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Field Guide Series – Invertebrate Fossils of Arizona

by | Jan 15, 2024

Gain fundamental, practical knowledge of your surroundings.

Invertebrate Fossils of Arizona“Small but Mighty” may be the best way to describe our Easy Field Guides, reviewed by our own Yvonne Prater, Director of Operations. Each book is fully illustrated, and filled with a plethora of interesting facts that are easy to understand to help answer the thoughtful question, “What is that?”

If you missed them, you can read Yvonne’s first nine Field Guide reviews here. This is the tenth guide in the series and is titled “Invertebrate Fossils of Arizona.”

Remnants of Oceans in Arizona

Fossils are remnants of organisms from a past geologic age, and aquatic environments are the most likely places to begin the process of forming a fossil. Arizona – despite the dry conditions found here today – was once covered by lakes, swamps and oceans, and is now rich with deposits of rock formed from water-deposited materials. For example, Paleozoic oceans deposited most of the strata of the Grand Canyon, and the Petrified Forest and Painted Desert are examples of lake-deposited formations containing fossils.

This Field Guide begins by giving you nine vocabulary terms, providing identifying factors of each type of fossil, i.e., the term “septa” refers to internal wall-like structures within the body of an animal separating the animal’s body into chambers, “symmetry” which refers to a regular or balanced arrangement on opposite sides of the same shell or the other half of the same shell, and “solitary” which refers to an animal which can live by itself and does not rely on the services or functions of other members of its species for survival.

Next, the guide asks you questions to try to identify the fossil’s type, i.e., do the septa project in a vertical direction, dividing the animal along its long axis? You will continue the identification process until you are led to a classification at a phylum, class or order level.

Biologists have classified living things into five kingdoms: Monera (bacteria), Fungi (mushrooms), Protista (algae), Metazoa (animals), and Metaphyta (plants). The smallest division of a kingdom is the species which represents a specific animal or plant. Next, we look at the intermediate division between kingdom and species: Kingdom, Phylum, Class, Order, Family, Genus, and Species.

To simplify, let’s put human beings within this framework. We are members of the Kindgom Metazoa, Phylum Chordata, Class Mammalia, Order Primates, Family Hominidae, Genus Homo, Species Homo Sapiens.

Towards the back of this guide, examples of common fossil forms are given with an explanation of the kind of animal the fossil represents, i.e., Rudists and Oysters, which are members of the Phylum Mollusca, Class Bivalvia, but their shells are often not formed with bilateral symmetry and more often than not, have no symmetry at all. They evolved prior to and during the Cretaceous Period and often formed reefs. Unlike other reef forming animals, they were not colonial but were solitary individuals.

The Cretaceous reef at Paul Spur between Douglas and Bisbee, Arizona, was formed by rudists, corals and algaes. The oysters survived, but the rudists did not survive the extinction event at the end of the Cretaceous Period, 144,000,000 years ago. Included in this guide is a geologic timeline, divided into era, period, epoch, and how many years ago each existed.

Visit Riverbanks Gift Shop

There is great pleasure to be had from gaining fundamental, practical knowledge of your surroundings. I hope you enjoy and anticipate each month the selected topics in this series. You can find much more information regarding Invertebrate Fossils of Arizona in this Easy Field Guide. These guides are published by American Traveler Press and can be found in the River of Time gift shop, Riverbanks. We are open Wednesdays through Saturdays from 10 a.m. to 4 p.m.