Dinosaurs dominated Mesozoic terrestrial ecosystems globally. However, whereas a pole-to-pole geographic distribution characterized ornithischian and theropod dinosaur, giant sauropods were restricted to lower latitudes. In new research, Dr. Alfio Alessandro Chiarenza from the University of Vigo and colleagues evaluated the role of climate in shaping these biogeographic patterns through the Jurassic-Cretaceous (201-66 million years ago).
Brontosaurus acted as an ecosystem engineer in a warm and vegetated landscape not dissimilar to modern-day savannah type biomes. Image credit: Emiliano Troco.
“Our research shows that some parts of the planet always seemed to be too cold for sauropods. They seem to have avoided any temperatures approaching freezing,” said Dr. Philip Mannion, a paleontologist in the Department of Earth Sciences at University College London.
“Other dinosaur types, in contrast, could thrive in Earth’s polar regions, from innermost Antarctica to polar Alaska — which, due to the warmer climate, were ice-free, with lush vegetation.”
“This suggests sauropods had different thermal requirements from other dinosaurs, relying more on their external environment to heat their bodies — slightly closer to being ‘cold-blooded,’ like modern-day reptiles. Their grand size hints that this physiology may have been unique.”
In the study, the authors analyzed the fossil record across the Mesozoic era, looking at occurrences of fossils of the three main dinosaur types: sauropods, which include Brontosaurus and Diplodocus; theropods, which include velociraptors and Tyrannosaurus rex; and ornithischians such as Triceratops.
Combining these fossil data with data about climate throughout the period, along with information about how continents have moved across the globe, they concluded that sauropods were restricted to warmer, drier habitats than other dinosaurs.
These habitats were likely to be open, semi-arid landscapes, similar to today’s savannahs.
Graphical abstract showing the latitudinally more restricted distribution of sauropod dinosaurs compared to other dinosaurs. Image credit: Alessandro Chiarenza et al., doi: 10.1016/j.cub.2021.11.061.
“It may be that sauropods were physiologically incapable of thriving in colder regions, or that they thrived less well in these areas than their dinosaurian cousins and were outcompeted,” Dr. Alessandro Chiarenza said.
“A mix of features may have helped sauropods shed heat more easily than mammals do today. Their long necks and tails would have given them a larger surface area, and they may have had a respiratory system more akin to birds, which is much more efficient.”
“Some species of theropods and ornithischians are known to have had feathers or downy fur helping them retain body warmth. This suggests they may have generated their own body heat. For sauropods, however, there is no evidence of this kind of insulation.”
“Sauropods’ strategies for keeping their eggs warm may also have differed from the other dinosaurs. Theropods probably warmed eggs by sitting on them, whereas ornithischians seem to have used heat generated by decaying plants. Sauropods, meanwhile, may have buried their eggs, relying on heat from the sun and the ground.”
In the study, the fossil record showed zero occurrences of sauropods above a latitude of 50 degrees north, an area encompassing most of Canada, northern Europe and the UK, or below 65 degrees south, encompassing Antarctica.
In contrast, there are rich records for theropods and ornithischians living above 50 degrees north in later periods (from 145 million years ago).
“Sauropods may have had a unique in-between physiology, closer to being cold-blooded than other dinosaur types,” the researchers said.
The study was published in the journal Current Biology.
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Alfio Alessandro Chiarenza et al. Climatic constraints on the biogeographic history of Mesozoic dinosaurs. Current Biology, published online December 17, 2021; doi: 10.1016/j.cub.2021.11.061
Source link: https://www.sci.news/paleontology/tropical-sauropod-dinosaurs-10380.html
