Sauropod Evolution Research Articles

Sauropod tail clubs from the Kota Formation (Lower to Middle Jurassic) of India and their implications for early sauropod evolution

ABSTRACT The Lower to Middle Jurassic Kota Formation of India has yielded abundant yet disarticulated skeletal remains attributed to the basally diverging sauropod Kotasaurus yamanpalliensis. The hypodigm of Kotasaurus yamanpalliensis includes four ellipsoidal elements that we identify as tail clubs, based on morphological similarities to tail clubs attributed to two basal sauropods from China: Shunosaurus lii, for which a fully articulated tail series was recovered, and Omeisaurus tianfuensis. Detailed comparison of the Chinese and Indian tail clubs suggests that they are composed of up to three individual elements that fuse in adulthood. Computed tomography of the Indian tail clubs reveals their internal structure, which shows incremental growth lines as well as other features whose origin and function remain unknown. The Indian and Chinese tail clubs share a similar temporal range (Early to Middle Jurassic) and similar morphologies, which raises the question of whether sauropod tail clubs evolved once, multiple times, or were gained and then lost within basally diverging members of Sauropoda. We describe four new characters to reflect the morphological constituents of sauropod tail clubs known to date.

The Appendicular Osteology of Patagotitan Mayorum (Dinosauria, Sauropoda)

ABSTRACT Its huge size, excellent preservation, and completeness make Patagotitan mayorum a unique opportunity to explore the anatomy, paleobiological, and phylogenetic aspects linked to gigantism within Sauropoda. In this regard, we describe the appendicular skeleton of this titanosaurian species from the late Albian-aged Cerro Barcino Formation of Chubut Province, Argentina. The diagnosis of Patagotitan mayorum is revised, increasing the number of identified autapomorphies (i.e., lateral surface of the scapular blade with two divergent crests; anterior surface of proximal humerus with paired muscle scars; combined bulges on the deltopectoral area of the humerus; ischium with well-developed and sharp ridge projecting from the ischial tuberosity to the distal blade). Several diagnostic characters of this species correspond to osteological correlates associated to appendicular musculature (e.g., Mm. deltoideus scapularis, deltoideus clavicularis, and teres major; M. coracobrachialis; Mm. supracoracoideus/deltoideus clavicularis and latissimus dorsi; Mm. flexor tibialis 3 and adductor femoris 2), which we discuss in the context of sauropod evolution. In the light of a modification of the scaling equation previously proposed and adjusting the long bone circumference for the humeri of Patagotitan, a new body mass estimate of this species ranges between 42–71 tons, with a mean value of 57 tons. Although considerably less than the value obtained by the original linear equation, the corrected quadratic equation used here provides a mean body mass estimate that is more consistent with those derived from volumetric reconstructions of Patagotitan.

Early Jurassic dinosaur fetal dental development and its significance for the evolution of sauropod dentition

Rare occurrences of dinosaurian embryos are punctuated by even rarer preservation of their development. Here we report on dental development in multiple embryos of the Early Jurassic Lufengosaurus from China, and compare these to patterns in a hatchling and adults. Histology and CT data show that dental formation and development occurred early in ontogeny, with several cycles of tooth development without root resorption occurring within a common crypt prior to hatching. This differs from the condition in hatchling and adult teeth of Lufengosaurus, and is reminiscent of the complex dentitions of some adult sauropods, suggesting that their derived dental systems likely evolved through paedomorphosis. Ontogenetic changes in successive generations of embryonic teeth of Lufengosaurus suggest that the pencil-like teeth in many sauropods also evolved via paedomorphosis, providing a mechanism for the convergent evolution of small, structurally simple teeth in giant diplodocoids and titanosaurids. Therefore, such developmental perturbations, more commonly associated with small vertebrates, were likely also essential events in sauropod evolution.

