Article

Ontogenetic influence on neural spine bifurcation in Diplodocoidea (Dinosauria: Sauropoda): a critical phylogenetic character

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  • Dickinson Museum Center, ND
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Abstract

Within Diplodocoidea (Dinosauria: Sauropoda), phylogenetic position of the three subclades Rebbachisauridae, Dicraeosauridae, and Diplodocidae is strongly influenced by a relatively small number of characters. Neural spine bifurcation, especially within the cervical vertebrae, is considered to be a derived character, with taxa that lack this feature regarded as relatively basal. Our analysis of dorsal and cervical vertebrae from small-sized diplodocoids (representing at least 18 individuals) reveals that neural spine bifurcation is less well developed or absent in smaller specimens. New preparation of the roughly 200-cm long diplodocid juvenile Sauriermuseum Aathal 0009 reveals simple nonbifurcated cervical neural spines, strongly reminiscent of more basal sauropods such as Omeisaurus. An identical pattern of ontogenetically linked bifurcation has also been observed in several specimens of the basal macronarian Camarasaurus, suggesting that this is characteristic of several clades of Sauropoda. We suggest that neural spine bifurcation performs a biomechanical function related to horizontal positioning of the neck that may become significant only at the onset of a larger body size, hence, its apparent absence or weaker development in smaller specimens. These results have significant implications for the taxonomy and phylogenetic position of taxa described from specimens of small body size. On the basis of shallow bifurcation of its cervical and dorsal neural spines, the small diplodocid Suuwassea is more parsimoniously interpreted as an immature specimen of an already recognized diplodocid taxon. Our findings emphasize the view that nonmature dinosaurs often exhibit morphologies more similar to their ancestral state and may therefore occupy a more basal position in phylogenetic analyses than would mature specimens of the same species. In light of this, we stress the need for phylogenetic reanalysis of sauropod clades where vital characters may be ontogenetically variable, particularly when data is derived from small individuals.

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... There is evidence of allometric growth in the tibia, with several character differences noted (Carpenter and McIntosh, 1994). Among diplodocines, isometric growth occurs in the shape of both the humerus and femur, and allometric growth occurs in the skull, vertebrae, and femoral proportions (see Table S3) (Curtice and Wilhite, 1996;Bonnan, 2004;Whitlock et al., 2010;Woodruff and Fowler, 2012;Tschopp and Mateus, 2013;Melstrom et al., 2016;Hanik et al., 2017;Woodruff et al., 2018). ...
... The camarasauromorph Europasaurus holgeri demonstrates isometric growth in the ischium, and allometric growth in the skull, vertebrae, humeri, ulnae, and metacarpals (Sander et al., 2006;Carballido and Sander, 2014;Marpmann et al., 2015;Carballido et al., 2020). Camarasaurus specimens vary greatly, with isometry reported in the cranium, vertebrae, coracoid, the shape of the humerus and femur, and metatarsals, but allometry identified in the dentary, vertebrae, sternal plate, scapula, coracoid, proportions of the femur, and fibula (see Table S3) (Gilmore, 1925;Carpenter and McIntosh, 1994;Curtice and Wilhite, 1996;Bonnan, 2004;Forster, 2005;Ikejiri et al., 2005;Woodruff and Fowler, 2012). The brachiosaurid Venenosaurus dicrocei and several titanosaurs (including Rinconsaurus caudamirus and Rapetosaurus krausei) evidently grew isometrically, as observed in the ribs, ulnae, and manus of Venenosaurus dicrocei (Tidwell and Wilhite, 2005), all preserved elements of Rinconsaurus caudamirus (Calvo and González Riga, 2003), and the vertebrae, long bones, metacarpal III, pubis, tibia, fibula, and metatarsal I of Rapetosaurus krausei (Curry Rogers and Forster 2001Forster , 2004Curry Rogers et al., 2016;Curry Rogers and Kulik, 2018). ...
... Ontogenetic osteological changes observed in numerous sauropod species have meant that the establishment of new species on the basis of juvenile specimens has proven to be problematic. One reason for this is that osteologically immature specimens often exhibit anatomical characters more aligned with their ancestral state, owing to the simplicity of their bones (Martin, 1994;Schwarz et al., 2007;Woodruff and Fowler, 2012;Carballido and Sander, 2014;Tschopp et al., 2015). For this reason, we acknowledge the possibility that a different taxonomic position for AODF 663 might be resolved in the future. ...
... Salgado (1999) suggested a link between the degree of neural spine bifurcation and ontogeny in diplodocids. Woodruff and Fowler (2012) showed that small (presumably immature) diplodocids exhibited rounded to weakly bifurcated neural spines, whereas neural spines were fully bifurcated in larger (and presumably more mature) individuals. Based on this observation, it was suggested that the degree of bifurcation could be used to infer maturity in diplodocids (and other methodologies have used morphology to predict maturity; such as the Morphologic Ontogenetic Stage [MOS] of Carballido and Sander, 2014; or the ontogenetic trajectory stages of Ikejiri et al., 2005). ...
... While some of these morphologic features have been incorporated into our understanding of sauropod ontogeny, the conclusions of Woodruff and Fowler (2012) have been the subject of ongoing discussion (Wedel and Taylor, 2013;Carballido and Sander, 2014;Hedrick et al., 2014;Woodruff and Foster, 2014;Tschopp et al., 2015). Aspects of this study that are considered contentious include: 1) the unknown precise serial placement for isolated vertebrae, and 2) the proper identification of maturational states to corroborate said morphological interpretations (Wedel and Taylor, 2013;Hedrick et al., 2014). ...
... We would argue that histologic analysis is the only repeatedly confirmed methodology to determine a specimen's maturational state. The current analysis tests the inferred maturational stages of Woodruff and Fowler (2012) using histologic examination. Additional features that may indicate relative maturity are also assessed. ...
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Determining maturity in sauropod dinosaurs histologically is problematic as rapid growth leads to remodeling of Lines of Arrested Growth (LAGs). Although a complimentary system has been devised utilizing several factors including relative amounts of remodeling (Histologic Ontogenetic Stage [HOS]), most assessments of sauropod maturity are based on morphologic indicators. To better assess skeletal maturity and morphologic change through ontogeny, we examined cranial and postcranial material from over 20 diplodocid individuals (Apatosaurus and Diplodocus) from the Upper Jurassic Morrison Formation. Here we describe consistent combinations of morphologic and histologic features that can be used to ascertain maturity. Small diplodocids (femoral lengths ≤120 cm) display non- to weakly bifurcated cervical and dorsal neural spines, acamerate to camerate centra, two to six preserved LAGs in dorsal ribs, and a maximum femoral designation of HOS 7. Larger individuals (femoral length ~125 cm) have more developed internal pneumatic structures, greater neural spine bifurcation, preserve up to eight LAGs, and a femoral designation of HOS 9. In contrast, skeletally mature sauropods (femoral lengths >150 cm) have complex pneumatic structures, extended neural spine bifurcation (also within anterior caudals), and a femoral HOS between 11-13. Further, all of the preserved small diplodocid skulls exhibit a postparietal foramen (previously suggested to be an apomorphy of Dicraeosauridae), which is absent in large skulls (where preserved), suggesting that it is an ontogenetic character. These findings support the hypothesis of significant ontogenetic morphological change in diplodocid sauropods and suggest caution when describing new taxa on the basis of small-bodied holotypes.
... Plesiomorphies are often found in juvenile specimens, which make it advisable to name new taxa based only on adult individuals (Rozhdestvensky 1965;Gould 1966;Sereno 2010). Woodruff and Fowler (2012) suggested that Suuwassea was a subadult specimen of another Morrison sauropod because its phylogenetic position was difficult to discern owing to plesiomorphic characters and that it appeared to be small in body size. The subadult status of ANS 21122 was inferred on the basis of neurocentral fusion and some fusion in the skull and braincase (Harris 2006c). ...
... Recently, Woodruff and Fowler (2012) suggested that Suuwassea was an immature version of a different Morrison sauropod taxon based on its modest amount of neural spine bifurcation, which they interpreted as an ontogenetically variable character. However, on the basis of the present analysis, ANS 21122 is a young adult (based on HOS). ...
... This implies that the modest neural spine bifurcation in ANS 21122 at a relatively late ontogenetic stage is a taxonomic character separating it from other diplodocoids (Harris 2006b), but a detailed analysis comparing the HOS of diplodocoids with degree of neural spine bifurcation has yet to be performed. Woodruff and Fowler (2012) base their assessment of Suuwassea on a sample set of 18 sauropod individuals, with only four preserving a relatively complete vertebral series. Neural spine bifurcation varies through the vertebral column interand intraspecifically, which may account for some of the variation interpreted by Woodruff and Fowler (2012) as ontogenetic (Wedel and Taylor 2013). ...
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editors before the paper is published in its final form. Please note that during the production process errors may be discovered which could affect the content. All legal disclaimers that apply to the journal pertain.. Bone microstructure and relative age of the holotype specimen of the diplodocoid sauropod dinosaur Suuwassea emilieae. Acta Palaeontologica Polonica 5X (X): xxx-xxx. We present the first study of bone microstructure in Suuwassea emilieae, a diplodocoid sauropod from the Morrison Formation. Although the holotype of Suuwassea was recently identified as a subadult, bone histology demonstrates that this individual had reached sexual maturity at approximately 75–80% of maximum adult size. The smaller size of the holotype of Suuwassea relative to contemporary sauropods is due to ontogeny rather than a true reflection of adult size. A fully adult individual would have likely been similar in size to a fully adult specimen of Apatosaurus. Suuwassea has a number of plesiomorphic characters that might have been explained by its supposed early ontogenetic status, and would then have called the validity of the taxon into question. However, our demonstration that it was an adult confirms that these features represent retention of plesiomorphic character states or evolutionary reversals in a derived animal. Additionally, the specimen shows extensive cortical drift and secondary osteon formation related to skeletal loading, which is often obscured by complete remodeling of Haversian systems in sauropod taxa. There are substantial differences in the microstructure across the bone, which could make histologic samples not based upon complete cross sections problematic. Suuwassea is one of four currently recognized dicraeosaurid taxa, and this study contributes potential taxonomic characters in sauropod bone microstructure.
... In a recently-published paper, Woodruff & Fowler (2012) argued that the degree of bifurcation of sauropod neural spines was ontogenetically controlled, with the simple, undivided spines of juveniles gradually separating into paired metapophyses over the course of posthatching ontogeny. Based on this inferred ontogenetic trajectory, Woodruff & Fowler (2012) further argued that currently recognized sauropod taxa are oversplit, and that when ontogenetic transformations were taken into account, it would be necessary to synonymize several taxa. ...
... In a recently-published paper, Woodruff & Fowler (2012) argued that the degree of bifurcation of sauropod neural spines was ontogenetically controlled, with the simple, undivided spines of juveniles gradually separating into paired metapophyses over the course of posthatching ontogeny. Based on this inferred ontogenetic trajectory, Woodruff & Fowler (2012) further argued that currently recognized sauropod taxa are oversplit, and that when ontogenetic transformations were taken into account, it would be necessary to synonymize several taxa. In particular, they argued that the Morrison Formation diplodocoid Suuwassea was a juvenile of a known diplodocid (Ibidem: 6-8), that Haplocanthosaurus and Barosaurus were likewise suspect (Ibidem: 9), and that rebbachisaurids were possibly paedomorphic dicraeosaurids (Ibidem: 8-9). ...
... Our goals in this paper are, first, to re-examine the evidence for an ontogenetic increase in neural spine bifurcation in sauropods, and then to evaluate the synonymies proposed by Woodruff & Fowler (2012). Although bifid neural spines also occur in other sauropods, as noted above, the hypotheses of Woodruff & Fowler (2012) depend on ontogenetic inferences drawn from Morrison Formation sauropod taxa, and therefore we are confining our discussion to those taxa (e.g. ...
Article
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It has recently been argued that neural spine bifurcation increases through ontogeny in several Morrison Formation sauropods, that recognition of ontogenetic transformation in this 'key character' will have sweeping implications for sauropod phylogeny, and that Suuwassea and Haplocanthosaurus in particular are likely to be juveniles of known diplodocids. However, we find that serial variation in sauropod vertebrae can mimic ontogenetic change and is therefore a powerful confounding factor, especially when dealing with isolated elements whose serial position cannot be determined. When serial position is taken into account, there is no evidence that neural spine bifurcation increased over ontogeny in Morrison Formation diplodocids. Through phylogenetic analysis we show that neural spine bifurcation is not a key character in sauropod phylogeny and that Suuwassea and Haplocanthosaurus are almost certainly not juveniles of known diplodocids. Skeletochronology based on the sequence of skeletal fusions during ontogeny can provide relative ontogenetic ages for some sauropods. Although such data are sparsely available to date and often inconsistent among sauropod genera they provide another line of evidence for testing hypotheses of ontogenetic synonymy. Data from skeletal fusions suggest that Suuwassea and Haplocanthosaurus are both valid taxa and that neither is an ontogenetic morph of a known diplodocid.
... [99]). However, based on the postcrania, Woodruff & Fowler [36] suggested that MOR 592 was instead a juvenile morphotype of a diplodocine. Woodruff & Foster [37] and Woodruff et al. [38,100] later went further and considered MOR 592 to be a juvenile specimen of Diplodocus. ...
