- Origins of Life
- Journey onto Land
- Paleozoic Seas
- Mammal-Like Reptiles
- Triassic Petrified Forest and Wetlands
- Kayenta Formation
- Cretaceous Seas
(4.5 billion to 65 million years ago)
Take a walk through time at the Arizona Museum of Natural History. From the origins of the universe, the formation of rocks and minerals, to the origins of life, explore Paleozoic Seas, Mammal-like Reptiles, Triassic Petrified Forests and Wetlands, Cretaceous Seas, and First Flight!
In this first gallery of the Arizona through Time, explore the origins of the universe, galaxies, comets, asteroids and the solar system. See and touch several meteorites, including a replica of the Tucson Meteorite and a piece of the Canyon Diablo Meteorite, which created Meteor Crater when it struck the earth in what is now Arizona.
Earth Science: Rocks, Minerals & Caves
In the Earth Science Hall, discover the difference between rocks and minerals. Learn how the three types of rocks, sedimentary, igneous and metamorphic, are formed. Discover the essential minerals and see blue and green copper minerals and red and orange lead minerals. Touch a drusy chrysocolla boulder and quartz crystals! Learn all about caves.
Origins of Life
Life originated on earth nearly 4 billion years ago, yet multicellular life, organisms composed of more than one, differentiated cells, did not appear for over 3 billion years. Thus most of the history of life on this earth is little known.
The emergence of vertebrates onto land, and the transition from fish to amphibian is well known. Less appreciated is the emergence onto land of plants and at least eleven other animal groups.
Symmorium, an ancestor of sharks, lived in the Pennsylvanian Period, 311-290 million years ago, when warm, shallow seas covered much of present day Arizona.
Inostrancevia belongs to the group of mammal-like reptiles known as therapsids. This individual lived during the Permian Period, about 245 million years ago, in what is now Russia. Note how the teeth are of different shapes and sizes, a trait he shares with mammals.
Estemmenosuchus was a mammal-like reptile with horns that remind one of a moose. He was about the size of a modern rhinoceros and lived in the Late Permian Period of Russia, 245 million years ago.
Postosuchus (left), a carnivore, confronts Placerias, a herbivore in the Late Triassic forest of Arizona, 225 million years ago. These animals lived in the forests that today we know as the "petrified forest" of northern Arizona.
Buettneria was a large amphibian that lived in the wetlands adjacent to what are now the petrified forests. A lie-in-wait predator, Buettneria lived in the Late Triassic, 225 million years ago.
Leptosuchus is a phytosaur, a group of reptiles that resemble crocodiles but evolved their form independently. He, along with Buettneria inhabited the wetlands adjacent what are now the petrified forests of Arizona.
Dilophosaurus is arguably the most famous dinosaur from Arizona. Notable for the two crests on its head, this predator lived in the Early Jurassic Period, about 200 million years ago. Dilophosaur remains and footprints have been found in the Kayenta Formation of northeastern Arizona.
100 million years ago a warm seaway teeming with marine life separated eastern and western North America. Some terrestrial reptiles returned to the sea in the earlier Triassic Period (252-201 million years ago), some much later. The three marine reptiles shown here, mosasaur, pliosaur and sea turtle, represent three separate re-invasions of the sea. Maps courtesy Ron Blakey, Colorado Plateau Geosystems, http://cpgeosystems.com/
This dramatic diorama represents the Black Mesa area of what is now Arizona during the Cretaceous Period. Marine reptiles congregate in a feeding frenzy near the shore on a warm night. The long-necked pliosaur has the toothy Encholus in its jaws, unaware that the mosasaur will deliver to it the same fate.
Mosasaurs are not closely related to other marine reptiles but are in actuality gigantic lizards that have returned to the sea from the land. These voracious predators developed an extra jaw hinge that allowed them to open their mouths widely and clamp down on their prey. Mosasaurs are most closely related to today's monitor lizards and Gila monsters. Fragmentary remains have been found in the deposits of Cretaceous seas covering northeastern Arizona 100 million years ago.
Pliosaurs are a type of plesiosaur, a marine reptile with a large bulbous body, long neck, small head and four large flippers. Pliosaurs had a shorter neck and longer head.
The sea turtle Desmatochelys belongs to the same lineage as modern sea turtles. Turtles are the only group of marine reptiles from the Cretaceous Period to survive today.
Xiphactinus audax was the largest bony fish of the Cretaceous, reaching a length of 20 feet or perhaps larger. Xiphactinus swallowed its prey whole, and several specimens have been found with large, undigested prey inside. It is likely that these Xiphactinus died from trying to swallow the large, struggling prey. Xiphactinus fossils have been found worldwide, including the middle Cretaceous Black Mesa sediments of Arizona, about 100 million years old.