Measurements of dinosaur body temperatures shed new light on 150-year debate

October 13, 2015, University of California, Los Angeles
An artist's rendering of oviraptorid theropods. Credit: Doyle Trankina and Gerald Grellet-Tinner

Were dinosaurs really fast, aggressive hunters like the ones depicted in the movie "Jurassic World"? Or did they have lower metabolic rates that made them move more like today's alligators and crocodiles? For 150 years, scientists have debated the nature of dinosaurs' body temperatures and how those temperatures influenced their activity levels.

New research by UCLA scientists indicates that some , at least, had the capacity to elevate their body temperature using heat sources in the environment, such as the sun. They also believe the animals were probably more active than modern-day alligators and crocodiles, which can be active and energetic, but only for brief spurts.

The researchers also found evidence that other dinosaurs they studied had lower body temperatures than , their only living relatives, and were probably less active.

The research is published today in the journal Nature Communications.

Led by Robert Eagle, a researcher in the department of earth, planetary and space sciences in the UCLA College, the scientists examined fossilized dinosaur eggshells from Argentina and Mongolia. Analyzing the shells' chemistry allowed them to determine the temperature at which the eggshells formed—information that had not been previously known.

"This technique tells you about the of the female dinosaur when she was ovulating," said Aradhna Tripati, a co-author of the study and a UCLA assistant professor of geology, geochemistry and geobiology. "This presents the first the direct measurements of theropod body temperatures."

The Argentine eggshells, which are approximately 80 million years old, are from large, long-necked titanosaur sauropods, members of a family that include the largest animals to ever roam the Earth. The shells from Mongolia's Gobi desert, 71 million to 75 million years old, are from oviraptorid theropods, much smaller dinosaurs that were closely related to Tyrannosaurus rex and birds.

Sauropods' body temperatures were warm—approximately 100 degrees Fahrenheit, according to the study. The smaller dinosaurs had substantially lower temperatures, probably below 90 degrees.

Warm-blooded animals, or endotherms, produce heat internally and typically maintain their body temperature, regardless of the temperature of their environment; they do so mainly through metabolism. Humans and other mammals fall into this category.

Cold-blooded animals, or ectotherms, including alligators, crocodiles and lizards, rely on external environmental heat sources to regulate their body temperature. Lizards, for example, often sit on rocks in the sun to absorb heat, which enables them to be more active.

Scientists have debated since the 19th century whether dinosaurs were endotherms or ectotherms. The UCLA research indicates that the answer could lie somewhere in between. The dinosaurs, at least the oviraptorid theropods, had the ability to elevate their body temperature above the environmental temperature.

"The temperatures we measured suggest that at least some dinosaurs were not fully endotherms like modern birds," Eagle said. "They may have been intermediate—somewhere between modern alligators and crocodiles and modern birds; certainly that's the implication for the oviraptorid theropods."

"This could mean that they produced some heat internally and elevated their body temperatures above that of the environment but didn't maintain as high temperatures or as controlled temperatures as modern birds," he added. "If dinosaurs were at least endothermic to a degree, they had more capacity to run around searching for food than an alligator would."

The study was the first direct measurement of body temperatures in two types of dinosaurs. Tripati said it shows clearly that they are different from each other.

The researchers also analyzed fossil soils, including minerals that formed in the upper layer of the soil on which the oviraptorid theropods' nests were built. This enabled them to estimate that the environmental temperature in Mongolia shortly before the dinosaurs went extinct was approximately 79 degrees Fahrenheit.

"The oviraptorid dinosaur were higher than the environmental temperatures—suggesting they were not truly cold-blooded, but intermediate," Tripati said.

Eagle, Tripati and their colleagues initially measured modern eggshells from 13 bird species and nine reptiles to establish their ability to measure body temperature from the chemistry of eggshells.

The researchers measured, in calcium carbonate minerals, the subtle differences in the abundance of chemical bonding between two rare, heavy isotopes: carbon-13 and oxygen-18. They studied the extent to which these heavy isotopes clustered together using a mass spectrometer—a technique that enabled them to determine mineral formation temperatures. Mineral forming inside colder bodies has more clustering of isotopes.

The scientists analyzed six fossilized eggshells from Argentina, three of which were well-preserved, and 13 eggshells from Mongolia's Gobi desert, again selecting three that are well-preserved. They determined whether the fossilized eggshells maintain their original chemistry or were altered over tens of millions of years. They also analyzed fossilized dinosaur eggshells from France, but found these were not well-preserved, and excluded them.

The researchers acquired the Argentine eggshells from the Los Angeles County Natural History Museum, and the eggshells from Mongolia's Gobi desert from New York's American Natural History Museum.

Eagle, Tripati and colleagues published the first analysis of fossilized dinosaur teeth in the journal Science in 2011. They studied the chemistry of fossil teeth to measure the body temperature of titanosaur sauropods, and determined their body temperature was between approximately 95 and 100.5 degrees Fahrenheit. The new research on eggshells is consistent with the 2011 findings, and adds new body temperature data on oviraptorid theropods.

Explore further: Body temperatures of dinosaurs measured for the first time

More information: Nature Communications, DOI: 10.1038/ncomms9296

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12 comments

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ogg_ogg
1 / 5 (1) Oct 13, 2015
For a different point of view about this, take a look at the concentration of Oxygen in the atmosphere in the Age of the Dinosaurs. It was (mostly) quite a bit higher than now (peaking at ~30% compared to today's 21%), meaning that it was easier to "burn" calories. (see Wikipedia, Earth's Atmosphere, Third Atmosphere graphic). So, assumptions have to be made to draw any conclusions about their metabolism then in comparison to a bird or croc's metabolism now. Not to mention assumptions about cloud cover, average temperature, etc. etc.
jeffensley
3 / 5 (2) Oct 13, 2015
"They determined whether the fossilized eggshells maintain their original chemistry or were altered over tens of millions of years."