... In a series of papers, Woodruff and co-workers have argued that this diversity is overestimated (see also [105]), and that many species considered valid in recent studies are synonymous, primarily interpreted as semaphoronts or 'ontogimorphs' (i.e. growth series) of a smaller number of valid taxa [36][37][38]40,92]. These putative synonyms include A. altus, Barosaurus lentus, Haplocanthosaurus priscus, Kaatedocus siberi, Smitanosaurus agilis and Suuwassea emilieae. ...
... We do not disagree that ontogeny is an important issue and one that needs to be considered, but there is currently no evidence to support the claim that Morrison sauropod diversity is overestimated as a result. As also concluded by Wedel & Taylor [99], we should be wary of placing too much emphasis on 'critical' phylogenetic characters (sensu [36]). ...
Article
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Sauropod dinosaurs were an abundant and diverse component of the Upper Jurassic Morrison Formation of the USA, with 24 currently recognized species. However, some authors consider this high diversity to have been ecologically unviable and the validity of some species has been questioned, with suggestions that they represent growth series (ontogimorphs) of other species. Under this scenario, high sauropod diversity in the Late Jurassic of North America is greatly overestimated. One putative ontogimorph is the enigmatic diplodocoid Amphicoelias altus , which has been suggested to be synonymous with Diplodocus . Given that Amphicoelias was named first, it has priority and thus Diplodocus would become its junior synonym. Here, we provide a detailed re-description of A. altus in which we restrict it to the holotype individual and support its validity, based on three autapomorphies. Constraint analyses demonstrate that its phylogenetic position within Diplodocoidea is labile, but it seems unlikely that Amphicoelias is synonymous with Diplodocus . As such, our re-evaluation also leads us to retain Diplodocus as a distinct genus. There is no evidence to support the view that any of the currently recognized Morrison sauropod species are ontogimorphs. Available data indicate that sauropod anatomy did not dramatically alter once individuals approached maturity. Furthermore, subadult sauropod individuals are not prone to stemward slippage in phylogenetic analyses, casting doubt on the possibility that their taxonomic affinities are substantially misinterpreted. An anatomical feature can have both an ontogenetic and phylogenetic signature, but the former does not outweigh the latter when other characters overwhelmingly support the affinities of a taxon. Many Morrison Formation sauropods were spatio-temporally and/or ecologically separated from one another. Combined with the biases that cloud our reading of the fossil record, we contend that the number of sauropod dinosaur species in the Morrison Formation is currently likely to be underestimated, not overestimated.
... Much has been made of the immense sizes attained by adult sauropods (e.g., Sander 2000;Sander and Clauss 2008;Preuschoft et al. 2011;Rauhut et al. 2011;Sander et al. 2011;Clauss et al. 2013;Xu and Zhao 2016), and a substantial literature exists on sauropod embryos and hatchlings (e.g., Carpenter and McIntosh 1994;Curtice and Wilhite 1996;Chiappe et al. 1998Chiappe et al. , 2001Salgado et al. 2005;García 2007; García and Cerda 2010;Grellet-Tinner and Fiorelli 2010;Wilson et al. 2010;Grellet-Tinner et al. 2011;Barrett et al. 2016), but relatively little is known about sauropod ontogenetic trajectories between hatchling and adult. What is known of post-hatchling juvenile sauropods is generally restricted to members of the neosauropod clade Macronaria (e.g., Lehman and Coulson 2002;Ikejiri et al. 2005;Schwarz et al. 2007;Carballido et al. 2012;Carballido and Sander 2014;Curry Rogers et al. 2016); comparably little data exist for juveniles of the other major neosauropod clade, Diplodocoidea (e.g., Peterson and Gilmore 1902;Carpenter and McIntosh 1994;Whitlock et al. 2010;Woodruff and Fowler 2012;Melstrom et al. 2016). This dearth of information is problematic in that it corresponds with a potentially important stage in sauropod life history, when the growth rates of these animals appear to have been the highest (Curry 1999;Sander 2000;Lehman and Woodward 2008). ...
... In DINO 2921, bifurcation is present, at least incipiently, posteriorly until the sixth dorsal vertebra; conversely, in CM 79038, bifurcation is present only in the fifth dorsal vertebra and then only as a subtle bifurcation of the apex of the neural spine. Although it has been suggested that neural spine bifurcation increased through sauropod ontogeny (Woodruff and Fowler 2012;Woodruff 2016), there generally exists some intraspecific variability with regard to the onset/loss of neural spine bifurcation in diplodocids (Wedel and Taylor 2013a). Within Barosaurus, the dorsal neural spines of DINO 2921 and YPM 429 remain distinctly bifid well into the middle of the sequence, up to dorsal vertebra 5 (Lull 1919;Wedel and Taylor 2013a;Melstrom et al. 2016). ...
... In CM 79038 and AMNH 6341, however, bifurcation diminishes earlier, such that by dorsal vertebra 5, only a slightly notched distal neural spine remains (McIntosh 2005). This appears to contradict the hypothesis of Woodruff and Fowler (2012) and Woodruff (2016), as there is no clear pattern of increased (or decreased) bifurcation in the multiple semaphoronts of Barosaurus. ...
Article
We describe five partial middle and posterior dorsal vertebrae from an upper Kimmeridgian exposure of the Upper Jurassic Morrison Formation at the Carnegie Quarry of Dinosaur National Monument (Utah, USA), and refer these vertebrae to the poorly known diplodocid sauropod dinosaur genus Barosaurus Marsh, 1890. The small size and unfused neurocentral junctions of these vertebrae indicate that they belonged to a subadult individual and the osteologically youngest specimen yet described for the genus. We also provide corroborating evidence for the pneumatic hiatus previously hypothesized for Barosaurus and identify a previously unrecognized autapomorphy of the genus, the presence of an anterodorsallyoriented accessory lamina arising from the spinodiapophyseal lamina on dorsal vertebrae. Furthermore, we document a temporal uncoupling of neural spine lamination and pneumatization of the centrum, such that full development of the laminae preceded development of sharp-lipped pleurocoels in dorsal vertebrae.
... Authors variously use terms like 'juvenile', 'subadult', 'adult', etc., without consistent meaning across the literature one author's 'juvenile', may be another's 'subadult', and one author may consider a sexually mature, but still growing, individual to be an adult, whereas another may consider this individual immature until cessation of growth (or some other measure of maturity) has been reached. For example, the diplodocid specimen 21122 (Academy of Natural Sciences, Drexel University) has been considered an 'adult' based on reproductive maturity (Hedrick, Tumarkin-Deratzian & Dodson, 2014b) but either 'immature' (Woodruff & Fowler, 2012) or 'subadult' (Wedel & Taylor, 2013) based on vertebral morphology and neurocentral suture fusion. Even where these terms are explicitly defined, the definitions often constrain their use to the specific method of assessing maturity being used. ...
... Among dinosaurs, paired depressions on cervicals (potentially related to pneumaticity) and cervical nutrient foramen morphology co-occurred with other so-called 'juvenile' character states in a coelurosaurian theropod (Makovicky & Sues, 1998), and the articular faces of centra of the nodosaurid Anoplosaurus are less expanded in immature individuals (Pereda Suberbiola & Barrett, 1999). Neural spine bifurcation has been suggested to be ontogenetically controlled in some sauropods (Woodruff & Fowler, 2012), but this is far from clear (Wedel & Taylor, 2013). ...
Article
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Morphology forms the most fundamental level of data in vertebrate palaeontology because it is through interpretations of morphology that taxa are identified, creating the basis for broad evolutionary and palaeobiological hypotheses. Assessing maturity is one of the most basic aspects of morphological interpretation and provides the means to study the evolution of ontogenetic changes, population structure and palaeoecology, life‐history strategies, and heterochrony along evolutionary lineages that would otherwise be lost to time. Saurian reptiles (the least‐inclusive clade containing Lepidosauria and Archosauria) have remained an incredibly diverse, numerous, and disparate clade through their ~260‐million‐year history. Because of the great disparity in this group, assessing maturity of saurian reptiles is difficult, fraught with methodological and terminological ambiguity. We compiled a novel database of literature, assembling >900 individual instances of saurian maturity assessment, to examine critically how saurian maturity has been diagnosed. We review the often inexact and inconsistent terminology used in saurian maturity assessment (e.g. ‘juvenile’, ‘mature’) and provide routes for better clarity and cross‐study coherence. We describe the various methods that have been used to assess maturity in every major saurian group, integrating data from both extant and extinct taxa to give a full account of the current state of the field and providing method‐specific pitfalls, best practices, and fruitful directions for future research. We recommend that a new standard subsection, ‘Ontogenetic Assessment’, be added to the Systematic Palaeontology portions of descriptive studies to provide explicit ontogenetic diagnoses with clear criteria. Because the utility of different ontogenetic criteria is highly subclade dependent among saurians, even for widely used methods (e.g. neurocentral suture fusion), we recommend that phylogenetic context, preferably in the form of a phylogenetic bracket, be used to justify the use of a maturity assessment method. Different methods should be used in conjunction as independent lines of evidence when assessing maturity, instead of an ontogenetic diagnosis resting entirely on a single criterion, which is common in the literature. Critically, there is a need for data from extant taxa with well‐represented growth series to be integrated with the fossil record to ground maturity assessments of extinct taxa in well‐constrained, empirically tested methods.
... With a total length of 30 cm, the skull is slightly larger than the juvenile Diplodocus CM 11255, and reaches approximately 58% of the length of the adult Diplodocus skull CM 11161 (Holland 1906;). In addition, the incomplete fusion of the parietals, the rounded muzzle (in contrast to the squared snout of adult Diplodocus and Apatosaurus), the restriction of the bifurcation of cervical neural spines to mid-and posterior cervical vertebrae, and relatively shorter cervical centra have recently been interpreted to be typical for a juvenile ontogenetic stage (Wedel et al. 2000;Woodruff & Fowler 2012). On the other hand, the complete co-ossification in all cervical vertebrae, and the presence of rugose tubercles, or roughened areas on laminae edges on both cranial and cervical elements indicate a higher ontogenetic age (Varricchio 1997;Ikejiri et al. 2005;Schwarz et al. 2007b). ...
... Character 97 describes the bifurcation of the cervical vertebrae, which starts in anterior elements in Diplodocus but more posteriorly in SMA 0004 and other taxa. The bifurcation is considered to happen continuously from the back to the front (Woodruff & Fowler 2012) during ontogeny. Basing on Haeckel's rule that phylogeny recapitulates ontogeny, the development of this bifurcation in adult specimens should replay this continuous change, and an ordering of this character therefore appears reasonable. ...
Article
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A new taxon of diplodocid sauropod, Kaatedocus siberi gen. et sp. nov., is recognized based on well-preserved cervical vertebrae and skull from the Morrison Formation (Kimmeridgian, Late Jurassic) of northern Wyoming, USA. A phylogenetic analysis places it inside Diplodocinae (Sauropoda: Flagellicaudata: Diplodocidae), as a sister taxon to a clade uniting Tornieria africana and the classical diplodocines Barosaurus lentus and Diplodocus. The taxon is diagnosed by a unique combination of plesiomorphic and derived traits, as well as the following unambiguous autapomorphies within Diplodocidae: frontals separated anteriorly by a U-shaped notch; squamosals restricted to the post-orbital region; presence of a postparietal foramen; a narrow, sharp and distinct sagittal nuchal crest; the paired basal tuber with a straight anterior edge in ventral view; anterior end of the prezygapophyses of mid- and posterior cervical vertebrae is often an anterior extension of the pre-epipophysis, which projects considerably anterior to the articular facet; anterodorsal corner of the lateral side of the posterior cervical vertebrae marked by a rugose tuberosity; posterior margin of the prezygapophyseal articular facet of posterior cervical vertebrae bordered posteriorly by conspicuous transverse sulcus; posterior cervical neural spines parallel to converging. The inclusion of K. siberi and several newly described characters into a previously published phylogenetic analysis recovers the new taxon as basal diplodocine, which concurs well with the low stratigraphical position of the holotype specimen. Dinheirosaurus and Supersaurus now represent the sister clade to Apatosaurus and Diplodocinae and therefore the most basal diplodocid genera. The geographical location in the less known northern parts of the Morrison Fm., where K. siberi was found, corroborates previous hypotheses on faunal provinces within the formation. The probable subadult ontogenetic stage of the holotype specimen allows analysis of ontogenetic changes and their influence on diplodocid phylogeny.
... The quarry has yielded over 2,500 fossils over the past two decades belonging to at least fifteen different Diplodocus individuals of a single indeterminate species (Myers & Storrs, 2007). Originally, the Diplodocus specimens were classified as "juveniles" and "subadults" due to their small size and unfused bones (Myers & Storrs, 2007;Storrs, Oser & Aull, 2012;Woodruff & Fowler, 2012). However, more recent analyses revealed that some of these individuals may be more histologically mature than previously thought, indicating there may be an additional dwarfed morphotype present in the Mother's Day Quarry (Woodruff et al., 2018). ...