Middle Jurassic Tracks of Sauropod Dinosaurs in a Deep Karst Cave in France

ABSTRACT Although the deep galleries of natural underground cavities are difficult to access and are sometimes dangerous, they have the potential to preserve trace fossils. Here, we report on the first occurrence of sauropod dinosaur tracks inside a karstic cave. Three trackways are preserved on the roof of the Castelbouc cave 500 m under the surface of the Causse Méjean plateau, southern France. The tracks are Bathonian in age (ca. 168–166 Ma), a crucial but still poorly known time interval in sauropod evolution. The three trackways yield sauropod tracks that are up to 1.25 m long and are therefore amongst the largest known dinosaur footprints worldwide. The trackmakers are hypothesized to be titanosauriforms. Some of the tracks are extremely well preserved and show impressions of digits, digital pads, and claws. We erect the new ichnogenus and ichnospecies Occitanopodus gandi, igen. et isp. nov. In order to characterize depositional environments, we conducted sedimentological, petrographic, and mineralogical analyses. The tracks from Castelbouc attest the presence of sauropods in proximal littoral environments during the Middle Jurassic. This discovery demonstrates the great potential of prospecting in deep karst caves that can occasionally offer larger and better-preserved surfaces than outdoor outcrops.

Phylogenetic analysis of Gondwanan basal eusauropods from the Early-Middle Jurassic of Patagonia, Argentina

Gondwanan Jurassic non-neosauropod eusauropods are key for the understanding of sauropod evolution, although their phylogenetic interrelationships remain poorly understood. However, following the revision of the holotype of a key taxon from the early Middle Jurassic Cañadón Asfalto Formation Patagonia, Argentina, Patagosaurus fariasi, the phylogenetic a ? nities need to be tested with new osteological information gathered during the redescription of the holotype of Patagosaurus. A new phylogeny presented here shows a close a ? liation of Patagosaurus with Cetiosaurus from the Middle Jurassic of the UK. The close relationship of Patagosaurus with Barapasaurus, often found in previous phylogenies, was not recovered here. Instead, Patagosaurus is retrieved as more derived than most Early and Middle Jurassic sauropods, although more basal to Mamenchisaurus, Omeisaurus, turiasaurians, and neosauropods. Another sauropod taxon found together with Patagosaurus, Volkheimeria, is retrieved several nodes more basal than the former, which shows, together with evidence of several other sauropod taxa in the Cañadón Asfalto Formation, that a high evolutionary diversity existed in Southwest Gondwana in the early Middle Jurassic, a pattern which is also seen in fossil groups other than sauropods (e.g., theropods).

Age of Jurassic basal sauropods in Sichuan, China: A reappraisal of basal sauropod evolution

Sauropoda are the largest terrestrial animals to have ever lived and represent the dominant herbivorous dinosaurs of the Mesozoic Era. The Lower Shaximiao Formation of the Sichuan Basin, Southwest China, hosts abundant Jurassic basal sauropods including the Shunosaurus-Omeisaurus Fauna. This formation was previously hypothesized to be Middle Jurassic based on biostratigraphic interpretations, but the exact depositional age is uncertain. Here we report the youngest inductively coupled plasma-mass spectrometry (ICP-MS) detrital zircon U-Pb age of 159 +/- 2 Ma for fossil-bearing strata from this formation as the maximum depositional age. This age falls very close to the Oxfordian age interpreted for the Shunosaurus-Omeisaurus Fauna and is younger than previously proposed. We suggest that when the widely distributed basal sauropods of the Early-Middle Jurassic were mostly replaced by the phylogenetically more-derived neosauropods in the Late Jurassic in other regions of Laurasia and Gondwana, some more basal members survived and diversified in the Sichuan Basin of southwestern China.

A revision of Sanpasaurus yaoi Young, 1944 from the Early Jurassic of China, and its relevance to the early evolution of Sauropoda (Dinosauria).

The Early Jurassic of China has long been recognized for its diverse array of sauropodomorph dinosaurs. However, the contribution of this record to our understanding of early sauropod evolution is complicated by a dearth of information on important transitional taxa. We present a revision of the poorly known taxon Sanpasaurus yaoi Young, 1944 from the late Early Jurassic Ziliujing Formation of Sichuan Province, southwest China. Initially described as the remains of an ornithopod ornithischian, we demonstrate that the material catalogued as IVPP V156 is unambiguously referable to Sauropoda. Although represented by multiple individuals of equivocal association, Sanpasaurus is nonetheless diagnosable with respect to an autapomorphic feature of the holotypic dorsal vertebral series. Additional material thought to be collected from the type locality is tentatively referred to Sanpasaurus. If correctly attributed, a second autapomorphy is present in a referred humerus. The presence of a dorsoventrally compressed pedal ungual in Sanpasaurus is of particular interest, with taxa possessing this typically ‘vulcanodontid’ character exhibiting a much broader geographic distribution than previously thought. Furthermore, the association of this trait with other features of Sanpasaurus that are broadly characteristic of basal eusauropods underscores the mosaic nature of the early sauropod–eusauropod transition. Our revision of Sanpasaurus has palaeobiogeographic implications for Early Jurassic sauropods, with evidence that the group maintained a cosmopolitan Pangaean distribution.

