Biology Of Dinosaurs Research Articles

How smart was T. rex? Testing claims of exceptional cognition in dinosaurs and the application of neuron count estimates in palaeontological research.

Recent years have seen increasing scientific interest in whether neuron counts can act as correlates of diverse biological phenomena. Lately, Herculano-Houzel (2023) argued that fossil endocasts and comparative neurological data from extant sauropsids allow to reconstruct telencephalic neuron counts in Mesozoic dinosaurs and pterosaurs, which might act as proxies for behaviors and life history traits in these animals. According to this analysis, large theropods such as Tyrannosaurus rex were long-lived, exceptionally intelligent animals equipped with "macaque- or baboon-like cognition", whereas sauropods and most ornithischian dinosaurs would have displayed significantly smaller brains and an ectothermic physiology. Besides challenging established views on Mesozoic dinosaur biology, these claims raise questions on whether neuron count estimates could benefit research on fossil animals in general. Here, we address these findings by revisiting Herculano-Houzel's (2023) work, identifying several crucial shortcomings regarding analysis and interpretation. We present revised estimates of encephalization and telencephalic neuron counts in dinosaurs, which we derive from phylogenetically informed modeling and an amended dataset of endocranial measurements. For large-bodied theropods in particular, we recover significantly lower neuron counts than previously proposed. Furthermore, we review the suitability of neurological variables such as neuron numbers and relative brain size to predict cognitive complexity, metabolic rate and life history traits in dinosaurs, coming to the conclusion that they are flawed proxies for these biological phenomena. Instead of relying on such neurological estimates when reconstructing Mesozoic dinosaur biology, we argue that integrative studies are needed to approach this complex subject.

Interpretation of fossil embryos requires reasonable assessment of developmental age

AbstractDinosaur embryos cause a lot of excitement in the scientific literature and are often widely reported because of the general public's interest in dinosaur biology. Well-preserved, articulated oviraptorosaur embryos in eggs are usually interpreted as representing a stage of development close to hatching because of their large size and good level of skeletal ossification. Based on this evidence, a recent report suggested that the position of the one embryo's head was reminiscent of an avian-like hatching position. Here we explore how the developmental stage of well-preserved oviraptorosaur embryos can be estimated, rather than assumed. This will help in our understanding of their developmental biology and its evolutionary consequences. Using quantitative methods and comparison with modern crocodilian embryos, we show that all articulated oviraptorosaur embryos are small relative to the egg and most likely at a stage of development equivalent to around 50%–60% of the developmental period, that is, not even close to hatching. This conclusion is supported by the fact that many elements of the crocodilian skeleton are well ossified many weeks before hatching and the position of oviraptorosaur embryos’ heads was also comparable to a crocodilian embryo many days before hatching. Misunderstandings about the stage of the developmental biology of these well-preserved oviraptorosaur embryos hampers our understanding of the true nature of their reproductive biology. We urge a more conservative approach to their interpretation. This is important, because misunderstandings in the minds of the public about dinosaur biology are hard to counter once poorly evidenced ideas have been reported around the world.

The influence of juvenile dinosaurs on community structure and diversity

Despite dominating biodiversity in the Mesozoic, dinosaurs were not speciose. Oviparity constrained even gigantic dinosaurs to less than 15 kg at birth; growth through multiple morphologies led to the consumption of different resources at each stage. Such disparity between neonates and adults could have influenced the structure and diversity of dinosaur communities. Here, we quantified this effect for 43 communities across 136 million years and seven continents. We found that megatheropods (more than 1000 kg) such as tyrannosaurs had specific effects on dinosaur community structure. Although herbivores spanned the body size range, communities with megatheropods lacked carnivores weighing 100 to 1000 kg. We demonstrate that juvenile megatheropods likely filled the mesocarnivore niche, resulting in reduced overall taxonomic diversity. The consistency of this pattern suggests that ontogenetic niche shift was an important factor in generating dinosaur community structure and diversity.

Not enough room

Paleontology Modern carnivore communities include species that span a range of body sizes. For example, on the African savannah, there are small species (mongooses), medium species (wild dogs), and large species (lions). This variation reflects available prey sources that best suit each group. Carnivorous dinosaur communities, however, were missing species that fall into the middle, or mesocarnivore, group as adults. Schroeder et al. looked across communities, space, and time and found that this absence appears to have been driven by the distinctive biology of dinosaurs, in which giant adults start out as tiny hatchlings. Growing juvenile dinosaurs thus filled the other niches and limited trophic species diversity. Science , this issue p. [941][1] [1]: /lookup/doi/10.1126/science.abd9220