... Although there is evidence present at the Mother's Day Quarry that the Diplodocus were "juvenile", some of the elements used to determine maturational status have been brought into question. For instance, increase in neural spine bifurcation was originally thought to be a key characteristic in diplodocid ontogeny (Woodruff & Fowler, 2012). However, other studies have shown that variation in sauropod vertebra can mimic ontogenetic features and are thus not reliable in determining maturational status (Wedel & Taylor, 2013). ...
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The life appearance of dinosaurs is a hotly debated topic in the world of paleontology, especially when it comes to dinosaur integument. In the case of sauropods, however, the topic is harder to properly discuss due to the limited amount of fossilized skin impressions that have been discovered. Thus far, the fossil record of sauropod integument fossils include titanosaur embryos from Patagonia, possible keratinous diplodocid dorsal spines, track ways with foot impressions, and other isolated skin impressions found in association with sauropod body fossils. Several prominent integument fossils have been found at the Mother’s Day Quarry, located in the Bighorn Basin, Montana. These discoveries may bring new important information about diplodocids, specifically Diplodocus sp. Here we describe newly uncovered fossilized skin that gives evidence of scale diversity in the genus Diplodocus . The scales themselves represent tubercles, and exhibit various shapes including rectangular, ovoid, polygonal, and globular scales. The tubercles are small in size, the biggest of which only reach about 10mm in length. Considering how diverse the scale shapes are in such a small area of skin, it is possible that these distinct scale shapes may represent a transition on the body from one region to another: perhaps from the abdomen to dorsal side, or abdomen to shoulder. Based on analysis of extant integument and scale orientation of crocodilians, it is possible to hypothesize on the location of the integument relative to the body as well as the size and relative maturational status of the individual.
... That is, young individuals will tend to be placed in more basal positions relative to their mature individuals in resultant cladograms (Carballido and Sander, 2014). This issue has been raised repeatedly with respect to sauropod dinosaurs (e.g., Woodruff and Fowler, 2012;Wedel and Taylor, 2013;Carballido and Sander, 2014;Hedrick et al., 2014;Tschopp et al., 2015;Woodruff et al. 2017) and is potentially important in this phylogenetic analysis because several skeletally immature individuals are operational taxonomic units (i.e., Kaatedocus, Tschopp and Mateus, 2013;Smitanosaurus;Suuwassea, Hedrick et al., 2014). Within Diplodocoidea, characters tagged as having the potential to be ontogenetically influenced tend to be proportional (e.g., length of a neural spine, development of a process; see Tschopp et al., 2015 for an in-depth investigation) rather than presence/absence. ...
... MOR 592 Recovered as a Dicraeosaurid-MOR 592 has most commonly been placed within Diplodocidae, variously as a specimen of Amphicoelias (Wilson and Smith, 1996), a specimen of Diplodocus (Woodruff and Foster, 2014;Woodruff et al., 2017), or an indeterminate diplodocine (Woodruff and Fowler, 2012). Wedel and Taylor (2013:16) examined the relationships of the specimen and concluded that it was "probably not a diplodocid," and Whitlock (2011) and the present analysis concur with that conclusion by recovering it as a dicraeosaurid. ...
Article
The holotypic materials of the sauropod ‘Morosaurus’ agilis—a partial skull, proatlases, and first three cervical vertebrae—have been a taxonomic and phylogenetic mystery since their initial description by O. C. Marsh in 1889 and redescription by C. W. Gilmore in 1907. Although most species of Morosaurus were subsumed into Camarasaurus in 1919, ‘M.’ agilis was left in the defunct genus without a proper taxonomic assignment. Similarities have been noted between ‘M.’ agilis and other Morrison Formation sauropod taxa, including Camarasaurus, Haplocanthosaurus, Diplodocus, and Brachiosauridae, but it had yet to be included in a phylogenetic analysis. Here we present new data following additional preparation and study that suggest ‘M.’ agilis is a basally diverging member of Dicraeosauridae, along with the recently described sauropod Kaatedocus. Based upon its recovery as a distinct taxon, we propose that ‘M.’ agilis receive the new generic name Smitanosaurus, yielding the new combination Smitanosaurus agilis. http://zoobank.org/urn:lsid:zoobank.org:pub:6977D649-EE6B-42EE-9E1C-C043A38AC2AC
... Hypotheses of ontogenetic change are more difficult to test in other Morrison Formation sauropod taxa due to taxonomic and positional/serial ambiguities stemming from the mostly disarticulated nature of the sauropod fossil record. For example, Woodruff and Fowler (2012) recently hypothesized that the degree of neural spine bifurcation increases through ontogeny in Diplodocoidea, but this hypothesis has been challenged due to the aforementioned ambiguities (Wedel and Taylor, 2013b). Despite a recent increase in collection, documentation, and study of juvenile sauropods, many of the morphological changes undergone by the vertebral column through ontogeny remain uncertain. ...
... The posterior cervical vertebrae (14-16) and anterior to middle dorsal vertebrae (1-6) are clearly bifurcated, whereas the neural spine of dorsal vertebra 7 and subsequent vertebrae are unbifurcated. This pattern of neural spine bifurcation matches that present in adult Barosaurus specimens, demonstrating that the degree of neural spine bifurcation does not vary over the available ontogenetic series of Barosaurus (juvenile to adult), in contrast to claims of Woodruff and Fowler (2012). Barosaurus is thus far the only diplodocoid for which patterns of ontogenetic variation in neural spine bifurcation have both serial and taxonomic control (see Wedel and Taylor 2013b). ...
Article
Well-preserved, articulated juvenile sauropod dinosaur material is very rare, hindering attempts to understand ontogenetic changes within the clade. Here, we describe an exceptionally preserved partial skeleton of a Barosaurus from the Morrison Formation of Dinosaur National Monument, Utah, U.S.A., that is only about one-third adult size. This small size and the lack of fusion of neurocentral and costovertebral sutures indicate that the individual is a juvenile. Apomorphy-based taxonomic identification of the specimen combined with the excellent preservation of its vertebral column allows documentation of both serial and ontogenetic morphological changes in Barosaurus. Each vertebra underwent substantial morphological change in the relative height of the neural spine and location of the zygapophyseal and diapophyseal articular facets during ontogeny but not in the degree of bifurcation of the neural spines. Pneumaticity in the dorsal vertebrae varies serially: large pneumatic fossae punctuate the centra of dorsal vertebrae 1–4 and 8–9, whereas these spaces are occupied by shallow depressions in dorsal vertebrae 5–7. This represents the first known caudal dorsal pneumatic hiatus in a sauropod dinosaur, which suggests that separate air sacs pneumatized the anterior and posterior regions of the dorsal vertebral column, congruent with the pattern observed in non-avian and avian theropod dinosaurs and the presence of an avian-style lung in sauropods. Citation for this article: Melstrom, K. M., M. D. D'Emic, D. Chure, and J. A. Wilson. 2016. A juvenile sauropod dinosaur from the Late Jurassic of Utah, U.S.A., presents further evidence of an avian style air sac system. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1111898.
... Although size is generally correlated with maturity (Brochu 1996), many factors influence growth rate. Indeed, identifying ontogenetic stages only with size (as was recently done by Woodruff & Fowler 2012) is ill-advised (e.g. Brinkman 1988;Brochu 1996;Irmis 2007). ...
... Given the recent popularity of proposing that some Mesozoic archosaurs from similar geographic areas and geologic ages may represent different ontogenetic morphs of the same taxon (e.g. Knoll et al. 2009;Horner & Goodwin 2009;Scannella & Horner 2010;Campione & Evans 2011;Woodruff & Fowler 2012), it is worth briefly addressing a recent hypothesis regarding early crocodylomorphs; namely, that Terrestrisuchus gracilis from the latest Triassic fissure fills of the United Kingdom are juveniles of Saltoposuchus connectens from the Löwenstein Formation (Late Triassic: Norian) of Germany (Allen 2003a, b). This hypothesis was based on the observation that the holotype (NHMUK R7557) and a referred specimen (NHMUK R10002) of Terrestrisuchus gracilis appear to display some juvenile characteristics, and therefore Allen (2003a, b) interpreted the differences between Terrestrisuchus gracilis and Saltoposuchus connectens discussed by Clark et al. (2001) to be ontogenetic rather than phylogenetic characters. ...
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Non-crocodyliform crocodylomorphs, often called 'sphenosuchians', were the earliest-diverging lineages of Crocodylomorpha, and document the stepwise acquisition of many of the features that characterize extant crocodylians. The first crocodylomorph fossils are approximately 230 million years old (upper Carnian, Late Triassic), and at least one of these early lineages persisted until at least 150 million years ago (Late Jurassic). These taxa occupied a wide variety of terrestrial environments from equatorial regions to high-paleolatitudes during the early Mesozoic. Despite a quarter-century of quantitative phylogenetic work, the interrelationships of early crocodylomorphs remain in a state of flux, though recent studies suggest that these lineages are paraphyletic with respect to Crocodyliformes, rather than forming a monophyletic early offshoot of Crocodylomorpha as some previously hypothesized. Nearly all early crocodylomorphs were upright quadrupedal small-bodied taxa, but lumping them all together as small cursorial faunivores masks ecological and morphological disparity in diet and limb functional morphology. With the accelerated pace of recent discovery of new specimens and taxa, future consensus on early crocodylomorph phylogeny will provide a solid framework for understanding their change in diversity and disparity through time, potential biogeographic patterns, and the morphological transformation leading to Crocodyliformes.
... This may strongly affect the validity of char− acters that define taxa based on immature remains, and their consequent phylogenetic position. Despite significant mor− phological changes through ontogeny in sauropods (Wedel 2003;Whitlock et al. 2010;Woodruff and Fowler 2010), de− velopment remains poorly understood, even for well known taxa (Schwarz et al. 2007;Carballido et al. 2010). The abun− dance of A. sanjuanensis remains in Maastrichtian rocks of the southwestern United States offers the best opportunity to col− lect a statistically significant sample of any giant sauropod. ...
Article
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Argentinosaurus (Cenomanian, Argentina) is generally accepted as being the largest dinosaur so far discovered and is one of several giant titanosaurian sauropods known from the Upper Cretaceous of South America and Asia, but surprisingly not from North America. Here we present the first evidence of giant titanosaurian sauropods from the Upper Cretaceous of North America: two enormous vertebrae and a partial femur, from the Naashoibito Member of the Ojo Alamo Formation, New Mexico, and referred to Alamosaurus sanjuanensis. One of the new vertebrae, a posterior cervical, is comparable in size to a posterior cervical described for Puertasaurus: an Argentinosaurus-sized titanosaurian from the Maastrichtian of Argentina. This makes A. sanjuanensis the largest dinosaur from North America, and among the largest in the world. These findings indicate that A. sanjuanensis is diagnosed based on immature remains, which may have implications for cladistic analyses.
... Consequently, most studies of comparative anatomy, phylogeny or functional morphology that include Diplodocus are mainly based on D. carnegii (e.g. Stevens & Parrish, 1999;Bedell & Trexler, 2005;McIntosh, 2005;Carrano, 2006;Harris, 2006;Taylor et al., 2009;Whitlock, 2011;Woodruff & Fowler, 2012;Tschopp & Mateus, 2013;Wedel & Taylor, 2013). 5. A fourth nominal species, Diplodocus hayi, was added to the genus by Holland (1924, p. 399), based on remains found at Quarry A at Red Fork of the Powder River in Wyoming. ...
... Consequently, most studies of comparative anatomy, phylogeny or functional morphology that include Diplodocus are mainly based on D. carnegii (e.g. Stevens & Parrish, 1999;Bedell & Trexler, 2005;McIntosh, 2005;Carrano, 2006;Harris, 2006;Taylor et al., 2009;Whitlock, 2011;Woodruff & Fowler, 2012;Tschopp & Mateus, 2013;Wedel & Taylor, 2013). 5. A fourth nominal species, Diplodocus hayi, was added to the genus by Holland (1924, p. 399), based on remains found at Quarry A at Red Fork of the Powder River in Wyoming. ...
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The purpose of this application, under Articles 78.1 and 81.1 of the Code, is to replace Diplodocus longus Marsh, 1878 as the type species of the sauropod dinosaur genus Diplodocus by the much better represented D. carnegii Hatcher, 1901, due to the undiagnosable state of the holotype of D. longus (YPM 1920, a partial tail and a chevron). The holotype of D. carnegii, CM 84, is a well-preserved and mostly articulated specimen. Casts of it are on display in various museums around the world, and the species has generally been used as the main reference for studies of comparative anatomy or phylogeny of the genus. Both species are known from the Upper Jurassic Morrison Formation of the western United States. The genus Diplodocus is the basis for the family-level taxa diplodocinae Marsh, 1884, diplodocidae Marsh, 1884, diplodocimorpha Marsh, 1884 (Calvo & Salgado, 1995) and diplodocoidea Marsh, 1884 (Upchurch, 1995). It is also a specifier of at least 10 phylogenetic clades. With the replacement of D. longus by D. carnegii as type species, Diplodocus could be preserved as a taxonomic name with generally accepted content. Taxonomic stability of the entire clade diplodocoidea, and the proposed definitions of several clades within Sauropoda, could be maintained.
