recognize different morphological ontogenetic stages (MOS). Whereas early stages lack derived characters (e.g. spinodiapophyseal lamina and prespinal lamina on dorsal vertebrae), all derived characters (including autapomorphies) are present in late immature specimens. Therefore, while late immature specimens provide the same phylogenetic signal as adult specimens of Europasaurus, more immature stages are recovered in a basal position among sauropods. Finally, we apply the MOS to other maturity criteria (e.g. neurocentral closure, sexual maturity) in a search for a wider definition of maturity.
The Cretaceous terrestrial strata of the Neuquén Basin (northern Patagonia, Argentina) are described together with their tetrapod records. Six local tetrapod assemblages are identified: Amargan (Barremian–Early Aptian), Lohancuran (Late Aptian–Albian), Limayan (Cenomanian–Early Turonian), Neuquenian (Late Turonian–Coniacian), Coloradoan (Santonian–Early Campanian) and Allenian [Late Campanian–Early Maastrichtian (= Alamitense = Alamitian SALMA)]. The last of these includes records from north-eastern Patagonia.
Pereda-Suberbiola, X., Galton, P.M., Mallison, H. & Novas, F. iFirst article. A plated dinosaur (Ornithischia, Stegosauria) from the Early Cretaceous of Argentina, South America: an evaluation. Alcheringa, 1–14. ISSN 0311-5518.A re-evaluation of several vertebrae and dermal plates from the Lower Cretaceous (La Amarga Formation, Puesto Antigual Member; Barremian–lower Aptian) of Neuquén in Argentina, originally described as a stegosaurian dinosaur and recently referred to an indeterminate ornithischian, confirms the former identification. The Neuquén remains have a combination of features that is only known among stegosaurs: cervical vertebrae with a proportionally large cross-section of the neural canal, the anterior height and width of which are half the height of the anterior centrum, as in the cervical vertebrae of Kentrosaurus, Dacentrurus and Stegosaurus; prominent lateral depressions on the cervical centra, as in the presacral vertebrae of Dacentrurus; and cervical dermal plates that are subtriangular, longer than high and reminiscent of those of Miragaia. Moreover, a small bone here interpreted to be an anterior supraorbital (= first palpebral) is similar to that of Stegosaurus and other stegosaurs in having an elongate form and a dorsal rugose surface. The remains from Argentina exhibit some differences relative to other stegosaurs, suggesting that it is potentially a distinct taxon, but their incompleteness advises against the erection of a new genus and species. Interestingly, it is the only known skeletal record of Stegosauria in South America. It provides the second conclusive evidence of the presence of this clade in the Early Cretaceous of the Gondwanan landmasses.
This chapter summarizes all dinosaur locations currently known worldwide. Geographic location is based on primary administrative divisions (e.g., states, departments, provinces, counties) of the countries in which dinosaur material has been found. Locations are annotated for lithostratigraphic unit (bed, formation, group, series), faunal composition, and stratigraphic horizon. The members of the fauna are present in rank order, roughly based on their phylogenetic relationships. The chapter also includes locations yielding skeletal remains and those that have produced tracks and/or trackways, as well as locations where eggs and eggshell fragments have been found.
A new medium-sized rebbachisaurid sauropod from the Castrillo la Reina Formation (Upper Barremian-Lower Aptian) in Burgos Province, Demandasaurus darwini gen. et sp. nov., is described. It is known from an incomplete but associated skeleton that includes cranial and post-cranial remains. Demandasaurus darwini gen. et sp. nov. presents 9 autapomorphies in the teeth and vertebrae. Demandasaurus is the first diplodocoid sauropod described from the Cretaceous of the Iberian Peninsula. Its inclusion in the Rebbachisauridae is well supported by our phylogenetic hypothesis, which situates it as a sister group of Nigersaurus from the Aptian of Niger, with which it shares various synapomorphies. The discovery of Demandasaurus provides further evidence of the sporadic use of the Apulian Route by dinosaurs during the Early Cretaceous for moving between the south of Europe (Laurasia) and the north of Africa (Gondwana).
