The Body Temperature Of Tyrannosaurus Rex

A creature's internal temperature plays a big role in its behavior. Over the past decades our understanding of the behavior of various dinosaur groups has evolved. A combination of bone histology (patterns of bone growth as an individual develops from juvenile to adult), energetics gleaned from anatomy and ecology, and fossil geographic distribution all suggest that at least some dinosaur groups evolved an ability to regulate their internal temperature (endothermy).

There is evidence from isotope work that some species within Theropod, Sauropod, and Ornithician dinosaur groups maintained a high body temperature. In contrast, specific biomolecules and inference of ecologic preference suggests that many other dinosaur lineages did not maintain endothermic metabolism. Dinosaur physiology and thermal regulation continues to be studied and debated.

What has been missing is a consistent and reliable method for ascertaining their body temperature.

Recently Randon J. Flores and coworkers applied a technique known as carbonate clumped isotopes to fossil teeth (enamel) of specimens of Tyrannosaurus rex to determine its body temperature. The sample was from the Cretaceous age Hell Creek Formation, North America. This technique measures the abundance of C13-O18 bonds in carbonate minerals that make up the enamel. These bonds of the heavier isotopes of carbon and oxygen are more common at lower temperatures. They are not affected by the isotope composition of the reacting fluids and is a direct indicator of the temperature of mineral formation.

 Image source: Randon J. Flores and coworkers: Science Advances 2026.

The results show that T. rex maintained a body temperature of about 36 deg C. This was substantially more that crocodilian species (~30 deg C) from the same strata and also more than that of the temperature of ancient water (~25 deg C) as estimated from an isotope analysis of fossil molluscs.

The distinct cluster of values strongly suggest that scientists were looking at a primary signal. Later reaction of water with buried fossils can reset chemical values, but then this would not have preserved the consistent difference between dinosaurs, crocodilians and mollusc samples.

Animal physiological effects also result in systematic differences between the oxygen isotope values of the water that the animal ingests and the value in the skeletal elements (known as body water) due to preferential incorporation of oxygen into the solid. Living endotherms vary in their body water oxygen isotope ratios from ectotherms (cold blooded animals). Just such a patterns was also observed in the sampled Tyrannosaurus rex and crocodilian samples.

The scientists interpret the results as best explained due to endothermy in T. rex.

Fossils of T. rex have been found over a wide range of paleo-latitudes from 85 deg N to more temperate climes. One interesting observation is of fossils of juvenile tyrannosaruids from Cretaceous age sediments from northern Alaska which was about 85 deg N at that time. This suggests an ability to withstand sub zero temperatures, compatible with endothermy. Based on knowledge of the thermal tolerance of living endotherms, scientists constructed a physiological response scenario across a wide temperature range and found that fossil occurrences of T. rex match well with the theoretical habitat suitability in Late Cretaceous North America. The fossil occurrences may in fact underestimate the range of these creatures since preservation potential of fossils is variable across different environments.

The ability to maintain internal body temperature made it possible for this group of dinosaurs to inhabit and disperse over a wide range of habitats with significant temperature variations.

Inspiration From The Galapagos Islands

From the famous Galapagos Islands comes news about a link between global warming and intensification of El Nino.

 

Imagery- Sentinel 2 Mosaic: Copernicus Browser

El Nino is a pattern of natural climatic variation which occurs when a weakening or reversal of easterly trade winds results in warm Pacific water piling up around the west coast of South America. This phenomenon depends upon subtle interactions between sea surface temperature, ocean currents, and winds, and climate models can’t reproduce these accurately. This means that often different models disagree on how El Nino might be affected by global warming.  Historical records don’t go too far back for us to assess whether there is a clear correlation between global warming and El Nino strength.

Now, a new method uses corals to tease out the temperature of sea water across centuries.

Coral skeletons grow by precipitating the mineral aragonite (CaCO3) in yearly growth bands. Scientists sampled these layers and measured the amount of element strontium and the ratio of heavy oxygen O18 to the lighter O16 in each layer. Aragonite incorporates less strontium and more O16 in warmer water. A sea surface temperature record stretching back a thousand years could be constructed.