... MOR 9728 was discovered at the MOR's O'Hair quarry (formerly known as the Strickland Creek quarry) in 2015 ( Fig. 1; T3S R9E). This site has also produced remains of Diplodocus, Apatosaurus, Camarasaurus, and Allosaurus (Cooley and Schmitt, 1998;Whitlock and Harris, 2010 [MOR 592];Woodruff and Fowler, 2012;DCW, unpubl. data). ...
Article
Stegosauria is a clade of ornithischian dinosaurs characterized by a bizarre array of dermal armor that extends from the neck to the end of the tail. Two genera of stegosaur are currently recognised from North America: the well-known Stegosaurus stenops and the much rarer Hesperosaurus mjosi. A new specimen of Hesperosaurus mjosi was discovered in some of the most northerly outcrops of the Upper Jurassic Morrison Formation near Livingston, Montana. The new specimen includes cranial, vertebral, and appendicular material as well as a dermal plate, and the excellent state of preservation of the palate reveals new anatomical information about this region in stegosaurs. Histological examination of the tibia indicates that the individual was not skeletally mature at time of death. Comparison with previously studied Stegosaurus and Hesperosaurus individuals indicates that Hesperosaurus mjosi may have been a smaller species than Stegosaurus stenops. Physiological processes scale with body mass, M, according to the relationship M0.75 in extant megaherbivores; thus, larger animals are better able to cope with more arid environments where forage is less abundant. Under this scenario, it is possible that Stegosaurus stenops and Hesperosaurus mjosi were environmentally partitioned, with the larger S. stenops occupying more arid environments. Analyses of the temporal overlap and latitudinal range of Morrison stegosaurs would allow this hypothesis to be investigated. Citation for this article: Maidment, S. C. R., D. C. Woodruff, and J. R. Horner. 2018. A new specimen of the ornithischian dinosaur Hesperosaurus mjosi from the Upper Jurassic Morrison Formation of Montana, U.S.A., and implications for growth and size in Morrison stegosaurs. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1406366.
... The distribution of neural spine bifurcation is highly homoplastic in sauropods and is also present in some turiasaurians (Turiasaurus, Moabosaurus) and various neosauropods (Wedel & Taylor 2013a), but is absent in Omeisaurus tianfuensis (He et al. 1988) and Bellusaurus (IVPP V17768). In the case of the latter taxon, the absence of neural spine bifurcation might reflect its ontogenetic stage (Woodruff & Fowler 2012; but see Taylor 2013a andMelstrom et al. 2016). As in other Core Mamenchisaurus-like Taxa, the neural spine does not project far above the dorsal surface of the postzygapophyseal ramus in Klamelisaurus; in cervicals 10-14, the SPOL makes a short (20-40 mm), near-vertical ascent to the dorsal surface of the spine . ...
Article
Fossil-rich deposits from the Middle and Late Jurassic of China have yielded a diverse array of sauropod dinosaurs, including numerous species referred to Mamenchisaurus and Omeisaurus. Despite an abundance of fossils and a proliferation of taxa, the anatomy of Middle–Late Jurassic Chinese sauropods remains poorly documented. Here, we comprehensively redescribe and illustrate Klamelisaurus gobiensis from the Middle–Late Jurassic Shishugou Formation of northwest China. Phylogenetic analyses conducted under parsimony and time-calibrated Bayesian optimality criteria consistently recover Klamelisaurus as a member of a predominantly Chinese radiation of exceptionally long-necked eusauropods that includes Mamenchisaurus spp., Chuanjiesaurus, Qijianglong and Wamweracaudia. In most analyses, this lineage also includes Euhelopus, reviving a ‘traditional’ Euhelopodidae and calling into question the macronarian affinities of Euhelopus. Klamelisaurus shares several features with Euhelopus that are unique to a subset of East Asian taxa or rare among sauropods, including a convex ventral margin of the prezygodiapophyseal lamina in middle–posterior cervical vertebrae, a ventrally bifurcated postzygodiapophyseal lamina in posterior cervical vertebrae, and development of a rugose projection extending anteriorly from the epipophysis into the spinodiapophyseal fossa in most cervical vertebrae. Anatomical comparisons of the cervical vertebrae of Klamelisaurus to several other sauropodomorphs and insights from myological studies of extant archosaurs strongly suggest that this latter structure, often considered part of an epipophyseal-prezygapophyseal lamina, is an epaxial muscle scar that is distinct from pneumatic structures of the lateral surface of the neural spine. The phylogenetic and comparative anatomical data presented here provide a foundation for future revision of the taxonomy and systematics of sauropods from the Junggar and Sichuan basins.
... However, within Diplodocoidea this feature appears only in flagellicaudatan sauropods (Whitlock, 2011b). Although this character has generally been used in phylogenetics and has been presumed to be of biomechanical significance (Tsuihiji, 2004), alternatively, an ontogenetic influence has also been proposed (but see Wedel and Taylor, 2013 for a challenge to that hypothesis; i.e., spine bifurcation is absent or less developed in smaller taxa, see Woodruff and Fowler, 2012). ...
Article
In this paper, we present an updated revision of fossil vertebrates from the Chubut Group, Golfo San Jorge Basin, while also describing some new remains. Extensive exposures of both Lower and Upper Cretaceous sedimentary sequences are present in central Patagonia. These outcrops have, over the past several decades, yielded a varied vertebrate fauna, including fishes, turtles, crocodyliforms, pterosaurs, and dinosaurs, currently herein characterized and described. Although vertebrate diversity in the Chubut Group in central Patagonia is remarkable, the most abundant vertebrates recovered are dinosaurs. The Matasiete Formation (Hauterivian?–Albian) is markedly less prolific in terms of fossils discoveries than either the Bajo Barreal Formation (Cenomanian–early Turonian) or the recently recognized Lago Colhué Huapi Formation (Coniacian–Maastrichtian). The Bajo Barreal fauna is, at a high level, typical of coeval Gondwanan faunas. However, interestingly, several taxa occupy a basal position within their respective groups. The Lago Colhué Huapi Formation has produced a more derived vertebrate fauna, again similar to those from other Gondwanan regions. Finally, in a broad context, the new materials described augment our understanding of Cretaceous terrestrial vertebrate assemblage of central Patagonia and add to the generally meager record of vertebrate in the Cretaceous of the Southern Hemisphere.
... Sauropod presacral vertebrae-and to some extent sacral and anterior caudal vertebrae-are complex, characterrich anatomical units, owing to the variation in the shape and position of their various projections (e.g., diapophyses, neural spine), patterns of internal and external pneumaticity, and vertebral laminae. This variation has heterogeneous sources, including taxonomic, serial, and ontogenetic factors (see Wilson, 2012;Woodruff and Fowler, 2012;Wedel and Taylor, 2013). For this reason, presacral, sacral, and anterior caudal vertebrae, especially those whose serial position and ontogenetic status can be constrained, can offer critical information on lower-level taxonomic identity that is not provided by other, more commonly preserved elements such as limb bones or mid-to posterior caudal vertebrae. ...
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Cretaceous dinosaurs were first reported from the Indian subcontinent in the late 1800s, and titanosaur sauropod and abelisauroid theropod remains are now known from central, western, and southern parts of India and from central western Pakistan. Although dinosaur remains are abundant, associated or articulated specimens are extremely rare, and so are complex skeletal elements such as cranial bones and presacral vertebrae. The historical pattern of sampling and collecting has limited the inferences about patterns of diversity, phylogenetic affinity, and paleobiogeographic relationships of Indian dinosaurs. Here we report on three titanosaur vertebrae representing regions of the skeleton that are complex and otherwise poorly represented in the Indian record, including two anterior dorsal vertebrae pertaining to a single individual from Rahioli, in Gujarat State (western India), and an anterior caudal neural arch from Bara Simla, in Madhya Pradesh State (central India). Phylogenetic analysis places the two individuals within Titanosauria, but further resolution of their affinities is precluded by their incompleteness and that of titanosaur vertebral columns in general, lack of coding of character data for titanosaur presacral and anterior caudal vertebrae, and relatively coarse understanding of the evolutionary relationships of titanosaurs. Comparisons with contemporaneous and spatially proximal titanosaurs from Indo-Pakistan, Madagascar, and South America provide insights into their affinities. The dorsal vertebrae share close affinity with Isisaurus from India and Mendozasaurus from Argentina. Few local comparisons are available for the anterior caudal vertebra, which shares characteristics with Tengrisaurus from the Early Cretaceous of Russia.
... This presents complications for phylogenetic analyses of trematopids because it is often predicted that taxa represented by immature specimens will be recovered in an earlier diverging position owing to the presence of plesiomorphies in immature individuals that are not equivalent to the retained plesiomorphies in early diverging taxa (e.g. Tykoski, 2005;Woodruff & Fowler, 2012;Carballido & Sander, 2014;Tsai & Fordyce, 2014). ...
Article
Trematopids are a clade of terrestrial Permo-Carboniferous temnospondyl amphibians. The intrarelationships of this clade are poorly known. This is largely attributable to a substantial disparity in size between type specimens, which range from the small-bodied lectotype of Mattauschia laticeps (< 4 cm skull length) to the large-bodied holotype of Acheloma cumminsi (> 15 cm skull length). Inferred correlation of size disparity with ontogenetic disparity has led previous workers either to omit taxa in phylogenetic analyses or to forgo an analysis altogether. Here, I take a specimen-level approach and multiple subsampling permutations to explore the phylogeny of the Trematopidae as a case study for assessing the effects of ontogenetic disparity on phylogenetic reconstruction in temnospondyls. The various analyses provide evidence that ontogenetic disparity confounds the phylogenetic inference of trematopids but without a directional bias. Tree topologies of most permutations are poorly resolved and weakly supported, reflecting character conflict that results from the inability of the analyses to differentiate retained plesiomorphies from juvenile features. These findings urge caution in the interpretation of phylogenetic analyses for which ontogenetic disparity exists, but is unaccounted for, and provide a strong impetus for more directed exploration of the interplay of ontogeny and phylogeny across Temnospondyli.
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Barosaurus is a diplodocid sauropod from the Upper Jurassic Morrison Formation of the western United States, and is known for its very long neck. It is related to the sympatric Diplodocus , and often thought of as more or less identical except with a longer neck. The holotype YPM 429 includes three and a half posterior cervical vertebrae, somewhat distorted and damaged, which are nevertheless very distinctive and quite different from those of Diplodocus . The cervicals of the better known and more complete referred Barosaurus specimen AMNH 6341 show the same characteristic features as the holotype, though not to the same extent: transversely broad but anteroposteriorly short zygapophyseal facets; prezygapophyses carried on broad, squared-off rami; zygapophyses shifted forward relative to the centrum; diapophyses, parapophyses and neural spines shifted backwards; and broad diapophyseal “wings”. These features form a single functional complex, enabling great lateral flexibility, but restricting vertical flexibility. This may indicate that Barosaurus used a different feeding style from other sauropods perhaps sweeping out long arcs at ground level. The Morrison Formation contains at least nine diplodocid species in six to eight genera whose relationships are not yet fully understood, but Barosaurus remains distinct from its relatives.
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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.
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In the summer of 1878, American paleontologist Edward Drinker Cope published the discovery of a sauropod dinosaur that he named Amphicoelias fragillimus. What distinguishes A. fragillimus in the annals of paleontology is the immense magnitude of the skeletal material. The single incomplete dorsal vertebra as reported by Cope was a meter and a half in height, which when fully reconstructed, would make A. fragillimus the largest vertebrate ever. After this initial description Cope never mentioned A. fragillimus in any of his scientific works for the remainder of his life. More than four decades after its description, a scientific survey at the American Museum of Natural History dedicated to the sauropods collected by Cope failed to locate the remains or whereabouts of A. fragillimus. For nearly a century the remains have yet to resurface. The enormous size of the specimen has generally been accepted despite being well beyond the size of even the largest sauropods known from verifiable fossil material (e.g. Argentinosaurus). By deciphering the ontogenetic change of Diplodocoidea vertebrae, the science of gigantism, and Cope’s own mannerisms, we conclude that the reported size of A. fragillimus is most likely an extreme over-estimation.
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Nils Knötschke (2014): Cranial anatomy of the Late Jurassic dwarf sauropod Europasaurus holgeri (Dinosauria, Camarasauromorpha): ontogenetic changes and size dimorphism, Journal of Systematic Palaeontology, makes every effort to ensure the accuracy of all the information (the "Content") contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at
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Sauropods were the most successful herbivorous group of dinosaurs during the Mesozoic era. Despite their supremacy as reflected in the fossil record, sauropod skulls are very rare and current knowledge of skull anatomy is based on just a few taxa. Juvenile skull bones are even rarer than adult skulls; thus, our understanding of their morphology and ontogenetic changes is limited. The recent discovery of several adult and juvenile specimens of a Late Jurassic taxon from Germany, Europasaurus holgeri, extends our knowledge of sauropod skull anatomy. A total of 123 skull bones, representing at least 14 skulls, were examined, described and compared to other taxa. The skull material includes several individuals of various ontogenetic stages. Because size alone is not sufficient to determine the morphological ontogenetic stage (MOS), sizeindependent characters were used to stage the bone elements. Detailed studies of the skull bones proved that the material represents two morphotypes, independent of ontogenetic stage. Since the original description of Europasaurus, new skull material has been found, and an updated skull reconstruction of an adult individual is presented here. All the autapomorphic characters of Europasaurus recognized in the skull (i.e. anteroposteriorly long and lateromedially narrow frontal; presence of postparietal fenestra; large participation of the jugal to the ventral rim of the skull and the orbit; presence of a postparietal foramen and single optic foramen) are plesiomorphic characters of basal sauropodomorphs and/ or present in embryos and juvenile sauropods. Therefore, we consider that in Europasaurus these characters evolved through paedomorphosis, which resulted in the dwarf condition of this taxon.