Although diplodocoid sauropods from Africa and the Americas are well known, their European record remains largely neglected. Here we redescribe Dinheirosaurus lourinhanensis from the Late Jurassic of Portugal. The holotype comprises two posterior cervical vertebrae, the dorsal series and a caudal centrum. Redescription demonstrates its validity on the basis of three autapomorphies: (1) posteriorly restricted ventral keel on posterior cervical vertebrae; (2) three small subcircular fossae posterior to the lateral coel on posterior cervical neural spines; (3) accessory lamina linking the hyposphene with base of the posterior centrodiapophyseal lamina in middle-posterior dorsal vertebrae. Phylogenetic analysis places Dinheirosaurus as the sister taxon to Supersaurus, and this clade forms the sister taxon to other diplodocines. However, this position should be treated with caution as Dinheirosaurus displays several plesiomorphic features absent in other diplodocids (including unbifurcated presacral neural spines, and dorsolaterally projecting diapophyses on dorsal vertebrae) and only four additional steps are required to place Dinheirosaurus outside of Flagellicaudata. We identify Amazonsaurus as the basal-most rebbachisaurid and recover Zapalasaurus outside of the South American Limaysaurinae, suggesting the biogeographic history of rebbachisaurids is more complex than previously proposed. Review of the European diplodocoid record reveals evidence for the earliest known diplodocid, as well as additional diplodocid remains from the Late Jurassic of Spain. A Portuguese specimen, previously referred to Dinheirosaurus, displays strong similarities to Apatosaurus from the contemporaneous Morrison Formation of North America, indicating the presence of a second Late Jurassic Portuguese diplodocid taxon. Along with Dinheirosaurus, these Portuguese remains provide further evidence for a Late Jurassic palaeobiogeographic connection between Europe and North America. No dicraeosaurids are currently known from Europe, but rebbachisaurids are present in the Early Cretaceous, with weak evidence for the earliest known representative from the Late Jurassic of Spain; however, more complete material is required to recognize early members of this clade.
A study of the abundant and undescribed isolated and associated bones and teeth from the La Amarga Formation (Barremian of Neuquén, Argentina) permitted the recognition of additional clades of sauropod dinosaurs: basal titanosauriforms, both basal and derived titanosaurs, and rebbachisauroid diplodocoids, which are now added to the already known dicraeosaurids and a recently published basal diplodocoid. These forms substantially increase the knowledge on the Early Cretaceous sauropod diversity in Gondwana.
Sauropoda is among the most diverse and widespread dinosaur lineages, having attained a near-global distribution
by the Middle Jurassic that was built on throughout the Cretaceous. These gigantic herbivores are characterized by
numerous skeletal specializations that accrued over a 140 million-year history. This fascinating evolutionary history
has fuelled interest for more than a century, yet aspects of sauropod interrelationships remain unresolved. This
paper presents a lower-level phylogenetic analysis of Sauropoda in two parts. First, the two most comprehensive
analyses of Sauropoda are critiqued to identify points of agreement and difference and to create a core of character
data for subsequent analyses. Second, a generic-level phylogenetic analysis of 234 characters in 27 sauropod taxa is
presented that identifies well supported nodes as well as areas of poorer resolution. The analysis resolves six sauropod
outgroups to Neosauropoda, which comprises the large-nostrilled clade Macronaria and the peg-toothed clade
Diplodocoidea. Diplodocoidea includes Rebbachisauridae, Dicraeosauridae, and Diplodocidae, whose monophyly and
interrelationships are supported largely by cranial and vertebral synapomorphies. In contrast, the arrangement of
macronarians, particularly those of titanosaurs, are based on a preponderance of appendicular synapomorphies. The
purported Chinese clade ‘Euhelopodidae’ is shown to comprise a polyphyletic array of basal sauropods and neosauropods.
