A Guide to the Orders of Trilobites

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Just Starting:
Introduction
Glossary of terms
Geological Time
Major Features
Site Map

Morphology:
Dorsal Morphology
Ventral Morphology
Internal Anatomy
Major Features
Facial Sutures
Hypostome
Cephalon
Thorax
Pygidium
Special Terms
Trilobite Eyes
Prosopon
Abnormalities
Glossary of terms

Classification:
Arthropods
Trilobite Origins
Trilobite Orders
Key to the Orders
Evolutionary trends
Pictorial Guides
Trilobite Families
Trilobite Genera
ICZN Business

Paleobiology:
Ecology
Trace Fossils
Feeding Habits
Paleogeography
Biostratigraphy
Trilobite Localities
Reproduction
Ontogeny
Molting
Enrollment
Extinction

Miscellaneous:
Trilobite FAQ
Trilobite Quiz
Trilobite Links
Trilobite Photos
Trilobite .Preparation
Drawing Trilobites
Trilobite .Imposters
Selected References
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Trilobite folio
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A Guide to the Orders of Trilobites
A website devoted to understanding trilobites
created and maintained by Sam Gon III

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walking trilobite ©2000
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Postikaolishania jingxiensis Zhu 2005
Sandu Fm., U. Cambrian, Furongian Ser.
Jingxi, Guole Cty., Guangxi Prov., China

From 2019 forward, the Trilobite of the Month will be posted in the Trilobites Group on Facebook. Look for detailed descriptions of these showcased trilobites at the start of each month. I end the monthly updates here with one of my favorites from the archives of nearly a decade of TOMs: Postikaolishania jingxiensis from China, a ceratopygid member of Order Asaphida, from the Furongian Series (Late Cambrian). I love its classic trilobite look, sharp pleural spines, graceful head shield, well-developed eyes, and the clearly differentiated central and paired lateral lobes that define "trilobite."

Images like this help explain why trilobites are one of the best-known and appreciated groups of prehistoric animals. Each month, a new example of trilobite diversity will be showcased here. With over 20,000 described species, we may never exhaust the possibilities! If you have a stunning image of a trilobite that you could share as a future "Trilobite of the Month," please let me know!

Maurotarion christyi is a good representative trilobite

Trilobites are the most diverse group of extinct animals preserved in the fossil record. Ten orders of trilobites are recognized, into which 20,000+ species are placed. Learn more about trilobite morphology, anatomy, ecology, behavior, reproduction, and development, and how they relate to trilobite origins, evolution, and classification. Explore trilobite biostratigraphy, paleobiogeography, persistence across geological time, and their ultimate extinction. View galleries of trilobite images from the web, examine fact sheets, pictorial guides, and an identification key for each order, refer to a family listing, a genus listing, or consult a trilobite glossary and bibliography, tour world famous trilobite localities, explore links to other web resources on trilobites, and review books on trilobites, including an exclusive hardcopy pictorial adaptation of this website.

Maurotarion christyi via Marc Behrendt.

Fact
Sheets

Order Agnostida: highly specialized design

The Redlichiida: Most primitive order of trilobites

Corynexochida: spiny Cambrian predator trilobites

some of the most ornate trilobites are Lichida

The eyes have it! Phacopid compound eyes are distinctive

One of the last survivors - Proetida persisted until the Permian

Over 20% of all trilobites belong to the large order Asaphida

trilobites with a fenestrated fringe -- order added in 2020

The fundamental trilobite design typifies this order

Click on the images, menu choices, or the FAQ listings below on this page to start exploring aspects of trilobite biology, and the salient characters that define the orders, constituent suborders, and superfamilies.

This site has enjoyed feedback from a growing number of trilobite workers from all over the world who have
generously offered their suggestions and corrections. I gratefully acknowledge their help and encouragement.
This website protected by copyright ©1999 - 2020 by S. M. Gon III

