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Fossil Sponges

Photo of a small fossil sponge. — Sponge fossil. Guadalupe Mountains National Park.
Identification Guide to the Fossils of the Guadalupe Mountains by Mary Carol Coleman and Cameron Coleman.

Introduction

Sponge fossils in national parks reveal important information about geologic history and the changing life in oceans through time. Sponges played a different ecological role in the Paleozoic versus more modern oceans. They were dominant reef builders in the Paleozoic.

Phylum Porifera

Sponges make up the phylum Porifera (meaning “pore bearer”). They are among the simplest of animals. They have no true tissues (i.e., muscles, nerves, and internal organs). Sponges live attached to the sea floor and feed by pumping water through their internal structure to filter out tiny pieces of food matter. Sponges are highly variable in shape: many are shaped like cups or flasks; others are like spheres or cauliflower; some form flat plates folded together; others are encrusting.

Only some sponges contain hard parts capable of being fossilized. Those that do usually have slender, pointed elements called “spicules,” which are composed of silica and serve as supportive skeletons. Sponges that have particularly well-developed silica frameworks are popularly known as “glass sponges” because 90% of their dry weight is “glass” (silica). A few have heavily calcified skeletons resembling corals or forming layered structures. Sponges are almost entirely marine organisms today and are assumed to have been so in the past.

Sponges have a long fossil record from the Precambrian onwards. In many places they were abundant enough to form widespread rock formations. They also have been prominent reef-building organisms, particularly in the Paleozoic. There are several groups of important fossil sponges that are now extinct.

Sponge Fossils in National Parks

^{The sponge Lemonea was one of the most common reef-builders of the Permian Reef in Guadalupe Mountains National Park.

Identification Guide to the Fossils of the Guadalupe Mountains by Mary Carol Coleman and Cameron Coleman.}

Photo of a fossil sponge. — NPS photo by Rod Horrocks.

^{Sponge fossils in Carlsbad Cavern National Park. Scale bar with 1-cm-scale black and white squares.

NPS photo by Rod Horrocks.}

^{Permian sponge Actinocoelia maeandrina in the Kaibab Formation. Scale bars are 3 cm. A. The outside of a concretion. B. A broken surface shows the sponge. Grand Canyon-Parashant National Monument.

NPS/2020 Field Inventory.}

Four photos of small fossils. — Sponge fossils in Great Basin National Park.
All photos by Gorden Bell.

Fossils of sponges are known in situ from at least 48 national park sites. Most sponge fossils that have been documented in national parks are in Paleozoic rocks, and generally represent forms with strongly developed mineralized skeletons.

The first reef-builders were archaeocyathid sponges, which flourished briefly in the Cambrian before becoming extinct. They have been found at parks as far apart as Yukon-Charley Rivers National Preserve in Alaska and Mojave National Preserve in California.

In the middle of the Paleozoic, layered sponges called stromatoporoids built reefs; examples have been found at Delaware Water Gap National Recreation Area in New Jersey and Pennsylvania, where they grew with corals. In the early Permian, sponges and algae built massive reefs that can be explored today at Carlsbad Caverns National Park in New Mexico and Guadalupe Mountains National Park in Texas. Permian sponges are also present in the Kaibab Formation on the rim of Grand Canyon National Park in Arizona and in the neighboring Grand Canyon-Parashant National Monument.