The phylogenetic relationships of sauropod dinosaurs

A data-matrix of 205 osteological characters for 26 sauropod taxa is subjected to cladistic analysis. Two most parsimonious trees are produced, differing only in the relationships between Euhelopus, Omeisaurus and Mamenchisaurus. The monophyly of the Euhelopodidae (including Shunosaurus) is supported by seven synapomorphies. The Cetiosauridae (Patagosaurus, Cetiosaurus and Haplocanthosaurus) is paraphyletic with respect to the Neosauropoda. The latter clade divides into two major radiations–the ‘Brachiosauria’ (Camarasaurus, brachiosaurids and titanosauroids), and the Diplodocoidea (nemegtosaurids, dicraeosaurids, diplodocids and Rebbachisaurus). Further evidence for the inclusion of Opisthocoelwaudia in the Titanosauroidea is presented. Phuwiangosaurus, a problematic sauropod from Thailand, may represent one of the most plesiomorphic titanosauroids. ‘Peg’-like teeth have evolved at least twice within the Sauropoda. The postspinal lamina, on the neural spines of middle and caudal dorsal vertebrae, represents a neomorph rather than a fusion of pre-existing structures. Forked chevrons may have evolved convergently in the Euhelopodidae and the diplodocid-dicraeosaurid clade, or they may have been acquired early in sauropod evolution and subsequently lost in the ‘Brachiosauria’. The strengths and weaknesses of the data-matrix and tree topologies are explored using bootstrapping, decay analysis and randomization tests. Several nodes are only poorly supported, but this seems to reflect the large proportion of missing data in the matrix (～46%), rather than an abnormally high level of homoplasy. The results of the randomization tests indicate that the ‘data-matrix’ probably contains a strong phylogenetic ‘signal’. The relationships of some forms, such as Haplocanthosaurus, are influenced by the inclusion or exclusion of certain taxa with unusual combinations of character states. Such a result suggests that there are dangers inherent in the view that ‘higher’ level sauropod phylogeny can be accurately reconstructed using only a small number of well-known taxa.     

Ethological variations in gauge in sauropod trackways from the Berriasian of Spain

Castanera, D., Pascual, C., Canudo, J.I., Hernández, N. & Barco, J., 2012: Ethological variations in gauge in sauropod trackways from the Berriasian of Spain. Lethaia, Vol. 45, pp. 476–489. Two sauropod trackways from the Early Cretaceous (Berriasian) of the Cameros Basin (Spain) show important variations in trackway gauge, along the same trackway. These variations seem to be associated with different behaviours; on the one hand with a significant variation in the direction of travel (turning phenomena) and on the other hand with a decrease in speed, probably associated with the properties of the substrate. These variations in sauropod trackways provide the trackway gauge debate with new data, supporting the hypothesis that the walking style and substrate properties may in some cases determine this sauropod character. The study of turning sauropod trackways improves our knowledge of sauropod locomotion. □Ethology, intermediate‐gauge, sauropod trackways, substrate properties, wide‐gauge.     

An alternative sauropod physiology and cardiovascular system that eliminates high blood pressures

Siegwarth, J.D., Smith, C.N. & Redman, P.D. 2010: An alternative sauropod physiology and cardiovascular system that eliminates high blood pressures. Lethaia, Vol. 44, pp. 46–57. The long neck of an adult sauropod has been found structurally unsuitable for high browsing while standing on all four feet. Some juveniles might have used a tripodal stance, but an analysis of the motion of the centre of mass shows a large adult sauropod could not. We propose here that sauropods could have browsed high by sitting, squatting or even kneeling on their hind legs to elevate their heads without a sharp bend at the base of the neck. A large sauropod needs a way to deal with very high blood pressure when high browsing. Arterial pumping is suggested here as a means of avoiding the need for high blood pressure. □Blood pressure, browsing posture, cardiovascular system, form vis‐à‐vis function, neck length, physiology, sauropods, tripodal stance.     

