The donut-like shapes on this limestone slab are cross sections through the branches of a tubular Pennsylvanian sponge, Amblysiphonella. The central cavity (the donut hole) is clearly visible. The fossil was collected in the upper part of the Avoca Limestone Member of the Lecompton Limestone in Greenwood County, Kansas.
Description: Sponges, members of the phylum Porifera, are one of the simplest multicellular animals living today. They're also among the oldest, with a fossil record extending back to the last part of the Precambrian, about 550 million years ago. Sponge fossils occur in rocks all over the world. In Kansas, fossil sponges can be found in the Pennsylvanian and Permian rocks in the eastern part of the state.
This Pennsylvanian sponge, belonging to the genus Maeandrostia, is an example of a branching form; note also the raised pores on the surface of the branches. These fossils were collected from the Hickory Creek Shale Member of the Plattsburg Limestone in Wilson County, Kansas.
Unlike most larger multicellular animals, sponges lack tissues, organs, and respiratory or circulatory systems. Instead, they rely on specialized cells to perform the different functions necessary for survival. Some cells, for example, equipped with flexible tails, or flagella, create one-directional currents that draw nutrient- and oxygen-bearing water into the sponge and help eliminate waste products. Other cells perform tasks associated with support, reproduction, or protection.
Sponges come in many different colors, shapes, and sizes. Some sponges have irregular shapes, or look like encrusting sheets, while others take the form of mounds, or tubes, or even a series of spheres reminiscent of beads on a necklace. They range in size from 1 cm to more than 2 meters. Many of the differences in size and shape are due to environmental factors, such as temperature, salinity, turbulence, and the amount of sediment in the water. This means that members of a single sponge species may look very different from each other.
In spite of differences in appearance, sponges have the same basic body plan (see drawing below). All sponges are characterized by numerous pores on their external surface (porifera means pore bearer). Water is drawn through these pores, flows through tubular or chamberlike canals, and passes out through one or more large openings, each called the osculum. Sponges circulate a vast amount of water each day, as much as 20,000 times their own volume.
Generalized simple sponge showing basic features (adapted from Boardman, Cheetham, and Rowell, 1987).
Two specimens of Heliospongia, a Pennsylvanian sponge, illustrate the openings, or oscula, through which water passed out from the sponge (top photo) and the central cavity (see cross section), as well as the pores on the external surface (lower photo). Both fossils were collected in the Hickory Creek Shale Member of the Plattsburg Limestone in Wilson County.
Sponges reproduce both sexually and asexually. Most sponges that reproduce sexually produce eggs and sperm at different times, with the sperm being broadcast into the water to fertilize eggs in an individual of the same species. The fertilized eggs develop into larvae, which attach and develop into new sponges. Budding is the simplest method of asexual reproduction, in which a branch grows off the parent sponge, constricts and separates at its base, and becomes an independent organism. Sponges have remarkable powers of regeneration and are generally able to produce fully developed animals from small fragments.
All sponges live in water, attached to rocks, shells, or bottom sediments. Although some live in freshwater habitats, most sponges live in the oceans. Their bodies are supported by a skeletal framework, which may be composed of calcium carbonate layers, needlelike spicules, or organic fibers called spongin. The spicules are made up either of calcium carbonate or silica; spongin is the material of natural bath sponges that humans have used for centuries.
One group of sponges, the coralline demosponges, secrete a basal skeleton of calcium carbonate and also contain spicules in the soft tissue associated with this basal skeleton. Modern members of this group live in underwater caves associated with coral reefs; ancient members include specialized sponges known as archaeocyathids, stromatoporoids, and chaetetids. Chaetitid fossils are somewhat conspicuous in several of the limestone beds of southeastern Kansas.
Chaetetid sponges from Pennslvanian limestones of eastern Kansas. Note the longitudinal view of the tubular canals in this specimen, collected from the Laberdie Limestone Member of the Pawnee Limestone in Linn County, Kansas. This magnified (×5) surface view shows the honeycomb pattern of the pores; this fossil was collected from the Higginsville Limestone Member of the Fort Scott Limestone in Bourbon County, Kansas.
The approximately 5,000 species of living sponges dwell at various depths in the world's oceans. Sponges from the Paleozoic and earliest Mesozoic, however, lived mostly in shallow water and were, at times, important reef builders.
Even though sponges have a long fossil record, they are not common fossils. This is partly due to their relatively delicate skeletons and to the low-sediment environments that ancient sponges seemed to prefer (which precluded the quick burial necessary for preservation). Most fossil sponges are known solely from mineralized spicules and are differentiated by the chemical composition of these spicules. Sponges are relatively inconspicuous fossils in the Pennsylvanian and Permian rocks of eastern Kansas: for example, chaetetid sponges are found in Labette, Crawford, Bourbon, and Neosho counties. They are, however, locally common in the Pennsylvanian Hickory Creek Shale Member of the Plattsburg Limestone in Wilson County and the Hartford Limestone Member of the Topeka Limestone, in Greenwood County.
In this specimen of Amblysiphonella (from the Hartford Limestone Member, Topeka Limestone, at the Hamilton Quarry in Greenwood County), the individual chambers (arranged like beads on a necklace) and central cavity are clearly visible. Amblysiphonella is believed to have been a branching form, and the two branches may have been connected.
Stratigraphic Range: Upper Precambrian to Holocene.
Taxonomic Classification: Sponges belong to the Kingdom Animalia, Phylum Porifera. The phylum is divided into several classes based on the composition of the skeleton: the classes Demospongea, Hexactinellida, and Calcarea.
Boardman, R. S., Cheetham, A. H., and Rowell, A. J., eds., Fossil Invertebrates: Boston, Blackwell Scientific Publications, 713 p.
Clarkson, E. N. K., 1979, Invertebrate Palaeontology and Evolution, 3rd Edition: London, Chapman and Hall, 434 p.
Doyle, Peter, 1996, Understanding Fossils--An Introduction to Invertebrate Paleontology: Chichester, Wiley, 409 p.
Gehling, J. G., and Rigby, J. K., 1996, Long expected sponges from the Neoproterozoic Ediacara fauna of South Australia: Journal of Paleontology, v. 70, no. 2, p. 185-195.
Rigby, J. K., 1987, Phylum Porifera; in, Fossil Invertebrates, R. S. Boardman, A. H. Cheetham, and A. J. Rowell, eds.: Boston, Blackwell Scientific Publications, p. 116-139.
Text by Liz Brosius, Kansas Geological Survey. Unless noted otherwise, illustrations by Jennifer Sims, Kansas Geological Survey; photographs by John Charlton, Kansas Geological Survey.