The conclusion was that over the past 40 years, temperature swings have become more extreme in El Nino years. This finding from the Galapagos is complimented by another analysis of corals from Kiribati in the Central Pacific. Scientist have a taken a step towards a firmer understanding of the variability of this phenomenon which causes extreme weather events around the globe.

Which other important scientific studies have come out of the Galapagos?

Ahem… there is off course the visit in the year 1835 by a certain Mr. Charles Darwin. His observations there made an important but not an outsized contribution towards his theories of evolution. Darwin was just as comfortable driving home his point using the example of the domesticated pigeon as he was describing the finches and mockingbirds of the Pacific Islands.

Jeff Wallace of the University of Glamorgan in his brilliant introduction to the Wordsworth Classics of World Literature edition of The Origin of Species makes this observation: 

"Readers thus soon find themselves continually shuttled to and fro across the distance between the ‘familiar’ and the ‘other’, the domestic and the exotic, in a text which seems to disdain the very boundary lines between such distinctions. With bewildering and unpredictable variation, we encounter the women-eating barbarians of Terra del Fuego; the small Asiatic cockroach; the thickened stems of the common  and Swedish turnip; the climbing hooks  used by the trailing bamboo of the Malay Archipelago; the egg carrying folds of skin of pendunuculated centipedes; the northern and southern downs of the Weald; the sedimented beds of the mouth of the Mississippi during the glacial period. Darwin’s task at once scientifically central to his work and yet only to be achieved through a vivid and creative use of language, is to make strange or 'astonishing’ the detail of the close and familiar world, and to bring the most extraordinary facets of the alien and unknown within the realms of common understanding. His success, in a text whose fascination is undiminished if not growing as we enter the peculiar concerns of the millennium, lies ultimately in indicating that these contrasting worlds are in fact one world".  

The variation in the beak of the Galapagos ground finches and mockingbirds did inspire Darwin to think about common descent and natural selection, but the legendary finches don’t even feature in his book. The reason is he failed to label his collection systematically! On his return to England he did turn over his collection of wrens, blackbirds, and finches to the ornithologist John Gould.

To his surprise, Gould informed him that despite the great differences in their beak shape and size, the ‘wrens’ and ‘blackbirds’ were in fact all ground finches. His grab bag collection was actually a closely related group of 13 species of finches. Darwin did label his collection of four mockingbirds by island, and they too, as Gould found out, were distinct species. Gould added one more crucial piece of information. All these birds had close but not identical relatives on the American mainland.

Darwin eventually saw the significance of this observation and it became an important piece of evidence for his theory of common descent. He hypothesized that one founder population of these birds must have reached the Galapagos from the South American mainland and then diverged into distinct species on different islands. The standard depiction of an evolutionary tree with branches splitting away from a common node owes its origins to the rather disorganized collection of a wide thinking naturalist and the keen observation of an ornithologist.

Many decades later two scientists did label those finches correctly. And studied them in excruciating detail.

 I am referring to Rosemary and Peter Grant’s epic 40 year study of the morphological evolution of the ground finches of the Galapagos. These two scientists painstakingly measured the variation in beak size and shape over many generations. This they complimented by comparing their genetic differences, and using all this data pieced together a tale of their evolution through changing climate patterns and food availability. Their study has provided a powerful validation of Darwin’s idea that natural selection can shape morphologic change and specialization in populations.

Jonathan Weiner’s Pulitzer Prize winning book, The Beak of the Finch, captures this story vividly. A more updated description of this research has been provided by the two scientists themselves through their publication - 40 Years Of Evolution: Darwin’s Finches On Daphne Major Island.

The Galapagos Islands began forming about 4 million years ago. The Nazca tectonic plate is moving eastwards in the Pacific over a heat source situated deep in the earth’s mantle. The eastern edge of the Nazca Plate is sinking beneath the South American tectonic plate. Sporadic volcanism over the mantle hot spot has created a chain of volcanic islands which become younger towards the west. Volcanoes on the western islands are still active.Today, the islands and the surrounding waters are a marine reserve, offering some protection to its unique biodiversity.

Although geologically young, the specific geologic and bio-geographic circumstance of these islands have proven to be a fertile ground for science. From climate change, to evolution, to conservation biology, scientists working there continue to probe and tease out insights that are proving crucial in navigating the currents of a rapidly changing world.