A Guide to the Orders of Trilobites

The Trilobite of the Month for February 2019 is classified as a primitive member of Order Harpetida from the Late Cambrian. It was a time when many of the more advanced trilobites were beginning to distinguish themselves from the primitive Redlichida and Ptychopariida, so we can sometimes see intriguing characteristics that suggest the affinities of the different orders. This complete specimen of Brachyhipposiderus, for example has a thorax and pygidium that is rather reminiscent of trinucleids, and its cephalic shape is also reminiscent of the trinucleid fringe, lacking the well-developed tall genal prolongations of advanced harpetids.

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!

Agnostida

Redlichiida

Corynexochida

Odontopleurida

Lichida

Phacopida

Proetida

Asaphida

Harpetida

Ptychopariida

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, 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

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 is considered by many the typical trilobite

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, 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

	2007
Proud and honored recipient of the
Listed as an earth sciences resource at: PSIgate Physical Sciences Information Gateway	Geoscience Information Society of the Geological Society of America .	Listed in the journal Volume 292:1803 [Netwatch]

Listed as a web resource on arthropod evolution at the:	Listed as a web resource in biological sciences at:	One of the Ten Cool sites in Natural History at the:
		San Francisco

Geoscience Information Society of the Geological Society of America .

Geoscience
Information Society
of the
Geological Society of America
.