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Bacteria meet the "titans": horizontal transfer of symbiotic microbiota as a possible driving factor of sociality in dinosaurs
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.
... The American palaeontologist has revolutionised our understanding of dinosaur ethology, studying for years certain extended nesting sites of Maiasaura, discovered and described by himself (Horner 1984b). These deposits have revealed the unexpected complexity of these animals, confirming the presence of parental care and a gregarious lifestyle in at least some clades of dinosaurs (see Romano and Farlow 2018). The herds must have been composed of hundreds or thousands of individuals, as observed today in the migrations of some large African herbivores. ...
Between the fifteenth and sixteenth centuries, the first naturalistic illustrations appeared in texts and treatises, marking the true and proper passage from simple literary works to real scientific contributions. Since that time, the geo-palaeontological literature and the world of scientific illustrations developed together. For a long time initially the scientist and artist coincided in the same person, until the emergence of the ‘paleoartist’, as a professional devoted to naturalistic representations. Here, we review the fundamental
steps of ‘co-evolution’ between advances in scientific knowledge and their representation in ‘paleoart’. The study led to the identification of six principal ‘Genres’; in addition, a subdivision of the history and evolution of ‘paleoart’ into six periods or major ‘eras’ is proposed. The analysis is based on a dataset with a total of 605 authors, considering a time range between the first half of the 18th century up to 2020, with paleoartists from 42 different countries. The relationship between scientist and ‘paleoartist’ has been, and
will be in the future, a constructive interaction of ‘reciprocal illumination’, where the questions asked by the artist represent a genuine propellant for the advancement of knowledge and the research itself.
... (The lost world, Arthur Conan Doyle, 1912) As expressed in the words of Arthur Conan Doyle's famous 1912 novel "The lost world", for a long time the term "prehistory" has been used to refer to all extinct organisms of the past. Amongst the 'prehistoric' organisms, dinosaurs have occupied center stage, iconic animals capable of attracting and stimulating the imagination of a very large audience Romano & Farlow, 2018). However far from being related to the past of science dissemination, this erroneous use of the term prehistory is widespread even today, as can be easily determined by a simple check on online search engine. ...
The word "prehistory" has been used for a long time to indicate all extinct organisms of the past, with dinosaurs occupying a center stage stimulating the imagination of a very large audience. Such erroneous use of the term prehistory is widespread even today, a word and concept originally referred to the period of human history which preceded writing, i.e. prior to documented history and embracing a time interval from about 2.6 million years ago to 4000 BC. Keeping in mind the crucial milestone of 'deep time' concept in geology the division of the extensive Earth history into only two sections of respectively 4.5429 billion years and 4000 years in our opinion is a misleading oversimplification. Over the past few centuries much effort has gone into the development of a hyper-detailed chronostratigraphic scale, substantiated by absolute dating, detailed biostratigraphy, and documentation of biological evolution. All this generation of knowledge, conducted by thousands of researchers over many years, is completely lost when, in a simplistic way the anthropocentric dichotomy is accepted.
... However, the few known cases in which multiple ankylosaur individuals are concentrated in a single horizon and form true mass death assemblages suggest that the social structuring in ankylosaurs may have been more diverse than previously thought. Several factors influence social behaviour of extant animals, including the diverse, dynamically changing costs and benefits of group formation (Alexander, 1974;Troyer, 1982;Rogers, 1985;Owen-Smith, 1988;Vermeij, 1994;Conrad, 1998;Lombardo, 2008;Owen-Smith and Mills, 2008;Romano and Farlow, 2018 and references therein), but only a few among these can potentially be inferred in fossils. Nevertheless, besides the traditional taphonomical and trace fossil evidences, assessing other important aspects that can be studied in fossils is essential in order to get a more complete understanding of the social behaviour of extinct herbivores, including ankylosaurs. ...
