Oxygen isotopes suggest elevated thermometabolism within multiple Permo-Triassic therapsid clades (original) (raw)
Related papers
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.
Papéis Avulsos de Zoologia (São Paulo), 2006
The origin of avian endothermy is a long-held question the answer of which cannot be provided by first level observations. Oological and reproductive characters have collectively provided a new source of data useful for phylogenetic analyses and paleobiological inferences. In addition, the observations of reproductive and oological evolutionary trends in saurischian dinosaurs lead to the interpretation that not only, the thermophysiology of these dinosaurs progressively became more avian-like but after re-examination allows to infer that deinonychosaurians represented here by three troodontids and one dromaeosaurid might already have developed an avian-like endothermy, thus predating the rise of avians. These results based on reproductive traits are independently corroborated by the discoveries of troodontid dinosaurs 1) in high latitudes, 2) covered with feathers in Chinese Lagerstätten, and recently 3) fossilized in a death pose identical to an avian sleeping posture.
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.
Philosophical Transactions of the Royal Society B: Biological Sciences
Teleosauridae and Metriorhynchidae were thalattosuchian crocodylomorph clades that secondarily adapted to marine life and coexisted during the Middle to Late Jurassic. While teleosaurid diversity collapsed at the end of the Jurassic, most likely as a result of a global cooling of the oceans and associated marine regressions, metriorhynchid diversity was largely unaffected, although the fossil record of Thalattosuchia is poor in the Cretaceous. In order to investigate the possible differences in thermophysiologies between these two thalattosuchian lineages, we analysed stable oxygen isotope compositions (expressed as δ 18 O values) of tooth apatite from metriorhynchid and teleosaurid specimens. We then compared them with the δ 18 O values of coexisting endo-homeothermic ichthyosaurs and plesiosaurs, as well as ecto-poikilothermic chondrichthyans and osteichthyans. The distribution of δ 18 O values suggests that both teleosaurids and metriorhynchids had body temperatures intermediate ...
Inner ear biomechanics reveals a Late Triassic origin for mammalian endothermy
Nature
Endothermy ("warm-bloodedness") underpins the ecological dominance of mammals and birds in diverse environmental settings^1-3. However, it is unclear when this crucial feature emerged during mammalian evolutionary history, as most fossil evidence is ambiguous^4-25. Here, we show that new information on this key evolutionary transition can be obtained from the morphology of the endolymph-lled semicircular ducts of the inner ear that monitor head rotations and are essential for motor coordination, navigation, and spatial awareness^26-31. Increased body temperature during the ectotherm-endotherm transition of mammal ancestors would decrease endolymph viscosity, negatively impacting the biomechanics of the semicircular ducts^32,33, while simultaneously increasing activity levels^34,35 required improved performance^36. Speci c morphological changes to the membranous ducts and enclosing bony canals were, therefore, necessary to maintain optimal functionality. We track these morphological changes in 341 vertebrates, including 56 extinct synapsids, and show that canals with relatively thin cross-sections and small radii of curvature are indicative of mammalian endothermy. This inner ear morphotype evolved abruptly ~233 million years ago, during the Late Triassic, in Mammaliamorpha. Our conclusion differs from previous suggestions3-17, and we interpret most stem-mammals as ectotherms. Endothermy as a crucial physiological characteristic joins other distinctive mammalian features that arose during this period of climatic instability^37-39. *Ricardo Araújo and Romain David contributed equally to this work. Main Text Endotherms can maintain high and nearly constant body temperature through metabolic heat production, allowing them to optimize chemical reactions and sustain aerobic activity for long periods of time while remaining relatively independent from external conditions 1,2,40. Compared to ectotherms, endotherms are more active, travel farther, and achieve higher locomotor speeds, all at the expense of higher energy costs 34,35 (Supplementary Data 1). Consequently, extant mammals and birds occupy a variety of ecological niches unrivalled by other vertebrates. Endothermy is a quintessentially mammalian feature, intimately related to other hallmarks such as lactation, sweat glands and fur 2,3. However, its evolution remains one of the great unsolved mysteries of palaeontology 2,3. Lines of evidence invoked to identify the emergence of mammalian endothermy rely mostly on skeletal anatomical features, but also on ichnological, histological and isotopic information, which have been used as correlates for aerobic
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.
A molecular model for the evolution of endothermy in the theropod-bird lineage
Journal of Experimental Zoology, 2001
Ectothermy is a primitive state; therefore, a shared common ancestor of crocodiles, dinosaurs, and birds was at some point ectothermic. Birds, the extant descendants of the dinosaurs, are endothermic. Neither the metabolic transition within this lineage nor the place the dinosaurs held along the ectothermic-endothermic continuum is defined. This paper presents a conceptual model for the evolution of endothermy in the theropod-bird lineage. It is recognized that other animals (some fish, insects, etc.) are functionally endothermic. However, endothermy in other clades is beyond the scope of this paper, and we address the onset of endothermy in only the theropod/bird clade. The model begins with simple changes in a single gene of a common ancestor, and it includes a series of concomitant physiological and morphological changes, beginning perhaps as early as the first archosaurian common ancestor of dinosaurs and crocodiles. These changes continued to accumulate within the theropod-avian lineage, were maintained and refined through selective forces, and culminated in extant birds. Metabolic convergence or homoplasy is evident in the inherent differences between the endothermy of mammals and the endothermy of extant birds. The strength and usefulness of this model lie in the phylogenetic, genetic, evolutionary, and adaptive plausibility of each of the suggested developmental steps toward endothermy. The model, although conceptual in nature, relies on an extensive knowledge base developed by numerous workers in each of these areas. In addition, the model integrates known genetic, metabolic, and developmental aspects of extant taxa that phylogenetically bracket theropod dinosaurs for comparison with information derived from the fossil record of related extinct taxa.