The synapomorphies supporting this topology allow more specific determination for the more than 50 fragmentary
sauropod taxa not included in this analysis. Their distribution and phylogenetic affinities underscore the
diversity of Titanosauria and the paucity of Late Triassic and Early Jurassic genera. The diversification of Titanosauria
during the Cretaceous and origin of the sauropod body plan during the Late Triassic remain frontiers
for future studies.
A partial skeleton of a new sauropod dinosaur from the Upper Jurassic Morrison Formation (?Tithonian) of Montana is described. Suuwassea emilieae gen. et sp. nov. is diagnosed by numerous cranial, axial, and appendicular autapomorphies. The holotype consists of a premaxilla, partial maxilla, quadrate, braincase with partial skull roof, several partial and complete cranial and middle cervical, cranial dorsal, and caudal vertebrae, ribs, complete scapulocoracoid, humerus, partial tibia, complete fibula, calcaneus, and partial pes. It displays numerous synapomorphies of the Diplodocoidea, including characters of both the Diplodocidae (Apatosaurus + (Diplodocus + Barosaurus)) and Dicraeosauridae (Dicraeosaurus + Amargasaurus). Preliminary phylogenetic analysis indicates that Suuwassea is a diplodocoid more derived than rebbachisaurids but in a trichotomy with both the Diplodocidae and Dicraeosauridae. Suuwassea represents the first well-supported, North American, non-diplodocid representative of the Diplodocoidea and provides new insight into the origins of both the Diplodocidae and Dicraeosauridae.
Although sauropods played a major role in terrestrial ecosystems during much of the Mesozoic Era, little effort has been directed toward diagnosing Sauropoda and establishing higher-level interrelationships among sauropods. As a consequence, the origin and evolution of major skeletal adaptations in sauropods has remained largely speculative.The cladistic analysis presented here focuses on higher-level relationships among sauropods. Based on 109 characters (32 cranial, 24 axial, 53 appendicular) for 10 sauropod taxa, the most parsimonious arrangement places four genera (Vulcanodon, Shunosaurus, Barapasaurus, and Omeisaurus) as a sequence of sister-taxa to a group of advanced sauropods, defined here as Neosauropoda. Neosauropoda, in turn, is composed of the sister-clades Diplodocoidea and Macronaria; the latter is a new taxon that includes Haplocanthosaurus, Camarasaurus, and Titanosauriformes. Titanosauriformes includes Brachiosauridae and Somphospondyli, a new taxon uniting Euhelopus and Titanosauria. Among macronarians, the position of Haplocanthosaurus is the least stable as a result of the absence of cranial remains.The basic structure of the phylogeny is resilient to various tests and establishes the evolutionary sequence of many functionally significant sauropod adaptations, such as the digitigrade posture of the manus in neosauropods. Other characteristic sauropod adaptations, such as narrow tooth crowns, increases in length and number of cervical vertebrae, and bifid neural spines, are shown to have evolved more than once. As these results underscore, the higher-level phylogeny of sauropods must be based on a broad sampling of character data.The fossil record of sauropods, although relatively limited during the early phase of the radiation (Late Triassic through Early Jurassic), nonetheless indicates that all major clades were established prior to the Late Jurassic, when substantial faunal interchange among major continental regions was still possible. The functional, temporal, and biogeographic implications of the higher-level phylogeny of sauropods are explored.