Gregarious behaviour of large bodied herbivorous dinosaurs, such as ceratopsians, hadrosaurs and
sauropods, has received much attention due to their iconic mass death assemblages (MDAs). Yet, social
lifestyle of ankylosaurs, a highly specialized group of armoured herbivores that flourished predominantly
during the Cretaceous Period, remains largely ambiguous. Whereas most ankylosaurs are found as isolated
individuals, which may suggest a dominantly solitary lifestyle, the few examples of ankylosaur
MDAs indicate that some members of this clade could have been gregarious. In this review, we assess
taphonomic history, ontogenetic composition of the MDAs, defence system and other comparative
anatomical attributes, and inferred habitat characteristics of ankylosaurs; aspects that may indicate and/
or influence group formation in extant herbivores and can also be studied in fossils. We show that the
ankylosaurian gross anatomy, such as their heavy armour, barrel-shaped body and usually stocky limbs,
combined with the rarity of their MDAs and multiple parallel trackways, all suggest a solitary adult life
with efficient anti-predator defence system, limited agility, and confined foraging range. However,
characteristics of the known MDAs of Pinacosaurus, Gastonia, and the Iharkút nodosaurids evaluated in
this study imply that at least some ankylosaurs formed groups. Nevertheless, we found no common and
consistent set of features to explain why these particular ankylosaurs were gregarious. While inefficient
anti-predator defence along with likely higher agility of juvenile Pinacosaurus living in open habitats
could account for their gregarious behaviour, such ontogenetic, anatomical and habitat features are not
combined either in Gastonia or in the Iharkút nodosaurid MDAs. Instead, members of each MDA likely
had their own specific conditions driving them to form relatively small herds, indicating a more complex
social structuring in ankylosaurs than previously acknowledged. Studying morphological and functional
disparity within Ankylosauria may help explain the repertoire of their social behaviour. Our holistic
approach shows that combining palaeontological and biological information is essential and can provide
new insights into the behavioural ecology of long extinct vertebrates.
... Bakker, 1968;Currie, 1983;Ostrom, 1985;Leonardi, 1989;Pittman and Gillette, 1989;Barnes and Lockley, 1994;Lockley et al., 1994b;Lockley, 1995;Matsukawa et al., 1997Matsukawa et al., , 1999Cotton et al., 1998;Day et al., 2004;Castanera et al., 2012;Lockley et al., 2012;Piñuela et al., 2016;Heredia et al., 2020). This interpretation seems to be indirectly reinforced by large shared nesting sites in some species (Horner and Makela, 1979;Horner, 1982Horner, , 2000Sander et al., 2008;Reisz et al., 2012;Romano and Farlow, 2018). ...
This year, 2020, marks the 150 th anniversary of the seminal work by Giulio Curioni (1870), representing the first published scientific contribution on tetrapod footprints from Italy. We took this opportunity to discuss the current state of the art on tetrapod ichnology in our country, with a jubilee volume, titled "Tetrapod ichnology in Italy: the state of the art". The volume involves the scholars who first pioneered this discipline in Italy in the seventies of the last century, along with all the authors who have worked on the topic in recent decades, and younger generations who have just started to enthusiastically contribute to vertebrate ichnology. After briefly introducing the idea at the base of the Special Volume, as well as some aspects of the discipline and the current methodologies involved in ichnological studies, we present each of the contributions to serve the Italian ichnological heritage.
... However, the few known cases in which multiple ankylosaur individuals are concentrated in a single horizon and form true mass death assemblages suggest that the social structuring in ankylosaurs may have been more diverse than previously thought. Several factors influence social behaviour of extant animals, including the diverse, dynamically changing costs and benefits of group formation (Alexander, 1974;Troyer, 1982;Rogers, 1985;Owen-Smith, 1988;Vermeij, 1994;Conrad, 1998;Lombardo, 2008;Owen-Smith and Mills, 2008;Romano and Farlow, 2018 and references therein), but only a few among these can potentially be inferred in fossils. Nevertheless, besides the traditional taphonomical and trace fossil evidences, assessing other important aspects that can be studied in fossils is essential in order to get a more complete understanding of the social behaviour of extinct herbivores, including ankylosaurs. ...
Ankylosaurian fossils are usually standard elements of Cretaceous continental vertebrate localities; however, bone-yielding horizons including more than one individual are extremely rare. Here, we present a unique assemblage of 12 partial, articulated or associated ankylosaurian skeletons and thousands of isolated bones and teeth discovered from the Santonian Iharkút vertebrate locality, western Hungary. Collected from an area of 600 m2 and from a single bone bed, this material is one of the richest ankylosaurian accumulation worldwide. The 12 skeletons are not monospecific but mostly based on the pelvic armour composition: six of them are from Hungarosaurus, two are referred to Struthiosaurus and four can be assigned to Nodosauridae indet. Sedimentological and taphonomical examinations revealed a single mass mortality event as the cause of the death and accumulation of these quadruped animals that are described here. The ankylosaur assemblage from Iharkút suggests at least a temporarily gregarious behaviour of these animals and also shows that Hungarosaurus and Struthiosaurus might live in the same moist habitat or at least preferred relatively close environments.
