Fossil Brachiopods

Brachiopod fossils. Supai Group. Grand Canyon National Park.

NPS photo by Michael Quinn.

Introduction

Brachiopods are one of the most common marine invertebrate fossils found in Paleozoic rocks in national parks. Brachiopods, sometimes called “lamp shells,” filled many of the ecological niches in Paleozoic oceans that bivalves have occupied in Mesozoic and Cenozoic oceans after approximately 95% of brachiopods species became extinct at the end of the Paleozoic.

Phylum Brachiopoda

Brachiopoda were a dominant group of marine organisms during the Paleozoic. Their name comes from the Greek words brachion, meaning “arm,” and podos, meaning “foot.” This references to their internal anatomy. Brachiopods were once thought to be mollusks, which have a muscular internal foot. Instead of a foot, brachiopods have a feeding organ (a lophophore—see below) that grows as two “arms,” leading to the name “arm-foot.” They are also sometimes called “lamp shells” because some of their shells resemble ancient oil lamps.

Brachiopods still exist today, but their shells are rarely found on beaches because most of them live in deep, cold marine waters. Their heyday was in the Paleozoic. Brachiopods first appeared in the Cambrian Period, and have one of the best fossil records of any invertebrate group.

Brachiopods generally have two shells (valves) that differ in size and shape. As a result, they have a superficial resemblance to bivalve mollusks. However, in most bivalve mollusks (except oysters), the two shells are mirror images of one another. In contrast, in brachiopods, each of the two shells have their own right-left symmetry but are not mirror images. One of the two shells usually supports a fleshy stalk-like organ called a pedicle that attaches the brachiopod to a surface. Many brachiopod shells have notable surface features such as ribbing, concentric ridges, growth lines, and fine spines. Overall, brachiopods have a lot of variety!

There are also fundamental differences between brachiopods and mollusks in internal anatomy and feeding habits. Brachiopods possess a distinctive feeding and respiratory organ called a lophophore—a ring of tentacles with the mouth inside. The tentacles move to create a current that brings water and food to the animal. The lophophore does not usually fossilize, but some brachiopods have a mineralized internal structure called a brachidium that supports the lophophore, and this can sometimes be found in well-preserved fossils. Brachiopods also lack the ligament that bivalves have that helps open a bivalve shell.

Brachiopods are generally divided into two informal groups: inarticulate and articulate. Articulate brachiopods have a toothed hinge and a simple muscle system for opening the shells. Inarticulate brachiopods lack hinges and had more complex musculature for opening the shells. The shell composition often differs as well: many inarticulate brachiopods have shells of calcium phosphate, like our bones, whereas all articulates have shells of calcium carbonate. This means that articulate shells are more prone to dissolution and replacement over geological time.

Brachiopod Fossils in National Parks

^{Late Devonian brachiopods from Noatak National Preserve.
Photo courtesy of Robert B. Blodgett.}

^{Permian productid brachiopod from Lake Mead National Recreation Area.
NPS photo by Andy Cattoir.}

^{Brachiopod. Guadalupe Mountains National Park.
Photo featured in Identification Guide to the Fossils of the Guadalupe Mountains by Mary Carol Coleman and Cameron Coleman.}

^{Molds and casts of brachiopods Mississippi National River and Recreation Area.
NPS photo by Justin Tweet.}

^{Well-preserved brachiopod fossil showing a wing-like brachidium. Carlsbad Caverns National Park, New Mexico.}

Early Ordovician inarticulate brachiopods. Great Basin National Park.

NPS photo by Gordon Bell.

Brachiopod fossils are known from at least 73 parks, mostly in assemblages that include other common Paleozoic marine invertebrates such as bryozoans and crinoids. Almost all of the records are Paleozoic in age. Death Valley National Park in California and Yukon-Charley National Preserve in Alaska have brachiopods from units that were deposited throughout most of the Paleozoic. St. Croix National Scenic Riverway in Wisconsin and Minnesota contains many Cambrian brachiopods, while Great Basin National Park in Nevada has both Cambrian and Ordovician brachiopods. Ordovician and Devonian brachiopods are among the most common fossils in Chesapeake and Ohio Canal National Historical Park in Washington, DC, Maryland, and West Virginia.

The rich fossil record of Devonian invertebrates at Delaware Water Gap National Recreation Area in Pennsylvania includes brachiopods and Mississippian brachiopods are evident at Mammoth Cave National Park in Kentucky.

Brachiopods were particularly diverse during the Permian, with important Permian fossils in parks like Carlsbad Caverns National Park in New Mexico.Many brachiopod species have been named from Grand Canyon National Park in Arizona, Guadalupe Mountains National Park in Texas, Yellowstone National Park in Wyoming, and Mississippi National River and Recreation Area in Minnesota.

Coloring Book Pages

Featured Parks

• Carlsbad Caverns National Park (CAVE), New Mexico—[CAVE Geodiversity Atlas] [CAVE Park Home] [CAVE npshistory.com]

• Chesapeake and Ohio Canal National Historical Park (CHOH), Washington DC, Maryland, and West Virginia—[CHOH Geodiversity Atlas] [CHOH Park Home] [CHOH npshistory.com]

• Death Valley National Park (DEVA), California and Nevada—[DEVA Geodiversity Atlas] [DEVA Park Home] [DEVA npshistory.com]

• Delaware Water Gap National Recreation Area (DEWA), New Jersey and Pennsylvania—[DEWA Geodiversity Atlas] [DEWA Park Home] [DEWA npshistory.com]

• Grand Canyon National Park (GRCA), Arizona—[GRCA Geodiversity Atlas] [GRCA Park Home] [GRCA npshistory.com]

• Grand Canyon-Parashant National Recreation Area

• Great Basin National Park (GRBA), Nevada—[GRBA Geodiversity Atlas] [GRBA Park Home] [GRBA npshistory.com]

• Guadalupe Mountains National Park (GUMO), Texas—[GUMO Geodiversity Atlas] [GUMO Park Home] [GUMO npshistory.com]

• Lake Mead National Recreation Area (LAKE), Arizona and Nevada—[LAKE Geodiversity Atlas] [LAKE Park Home] [LAKE npshistory.com]

• Mississippi National River and Recreation Area (MISS), Minnesota—[MISS Geodiversity Atlas] [MISS Park Home] [MISS npshistory.com]

• Noatak National Preserve (NOAT), Alaska—[NOAT Geodiversity Atlas] [NOAT Park Home] [NOAT npshistory.com]

• Yellowstone National Park (YELL), Idaho, Montana, and Wyoming—[YELL Geodiversity Atlas] [YELL Park Home] [YELL npshistory.com]

• Yukon-Charley Rivers National Preserve (YUCH), Alaska—[YUCH Geodiversity Atlas] [YUCH Park Home] [YUCH npshistory.com]

Related Links

• Grand Canyon—Bracioipod

Body Fossils