Cranial biomechanics underpins high sauropod diversity in resource-poor environments

High megaherbivore species richness is documented in both fossil and contemporary ecosystems despite their high individual energy requirements. An extreme example of this is the Late Jurassic Morrison Formation, which was dominated by sauropod dinosaurs, the largest known terrestrial vertebrates. High sauropod diversity within the resource-limited Morrison is paradoxical, but might be explicable through sophisticated resource partitioning. This hypothesis was tested through finite-element analysis of the crania of the Morrison taxa Camarasaurus and Diplodocus. Results demonstrate divergent specialization, with Camarasaurus capable of exerting and accommodating greater bite forces than Diplodocus, permitting consumption of harder food items. Analysis of craniodental biomechanical characters taken from 35 sauropod taxa demonstrates a functional dichotomy in terms of bite force, cranial robustness and occlusal relationships yielding two polyphyletic functional ‘grades’. Morrison taxa are widely distributed within and between these two morphotypes, reflecting distinctive foraging specializations that formed a biomechanical basis for niche partitioning between them. This partitioning, coupled with benefits associated with large body size, would have enabled the high sauropod diversities present in the Morrison Formation. Further, this provides insight into the mechanisms responsible for supporting the high diversities of large megaherbivores observed in other Mesozoic and Cenozoic communities, particularly those occurring in resource-limited environments.     

A new sauropod dinosaur from the Lower Cretaceous Ilek Formation,Western Siberia,Russia

Sibirotitan astrosacralis nov. gen., nov. sp., is described based on isolated but possibly associated cervical and dorsal vertebrae, sacrum, and previously published pedal elements from the Lower Cretaceous (Barremian?) Ilek Formation at Shestakovo 1 locality (Kemerovo Province, Western Siberia, Russia). Some isolated sauropod teeth from the Shestakovo 1 locality are referred to the same taxon. The phylogenetic parsimony analyses place Sibirotitan astrosacralis nov. gen., nov. sp., as a non-titanosaurian somphospondyl titanosauriform. The new taxon exhibits four titanosauriform and one somphospondylan synapomorphies, and one autapomorphy – a hyposphene ridge that extends between the neural canal and the postzygapophyses. It differs from all other Somphospondyli by having only five sacral vertebrae. The new taxon shares with Euhelopus and Epachtosaurus sacral ribs that converge towards the middle of the sacrum in dorsal view. Sibirotitan astrosacralis nov. gen., nov. sp., is only the second sauropod taxon from Russia and one of the oldest titanosauriform described so far in Asia.     

Biology of the sauropod dinosaurs: the evolution of gigantism

The herbivorous sauropod dinosaurs of the Jurassic and Cretaceous periods were the largest terrestrial animals ever, surpassing the largest herbivorous mammals by an order of magnitude in body mass. Several evolutionary lineages among Sauropoda produced giants with body masses in excess of 50 metric tonnes by conservative estimates. With body mass increase driven by the selective advantages of large body size, animal lineages will increase in body size until they reach the limit determined by the interplay of bauplan, biology, and resource availability. There is no evidence, however, that resource availability and global physicochemical parameters were different enough in the Mesozoic to have led to sauropod gigantism. We review the biology of sauropod dinosaurs in detail and posit that sauropod gigantism was made possible by a specific combination of plesiomorphic characters (phylogenetic heritage) and evolutionary innovations at different levels which triggered a remarkable evolutionary cascade. Of these key innovations, the most important probably was the very long neck, the most conspicuous feature of the sauropod bauplan. Compared to other herbivores, the long neck allowed more efficient food uptake than in other large herbivores by covering a much larger feeding envelope and making food accessible that was out of the reach of other herbivores. Sauropods thus must have been able to take up more energy from their environment than other herbivores. The long neck, in turn, could only evolve because of the small head and the extensive pneumatization of the sauropod axial skeleton, lightening the neck. The small head was possible because food was ingested without mastication. Both mastication and a gastric mill would have limited food uptake rate. Scaling relationships between gastrointestinal tract size and basal metabolic rate (BMR) suggest that sauropods compensated for the lack of particle reduction with long retention times, even at high uptake rates. The extensive pneumatization of the axial skeleton resulted from the evolution of an avian‐style respiratory system, presumably at the base of Saurischia. An avian‐style respiratory system would also have lowered the cost of breathing, reduced specific gravity, and may have been important in removing excess body heat. Another crucial innovation inherited from basal dinosaurs was a high BMR. This is required for fueling the high growth rate necessary for a multi‐tonne animal to survive to reproductive maturity. The retention of the plesiomorphic oviparous mode of reproduction appears to have been critical as well, allowing much faster population recovery than in megaherbivore mammals. Sauropods produced numerous but small offspring each season while land mammals show a negative correlation of reproductive output to body size. This permitted lower population densities in sauropods than in megaherbivore mammals but larger individuals. Our work on sauropod dinosaurs thus informs us about evolutionary limits to body size in other groups of herbivorous terrestrial tetrapods. Ectothermic reptiles are strongly limited by their low BMR, remaining small. Mammals are limited by their extensive mastication and their vivipary, while ornithsichian dinosaurs were only limited by their extensive mastication, having greater average body sizes than mammals.     

