The latest dinosaur blockbuster， “Jurassic World: Dominion，” is currently in theaters. The plot of this installment suggests that dinosaurs that escaped into the wild in previous films died off in large numbers due to their inability to “adapt to modern climates.” Specifically， the film posits that modern atmospheric oxygen levels are too low and temperatures too cold for dinosaurs， allowing them to survive only near the equator.
However， this portrayal starkly contrasts with the latest scientific research on dinosaurs. The notion that dinosaurs would struggle in modern atmospheric conditions and temperatures is largely a misconception， catering to a popular， albeit inaccurate， image of these ancient creatures.
Still from “Jurassic World: Dominion.” Image source: Baidu Baike entry.
For instance， the teeth of stegosaurs were only about seven millimeters wide， and their jaws could not fully close， meaning they were ill-equipped for chewing. They could only snip or cut vegetation， indicating their teeth were small and relatively weak.
1. Would Dinosaurs Perceive Modern Oxygen Levels as Low?
Contrary to popular belief， oxygen levels during the age of dinosaurs were not necessarily much higher than today. In the Late Triassic， when dinosaurs first appeared， atmospheric oxygen content was around 15%， significantly lower than the current 21%. The scarcity of fossil charcoal in sedimentary rocks from that era further suggests a lower incidence of wildfires due to this lower oxygen concentration.
Even during the Jurassic period， often considered the peak of dinosaur dominance， oxygen levels did not dramatically exceed those of the Triassic. While oxygen levels did rebound by the Cretaceous period， when dinosaurs were at their most diverse， they were still comparable to modern levels.
The blue line in the image illustrates oxygen level fluctuations from the Triassic to the Jurassic. It’s evident that oxygen levels were significantly lower than today during this period. Image source: bioprinciples.biosci
A depiction of the Triassic landscape from the documentary “Walking with Dinosaurs.” Image source: Documentary still.
Some might argue that the higher oxygen levels of the Carboniferous period， which supported giant insects like Meganeura and Arthropleura， indicate a generally oxygen-rich atmosphere throughout dinosaur eras. This， they might claim， allowed dinosaurs to achieve their immense sizes. However， attributing the large size of dinosaurs solely to higher oxygen levels oversimplifies the matter. A more significant factor in their massive stature was their physiological efficiency.
Dinosaurs， closely related to modern birds， possessed an **air sac system**， much like birds do. These air sacs stored air during inhalation and then efficiently pushed it into the lungs during exhalation， facilitating continuous gas exchange. This unique respiratory system allowed dinosaurs to maintain high respiratory efficiency even in lower oxygen environments.
Furthermore， even if we assume dinosaur-era oxygen levels were higher than in the Cenozoic. The fact that numerous colossal megafauna， such as the Indricotherium， Megalodon， and Livyatan melvillei， as well as the largest animal ever known， the blue whale， all lived during the Cenozoic era suggests that atmospheric oxygen content may not be the sole or even primary determinant of animal size.
Therefore， it’s evident that **atmospheric oxygen levels are not strongly correlated with an animal’s size.**
Saurischian dinosaurs， like these large sauropods， also had a bird-like air sac system. Image source: researchgate
The Mamenchisaurus， one of China’s largest dinosaurs， achieved its immense size primarily due to efficient respiration and feeding methods. Image source: famousbio
2. Would Dinosaurs Only Survive Near the Equator Today?
While it is true that dinosaur-era temperatures were generally higher than today， with the mid-to-late Cretaceous period (around 96 million years ago) potentially being the warmest period in the Phanerozoic eon， this does not mean that colder environments did not exist on Earth during that time.
The Jehol Biota， found in western Liaoning， China， is a well-known example of fossilized fauna from a cooler climate. This region hosted famous dinosaurs like Microraptor， Dilong， and Beipiaosaurus. Furthermore， the poles during the age of dinosaurs experienced polar nights， yet dinosaurs thrived even in these perpetually dim and cold conditions.
In the Arctic regions， dinosaurs like Nanuqsaurus， Pachyrhinosaurus， and Troodon have been found. In the Antarctic (which， during the Cretaceous， included not only Antarctica but also parts of Australia and southern South America)， dinosaurs such as Cryolophosaurus， Yunnanosaurus (sometimes referred to as “Yunnanosaurus” in paleontological contexts， though the original text says “Leaellynasaura，” suggesting a possible translation discrepancy)， and Unaysaurus have been discovered. The diversity of species in these polar regions indicates that dinosaurs were well-adapted to such environments.
A world map from the Early Cretaceous (approximately 105 million years ago). Image source: Wikipedia.
Even dinosaurs that preferred warmer climates would not be restricted solely to equatorial regions for survival today. Iconic dinosaurs like Tyrannosaurus Rex and Triceratops lived in the Late Cretaceous of Montana， USA， where temperatures ranged from 16-25 degrees Celsius. This is comparable to the climate of Florida today， a state that， while known as the Sunshine State， is largely north of the Tropic of Cancer and far from equatorial latitudes.
