Mesozoic Era: Triassic Period 

251–201 Ma

The Triassic: wasteland survivors

The Great Dying, a foremost cause of which was the massive eruption of flood basalts that created the Siberian Traps, left the Triassic biosphere a decimated and impoverished wasteland. The flood basalt eruptions released immense amounts of sulfur dioxide, carbon dioxide and methane, seen here in our cloud plumes, which acidified rain waters and the ocean, reduced oxygen content and increased sulfur in the ocean (a condition called euxinia), and drastically increased global temperatures from the relatively cool Permian Period. Nonetheless, life found a way. While woody plants returned within the first ten million years of the period, the extinction survivor species took nearly 30 million years to reestablish complex terrestrial food webs in the Triassic. Of those that experienced an explosion of diversity were the archosauromorph reptiles, fitting within the formerly established sauropsids from the later Carboniferous and Permian. This diversification included the emergence of several new groups, such as the rauisuchians, phytosaurs, and crocodylomorphs. Together, these clades were more closely related to crocodilians than to birds or other dinosaurs. The phytosaurs, as pictured on the shore and taking a dip here, are long-snouted, semi-aquatic, and wear a heavy coat of scaly armor, much like modern crocodiles, but they likely evolutionarily branched from the archosaurs before the split of crocodile- and bird-like ancestors. A former faculty member here at Mizzou over 100 years ago, M.G. Mehl, worked to describe Angistorhinus, a phytosaur from the Triassic of Texas and Wyoming—one of the type specimens of which remains here in our collections. The other organisms pictured here tell an interesting story of convergent evolution through the Permian and Triassic. Earlier in the Permian, non-mammalian synapsids like Dimetrodon and Edaphosaurus were noted for their large sails extending from their spines, most likely evolving as a mechanism for temperature regulation and display to attract a mate or threaten potential rivals. While Dimetrodon and Edaphosaurus didn’t survive beyond the Permian Period, flashing forward into the Triassic in the aftermath of the huge extinction, sailbacks were still fashionable—but this time on the backs of other animals, the rauisuchians, part of the archosauromorphs, and including several taxa like Ctenosauriscus, Arizonasaurus, Lotosaurus, and Xilosuchus. These archosaurs, as sauropsids, are on the other side of the amniote divergence from the synapsids like Dimetrodon, but their sails were very similar in both form and presumed function