Artist’s impression of a dromaeosaur, a type of feathered theropod, in the snow. This raptor was a relative of Velociraptor.
Davide Bonadonna/Universidade
First ‘warm-blooded’ dinosaurs may have emerged 180 million years ago | UCL News - UCL – University College London
Of all the different orders of living organisms' only mammals and birds today are warm-blooded, i.e., they are able to maintain a body temperature, within a certain range of ambient temperatures, by either producing heat or losing it, as necessary.
It might be thought that this indicates that the ability evolved in a common ancestor but of the ancestors of birds, the evidence suggests that many dinosaurs were cold-blooded like today's reptiles, and mammals are descendants of an earlier, pre-dinosaurian reptiles, so these similar processes for maintaining the body temperature may be more a matter of convergence than common ancestry.
Do mammals and birds use the same method to maintain their body temperature, and if not, how do they differ?
Mammals and birds both maintain their body temperatures through endothermy, meaning they generate and regulate heat internally to keep their body temperatures stable. However, there are differences in how they achieve this due to variations in their physiology and behaviors. Here’s an overview of the similarities and differences:
Similarities in Temperature Regulation
- Metabolic Heat Production:
- Both mammals and birds generate heat through metabolic processes. This involves breaking down food to produce energy, with heat being a byproduct.
- Insulation:
- Both groups have evolved insulating layers to retain heat. Mammals have fur or hair, while birds have feathers. These layers trap air and provide a barrier against the cold.
- Shivering Thermogenesis:
- Both can generate additional heat through shivering, which involves rapid muscle contractions that produce heat.
- Behavioral Adjustments:
- Both mammals and birds engage in behaviors to manage their temperature, such as seeking shade or shelter, sunning themselves, or altering their activity levels based on the ambient temperature.
Differences in Temperature Regulation
- Physiological Mechanisms:
- Sweating and Panting: Mammals often use sweating and panting to cool down. Sweat glands secrete moisture that evaporates, taking heat away from the body. Dogs, for instance, pant to evaporate moisture from their respiratory tract. Birds, on the other hand, do not sweat. Instead, they often rely on a behavior called gular fluttering, where they rapidly move the skin in their throat to increase evaporation and cool down.
- Brown Adipose Tissue (BAT): Many mammals, especially small ones and those living in cold environments, have brown adipose tissue that generates heat through non-shivering thermogenesis. Birds lack this type of tissue.
- Heat Exchange Systems:
- Countercurrent Heat Exchange: Birds have highly efficient countercurrent heat exchange systems in their legs and feet, which minimize heat loss. Blood vessels are arranged such that warm arterial blood warms the cooler venous blood returning to the body, conserving heat. While some mammals also use countercurrent heat exchange (such as in extremities), the systems are particularly pronounced and crucial in birds.
- Basal Metabolic Rate:
- Birds generally have higher basal metabolic rates compared to mammals of similar size, which means they produce more heat relative to their body size. This higher metabolic rate is partly due to the high energy demands of flight.
- Hibernation and Torpor:
- Many mammals can enter states of torpor or hibernation to conserve energy and reduce body temperature during periods of cold or food scarcity. While some birds also enter torpor, true hibernation is rare in birds. Instead, some birds migrate to warmer regions to avoid cold weather.
Behavioral Differences
- Migration:
- Migration is a key strategy for many birds to avoid extreme temperatures. While some mammals also migrate, it is far more common and pronounced in birds.
- Nesting and Roosting:
- Birds often build insulated nests or seek out warm roosting spots to maintain body temperature, especially during breeding seasons or cold nights. Mammals, on the other hand, may use burrows, dens, or other insulated shelters.
In summary, while both mammals and birds use endothermic processes to maintain their body temperatures, the specific physiological and behavioral strategies they employ can differ significantly due to their distinct evolutionary paths and physical characteristics.
A team of researchers led by University College London (UCL) and Universidade de Vigo, Spain, scientists has concluded that dinosaurs may have evolved warm-bloodedness as long ago as 180 million years ago, some 50 million years after the first dinosaurs evolved.
They concluded this after relating the evolutionary tree of the dinosaurs throughout the Mesozoic era to climate and geographical changes over the same time period and examining 1000 dinosaur fossils.
Their findings are the subject of an open access paper in the Cell Press journal,
Current Biology. Their work is also explained in a UCL news release:
The ability to regulate body temperature, a trait all mammals and birds have today, may have evolved among some dinosaurs early in the Jurassic period about 180 million years ago, suggests a new study led by UCL and University of Vigo researchers.
In the early 20th century, dinosaurs were considered slow-moving, “cold-blooded” animals like modern-day reptiles, relying on heat from the sun to regulate their temperature. Newer discoveries indicate some dinosaur types were likely capable of generating their own body heat but when this adaptation occurred is unknown.
The new study, published in the journal Current Biology, looked at the spread of dinosaurs across different climates on Earth throughout the Mesozoic Era (the dinosaur era lasting from 230 to 66 million years ago), drawing on 1,000 fossils, climate models and the geography of the period, and dinosaurs’ evolutionary trees.