Fossils of the Early Cretaceous dinosaur, Nigersaurus taqueti, document for the first time the cranial anatomy of a rebbachisaurid sauropod. Its extreme adaptations for herbivory at ground-level challenge current hypotheses regarding feeding function and feeding strategy among diplodocoids, the larger clade of sauropods that includes Nigersaurus. We used high resolution computed tomography, stereolithography, and standard molding and casting techniques to reassemble the extremely fragile skull. Computed tomography also allowed us to render the first endocast for a sauropod preserving portions of the olfactory bulbs, cerebrum and inner ear, the latter permitting us to establish habitual head posture. To elucidate evidence of tooth wear and tooth replacement rate, we used photographic-casting techniques and crown thin sections, respectively. To reconstruct its 9-meter postcranial skeleton, we combined and size-adjusted multiple partial skeletons. Finally, we used maximum parsimony algorithms on character data to obtain the best estimate of phylogenetic relationships among diplodocoid sauropods. Nigersaurus taqueti shows extreme adaptations for a dinosaurian herbivore including a skull of extremely light construction, tooth batteries located at the distal end of the jaws, tooth replacement as fast as one per month, an expanded muzzle that faces directly toward the ground, and hollow presacral vertebral centra with more air sac space than bone by volume. A cranial endocast provides the first reasonably complete view of a sauropod brain including its small olfactory bulbs and cerebrum. Skeletal and dental evidence suggests that Nigersaurus was a ground-level herbivore that gathered and sliced relatively soft vegetation, the culmination of a low-browsing feeding strategy first established among diplodocoids during the Jurassic.
This beautifully illustrated 2007 volume describes the entire flora and fauna of the famous Lower Cretaceous Crato Formation of Brazil - one of the world's most important fossil deposits, exhibiting exceptional preservation. A wide range of invertebrates and vertebrates are covered, including extended sections on pterosaurs and insects. Two chapters are devoted to plants. Many of the chapters include descriptions of new species and re-descriptions and appraisals of taxa published in obscure places, rendering them available to a wider audience. Fossil descriptions are supported by detailed explanations of the geological history of the deposit and its tectonic setting. Drawing on expertise from around the world and specimens from the most important museum collections, this book forms an essential reference for researchers and enthusiasts with an interest in Mesozoic fossils.
Introduction The Crato Formation crops out around the northern, eastern and south-eastern flanks of the Chapada do Araripe plateau that sits at the boundaries of southern Ceará, western Pernambuco and south-eastern Piauí in north-eastern Brazilian caatinga (Martill, 1993; Neumann and Cabrera, 1999). The formation comprises a heterolithic sequence of clastic and carbonate strata currently restricted to within the Araripe Basin and a few smaller, interconnected basins such as the Serra do Vermelha and Cedro Basins (Assine, 1990, 1992; Carvalho, 2001). It is remarkable for its exceptionally well-preserved fossil assemblages and its limestones are economically important for cement manufacture and building materials (see Chapter 5). Parts of the formation, especially some of the limestone units, are also remarkable for their lateral continuity considering how thin some of the units are and how lithologically variable the sequence is vertically. There have been few detailed studies of the geology, stratigraphy or sedimentology of the Crato Formation as a stratigraphic unit, but the palaeontology of the lowermost of its limestone members has received considerable attention. The unit was first mapped in detail during the Projeto Santana as a separate entity (Moraes et al., 1976), although its definition was unclear. Beurlen (1962, 1963) provided a series of cross-sections across the Chapada do Araripe demonstrating its unconformable relationship with the basement and overlap by younger strata.
This chapter examines the evolutionary relationships of sauropods using cladistic analysis. It also describes in the detail their paleobiology, taphonomy, and paleoecology. Sauropod dinosaurs include the largest terrestrial animals ever to have existed. At present, Sauropoda comprises twenty-two genera. Sauropods have small skulls in relation to their body size, extremely elongate necks and tails, columnar limbs, and stout, barrel-shaped bodies. Sauropod remains have been recovered from all continents except Antarctica. They are found in mass accumulations (bone beds) in the Morrison Formation of the western United States, in the Tendaguru Beds of East Africa, in the Kota Formation of India, in the Lower Shaximiao Formation of the Sichuan Basin in China, and in the Cañodon Asfalto Formation of Patagonia.
