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... 'Gigantosaurus' was preoccupied and was replaced with the generic name Tornieria by Sternfeld (1911) and G. dixeyi from Malawi became known as Tornieria dixeyi without further justification [3]. The generic name Tornieria was later changed to Janenschia by Wild (1991) [4]. Because the taxon from Malawi is distinct from the titanosaurid genus Janenschia, which was recovered from Jurassic beds in Tanzania, a new generic name, Malawisaurus, was erected by Jacobs et al. (1993) to accommodate the titanosaurid species from Malawi [5]. ...
... 'Gigantosaurus' was preoccupied and was replaced with the generic name Tornieria by Sternfeld (1911) and G. dixeyi from Malawi became known as Tornieria dixeyi without further justification [3]. The generic name Tornieria was later changed to Janenschia by Wild (1991) [4]. Because the taxon from Malawi is distinct from the titanosaurid genus Janenschia, which was recovered from Jurassic beds in Tanzania, a new generic name, Malawisaurus, was erected by Jacobs et al. (1993) to accommodate the titanosaurid species from Malawi [5]. ...
A braincase of the Cretaceous titanosaurian sauropod Malawisaurus dixeyi, complete except for the olfactory region, was CT scanned and a 3D rendering of the endocast and inner ear was generated. Cranial nerves appear in the same configuration as in other sauropods, including derived features that appear to characterize titanosaurians, specifically, an abducens nerve canal that passes lateral to the pituitary fossa rather than entering it. Furthermore, the hypoglossal nerve exits the skull via a single foramen, consistent with most titanosaurians, while other saurischians, including the basal titanosauriform, Giraffatitan, contain multiple rootlets. The size of the vestibular labyrinth is smaller than in Giraffatitan, but larger than in most derived titanosaurians. Similar to the condition found in Giraffatitan, the anterior semicircular canal is larger than the posterior semicircular canal. This contrasts with more derived titanosaurians that contain similarly sized anterior and posterior semicircular canals, congruent with the interpretation of Malawisaurus as a basal titanosaurian. Measurements of the humerus of Malawisaurus provide a body mass estimate of 4.7 metric tons. Comparison of body mass to radius of the semicircular canals of the vestibular labyrinth reveals that Malawisaurus fits the allometric relationship found in previous studies of extant mammals and Giraffatitan brancai. As in Giraffatitan, the anterior semicircular canal is significantly larger than is predicted by the allometric relationship suggesting greater sensitivity and slower movement of the head in the sagittal plane.
... However, the proximal morphology of MMS-PV-16 is rather rounded, as in Wintonotitan and Argyrosaurus (Lydekker, 1893;Hocknull et al., 2009), and differs from the "V-shape" seen in most neosauropods and several titanosaurians, such as Elaltitan, Dreadnoughtus, Bonitasaura, and Kaijutitan (Apesteguía, 2004;Mannion and Otero, 2012;Lacovara et al., 2014;Filippi et al., 2019). In anterior view, the proximal surface is convex due to the development of the olecranon process that rises above the proximal articular surface on the posterior margin of the epiphysis, as in Janenschia and several titanosaurians, such as Neuquensaurus, Kaijutitan, Argyrosaurus, and Elaltitan (Lydekker, 1893;Wild, 1991;Filippi et al., 2019;Mannion and Otero, 2012;Mannion et al., 2019). The anterior (radial) fossa is wide and slightly deeper on the medial margin, where it is limited by a prominent and anteriorly directed medial process (Fig. 5C). ...
In the Neuquén Basin, the Portezuelo Formation (Turonian-Coniacian, Upper Cretaceous) is represented by extended fluvial outcrops that are well-known for yielding an abundant and diversified vertebrate fossil record. However, most of the sauropod fossil record is represented by incomplete specimens, and only two taxa are formally described for the upper Turonian–lower Santonian of the Neuquén Basin: Malarguesaurus and Futalognkosaurus. In this contribution we report new sauropod specimens composed of partially associated axial and appendicular elements coming from the upper section of the Portezuelo Formation of the Los Bastos locality, in the southern Neuquén Basin. The bones show a set of morphological features that allow us to refer them to a titanosaur sauropod: a “cone-chisel-like” tooth, procoelic caudal vertebrae, a dorsally expanded ulna olecranon, and a femur with a prominent lateral bulge and an elliptical diaphysis in cross-section. The phylogenetic analysis recovers the sauropod remains as an unstable colossosaurian within Titanosauria, an effect likely attributable to the incomplete condition of the specimens. Nevertheless, osteological and phylogenetic analyses, together with morphological comparisons with the sauropod fossil record of the Portezuelo Formation, suggest that the new specimens represent a titanosaur different to previously known taxa. Pending better preserved and more complete remains from Los Bastos, the new evidence allows us to improve our knowledge of sauropod diversity during the upper Turonian–lower Santonian, at least in the southern Neuquén Basin.