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editors before the paper is published in its final form. Please note that during the production process errors may be discovered which could affect the content. All legal disclaimers that apply to the journal pertain.. Bone microstructure and relative age of the holotype specimen of the diplodocoid sauropod dinosaur Suuwassea emilieae. Acta Palaeontologica Polonica 5X (X): xxx-xxx. We present the first study of bone microstructure in Suuwassea emilieae, a diplodocoid sauropod from the Morrison Formation. Although the holotype of Suuwassea was recently identified as a subadult, bone histology demonstrates that this individual had reached sexual maturity at approximately 75–80% of maximum adult size. The smaller size of the holotype of Suuwassea relative to contemporary sauropods is due to ontogeny rather than a true reflection of adult size. A fully adult individual would have likely been similar in size to a fully adult specimen of Apatosaurus. Suuwassea has a number of plesiomorphic characters that might have been explained by its supposed early ontogenetic status, and would then have called the validity of the taxon into question. However, our demonstration that it was an adult confirms that these features represent retention of plesiomorphic character states or evolutionary reversals in a derived animal. Additionally, the specimen shows extensive cortical drift and secondary osteon formation related to skeletal loading, which is often obscured by complete remodeling of Haversian systems in sauropod taxa. There are substantial differences in the microstructure across the bone, which could make histologic samples not based upon complete cross sections problematic. Suuwassea is one of four currently recognized dicraeosaurid taxa, and this study contributes potential taxonomic characters in sauropod bone microstructure.
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In the summer of 1878, American paleontologist Edward Drinker Cope published the discovery of a sauropod dinosaur that he named Amphicoelias fragillimus. What distinguishes A. fragillimus in the annals of paleontology is the immense magnitude of the skeletal material. The single incomplete dorsal vertebra as reported by Cope was a meter and a half in height, which when fully reconstructed, would make A. fragillimus the largest vertebrate ever. After this initial description Cope never mentioned A. fragillimus in any of his scientific works for the remainder of his life. More than four decades after its description, a scientific survey at the American Museum of Natural History dedicated to the sauropods collected by Cope failed to locate the remains or whereabouts of A. fragillimus. For nearly a century the remains have yet to resurface. The enormous size of the specimen has generally been accepted despite being well beyond the size of even the largest sauropods known from verifiable fossil material (e.g. Argentinosaurus). By deciphering the ontogenetic change of Diplodocoidea vertebrae, the science of gigantism, and Cope’s own mannerisms, we conclude that the reported size of A. fragillimus is most likely an extreme over-estimation.
Article
Vertebral neural spine bifurcation has been historically treated as largely restrictive to sauropodomorph dinosaurs; wherein it is inferred to be an adaptation in response to the increasing weight from the horizontally extended cervical column. Because no extant terrestrial vertebrates have massive, horizontally extended necks, extant forms with large cranial masses were examined for the presence of neural spine bifurcation. Here, I report for the first time on the soft tissue surrounding neural spine bifurcation in a terrestrial quadruped through the dissection of three Ankole-Watusi cattle. With horns weighing up to a combined 90 kg, the Ankole-Watusi is unlike any other breed of cattle in terms of cranial weight and presence of neural spine bifurcation. Using the Ankole-Watusi as a model, it appears that neural spine bifurcation plays a critical role in supporting a large mobile weight adjacent to the girdles. In addition to neural spine bifurcation being recognized within nonavian dinosaurs, this vertebral feature is also documented within many members of temnospondyls, captorhinids, seymouriamorphs, diadectomorphs, Aves, marsupials, artiodactyls, perissodactyls, and Primates, amongst others. This phylogenetic distribution indicates that spine bifurcation is more common than previously thought, and that this vertebral adaptation has contributed throughout the evolutionary history of tetrapods. Neural spine bifurcation should now be recognized as an anatomical component adapted by some vertebrates to deal with massive, horizontal, mobile weights adjacent the girdles. J. Morphol., 2014. © 2014 Wiley Periodicals, Inc.
Article
A cervical vertebra preserved at the famous and productive Cleveland-Lloyd Dinosaur Quarry in the Upper Jurassic Morrison Formation of Utah is that of an Apatosaurus, a sauropod dinosaur genus not previously recognized at the site and the first new dinosaur taxon identified at the site in years. The presence of Apatosaurus at a mudstone site dominated by other taxa, both theropod and sauropod, suggests a pattern of preservation within the Morrison Formation in which sites in fine-grained sediments yield dramatically uneven relative abundances of dinosaurs, with variable dominant taxa by site, compared with more time-averaged and attritional coarse-grained channel sandstone deposits. In addition, the continued demonstration of the wide-spread occurrence and abundance of Apatosaurus within the Morrison Formation, and the absence of its clade among diplodocid faunas on other continents, suggest that this group may have been endemic to North America during the Late Jurassic and that it may have originated there, though this is far from clear.
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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.
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Bellusaurus sui is an enigmatic sauropod dinosaur from the Middle-Late Jurassic Shishugou Formation of northwest China. Bellusaurus is known from a monospecific bonebed preserving elements from more than a dozen juvenile individuals, including numerous bones of the skull, providing rare insight into the cranial anatomy of juvenile sauropods. Here, we present a comprehensive description of the cranial anatomy of Bellusaurus , supplementing the holotypic cranial material with additional elements recovered from recent joint Sino-American field expeditions. Bellusaurus is diagnosed by several unique autapomorphies, including a neurovascular foramen piercing the ascending process of the maxilla at midheight, the frontal process of the nasal extending farther posteriorly onto the frontal than the prefrontal, and U-shaped medial and lateral notches in the posterior margin of the ventral process of the squamosal. Several features identified here, including a preantorbital opening in the maxilla, a stepped dorsal margin of the vomerine process of the pterygoid, and the partitioning of the dorsal midline endocranial fossae associated with the dural venous sinuses into anterior and posterior components by a transverse ridge of the parietal, are consistent with recent phylogenetic hypotheses that recover Bellusaurus as a basal macronarian or close relative of Neosauropoda. We review the current state of knowledge of sauropod cranial ontogeny, placing several aspects of the cranial anatomy of Bellusaurus in an ontogenetic context and providing explicit hypotheses of ontogenetic transformations that can be tested by future discoveries of ontogenetic variants of sauropod skulls. While scoring ontogenetically variable characters as unknown may help to alleviate the biasing effects of ontogeny on the phylogenetic position of juvenile specimens, we caution that this approach may remove phylogenetically informative character information, and argue that inference methods that are known to be less sensitive to homoplasy than equal weights parsimony (i.e., implied weights parsimony; Bayesian approaches) should also be employed.
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The plated dinosaur Stegosaurus longispinus came from the Morrison Formation (Upper Jurassic) near Alcova, Wyoming, USA. Only the femur and plaster casts of the posterior pair of long dermal tail spines survived destructive water damage in the 1920s. This surviving material and archival photographs showing the bones in the quarry and as exhibited allow us to expand the original description. S. longispinus Gilmore, 1914 is made the type species of Alcovasaurus n. gen. as A. longispinus (Gilmore, 1914). Autapomorphies include the continuation of transverse processes to the distal caudal vertebrae; distal caudal centra anteroposteriorly short so height exceeds length; both distal dermal spine pairs with a very long slender shaft at ~90% of femoral length, and posterior pair widest at 25% of length. Natronasaurus longispinus was proposed by Ulansky (2014) for S. longispinus. However this failed to meet the requirements of the International Code of Zoological Nomenclature, as is also true for 17 other names proposed for basal thyreophorans and stegosaurs.
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Historically, sauropods have been largely perceived as having vertical, ‘S’-curved necks which were hypothesised to allow them to feed from the canopy of trees. Within the past two decades, this popular perception has been questioned, resulting in a debate over neck posture. The osteological differences between sauropods with horizontal neck posture (Diplodocus), and less horizontally inclined necks (Brachiosaurus) suggest differing life and feeding styles. One differing vertebral feature between these polarised bauplans is the bifurcated neural spine. Regardless of the spine condition, sauropods with and without bifurcated spines have been reconstructed exhibiting the same neck posture. Corroborating histology and morphology in extant taxa highlights the presence of modified vertebral ligaments associated with bifurcated spines. Using these extant taxa to better understand the biomechanics of bifurcated spines, this study proposes alternative soft tissue reconstructions. Previous depictions had the bifurcation trough entirely open or harbouring pneumatic diverticula or muscles; conversely this study proposes that the apices of the bifurcated spines were the anchoring points for a split nuchal ligament, and that the trough of bifurcation was predominantly filled with interspinal ligaments. Ligaments provide energy-efficient elastic rebound, and a paired ligament in the cervical series would aid in prolonged, lateral movement in a horizontal plane (i.e. feeding).
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Barosaurus is a diplodocid sauropod from the Upper Jurassic Morrison Formation of the western United States, and is known for its very long neck. It is closely related to the sympatric Diplodocus , and often thought of as more or less identical except with a longer neck. The holotype YPM 429 includes three and a half posterior cervical vertebrae, somewhat distorted and damaged, which are nevertheless very distinctive and quite different from those of Diplodocus . The cervicals of the better known and more complete referred Barosaurus specimen AMNH 6341 show the same characteristic features as the holotype, though not to the same extent: transversely broad but anteroposteriorly short zygapophyseal facets; prezygapophyses carried on broad, squared-off rami; zygapophyses shifted forward relative to the centrum; diapophyses, parapophyses and neural spines shifted backwards; and broad diapophyseal “wings”. These features form a single functional complex, enabling great lateral flexibility, but restricting vertical flexibility. This may indicate that Barosaurus used a different feeding style from other sauropods perhaps sweeping out long arcs at ground level. The Morrison Formation contains at least nine diplodocid species in six to eight genera whose relationships are not yet fully understood, but Barosaurus remains distinct from its relatives.
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Barosaurus is a diplodocid sauropod from the Upper Jurassic Morrison Formation of the western United States, and is known for its very long neck. It is closely related to the sympatric Diplodocus, and often thought of as more or less identical except with a longer neck. The holotype YPM 429 includes three and a half posterior cervical vertebrae, somewhat distorted and damaged, which are nevertheless very distinctive and quite different from those of Diplodocus. The cervicals of the better known and more complete referred Barosaurus specimen AMNH 6341 show the same characteristic features as the holotype, though not to the same extent: transversely broad but anteroposteriorly short zygapophyseal facets; prezygapophyses carried on broad, squared-off rami; zygapophyses shifted forward relative to the centrum; diapophyses, parapophyses and neural spines shifted backwards; and broad diapophyseal “wings”. These features form a single functional complex, enabling great lateral flexibility, but restricting vertical flexibility. This may indicate that Barosaurus used a different feeding style from other sauropods perhaps sweeping out long arcs at ground level. The Morrison Formation contains at least nine diplodocid species in six to eight genera whose relationships are not yet fully understood, but Barosaurus remains distinct from its relatives.
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Diplodocids are among the best known sauropod dinosaurs. Numerous specimens of currently 15 accepted species belonging to ten genera have been reported from the Late Jurassic to Early Cretaceous of North and South America, Europe, and Africa. The highest diversity is known from the Upper Jurassic Morrison Formation of the western United States: a recent review recognized 12 valid, named species, and possibly three additional, yet unnamed ones. One of these is herein described in detail and referred to the genus Galeamopus. The holotype specimen of Galeamopus pabsti sp. nov., SMA 0011, is represented by material from all body parts but the tail, and was found at the Howe-Scott Quarry in the northern Bighorn Basin in Wyoming, USA. Autapomorphic features of the new species include a horizontal canal on the maxilla that connects the posterior margin of the preantorbital and the ventral margin of the antorbital fenestrae, a vertical midline groove marking the sagittal nuchal crest, the presence of a large foramen connecting the postzygapophyseal centrodiapophyseal fossa and the spinopostzygapophyseal fossa of mid- and posterior cervical vertebrae, a very robust humerus, a laterally placed, rugose tubercle on the concave proximal portion of the anterior surface of the humerus, a relatively stout radius, the absence of a distinct ambiens process on the pubis, and a distinctly concave posteroventral margin of the ascending process of the astragalus. In addition to the holotype specimen SMA 0011, the skull USNM 2673 can also be referred to Galeamopus pabsti. Histology shows that the type specimen SMA 0011 is sexually mature, although neurocentral closure was not completed at the time of death. Because SMA 0011 has highly pneumatized cervical vertebrae, the development of the lamination appears a more important indicator for individual age than neurocentral fusion patterns. SMA 0011 is one of very few sauropod specimens that preserves the cervico-dorsal transition in both vertebrae and ribs. The association of ribs with their respective vertebrae shows that the transition between cervical and dorsal vertebrae is significantly different in Galeamopus pabsti than in Diplodocus carnegii or Apatosaurus louisae, being represented by a considerable shortening of the centra from the last cervical to the first dorsal vertebra. Diplodocids show a surprisingly high diversity in the Morrison Formation. This can possibly be explained by a combination of geographical and temporal segregation, and niche partitioning.
