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Bacteria meet the "titans": horizontal transfer of symbiotic microbiota as a possible driving factor of sociality in dinosaurs

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Abstract

In the last decades several new dinosaurs species have been described from both Laurasia and Gondwana and a complex, multi-dimensional picture of the physiology, evolution and behavior of dinosaurs has emerged. One of the central elements of new discoveries is the recognition of a complex sociality in this vertebrate clade, especially in herbivorous taxa. Herbivores are not genetically provided with the enzymes needed to break down and metabolize cellulose, thus need gut symbiotic bacteria communities, able to digest plant-derived materials. In this short contribution, we discuss the hypothesis that precisely the need to horizontally exchange bacteria among individual ls of different ages, has triggered a growing sociality in herbivorous dinosaurs.

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Five factors, mobile terrestrial lifestyle, oviparity, parental care, multi-year maturation and juvenile sociality, contribute to a distinct life history for Mesozoic dinosaurs in comparison to extant archosaurs and mammals. Upright, para-sagittal gait reflects several synapomorphies of Dinosauria, and wide histological sampling suggests that multi-year maturation typified dinosaurs across a range of body sizes. Fossil support for juvenile sociality exceeds that for either oviparity or parental care. Implications of these factors include temporal segregation of adults for an extended, perhaps months-long reproductive cycle; spatial separation of adults and perhaps hatchlings to suitable nesting sites; increased likelihood for territoriality; reduced potential for long migrations; intraspecific niche segregation by age; population and community structure and macroevolutionary patterns. Fossil evidence for oviparity, parental care and juvenile sociality consists of combinations of adults, juveniles, embryos, eggs or traces and emphasises the importance of bonebeds and taphonomy in understanding dinosaur life-history strategies. Oviparity and parental care, predicted for dinosaurs by their extant phylogenetic bracket, have the least fossil support and cautions against overextending parsimonious interpretations to extinct taxa with the risk of obscuring novel or intermediate behaviours. Given the great diversity of Mesozoic dinosaurs, the proposed life history is hypothesised to represent only a general tendency.
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A series of polished slabs, cut vertically through a Grallator footprint, proved to be very useful in the reconstruction of the walking dynamics of theropod dinosaurs, and to an understanding of the animal‐substrate interactions. The trampled layer comprises a succession of plastic sediments and elastic cyanobacterial laminites, capped by semiliquid carbonate mud. The sections display records of the different pressures exerted onto the substrate by variable morphologic elements of the foot. Consequently it is possible to reconstruct the way the producing dinosaur walked. A progressive shift of the center of gravity is recorded by the different function of the digits in the different movement phases. The IV digit had a dominant function during the touch‐down and the beginning of the weight‐bearing phase. The II digit appears to have played an unexpected dominant function during the whole touch‐down and weight‐bearing phase, with a marked inward tangential translation and a diagonal penetration into the sediment. In the last phases of weight‐bearing and the kick‐off, the III digit had a functional dominance. In the propelling phase, it penetrated deeper than any other into the substrate. Such a study provides evidence for the correct interpretation, as dinosaur footprints, of deformation structures that crop out in the stratigraphic succession.
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1080, Bakker overgeneralizes the (hind)limb postures of reptiles and mammals. All reptiles have a sprawling posture (what about crocodilians?) and nearly all living birds and mammals have an erect posture. Not only does he incorrectly use these terms, but he equates gait with posture, i.e. sprawling gait and posture. What is a sprawling gait anyway? Nowhere on Hildebrand's functional kinetospace can you find sprawling or erect gaits. Bakker continues with this dubious terminology and restores sauropod and elephant forelimbs in a 100% columnar fashion that is inaccurate with anatomy.
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Early Cretaceous slender-toed bipedal dinosaur tracks are reported from the eastern part of the Tetori area, central Japan. They are small, bipedal and tridactyl impressions assigned toToyamasauripus masuiaeichnogen. and ichnosp. nov. based on biometric analysis. Thirty-three individuals ofToyamasauripus masuiaeshow the highest density of footprints of any dinosaur track-sites in Japan. This is also the first trackway evidence of gregarious dinosaurs reported from Japan.Toyamasauripus masuiaeappears to represent a small bipedal dinosaur track-maker that was relatively abundant. As no bones are known from the track-bearing beds, the footprints add much to our knowledge of dinosaur faunas at this time.
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Evidence of communal nesting and site fidelity in hadrosaurian dinosaurs from the Late Cretaceous Two Medicine Formation of Montana indicates a close parallel with herbivorous iguanine lizards. Raised nests prevented egg drowning, while communal habits and site fidelity facilitated fecal ingestion by young, which infected them with a microflora appropriate for herbivory.
