Fossil Cnidarians - Corals, Jellyfish, and Sea Anemones

The tabulate coral Eofletcheria utahia in Great Basin National Park.

NPS photo by Gordon Bell.

Introduction

Corals are the most well-known members of the phylum Cnidaria. These colonial animals have lived in the oceans from the Paleozoic through modern times, although the types of corals have changed through time. The major groups of Paleozoic corals are now extinct. Modern stony corals are major reef builders and are found in warm shallow waters.

Phylum Cnidaria

Cnidarians are a varied group of animals with cells organized into definite tissues. This group includes corals, jellyfish, and sea anemones. They have a stomach and a mouth surrounded by tentacles. Moreover, as their Greek name “cnidos”—meaning stinging nettle—implies, all cnidarians have specialized cells that can inject poison into their prey or hapless passers-by.

Surprisingly, soft-bodied cnidarians such as jellyfish do have a fossil record, but it is quite sparse. None are known from National Park Service units, although what was once thought to be a Precambrian jellyfish (now known to be an inorganic structure) was reported from Grand Canyon National Park.

On the other hand, corals with their hard skeletons left a significant legacy of their existence. Corals are essentially sea anemones that support their bodies by building skeletons of calcium carbonate. Corals with hard structures appeared for the first time in the geologic record in tropical Ordovician environments. These Paleozoic corals, including the distinctive solitary horn corals, represent now-extinct lineages. Most Paleozoic corals were not reef-builders the way that modern corals are. Instead, Paleozoic reefs were often dominated by other groups, such as microbes and sponges. Modern corals are first seen in the fossil record in the Triassic.

Cnidarian Fossils in National Parks

Corals

^{Horn coral in the Upper Devonian–Lower Mississippian Englewood Limestone in Wind Cave National Park. A. Side profile. B. Cross-section.
NPS photo by Theodore Herring.}

Colonial rugose coral, Pakoon Limestone, Grand Canyon-Parashant National Monument.
NPS/2020 Field Inventory.

Fossil stony coral is common in the Pliocene and Pleistocene bedrock of Everglades National Park.

NPS Photo by Denise Diaz.

The National Park System contains a diverse fossil record of corals, with at least 74 parks being identified as containing this kind of cnidarian. Coral fossils are found in marine sedimentary rocks deposited throughout the Phanerozoic, although as mentioned, different groups lived in the Paleozoic versus the Mesozoic and Cenozoic.

Most coral fossils are of one of three groups:

• Rugose corals: Paleozoic solitary and colonial corals with complex vertical structures in the corallites (dwelling cells of individual coral animals). Solitary rugose corals are commonly known as horn corals because of their characteristic shape, resembling an animal horn. They were attached to the sea floor at the narrow end, and the coral organism extended out of an opening at the large end. Corallites of both colonial rugose corals and horn corals are relatively large, sometimes a centimeter or more across. Petoskey stones are rounded and polished fossils of the colonial rugose coral Hexagonaria.

• Tabulate corals: Paleozoic colonial corals that had poorly developed or no vertical partitions in corallites and well-developed horizontal partitions (“tabulae”). Another way to distinguish tabulates from rugose corals is the size of the corallites: tabulates generally had much smaller corallites, on the order of a few millimeters across at most. Some notable examples of tabulate corals include Favosites (“honeycomb coral”), Halysites (“chain coral”), and Syringopora (“organ pipe coral”).

• Stony corals: Mesozoic and Cenozoic reef-forming corals.

Parks with Paleozoic marine sedimentary rocks frequently contain rugose or tabulate coral fossils. Outstanding examples are known from parks such as Death Valley National Park in California and Nevada, Delaware Water Gap National Recreation Area in New Jersey and Pennsylvania, Grand Canyon National Park and its neighbor parks in Arizona and Nevada, Great Basin National Park in Nevada, Mammoth Cave National Park in Kentucky (where corals can be seen in the cave walls), and Yellowstone National Park in Idaho, Montana, and Wyoming. The first fossil described from what is now Dinosaur National Monument was not a dinosaur, but a species of horn coral collected by a John Wesley Powell expedition in Utah. Horn corals are also the largest fossils found in the building stone at Fort Scott National Historic Site in Kansas.

Fossils of stony corals, which have been major reef-builders in the Mesozoic and Cenozoic, are known from parks like Colonial National Historical Park in Virginia, Dry Tortugas National Park in Florida, Everglades National Park in Florida, and Vicksburg National Military Park in Mississippi and Louisiana. The NPS records of stony corals are almost entirely Cenozoic because Mesozoic rocks from the proper marine settings are rare in the National Park System.

Conulariid Conularia kaibabensis in the Kaibab Formation at Grand Canyon National Park, named by legendary Grand Canyon geologist (and former park naturalist) Eddie McKee.

Conulariids have been classified as cnidarians, but there are still many questions about their anatomy. They probably were somewhat like horn corals, with a tentacled predatory animal living within an elongate pyramid-shaped structure anchored to a surface at the tip. The dwelling structures of conulariids are made up of tiny stacked mineralized rods in a “herringbone” pattern. These animals lived throughout the Paleozoic and Triassic.

Conulariids have been documented in at least 8 national parks including Grand Canyon National Park in Arizona.

Coloring Book Pages

Related Parks

• Colonial National Historical Park (COLO), Virginia—[COLO Geodiversity Atlas] [COLO Park Home] [COLO 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]

• Dinosaur National Monument (DINO), Colorado and Utah—[DINO Geodiversity Atlas] [DINO Park Home] [DINO npshistory.com]

• Dry Tortugas National Monument (DRTO), Florida—[DRTO Geodiversity Atlas] [DRTO Park Home] [DRTO npshistory.com]

• Everglades National Park (EVER), Florida—[EVER Geodiversity Atlas] [EVER Park Home] [EVER npshistory.com]

• Fort Scott National Historic Site (FOSC), Kansas—[FOSC Geodiversity Atlas] [FOSC Park Home] [FOSC npshistory.com]

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

• Grand Canyon-Parashant National Monument (PARA), Arizona—[PARA Geodiversity Atlas] [PARA Park Home] [PARA npshistory.com]

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

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

• Mammoth Cave National Park (MACA), Kentucky—[MACA Geodiversity Atlas] [MACA Park Home] [MACA npshistory.com]

• Mojave National Preserve (MOJA), California—[MOJA Geodiversity Atlas] [MOJA Park Home] [MOJA npshistory.com]

• Vicksburg National Military Park (VICK), Louisiana and Mississippi—[VICK Geodiversity Atlas] [VICK Park Home] [VICK npshistory.com]

• Wind Cave National Park (WICA), South Dakota—[WICA Geodiversity Atlas] [WICA Park Home] [WICA npshistory.com]

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

Body Fossils