Dinosaur Macroevolution and Macroecology

Dinosaurs were large-bodied land animals of the Mesozoic that gave rise to birds. They played a fundamental role in structuring Jurassic–Cretaceous ecosystems and had physiology, growth, and reproductive biology unlike those of extant animals. These features have made them targets of theoretical macroecology. Dinosaurs achieved substantial structural diversity, and their fossil record documents the evolutionary assembly of the avian body plan. Phylogeny-based research has allowed new insights into dinosaur macroevolution, including the adaptive landscape of their body size evolution, patterns of species diversification, and the origins of birds and bird-like traits. Nevertheless, much remains unknown due to incompleteness of the fossil record at both local and global scales. This presents major challenges at the frontier of paleobiological research regarding tests of macroecological hypotheses and the effects of dinosaur biology, ecology, and life history on their macroevolution.

Inside Dinosaurs: A Broader Impacts Program for Research, Teaching and Public Education Through Dinosaur Biology, Physics and Evolution

Inside Dinosaurs is a NSF‐funded, multi‐pronged broader impacts program that immerses undergraduate research interns, secondary‐school science teachers, and the public in evolution, biomechanics and avian origins through a series of parallel and complementary activities. It incorporates STEM disciplines and offers opportunities for graduate and undergraduate lab members to interact with the local public and grade 6–12 teachers through science communication and outreach activities. Besides annual REU lines for University of Missouri undergraduates, we host two undergraduates from other institutions each summer to learn new experimental, modeling and anatomical techniques. Additionally, we recruit a local teacher each summer who, while embedded in the lab, conducts research and helps translate our discoveries into secondary school‐ level learning activities that fit within the Next Generation Science Standards. Together, the PIs, students, and teachers are developing and testing new classroom activities that are disseminated to interested Missouri teachers through a series of workshops. Besides these intense, lab‐based interactions, Inside Dinosaurs sponsors the Dinosaurs and Cavemen Science Expo, a pop‐up natural history museum exhibit that hosts two dozen activities put on by over thirty faculty and students and experiences crowds from 500–1000 people each year. These synergistic activities among faculty, teachers and visiting students help design and develop more specific learning activities to help bring paleontology, biomechanics, and anatomy to Central Missouri and the rest of the country.Support or Funding InformationNSF IOS 1457319

Evolution of dinosaur epidermal structures.

Spectacularly preserved non-avian dinosaurs with integumentary filaments/feathers have revolutionized dinosaur studies and fostered the suggestion that the dinosaur common ancestor possessed complex integumentary structures homologous to feathers. This hypothesis has major implications for interpreting dinosaur biology, but has not been tested rigorously. Using a comprehensive database of dinosaur skin traces, we apply maximum-likelihood methods to reconstruct the phylogenetic distribution of epidermal structures and interpret their evolutionary history. Most of these analyses find no compelling evidence for the appearance of protofeathers in the dinosaur common ancestor and scales are usually recovered as the plesiomorphic state, but results are sensitive to the outgroup condition in pterosaurs. Rare occurrences of ornithischian filamentous integument might represent independent acquisitions of novel epidermal structures that are not homologous with theropod feathers.

On Dinosaur Growth

Despite nearly two centuries of investigation, a comprehensive understanding of dinosaur biology has proven intractable. The recent development of means to study tissue-level growth, age these animals, and make growth curves has revolutionized our knowledge of dinosaur lives. From such data it is now understood that dinosaurs grew both disruptively and determinately; that they rarely if ever exceeded a century in age; that they became giants through accelerated growth and dwarfed through truncated development; that they were likely endothermic, sexually matured like crocodiles, and showed survivorship like populations of large mammals; and that basal birds retained dinosaurian physiology.

Allometric equations for predicting body mass of dinosaurs

AbstractWe use data from the literature to compare two statistical procedures for estimating mass (or size) of quadrupedal dinosaurs and other extraordinarily large animals in extinct lineages. Both methods entail extrapolation from allometric equations fitted to data for a reference group of contemporary animals having a body form similar to that of the dinosaurs. The first method is the familiar one of fitting a straight line to logarithmic transformations, followed by back‐transformation of the resulting equation to a two‐parameter power function in the arithmetic scale. The second procedure entails fitting a two‐parameter power function directly to arithmetic data for the extant forms by nonlinear regression. In the example presented here, the summed circumferences for humerus plus femur for 33 species of quadrupedal mammals was the predictor variable in the reference sample and body mass was the response variable. The allometric equation obtained by back‐transformation from logarithms was not a good fit to the largest species in the reference sample and presumably led to grossly inaccurate estimates for body mass of several large dinosaurs. In contrast, the allometric equation obtained by nonlinear regression described data in the reference sample quite well, and it presumably resulted in better estimates for body mass of the dinosaurs. The problem with the traditional analysis can be traced to change in the relationship between predictor and response variables attending transformation, thereby causing measurements for large animals not to be weighted appropriately in fitting models by least squares regression. Extrapolations from statistical models obtained by back‐transformation from lines fitted to logarithms are unlikely to yield reliable predictions for body size in extinct animals. Numerous reports on the biology of dinosaurs, including recent studies of growth, may need to be reconsidered in light of our findings.