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A partial skeleton from the Little Snowy Mountains of central Montana is the first referable specimen of the Morrison Formation macronarian sauropod Camarasaurus. This specimen also represents the northernmost occurrence of a sauropod in the Morrison. Histological study indicates that, although the specimen is relatively small statured, it is skeletally mature; this further emphasizes that size is not a undeviating proxy to maturity in dinosaurs, and that morphologies associated with an individual’s age and stature may be more nebulous in sauropods.
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COX-2 is expressed highly in pancreatic cancer and implicated in tumor progression. COX-2 inhibition can reduce tumor growth and augment therapy. The precise function of COX-2 in tumors remains poorly understood, but it is implicated in tumor angiogenesis, evasion of apoptosis, and induction of epithelial-to-mesenchymal transition (EMT). Current therapeutic regimens for pancreatic cancer are minimally effective, highlighting the need for novel treatment strategies. Here, we report that apricoxib, a novel COX-2 inhibitor in phase II clinical trials, significantly enhances the efficacy of gemcitabine/erlotinib in preclinical models of pancreatic cancer. Human pancreatic cell lines were evaluated in vitro and in vivo for response to apricoxib ± standard-of-care therapy (gemcitabine + erlotinib). Tumor tissue underwent posttreatment analysis for cell proliferation, viability, and EMT phenotype. Vascular parameters were also determined. COX-2 inhibition reduced the IC(50) of gemcitabine ± erlotinib in six pancreatic cancer cell lines tested in vitro. Furthermore, apricoxib increased the antitumor efficacy of standard combination therapy in several orthotopic xenograft models. In vivo apricoxib combination therapy was only effective at reducing tumor growth and metastasis in tumors with elevated COX-2 activity. In each model examined, treatment with apricoxib resulted in vascular normalization without a decrease in microvessel density and promotion of an epithelial phenotype by tumor cells regardless of basal COX-2 expression. Apricoxib robustly reverses EMT and augments standard therapy without reducing microvessel density and warrants further clinical evaluation in patients with pancreatic cancer. Clin Cancer Res; 18(18); 5031-42. ©2012 AACR.
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Rebbachisauridae are poorly known 'bizarre' sauropods with two nearly complete skeletons collected: Limaysaurus tessonei and Nigersaurus taqueti. Whereas the latter taxon allowed the understanding of their cranial novelties, other species show some peculiarities in the postcranium. L. tessonei, Rebbachisaurus garasbae and a new form (MMCH-Pv-49) from Villa El Chocón, Patagonia, exhibit peculiar pectoral girdles and the loss of the hyposphene-hypantrum accessory articulations in their amphiplathyan dorsal vertebrae. Actually, the postzygapophyses are not only devoid of hyposphenal locks but also additionally show a curved postzygapophyseal eave that allows a sliding over the corresponding structure of the anterior side of the neural arch, a curved concave and elongated platform continuous along both prezygapophyses: the prezygapophyseal shelf. As the 'ball and socket' opisthocoelous centra in macronarians optimised mobility, the 'U-eaves and shelf complex' of rebbachisaurids permitted wider movements between successive vertebrae. While in titanosaurs the increased mobility occurred related to the centrum shape, in rebbachisaurids it is related to a complex system in the neural arch. Furthermore, whereas macronarians show large centra, rebbachisaurids underwent a minimisation of the centrum. These changes in both sauropod lineages probably had an outstanding relevance in the diversity and ecological roles that sauropods experienced in Cretaceous terrestrial ecosystems.
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The stress on the intervertebral discs in the necks of Brachiosaurus brancai, Diplodocus carnegii, and Dicraeosaurus hansemanni are calculated for various hypothetical neck postures. Assuming similar safety factors along the neck and a predominance of static or quasistatic forces, neck postures in which the stress is not more or less constant along the neck are rejected. The necks of two large and long-necked recent mammals, Giraffa camelopardalis and Camelus sp., are examined in the same way in order to test the method. The method is shown to be suitable for the reconstruction of the habitual posture of longnecked terrestrial vertebrates, even if the distribution of mass along the head and neck and the lever arms of the neck muscles and ligaments are only roughly estimated. Among sauropods, the neck posture differed considerably, being nearly vertical in Brachiosaurus brancai, but more horizontal in Dicraeosaurus hansemanni and especially in Diplodocus carnegii. Therefore, Brachiosaurus brancai appears to have been an extremely specialised high browser, whereas in Diplodocus carnegii and in Dicraeosaurus hansemanni the long neck permitted a large feeding volume. The constrast in neck posture is reflected in the overall body design, especially in tail and limb length. Für verschiedene Halsstellungen von Brachiosaurus brancai, Diplodocus carnegii und Dicraeosaurus hansemanni wurde der Druck auf den Gelenkknorpel der Zwischenwirbelgelenke berechnet. Halsstellungen, die nicht zu einem mehr oder weniger konstanten Druck entlang des Halses führten, wurden verworfen. Dabei wurden gleiche Sicherheitsfaktoren des Gelenkknorples sowie das Vorherrschen von statischen und quasistatischen Kräften entlang des Halses angenommen. Die Hälse zweier langhalsiger Säugetiere, Giraffa camelopardalis und Camelus sp., wurden in gleicher Weise analysiert, um die Methode zu überprüfen. Diese erwies sich als geeignet, die habituelle Halsstellung eines langhalsigen terrestrischen Wirbeltieres zu rekonstruieren, selbst wenn die Massenverteilung entlang des Halses und die Hebelarme der epaxialen Muskeln, Sehnen und Bänder nur grob geschätzt werden können. Unter den Sauropoden variierte die Halsstellung erheblich von nahezu vertikal bei Brachiosaurus brancai bis zu eher horizontal bei Diplodocus carnegii. Die Halsstellung von Dicraeosaurus hansemanni lag näher bei der Halsstellung von Diplodocus als von Brachiosaurus. Offenbar war Brachiosaurus darauf spezialisiert, Nahrung aus großen Höhen aufzunehmen, während Diplodocus und Dicraeosaurus ihre langen Hälse zum Abweiden eines weiten Areals nutzten. Die Unterschiede in der Halsstellung spiegeln sich in der Körperform, insbesondere in der Schwanz- und Beinlänge, wider. doi:10.1002/mmng.20020050116
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The vertebrae of sauropod dinosaurs are characterized by complex architecture involving laminae, fossae, and internal chambers of various shapes and sizes. These structures are interpreted as osteological correlates of an intricate system of air sacs and pneumatic diverticula similar to that of birds. In basal sauropods pneumatic features are limited to fossae. Camerae and camellae are internalized pneumatic chambers independently acquired in neosauropods and some Chinese forms. The polycamerate and camellate vertebrae of higher neosauropods are characterized by internal pneumatic chambers of considerable complexity. The independent acquisition of these derived morphologies in Mamenchisaurus, derived diplodocids, and most titanosauriforms is correlated with increasing size and neck length. The presacrai vertebrae of basal sauropods were probably pneumatized by diverticula of cervical air sacs similar to those of birds. Although pneumatic characters in sauropods are most extensive and complex in presacrai vertebrae, the sacrum was also pneumatized in most neosauropods. Pneumatization of the proximal caudal vertebrae was achieved independently in diplodocids and titanosaurids. In birds, the synsacrum is pneumatized via abdominal air sacs which function primarily in lung ventilation. The presence of pneumatized sacral and caudal vertebrae in neosauropods indicates that abdominal air sacs were probably present in at least some sauropods.
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The holotype of the Late Jurassic sauropod dinosaur Seismosaurus hallorum consists of part of the thoracic and caudal vertebrae, most of the sacrum and pelvis, some ribs and chevrons and an incomplete femur. Reexamination of the holotype indicates that Seismosaurus hallorum differs little from Diplodocus, and none of the morphological differences are significant enough to justify a separate genus. Particularly important to this conclusion has been careful re-examination and further preparation of the ischium of the S. hallorum holotype, which indicates that the distal, hook-like process originally described was actually the tip of a vertebral neural spine and sandstone matrix adhering to the ischium. We consider Seismosaurus to be a junior subjective synonym of Diplodocus. We suggest that Diplodocus hallorum is also a junior subjective synonym of D. longus, but a careful taxonomic revision of the species of Diplodocus is needed to verify this suggestion.
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More than any other sauropod dinosaur group, the long-necked herbivores belonging to Diplodocoidea have been defined by their skulls. Their unique skull shape, which is extremely elongate antorbitally, with a transversely broad, square snout packed at its anterior extreme with narrow-crowned, pencil-like teeth, has served as a touchstone for describing the biology of these animals ever since the discovery of the first skull in the late 19th century. In particular, the unusual diplodocoid skull has been discussed frequently in the context of examining feeding behavior, spawning hypotheses ranging from branch stripping, propalinal shearing, and aquatic plant ‘grazing.’ Here, we describe a juvenile skull of Diplodocus (Carnegie Museum 11255) that does not share the unusually blunted snout and anteriorly sequestered teeth seen in adult specimens, suggesting that adults and juveniles may have differed greatly in their feeding behavior, an ontogenetic distinction that may be unique among sauropodomorphs.
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A nearly complete skeleton of a juvenile sauropod from the Lower Morrison Formation (Late Jurassic, Kimmeridgian) of the Howe Ranch in Bighorn County, Wyoming is described. The specimen consists of articulated mid-cervical to mid-caudal vertebrae and most appendicular bones, but cranial and mandibular elements are missing. The shoulder height is approximately 67 cm, and the total body length is estimated to be less than 200 cm. Besides the body size, the following morphological features indicate that this specimen is an early juvenile; (1) unfused centra and neural arches in presacral, sacral and first to ninth caudal vertebrae, (2) unfused coracoid and scapula, (3) open coracoid foramen, and (4) relatively smooth articular surfaces on the limb, wrist, and ankle bones. A large scapula, short neck and tail and elongate forelimb bones relative to overall body size demonstrate relative growth. A thin-section of the mid-shaft of a femur shows a lack of annual growth lines, indicating an early juvenile individual possibly younger than a few years old. Pneumatic structures in the vertebral column of the specimen SMA 0009 show that pneumatisation of the postcranial skeleton had already started in this individual, giving new insights in the early ontogenetic development of vertebral pneumaticity in sauropods. The specimen exhibits a number of diplodocid features (e.g., very elongate slender scapular blade with a gradually dorsoventrally expanded distal end, a total of nine dorsal vertebrae, presence of the posterior centroparapophyseal lamina in the posterior dorsal vertebrae). Although a few diplodocid taxa, Diplodocus, cf. Apatosaurus, and cf. Barosaurus, are known from several fossil sites near the Howe Ranch, identification of this specimen, even at a generic level, is difficult due to a large degree of ontogenetic variation.
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A new specimen of Supersaurus vivianae is described, providing additional information about the osteology of Supersaurus. The single Supersaurus individual that the WDC quarry produced allows a re- examination of elements referred to Supersaurus from the Dry Mesa quarry. The osteology supports maintaining the generic distinction of Supersaurus. Phylogenetic evaluation finds a monophyletic Apatosaurinae containing (Apatosaurus + Supersaurus) + Suuwassea, and a monophyletic Diplodocinae containing (Diplodocus + Seismosaurus) + Barosaurus, although the generic distinction of Seismosaurus is not supported in the current analysis. RESUMO: Morfologia de um espécime de Supersaurus (Dinosauria, Sauropoda) da Formação Morrison de Wyoming e uma reavaliação da filogenia de diplodocídeos. Um novo espécime de Supersaurus vivianae é descrito, acrescentando informações sobre a osteologia de Supersaurus. O único indivíduo de Supersaurus coletado no afloramento WDC permite o re-exame dos elementos referidos a Supersaurus do afloramento de Dry Mesa. A osteologia suporta a manutenção da distinção genérica de Supersaurus. Uma avaliação filogenética resultou em um grupo monofilético Apatosaurinae contendo (Apatosaurus + Supersaurus) + Suuwassea, e um grupo monofilético Diplodocinae contendo (Diplodocus + Seismosaurus) + Barosaurus, embora a distinção genérica de Seismosaurus não esteja suportada na presente análise.
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Lower Cretaceous fossils from central Niger document the succession of sauropod dinosaurs on Africa as it drifted into geographic isolation. A new broad-toothed genus of Neocomian age (∼135 million years ago) shows few of the specializations of other Cretaceous sauropods. A new small-bodied sauropod of Aptian-Albian age (∼110 million years ago), in contrast, reveals the highly modified cranial form of rebbachisaurid diplodocoids. Rates of skeletal change in sauropods and other major groups of dinosaurs are estimated quantitatively and shown to be highly variable.