Mechanical implications of pneumatic neck vertebrae in sauropod dinosaurs

The pre-sacral vertebrae of most sauropod dinosaurs were surrounded by interconnected, air-filled diverticula, penetrating into the bones and creating an intricate internal cavity system within the vertebrae. Computational finite-element models of two sauropod cervical vertebrae now demonstrate the mechanical reason for vertebral pneumaticity. The analyses show that the structure of the cervical vertebrae leads to an even distribution of all occurring stress fields along the vertebrae, concentrated mainly on their external surface and the vertebral laminae. The regions between vertebral laminae and the interior part of the vertebral body including thin bony struts and septa are mostly unloaded and pneumatic structures are positioned in these regions of minimal stress. The morphology of sauropod cervical vertebrae was influenced by strongly segmented axial neck muscles, which require only small attachment areas on each vertebra, and pneumatic epithelia that are able to resorb bone that is not mechanically loaded. The interaction of these soft tissues with the bony tissue of the vertebrae produced lightweight, air-filled vertebrae in which most stresses were borne by the external cortical bone. Cervical pneumaticity was therefore an important prerequisite for neck enlargement in sauropods. Thus, we expect that vertebral pneumaticity in other parts of the body to have a similar role in enabling gigantism.     

Hearts, neck posture and metabolic intensity of sauropod dinosaurs

Hypothesized upright neck postures in sauropod dinosaurs require systemic arterial blood pressures reaching 700 mmHg at the heart. Recent data on ventricular wall stress indicate that their left ventricles would have weighed 15 times those of similarly sized whales. Such dimensionally, energetically and mechanically disadvantageous ventricles were highly unlikely in an endothermic sauropod. Accessory hearts or a siphon mechanism, with sub-atmospheric blood pressures in the head, were also not feasible. If the blood flow requirements of sauropods were typical of ectotherms, the left-ventricular blood volume and mass would have been smaller; nevertheless, the heart would have suffered the serious mechanical disadvantage of thick walls. It is doubtful that any large sauropod could have raised its neck vertically and endured high arterial blood pressure, and it certainly could not if it had high metabolic rates characteristic of endotherms.     

Large sauropod and theropod tracks from the Middle Jurassic Chuanjie Formation of Lufeng County,Yunnan Province and palaeobiogeography of the Middle Jurassic sauropod tracks from southwestern China

Tracks of large theropods and a single sauropod footprint are reported from red beds at Beikeshan locality in the Middle Jurassic Chuanjie Formation, of Lufeng County, near the large World Dinosaur Valley Park complex. The Chuanjie theropod tracks are assigned to the ichnogenus Eubrontes and the large sauropod track is given the provisional label Brontopodus. All occur as isolated tracks, i.e., trackways are not preserved. Saurischian dominated ichnofaunas are relatively common in the Jurassic of China. The producers of the Chuanjie tracks may have been similar to the basal tetanuran theropod Shidaisaurus and to mamenchisaurid sauropods, which were widely distributed throughout China, during the Jurassic, and are known from skeletal remains found in the same unit. Other potential sauropod trackmakers include titanosauriforms or as-yet-unknown basal eusauropods. The ichno- and skeletal records from the Jurassic of the Lufeng Basin are largely consistent, and both document the presence of middle-large sized theropods and sauropods.     

Molecular preservation in Late Cretaceous sauropod dinosaur eggshells

Exceptionally preserved sauropod eggshells discovered in Upper Cretaceous (Campanian) deposits in Patagonia, Argentina, contain skeletal remains and soft tissues of embryonic Titanosaurid dinosaurs. To preserve these labile embryonic remains, the rate of mineral precipitation must have superseded post-mortem degradative processes, resulting in virtually instantaneous mineralization of soft tissues. If so, mineralization may also have been rapid enough to retain fragments of original biomolecules in these specimens. To investigate preservation of biomolecular compounds in these well-preserved sauropod dinosaur eggshells, we applied multiple analytical techniques. Results demonstrate organic compounds and antigenic structures similar to those found in extant eggshells.     