Five new partial skulls of the hadrosaurid dinosaur Maiasaura peeblesorum from the Linster Quarry bone bed (Two Medicine Formation, Campanian) in Montana, USA, provide the basis for a description of the skull roof and braincase morphology of this taxon. These skulls additionally form an ontogenetic series consisting of one subadult, two small “intermediate adults”, and two larger “mature adults”. The subadult skull is approximately two thirds as wide as the largest adult and lacks a nasofrontal crest, suggesting that the crest formed relatively late in ontogeny compared to some other hadrosaurids. As in closely related taxa, larger skulls of M. peeblesorum have a proportionately wider braincase and a larger, more rugosely ridged nasofrontal contact for supporting a larger crest. In the two largest adults, the skull roof incipiently overhangs the anterior margin of the dorsotemporal fenestrae. In the largest skull examined, the crest is semicircular in anterior view and incorporates flared, anteriorly concave prefrontals in its lateral margins. Intraspecific variation in M. peeblesorum is observed in cranial characters previously discussed as interspecific variation in related taxa, including the prominence of dorsal depressions on the frontal, and the position of the foramen for the facial nerve (CN VII). Although cranial ontogeny in Maiasaura shares some trends with Brachylophosaurus and Probrachylophosaurus, it deviates in other ways from the previous heterochronic model proposed for the evolution of Maiasaurini.
Evolution by natural selection can proceed at different levels, from genes to ecosystems. Most biologists focus on the individual as the level of selection. However, there are no individual animals or plants in the natural world—all are holobionts consisting of the host and many species of microorganisms and viruses. The hologenome concept considers the holobiont with its hologenome as a unique biological entity and therefore a natural level of selection in the evolution of organisms. Evolution of the holobiont, the host, and the microbiota, individually and by groups, can also occur via random drift and not only by natural selection. Cooperation within holobionts, between microbes and between microbes and hosts, is a stable property that has persisted in some cases for millions of years. One of the important means of achieving this was by preventing potential cheaters from becoming abundant by a variety of mechanisms, the main one being—the immune system. Evolution by cooperation can occur by acquisition of microbiota (e.g., cellulose-degrading microbes in termites and ruminants) and/or by acquiring microbial and viral genes by horizontal gene transfer (e.g., synctin genes in placental mammals). Evolution can proceed not only by mutation and selection, but also most significantly by selection following the acquisition of pre-evolved information from microorganisms and viruses. Microbiota have also been shown to contribute to the origin of species The hologenome concept leads to the conclusion that evolution of animals and plants occurred primarily by natural selection for cooperation.
Evolution by natural selection relies on genetic variation in a population. According to the hologenome concept of evolution, genetic variation can arise from changes in both the host and the symbiotic microbiota genomes. In addition to mutation, holobionts give rise to several underappreciated mechanisms of variation, including acquisition of novel microbes from the environment, amplification, and reduction of specific microbiota, and horizontal gene transfer (between microbes and between microbes and host). Variations in symbiotic microbiota may allow the holobiont to adapt and survive under rapidly changing environmental conditions, thus providing the time necessary for the host genome to evolve. In addition to constructing new genes by mutations, animals and plants have the potential to acquire pre-evolved genetic information and functions from microorganisms, including viruses, either by horizontal gene transfer of microbial genes into the host genome, or by acquisition of novel microbes from the environment into the microbiome. The hologenome concept of genetic variation by acquisition of novel microbes and amplification contains Lamarckian aspects within a Darwinian framework.
Since the 1969 description of Deinonychus antirrhopus Ostrom, cooperative pack hunting behavior for this species and, subsequently, for many other nonavian theropods, has attained wide acceptance. In this paper we assess the hypothesis of mammal-like cooperative pack hunting in D. antirrhopus and other nonavian theropods by examining the behaviors of extant diapsids. Through phylogenetic inference and character optimization, we conclude that this hypothesis is both unparsimonious and unlikely for these taxa and that the null hypothesis should therefore be that nonavian theropod dinosaurs were solitary hunters or, at most, foraged in loose associations. Moreover, we present new evidence from the D. antirrhopus type locality of probable intraspecific aggression in this species. Additionally, our study suggests that some evidence that has previously been proposed in support of highly gregarious, mammal-like behavior in nonavian theropods (e.g., certain theropod-dominated fossil assemblages, preserved bite-mark injuries on some specimens, and the preponderance of theropod trackways at some sites) may alternatively be interpreted as evidence that nonavian theropod behavior was more agonistic, cannibalistic, and diapsid-like than has been widely believed.