... Ornithischians are much less diverse and are represented only by the stegosaur Kentrosaurus aethiopicus and the small ornithopod Dysalotosaurus lettowvorbecki (Hennig 1925, Janensch 1955 et al. , Remes 2006, the theropods Elaphrosaurus bambergi and at least four more taxa, including two tetanurans and two ceratosaurs (Janensch 1925, Rauhut, unpublished data Raath and McIntosh 1987], but the material collected so far is fragmentary and identifications of taxa have to be treated with caution. Raath and McIntosh (1987) identified at least four, possibly five sauropod taxa from these beds, and referred them to the genera Brachiosaurus, Janenschia (=Tornieria in the cited work, for the convoluted taxonomic history of this genus see Wild 1991), Dicraeosaurus, Barosaurus, and, possibly, Camarasaurus. However, only the remains referred to Brachiosaurus might be diagnostic on generic level, the rest of the material would better be understood as basal titanosaur indet., two diplodocoids indet. ...
... From the Gondwanan Late Jurassic, referred titanosauriforms are Giraffatitan (Janensch 1929) and, possibly, Janenschia (see McIntosh 1990bWild 1991;Wilson 2002;Upchurch et al. 2004). Finally, Rauhut (2006) identified a new brachiosaurid in Cañadón Calcáreo Formation in Chubut (Argentina) from Tithonian sediments. ...
Lusotitan atalaiensis was one of the first sauropod taxa established for the Upper Jurassic of the Lusitanian Basin (Portugal). The lectotype of L. atalaiensisfound in Peralta (Lourinhã) was firstly considered as new species of Brachiosaurus, considering the similarities with Brachiosaurusand Giraffatitan. This specimen was originally considered as a brachiosaurid, and more recently, a cladistics analysis, suggested Lusotitan as a basal macronarian and a possible member of Brachiosauridae. In this study, new information is provided about the Lusotitanlectotype, with reinterpretation and description of previously described and undescribed elements (e.g. sacral vertebrae, chevrons, ulna, ischium, pubis or fibula). The validity of this taxon is confirmed by a revised diagnosis. The present comparative study and the phylogenetic analyses suggest the assignation of Lusotitanto Brachiosauridae supported by the presence of pronounced and dorsoventrally short deltopectoral crest, short ischiatic contribution to the acetabulum and radius length/tibia length ratio >1. The presence of brachiosaurids in the Portuguese Upper Jurassic record is confirmed, supporting the presence of a wide paleobiogeographic distribution for Brachiosauridae during the Late Jurassic, being present in Europe, North America and Africa
... From the Gondwanan Late Jurassic, referred titanosauriforms are Giraffatitan (Janensch 1929) and, possibly, Janenschia (see McIntosh 1990bWild 1991;Wilson 2002;Upchurch et al. 2004). Finally, Rauhut (2006) identified a new brachiosaurid in Cañadón Calcáreo Formation in Chubut (Argentina) from Tithonian sediments. ...
Mocho P, Royo-Torres R, Ortega F. 2016. Evolutionary history of Late Jurassic sauropods of the Lusitanian Basin (Portugal) and presentation of a new basal macronarian form, p.190. In: Farke A, MacKenzie A, Miller-Camp J (eds.), Society of Vertebrate Paleontology, October 2016, Abstract of papers, 76th Annual Meeting, Grand America Hotel, Salt Lake City, Utah, USA, October 26–29, 2016
... Arratia et al. (2002) described interesting fish assemblages (hybodonts, batoids and neopterygians) from the three Saurian Beds, but they provide no additional information about their age. Seven sauropod species are currently known from Tendaguru, namely the brachiosaurid Giraffatitan brancai (Janensch, 1914;Paul, 1988;Taylor, 2009), the diplodocids Tornieria africana (Fraas, 1908; see Remes, 2006), Australodocus bohetii (Remes, 2007), two species of the dicraeosaurid Dicraeosaurus (D. hansemanni and D. sattleri) (Janensch, 1914), Janenschia robusta Wild, 1991 andTendaguria tanzaniensis Bonaparte et al., 2000, the relationships of which among sauropods are unclear. Theropods include among others a possible primitive spinosaur (Buffetaut, 2008, in press). ...
... Therefore the previous earliest substantiated "titanosaur" tracks are from the Late Jurassic (Wilson, and Carrano, 1999;Day et al, 2002). The oldest known remains of titanosaurs belong to Janenschia (Wild, 1991) and Brohisaurus from the Late Jurassic of Tanzania and Pakistan respectively. Thus after the wide gauge sauropod tracks from Ardley (U.K), the Baroch site (Pakistan) is the second locality which provide the direct evidence that titanosaurs had diverged from other sauropods by the Bathonian. ...
... Tendaguru sauropods, such as Janenschia (Wild, 1991) and ...
A description is provided of the first sauropod remains (i.e., isolated vertebrae and appendicular bones) from the Late Jurassic of Aysén, in Chilean Patagonia (Toqui Formation, late Tithonian). Although the bones found are fragmentary, they still allow the recognition of an unsuspected sauropod diversity for this period in South America. The materials suggest the presence of at least three different sauropod lineages: an indeterminate group of sauropods, possible Titanosauriformes, and Diplodocoidea. A phylogenetic analysis of this last clade supports the placement of the remains within Diplodocinae and also provides the first unequivocal record of this clade in Late Jurassic rocks of South America. These records provide important information about the poorly known evolutionary history of sauropods in South America before the Cretaceous.
