The macroecology of Mesozoic dinosaurs
By: Alfio Alessandro Chiarenza
Summarized by: Olive Drury is a Biology and English undergraduate at Binghamton University. She spends most of her days typing stories and sewing dresses. She is generally a fan of ocean creatures such as the jellyfish and aspires to live in a submarine or perhaps a blimp. Olive’s favorite dinosaur is a Diplodocus. One fun fact about Olive is that she is very good at award winning board game Bananagrams.
Purpose: Large-scale geological shifts during the Mesozoic (251–65 million years ago) brought about major transformations for global ecology. For non-avian dinosaurs, Earth’s tectonic remodeling across the Jurassic as continents moved (Figure 1) led to the permanent alteration of ecosystems, isolating dinosaur populations and impacting area availability, spatial patterns, and climate. The fallout of this fragmentation (particularly from the Late Triassic through the Cretaceous within the Mesozoic) drove the evolution of new species across terrestrial ecologies. Body mass, diet, and breeding habits all experienced major shifts, described in the study through a method called SAR (species-area relationship) modeling. This can offer insight into some interesting paleontological questions: how were enormous herbivories, which exerted great browsing pressure on their ecosystems, able to cohabitate with other organisms? How was the relative size of organisms impacted by vast geological changes, and how did these changes influence biodiversity? These inquiries, however, are unfortunately affected by undersampling. Certain areas of the globe are more sparsely recognized in the fossil record due to research bias—which only stresses the import of increased interdisciplinary (paleontology, geochemistry, climatology, sedimentology) research in less- studied regions.
Data: To describe how speciation was impacted by changes in macroecology shifts (that is, ecology shifts across millions of years), this study primarily utilizes a set of paleontological rules that have been developed by scientists through many studies. Allen’s rule describes how warm-blooded creatures in cooler climates have a smaller surface area to volume ratio in order to conserve heat, and Bergmann’s rule states such organisms are typically larger for heat retention. These are both relevant to changes in body mass at higher latitudes due to continental shifts, for example, dinosaurs at higher latitudes would potentially appear stockier and with shorter limbs, allowing researchers to identify plausible habitats. Additionally, spatial rules such as Damuth’s Law, describes how the relationship between body mass and population density is inverse, such as in the case of Tyrannosaurus rex, where at its massive size, fewer were present in a region. However, because the Earth is not sampled equally, these ‘rules’ can be challenging to test scientifically. This ultimately challenges research, as potential fossil recovery diminishes with less dense populations. By reevaluating past data, broadening our scope of study, and persisting current research, more about the macroecology of the fossil record can be understood
Results: Lower latitudes were more likely homes to populations of sauropods (four-legged, long-necked herbivores like Brachiosaurus). Ornithischian (like the Stegosaurus and Triceratops) populations, however, thrived at higher latitudes. Factors such as tooth size and variation in eggshells were notable features contributing to body-size and spatial-variation research. Teeth can be an indicator of size and diet, while eggshells are an eggcellent proxy for habitat—certain pigments in the shells were thermoregulators (i.e. heat-controlling) or could suggest a need for camouflage, as well as nesting habits. As an example, a sauropod’s sandy hole-nests were likely a reliance on using the heat from the ground,, thus, they likely lived in a warmer climate.
This image shows large-scale dinosaur evolution in terms of varying temperature and continental fragmentation over time, including a genus-level tree connecting included taxa.
Significance: By using paleontological principles including Allen’s Rule, Bergmann’s Rule, and Damuth’s Law, researchers can better investigate broad shifts in dinosaur macroecology, and their application to taxonomy, evolution, climate, and geography. The impact of these features’ development in Mesozoic terrestrial ecosystems could offer insight into modern organism’s response to environmental changes, including biotic and abiotic drivers in association with latitude.
Broader Impacts: Going forward, anatomically precise descriptions and perpetually revisited data are essential for accurate descriptions of Mesozoic life, stressing the importance of further research. Sadly, incomplete patches in the terrestrial fossil record makes conclusive data for macroecological trends challenging. Increased data and more even sampling across the globe can help better construct the chronology for these prehistoric communities.
Citation: Chiarenza, A. A. (2024). The macroecology of Mesozoic dinosaurs. Biology Letters (2005), 20(11), 20240392. https://doi.org/10.1098/rsbl.2024.0392