Evolução dos Amniotas, Contribuições da paleontologia para o ensino de Ciências Biológicas

Abstract

This review explores the evolution of amniotes, focusing on taxonomic groups such as mammals, lizards, and turtles, with an emphasis on the ecological and evolutionary shifts triggered by the mass extinction at the Permo-Triassic boundary. This event led to a significant reorganization of terrestrial ecosystems, promoting the emergence of new groups like archosaurs (including dinosaurs and crocodiles) over synapsids, the ancestors of mammals. The evolution of upright postures among dinosaurs and crurotarsans made locomotion more efficient, facilitating greater activity and possibly favoring the evolution of endothermy. Dinosaurs showed superior adaptation to the arid climate of the Late Triassic, exhibiting traits like waterproof skin and semi-solid urine, which advantaged them over mammals, whose physiology required more water for homeostasis. Additionally, this review discusses the evolution of early mammals, which coexisted with dinosaurs and explored varied ecological niches, despite being small and rare in the Mesozoic. Notable specializations included burrowing (Fruitafossor), gliding (Volaticotherium), and aquatic lifestyles (Castorocauda). The origin of turtles is also examined, highlighting their unique evolutionary features, such as the dorsal carapace and ventral plastron, and the complexity of their ancestry, illustrated by fossils like Chinlechelys and Odontochelys. The text further examines the evolutionary trajectory of crocodiles, which initially occupied terrestrial habitats but adapted to aquatic environments after the extinction of phytosaurs and temnospondyl amphibians at the end of the Triassic, establishing themselves as aquatic predators from the Jurassic onward. The Triassic-Jurassic transition marks a crucial period for the evolution of both terrestrial and marine vertebrates. In the Late Triassic, the first modern bony fishes, the teleosts, represented by Pholidophorus, emerged with adaptations like reduced scales and efficient caudal fins, facilitating their expansion in aquatic ecosystems. Simultaneously, neoselachians replaced hybodonts as primary predators, benefiting from calcified vertebral columns that enhanced their strength and speed. Changes in terrestrial ecosystems are also discussed, including the mass extinction of specialized herbivores such as dicynodonts and rhynchosaurs, and the adaptive success of generalist dinosaurs in arid conditions. In marine environments, despite overall stability, there was an accelerated diversification of teleosts and modern sharks in response to the conditions of the Tethys Sea, providing an ideal setting for the emergence of these lineages. This period is marked by the rise of new lineages adapted for speed and agility in both terrestrial and marine vertebrates. This review synthesizes recent paleontological findings on major evolutionary transformations of vertebrates in the Triassic and Jurassic, offering updated support material for advanced courses in Biological Sciences and fostering a broad understanding of the evolutionary dynamics that shaped Mesozoic fauna.