... The proximal triradiate articular surface is nearly flat and devoid of the conspicuous olecranon process present in most titanosaurs. Instead, the olecranon is low, as in all sauropods except derived titanosaurs and Janenschia (Wild, 1991). This condition could be related to ontogenetic variation (Tidwell and Wilhite, 2005) and the juvenile ontogenetic stage of the holotype (Gallina, 2012). ...
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.
... Considered for a long time as the most endemic group of Gondwanan dinosaurs, titanosauriforms (Titanosauria) are now known from an increasing number of localities of the northern hemisphere, including Europe (Sanz et al., 1999;Mannion and Upchurch, 2011;Vila et al., 2012;Diez Diaz et al., 2013;, and China (Tang et al., 2001;Mo et al., 2006;Xu et al., 2006;Barrett and Wang, 2007) (see also Wilson, 2006;Fanti, 2012). The oldest representative of the titanosaurian lineage are probably Australodocus and Janenschia, from the Tithonian beds of Tanzania (Janensch, 1961;Wild, 1991;Upchurch et al., 2004;Curry Rogers, 2005;Remes, 2007), although the affinities of both are controversial (see also Carballido et al., 2011;D'Emic, 2012;. In continental Afro-Arabia, Cretaceous titanosaurians have been also reported from Niger (Sereno and Brusatte, 2008), Malawi (Jacobs et al., 1993;Gomani, 2005), Egypt (Rauhut and Werner, 1997;Smith et al., 2001), and more recently from Kenya (Sertich et al., 2006), Angola (Jacobs et al., 2006;Mateus et al., 2011), Jordan , and Morocco (Mannion and Barrett, 2013) supporting a Pan-African distribution of this clade. ...
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.
... The trochanter anterior is a well developed depression. The Upper Jurassic Janenschia was included in the Titanosauridae e. g. by MCINTOSH (1990) and WILD (1991), but BONAPARTE et al. (2000 redescribed Janenschia as a camarasaurid. The earlier conclusion is now again supported by the lack of a strong developed, steep linea diagonalis fibulae known only in the camarasaurid Camarasaurus and RUC1999I 207. ...
Fragmentary isolated remains of large (up to 20 m or more) sauropods from the Middle Jurassic (Bajocian) Khadir Formation
of Khadir Island (Kachchh, W India) are described and compared in detail. Three of the bone fragments (a metacarpal, a first
pedal claw and a fibula) can be assigned with confidence to the Camarasauromorpha and represent the oldest known record of
that derived dinosaur group. The new finds from western India further close a temporal and geographical gap in our knowledge
of sauropods and contribute to understanding their early phylogeny.
Isolierte Überreste eines großen (bis zu 20 m oder mehr langen) Sauropoden werden aus der mitteljurassischen (Bajocium) Khadir
Formation auf Khadir Island (Kachchh, W Indien) beschrieben und detailliert verglichen. Drei der Knochenfragmente (ein Metacarpale,
eine erste Fußklaue und eine Fibula) können mit Sicherheit einem Vertreter der Camarasauromorpha zugeordnet werden und repräsentieren
damit den ältesten Nachweis dieser abgeleiteten Dinosaurier-Gruppe. Die neuen Funde aus dem westlichen Indien schließen eine
zeitliche und geographische Lücke in unserer Kenntnis der Sauropoden und tragen zum Verständnis ihrer frühen Phylogenie bei.
A juvenile specimen of the titanosaurid sauropod Alamosaurus sanjuanensis, recovered from just below the Cretaceous/Tertiary boundary horizon in Big Bend National Park, Texas, is from an individual less than half the size of adult specimens referred to this species. The disarticulated skeleton was preserved in deposits of a shallow flood-plain pond and includes elements not previously described, allowing for an improved diagnosis for this species. The elongate opisthocoelous cervical vertebrae have non-bifid posteriorly deflected neural spines with deep postspinal fossae. The dorsal vertebrae have wide spatulate neural spines with strong prespinal laminae, and lack hyposphene-hypantrum articulations. Alamosaurus sanjuanensis exhibits a unique morphology of the ischium, evident even in this juvenile specimen. Comparison with other titanosaurid species suggests that A. sanjuanensis is most closely related to an unnamed titanosaur from Peiropolis, Brazil and Neuquensaurus australis from Argentina.
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 juvenile specimen of the titanosaurid sauropod Alamosaurus sanjuanensis, recovered from just below the Cretaceous/Tertiary boundary horizon in Big Bend National Park, Texas, is from an individual less than half the size of adult specimens referred to this species. The disarticulated skeleton was preserved in deposits of a shallow flood-plain pond and includes elements not previously described, allowing for an improved diagnosis for this species. The elongate opisthocoelous cervical vertebrae have non-bifid posteriorly deflected neural spines with deep postspinal fossae. The dorsal vertebrae have wide spatulate neural spines with strong prespinal laminae, and lack hyposphene-hypantrum articulations. Alamosaurus sanjuanensis exhibits a unique morphology of the ischium, evident even in this juvenile specimen. Comparison with other titanosaurid species suggests that A. sanjuanensis is most closely related to an unnamed titanosaur from Peiropolis, Brazil and Neuquensaurus australis from Argentina.