According to a traditional view, the specific diet in vertebrates is one of the key factors structuring the composition of the gut microbiota. In this interpretation, the microbiota assumes a subordinate position, where the larger host shapes, through evolution and its fitness, the taxonomical composition of the hosted microbiota. The present contribution shows how the evolution of herbivory, framed within the new concept of holobiont, the possibility of inter-kingdom crosstalk and its epigenetic effects, could pave the way to a completely reversed interpretation: instead of being passively shaped, the microbiota can mold and shape the general host body structure to increase its fitness. Central elements to consider in this context are the inter-kingdom crosstalk, the possibility of transporting RNAs through nanovesicles in feces from parents to offspring, and the activation of epigenetic processes passed on vertically from generation to generation. The new hypothesis is that the gut microbiota could play a great role in the macroevolutionary dynamics of herbivorous vertebrates, causing directly through host-microbiota dialogue of epigenetic nature (i.e., methylation, histone acetylation, etc.), major changes in the organisms phenotype. The vertical exchange of the same microbial communities from parents to offspring, the interaction of these microbes with fairly uniform genotypes, and the socially restricted groups where these processes take place, could all explain the reasons why herbivory has appeared several time (and independently) during the evolution of vertebrates. The new interpretation could also represent a key factor in understanding the convergent evolution of analogous body structures in very distant lineages.
A monodominant bonebed of Avimimus from the Nemegt Formation of Mongolia is the first oviraptorosaur bonebed described and the only recorded maniraptoran bonebed from the Late Cretaceous. Cranial elements recovered from the bonebed provide insights on the anatomy of the facial region, which was formerly unknown in Avimimus. Both adult and subadult material was recovered from the bonebed, but small juveniles are underrepresented. The taphonomic and sedimentological evidence suggests that the Avimimus bonebed represents a perimortem gregarious assemblage. The near absence of juveniles in the bonebed may be evidence of a transient age-segregated herd or ‘flock’, but the behaviour responsible for this assemblage is unclear. Regardless, the Avimimus bonebed is the first evidence of gregarious behaviour in oviraptorosaurs, and highlights a potential trend of increasing gregariousness in dinosaurs towards the end of the Mesozoic.
That holobionts (microbial communities and their animal or plant hosts) are units of selection squares poorly with the observation that microbes are often recruited (horizontally acquired) from the environment, not passed down vertically from parent to offspring, as required for collective reproduction. The taxonomic makeup of a holobiont’s microbial community may vary over its lifetime and differ from that of conspecifics. In contrast, biochemical functions of the microbiota and contributions to host biology are more conserved, with taxonomically variable but functionally similar microbes recurring across generations and hosts. To save what is of interest in holobiont thinking, we propose casting metabolic and developmental interaction patterns, rather than the taxa responsible for them, as units of selection. Such units need not directly reproduce or form parent-offspring lineages: their prior existence has created the conditions under which taxa with the genes necessary to carry out their steps have evolved in large numbers. These taxa or genes will reconstruct the original interaction patterns when favorable conditions occur. Interaction patterns will vary (for instance by the alteration or addition of intermediates) in ways that affect the likelihood of and circumstances under which such reconstruction occurs. Thus, they vary in fitness, and evolution by natural selection will occur at this level. It is on the persistence, reconstruction, and spread of such interaction patterns that students of holobiosis should concentrate, we suggest. This model also addresses other multi-species collectively beneficial interactions, such as biofilms or biogeochemical cycles maintaining all life.
We compare theropod footprints with elongate metatarsal prints from central Italy with known autopod structures in major theropod groups, in order to more accurately define the trackmaker attribution. Our work, using morphometric analysis, shows the considerable potential of explorative methods such as PCA (principal component analysis) and cluster analysis when describing important characters for a given taxonomic group (body and ichnofossils) and identifying important anatomical regions. Moreover, the results of the analysis suggest that the putative trackmaker is likely a member of Ornithomimosauria, with significant affinities in the posterior autopod structure with the genus Struthiomimus . The fundamental importance of integrating both osteological and ichnological data, when investigating locomotor and behavioural hypotheses, is highlighted. This approach could also contribute positively to the complex cognitive process of trackmaker identification and be favourable for the attainment of a more natural definition of ichnotaxa.
New dinosaur footprints were recently discovered in southern Latium (Italy). The
tracks all appear slightly differently preserved and are characterized by elongated
metatarsal impressions, recording the complex locomotor behaviour of a medium-sized
theropod. The spatial distribution and the features of the footprints indicate that the
trackmaker adopted a “crouched” position as part of an activity as well as a resting
phase suggested by sub-parallel, calcigrade tracks. These new data once again highlight
the great potential of ichnological evidence in the study of the biology and
behaviour of extinct tetrapods.
