Dinosaurs, mesozoic land rulers, are also the most famous paleontological taxa. When it comes to them, most people often think of adjectives such as "huge", "cold-blooded", and "violent".
Whether dinosaurs were really as large as we think, and how they became as large, this article is not listed for the time being, see (Why did dinosaurs grow into behemoths?). http://www.kepu.net.cn/gb/ydrhcz/ydrhcz_wap/ydrhcz_wap_zpzs/201909/t20190903_33409.html）。
Today we want to talk about, are dinosaurs really the legendary "cold-blooded killers"?
Speaking of "cold-blooded killers", there are indeed many famous representatives in the animal kingdom today. Whether it is a huge and fierce crocodile, shark, or a small and agile gecko, frogs, they are the representative of "cold-blooded killers".
Of course, the "cold-blooded" here does not mean that they are cruel and ruthless, but that is, their thermoregulation method, which is what we often call "cold-blooded animals".
· Nature's "cold-blooded tough guys" (Image: https://www.pinterest.co.uk/)
Cold-blooded or warm-blooded? It depends on whether the temperature is your decision or the environment
Although people often use the terms "cold-blooded animals" and "warm-blooded animals" to distinguish between animals with different thermoregulation methods, in fact, these two terms are no longer a definite and effective academic term.
At present, the scientific community is more popular to use "extra-warm animals" and "internal warm animals" to distinguish between these two types of animals. Extratrophobeic animals correspond to cold-blooded animals, which are generally said to be affected by the external environment, and living reptiles, amphibians, etc. belong to this category. Internal thermogenesis, on the other hand, refers to a type of animal that can independently maintain or regulate body temperature independently of ambient temperature, typically mammals and birds.
Internal and external temperature are more precisely defined than traditional cold-blooded and warm-blooded. In terms of internal temperature, it describes the ability to maintain a body temperature relative to the environment. For example, human beings are typical internal warm animals and "warm-blooded animals".
Human beings can maintain a constant body temperature whether it is in the summer when the ambient temperature is higher than the body temperature or in the winter when the temperature is lower than the body temperature, which is the meaning of internal temperature. But if we use warm blood to describe human beings, it is not appropriate in the summer. Because when the ambient temperature is 40 ° C, human blood (37 ° C) is relatively "cold"! In the same way, in the cold winter, the blood temperature of humans wearing heavy warm clothing is extremely hot compared to the environment.
"Warm blood" and "cold blood" are only relative concepts, the environment is different, we humans can also switch between "warm blood" and "cold blood".
· The relativity of "warm" and "cold" (Image source: https://www.menshealth.com/uk/health/a29084106/scientists-may-have-found-a-cure-for-the-common-cold/)
Ancestors warm outside, descendants inner temperature Dinosaurs: Guess what I am
When we observe the living vertebrates, it is not difficult to find that the two groups of animals closest to the dinosaurs, the living reptiles and birds, happen to belong to the extrapatent and the internal warm, respectively.
Dinosaurs are close relatives of living reptiles, especially crocodiles, and are also the direct ancestors of birds. So, were dinosaurs as cold as their extratrophotonic creeping ancestors? Or are they as active and warm as their offspring birds?
As early as the second half of the nineteenth century, scientists have proposed that dinosaurs belong to thermophilic animals, but this view did not become the mainstream at that time, after all, dinosaurs have always been a cold, slow and leisurely behemoth image.
The reality may be more complex, with most of the evidence supporting dinosaurs falling into the latter category, with at least some dinosaurs being active endothermic animals.
Evidence 1: Dinosaur body structure is similar to that of birds
Since the 1960s, dinosaur research has ushered in the "Renaissance". American paleontologist Buck and others have shown through the discovery and study of a series of fossils that dinosaurs may not be "cold-blooded" and lazy images, but "warm-blooded" and active animals. This Renaissance also became an important bridge between dinosaurs and living birds.
One of the evidences is that some of the most important theropod dinosaur fossils have been discovered, most notably Balanced Dinosaur. Scientists represented by John Ostrom have found that they are very similar in body structure to living birds and should be agile predators, which is very different from the previous image.
· Balancing the skeleton of dinosaurs, much like slender birds. (Image source: Wikipedia)
Evidence two: Bone histology sounds, dinosaur bones closer to mammals and birds
Dinosaur fossil bone histology that Buck et al. have been working on for a long time (see "Cutting the Thighs – Bone Tissue Discipline."
http://www.kepu.net.cn/gb/ydrhcz/ydrhcz_zpzs/ydrh_201904/201904/t20190404_32526.html" also provides a lot of evidence to support the internal temperature of dinosaurs.
For example, the skeleton of dinosaurs has a typical Harvard system, which is a bone tissue structure that only exists in living endothermic animals. Dinosaurs also had faster growth rates, but many of them had limited growth, with peripheral rest line structures, which were closer to the bones of mammals or birds.
Evidence three: Feathered dinosaur fossils were found
At the end of the 20th century, another revolution in the field of dinosaur research provided more sufficient evidence for the internal temperature of dinosaurs, that is, the discovery of "feathered dinosaurs".
· The most famous fossil of a feathered dinosaur is a orthographic specimen of Gu's little robber. (Image source: Fossil Network)
Fossils, mainly in northern China, produced a large number of feathered dinosaur fossils, and a large part of the fossils had primitive feathers that did not have the function of flight. In addition to the decorative effect, scientists pointed out that these feathers are similar to the down feathers of today's chicks and are very good insulation materials. The emergence of this structure also proves from the side that dinosaurs maintained body temperature above the ambient temperature, which is an important embodiment of internal temperature.
