Modeling Dragons: Using linked mechanistic physiological and microclimate models to explore environmental, physiological, and morphological constraints on the early evolution of dinosaurs (original) (raw)
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Thermoregulation of Non-Avian Dinosaurs
2016
The aim of this monography is to evaluate the debate around non-avian dinosaurian thermoregulation strategy. Discussions have begun with the discovery and the description of first dinosaurian fossils in the eighteenth century and they continue today. It is a very active domain where opinions and theories are disparate about their physiology and lifestyle. This current work will approach subjects such as thermoregulation strategies, controversial theories about dinosaurs biology and compared anatomy. We will see the impact of pulmonary ventilation on metabolic activities, the growth rates signification and importance in understanding ontogenic metabolism. We will describe the interesting case of inertial homeothermy which could have led dinosaurs to gigantism and to become the biggest terrestrial animals who had ever lived. Birds and crocodilians are the nearest relatives to non-avian dinosaurs. Studies about their similarities with dinosaurs, histology, geochemistry permit to estimate the dinosaurs biology. The biggest debate is about to know if non-avian dinosaurs had more similarities with endothermic modern birds or with ectothermic crocodiles. Through this work we will consider the different arguments put forward to support the two hypotheses and their counter-arguments. Anatomically, the dinosaurs were more similar to crocodiles than to birds. This may suggest that like crocodilians, they were ectotherms. Investigations about pulmonary capacities have comparable conclusion. Nevertheless, studies about growth rates question this point of view as well as studies about body temperature whose conclusions are more uncertain about the metabolic status of non-avian dinosaurs. Discussions put non-avian dinosaurs somewhere between ecto-and endothermy.
Eggshell geochemistry reveals ancestral metabolic thermoregulation in Dinosauria
Science Advances, 2020
Studying the origin of avian thermoregulation is complicated by a lack of reliable methods for measuring body temperatures in extinct dinosaurs. Evidence from bone histology and stableisotopes often relies on uncertain assumptions about the relationship between growth rate and body temperature, or the isotopic composition ( 18 O) of body water. Clumped isotope ( 47) paleothermometry, based on binding of 13 C to 18 O, provides a more robust tool, but has yet to be applied across a broad phylogenetic range of dinosaurs while accounting for paleoenviron-mental conditions. Applying this method to well-preserved fossil eggshells demonstrates that the three major clades of dinosaurs, Ornithischia, Sauropodomorpha, and Theropoda, were characterized by warm body temperatures. Dwarf titanosaurs may have exhibited similar body temperatures to larger sauropods, although this conclusion isprovisional, given current uncertainties in taxonomic assignment of dwarf titanosaur eggshell. Our results nevertheless reveal that metabolically controlled thermoregulation was the ancestral condition for Dinosauria.
Thermophysiology and Biology of Giganotosaurus: Comparison with Tyrannosaurus
1999
Large carnivorous dinosaurs present many interesting biological and ecological questions. The most important information for understanding the ecology of these dinosaurs is their metabolism and thermal physiology. These factors in conjunction with their body mass determine the quantity of meat these animals needed to consume, how rapidly they grew and behavioral characteristics such as range size and reproduction. Oxygen isotope values of bone phosphate may be used to determine the relative temperature variations experienced by skeletal regions during bone deposition. Temperature variations relate to an animal's thermal physiology and can be used to estimate their metabolic physiology. Previously, we reported (Barrick and Showers 1994) on the thermophysiology of Tyrannosaurus rex using this methodology. Here, we present the results of the even larger South American carnivorous dinosaur Giganotosaurus carolinii. Comparisons of the isotopic patterns are used as a basis for a preliminary discussion of the biology of these large theropods. Data support the interpretation that both theropods support homeothermy by means of intermediate metabolic rates
Oxygen isotopes from biogenic apatites suggest widespread endothermy in Cretaceous dinosaurs
Chemical Geology, 2004
The much debated question of dinosaur thermophysiology has not yet been conclusively solved despite numerous attempts. We used the temperature-dependent oxygen isotope fractionation between vertebrate body water (δ 18 O body water ) and phosphatic tissues (δ 18 O p ) to compare the thermophysiology of dinosaurs with that of non-dinosaurian ectothermic reptiles. Present-day δ 18 O p values of vertebrate apatites show that ectotherms have higher δ 18 O p values than endotherms at high latitudes due to their lower body temperature, and conversely lower δ 18 O p values than endotherms at low latitudes. Using a data set of 80 new and 49 published δ 18 O p values, we observed similar and systematic differences in δ 18 O p values (Δ 18 O) between four groups of Cretaceous dinosaurs (theropods, sauropods, ornithopods and ceratopsians) and associated fresh water crocodiles and turtles. Expressed in terms of body temperatures (T b ), these Δ 18 O values indicate that dinosaurs maintained rather constant T b in the range of endotherms whatever ambient temperatures were. This implies that high metabolic rates were widespread among Cretaceous dinosaurs belonging to widely different taxonomic groups and suggest that endothermy may be a synapomorphy of dinosaurs, or may have been acquired convergently in the studied taxa.
