The Triassic Transition The Age of Reptiles Begins As the Paleozoic drew to a close through the Carboniferous and Permian several important processes were at work. Assembly of Pangea Evolutionary radiation of seed-bearing plants Evolutionary radiation of large amphibians Labyrinthodonts Evolutionary radiation of the Synapsids
Temnospondyl Amphibians frog-gators Temnospondyl Amphibians frog-gators
Permian Period - Synapsids rule the Earth Synapsids were the ancestors of mammals. Pelycosaurs - reptile - like Therapsids - probably much more mammalian Cynodonts - mostly carnivorous Dicynodonts - mostly herbivorous Pelycosaurs - Permian synapsids ancestors of later therapsids and mammals Dicynodont synapsids Cynodont synapsids
Dicynodont Permo-Triassic Mass Extinction Occurs in several pulses at the end of the Permian. 90% - 95% of all marine animal species go extinct. Many species of synapsids and labyrinthodonts go extinct. The Triassic world is depauperate. Reptiles begin a long adaptive radiation. All major clades of archosaurs evolve in the Triassic
Ma T r i a s s i c Jur. Early Middle Late 245 240 230 208 Reptilia Archosaurs Other Misc. primitive Archosauromorph groups Ichthyosaurs Rhynchosaurs Crocodilians Ornithsuchians Rauisuchians Lagosuchids Placodonts Nothosaurs Phytosaurs Aetosaurs Dinosaurs Pterosaurs Turtles Synapsida Dicynodonts Cynodonts Mammals "Amphibia" Labyrinthodonta Capitosauroids Plagiosaurs Brachyopoids Lissamphibia Metoposaurs "mostly Paleozoic holdovers" "diapsid evolutionary radiation" "evolution of later Mesozoic fauna" Triassic Ichthyosaurs Middle Triassic Many new archosaur clades evolve - thecodonts. Archosaurs become large, top carnivores. Archosaur clades divided into two groups based on ankle structure. Crocodile normal. Crocodile reverse.
Ma T r i a s s i c Jur. Early Middle Late 245 240 230 208 Reptilia Archosaurs Other Misc. primitive Archosauromorph groups Ichthyosaurs Rhynchosaurs Crocodilians Ornithsuchians Rauisuchians Lagosuchids Placodonts Nothosaurs Phytosaurs Aetosaurs Dinosaurs Pterosaurs Turtles Synapsida Dicynodonts Cynodonts Mammals "Amphibia" Labyrinthodonta Capitosauroids Plagiosaurs Brachyopoids Lissamphibia Metoposaurs "mostly Paleozoic holdovers" "diapsid evolutionary radiation" "evolution of later Mesozoic fauna" Ankle Structure in Archosaurs Tibia Fibula Astragalus hinge Calcaneum hinge Crocodile Normal Crocodile Reverse Terrestrisuchus 10 cm Gracilisuchus Crocodile normal Small terrestrial crocodilians
Paradepedon 1 meter Rhynchosaur Ticinosuchus Crocodile normal Rauisuchid Crocodile reverse 1 meter Ornithosuchus Ornithosuchid Most dinosaur-like Thecodont Lagosuchus Prestosuchus Crocodile reverse
Late Triassic Additional new archosaur clades evolve. Phytosaurs (very crocodile-like) Aetosaurs (armored herbivores) Pterosaurs (flying reptiles) Dinosaurs Turtles evolve. True mammals evolve. Ma T r i a s s i c Jur. Early Middle Late 245 240 230 208 Reptilia Archosaurs Other Misc. primitive Archosauromorph groups Ichthyosaurs Rhynchosaurs Crocodilians Ornithsuchians Rauisuchians Lagosuchids Placodonts Nothosaurs Phytosaurs Aetosaurs Dinosaurs Pterosaurs Turtles Synapsida Dicynodonts Cynodonts Mammals "Amphibia" Labyrinthodonta Capitosauroids Plagiosaurs Brachyopoids Lissamphibia Metoposaurs "mostly Paleozoic holdovers" "diapsid evolutionary radiation" "evolution of later Mesozoic fauna" Parasuchus 1 meter Phytosaur Stagonolepus Crocodile normal Aetosaur
Phytosaurs Aetosaurs 26 Dimorphodon Pterosaurs - flying reptiles
Proganochelys Chelonians - turtles Therapsids evolve into primitive mammals. Staurikosaurus 1 meter Dinosauria
General Characteristics of Triassic Dinosaurs Low diversity / low abundance. Small size. Bipedal. The first dinosaurs were not ecologically dominant. Why do they take over in the Jurassic? Ma Hettangian 208 Jurassic Boundary (Rhaetian) 211 Dinosaurs become common. U Norian M Dinosaurs become more abundant and diverse. L 225 230 Carnian Ladinian Prosauropods Theropods Ornithischians Saurischians Dinosaurs evolve? Pisanosaurus Other ornithischians Prosauropoda Eoraptor Herrerasauridae Other Theropods Ornithischia Theropoda No fossil record Saurischia DINOSAURIA
Carnian Dinosaur Species Carnivores - primitive theropods Eoraptor - Argentina Staurikosaurus - Argentina Herrerasaurus - Argentina Herbivores - primitive ornithischians Pisanosaurus - Argentina Technosaurus - Texas Herbivores - prosauropods Azendohsaurus (teeth) - Morocco Lesothosaurus 1 meter Ornithischian Early Dinosaurs Prosauropod Pisanosaurus merti Oldest known herbivorous dinosaur. Many ornithischian characteristics.
Staurikosaurus pricei Similar to Herrerasaurus. Only two sacral vertebrae. Basal theropod? Eoraptor lunensis Most primitive dinosaur known - very similar to Lagosuchus. 3-fingered hand. 3-toed foot. Basal theropod? Herrerasaurus Difficult to classify Characters in common with theropods, sauropods, and ornithischians. Most likely a basal theropod. May predate split between saurischians and ornithischians.
Herrerasaurus - definitely a dinosaur! Digits IV and V reduced Hinge-like ankle joint hole in hip socket 3-toed foot