Groundbreaking research on the universality and diversity of microorganisms is now challenging the life sciences to upgrade fundamental theories that once seemed untouchable. To fully appreciate the change that the field is now undergoing, one has to place the epochs and foundational principles of Darwin, Mendel, and the modern synthesis in light of the current advances that are enabling a new vision for the central importance of microbiology. Animals and plants are no longer heralded as autonomous entities but rather as biomolecular networks composed of the host plus its associated microbes, i.e., "holobionts." As such, their collective genomes forge a "hologenome," and models of animal and plant biology that do not account for these intergenomic associations are incomplete. Here, we integrate these concepts into historical and contemporary visions of biology and summarize a predictive and refutable framework for their evaluation. Specifically, we present ten principles that clarify and append what these concepts are and are not, explain how they both support and extend existing theory in the life sciences, and discuss their potential ramifications for the multifaceted approaches of zoology and botany. We anticipate that the conceptual and evidence-based foundation provided in this essay will serve as a roadmap for hypothesis-driven, experimentally validated research on holobionts and their hologenomes, thereby catalyzing the continued fusion of biology's subdisciplines. At a time when symbiotic microbes are recognized as fundamental to all aspects of animal and plant biology, the holobiont and hologenome concepts afford a holistic view of biological complexity that is consistent with the generally reductionist approaches of biology.
Data concerning dinosaur tracks from 38 tracksites of South America are summarized and studied statistically. The distribution of dinosaurs by period, region, latitude, climate, environments, behavior and direction is examined. i) dinosaurs were rare in the Triassic in South America and were mainly bipedal; ii) thereafter, South America possessed a dinosaurian fauna that was abundant and varied. iii) Dinosaurs increased in individual and species number in the Jurassic and even more so in the Cretaceous. iv) Theropod tracks were consistently the most abundant. v) The ratio Sauropoda/Ornithopoda = 1/2 is probably due to a different ethology and ecology. vi) Coelurosaurs decreased proportionately from the Triassic to the Cretaceous whereas carnosaurs increased. The former were better adapted to arid and temperate regions than were the other dinosaur groups. viii) Ornithopods were more abundant in the south than in the north. -from Author
We present a holistic approach to the study of early archosauriform evolution by integrating body and track records. The ichnological record supports a Late Permian–Early Triassic radiation of archosauriforms not well documented by skeletal material, and new footprints from the Upper Permian of the southern Alps (Italy) provide evidence for a diversity not yet sampled by body fossils. The integrative study of body fossil and footprint data supports the hypothesis that archosauriforms had already undergone substantial taxonomic diversification by the Late Permian and that by the Early Triassic archosauromorphs attained a broad
geographical distribution over most parts of Pangea. Analysis of body size, as deduced from track size, suggests that archosauriform average body size did not change significantly from the Late Permian to the Early Triassic. A survey of facies yielding both skeletal and track record indicate an ecological preference for inland fluvial (lacustrine) environments for early archosauromorphs. Finally, although more data is needed, Late Permian chirotheriid imprints suggest a shift from sprawling to erect posture in archosauriforms before the end-Permian mass extinction event. We highlight the importance of approaching palaeobiological
questions by using all available sources of data, specifically through integrating the body and track fossil record.
The theropod footprint taxon Eubrontes is common in Early Jurassic rocks of the Hartford Basin. Aligned Eubrontes trackways at one site in Holyoke, Massachusetts, have led to the hypothesis that the track makers were gregarious; however, trackways are not aligned at several other sites. To test the gregariousness hypothesis, we measured trackway orientations at Powder Hill Dinosaur Park in Middlefield, Connecticut, where exposed rocks were deposited in an ephemeral lake environment, and compared these orientations to those of two additional track sites from similar sedimentary facies. The Eubrontes trackways produced in the ephemeral lake environments have no preferred orientation and provide no evidence of gregarious behavior. We suggest that the alignment of tracks in Holyoke reflects behavior in response to environmental settings rather than group behavior. Trackways may be aligned next to large, permanent lakes because of shoreline-parallel travel, but random orientations characterize other habitats. This study underscores the value of examining track sites from different paleoenvironments when inferring dinosaur behavior.
In modern terrestrial ecosystems, the population size of large predators is low, and a similar pattern has usually been assumed for dinosaurs. However, fossil finds of monospecific, large theropod accumulations suggest that population dynamics were more complex. Here, we report two Early Cretaceous tracksites dominated by large theropod footprints, in Querulpa Chico (Peru) and Chacarilla (Chile). The two sites correspond to distinct depositional environments-tidal basin/delta (Querulpa Chico) and meandering river (Chacarilla)-with both subject to extensive arid or semiarid palaeoclimatic conditions. Although most trackways show no preferred orientation, a clear relationship between two trackmakers is observed in one instance. This observation, coupled with the high abundance of trackways belonging to distinct large theropods, and the exclusion of tracks of other animals, suggests some degree of grouping behaviour. The presence of freshwater sources in a dry climate and perhaps social behaviour such as pair bonding may have promoted interactions between large carnivores. Further, the occurrence of these two tracksites confirms that large theropod dinosaurs, possibly spinosaurids and/or carcharodontosaurids, existed on the western margin of Gondwana as early as the earliest Cretaceous.