Titanosauriformes was a globally distributed, long-lived clade of dinosaurs that contains both the largest and smallest known sauropods. These common and diverse megaherbivores evolved a suite of cranial and locomotory specializations perhaps related to their near-ubiquity in Mesozoic ecosystems. In an effort to understand the phylogenetic relationships of their early (Late Jurassic–Early Cretaceous) members, this paper presents a lower-level cladistic analysis of basal titanosauriforms in which 25 ingroup and three outgroup taxa were scored for 119 characters. Analysis of these characters resulted in the recovery of three main clades: Brachiosauridae, a cosmopolitan mix of Late Jurassic and Early Cretaceous sauropods, Euhelopodidae, a clade of mid-Cretaceous East Asian sauropods, and Titanosauria, a large Cretaceous clade made up of mostly Gondwanan genera. Several putative brachiosaurids were instead found to represent non-titanosauriforms or more derived taxa, and no support for a Laurasia-wide clade of titanosauriforms was found. This analysis establishes robust synapomorphies for many titanosauriform subclades. A re-evaluation of the phylogenetic affinities of fragmentary taxa based on these synapomorphies found no body fossil evidence for titanosaurs before the middle Cretaceous (Aptian), in contrast to previous reports of Middle and Late Jurassic forms. Purported titanosaur track-ways from the Middle Jurassic either indicate a substantial ghost lineage for the group or – more likely – represent non-titanosaurs. Titanosauriform palaeobiogeographical history is the result of several factors including differential extinction and dispersal. This study provides a foundation for future study of basal titanosauriform phylogeny and the origins of Titanosauria.
© 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 166, 624–671.
The main features of the phylogeny program TNT are discussed. Windows versions have a menu interface, while Macintosh and Linux versions are command-driven. The program can analyze data sets with discrete (additive, non-additive, step-matrix) as well as continuous ...
The carnivorous Dinosauria form a well-marked order, which the writer has called the Theropoda , in his classification of this group. Although much has been written about these reptiles since Buckland described Megalosaurus in 1824, but little has really been made out in regard to the structure of the skull, and many portions of the skeleton still remain to be determined.
Amargasuchus minor is described from the Early Cretaceous (Neocomian, of the La Amarga Formation of northwest Patagonia (Argentina). This species possesses a moderately high and narrow snout, strong festooning, a relatively large number of maxillary teeth and a well developed antorbital fenestra, and it lacks hypertrophied teeth, a combination of characters which suggests that it belongs to the crocodile family Trematochampsidae. Amargasuchus differs, however, from Trematochampsa in several respects. These include an almost straight lateral edge of the maxilla in dorsal aspect, a different distribution of the largest teeth, a longer snout, and laterally compressed alveoli. The new material supports a Gondwanan origin of the Trematochampsidae and agrees with a new phylogenetic hypothesis which considers trematochampsids to be the ancestral group of certain lineages of ziphodont mesosuschian crocodiles.
An incomplete skeleton from Puesto Morales (Neuquén Province, Argentina) is described as a new species of sauropod, Zapalasaurus bonapartei. The unit that yielded the holotype of this dinosaur is the Piedra Parada Member of the La Amarga Formation, whose age is regarded as Barremian-lower Aptian. Several characters are interpreted as autapomorphies of Zapalasaurus bonapartei: cervical vertebrae with a lamina
uniting the prezygapophysis and the zygapophyseal portion of the postzygodiapophyseal lamina, cervical vertebrae with the diapophyseal portion of the postzygodiapophyseal lamina reduced, cervical vertebrae with poorly developed spinoprezygapophyseal laminae, mid and posterior caudal vertebrae with anteroposteriorly elongated neural spines, whose anterodorsal corners are higher than their posterodorsal ones, and caudal centrum length doubles over first 20 vertebrae. Zapalasaurus bonapartei is considered as the sister group of the other diplodocoids (excluding Haplocanthosaurus). Diplodocoids were abundant in the Early Cretaceous, becoming extinct by the early Late Cretaceous. The record of Zapalasaurus bonapartei shows that, at least in the Neuquina Basin, basal diplodocoids were more diverse than previously thought.