Since the holotype of Janenschia robusta (E. FRAAS) is based on an incomplete right hind limb, only specimens with comparable parts of the skeleton can be properly referred to that species. This is the case with the material from Tendaguru site P (JANENSCH 1925, 1929a), which consists of fore and hind limb skeletons from two individuals. The remaining sauropod skeletal material, i. e. the isolated anterior dorsal vertebrae, an articulated tail, and an anterior caudal vertebra, collected in the surroundings of Tendaguru Hill (JANENSCH 1929a) can not be properly referred to Janenschia due to the incompleteness of the type material of Janenschia robusta (E. FRAAS). Janenschia robusta (E. FRAAS) is redescribed and diagnosed, on the basis of the holotype and referred specimens from Tendaguru site P. Morphological comparisons suggest closer relationships between Janenschia and Camarasaurus. A new genus and species, Tendaguria tanzaniensis gen. et sp. nov. is proposed for two anterior dorsal vertebrae collected at Nambango (JANENSCH 1929a). Tendaguria gen. nov. is mainly diagnosed by extremely reduced neural spines which are not higher than the neural arch. They are connected with the postzygapophysial laminae and the epipophyses building a common dorsal plane. Comparison of these anterior dorsal vertebrae with those of different sauropod genera suggests that the vertebrae of Tendaguria gen. nov. represent the more derived type. The neural arch pattern in Tendaguria tanzaniensis gen. et sp. nov. points to a strong modification in the position and function of the episomatic musculature whose origin and insertion are both on these vertebrae. An articulated tail consisting of 30 caudal vertebrae collected at site G near Tendaguru Hill (JANENSCH 1929a), formerly referred to Janenschia and considered to have titanosaurid affinities, is described and compared to other titanosaurs. This caudal vertebrae series exhibits decreasing procoely posteriorly. The first 10 vertebrae are procoelous, the following 3 caudals are nearly amphiplatyan, and the last 17 are slightly amphicoelous. The procoelous condition in anterior caudal vertebrae is also known in Jurassic sauropods from China (e. g. Bellusaurus, Mamenchisaurus). This vertebral type was developed independently in different sauropod lineages. In the Late Cretaceous family Titanosauridae, all caudal vertebrae are characterized by procoely. It is concluded that sauropod families can not be distinguished by their procoelous anterior caudal vertebrae.
This study demonstrates that the presacral vertebrae represent a rich source of information for understanding the evolution and systematics of sauropodomorphs. In the basal dinosauromorph Marasuchus three morphological types of vertebrae are recognized, a condition further developed by sauropodomorphs. Within Prosauropoda, the melanorosaurid Riojasaurus shows the most primitive condition in the number and organization of the cervical vertebrae: it has 9 cervicals, the first 5 of which exhibit the cervical morphological type, whereas the last 4 correspond to the dorsal morphological type. Plateosaurus is more derived than Riojasaurus in characters of the neck. The primitive sauropod-type of vertebra is more advanced than the typical prosauropod vertebra, but it shows more primitive characters than the cetiosaurid type. It is considered that the presacrals of cetiosaurid type correspond to an evolutionary stage that might have made gigantism possible, triggering the adaptive radiation recorded in the Upper Jurassic of North America, Africa and Asia. In diplodocids the presacrals show clear relationships to the cetiosaurid type, but there are a higher number of cervicals, and opisthocoely of centra is more developed. Significant differences in the cervical vertebrae of Apatosaurus with respect to those of Diplodocus, Camarasaurus and other sauropods suggest that Apatosaurus should be placed in a family of its own: Apatosauridae nov. Presacrals of brachiosaurid type, examined in Brachiosaurus brancai only because the generic placement of B. altithorax is doubtful, posess several characters, such as opisthocoely extending to the last dorsal, that are more advanced than in Patagosaurus and Diplodocus. Other characters of the brachiosaurid type of vertebrae are more primitive than those of the Diplodocus, thus suggesting origin from a condition more primitive than that exemplified by the cetiosaurid type. Restudy of presacrals of camarasaurid type does noconfirm previous interpretations of these vertebrae as primitive; furthermore, several features are more derived than in Diplodocus. Also, it is proposed that the dicraeosaurid type might have evolved independently of other presacral types, the cetiosaurid type probably representing the ancestral condition. Presacrals of Haplocanthosaurus have a distinct morphology; thus, this genus is included in Haplocanthosauridae nov. Titanosaurs exhibit several morphological types of presacrals, indicating several levels of organization. Distinctive features are present in the cervical region of members of Titanosauridae s.str., e.g., a unique design of the infrapostzygapophyseal constriction, the reduced distance between the centrum and the zygapophyses, the near absence of neural spines. In general, Malawisaurus, Andesaurus and Argentinosaurus are more primitive than Titanosauridae s.str. Tentative interpretation of the significance of several complex characters involving presacral vertebrae, such as the sigmoid neck, the dorsoventral extension of the dorsals, the transversely wide neural spines, the relation between the number of cervicals and dorsal, the pleurocoels and the supraneural cavity, are discussed. In addition, a new prosauropod genus and species, Lessemsaurus sauropoides, diagnosed by its high neural arches and infrapostzygapophyseal constriction of the posterior cervicals is erected.