Temporal and phylogenetic evolution of the sauropod dinosaur body plan.

The colossal size and body plan of sauropod dinosaurs are unparalleled in terrestrial vertebrates. However, to date, there have been only limited attempts to examine temporal and phylogenetic patterns in the sauropod bauplan. Here, we combine three-dimensional computational models with phylogenetic reconstructions to quantify the evolution of whole-body shape and body segment properties across the sauropod radiation. Limitations associated with the absence of soft tissue preservation in fossils result in large error bars about mean absolute body shape predictions. However, applying any consistent skeleton : body volume ratio to all taxa does yield changes in body shape that appear concurrent with major macroevolutionary events in sauropod history. A caudad shift in centre-of-mass (CoM) in Middle Triassic Saurischia, associated with the evolution of bipedalism in various dinosaur lineages, was reversed in Late Triassic sauropodomorphs. A craniad CoM shift coincided with the evolution of quadrupedalism in the Late Triassic, followed by a more striking craniad shift in Late Jurassic–Cretaceous titanosauriforms, which included the largest sauropods. These craniad CoM shifts are strongly correlated with neck enlargement, a key innovation in sauropod evolution and pivotal to their gigantism. By creating a much larger feeding envelope, neck elongation is thought to have increased feeding efficiency and opened up trophic niches that were inaccessible to other herbivores. However, we find that relative neck size and CoM position are not strongly correlated with inferred feeding habits. Instead the craniad CoM positions of titanosauriforms appear closely linked with locomotion and environmental distributions, potentially contributing to the continued success of this group until the end-Cretaceous, with all other sauropods having gone extinct by the early Late Cretaceous.

A new basal sauropod from the pre-Toarcian Jurassic of South Africa: evidence of niche-partitioning at the sauropodomorph-sauropod boundary?

The early evolution of sauropod dinosaurs remains poorly understood, with a paucity of unequivocal sauropod taxa known from the first twenty million years of the Jurassic. Recently, the Early Jurassic of South Africa has yielded an assemblage of dental and post-cranial remains displaying a more apomorphic character suite than any other similarly aged sauropodomorph. These remains are interpreted as a new species of basal sauropod and recovered cladistically as the sister taxon to Vulcanodon +more derived Sauropoda, underscoring its importance for our understanding of this pivotal period of sauropod evolution. Key changes in the dentition, axial skeleton and forelimb of this new species suggest a genuine functional distinction occurring at the sauropodiform-sauropod boundary. With reference to these changes, we propose a scenario in which interdependent refinements of the locomotory and feeding apparatus occurred in tandem with, or were effected by, restrictions in the amount of vertical forage initially available to the earliest sauropods. The hypothesized instance of niche-partitioning between basal sauropodan taxa and higher-browsing non-sauropodan sauropodomorphs may partially explain the rarity of true sauropods in the basal rocks of the Jurassic, while having the added corollary of couching the origins of Sauropoda in terms of an ecologically delimited ‘event’.

New Information on Tataouinea hannibalis from the Early Cretaceous of Tunisia and Implications for the Tempo and Mode of Rebbachisaurid Sauropod Evolution.