Recent evidence suggests that natural selection operating on hosts to maintain their microbiome contributes to the emergence of new species, that is, the ‘hologenomic basis of speciation’. Here we analyse the gut microbiota of two house mice subspecies, Mus musculus musculus and M. m. domesticus, across their Central European hybrid zone, in addition to hybrids generated in the lab. Hybrid mice display widespread transgressive phenotypes (that is, exceed or fall short of parental values) in a variety of measures of bacterial community structure, which reveals the importance of stabilizing selection operating on the intestinal microbiome within species. Further genetic and immunological analyses reveal genetic incompatibilities, aberrant immune gene expression and increased intestinal pathology associated with altered community structure among hybrids. These results provide unique insight into the consequences of evolutionary divergence in a vertebrate ‘hologenome’, which may be an unrecognized contributing factor to reproductive isolation in this taxonomic group.
Monodominant bonebeds are a relatively common occurrence for non-avian dinosaurs, and have been used to infer associative, and potentially genuinely social, behavior. Previously known assemblages are characterized as either mixed size-classes (juvenile and adult-sized specimens together) or single size-classes of individuals (only juveniles or only adult-sized individuals within the assemblage). In the latter case, it is generally unknown if these kinds of size-segregated aggregations characterize only a particular size stage or represent aggregations that happened at all size stages. Ceratopsians ("horned dinosaurs") are known from both types of assemblages.
Here we describe a new specimen of the ceratopsian dinosaur Protoceratops andrewsi, Granger and Gregory 1923 from Mongolia representing an aggregation of four mid-sized juvenile animals. In conjunction with existing specimens of groups of P. andrewsi that includes size-clustered aggregations of young juveniles and adult-sized specimens, this new material provides evidence for some degree of size-clustered aggregation behaviour in Protoceratops throughout ontogeny. This continuity of size-segregated (and presumably age-clustered) aggregation is previously undocumented in non-avian dinosaurs.
The juvenile group fills a key gap in the available information on aggregations in younger ceratopsians. Although we support the general hypothesis that many non-avian dinosaurs were gregarious and even social animals, we caution that evidence for sociality has been overstated and advocate a more conservative interpretation of some data of 'sociality' in dinosaurs.
A remarkable specimen of the small neoceratopsian dinosaur Protoceratops andrewsi (Late Cretaceous, Mongolia) reveals the first nest of this genus, complete with fifteen juveniles. The relatively large size of the individuals and their advanced state of development suggests the possibility that Protoceratops juveniles remained and grew in their nests during at least the early stages of postnatal development. The nest further implies that parental care and sociality are phylogenetically basal behaviors in Ceratopsia. Finally, it reaffirms the conclusion that Protoceratops lived (and died) in the sandy aeolian dune fields of the central Asian craton.
At least fourteen ornithomimid skeletons were recovered from the Upper Cretaceous Ulansuhai Formation in Nei Mongol (Inner Mongolia) Autonomous Region of China. They are assigned to a new genus and species. Sinornithomimus dongi. The anatomy of the species is described. Comparative and phylogenetic studies of ornithomimosaurs prove that these skeletons represent a new taxon that is more derived than Archaeornithomimus and more basal than the clade of [(Anserimimus + Gallimimus) + [Struthiomimus + (Dromiceiomimus + Ornithomimus)]]. The phylogenetic analysis suggests that the structure of the hand is similar to Archaeornithomimus and represents an intermediate condition between the primitive (Harpymimus) and the derived (Anserimimus. Gallimimus, Struthiomimus, Dromiceiomimus, and Ornithomimus) conditions. The monophyly of Ornithomimidae is supported by a single synapomorphy (arctometatarsalian condition) in this analysis, indicating that the family is not as strongly supported as previously suggested. The analysis also implies that the shape of the rhamphotheca in North American taxa may have been different from that in Asian taxa. Previous study suggests herbivorous habits of this dinosaur based on characteristics of the gastroliths. The skeletons of Sinornithomimus were collected from a single monospecific bonebed with a high ratio of juvenile individuals (11 of the 14), suggesting gregarious behavior for protection from predators. The abundance of juveniles indicates high mortality of juveniles or a catastrophic mass mortality of a population with a high proportion of juveniles. An increase in the relative ratio of the tibia to femur through the ontogeny of Sinornithomimus suggests higher cursoriality in adult individuals than in juveniles.