The research team found that two of the three main groupings of dinosaurs, theropods (such as T. rex and Velociraptor) and ornithischians (including relatives of the plant eaters Stegosaurus and Triceratops), moved to colder climates during the Early Jurassic, suggesting they may have developed endothermy (the ability to internally generate heat) at this time. In contrast, sauropods, the other main grouping which includes the Brontosaurus and the Diplodocus, kept to warmer areas of the planet.
Previous research has found traits linked to warm-bloodedness among ornithischians and theropods, with some known to have had feathers or proto-feathers, insulating internal heat.
Our analyses show that different climate preferences emerged among the main dinosaur groups around the time of the Jenkyns event 183 million years ago, when intense volcanic activity led to global warming and extinction of plant groups. At this time, many new dinosaur groups emerged. The adoption of endothermy, perhaps a result of this environmental crisis, may have enabled theropods and ornithischians to thrive in colder environments, allowing them to be highly active and sustain activity over longer periods, to develop and grow faster and produce more offspring.
Dr Alfio Alessandro Chiarenza, first author
Centro de Investigación Mariña
Departamento de Ecoloxía e Bioloxía Animal
Universidade de Vigo, Vigo, Spain
And Department of Earth Sciences
University College London, London, UK.
Theropods also include birds and our study suggests that birds’ unique temperature regulation may have had its origin in this Early Jurassic epoch. Sauropods, on the other hand, which stayed in warmer climates, grew to a gigantic size at around this time – another possible adaptation due to environmental pressure. Their smaller surface area to volume ratio would have meant these larger creatures would lose heat at a reduced rate, allowing them to stay active for longer.
Dr Sara Varela, Co-author
Centro de Investigación Mariña
Departamento de Ecoloxía e Bioloxía Animal
Universidade de Vigo, Vigo, Spain.
This research suggests a close connection between climate and how dinosaurs evolved. It sheds new light on how birds might have inherited a unique biological trait from dinosaur ancestors and the different ways dinosaurs adapted to complex and long-term environmental changes.
Dr Juan L. Cantalapiedra, co-author
Departamento de Paleobiología
Museo Nacional de Ciencias Naturales (CSIC), Madrid, Spain.
Highlights
- Warm-blooded dinosaurs flourished in varied climates.
- Dinosaur groups adapted differently to climate, suggesting diverse thermophysiologies.
- Endothermy in theropods and possibly ornithischians evolved by the Early Jurassic
- Sauropod niche conservatism suggests higher thermal sensitivity and poikilothermy.
Graphical Abstract
A fundamental question in dinosaur evolution is how they adapted to long-term climatic shifts during the Mesozoic and when they developed environmentally independent, avian-style acclimatization, becoming endothermic.1,2 The ability of warm-blooded dinosaurs to flourish in harsher environments, including cold, high-latitude regions,3,4 raises intriguing questions about the origins of key innovations shared with modern birds,5,6 indicating that the development of homeothermy (keeping constant body temperature) and endothermy (generating body heat) played a crucial role in their ecological diversification.7 Despite substantial evidence across scientific disciplines (anatomy,8 reproduction,9 energetics,10 biomechanics,10 osteohistology,11 palaeobiogeography,12 geochemistry,13,14 and soft tissues15,16,17), a consensus on dinosaur thermophysiology remains elusive.1,12,15,17,18,19 Differential thermophysiological strategies among terrestrial tetrapods allow endotherms (birds and mammals) to expand their latitudinal range (from the tropics to polar regions), owing to their reduced reliance on environmental temperature.20 By contrast, most reptilian lineages (squamates, turtles, and crocodilians) and amphibians are predominantly constrained by temperature in regions closer to the tropics.21 Determining when this macroecological pattern emerged in the avian lineage relies heavily on identifying the origin of these key physiological traits. Combining fossils with macroevolutionary and palaeoclimatic models, we unveil distinct evolutionary pathways in the main dinosaur lineages: ornithischians and theropods diversified across broader climatic landscapes, trending toward cooler niches. An Early Jurassic shift to colder climates in Theropoda suggests an early adoption of endothermy. Conversely, sauropodomorphs exhibited prolonged climatic conservatism associated with higher thermal conditions, emphasizing temperature, rather than plant productivity, as the primary driver of this pattern, suggesting poikilothermy with a stronger dependence on higher temperatures in sauropods.
Dinosaurs have always been a problem for creationists because their existence betrays the fact that the age of Earth as calculated from the Bible geneaolgies is wildly inaccurate by several orders of magnitude, but this paper piles on the agony by showign a clear evolutionary pathway from poikilothermy (cold-bloodedness) to homeothermy (warm-bloodedness) supported by geological, geographical and climatological evidence sometime around 180 million years before the biblical 'Creation Week'.
And it goes without saying that, being biologists, the authors of the paper show no sign of abandoning the TOE in favour of the childish notion of magic creation by an unproven supernatural entity. Indeed, they could scarcely be considered scientists if they included magic and superstition in their explanation for natural phenomena like creationists pseud-scientists are obliged to for contractual reasons.
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