The rebbachisaurid sauropod Tataouinea hannibalis represents the first articulated dinosaur skeleton from Tunisia and one of the best preserved in northern Africa. The type specimen was collected from the lower Albian, fluvio-estuarine deposits of the Ain el Guettar Formation (southern Tunisia). We present detailed analyses on the sedimentology and facies distribution at the main quarry and a revision of the vertebrate fauna associated with the skeleton. Data provide information on a complex ecosystem dominated by crocodilian and other brackish water taxa. Taphonomic interpretations indicate a multi-event, pre-burial history with a combination of rapid segregation in high sediment supply conditions and partial subaerial exposure of the carcass. After the collection in 2011 of the articulated sacrum and proximalmost caudal vertebrae, all showing a complex pattern of pneumatization, newly discovered material of the type specimen allows a detailed osteological description of Tataouinea. The sacrum, the complete and articulated caudal vertebrae 1–17, both ilia and ischia display asymmetrical pneumatization, with the left side of vertebrae and the left ischium showing a more extensive invasion by pneumatic features than their right counterparts. A pneumatic hiatus is present in caudal centra 7 to 13, whereas caudal centra 14–16 are pneumatised by shallow fossae. Bayesian inference analyses integrating morphological, stratigraphic and paleogeographic data support a flagellicaudatan-rebbachisaurid divergence at about 163 Ma and a South American ancestral range for rebbachisaurids. Results presented here suggest an exclusively South American Limaysaurinae and a more widely distributed Rebbachisaurinae lineage, the latter including the South American taxon Katepensaurus and a clade including African and European taxa, with Tataouinea as sister taxon of Rebbachisaurus. This scenario would indicate that South America was not affected by the end-Jurassic extinction of diplodocoids, and was most likely the centre of the rapid radiation of rebbachisaurids to Africa and Europe between 135 and 130 Ma.

New anatomical information on Rhoetosaurus brownei Longman, 1926, a gravisaurian sauropodomorph dinosaur from the Middle Jurassic of Queensland, Australia

ABSTRACT Rhoetosaurus brownei is the only known named pre-Cretaceous sauropod from Australia. It is therefore a potentially important taxon for understanding global paleobiogeographic and phylogenetic patterns among early sauropods. Despite its obvious significance, Rhoetosaurus has been too poorly understood to be included in most recent analyses of early sauropod evolution. With this in mind, we evaluated the osteology and phylogeny of undescribed materials of Rhoetosaurus, in order to attempt to close the gap in this understanding. The lower hind limb of Rhoetosaurus highlights a plethora of differences from other sauropods, supporting the distinctiveness of Rhoetosaurus even in the absence of other materials. Some unique traits include prominent crests and sulci on the tibia medially, a narrow metatarsal articular bridge, and pedal claws with an accessory groove or fossa. The pes plesiomorphically retains four claws where most sauropods have three, and bears superficial similarity to that of Shunosaurus. Preliminary cladistic analysis confirms that Rhoetosaurus is a non-neosauropod gravisaurian, although weak support for the most parsimonious topology suggests further findings are required to improve upon incompleteness in the character data. Examination of alternative phylogenetic hypotheses rules out a close relationship between Rhoetosaurus and East Asian Jurassic sauropods, and indicates a closer examination of the potential relationships between Rhoetosaurus and other contemporaneous Middle Jurassic Gondwanan sauropods is necessary.

The Appendicular Skeleton ofNeuquensaurus, a Late Cretaceous Saltasaurine Sauropod from Patagonia, Argentina

Neuquensaurus, from the Late Cretaceous of Argentina and one of the first dinosaurs described from Patagonia, is one of the most derived sauropod dinosaurs, and its proportions and size place it among the smallest sauropods ever known. In this context, Neuquensaurus is central to understanding late stages of sauropod evolution. This contribution offers a full description of the appendicular skeleton of Neuquensaurus. The anatomical analysis reveals that the appendicular skeleton of Neuquensaurus exhibits unique characteristics only shared with closely related saltasaurine titanosaurs; for example, the laterally directed preacetabular lobe of the ilium, the prominent fibular lateral tuberosity, and the presence of an intermuscular line on the femoral shaft, which is proposed here as a synapomorphy of Saltasaurinae. Neuquensaurus also displays many reversals to primitive character states, such as the presence of a prominent olecranon process of the ulna, a trochanteric shelf, a lesser trochanter and an isch...

A revision of the sauropod dinosaur genus ‘Bothriospondylus’ with a redescription of the type material of the Middle Jurassic form ‘B. madagascariensis’