A well-preserved, essentially complete and distinctive trace fossil of a crouching, medium-sized theropod dinosaur is reported from the northern slope ofthe Holy Cross Mountains, Poland. Crouching theropod traces are rare, and currently known from only six specimens from the Jurassic ofNorth America and Asia. Thus, this new specimen adds a seventh specimen to the dinosaur track record. The specimen was found in the Early Jurassic (Late Pliensbachian) sandstones mined in the Szydlowek quarry, in the vicinity of Szydlowiec.
Central Patagonia, Argentina, preserves an abundant and rich fossil record. Among vertebrate fossils from the Upper Cretaceous Bajo Barreal Formation of Patagonia, five individuals of the small, non-avian theropod dinosaur Aniksosaurus darwini were recovered. Group behavior is an important aspect of dinosaur paleoecology, but it is not well-documented and is poorly understood among non-avian Theropoda.
The taphonomic association of individuals from the Bajo Barreal Formation and aspects of their bone histology suggest gregarious behavior for Aniksosaurus, during at least a portion of the life history of this species. Histology indicates that the specimens were juvenile to sub-adult individuals. In addition, morphological differences between individuals, particularly proportions of the appendicular bones, are probably related to body-size dimorphism rather than ontogenetic stage.
Gregarious behaviour may have conferred a selective advantage on Aniksosaurus individuals, contributing to their successful exploitation of the Cretaceous paleoenvironment preserved in the Bajo Barreal Formation. The monospecific assemblage of Aniksosaurus specimens constitutes only the second body fossil association of small, coelurosaurian theropods in South America and adds valuable information about the paleoecologies of non-avian theropod dinosaurs, particularly in the early Late Cretaceous of Patagonia.
It has hitherto been hard to prove that any association of juvenile dinosaurs represents original behaviour rather than sedimentary accumulation, and it has been hard also to determine the ages of such juveniles. A previously described specimen, which consists of an ‘adult’ Psittacosaurus with 34 fully articulated juveniles, turns out to be a composite: the ‘adult’ skull has been added, and in any case it is below breeding age. Other juvenile-only clusters have been reported, but the best examples that likely reflect behaviour rather than sedimentary accumulation are specimens from the Early Cretaceous Lujiatun beds in NE China, which were entombed beneath pyroclastic flow deposits. A remarkable juvenile-only cluster of Psittacosaurus shows clear evidence of different ages (five 2-year olds and one 3-year old) based on bone histological analysis. These juveniles may have associated together as a close knit, mixed-age herd either for protection, to enhance their foraging, or as putative helpers at the parental nest.
An Erpetopus trackway recorded in the Lower Permian Collio Formation (Orobic Alps, northern Italy) is investigated as a source of data to reconstruct ancestral patterns of locomotion in eureptiles. The inferred small-sized captorhinid-''protorothyridid'' producer cut an inclined muddy surface dragging its front limb digits, tail, and belly on the ground. Integrating ichnological and anatomical data we suggest that small captorhinids (''protorothyridids'') locomotion was performed with an obligatory, rigid sprawling posture with the trunk only slightly lifted from the substrate in a low, sprawled 'belly walk'.
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.
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.
One of the greatest mysteries associated with dinosaurs is the rarity of juveniles. With the notable exception of the Djadochta and Iren Dabasu Formations of Mongolia and the Two Medicine Formation of Montana, skeletal elements of very young dinosaurs are exceedingly uncommon1–3, leaving a gap in the understanding of dinosaur social structures1,3,4. The most popular explanation, based chiefly on negative evidence, is that the eggs and young were ‘kept’ in the uplands where they were rarely covered by sediments and as a result were destroyed by erosion2. The discovery of fifteen 1-m long hadrosaurian (‘duck-billed’) skeletons together in a nest-like structure offers the first tangible evidence of the social behaviour of at least one group of dinosaurs. They were discovered by Marion Brandvold in terrestrial sediments of the Two Medicine Formation (Upper Cretaceous) near Choteau, Teton County, Montana.
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, originally published in 2000, represented the first 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 structural adaptations for, and the evolutionary history of, feeding on plants in the major groups of land-dwelling vertebrates, especially dinosaurs and ungulate mammals. As such it will be the definitive reference source on this topic for evolutionary biologists and vertebrate paleontologists alike.