Seasonal bone growth and physiology in endotherms shed light on dinosaur physiology
Cyclical growth leaves marks in bone tissue that are in the forefront of discussions about physiologies of extinct vertebrates. Ectotherms show pronounced annual cycles of growth arrest that correlate with a decrease in body temperature and metabolic rate; endotherms are assumed to grow continuously until they attain maturity because of their constant high body temperature and sustainedmetabolic rate1,2. This apparent dichotomy has driven the argument that zonal bone denotes ectotherm-like physiologies, thus fuelling the controversy on dinosaur thermophysiology and the evolution of endothermy in birds and mammal-like reptiles1–4. Here we show, from a comprehensive global study of wild ruminants from tropical to polar environments, that cyclical growth is a universal trait of homoeothermic endotherms. Growth is arrested during the unfavourable season concurrently with decreases in body temperature, metabolic rate and bone-growth-mediating plasma insulinlike growth factor-1 levels, forming part of a plesiomorphic thermometabolic strategy for energy conservation. Conversely, bouts of intense tissue growth coincide with peak metabolic rates and correlated hormonal changes at the beginning of the favourable season, indicating an increased efficiency in acquiring and using seasonal resources. Our study supplies the strongest evidence so far that homeothermic endotherms arrest growth seasonally, which precludes the use of lines of arrested growth as an argument in support of ectothermy. However, high growth rates are a distinctive trait of mammals, suggesting the capacity for endogenous heat generation. The ruminant annual cycle provides an extant model on which to base inferences regarding the thermophysiology of dinosaurs and other extinct taxa.
Special publication, 1994
Our studies using American alligators, Alligator mississippiensis, green turtles, Chelonia mydas, and leatherback turtles, Dermochelys coriacea, have provided insights into the physiology of large extant and extinct reptiles. Respiratory and metabolic physiology studies indicate that many living large reptiles exhibit heat conservation adaptations and mechanisms which allow them to maintain constant warm body temperatures in cold environments with low "reptilian" metabolism. For example, leatherback turtles which are found in the oceans as far north as the Arctic Circle can maintain constant body temperatures above 25°C while water temperatures are below 7°C. This dramatic ability to maintain warm temperatures in cold, highly conductive water, that would quickly cause hypothermia and kill most endotherms, is made possible by a mechanism we describe as gigantothenny. Gigantothermy is the ability to maintain constant warm body temperatures with low energy consumption, control of peripheral circulation and extensive insulation due to large body size.
Respiratory physiology of the dinosaurs
BioEssays, 1998
Dinosaurs were among the most distinctive and successful of all land vertebrates. Attempts at reconstructing their biology have become commonplace. However, given the absence of closely comparable living models, deciphering their physiology necessarily remains speculative and determination of their metabolic status has been particularly problematical. Nevertheless, many paleontologists have advocated the notion that they were probably ''warm-blooded'' (endothermic), thus providing a model supposedly essential to the interpretation of these animals as having led particularly active, interesting lives. Those suppositions notwithstanding, the apparent absence of respiratory turbinates in dinosaurs, as well as likely ectothermic patterns of thermoregulation in very early birds, argues strongly that these animals were unlikely to have achieved the metabolic status of modern terrestrial endotherms. These data are not necessarily inconsistent with current models of active lifestyles of dinosaurs.
Oxygen isotopes suggest elevated thermometabolism within multiple Permo-Triassic therapsid clades
eLife, 2017
The only true living endothermic vertebrates are birds and mammals, which produce and regulate their internal temperature quite independently from their surroundings. For mammal ancestors, anatomical clues suggest that endothermy originated during the Permian or Triassic. Here we investigate the origin of mammalian thermoregulation by analysing apatite stable oxygen isotope compositions (δ(18)Op) of some of their Permo-Triassic therapsid relatives. Comparing of the δ(18)Op values of therapsid bone and tooth apatites to those of co-existing non-therapsid tetrapods, demonstrates different body temperatures and thermoregulatory strategies. It is proposed that cynodonts and dicynodonts independently acquired constant elevated thermometabolism, respectively within the Eucynodontia and Lystrosauridae + Kannemeyeriiformes clades. We conclude that mammalian endothermy originated in the Epicynodontia during the middle-late Permian. Major global climatic and environmental fluctuations were th...