ULTRASTRUCTURAL AND FUNCTIONAL MORPHOLOGY OF EGGSHELLS SUPPORTS THE IDEA THAT DINOSAUR EGGS WERE INCUBATED BURIED IN A SUBSTRATE

Abstract: The reproductive biology of dinosaurs is of great interest, particularly in light of the many fossil eggs assigned to this group. The ultrastructural characteristics of dinosaur eggshells are examined in order to calculate water vapour conductance, which indicates the nesting environment. Data were mainly derived from the literature but new values are also presented. Allometric analyses were carried out on a variety of shell parameters against predicted egg mass, and comparison was made with allometric equations for bird eggs. Shell thickness was generally larger than seen for extant birds. Total pore number and pores per unit area were similar to values predicted from bird eggs. Total pore area showed an isometric increase with egg mass, parallel to the relationship for birds, but the constant value was an order to magnitude higher than the bird values. Pore radius was unaffected by egg mass. Water vapour conductance showed an allometric increase with egg mass, parallel to the bird values, but for any given egg mass values for dinosaurs were an order of magnitude higher. Mass‐specific water vapour conductance was unaffected by egg mass but was an order of magnitude higher than the bird values. Water vapour conductance per pore showed an allometric decrease with egg mass but again the predicted values were an order of magnitude higher than for bird eggs. The ultrastructural characteristics of dinosaur eggshells indicate that the nesting environment had to be saturated with water vapour and that dinosaur eggs had to be fully buried in a substrate. In this sense, therefore, dinosaur eggs resemble more those of modern reptiles than those of birds. As a consequence, maintenance of incubation conditions would have depended on the prevailing environment.

The microstructure of dinosaur bone: deciphering biology with fine-scale techniques

For millions of years, clues to the biology of dinosaurs lie locked within the microscopic structure of their bones. Here one of the world's leading experts on fossil bone microstructure synthesizes more than 150 years of research to expose the meaning of dinosaur bone microstructure. In this first book dedicated to dinosaur bone microstructure, Anusuya Chinsamy-Turan begins with a general overview of living bone structure and composition and then explains how bone structure changes upon death and during fossilization. She meticulously unravels why the microscopic structure of fossil bone remains intact after millions of years of fossilization. She also provides a photographic atlas of the kinds of bone tissue found in dinosaurs and expounds on their biological significance. The final chapters offer insight into growth patterns of dinosaurs and the biology of Mesozoic birds. The book concludes with a reflective discussion on what bone microstructure can and cannot disclose about dinosaur physiology. Drawing from sources across the field of bone histology, Chinsamy-Turan paints a holistic view of the current state of the science and presents a fresh perspective on the relevance of the field to understanding the Dinosauria.

Respiratory and reproductive paleophysiology of dinosaurs and early birds.

In terms of their diversity and longevity, dinosaurs and birds were/are surely among the most successful of terrestrial vertebrates. Unfortunately, interpreting many aspects of the biology of dinosaurs and the earliest of the birds presents formidable challenges because they are known only from fossils. Nevertheless, a variety of attributes of these taxa can be inferred by identification of shared anatomical structures whose presence is causally linked to specialized functions in living reptiles, birds, and mammals. Studies such as these demonstrate that although dinosaurs and early birds were likely to have been homeothermic, the absence of nasal respiratory turbinates in these animals indicates that they were likely to have maintained reptile-like (ectothermic) metabolic rates during periods of rest or routine activity. Nevertheless, given the metabolic capacities of some extant reptiles during periods of elevated activity, early birds were probably capable of powered flight. Similarly, had, for example, theropod dinosaurs possessed aerobic metabolic capacities and habits equivalent to those of some large, modern tropical latitude lizards (e.g., Varanus), they may well have maintained significant home ranges and actively pursued and killed large prey. Additionally, this scenario of active, although ectothermic, theropod dinosaurs seems reinforced by the likely utilization of crocodilian-like, diaphragm breathing in this group. Finally, persistent in vivo burial of their nests and apparent lack of egg turning suggests that clutch incubation by dinosaurs was more reptile- than birdlike. Contrary to previous suggestions, there is little if any reliable evidence that some dinosaur young may have been helpless and nestbound (altricial) at hatching.