How on Earth do you do that without the ability to analyze an egg right after it is formed within a living dinosaur? They assume the "well-preserved" ones represent conditions at formation?
malapropism
5 / 5 (5) Oct 13, 2015
Why do these articles still quote only the Fahrenheit temperature scale when, according to several presumably reputable sources, only 4 countries (including the USA) have not yet officially adopted SI metric units?

Oh, right, the rest of the world doesn't matter. Silly me, I forgot.
malapropism
5 / 5 (6) Oct 13, 2015
Update:
Oops, my bad. Apparently Canada do now officially use the metric system so only 3 countries are now stuck on non-SI units: Liberia, Myanmar (Burma) and the USA.

Actually, one would think that anything with the title "Imperial" would be anathema to the US but it seems they really enjoy their British colonial left-overs after all.
Torbjorn_Larsson_OM
3 / 5 (2) Oct 14, 2015
Coo... eh, moderately warm! Mammals should have transited similarly at the time as the dinosaurs did, where the extant ones are fully endotherm too. [ https://en.wikipe...ndotherm ]

@ogg_ogg: Irrelevant, since it is about regulation ability. As a simpler no-go, see the link above: fishes can be endotherms, and they live with much less oxygen. (Their trouble is rather with maintaining heat despite having gills.)

@jeffensley: How on Earth can you ask us, when we all have to look at the paper to see their method!? =D

Possible ways is to look for chemical markers that would change if the egg is mineralized from outside. My guess is that they have looked at egg mineral clumped isotopes, same as how they measure formation temperature in fossil teeth/bones, also on minerals. [ http://www.caltec...ime-1699 ]
Torbjorn_Larsson_OM
5 / 5 (1) Oct 14, 2015
Added: Yep, they did, it's in the abstract: "Here we show that clumped isotope analysis of eggshells can be used to determine body temperatures of females during periods of ovulation."
jeffensley
not rated yet Oct 14, 2015
Added: Yep, they did, it's in the abstract: "Here we show that clumped isotope analysis of eggshells can be used to determine body temperatures of females during periods of ovulation."


Right I understand that as well as I can... they clump a particular way at certain temperatures of formation. The catch is finding "well-preserved" samples which suggests to me that these clumps can change over time... that being the case, wouldn't you need to know the conditions to which the fossils have been exposed to know how they changed?
Captain Stumpy
3 / 5 (4) Oct 14, 2015
Why do these articles still quote only the Fahrenheit temperature scale when, according to several presumably reputable sources, only 4 countries (including the USA) have not yet officially adopted SI metric units?

Oh, right, the rest of the world doesn't matter. Silly me, I forgot.
@malapropism
PO is simply a clearinghouse for articles... and this article is from Nature.com and the University of CA, Los Angeles, so it is almost entirely US and likely written for US readers ... and likely was written with US spell check and other programs

should it be metric? yes. i can't argue with that. it is easier to remember and work with.
but that doesn't change the cultural influences of the author or their surroundings & equipment

malapropism
5 / 5 (2) Oct 14, 2015
@Captain S
Yes, I agree with you 100% and did notice that the article was not original PO writing. I was simply whingeing sarcastically to take a (small) stand for Standards (journalistic and SI) and perhaps to make a point.

I'm actually rather surprised (not to say, appalled) that Nature Communications, UCLA and the various syndicating sites and journals would allow a science writer to get away with using these units and not at least offering a metric conversion in parentheses, especially when the paper includes the temperatures in Celsius as would be expected of any reputable scientist (in the Abstract anyway; I'm not all that keen to spend $32 on getting the paper just to prove the point).

As you rightly say, it's down to the local cultural influences on the author. And I'd add: and his or her degree of parochialism.
1andreasse
not rated yet Oct 19, 2015
They should use Celsius as the temperature scale, not Fahrenheit. This is the international standard, and it may wrongly make the article authors be seen of defenders of an imperalistic mindset. The entire World, except USA and 1 or 2 more countries, have agreed on Celsius. What is it with some writers that they think that democracy only matters if they agree? Use Celsius if you really Believe in democracy. It Is a big deal as it sends signals to how you percieve the World, and your place in it. And in this case, how you percieve global agreements. Use Celsius. Period.
bluehigh
5 / 5 (1) Oct 19, 2015
UCLA Scientists don't know of (or accept) the International System of Units?

Captain, I tend to agree with your comment generally but .. Scientists?

Captain Stumpy
5 / 5 (2) Oct 19, 2015
UCLA Scientists don't know of (or accept) the International System of Units?
Captain, I tend to agree with your comment generally but .. Scientists?
@Blue
Yeah... i know.
Mal actually has a very valid point... and i personally agree with it, too.

however... what i think, IMHO, is that the articles are written for the typical American who is not scientifically literate!

they're written more as a draw into the science and world

as Mal noted, there are metric notes in the abstract

wide variety is great for general knowledge and to help drive excitement/interest in science... the PO site used to be regularly used by students (pre-college) in my area, but is now banned because of the flood of pseudoscience in the comment sections

if someone were to be educated in a STEM field, it would require the knowledge, but there are a lot of interested second parties who major in other fields

PO articles, stuff like above, are written primarily for them, i think

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