From the Arizona Geological Survey:
Susan Celestian of Phoenix’s Earth Science Museum cobbled together a nice pictorial on common fossils of Arizona to round out Earth Science Week 2020. You can view or download the 12-page report here.
What is a fossil? Fossils are the prehistoric physical remains (or traces) of organic life. By definition, prehistoric means older than 6000 years, although some people define the minimum age of 10,000 years, before a specimen is called a fossil.
It is hard to become a fossil. While billions of organisms have lived and died through geologic time, very few of them have been preserved in the fossil record.
By using fossils, we can develop a history of lifeforms & increase our understanding of biological evolution.
Fossils assist geologists in establishing a chronological order to geological events and strata. Fossils can be used to establish a relative age date1 for a rock unit. This is best employed by using index fossils (fossils with short and distinct spans of existence, and wide geographic distribution) and unique assemblages of fossils (rather than individual fossils).
This report contains a further explanation of fossils and shows many photographs.
One fossil not mentioned in the report is that of a dinosaur.
Dinosaurs roamed the land, including Arizona’s Sonorasaurus thompsoni, a new species of brachiosaurid dinosaur whose remains were first discovered in the Whetstone mountains by UofA graduate geology student Richard Thompson in 1994. Sonorasaurus is estimated to have been about 50 feet long and 27 feet tall, about one third of the size of other brachiosaurus. It may have been a juvenile or just a small dinosaur species. Sonorasaurus was an herbivore. Tooth gouges on its bones suggest it was killed and eaten by a larger dinosaur. A single blade-like tooth of a huge meat eater called Acrocanthosaurus was found near the bones and suggests that this was the predator that killed Sonorasaurus. You can see an exhibit dedicated to Sonorasaurus at the Arizona-Sonora Desert Museum.