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Although herbivory probably first appeared over 300 million years ago, it only became established as a common feeding strategy during Late Permian times. Subsequently, herbivory evolved in numerous lineages of terrestrial vertebrates, and the acquisition of this mode of feeding was frequently associated with considerable evolutionary diversification in those lineages. This book represents a comprehensive overview of the evolution of herbivory in land-dwelling amniote tetrapods in recent years. In Evolution of Herbivory in Terrestrial Vertebrates, leading experts review the evolutionary history and structural adaptations required for feeding on plants in the major groups of land-dwelling vertebrates, especially dinosaurs and ungulate mammals. As such, this volume will be the definitive reference source on this topic for evolutionary biologists and vertebrate paleontologists.
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The known relationships of speed, gait and body size (derived mainly from mammals) are used to determine the gaits and theoretical maximum speeds of dinosaurs. Speed estimates are made for 62 dinosaurs (representing 51 genera) and are supplemented with information from comparative anatomy and from dinosaur trackways. It is concluded that smaller bipedal dinosaurs were capable of running at speeds up to 35 or 40 km/h. The so-called “ostrich dinosaurs” are credited with maximum speeds less than 60 km/h, and possibly as low as 35 or 40 km/h. Larger bipedal dinosaurs were probably restricted to walking or slow trotting gaits, with maximum speeds in the range 15–20 km/h. Most quadrupedal dinosaurs seem to have been restricted to a walking gait. Stegosaurs and ankylosaurs may have had maximum speeds as low as 6–8 km/h. Sauropods may have attained 12–17 km/h, and some ceratopsians may have been capable of trotting at speeds up to 25 km/h. On a weight-for-weight basis the speeds of dinosaurs are generally lower than those of mammals.
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Studying the trackways of extinct animals is one of the few ways to determine social behaviors, especially herding. We present an analysis of footprint data following the method of Alexander (1989) from the Caririchnium tracksite at Mosquero Creek, New Mexico described by Lockley and Hunt (1995a). This analysis indicates that the distribution of the directions and speeds of the trackmakers is consistent with movement as a group. In addition, there is an anticorrelation (correlation coefficient=‐0.36) between footprint size and relative stride in the sense that the larger animals, were exerting less effort than the smaller animals but moving at approximately the same physical speed. As a test of the technique, a Late Triassic tracksite which was not expected to show organized movement was analyzed. This tracksite, Apache Canyon, New Mexico, had tracks of ichnogenera Pseudotetrasauropus and Grallator which show a large scatter in speed and direction.
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Fossil footprints are very widespread in the Late Paleozoic and Mesozoic rocks of eastern Utah, but until recently have not been studied in detail. This is surprising in light of the fact that skeletal remains of fossils in this area are generally rare, whereas footprints are common and very informative about the distribution and behavior of ancient vertebrates.In this report we describe more than three dozen tracksites in the Glen Canyon National Recreation Area (GCNRA) and immediate vicinity, from eight formations (Cedar Mesa, Moenkopi, Chinle, Wingate, Kayenta, Navajo, Summerville, and Morrison) that range in age from Permian through Jurassic. Tracks in the Permian, cf. Anomalopus (or Chelichnus) and Stenichnus, represent at least two types of pre‐archosaurian reptiles, and reveal evidence of predator–prey interaction and digging activity. Footprints in the Moenkopi include a large number of swim traces attributable to amphibians, and horseshoe crabs. Footprints in the Chinle Group include the first example of Atreipus from the western United States–a track attributed to an early, turkey–sized bipedal dinosaur. Footprints in the Wingate and Kayenta Formations are assigned to Grallator and Eubrontes and represent theropod dinosaurs. One Kayenta occurrence of theropod tracks resembles the famous so‐called “man tracks” of Texas.The Navajo Formation has produced a large number of track‐bearing localities including sites that reveal theropod footprints (Grallator and Eubrontes), mammal‐like reptile footprints (cf. Brasilichnium), tracks probably attributable to prosauropods, or thyreophorans (Otozoum) and ornithopods (cf. Anomoepus). Footprints from the Summerville and Morrison Formations include the first brontosaur ichnites (cf. Brontopodus) with skin impressions and well‐preserved digit impressions, and pterosaur tracks (Pteraichnus).Fossil footprints are an important, non‐renewable resource in this area, that provide special management challenges. Part of these challenges involve a dialogue between paleontologists and land management authorities that permits an understanding of the resource and promotes the use of non‐technical terminology. To this end, this manuscript is written with both audiences in mind. Both groups are responsible for distinguishing between more‐ and less‐important sites and guiding or prioritizing conservation, collection and public education/ viewing policies. Tracksites can not all be removed to museums for safekeeping. Similarly they can not all be made available for public viewing, nor can they be completely protected from weathering and vandalism.