The first evidence of osteomyelitis in a sauropod dinosaur

Osteomyelitis is reported for the first time in a sauropod dinosaur. The material (MCS‐PV 183) comes from the Anacleto Formation (Campanian, Late Cretaceous), at the Cinco Saltos locality, Río Negro Province, Argentina. The specimen consists of 16 mid and mid‐distal caudal vertebrae of a titanosaur sauropod. Evidence of bacterial infection is preserved in all of these vertebrae. The main anomalies are as follows: irregular ‘microbubbly’ texture of bone surfaces produced by periosteal reactive bone, abscesses on the rims of the anterior articular surfaces of two centra, numerous pits on centra anterior articulation surfaces, erosions on the anterior articulation of the vertebral centra, a vertical groove in posterior articular face of all the centra and disruption of the prezygapophysis and postzygapophysis (mainly the articular face) from the vertebra 19 and beyond. The last anomaly is increasingly pronounced in more distal elements of the series. Thin sections reveal that the anomalous cortical tissue is composed of avascular and highly fibrous bone matrix. The fibres of the bone matrix are organized into thick bundles oriented in different directions. Both morphological and histological abnormalities in the MCS‐PV 183 specimen are pathognomonic for osteomyelitis.     

Simulating sauropod manus-only trackway formation using finite-element analysis

The occurrence of sauropod manus-only trackways in the fossil record is poorly understood, limiting their potential for understanding locomotor mechanics and behaviour. To elucidate possible causative mechanisms for these traces, finite-element analyses were conducted to model the indentation of substrate by the feet of Diplodocus and Brachiosaurus. Loading was accomplished by applying mass, centre of mass and foot surface area predictions to a range of substrates to model track formation. Experimental results show that when pressure differs between manus and pes, as determined by the distribution of weight and size of respective autopodia, there is a range of substrate shear strengths for which only the manus (or pes) produce enough pressure to deform the substrate, generating a track. If existing reconstructions of sauropod feet and mass distributions are correct, then different taxa will produce either manus- or pes-only trackways in specific substrates. As a result of this work, it is predicted that the occurrence of manus- or pes-only trackways may show geo-temporal correlation with the occurrence of body fossils of specific taxa.     

Impact of sauropod dinosaurs on lagoonal substrates in the Broome Sandstone (Lower Cretaceous), Western Australia

Existing knowledge of the tracks left by sauropod dinosaurs (loosely 'brontosaurs') is essentially two-dimensional, derived mainly from footprints exposed on bedding planes, but examples in the Broome Sandstone (Early Cretaceous) of Western Australia provide a complementary three-dimensional picture showing the extent to which walking sauropods could deform the ground beneath their feet. The patterns of deformation created by sauropods traversing thinly-stratified lagoonal deposits of the Broome Sandstone are unprecedented in their extent and structural complexity. The stacks of transmitted reliefs (underprints or ghost prints) beneath individual footfalls are nested into a hierarchy of deeper and more inclusive basins and troughs which eventually attain the size of minor tectonic features. Ultimately the sauropod track-makers deformed the substrate to such an extent that they remodelled the topography of the landscape they inhabited. Such patterns of substrate deformation are revealed by investigating fragmentary and eroded footprints, not by the conventional search for pristine footprints on intact bedding planes. For that reason it is not known whether similar patterns of substrate deformation might occur at sauropod track-sites elsewhere in the world.     

Thunder lizard handstands: Manus-only sauropod trackways from the Glen Rose Formation (Lower Cretaceous,Kendall County,Texas)

Abstract

Three parallel, manus-only sauropod trackways from the Coffee Hollow A-Male tracksite (Glen Rose Formation, Kendall County, Texas) were studied separately by researchers from the Heritage Museum of the Texas Hill Country and the Houston Museum of Natural Sciences. Footprint and trackway measurements generally show good agreement between the two groups’ data sets. Footprints appear to be shallowly impressed true tracks rather than undertracks. One of the Coffee Hollow trackways shows marked asymmetry in the lengths of paces that begin with the left as opposed to the right forefoot, and two of the Coffee Hollow trackways are unusually broad. The Coffee Hollow trackways differ enough from the manus portions of other Glen Rose Formation sauropod trackways to suggest that they were made by a different kind of sauropod. Greater differential pressure exerted on the substrate by the forefeet than the hindfeet probably explains the Coffee Hollow trackways, like other manus-only sauropod trackways, but the possibility that they indicate unusual locomotion cannot at present be ruled out.     