Upper Jurassic and Lower Cretaceous sedimentary layers are represented in the Brazilian Paran�a Basin by
the fluvioeaeolian Guar�a Formation and the Botucatu Formation palaeoerg, respectively, overlapped by
the volcanic Serra Geral Formation. In Uruguay, the corresponding sedimentary units are named Batoví
and Rivera Members (both from the Tacuaremb�o Formation), and the lava flows constitute the Arapey
Formation (also in Paran�a Basin). Despite the lack of body fossils in the mentioned Brazilian formations,
Guar�a/Batoví dinosaur fauna is composed of theropod, ornithopod and wideegauge sauropod tracks and
isolated footprints, as well as theropod teeth. In turn, the Botucatu/Rivera dinosaur fauna is represented
by theropod and ornithopod ichnofossils smaller than those from the underlying units. The analysis of
these dinosaur ichnological records and comparisons with other global Mesozoic ichnofauna indicates
that there is a size reduction in dinosaur fauna in the more arid Botucatu/Rivera environment, which is
dominated by aeolian dunes. The absence of sauropod trackways in the Botucatu Sandstone fits with the
increasingly arid conditions because it is difficult for heavy animals to walk on sandy dunes, as well as to
obtain the required amount of food resources. This comparison between the Upper Jurassic and Lower
Cretaceous dinosaur fauna in south Brazil and Uruguay demonstrates the influence of aridization on the
size of animals occupying each habitat.
The disappearance of nonavian dinosaurs is only a small part of a greater class of extinctions known as “mass extinctions.” Mass extinctions are global events characterized by unusually high rates of extinction. The five episodes of mass extinctions in Earth history are the Permo-Triassic extinction, the Late Ordovician extinction, the Late Devonian extinction, the Triassic-Jurassic extinction, and the Cretaceous-Tertiary (K/T) extinction. This chapter focuses on patterns of geologic and biotic changes that occurred during the Cretaceous-Tertiary (K/T) extinction. It also highlights the similarities and differences in interpretations of geologic and fossil records. It concludes with two scenarios explaining the differing views about dinosaur extinction.
Wintonotitan wattsi, a Cretaceous titanosauriform sauropod from central Queensland, Australia, is redescribed following a full revision of its osteology. The holotype specimen, a partial postcranial skeleton derived from the lower Upper Cretaceous Winton Formation, comprises axial and appendicular elements. Wintonotitan has been commonly resolved as a non-titanosaurian somphospondylan titanosauriform since its description, in contrast to its more derived contemporary Diamantinasaurus matildae. We provide a detailed redescription, taking this opportunity to correct four misinterpretations made in the original description of Wintonotitan that impact on our understanding of this taxon: the right ulna was originally described as the left and vice versa; the left metacarpus was incorrectly described as being from the right side; metacarpal IV was described as metacarpal V and vice versa; and the ilium was incorrectly oriented. The reassessment of the metacarpus is particularly important, since it shows that a proximal fossa is present on metacarpals I, II and III, which might have been occupied by either the strongly convex distal end of the radius or a (possibly unossified) carpal element. We provide a review of titanosauriform metacarpal morphology to support our reassessments. Our revision of the osteology of Wintonotitan results in the identification of several previously unrecognized autapomorphies, augmenting and revising its original diagnosis. We provide additional support for the previous referral of four caudal vertebrae from south-east of Winton, Queensland, to W. wattsi. Furthermore, we demonstrate that a tentative report of titanosaur osteoderms from the Winton Formation was based on misidentification of dorsal vertebral neural spines pertaining to the holotype of W. wattsi. Consequently, titanosaur osteoderms are currently unknown from Australia. Following our revision and reinterpretation of a number of elements, we re-examine the phylogenetic placement of Wintonotitan, supporting its position as a non-titanosaurian somphospondylan titanosauriform, with no close relationship with the contemporaneous lithostrotian titanosaur Diamantinasaurus.
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.
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 osteology of Diamantinasaurus matildae, the most complete Cretaceous sauropod described from Australia to date, is comprehensively reassessed. The preparation of additional material from the type locality, pertaining to the same individual as the holotype, sheds light on the morphology of the axial skeleton and provides additional information on the appendicular skeleton. The new material comprises two dorsal vertebrae, an incomplete sacrum (including four partial coalesced vertebrae), the right coracoid, the right radius, and a previously missing portion of the right fibula. In this study we identify thirteen autapomorphic characters of Diamantinasaurus, and an additional five characters that are locally autapomorphic within Titanosauriformes. This work provided an opportunity to revisit the phylogenetic placement of Diamantinasaurus. In two independent data matrices, Diamantinasaurus was recovered within Lithostrotia. One analysis resolved Diamantinasaurus as the sister taxon to the approximately coeval Tapuiasaurus from Brazil, whereas the second analysis recovered Diamantinasaurus as the sister taxon to Opisthocoelicaudia from the latest Cretaceous of Mongolia. The characters supporting the recovered relationships are analysed, and the palaeobiogeographical implications of the lithostrotian status of Diamantinasaurus, and of the body fossil record of Australian Cretaceous terrestrial vertebrates as a whole, strongly suggest close ties to South America in particular, and to Gondwana more generally.