ARE CURRENT CRITIQUES OF THE THEROPOD ORIGIN OF BIRDS SCIENCE? REBUTTAL TO FEDUCCIA (2002)

IN MY Perspectives in Ornithology essay (Prum 2002), I advocated that all ornithologists should be excited about research on the theropod origin of birds. Although I did address some criticisms of the theropod hypothesis, I spent most of the essay outlining the data in support of the theropod origin and, most exciting to me, describing the new directions in evolutionary ornithological research that have opened up as a consequence. I concluded that one of the most important frontiers in ornithological research in this century will be the establishment of a thorough scientific understanding of the evolution of avian biology in light of the theropod origin of birds. From nesting biology and physiology to behavior and locomotion, the rewards of studying ornithology as extant dinosaur biology are only just beginning to be reaped (Prum 2002). In his critique of my essay, A. Feduccia (2002) reviewed much of his previous work but also sprang a new, surprise ending. In summary, he hypothesized that birds evolved from an unknown lineage of early basal archosaurs, and that rampant convergent evolution renders the many derived morphological characters shared by birds and theropods unreliable. However, Feduccia can no longer deny the conclusive evidence that basal dromaeosaurs had feathers (Xu et al. 1999, 2000, 2001, 2003; Czerkas et al. 2002; Norell et al. 2002). In the end, he concedes that dromaeosaurs had feathers. In a rhetorical tour de force that conflicts with decades of his own work and most of his commentary, Feduccia (2002) then hypothesizes that dromaeosaurs are birds, but that the birds, now including the dromaeosaurs, still originated from some

Vegetation of the Dinosaur World

The process of photosynthesis is critical to the existence of almost all the Earth's ecosystems by providing the fundamental mechanism through which the Sun's energy is harnessed to convert carbon dioxide and water into sugars and oxygen. These sugars ultimately provide the basic source of energy (primary production) on which most life depends. In terrestrial ecosystems macroscopic land plants are responsible for virtually all primary production and therefore provide the basic sustenance that supports all land animals, either directly or indirectly. An accurate knowledge of Mesozoic plants and vegetation is therefore critical to understanding the ecology of dinosaurs and the ecosystems in which they flourished. Similarly, because large herbivorous dinosaurs must have exerted a major influence on terrestrial ecosystems some knowledge of dinosaur biology is crucial to understanding the ecological pressures to which Mesozoic plants were subjected. Because there is also a close correlation between the climate of an area and the kind of vegetation that it supports, fossil plants also provide important evidence on the paleoclimates of the dinosaur world.

Morphology, preservation and palaeobiological significance of dinosaur copralites

This paper reviews the coprolites (fossil excrements) of terrestrial vertebrates, giving particular attention to examples that may have originated from dinosaurs. Factors affecting the preservation of corprolites and briefly surveyed, and the internal and extent morphology of these fossils is examined in detail. Coprolites furnish small, but sometimes important, pieces of evidence about dinosaur biology: such evidence is rarely conclusive or unbiased, though in favourable circumstances it can be used to ascertain the identity, behaviour, habitats and diets of dinosaurs. Information derived from coprolites is best appraised in the context of broad-based studies which also consider the anatomical adaptations of dinosaurs, their gut contents and their feeding traces, along with any associated fossils that might betray the potential sources of food exploited by dinosaurs.

Vertebrate paleontology: new approaches and new insights

In the past fifteen years, the biological interpretation of vertebrate fossils has been markedly advanced by the application of experimental techniques in functional morphology, biomechanical and allometric modelling, more rigorously-derived empirical correlations between form and function in living species, and studies of modern community structure and of the taphonomic processes by which fossil assemblages are formed. Traditional paleontological methods of phylogenetic analysis are under attack by the advocates of cladistics; the resulting debate is leading to increased rigor in paleontological systematics. Paleobiogeographical studies of vertebrates has become an extremely active area of research due to the need to reanalyze past distribution patterns in the light of plate tectonics.New information has extended the fossil record of vertebrates back to the Late Cambrian, but little more is known about the nature of the earliest vertebrates or of the pre-vertebrate ancestors. Much has been learned of the fishes antecedent to tetrapods but little of the earliest tetrapods. The early reptiles are now well known, but the nature of their amphibian ancestors is uncertain. Restudy ofArchaeopteryxhas suggested a dinosaurian ancestry for birds. The origin and early evolution of mammals is the subject of extensive research as a result of greatly augmented recent collecting. The most active and innovative research is on the biology of dinosaurs, especially on their physiology. Among Cenozoic mammals, the fossil record of primates has been greatly expanded and knowledge of primate history, from the basal prosimians of the Paleocene to early man, is increasing rapidly.