Evidence of permafrost from the Early Cretaceous found in Chaoyang City， Liaoning， indicates a considerably cold climate in the region at that time. Image source: Author’s own photograph.
A reconstruction of the environment in western Liaoning during the Early Cretaceous. Illustration by: Brain Choo
A scene from the documentary “Prehistoric Planet” depicting a Nanuqsaurus attacking a Pachyrhinosaurus. Both dinosaurs lived in what is now Alaska， which was still an icy region during the Cretaceous. Image source: Documentary still.
The Hell Creek Formation， where Tyrannosaurus Rex lived， may have had a climate similar to present-day northern Florida. Image source: Eduard Solà
3. The Unforeseen Challenge: Food Availability
Beyond temperature and oxygen levels， a significant factor that many overlook is the potential for some herbivorous dinosaurs to starve in the modern era. This challenge arises from the evolution of plant life.
During the Jurassic period， softer ferns and gymnosperms were the dominant vegetation. However， by the Early Cretaceous， angiosperms (flowering plants) had rapidly diversified and become the leading plant group. Concurrently， the more established gymnosperms also evolved. This period is known as the “Cretaceous Terrestrial Revolution.”
These new plants were tougher and more fibrous than their predecessors， making them harder to digest and potentially containing novel toxins. Their emergence also led to a significant shift within dinosaur communities. Dinosaurs in the “Jurassic” film series， whether in parks or in the wild， would encounter modern vegetation shaped by this revolution. For dinosaurs that lived before the Cretaceous Terrestrial Revolution， such as Stegosaurus， Apatosaurus， and Mamenchisaurus， a landscape dominated by modern plants would essentially be a “green desert.” Conversely， Cretaceous dinosaurs that adapted to these new plants， like Alamosaurus， Triceratops， and Ankylosaurus， would have had a greater chance of survival.
Fossils and a reconstruction of “Sinopoda” (Chinese ancient fruit)， an early angiosperm from the Early Cretaceous. Image source: Author’s own photograph.
These are the teeth of stegosaurian dinosaurs. Image source: Billon-Bruyat， J.-P.， Mazin， J.-M.， & Pouech， J. (2010)
Stegosaurian teeth， only about seven millimeters wide and unable to close fully， were best suited for snipping rather than chewing， making them relatively small and weak for processing tougher vegetation. While sufficient for the softer plants of the Jurassic， these teeth would have struggled against the emerging angiosperms of the Cretaceous.
This dietary adaptation explains why ornithopod dinosaurs like hadrosaurs， ceratopsians like Triceratops， and ankylosaurs with their robust chewing mechanisms， as well as titanosaurs with their massive digestive systems， became dominant in the Cretaceous. In contrast， more visually imposing dinosaurs like the Stegosaurus saw their species dwindle to a mere handful that could be counted on one’s fingers.
Phytolith residue found in the teeth of the early hadrosaur， “Equus magnificus，” providing evidence that this dinosaur was already feeding on tougher plants. Image source: Yan Wu; Hai-Lu You; Xiao-Qiang Li (2017). “Dinosaur-associated Poaceae epidermis and phytoliths from the Early Cretaceous of China”. National Science Review. in press. doi:10.1093/nsr/nwx145.
References:
1.Billon-Bruyat， J.-P.， Mazin， J.-M.， & Pouech， J. (2010). A stegosaur tooth (Dinosauria， Ornithischia) from the Early Cretaceous of southwestern France. Swiss Journal of Geosciences， 103， 143–153.
2.Schuneman， Patrick Jerome. “Pyrogenic Polycyclic Aromatic Hydrocarbons from Carboniferous， Triassic， and Modern Chars: Potential Relations to Paleoatmospheric Oxygen Content.” TRACE: Tennessee Research and Creative Exchange， Aug. 2006， trace.tennessee.edu/utk_gradthes/1790/.
3.Wedel， Mathew. “Evidence for Bird-like Air Sacs in Saurischian Dinosaurs.” ResearchGate， 2016， www.researchgate.net/publication/213776045_Evidence_for_bird-like_air_sacs_in_saurischian_dinosaurs?_tp=eyJjb250ZXh0Ijp7ImZpcnN0UGFnZSI6Il9kaXJlY3QiLCJwYWdlIjoiX2RpcmVjdCJ9fQ. Accessed 10 July 2025.
4.Yan Wu; Hai-Lu You; Xiao-Qiang Li (2017). “Dinosaur-associated Poaceae epidermis and phytoliths from the Early Cretaceous of China”. National Science Review. in press. doi:10.1093/nsr/nwx145.
Author: Qianxijun
Review: Liu Ying， Li Peiyuan
Expert Reviewer: Xing Lida， Associate Professor， School of Earth Sciences and Resources， China University of Geosciences (Beijing)， Young Paleontologist.
