Extreme ecosystem instability suppressed tropical dinosaur dominance for 30 million years

Abstract

A major unresolved aspect of the rise of dinosaurs is why early dinosaurs and their relatives were rare and species-poor at low paleolatitudes throughout the Late Triassic Period, a pattern persisting 30 million years after their origin and 10-15 million years after they became abundant and speciose at higher latitudes. New palynological, wildfire, organic carbon isotope, and atmospheric pCO 2 data from early dinosaur-bearing strata of low paleolatitudes in western North America show that large, high-frequency, tightly correlated variations in δ 13 C org and palynomorph ecotypes occurred within a context of elevated and increasing pCO 2 and pervasive wildfires. Whereas pseudosuchian archosaur-dominated communities were able to persist in these same regions under rapidly fluctuating extreme climatic conditions until the end-Triassic, large-bodied, fastgrowing tachymetabolic dinosaurian herbivores requiring greater resources were unable to adapt to unstable high CO 2 environmental conditions of the Late Triassic.Early Mesozoic | carbon cycling | atmospheric CO 2 | terrestrial ecosystems | wildfires

The precise temporal calibration of dinosaur origins

“…Accordingly, the origin of dinosaurs did not immediately cause a major shift in ecosystem composition and function at least in the highlatitude tetrapod communities of Gondwana, where they first became dominant. Moreover, these results, along with the delayed rise of dinosaurs in the tropics (38), would reinforce the conclusion that it is unlikely that there was one cause for dinosaurian success and their subsequent dominance. After their origin and rapid initial diversification, dinosaurs were likely part of a gradual evolutionary process that involved several other contingencies, such as climatic change and the end-Triassic extinction of other tetrapod clades, which led to the ultimate global success of the group for the rest of the Mesozoic Era.…”

Dating the origin of dinosaurs

“…This suggests that the initial appearance of dinosaurs was not linked to profound changes in the composition of these ecosystems. dinosaurs gradually diversified at middle to high paleolatitudes, a view consistent with a recent study by Whiteside et al (11) that argued for a considerably delayed rise to dominance of dinosaurs at tropical paleolatitudes. Based on the currently available information, dinosaurs did not become dominant in many ecological roles in continental ecosystems until after the end-Triassic extinction event (12).…”

Dinosaur biogeographical structure and Mesozoic continental fragmentation: a network‐based approach

“…Although this study does not consider palaeocoastline and climatic barriers as these are poorly known in contrast to the well‐constrained continental positions (Upchurch, ), effects of changing coastlines across entire networks are accounted for by incorporating SL into the models. Climatic barriers almost certainly would have limited dispersal of certain dinosaurian taxa, both within and between continental landmasses, and evidence for climatic control on terrestrial tetrapod diversity has been detected in Permo‐Triassic Pangaean (Sidor et al ., ; Ezcurra, ; Whiteside et al ., , ) and Cretaceous Gondwanan (Benson et al ., ; Amiot et al ., ) communities. However, climatic barriers were most likely far less pronounced than in the present day as through much of the Mesozoic pole‐equator gradients were as low as at any other point in the entire Phanerozoic (Huber et al ., ; Holtz et al ., ; Mannion et al ., , ) and dinosaurs appear to have been able to migrate large distances and transcend climate belts in order to colonize new environments (Longrich, ).…”