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Bones of Alamosaurus sanjuanensis were collected from the Upper Cretaceous Javelina and Black Peaks formations in Big Bend National Park, Texas, for use in the first extensive histological study of a titanosaurian sauropod dinosaur. Samples include cervical, dorsal, and caudal vertebrae; ribs; a scapula; humeri; an ulna; a metacarpal; an ischium; femora; a tibia; fibulae; and a metatarsal, representing a minimum of twenty two individuals between 35% and 100% maximum length. In elements of less than 60% maximum length, cortical tissue is primarily reticular or plexiform fibro-lamellar, often with modulations. Resorption in some specimens appears to have proceeded as outwardly expanding bands. In larger specimens (70–79% maximum length), primary tissue is only visible interstitially as either fibro-lamellar or parallel-fibered with low vascularity and annuli. Secondary osteons are in many places linearly arranged. Haversian systems are so pervasive in many of the largest specimens (80–100% maximum length) that virtually no primary tissue remains. However, one adult sized femur possesses laminar fibro-lamellar tissue in its outer cortex, suggesting that the adult size for Alamosaurus may have been underestimated. Camellae typical of titanosaur dorsal vertebrae are present in Alamosaurus but absent in caudal vertebrae. Although pneumatic dorsal ribs characterize Titanosauriformes, sections of ribs analyzed in this study show the cavities in Alamosaurus are much more extensive than most previously described. Overall, Alamosaurus bone histology combines characteristics found in less derived sauropods, such as an early onset of secondary reconstruction, with novel characters such as extensively pneumatic ribs and longer retention of juvenile tissue.
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A juvenile skull of the tyrannosaurid Tarbosaurus bataar found in the Bugin Tsav locality in the Mongolian Gobi Desert is described. With a total length of 290 mm, the present specimen represents one of the smallest skulls known for this species. Not surprisingly, it shows various characteristics common to juvenile tyrannosaurids, such as the rostral margin of the maxillary fenestra not reaching that of the external antorbital fenestra and the postorbital lacking the cornual process. The nasal bears a small lacrimal process, which disappears in adults. Lacking some of the morphological characteristics that are adapted for bearing great feeding forces in adult individuals, this juvenile specimen suggests that T. bataar would have changed its dietary niches during ontogeny. The numbers of alveoli in the maxilla (13) and dentary (14 and 15) are the same as those in adults, suggesting that they do not change ontogenetically in T. bataar and thus are not consistent with the hypothesis that the numbers of alveoli decreases ontogenetically in tyrannosaurids.
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Two embryonic skeletons preserved inside thin-shelled eggs of a partially preserved clutch from the Upper Elliot Formation (Lower Jurassic) of South Africa have been attributed to the sauropodomorph dinosaur Massospondylus carinatus. A virtually complete skeleton is exposed in right lateral view, with the slightly telescoped skull and several cervical vertebrae extending beyond the eggshell. A second, partial skeleton has a skull preserved in dorsal view. The embryos have proportionately very large skulls, with the broad skull table formed by wide parietals and frontals. The wide posterolateral wing of the frontal separates the postorbital from contact with the parietal. The embryos have short rather than elongated cervical vertebrae, with tall rather than low neural arches. The large forelimbs are only slightly shorter than the hind limbs, which suggests an obligatory quadrupedal posture for the hatchlings. This pattern may represent an ontogenetic constraint related to the large size of the head and horizontally oriented neck. Similarities between the embryonic and post-hatchling specimens include the slenderness of the lower jaw and slight ventral curvature of the symphyseal portion of the dentary, the large supraorbital process of the prefrontal, and the tall antorbital and infratemporal fenestrae. There are 10 cervical, 14 dorsal, and three sacral vertebrae. The large distal claw-bearing phalanx of manual digit 1 is longer than any other phalangeal element of either manus or pes. The embryos of Massospondylus carinatus represent the oldest dinosaurian embryos known to date.
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The vertebrae of sauropod dinosaurs are characterized by complex architecture involving laminae, fossae, and internal chambers of various shapes and sizes. These structures are interpreted as osteological correlates of an intricate system of air sacs and pneumatic diverticula similar to that of birds. In basal sauropods pneumatic features are limited to fossae. Camerae and camellae are internalized pneumatic chambers independently acquired in neosauropods and some Chinese forms. The polycamerate and camellate vertebrae of higher neosauropods are characterized by internal pneumatic chambers of considerable complexity. The independent acquisition of these derived morphologies in Mamenchisaurus, derived diplodocids, and most titanosauriforms is correlated with increasing size and neck length.The presacrai vertebrae of basal sauropods were probably pneumatized by diverticula of cervical air sacs similar to those of birds. Although pneumatic characters in sauropods are most extensive and complex in presacrai vertebrae, the sacrum was also pneumatized in most neosauropods. Pneumatization of the proximal caudal vertebrae was achieved independently in diplodocids and titanosaurids. In birds, the synsacrum is pneumatized via abdominal air sacs which function primarily in lung ventilation. The presence of pneumatized sacral and caudal vertebrae in neosauropods indicates that abdominal air sacs were probably present in at least some sauropods.
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Long bones (femora, humeri) are the most abundant remains of sauropod dinosaurs. Their length is a good proxy for body length and body mass, and their histology is informative about ontogenetic age. Here we provide a comparative assessment of histologic changes in growth series of several sauropod taxa, including diplodocids (Apatosaurus, Diplodocus, indeterminate Diplodocinae from the Tendaguru Beds and from the Morrison Formation), basal macronarians (Camarasaurus, Brachiosaurus, Europasaurus), and titanosaurs (Phuwiangosaurus, Ampelosaurus). A total of 167 long bones, mainly humeri and femora, and 18 limb girdle bones were sampled. Sampling was performed by core drilling at prescribed locations at midshaft, and 13 histologic ontogenetic stages (HOS stages) were recognized. Because growth of all sauropod long bones is quite uniform, with laminar fibrolamellar bone being the dominant tissue, HOS stages could be recognized across taxa, although with minor differences. Histologic ontogenetic stages generally correlate closely with body size and thus provide a means to resolve important issue like the ontogenetic status of questionable specimens. We hypothesize that sexual maturity was attained at HOS-8, well before maximum size was attained, but we did not find sexually differentiated growth trajectories subsequent to HOS-8. On the basis of HOS stages, we detected two morphotypes in the Camarasaurus sample, a small one (type 1) and a larger one (type 2), presumably representing different species or sexual dimorphism.
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D. 2009. Head and neck posture in sauropod dinosaurs inferred from extant ani− mals. Acta Palaeontologica Polonica 54 (2): 213–220. The neck posture of sauropod dinosaurs has long been controversial. Recent reconstructions position the cervical verte− brae and skull in an "osteological neutral pose" (ONP), the best fit arrived at by articulating the vertebrae with the zygapophyses in maximum contact. This approach in isolation suggests that most or all sauropods held their necks hori− zontally. However, a substantial literature on extant amniotes (mammals, turtles, squamates, crocodilians and birds) shows that living animals do not habitually maintain their necks in ONP. Instead, the neck is maximally extended and the head is maximally flexed, so that the mid−cervical region is near vertical. Unless sauropods behaved differently from all extant amniote groups, they must have habitually held their necks extended and their heads flexed. The life orientation of the heads of sauropods has been inferred from the inclination of the semi−circular canals. However, extant animals show wide variation in inclination of the "horizontal" semi−circular canal: the orientation of this structure is not tightly con− strained and can give only a general idea of the life posture of extinct animals' heads.
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Rebbachisauridae are poorly known 'bizarre' sauropods with two nearly complete skeletons collected: Limaysaurus tessonei and Nigersaurus taqueti. Whereas the latter taxon allowed the understanding of their cranial novelties, other species show some peculiarities in the postcranium. L. tessonei, Rebbachisaurus garasbae and a new form (MMCH-Pv-49) from Villa El Chocón, Patagonia, exhibit peculiar pectoral girdles and the loss of the hyposphene – hypantrum accessory articulations in their amphyplathian dorsal vertebrae. Actually, the postzygapophyses are not only devoid of hyposphenal locks but also additionally show a curved postzygapophyseal eave that allows a sliding over the corresponding structure of the anterior side of the neural arch, a curved concave and elongated platform continuous along both prezygapophyses: the prezygapophyseal shelf. As the 'ball and socket' opisthocoelous centra in macronarians optimised mobility, the 'U-eaves and shelf complex' of rebbachisaurids permitted wider movements between successive vertebrae. While in titanosaurs the increased mobility occurred related to the centrum shape, in rebbachisaurids it is related to a complex system in the neural arch. Furthermore, whereas macronarians show large centra, rebbachisaurids underwent a minimisation of the centrum. These changes in both sauropod lineages probably had an outstanding relevance in the diversity and ecological roles that sauropods experienced in Cretaceous terrestrial ecosystems.
Article
The vertebrae of sauropod dinosaurs are characterized by complex architecture involving laminae, fossae, and internal chambers of various shapes and sizes. These structures are interpreted as osteological correlates of an intricate system of air sacs and pneumatic diverticula similar to that of birds. In basal sauropods pneumatic features are limited to fossae. Camerae and camellae are internalized pneumatic chambers independently acquired in neosauropods and some Chinese forms. The polycamerate and camellate vertebrae of higher neosauropods are characterized by internal pneumatic chambers of considerable complexity. The independent acquisition of these derived morphologies in Mamenchisaurus, derived diplodocids, and most titanosauriforms is correlated with increasing size and neck length. The presacrai vertebrae of basal sauropods were probably pneumatized by diverticula of cervical air sacs similar to those of birds. Although pneumatic characters in sauropods are most extensive and complex in presacrai vertebrae, the sacrum was also pneumatized in most neosauropods. Pneumatization of the proximal caudal vertebrae was achieved independently in diplodocids and titanosaurids. In birds, the synsacrum is pneumatized via abdominal air sacs which function primarily in lung ventilation. The presence of pneumatized sacral and caudal vertebrae in neosauropods indicates that abdominal air sacs were probably present in at least some sauropods.
Article
This chapter discusses the method for three-dimensional reconstructions of sauropod skeletons, focusing on the pose of the neck and its implications for sauropod herbivory. It determines that most sauropods as medium to low browsers. Neutral pose reconstructions suggest that most sauropods would have their necks held horizontally or subhorizontally when not actively feeding or otherwise raising their heads. The feeding envelope for a given taxon can be visualized as the extremes of head reach allowed by the flexibility of its neck. It is clear from the cranial and dental studies that significant differences existed among sauropod feeding mechanisms. Brachiosaurus and, perhaps, Camarasaurus (at the upward extent of its feeding envelope) appear to have been the only Jurassic sauropods clearly capable of feeding as “high browsers” on arborescent gymnosperms.
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The Extant Phylogenetic Bracket approach is applied to infer the kind of soft tissue that would have been associated with the bifurcated neural spines of the cervical vertebrae of sauropods. A median ligament ("ligamentum nuchae" or lig. supraspinale) extends along the tips of the neural spines and attaches to them in the cervical region of extant avian and non-avian diapsids, thus enabling a parsimonious inference that a homologous ligament would also have attached to the same sites in extinct diapsids, including sauropods. In the extant ratite bird, Rhea americana, "lig. nuchae" splits ventrally into two halves as the neural spines become bifurcated in the posterior cervical region, thereby maintaining its connection to both tips of each bifurcated neural spine. This shows the conservative nature of the connection between "lig. nuchae" and its osteological correlate. Furthermore, this ligament and the notches of the bifurcated neural spines enclose another ligament, lig. elasticum interspinale, that arises from the non-bifid neural spine of the most posterior "cervico-dorsal" and gives off branches inserting on the posterior surfaces of the neural spines of the middle to posterior cervicals in Rhea. This ligament in Rhea is suggested to be a good modern analog to the structure occupying the notches of the bifurcated neural spines of sauropods. A hypothetical reconstruction of the proposed ligament system is given using Camarasaurus and Apatosaurus as examples.
Article
The bone microstructure of an ontogenetic series of Apatosaurus radii, ulnae, and scapulae suggests that Apatosaurus underwent three distinct osteogenic phases. Primary laminar to plexiform fibro-lamellar bone tissue, devoid of lines of arrested growth (LAG), occurs in individuals up to 91% adult size. LAGs and longitudinally vascularized lamellar tissue are deposited for the first time in the external cortices of sub-adult individuals. Slow growth and additional deposition of accretionary lamellar bone occurs in adulthood, and indicates attainment of maximum size in Apatosaurus. All scapulae examined show cyclicity in vascularity indicative of regular variation in speeds of osteogenesis. In contrast, Apatosaurus radii and ulnae show consistent bone depositional rates throughout ontogeny. Despite inter-element variability, all Apatosaurus bones sampled corroborate the hypothesis of sustained rapid growth rates for most of ontogeny, followed by gradual decline with attainment of maximum size. Estimation of ages of ~10 years for large sub-adults refutes the hypothesis that slow, indeterminate growth was required for Apatosaurus and other sauropods to achieve extremely large body sizes.