Suuwassea
emilieae is a recently described dinosaur taxon discovered in the Upper Jurassic Morrison Formation of the western United States and the only non-diplodocid flagellicaudatan (Dinosauria: Sauropoda) known from North America. It retains sauropod symplesiomorphies that are unexpected in a Late Jurassic taxon and thus sheds light on the evolutionary origins of the Flagellicaudata. Despite being comparatively small, the holotype of Suuwassea demonstrates hallmarks of relatively advanced age. A phylogenetic analysis of 30 taxa and 331 characters retains Suuwassea in a trichotomy with the Diplodocidae (Apatosaurus + (Diplodocus + Barosaurus)) and the Dicraeosauridae (Dicraeosaurus + Amargasaurus). This lack of resolution is probably due to a combination of missing data, character conflict and poor incorporation of specimens referred to diplodocid taxa that differ from their holotype specimens and species holotypes. Middle Jurassic palaeobiogeographical reconstructions conflict with the hypothetical distribution of flagellicaudatans in the Middle and Late Jurassic based on their phylogeny, implying that physical barriers, such as epeiric seas, were not responsible for limiting their initial radiation. The postparietal foramen shared by Suuwassea, Dicraeosaurus, Tornieria and Amargasaurus may correlate to preferred existence in near-shore, terrestrial environments.
The main features of the phylogeny program TNT are discussed. Windows versions have a menu interface, while Macintosh and Linux versions are command-driven. The program can analyze data sets with discrete (additive, non-additive, step-matrix) as well as continuous characters (evaluated with Farris optimization). Effective analysis of large data sets can be carried out in reasonable times, and a number of methods to help identifying wildcard taxa in the case of ambiguous data sets are implemented. A variety of methods for diagnosing trees and exploring character evolution is available in TNT, and publication-quality tree-diagrams can be saved as metafiles. Through the use of a number of native commands and a simple but powerful scripting language, TNT allows the user an enormous flexibility in phylogenetic analyses or simulations.
© The Willi Hennig Society 2008.
Diplodocoidea includes some of the first well-known sauropod dinosaurs, including such late 19th century and early 20th century discoveries as Apatosaurus, Diplodocus, and Dicraeosaurus. As a consequence of their long history of study, the basic set of suprageneric diplodocoid interrelationships is well resolved, and the diagnostic features of each genus are well established. However, intergeneric relationships are less resolved, including the relationships of putatively basal taxa like Amphicoelias and Haplocanthosaurus, the flagellicaudatan Suuwassea, and the highly specialized rebbachisaurids. For the rebbachisaurids, this uncertainty is coupled with a recent surge in the discovery of new taxa. Comparative cladistic methods demonstrate that character and taxon sampling need to be improved before greater phylogenetic resolution can be expected. Here, I present a new phylogenetic analysis that resolves many of the outstanding questions regarding the relationships within Diplodocoidea and examines palaeobiogeographical trends within the group. Suuwassea is recovered as a basal dicraeosaurid (the only Laurasian member of the group), and two distinct clades of rebbachisaurids are identified: a group closely allied with Nigersaurus and a clade associated with Limaysaurus. Amphicoelias, Amazonsaurus, and Haplocanthosaurus are provisionally placed as successively less-derived taxa at the base of Diplodocoidea. A North American origin for Diplodocoidea and Flagellicaudata is hypothesized based on the geographical and temporal distribution of those taxa. Rebbachisaurid taxa demonstrate a South American/African vicariance pattern, but the timing of the event pre-dates the proposed final rifting of those continents by c. 40 million years; the meaning of this discrepancy is uncertain.
© 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161, 872–915.