In her influential 1967 paper, Lynn Margulis synthesized a range of data to support the idea of endosymbiosis. Building on the success of this work, she applied the same methodology to promote the role of symbiosis more generally in evolution. As part of this broader project, she coined the term ‘holobiont’ to refer to a unified entity of symbiont and host. This concept is now applied with great gusto in microbiome research, and often implies not just a physiological unit but also various senses of an evolving system. My analysis will track how Margulis came to propose the term, its current use in microbiome research, and how those applications link back to Margulis. I then evaluate what contemporary use says about Margulis's legacy for microbiome research.
Thousands of sauropod dinosaur tracks atop a thin limestone bed within the Lower Cretaceous De Queen Formation were discovered in 1983 at Briar Plant Quarry, 20km north of Nashville, Howard County, Arkansas. No tracks of juvenile sauropods have been observed at the site. The average stride length of a typical trackway is ~2.5m; rear paces average 1.65m; and front paces, 1.45m. Quality and depth of tracks vary. Claws of digits III and IV were usually oriented in a posterior direction, as suggested by track outlines. Aerial photographs reveal an alignment of hundreds of tracks, recording the movement of a group of at least about 10 sauropods across the lime mud surface in one area. Both trackbeds were deposited very nearshore and possess features indicating variable depositional conditions ranging from shallow subtidal to supratidal. -from Authors
Since their initial formal recognition by Richard Owen in 1842, dinosaurs have always stood out in the collective imagination for their size and unusual appearance. Therefore, these marvellous animals are a source of curiosity and wonder for people of all ages, social and cultural backgrounds. Thanks to improved research techniques, paleontologists have been able to work reconstructing the most plausible appearance of dinosaurs. Starting with petrified bones they tried to make a dream come true – to bring the planet’s ancient inhabitants back to life. The new Italian exhibition Dinosaurs in the Flesh: Science and Art bring the Rulers of a Lost World Back to Life, reveals the marriage of science and art that brings back to life animals that lived tens or hundreds of millions of years ago. Paleontologists and artists collaborate on reconstructing the appearance of organisms from the distant past through study of the fossils, often with the aid of new technologies. The new project, which takes up the idea of Waterhouse Hawkins and Owen and their legacy to restore these ancient vertebrates based on solid scientific foundations, represents to date the only way to reanimate these fascinating lost animals.
A study carried out on some excellently preserved footprints has revealed the vital importance of functionality analysis, together with morphological analyses, in settling systematics and attribution issues in ichnological studies. To test the alleged reliability of functionality studies in tetrapod ichnology, a careful analysis of numerous specimens (both trackways and isolated footprints) of the Gotha collection, referred to the Permian ichnotaxa Ichniotherium and Dimetropus, has been carried out. The method, in addition to the classical ichnological protocol, includes a careful and basic analysis of the differential depth of the impression to evaluate biomechanics and functional potentiality of the putative trackmaker in the light of osteological structures. The analysis has led to the recognition of two well-separated particular functionalities (over a complete locomotion cycle), sharply distinguishable in Ichniotherium and Dimetropus. The Ichniotherium trackmaker presents a functional axis in the fore and hind limbs moved always along the medial side during the stroke progression; in Dimetropus trackmaker there are at least two functional axes, the first moved laterally in the initial stroke phase and the second moved medially during the maximum load phase. Those different functionalities are intimately linked to the particular osteological characters present in diadectids and non-therapsid synapsids. Thus, functionality analysis in the ichnological practice is a valuable tool strongly recommended for use whenever possible.
Herbivorous vertebrates rely on complex communities of mutualistic gut bacteria to facilitate the digestion of celluloses and hemicelluloses. Gut microbes are often convergent based on diet and gut morphology across a phylogenetically diverse group of mammals. However, little is known about microbial communities of herbivorous hindgut-fermenting reptiles. Here, we investigate how factors at the individual level might constrain the composition of gut microbes in an obligate herbivorous reptile. Using multiplexed 16S rRNA gene sequencing, we characterized the fecal microbial community of a population of gopher tortoises (Gopherus polyphemus), and examined how age, genetic diversity, spatial structure, and kinship influence differences among individuals. We recovered phylotypes associated with known cellulolytic function, including candidate phylum Termite Group 3, suggesting their importance for gopher tortoise digestion. Although host genetic structure did not explain variation in microbial composition and community structure, we found that fine-scale spatial structure, inbreeding, degree of relatedness, and possibly ontogeny shaped patterns of diversity in fecal microbiomes of gopher tortoises. Our findings corroborate widespread convergence of fecal-associated microbes based on gut morphology and diet, and demonstrate the role of spatial and demographic structure in driving differentiation of gut microbiota in natural populations. This article is protected by copyright. All rights reserved.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Recognition of endothermy in dinosaurs can explain both the success and
the extinction of this group in the Mesozoic.
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.
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.