Climate as the Hidden Driver of Dinosaur Distribution and Migration

Geographic distribution of the three major dinosaur clades (Chiarenza, A. A., Mannion, P. D., Farnsworth, A., Carrano, M. T., Varela, S. (2022))

For most of the Mesozoic Era, non-avian dinosaurs (hereafter referred to simply as dinosaurs) were extraordinarily abundant and diverse across the globe. They evolved a wide range of body forms, occupied an enormous spectrum of body sizes, and developed physiological systems suited to many ecological roles. Given the substantial differences among dinosaur groups, researchers have long suspected that climate played a major role in shaping both their evolutionary trajectories and their geographic distributions.

Previous studies of dinosaur fossils revealed an intriguing pattern: dinosaur diversity often peaked in higher-latitude regions outside the tropics. Yet the three major dinosaur clades did not share identical geographic limits. Sauropods appeared to be more restricted by latitude than ornithischians and theropods. No fossil evidence indicates that sauropods inhabited regions beyond paleolatitudes of about 65° north or south. In contrast, ornithischians and theropods reached their highest diversity at comparatively high latitudes in both hemispheres. This contrast suggests that sauropods may have differed substantially from other dinosaurs in their physiological tolerances.

Despite these observations, the influence of climate on the global distribution of dinosaurs had not previously been examined in detail. To address this gap, the research team behind the study combined a global dataset of dinosaur fossil localities with reconstructions of ancient climate conditions, aiming to evaluate how environmental factors correlated with dinosaur distribution patterns.

Before conducting the analysis, the researchers carefully screened the fossil dataset and identified 12,939 localities that could be considered reliable. These included 6,019 occurrences of ornithischians, 2,154 of sauropods, and 4,766 of theropods. Using plate-tectonic reconstruction models, the team then converted the modern coordinates of each fossil locality into its corresponding paleogeographic position at the time when the animals lived.

The results reveal that during the Tithonian stage of the Late Jurassic (approximately 154–145 million years ago), the distributions of all three major dinosaur groups were still geographically restricted. At that time, neither ornithischians nor sauropods had reached polar regions. By the Albian stage of the Early Cretaceous (roughly 113–100 million years ago), the geographic ranges of ornithischians and theropods had expanded to cover most regions of the world, whereas sauropods remained largely absent from high-latitude environments. By the Maastrichtian stage of the Late Cretaceous (about 72–66 million years ago), theropods and ornithischians had essentially achieved a global distribution, yet sauropods continued to be missing from polar areas.

An additional pattern emerged from the data. The distribution of sauropods resembles that of many modern animal groups: diversity peaks in tropical regions and gradually declines toward the poles. Ornithischians and theropods show a different trend. Their diversity tends to be relatively low in the tropics but rises sharply around 40° to 50° latitude in both hemispheres, producing a bimodal distribution with two diversity peaks.

These patterns indicate that sauropods differed markedly from theropods and ornithischians in their geographic ecology. The data strongly suggest that sauropods were more constrained by temperature than other dinosaurs. Even during warmer climatic intervals, they appear to have had limited ability to expand into high-latitude environments. Temperature may also help explain the decline of sauropods in the Northern Hemisphere. At the same time, large portions of Gondwana—including India, South America, and Africa—remained within suitable climatic conditions for sauropods during the same period.

When climatic variables were incorporated into the analysis, another trend became apparent: sauropod diversity tended to peak in semi-arid environments. In contrast, the distributions of ornithischians and theropods extended more strongly into regions with higher precipitation. This pattern suggests that sauropods were comparatively more tolerant of dry conditions than the other two major dinosaur groups.

During their analysis, the researchers also noted that sauropod distribution patterns resemble those of Crocodylomorpha. Temperature is known to be the principal factor limiting the distribution of modern crocodylomorphs. Because living crocodilians are ectothermic animals, the researchers proposed that sauropods may have possessed a somewhat similar thermoregulatory strategy. Given the evidence for relatively high metabolic rates in sauropods, the authors suggest that these dinosaurs may have been mesothermic—maintaining body temperatures higher than the surrounding environment without sustaining a constant internal temperature.

Another observation further supports this interpretation. In modern crocodilians, body size is positively correlated with environmental temperature. This relationship may help explain size variation among sauropods through time. During the Albian to Cenomanian stages of the Cretaceous, when global temperatures rose, the largest sauropods in history appeared. Later, during the Campanian to Maastrichtian stages, global cooling coincided with the emergence of smaller-bodied sauropod species.

Theropod dinosaurs, ornithischian dinosaurs, and pterosaurs are all known to have possessed feathers or feather-like structures, which could aid in maintaining stable body temperatures. This suggests that endothermic physiology may have evolved before the appearance of dinosaurs themselves. Sauropods, however, appear to have lost this thermoregulatory mode at some point in their evolutionary history. The reasons for this shift remain unclear and will require additional fossil evidence and future research.

Earlier hypotheses proposed that prolonged climatic fluctuations during the Late Cretaceous were the main cause of declining dinosaur diversity. The present analysis challenges that view. The results indicate that even major long-term climate changes did not produce widespread or sustained negative effects on dinosaur diversity. Instead, dinosaurs appear to have been highly adaptable to gradual climatic variation. Their resilience may only have been disrupted by sudden environmental catastrophes, such as the asteroid impact at the end of the Cretaceous.

Finally, this study introduces a new analytical framework. By integrating fossil occurrence data with Earth-system reconstructions, the approach offers a promising way to investigate the environmental drivers behind biological dispersal. Such methods may also provide fresh perspectives on long-standing paleontological puzzles—for example, why tyrannosaurs never dispersed into South America.

Author: Bai Leng

Reference:

Chiarenza, A. A., Mannion, P. D., Farnsworth, A., Carrano, M. T., Varela, S. (2022). Climatic constraints on the biogeographic history of Mesozoic dinosaurs. Current Biology.