Sauropoda is among the most diverse and widespread dinosaur lineages, having attained a near-global distribution by the Middle Jurassic that was built on throughout the Cretaceous. These gigantic herbivores are characterized by numerous skeletal specializations that accrued over a 140 million-year history. This fascinating evolutionary history has fuelled interest for more than a century, yet aspects of sauropod interrelationships remain unresolved. This paper presents a lower-level phylogenetic analysis of Sauropoda in two parts. First, the two most comprehensive analyses of Sauropoda are critiqued to identify points of agreement and difference and to create a core of character data for subsequent analyses. Second, a generic-level phylogenetic analysis of 234 characters in 27 sauropod taxa is presented that identifies well supported nodes as well as areas of poorer resolution. The analysis resolves six sauropod outgroups to Neosauropoda, which comprises the large-nostrilled clade Macronaria and the peg-toothed clade Diplodocoidea. Diplodocoidea includes Rebbachisauridae, Dicraeosauridae, and Diplodocidae, whose monophyly and interrelationships are supported largely by cranial and vertebral synapomorphies. In contrast, the arrangement of macronarians, particularly those of titanosaurs, are based on a preponderance of appendicular synapomorphies. The purported Chinese clade 'Euhelopodidae' is shown to comprise a polyphyletic array of basal sauropods and neosauropods. The synapomorphies supporting this topology allow more specific determination for the more than 50 fragmentary sauropod taxa not included in this analysis. Their distribution and phylogenetic affinities underscore the diversity of Titanosauria and the paucity of Late Triassic and Early Jurassic genera. The diversification of Titanosauria during the Cretaceous and origin of the sauropod body plan during the Late Triassic remain frontiers for future studies.
A data-matrix of 205 osteological characters for 26 sauropod taxa is subjected to cladistic analysis. Two most parsimonious trees are produced, differing only in the relationships betweenEuhelopus,OmeisaurusandMamenchisaurus. The monophyly of the Euhelopodidae (includingShunosaurus) is supported by seven synapomorphies. The Cetiosauridae (Patagosaurus,CetiosaurusandHaplocanthosaurus) is paraphyletic with respect to the Neosauropoda. The latter clade divides into two major radiations—the «Brachiosauria» (Camarasaurus, brachiosaurids and titanosauroids), and the Diplodocoidea (nemegtosaurids, dicraeosaurids, diplodocids andRebbachisaurus). Further evidence for the inclusion ofOpisthocoelicaudiain the Titanosauroidea is presented.Phuwiangosaurus, a problematic sauropod from Thailand, may represent one of the most plesiomorphic titanosauroids. ‘Peg’-like teeth have evolved at least twice within the Sauropoda. The postspinal lamina, on the neural spines of middle and caudal dorsal vertebrae, represents a neomorph rather than a fusion of pre-existing structures. Forked chevrons may have evolved convergently in the Euhelopodidae and the diplodocid-dicraeosaurid clade, or they may have been acquired early in sauropod evolution and subsequently lost in the «Brachiosauria». The strengths and weaknesses of the data-matrix and tree topologies are explored using bootstrapping, decay analysis and randomization tests. Several nodes are only poorly supported, but this seems to reflect the large proportion of missing data in the matrix (46%), rather than an abnormally high level of homoplasy. The results of the randomization tests indicate that the data-matrix probably contains a strong phylogenetic ‘signal’. The relationships of some forms, such asHaplocanthosaurus, are influenced by the inclusion or exclusion of certain taxa with unusual combinations of character states. Such a result suggests that there are dangers inherent in the view that ‘higher’ level sauropod phylogeny can be accurately reconstructed using only a small number of well-known taxa.
- H A Leanza
- S Apesteguía
- F E Novas
- M S De La Fuente
Leanza, H.A., Apesteguía, S., Novas, F.E., de la Fuente, M.S., 2004. Cretaceous
terrestrial beds from the Neuqu en Basin (Argentina) and their tetrapod assemblages. Cretaceous Research 25, 61e87.
Supplementary data Supplementary data related to this article can be found at http
- A Appendix
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://dx.doi.org/10.
1016/j.cretres.2016.04.002.