In the 169 years since Owen named a tooth as Cardiodon, the study of sauropod dinosaurs has gone through several distinct periods. In the early years, a sequence of descriptions of isolated skeletal elements gave rise to a gradually emerging understanding of the animals that would later be known as sauropods. The second phase began in 1871 with Phillips's description of Cetiosaurus oxoniensis, the first reasonably complete sauropod, and continued with the Marsh-Cope Bone Wars and the description of the nearly complete sauropods Camarasaurus and 'Brontosaurus' (= Apatosaurus). As these and other genera became better known, a third phase began, exploring not just the remains but the lives of these giants, with arguments about posture and habitat to the fore, and with the public becoming increasingly aware of sauropods owing to skeletal mounts. A 'dark age' followed during and after World War II, with sauropods considered uninteresting evolutionary dead ends and largely ignored. This was brought to an end by the 'dinosaur renaissance' that began in the late 1960s, since when work has recommenced with new vigour, and the public has been introduced to a more vigorous and terrestrial image of sauropods through film and television. Both diversity and disparity of sauropods continue to increase through new descriptive work, and the group is now seen as more fascinating and worthy of study than ever before.
Body-mass estimates have been made for 220 of the over 300 generally accepted dinosaur genera. The 1–10 ton body-mass category is the modal one for all dinosaur genera, dinosaurs on nearly every continent, dinosaurs during most stages of the Mesozoic, and dinosaurs in two of the three peak historical periods of dinosaur discoveries. Carnivorous dinosaurs were much smaller than herbivores during the Late Jurassic and again in the Late Cretaceous: at other times the two were roughly equivalent in mass. In terms of discovery of dinosaur genera over time, there has been a simultaneous increase in proportion of very small (under 10 kg) dinosaurs and a relative decline in giant dinosaurs (10–100 tons). This suggests that early researchers tended to collect giant dinosaurs.
Dinosaurian biogeography may have been largely controlled by the Mesozoic fragmentation of Pangea and the reassembly of its fragments into a new, boreal supercontinent (Laurasia). Although Late Triassic and Early Jurassic dinosaurs were globally distributed, Chinese assemblages were dominated by endemic forms from Middle Jurassic into Early Cretaceous time. The affinities of Aptian - Albian immigrants to Asia were strongest with North America and Europe rather than Gondwana, indicating that the northern and southern hemispheres had by then attained their biogeographic identity. This distinctiveness was maintained through Cretaceous time. Europe seems to have been a buffer area between Paleolaurasia and Gondwana; of the northern continents it was the most strongly influenced by Gondwana dispersants. Late Jurassic dinosaur assemblages in North America exhibited Gondwana affinities, but by Late Cretaceous time they were dominated by forms of Asian ancestry.
The history of dispersal of biota during the Mesozoic in the southern hemisphere is
much debated. Clearly, the sequential break-up of Gondwana produced physical barriers
that must, variously, have hampered dispersal events, and therefore impacted
the phylogenetic hypotheses. Did various terrestrial organisms undergo dispersal via
recently claimed continental bridges? When were the geographic and environmental
conditions at an optimum for diffusion during Mesozoic times? Dinosaurs are
arguably the most relevant group for illuminating the biogeography of the southern
landmasses during the Cretaceous. Their vast stratigraphic and geographic occurrence
is intimately linked to the evolution of Gondwana. Recent discoveries from
all southern landmasses challenge several vicariant models. This study summarizses
the most significant geologic, palaeogeographic, palaeontologic, and phylogenetic
data on Cretaceous Gondwanan dinosaur evolution, with particular emphasis on the
ephemeral land bridges that bulk large in recently developed biogeographic models.
Comparison between different datasets accords with a complex and sequential mix
of vicariance and dispersal patterns characterizing the fabric of dinosaurian faunas at
that time. This study probes the significance of ephemeral intercontinental connections
with regard to the biotic dispersal in the Late Cretaceous. An earlier peak in
dinosaur diversity and dispersals seems likely.
Quetecsaurus rusconii gen. et sp. nov. is a new titanosaur (Dinosauria, Sauropoda) from the Neuquen Basin of Mendoza Province, Argentina. The specimen comes from red mudstones of the Cerro Lisandro Formation (middle-late Turonian, Upper Cretaceous), and is the first sauropod with well-preserved remains to be discovered in this formation. The holotype includes a postorbital, teeth, the atlas, a posterior cervical vertebra, an incomplete dorsal vertebra, a posterior caudal centrum, dorsal ribs, a coracoid, fragments of a humerus, radius and ulna, and five metacarpals. It is characterized by the following combination of autapomorphies: (1) intercentrum of atlas with a prominent anteroventral border and expanded posteroventral processes; (2) posterior cervical neural spines with incipient lateral expansions; and (3) humerus with strongly sigmoid proximal border, rounded proximomedial border, and angular proximolateral corner. A preliminary cladistic analysis placed Quetecsaurus as a sister taxon of Lognkosauria (Mendozasaurus + Futalognkosaurus). Quetecsaurus shares with the lognkosaurs the presence of cervical neural spines with 'lateral laminae', but relatively reduced in comparison with those taxa. This discovery provides new information on the diagnosis of Lognkosauria within South American titanosaurs.
