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Petrified Wood from the Triassic (208 to 245 million years ago) Chinle Formation of Arizona

During the Triassic period over 200 million years ago, ancestral Arizona was located in the northwestern corner of the supercontinent Pangaea. At that time, the area had a tropical climate and a vast forest grew upon a relatively flat-lying terrain. Downed trees that accumulated in river flood plains and channels were periodically buried by floods carrying fine-sediment. Over time, these logs were buried deep under thousands of feet of sediment and eventually became petrified. Uplift and erosion once again exposed the wood at the surface; however, this time the wood was replaced with quartz and agate and more resistant to weathering than the fine-sediments that encompassed them. Now, the petrified wood is exposed and broken logs and fragments cover the ground in places.

Araucarioxylon arizonicum, is an extinct species of conifer and the state fossil of Arizona. It represents the most abundant petrified wood found in the Chinle Formation. It is commonly called “Rainbow Wood” due to the large variety of colors it can exhibit. Iron and its oxide mineral forms produce the varying colors within the agatized structure of the wood. A. arizonicum grew to 200 feet (60 meters) tall.

Woodworthia arizonica is probably the second most common tree in the Petrified Forest. It is characterized by circular small scars on the outer surface of the tree rounds. In cross-section view these scars are usually shone as white veins radiating outward from the central core of the tree. W. arizonica grew to 105 feet (32 meters) tall.

Schilderia adamanica is somewhat rare in the Petrified Forest. Based upon a cross-sectional view, it is recognized by its numerous thin veins radiating outward from the central core. Its classification in relation to other members of the plant Kingdom is uncertain. S. adamanica grew to 118 feet (36 meters) tall.

Charles Darwin Sculpture

Darwin displayDr. Daniel J. Fairbanks (Professor of Biology and Research Geneticist, Brigham Young University) sculpted this bust of Charles Darwin while lecturing on our genetic heritage as part of Sierra College’s Natural History Museum Lecture series titled “Relics of Eden: The Powerful Evidence of Evolution in Human DNA” (February 2010).

New in the History of Life Exhibit

Anomalocaris - Predator of the Cambrian Seas

AnomalocarisSometimes it is difficult to describe what a 600 million year old animal looks like when you only have fossil parts to work with. The museum invested in an Anomalocaris model to portray what these animals may have actually looked like. This model was modified and painted by museum volunteer Tom Johnston, and goes well with the fossilized spiked-arm fragments that Tom found in Nevada and graciously donated to the Museum. The barbed spikes of the two arms were used to pull their victim (usually a trilobite) toward their disk-like mouth that would crush the hard shell of their prey. Anomalocaris was a gigantic creature of its time and could grow to one meter (~3 feet) in length.

What in the world is a Tully Monster you ask?

Tully MonsterGood question. In order to answer this question, the Museum purchased a model of a Tully Monster (Tullimonstrum gregarium) to go with the fossilized specimen donated to the Museum by Stanley Davis. The Tully Monster was named after Francis Tully who discovered this creature in 1958. It is the State Fossil of Illinois because the fossil remains of these creatures are unique to a formation in this state. A Tully Monster is described as a strangely-designed, soft-bodied, marine, vertebrate that hunted its prey in shallow estuaries 300 million years ago. As the model demonstrates, it was a very interesting creature. New information has shown it to be a vertibrate.


TiktaalikIn order to show the transition or link between fish and amphibians, the Museum purchased a replica of the fossil remains of Tiktaalik (tik-ta-lik). This fish lived 375 million years ago in Devonian times. Tiktaalik was a lobe-finned fish with features similar to four-legged (tetrapod) animals. Its front fins have basic wrist and finger bones that could support its weight unlike an ordinary fish fin. Thus the term “fishapod” was coined - fish with feet. Tiktaalik may have been the first fish that ventured out onto land.

Horseshoe Crab

This horseshoe crab has been mounted near the trilobite display because it is more closely related to the extinct trilobites than crabs. Horseshoe crabs are “Living Fossils” meaning that they survived millions of years with little change to their physical form. Fossilized specimens have been found in Ordovician (~455 million years ago) aged rocks in North America. It is speculated that they may have existed since the Cambrian period (~600 million years ago). As with trilobites, a horseshoe crab grows larger by molting and shedding its shell. During its lifespan, and if conditions are right, one crab or trilobite can produce several potential fossils from its molted shells.

There are four species of horseshoe crabs alive today. They can be found on the eastern coasts of North and Central America, and in the Indo-Pacific (Japan’s Seto Inland Sea and along the east coast of India). The larva and adult stages of the Japanese version look very similar to the earliest forms of trilobites. During full and new moons in May and June at high tides, the adult horseshoe crabs swarm the wave protected beaches of bays and coves to spawn.

A female crab, which is much larger than the male, can develop 80,000 eggs in one spawning season. Most of these eggs are consumed by birds and fish.

The blood (copper based instead of iron) of horseshoe crabs is used to ensure that intravenous drugs, vaccines, and medical devices, are free of bacterial contamination before they are used on humans.

From the Ceiling

Thalattosaur - “Ocean Lizard”

ThalattosaurRick Campbell of Sacramento created this life-size model of a prehistoric marine reptile called a Thalattosaurus. Thalattosaurs lived in shallow seas of the Triassic period 210 million years ago. Fossils of these animals have been recovered from limestone outcrops of Shasta County, California. This model is a spectacular addition to the Museum and it is displayed near the Ichthyosaur wall-mount replica on loan from the California Academy of Science. The ichthyosaur is also a marine reptile of the Triassic so these animals coexisted in the shallow sea that once covered California over 200 million years ago.

Amethyst crystals close-up


Some amethyst tubes are created in pockets (vugs) formed by volcanic material flowing over trees. The crystals produced vary in color from medium liac to a darker purple. A five foot amethyst tube is now on display near the entrance to S110.

What's This Going to Be?

Fossil from the JurassicThis lump was donated to us and we are slowly exposing its secrets. It is from the Morrison Formation in Utah and dates from the Jurassic. This photo is what it looked like a while back, but we've chipped away more sandstone since then. You'll have to wait until it is on display to see what it is. (Unless you can guess now!)

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