Article
One century ago, a field party from the American Museum of Natural History discovered a bonebed in the Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada. Excavations by that museum, the Royal Tyrrell Museum of Palaeontology, and the University of Alberta have revealed the presence of at least a dozen individuals - represented by articulated partial skeletons, associated skeletons, and disarticulated isolated elements - of Albertosaurus sarcophagus. Tyrannosaurids dominate the bonebed assemblage, which also includes an adult Hypacrosaurus altispinus, two individuals of Albertonykus borealis, and numerous other, predominantly terrestrial, vertebrates. Skeletal morphology, phylogenetic inference, monodominant bonebeds, trackway sites, and ecological inferences support the notion that some non-avian theropods were gregarious animals. And specifically in the Albertosaurus bonebed, associated geologic and taphonomic evidence do not rule out a behavioural component in this catastrophic, mass-death assemblage.
Article
At least six sites with multiple parallel ornithopod trackways and one site with three parallel sauropod trackways have been mapped in the track-rich Cretaceous sequence on Sado and Chudo islands, Yeosu City area, South Korea. A preliminary study of the stratigraphic context of these tracks indicates that they were made by gregarious subadult or adult dinosaurs that frequented lake basin settings subject to a cyclic depositional regime and periodic ash fall. Bird and theropod dinosaur tracks also occur in the sequence. Mapped sites reveal between 4 and 14 regularly spaced, ornithopod trackways suggestive of herding behavior. One site reveals an 84 m-long trackway, the longest on record for an ornithopod. Only one site reveals parallel sauropod trackways indicating three animals of equal size traveling eastwards with an inter-trackway spacing of about 2.25–2.5 m. The footprints show well preserved pes claw impressions, slightly wide gauge and large manus/pes ratios (low heteropody). The sedimentological and ichnofaunal sequences share some similarities with the famous Jindong successions 50 km to the east, but they also differ significantly in age and ichnofaunal composition.
Article
A method for estimating the speed of a dinosaurian trail-maker from the size of its footprints and stride has been described by Alexander1. However, when applied to known trackways, this method gave rather low speeds (1.0–3.6 m s−1). Russell and Béland2 estimated a speed of 1.77 m s−1 for a slowly moving ornithomimid and 7.54 m s−1 for an allegedly rapidly running ornithopod. The latter estimate is questionable as there is some doubt concerning the number of prints (and thus the stride length) of the trail3,4. Dinosaurs responsible for trackways in British Columbia5, South Wales6 and Queensland7 all seem to have been moving slowly. Thus reliable estimates of dinosaur speeds are all rather low. Here I report dinosaur speeds based on trails at a new site from the Lower Cretaceous of Texas, some of which appear quite fast by Alexander's method1.
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Recognition of endothermy in dinosaurs can explain both the success and the extinction of this group in the Mesozoic.
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Avanzini, M., Piñuela, L. & García-Ramos, J.C. 2011: Late Jurassic footprints reveal walking kinematics of theropod dinosaurs. Lethaia, Vol. 45, pp. 238–252. This study describes a set of theropod footprints collected from the Late Jurassic Lastres Formation (Asturias, N Spain). The footprints are natural casts (tracks and undertracks) grouped into three morphotypes, which are characterized by different size frequency, L/W relationship and divarication angles: ‘Grallatorid’ morphotype, ‘Kayentapus–Magnoavipes’ morphotype, ‘Hispanosauropus’ morphotype. The tracks were produced in firm, stiff and soft sediments. The infills of deep tracks, which are typically formed in soft mud, lack fine anatomical details, but they can reveal the walk kinematics of the trackmaker through the morphology of internal track fills and sinking traces. In all footprints, a horizontal outwardly directed translation movement and rotation are recognizable. The amount and geometry of digit penetration in the ground also show a pronounced difference. It can be inferred from the described sample that different theropoda-related ichnogenera share common kinematics. □Asturias, dinosaur footprint, late jurassic, theropods, walking kinematics.
Article
Numerous and well-preserved trackways in mid-Cretaceous sediments of West Central Queensland, Australia, are attributed to a stampede of small to medium-sized bipedal dinosaurs - both herbivores (ornithopods) and minor-league predators (coelurosaurs). The tracks of a single large predator (carnosaur) suggest a reason for the stampede. These trackway data permit calculation of sustained running speeds for the coelurosaurs and ornithopods.