The fossil record of archosaurs - crocodylomorphs, pterosaurs and dinosaurs - from the Jurassic of the Southern Hemisphere is critically reviewed, and its evolutionary implications are evaluated. Although several important faunas and also isolated finds are known from Gondwana, the record in total is still very patchy, and any evolutionary scenario based on this record should be seen as tentative. Compared to the Northern Hemisphere, southern archosaurs are much more poorly known, which is especially true for terrestrial crocodiles and pterosaurs. Marine crocodiles are rather well represented in south-western South America, whereas the report of terrestrial archosaurs is currently best for Africa. However, in South America, important and especially promising archosaur faunas are known from the Callovian Cañadón Asfalto and the (?)Tithonian Cañadón Calcáreo formations of Chubut province, Argentina. Early and Middle Jurassic Gondwanan archosaurs demonstrate that the faunas of that period still had a generally Pangean distribution, whereas first indications of differential archosaur evolution in the Northern and Southern Hemispheres are evident in Late Jurassic Gondwanan faunas.
The incompletely known sauropod Tornieria africana from the Upper Jurassic (Tithonian) of Tendaguru, Tanzania, has for over 80 years been regarded to represent a Gondwanan species of the North American genus Barosaurus Marsh (Morrison Formation: Kimmeridgian-Tithonian), but this identification has recently been questioned. The holotype and referred specimens are redescribed here, and the characters present are reevaluated in light of current knowledge of sauropod phylogeny. Synapomorphies of the skull (prefrontal with triangular posterior process) and anterior caudal vertebrae (procoelous centra, presence of diapophyseal laminae, and presence of a pleurocoel) indicate that the Tendaguru material represents a member of the Diplodocinae (Diplodocoidea, Diplodocidae) and is therefore very closely related to Barosaurus and Diplodocus. It differs from all other diplodocine genera in several characters, such as robust anterior caudals with pleurocoels located in the upper third of the centrum and ventral excavations, and stout hind limb proportions similar to Apatosaurus (tibia:femur length ratio less than 0.64). In a phylogenetic analysis, the African form consistently emerges as the sister taxon to Barosaurus+Diplodocus. Therefore, previous suggestions that Tornieria africana is the available name for this taxon are supported by this analysis. The existence of this form in Gondwana contradicts the idea of Laurentian endemism of the diplodocid clade, and is best explained by a vicariance model of diplodocoid paleobiogeography. This implies an extensive ghost lineage of this group, extending back at least as far as the upper Middle Jurassic.
A new sampling technique for fossil bone (coring with a 5/8” bit) was used to sample longbones of all four sauropod genera from the Upper Jurassic Tendaguru beds of Tanzania for paleohistological study. Brachiosaurus and Barosaurus are represented by growth series of humeri and femora, while Dicraeosaurus could be sampled in fewer specimens and only one bone of Janenschia was available. Although all samples are dominated by fibrolamellar bone tissue, taxa can be distinguished by the degree and nature of bone remodeling and the presence and spacing of a peculiar kind of growth line (here termed “polish lines”). In addition, Barosaurus bone revealed two types of histology, tentatively interpreted as sexual morphs. The Tendaguru sauropods show a common growth pattern in which growth is determinate but sexual maturity is achieved well before maximum size is reached. For Brachiosaurus and Barosaurus, size at sexual maturity can be estimated and was reached at about 40% and 70% maximum size, respectively. Quantification of growth is possible in Janenschia using polish lines: the specimen studied reached sexual maturity at ≥11 years, attained maximum size at ≥26 years, and died at ≥38 years.
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.
Franz Baron Nopcsa recognised that the Late Cretaceous titanosaurid sauropod from Transylvania, Magyarosaurus dacus, was much smaller than the better known sauropods from the Upper Jurassic of the United States and even from Late Cretaceous deposits elsewhere in the world. In keeping with his biogeographic interpretations, Nopcsa viewed this difference as a consequence of body-size effects via island habitation. We present a preliminary re-evaluation of Nopcsa's claims and their heterochronic consequences using two approaches, viz. (1) regression analysis of humeral data as a means of establishing patterns in body size among titanosaurids, and (2) optimisation of humeral data onto titanosaurid cladograms to evaluate evolutionary trends within the clade. Our regression analysis is based on twenty species distributed among fourteen genera of neosauropods and uses length and mid-shaft mediolateral width of the humerus of presumed fully adult forms, and of growth samples that consist of postnatal to adult individuals. Linear regression analysis suggests that, among adult neosauropods, M. dacus appears to be represented by the smallest individuals; that M. dacus humeri appear to be more similar to those of subadults than to adults of other taxa; and that this juvenile morphology may constitute dwarfing in M. dacus by paedomorphosis. In order for these regressions to reflect their evolutionary context more fully, we also present optimisation analyses of humeral form within Titanosauroidea. Although many aspects of the phylogeny of this clade are relatively poorly resolved, preliminary results of our analyses are consistent with the conclusion that M. dacus was a heterochronic dwarf.