A new transitional sauropodomorph dinosaur from the Early Jurassic of South Africa and the evolution of sauropod feeding and quadrupedalism

Aardonyx celestae gen. et sp. nov. is described from the upper Elliot Formation (Early Jurassic) of South Africa. It can be diagnosed by autapomorphies of the skull, particularly the jaws, cervical column, forearm and pes. It is found to be the sister group of a clade of obligatory quadrupedal sauropodomorphs (Melanorosaurus + Sauropoda) and thus lies at the heart of the basal sauropodomorph–sauropod transition. The narrow jaws of A. celestae retain a pointed symphysis but appear to have lacked fleshy cheeks. Broad, U-shaped jaws were previously thought to have evolved prior to the loss of gape-restricting cheeks. However, the narrow jaws of A. celestae retain a pointed symphysis but appear to have lacked fleshy cheeks, demonstrating unappreciated homoplasy in the evolution of the sauropod bulk-browsing apparatus. The limbs of A. celestae indicate that it retained a habitual bipedal gait although incipient characters associated with the pronation of the manus and the adoption of a quadrupedal gait are evident through geometric morphometric analysis (using thin-plate splines) of the ulna and femur. Cursorial ability appears to have been reduced and the weight bearing axis of the pes shifted to a medial, entaxonic position, falsifying the hypothesis that entaxony evolved in sauropods only after an obligate quadrupedal gait had been adopted.     

High European sauropod dinosaur diversity during Jurassic–Cretaceous transition in Riodeva (Teruel, Spain)

Abstract:  Up to now, more than 40 dinosaur sites have been found in the latest Jurassic – earliest Cretaceous sedimentary outcrops (Villar del Arzobispo Formation) of Riodeva (Iberian Range, Spain). Those already excavated, as well as other findings, provide a large and diverse number of sauropod remains, suggesting a great diversity for this group in the Iberian Peninsula during this time. Vertebrae and ischial remains from Riodevan site RD-13 are assigned to Turiasaurus riodevensis (a species described in RD-10, Barrihonda site), which is part of the Turiasauria clade. This is the first time that a taxon is attributed to Turiasaurus genus out of its type site. A Neosauropod caudal vertebra from the RD-11 site has been classified as Diplodocinae indet., supporting the previous attribution on an ilion also found in Riodeva (CPT-1074) referring to the Diplodocidae clade. New remains from the RD-28, RD-41 and RD-43 sites, of the same age, among which there are caudal vertebrae, are assigned to Macronaria. New sauropod footprints from the Villar del Arzobispo Formation complete the extraordinary sauropod record coming to light in the area. The inclusion of other sauropods from different contemporaneous exposures in Teruel within the Turiasauria clade adds new evidence of a great diversity of sauropods in Iberia during the Jurassic–Cretaceous transition. Turiasauria distribution contributes to the understanding of European and global palaeobiogeography.     

Adaptive radiation in sauropod dinosaurs: bone histology indicates rapid evolution of giant body size through acceleration

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.     

What's inside a sauropod limb? First three-dimensional investigation of the limb long bone microanatomy of a sauropod dinosaur,Nigersaurus taqueti (Neosauropoda,Rebbachisauridae), and implications for the weight-bearing function

Various terrestrial tetrapods convergently evolved to gigantism (large body sizes and masses), the most extreme case being sauropod dinosaurs. Heavy weight-bearing taxa often show external morphological features related to this condition, but also adequacy in their limb bone inner structure: a spongiosa filling the medullary area and a rather thick cortex varying greatly in thickness along the shaft. However, the microanatomical variation in such taxa remains poorly known, especially between different limb elements. We highlight for the first time the three-dimensional microstructure of the six limb long bone types of a sauropod dinosaur, Nigersaurus taqueti. Sampling several specimens of different sizes, we explored within-bone, between-bones, and size-related variations. If a spongiosa fills the medullary area of all bones, the cortex is rather thin and varies only slightly in thickness along the shaft. Zeugopod bones appear more compact than stylopod ones, whereas no particular differences between serially homologous bones are found. Nigersaurus' pattern appears much less extreme than that in heavy terrestrial taxa such as rhinoceroses, but is partly similar to observations in elephants and in two-dimensional sauropod data. Thus, microanatomy may have not been the predominant feature for weight-bearing in sauropods. External features, such as columnarity (shared with elephants) and postcranial pneumaticity, may have played a major role for this function, thus relaxing pressures on microanatomy. Also, sauropods may have been lighter than expected for a given size. Our study calls for further three-dimensional investigations, eventually yielding a framework characterizing more precisely how sauropod gigantism may have been possible.