Article
A study of ontogenetic variation is used to clarify aspects of tyrannosaurid taxonomy and investigate the supposed phenomenon of dwarfism in the clade. A hypothetical ontogenetic trajectory is described for the relatively well-represented taxon Albertosaurus libratus. The type specimen of the purported “pygmy” tyrannosaurid Nanotyrannus lancensis was compared with specimens of A. libratus and found to share many morphological characters that exemplify immature specimens of the latter taxon. Most of the cortical surface of the Cleveland skull of N. lancensis has immature bone grain. Also, the skull shares unique derived characters with mature specimens of Tyrannosaurus rex, suggesting that the specimen is a young T. rex and not a dwarf tyrannosaurid. An increase in tooth width, accompanied by loss of tooth positions, and a global shift from an immature gracile to a mature robust morphotype in the craniofacial skeleton typifies the ontogenetic changes in T. rex. Similarly, on the basis of immature characters, Maleevosaurus novojilovi is considered to be an immature Tarbosaurus bataar.
Article
Seismosaurus halli, gen. et sp. nov. (Sauropoda, Diplodocidae) is a new large sauropod from the Brushy Basin Member of the Morrison Formation (Upper Jurassic/Lower Cretaceous) of central New Mexico. The holotype is a partially articulated skeleton consisting to date of approximately 20 caudal vertebrae, five sacral vertebrae, eight dorsal vertebrae, partial pelvis, five chevrons, and ribs. Distinguishing features include the structure of the caudal vertebrae, pelvis, and chevrons. The extraordinary dimensions of these bones indicate an axial length of 39–52 meters.
Article
Although they have been considered distinct genera for over a century, ontogenetic analyses reveal that Triceratops and “Torosaurus” actually represent growth stages of a single genus. Major changes in cranial morphology—including the opening of parietal fenestrae and the elongation of the squamosals—occur rapidly, very late in Triceratops ontogeny and result in the characteristic ‘Torosaurus’ morphology. This report presents the results of a 10-year field study of the dinosaurs of the Hell Creek Formation in Montana and is based on a collection of over 50 specimens of Triceratops, including over 30 skulls, which have been amassed in that time, in addition to specimens from numerous other North American museums. This large sample of individuals reveals the full ontogenetic spectrum of Triceratops. The synonymy of Triceratops and ‘Torosaurus’ contributes to an unfolding view of extremely reduced dinosaur diversity just before the end of the Mesozoic Era.
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Thoracic epaxial muscles of diplodocid and dicraeosaurid sauropods are reconstructed for the first time using an Extant Phylogenetic Bracket approach. In the dorsal vertebral column, three different epaxial muscle groups were present. The medialmost m. transversospinalis and the laterally adjacent m. longissimus dorsi were connected to the neural arches. The lateralmost m. iliocostalis was connected to the dorsal ribs. The medial part of m. transversospinalis of diplodocids and dicraeosaurids comprised at least two tendon systems that had a trellis-like arrangement. Osteological characters of the dorsal vertebrae in related taxa suggest a similar configuration of the thoracic epaxial muscles in all eusauropods, although there was variation in tendon arrangements and in the cross-section of each muscle. The thoracic epaxial musculature in eusauropods played an important role for trunk support; its variation in different eusauropods is directly connected with bony support structures and influenced the mobility of the trunk and locomotion. Modifications in the thoracic epaxial musculature are especially apparent in Saltasauridae, which suggests differences in their locomotor capabilities, such as increased trunk mobility or larger stride lengths.
Article
Appendicular elements of the sauropod dinosaur Suuwasseaemilieae, from the Upper Jurassic Morrison Formation of Montana, USA, display a peculiar mix of autapomorphic and plesiomorphic features. While more similar in overall morphology to Apatosaurus than other flagellicaudatans, the coracoid of Suuwassea lacks the quadrangular shape of Apatosaurus. The humerus of Suuwassea bears a pronounced proximal tuberculum, a feature seen elsewhere only in saltasaurine titanosaurian sauropods. The rectangular proximal articular surface of the tibia is proportioned neither like Diplodocus nor Apatosaurus type specimens, although this region may be intraspecifically variable. The pes of Suuwassea possesses plesiomorphically elongate phalanges and a small, uncompressed ungual, unlike other flagellicaudatans except Dyslocosaurus. The localization of tooth marks on the pedal elements suggests that sauropod feet may have been singled out by scavengers, as has been noted for elephants.
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of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007
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Sauropod cranial elements, despite their rarity, contain a significant proportion of the known phylogenetically important character data (see Wilson, 2002; Upchurch et al., 2004). In particular, cranial characters are important in distinguishing between the two main neosauropod lineages, Diplodocoidea and Macronaria, as well as between the various lineages of diplodocoid sauropods. One recently described diplodocoid, Suuwassea emilieae, has proven difficult to place phylogenetically despite a relative wealth of cranial data (Harris, 2006a). As a putatively basal member of the Late Jurassic radiation of diplodocoids, Suuwassea is an important taxon for the understanding of diplodocoid sauropod evolution. Although it has been variously recovered as a member of either the primarily Laurasian diplodocids or the Gondwanan dicraeosaurids, the precise relationship between those lineages and Suuwassea has remained uncertain. Here we describe a recently discovered dentary assignable to the holotypic specimen of Suuwassea emilieae (Academy of Natural Sciences 21122). This dentary possesses important character data that suggest dicraeosaurid affinities for Suuwassea; as a consequence, Suuwassea is potentially the only recognized Laurasian member of Dicraeosauridae. The description of this dentary also adds to our scarce knowledge of sauropod dentaries.
Article
The immensely long neck of a sauropod is one of the most familiar and striking of anatomical specializations among dinosaurs. Here, I use recently collected neontological and paleontological information to test the predictions of two competing hypotheses proposed to explain the significance of the long neck. According to the traditional hypothesis, neck elongation in sauropods increased feeding height, thereby reducing competition with contemporaries for food. According to the other hypothesis, which is advanced for the first time here, neck elongation in sauropods was driven by sexual selection. Available data match the predictions of the sexual selection hypothesis and contradict the predictions of the feeding competition hypothesis. It is therefore more plausible that increases in sauropod neck lengths were driven by sexual selection than by competition for foliage.
The stress on the intervertebral discs in the necks of Brachiosaurus brancai, Diplodocus carnegii, and Dicraeosaurus hansemanni are calculated for various hypothetical neck postures. Assuming similar safety factors along the neck and a predominance of static or quasistatic forces, neck postures in which the stress is not more or less constant along the neck are rejected. The necks of two large and long-necked recent mammals, Giraffa camelopardalis and Camelus sp., are examined in the same way in order to test the method. The method is shown to be suitable for the reconstruction of the habitual posture of longnecked terrestrial vertebrates, even if the distribution of mass along the head and neck and the lever arms of the neck muscles and ligaments are only roughly estimated. Among sauropods, the neck posture differed considerably, being nearly vertical in Brachiosaurus brancai, but more horizontal in Dicraeosaurus hansemanni and especially in Diplodocus carnegii. Therefore, Brachiosaurus brancai appears to have been an extremely specialised high browser, whereas in Diplodocus carnegii and in Dicraeosaurus hansemanni the long neck permitted a large feeding volume. The constrast in neck posture is reflected in the overall body design, especially in tail and limb length. Für verschiedene Halsstellungen von Brachiosaurus brancai, Diplodocus carnegii und Dicraeosaurus hansemanni wurde der Druck auf den Gelenkknorpel der Zwischenwirbelgelenke berechnet. Halsstellungen, die nicht zu einem mehr oder weniger konstanten Druck entlang des Halses führten, wurden verworfen. Dabei wurden gleiche Sicherheitsfaktoren des Gelenkknorples sowie das Vorherrschen von statischen und quasistatischen Kräften entlang des Halses angenommen. Die Hälse zweier langhalsiger Säugetiere, Giraffa camelopardalis und Camelus sp., wurden in gleicher Weise analysiert, um die Methode zu überprüfen. Diese erwies sich als geeignet, die habituelle Halsstellung eines langhalsigen terrestrischen Wirbeltieres zu rekonstruieren, selbst wenn die Massenverteilung entlang des Halses und die Hebelarme der epaxialen Muskeln, Sehnen und Bänder nur grob geschätzt werden können. Unter den Sauropoden variierte die Halsstellung erheblich von nahezu vertikal bei Brachiosaurus brancai bis zu eher horizontal bei Diplodocus carnegii. Die Halsstellung von Dicraeosaurus hansemanni lag näher bei der Halsstellung von Diplodocus als von Brachiosaurus. Offenbar war Brachiosaurus darauf spezialisiert, Nahrung aus großen Höhen aufzunehmen, während Diplodocus und Dicraeosaurus ihre langen Hälse zum Abweiden eines weiten Areals nutzten. Die Unterschiede in der Halsstellung spiegeln sich in der Körperform, insbesondere in der Schwanz- und Beinlänge, wider.
Article
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.
Article
Body masses of some South American dinosaurs are estimated. The sauropod Argentinosaurus huinculensis reached 73 tonnes, and therefore, is the largest of all land animals whose mass has been rigorously obtained. Another sauropod, Antarctosaurus giganteus, was the second largest, at nearly 69 tonnes, while Antarctosaurus wichmannianus reached 34 tonnes. A third sauropod, the bizarre-looking Amargasaurus cazaui, was much smaller, with a body mass of only 2.5 tonnes. Among theropods, the body mass of the strangely looking, horned Carnotaurus sastrei, was volumetrically estimated at 1.5 tonnes, while allometric equations on limb measure-ments yielded overestimations. Moreover, the holotype specimen of Giganotosaurus carolinii (MUCPv-CH-1) was about as large as the average-sized Tyrannosaurus rex, and only marginally smaller than "Sue", the largest specimen. However, a new dentary of Giganotosaurus (MUCPv-95) is 8% longer than that of the holotype. Assuming geometric similarity, that individual must have had a body mass above 8 tonnes and hence must have been the largest theropod ever found.
Article
  Vertebrae of Suuwassea demonstrate an interesting combination of plesiomorphies and autapomorphies among known members of the Flagellicaudata. The cranial cervical vertebrae have proportions close to Diplodocus but resemble those of Apatosaurus except by having greatly reduced cranial and caudal spinozygapophyseal laminae. As a result, they have craniocaudally compressed, caudally positioned spinous processes excavated on all sides by fossae. The cranial thoracic vertebrae are again similarly proportioned as those of Diplodocus but are morphologically similar to those of Apatosaurus. The most distinguishing feature of Suuwassea caudal vertebrae are the short, amphiplatyan, distalmost ‘whiplash’ caudal vertebrae. These may be either a retention of or a reversal to the plesiomorphic sauropod condition because classic flagellicaudatan, biconvex distalmost caudals occur in the Middle Jurassic of England.
Article
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.
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Centrosaurine ceratopsians are characterized by well developed nasal horncores or bosses, relatively abbreviated supraorbital horncores or bosses, and adorned parietosquamosal frills. Recent study of several paucispecific (low diversity) bonebed assemblages in Alberta and Montana has contributed greatly to our understanding of ontogenetic and taxonomic variation in the skulls of centrosaurines. Relative age determination of centrosaurines is now possible through examination of ontogenetic change in several characters, including the surface bone morphology of specific skeletal elements. The within-group taxonomy of centrosaurines is based almost entirely on characters of the skull roof, relating particularly to horns and frills. Juvenile and sub-adult centrosaurines are characterized by relatively simple, unadorned skulls compared to their adult counterparts. As in numerous living taxa, the cranial ornaments of centrosaurines developed late in ontogeny, as individuals approached or attained adult size. An important implication arising directly from this study is that juvenile and sub-adult centrosaurines are difficult to distinguish taxonomically at the specific level. Two monospecific genera represented only by immature materials,Brachyceratops montanensisandMonoclonius crassus, cannot be defended and should be considerednomina dubia. The late ontogenetic development and diverse taxonomic variation of horn and frill morphologies support the contention that these structures are best interpreted as reproductive characters employed in mate competition.
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Questions about the taxonomic status, diversity, and pace of evolution of basal ornithischian dinosaurs persist in part because some historically important taxa have been based on incomplete material of uncertain ontogenetic status. We examined the morphology of critical “fabrosaurid” specimens and analyzed the bone tissues of small and large individuals. We conclude that the case for the existence of a non-heterodontosaurid ornithischian distinct from Lesothosaurus diagnosticus in the upper Elliot Formation of southern Africa is not conclusive and we suggest that this species and Stormbergia dangershoeki may actually represent ontogenetic stages of one taxon that reached maturity in approximately four years.
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The well-preserved histology of the geologically oldest sauropod dinosaur from the Late Triassic allows new insights into the timing and mechanism of the evolution of the gigantic body size of the sauropod dinosaurs. The oldest sauropods were already very large and show the same long-bone histology, laminar fibro-lamellar bone lacking growth marks, as the well-known Jurassic sauropods. This bone histology is unequivocal evidence for very fast growth. Our histologic study of growth series of the Norian Plateosaurus indicates that the sauropod sistergroup, the Late Triassic and early Jurassic Prosauropoda, reached a much more modest body size in a not much shorter ontogeny. Increase in growth rate compared to the ancestor (acceleration) is thus the underlying process in the phylogenetic size increase of sauropods. Compared to all other dinosaur lineages, sauropods were not only much larger but evolved very large body size much faster. The prerequisite for this increase in growth rate must have been a considerable increase in metabolic rate, and we speculate that a bird-like lung was important in this regard.