Most recent studies of dinosaur phylogeny have concentrated on theropods and ornithischians. As a result, the evolutionary relationships of sauropod dinosaurs are poorly understood. In this paper previous studies of sauropod phylogeny are reviewed and contrasted with the results of a recent cladistic analysis. This analysis forms the basis for a reconstruction of sauropod phylogeny. Sauropods diverged from other dinosaurs at some time in the Upper Triassic, but a large part of their early history is totally unknown. Vulcanodon is currently the most primitive sauropod. Many, but perhaps not all, of the Jurassic Chinese sauropods form a monophyletic radiation (the Euhelopodidae) which may reflect the geographic isolation of China during the Lower Jurassic. Members of the Euhelopodidae, such as Mamenchisaurus, are not considered to be closely related to the Diplodocidae. `Forked' chevrons, which have played such an important role in previous studies of sauropod phylogeny, are here considered to have evolved twice within the Sauropoda. This convergence may reflect a correlation between chevron shape and the use of the tail as a weapon within these two sauropod families. The `Neosauropoda' (sister group to the Euhelopodidae) contains the Brachiosauridae, Camara-sauridae and the new superfamilies Titanosauroidea and Diplodocoidea. The Cetiosauridae (here defined in a rather restricted sense) is also provisionally included within the Neosauropoda, but may be removed in future studies. The enigmatic Upper Cretaceous sauropod, Opisthocoelicaudia, is thought to be the sister taxon to the Titanosauridae and not a camarasaurid as previously suggested. The Diplodocoidea contains two well established families, the Dicraeosauridae and Diplodocidae, and the new family Nemegtosauridae. Finally, an overview of sauropod phylogeny is compared with recently published palaeogeographic reconstructions. There are many difficulties associated with the analysis of sauropod biogeographic distribution. Nevertheless, some aspects of sauropod phylogeny may be linked to the break-up of Laurasia and Gondwanaland during the Jurassic and Cretaceous.
Xenoposeidon proneneukos gen. et sp. nov. is a neosauropod represented by BMNH R2095, a well-preserved partial mid-to-posterior dorsal vertebra from the Berriasian- Valanginian Hastings Beds Group of Ecclesbourne Glen, East Sussex, England. It was briefly described by Lydekker in 1893, but it has subsequently been overlooked. This speci- men's concave cotyle, large lateral pneumatic fossae, complex system of bony laminae and camerate internal structure show that it represents a neosauropod dinosaur. However, it differs from all other sauropods in the form of its neural arch, which is taller than the centrum, covers the entire dorsal sur- face of the centrum, has its posterior margin continuous with that of the cotyle, and slopes forward at 35 degrees rela- tive to the vertical. Also unique is a broad, flat area of fea- tureless bone on the lateral face of the arch; the accessory infraparapophyseal and postzygapophyseal laminae which meet in a V; and the asymmetric neural canal, small and round posteriorly but large and teardrop-shaped anteriorly, bounded by arched supporting laminae. The specimen cannot be referred to any known sauropod genus, and clearly represents a new genus and possibly a new 'family'. Other sauropod remains from the Hastings Beds Group represent basal Titanosauriformes, Titanosauria and Diplodocidae; X. proneneukos may bring to four the number of sauropod 'families' represented in this unit. Sauropods may in general have been much less morphologically conservative than is usually assumed. Since neurocentral fusion is complete in R2095, it is probably from a mature or nearly mature ani- mal. Nevertheless, size comparisons of R2095 with corre- sponding vertebrae in the Brachiosaurus brancai holotype HMN SII and Diplodocus carnegii holotype CM 84 suggest a rather small sauropod: perhaps 15 m long and 7600 kg in mass if built like a brachiosaurid, or 20 m and 2800 kg if built like a diplodocid.
At least two titanosaurian sauropod taxa have been discovered in the Early Cretaceous Dinosaur Beds of northern Malawi, Africa. One of these, Malawisaurus dixeyi, is represented by cranial elements, 18 cervical vertebrae, 10 dorsal vertebrae, a sacrum, 51 caudal vertebrae, 24 chevrons, pectoral elements, pelvic elements, and dermal armor, all of which are described and illustrated. The cranial elements indicate that Malawisaurus had a short, high macronarian skull. Karongasaurus gittelmani gen. et sp. nov. is more derived than Malawisaurus but is represented only by a dentary and isolated teeth. Some indeterminate vertebrae may also belong to Karongasaurus or another taxon, but not to Malawisaurus. The shape of the teeth and jaw, and the restriction of teeth toward the anterior part of the jaw in Karongasaurus are different from Malawisaurus and suggest that Karongasaurus had a long, low skull. Thus, the sauropods from the Malawi Dinosaur Beds demonstrate extreme morphological variation in titanosaurian jaws, teeth, and probably skull shape. Variation in tooth and skull morphology, because of its relevance to feeding, was likely of significance in resource partitioning among titanosaurian sauropods in the Early Cretaceous ecosystem.
A juvenile specimen of the titanosaurid sauropod Alamosaurus sanjuanensis, recovered from just below the Cretaceous/Tertiary boundary horizon in Big Bend National Park, Texas, is from an individual less than half the size of adult specimens referred to this species. The disarticulated skeleton was preserved in deposits of a shallow flood-plain pond and includes elements not previously described, allowing for an improved diagnosis for this species. The elongate opisthocoelous cervical vertebrae have non-bifid posteriorly deflected neural spines with deep postspinal fossae. The dorsal vertebrae have wide spatulate neural spines with strong prespinal laminae, and lack hyposphene-hypantrum articulations. Alamosaurus sanjuanensis exhibits a unique morphology of the ischium, evident even in this juvenile specimen. Comparison with other titanosaurid species suggests that A. sanjuanensis is most closely related to an unnamed titanosaur from Peiropolis, Brazil and Neuquensaurus australis from Argentina.
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.
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