Abstract: The sauropod dinosaur ‘Bothriospondylus’, originally named on the basis of Late Jurassic remains from England, is demonstrated to be invalid, and the characters used to diagnose it are shown to be obsolescent features which are widespread throughout Sauropoda. Material referred to this genus spans a temporal range from the Middle Jurassic until the early Late Cretaceous and has been described from five different countries, across three continents. These remains represent a wide array of sauropod groups, comprising non‐neosauropod eusauropods, a macronarian, titanosauriforms (including at least one definite brachiosaurid) and a rebbachisaurid. The type material of the Middle Jurassic ‘B. madagascariensis’ represents a derived non‐neosauropod eusauropod and possesses two potential autapomorphies. However, as a result of the fragmentary nature of the material and the uncertainty surrounding its association, a new taxon is not erected. Of the numerous specimens referred to ‘Bothriospondylus’, however, several remains are considered diagnostic: Ornithopsis hulkei (Early Cretaceous, UK), Lapparentosaurus madagascariensis (Middle Jurassic, Madagascar) and Nopcsaspondylus alarconensis (early Late Cretaceous, Argentina). At least three types of sauropod were present in the Bathonian (Middle Jurassic) of north‐west Madagascar, with a basal eusauropod (Archaeodontosaurus), a more derived eusauropod (‘B. madagascariensis’) and a titanosauriform (Lapparentosaurus) all approximately contemporaneous. Palaeocontinental reconstructions suggest that Middle Jurassic Madagascan sauropods would still have been capable of global biotic interchange, and this is perhaps reflected in their diverse assemblage. Re‐evaluation of these Malagasy forms has shed new light on this important time period in sauropod evolution.

A new basal sauropod dinosaur from the middle Jurassic of Niger and the early evolution of sauropoda.

BackgroundThe early evolution of sauropod dinosaurs is poorly understood because of a highly incomplete fossil record. New discoveries of Early and Middle Jurassic sauropods have a great potential to lead to a better understanding of early sauropod evolution and to reevaluate the patterns of sauropod diversification.Principal FindingsA new sauropod from the Middle Jurassic of Niger, Spinophorosaurus nigerensis n. gen. et sp., is the most complete basal sauropod currently known. The taxon shares many anatomical characters with Middle Jurassic East Asian sauropods, while it is strongly dissimilar to Lower and Middle Jurassic South American and Indian forms. A possible explanation for this pattern is a separation of Laurasian and South Gondwanan Middle Jurassic sauropod faunas by geographic barriers. Integration of phylogenetic analyses and paleogeographic data reveals congruence between early sauropod evolution and hypotheses about Jurassic paleoclimate and phytogeography.Conclusions Spinophorosaurus demonstrates that many putatively derived characters of Middle Jurassic East Asian sauropods are plesiomorphic for eusauropods, while South Gondwanan eusauropods may represent a specialized line. The anatomy of Spinophorosaurus indicates that key innovations in Jurassic sauropod evolution might have taken place in North Africa, an area close to the equator with summer-wet climate at that time. Jurassic climatic zones and phytogeography possibly controlled early sauropod diversification.

Lower Cretaceous rebbachisaurid sauropods from Cerro Aguada del León (Lohan Cura Formation), Neuquén Province, northwestern Patagonia, Argentina

ABSTRACT We describe sauropod material from the Lower Cretaceous (Aptian-Albian) Puesto Quiroga Member of the Lohan Cura Formation, exposed at the Cerro Aguada del León locality (La Picaza area, Neuquén Province, Argentina). The remains consist of disarticulated elements of at least three individuals, and are assigned to an indeterminate species of the rebbachisaurid diplodocoid Limaysaurus gen. nov. Elements from various parts of the skeleton are represented: a tooth, partial dorsal, sacral, and caudal vertebrae, a haemal arch, coracoid, humerus, ilium, pubes, ischium, femora, a tibia fragment, and an incomplete fibula. The Lohan Cura specimens are strongly reminiscent of corresponding elements in the holotype of Limaysaurus tessonei (= “Rebbachisaurus” tessonei, “Rayososaurus” tessonei) from the overlying Upper Cretaceous (lower Cenomanian) Candeleros Formation. We evaluate the phylogenetic relationships of Limaysaurus gen. nov. and other diplodocoids, and provide hypotheses regarding sauropod evolution during the Cretaceous.

The earliest known sauropod dinosaur.

Sauropods were a very successful group of dinosaurs during the Jurassic and Cretaceous periods, but their earlier history is poorly known. Until now, the earliest reported sauropod bones were from the Early Jurassic, and the only tentative evidence of earlier sauropods was in the form of controversial footprints. Here we report the discovery of an incomplete sauropod skeleton from the Late Triassic period of Thailand, which provides the first osteological evidence of pre-Jurassic sauropods. This dinosaur is markedly different from prosauropods and substantiates theoretical predictions that there was a fairly long period of sauropod evolution during the Triassic.

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

The phylogenetic relationships of sauropod dinosaurs

Abstract 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 Opisthocoelicaudia 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.