Among the dinosaurs that may have insulating feathers, it is the most peculiar of the gorgeous feathered king dragons. Because The Magnificent Feathered Dragon was a large tyrannosaur dinosaur, feathers had never been found on such a large dinosaur fossil before. Scientists speculate that these large dinosaurs also grew feathers, possibly to adapt to some of the colder environments in the Cretaceous interior, such as the low temperature environment and high altitude environment brought about by the staged Xiaoice period.
· Restoration of the life of a large tyrannosaur with feathers (Source: Institute of Ancient Spine, Chinese Academy of Sciences, http://www.ivpp.cas.cn/xwdt/kyjz/201811/t20181103_5155250.html)
Based on the above evidence, a growing number of scientists believe that dinosaurs may have been a class of animals with considerable body temperature maintenance. But there is still a lack of solid evidence to be implemented, that is, the data of body temperature and temperature.
The body temperature of internal temperature animals is generally higher than that of outer temperature animals, which is very easy to collect data in live animals. However, the dinosaur taxon has disappeared from the earth for more than 66 million years, how can we measure the body temperature of dinosaurs?
Evidence Four: "Taking" the temperature of extinct dinosaurs
Paleontologists have tried to solve this problem using research methods of stable isotope geochemistry. In the study of stable isotope geochemistry, the stable isotope fractionation of oxygen is often used as a temperature for reducing the paleoceanic and paleoenvironmental environments.
The basic principle of this analysis method is that the oxygen isotopes of different qualities are not as fast as the speed of "running" at the same temperature, the light "running" is fast, the heavy is slower, and the higher the temperature, the more obvious the difference, so that according to the record of the fractionation of oxygen isotopes, the ancient temperature can be reduced.
So can this method be applied to the body temperature study of dinosaurs? Although early studies have been attempted, it is difficult to figure out whether the measured values reflect the ambient temperature or the temperature of the organism itself.
With the development of geochemistry, a new method for studying paleothermia, the carbon-oxygen group thermometer, began to be gradually applied to the determination of paleoenvironment temperature. This method has a very big advantage, that is, it can obtain the ambient temperature of calcium carbonate when it is formed.
Scientist Robert Eagle began to apply this method to the study of dinosaur body temperature, and obtained a very accurate dinosaur temperature. The temperature of the dinosaur's body was analyzed by studying the calcium carbonate synthesized inside the dinosaur body, that is, the calcium carbonate from the teeth and the eggshell of the dinosaur, respectively.
· Robert Eagle studied dinosaur body temperature and its relationship to living extracerobates (green segments), mammals (brown dots), and birds (red dots). (Image source: Eagle.et.al 2015)
Although the types of dinosaurs studied are relatively limited, Robert Eagle's findings are very interesting. Both the small theropod dinosaurs and the large sauropods involved in the study had body temperatures above 30 degrees Celsius. Small theropod dinosaurs have a body temperature similar to that of mammals with lower body temperatures or some extratemperaminate animals with higher body temperatures. The body temperature of large sauropods was much higher, basically the same as that of most mammals.
That is to say, the body temperature gap within the dinosaur may also be very large, but overall, the body temperature of the dinosaur is relatively high, very close to the mammalian level.
At the same time, Robert Eagle also believes that the reason for the higher body temperature of sauropods may be their huge size, and the phenomenon of huge temperature produced by their huge size (for the study of the hugeness of sauropods, refer to "How did dinosaurs grow into behemoths?"). ）。
Although Robert Eagle and other scientists from 2011 to 2013 have produced some of the most accurate dinosaur body temperatures to date, due to the complexity of research methods, the scarcity of research materials and other issues, the specific body temperature of most dinosaurs is still a mystery, so it is inevitable to assert that all dinosaurs are internal warm animals.
The story is far from over. Excitingly, recent research on other aspects of dinosaurs, such as hatching behavior, growth rate, etc., also mostly supports that dinosaurs may be a class of endothermic animals. Perhaps dinosaurs, as the ancestors of the most prosperous endothermic animals, birds, will one day completely get rid of their cold, slow-moving stereotypes and live on the big screen and in the hearts of every dinosaur lover.
· Image source: Jurassic World movie scene, the author has changed
Jurassic World producer, did you hear that? Please add feathers to the dinosaurs in the movie!
bibliography:
1. Eagle, R. A., M. Enriquez, G. Grellet-Tinner, A. Pérez-Huerta, D. Hu, T. Tütken, S. Montanari, S. J. Loyd, P. Ramirez, A. K. Tripati, M. J. Kohn, T. E. Cerling, L. M. Chiappe and J. M. Eiler (2015). "Isotopic ordering in eggshells reflects body temperatures and suggests differing thermophysiology in two Cretaceous dinosaurs." Nature Communications 6(1): 8296.
2. Eagle, R. A., T. Tutken, T. S. Martin, A. K. Tripati, H. C. Fricke, M. Connely, R. L. Cifelli and J. M. Eiler (2011). "Dinosaur Body Temperatures Determined from Isotopic (C-13-O-18) Ordering in Fossil Biominerals." Science 333(6041): 443-445.
3. Xu, X., K. Wang, K. Zhang, Q. Ma, L. Xing, C. Sullivan, D. Hu, S. Cheng and S. Wang (2012). "A gigantic feathered dinosaur from the Lower Cretaceous of China." Nature 484(7392): 92-95.
Producer: Popular Science China
Producer: Qin Zichuan (DinosaurX Team)
Producer: Computer Network Information Center, Chinese Academy of Sciences