The Trilobite FAQ
Use the links on the right to answer the Qs on the left

	Unfamiliar with trilobites altogether?		Introduction to Trilobites
	What are trilobite body parts called?		Trilobite Dorsal Morphology
	Unfamiliar with trilobite undersides?		Trilobite Ventral Morphology
	What about the inside of a trilobite?		Trilobite Internal Anatomy
	What was special about trilobite eyes?		Trilobite Eyes & Vision
	Want definitions of trilobite terms?		Glossary of Trilobite Terms
	How are the trilobite orders related?		Trilobite Systematic Relationships
	Want a list of all trilobite families?		Phylogenetic List of Trilobite Families
	Want a list of all trilobite genera?		List of 5000 Trilobite Generic Names
	How long ago did trilobites exist?		Geological Time relevant to Trilobites
	Can trilobites help determine geological time?		Trilobite Biostratigraphy
	What ecological roles did trilobites play?		Trilobite Ecology and Environments
	How do we know about trilobite behavior?		Trilobite Trace Fossils
	What and how did trilobites eat?		Trilobite Feeding Habits
	How did trilobites reproduce and grow?		Trilobite Reproduction & Development
	What roles did sutures play in molting?		Trilobite Sutures & Molting
	What about trilobite bumps and spines?		Trilobite Prosopon
	How did trilobites defend themselves?		Trilobite Enrollment & Coaptation
	How did trilobites evolve?		Trilobite Evolutionary Trends
	What is the origin of trilobites?		Trilobites Origins
	What were the first trilobites?		The First Trilobites
	What were the last trilobites?		Trilobite Extinction
	Did trilobites show any signs of disease?		Trilobite Abnormalities
	Didn't I see a living trilobite?		Trilobite Imposters
	Where in the world are trilobites found now?		World Trilobite Localities
	How did the Earth look when trilobites lived?		Trilobite Paleogeography
	Think you know about trilobites now?		Take the Trilobite Identification Quiz!
	How big did trilobites get?		World's Largest Trilobites
	How do you prepare a trilobite fossil?		Trilobite Preparation
	Is this site available in hardcopy form?		Yes! Preview the folio pages here
	Are there many books on trilobites?		Review recommended trilobite books!
	Found mistakes or refinements needed?		Please tell me about them

SEARCH THIS WEBSITE THIS SITE OPTIMIZED FOR VIEWING AT 1024 X 768 RESOLUTION

In these pages, you may recognize species that are common, well-known, or sitting in a familiar museum collection!
This guide might help you arrange trilobite diversity systematically, aid in identification of specimens, and enhance your understanding of these fascinating elements of Paleozoic biodiversity. Happy browsing! -- Sam Gon III

Trilobite Order Fact Sheets
detailed, descriptive characters and representative line drawings

Click on any of the images above to be sent to a page featuring details on trilobites in that Order
...

Trilobite Order Galleries
trilobite images from various locations on the web, arranged by order

Agnostida Redlichiida Corynexochida Odontopleurida Lichida Phacopida Proetida Trinucleida Asaphida Harpetida Ptychopariida

Click on any of the images above to be sent to a gallery featuring photos of trilobites in that Order


Asaphus kowalewski Order Asaphida	SOURCES: The information in these pages was developed via examination and synthesis of the data present in a variety of works, including the two "Trilobite Treatises:" Moore 1959 (Treatise on Invertebrate Paleontology, Part O, Arthropoda 1, including Trilobitomorpha) and Whittington et al 1997 (Treatise on Invertebrate Paleontology, Part O, Arthropoda 1, Trilobita, Revised, Volume 1: Introduction). Both may be reviewed here. Other important sources are cited in specific pages of this site, and are also listed in a brief bibliography. Sources of photos and line drawings (where not original) are clearly cited. Other trilobite web sites and individuals were inspirational sources and are cited where relevant. The three trilobite thumbnail images in the left column, for example, are c/o Andrew Milner. If you find your information or images on these pages without proper attribution, this is unintentional. Please contact me to rectify the situation.
Elrathia kingi Order Ptychopariida	CAVEATS: Information about extinct animals is always subject to interpretation and differences of opinion. In particular, the higher classification of arthropods and trilobites is neither simple nor agreed upon by all trilobite workers. The summaries here are complicated by the fact that the 1997 revision of the Treatise only covers two orders in detail: Agnostida and Redlichiida. The others are in preparation, so my attempts to synthesize data on the other orders is likely to be incomplete, although the arrangement of the families and some characteristic descriptions were provided by Fortey (in Whittington et al 1997), and adjusted via recent articles (e.g., papers dealing with higher classification of the Asaphida, Proetida, Harpetida, Agnostida, Trinucleida, and Lichida). Additional revisions continue to be suggested by various workers. Any errors in the information here should be attributed to the compiler, Sam Gon III. Please inform him of any problems in accuracy or interpretation.
.... Sthenarocalymene celebra Order Phacopida	ABOUT THE AUTHOR: This site's pages (and the majority of its figures) were designed and created by Dr. Sam Gon III, a biologist (PhD, Animal Behavior; MA, Zoology (Ecology, Behavior and Evolution) who is greatly intrigued by the expression of ancient biodiversity that trilobites represent. Sam's professional work is in the conservation of global biodiversity today. He serves as the Senior Scientist for The Nature Conservancy's Hawai‘i Field Office in Honolulu. Sam has long been interested in paleobiology, and in teaching himself about trilobites, using hyperlinks to cross-reference terminology and concepts, found himself developing a web resource of potential interest to a broader audience. The site was first unveiled in August 1999 and has attracted feedback from around the world, generating ongoing updates. For all the accolades this site has gathered, Sam is not a professional trilobitologist, but a devoted trilobitophile! In 2006 this culminated in his first paleontological publication, dealing with trilobite origins. Dr. Sam Gon III c/o The Nature Conservancy of Hawai‘i, 923 Nuuanu Avenue, Honolulu, HI 96817, USA

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Elrathia kingi are one of the most abundant trilobites in the world
These ptychopariids are found in Cambrian deposits in Utah, USA

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