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PALEONTOLOGICAL MUSEUM and STUDY COLLECTION
A. Hugh Adams Central Campus - John H. Payne Hall
GASTROPODA - View Galleries |
Cambrian - Recent |
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Fossil gastropods exhibit a single, usually spirally coiled shell into which the body can be withdrawn. Members of Class Gastropoda that have shells are referred to as "snails", members that do not have shells are not well-represented in the fossil record. Examples of shell-less gastropods are "slugs" although the marine and terrestrial slugs are not closely related to one another.
Earliest undisputed gastropods date from the Late Cambrian Period around 500 million years ago (500 ma). By the end of the Cambrian, gastropods were abundant and diverse, and they continued to be so up to present day where they represent about 80% of the living species of the Phylum Mollusca and are only second to the Class Insecta for most diversity.
There are currently 15,000 named species of fossil gastropods and about 35,000 named living species. However, because of diversity and abudance, gastropods are constantly being re-evaluated in their discovery and classifications.
The soft body part of living shelled gastropods are studied by paleontologists for information about the anatomy of their ancient relatives since the fossil record is based almost exclusively on the shells.
The gastropod shell forms a hollow, twisted or coiled cone that increases in width from its apex (inital point) to the opening from which the head and foot protrude.
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| Figure 1 The gastropod on the left exhibits sinistral coiling while the one on the right is dextrally coiled (Florida). (Lynn Curtis 2006) |
Most gastropod shells are coiled. Coiling may be in one plane such as ammonites or coiled in such a way as to produce spires of varying heights. The outer surface of the shells may be ornamental with ridges, grooves, bumps, spires, or other markings. Coiling may be sinistral (left) or dextral (right). A sinistral gastropod shell is one with the apex upward having its opening on the left when facing the observer (Figure 1). Paleontologists may determine paleoclimate and paleoenvironment by observing the coiling of fossil gastropds. Changes in ocean temperature and salinity as well as oxygen content may affect the direction in which the gastropods grow.
The earliest gastropods were marine but by the Mesozoic Era (249 ma) many had adapted to terrestrial and freshwater environments.
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Figure 2 Drill hole from predatory snail. (Lynn Curtis 2006) |
Gastropods had also developed different ways of obtaining food. Some are carnivores, herbivores,omnivores, deposit feeders, scavengers, suspension feeders, and parasites. Some carnivorous gastropods use their radula (toothed tongue) to rasp holes, through the shells of other gastropods or bivalves, drilling neat perfectly round holes through which they inject a muscle relaxant (Figure 2). Fossil shells with drill holes are evidence of gastropod predation, probably dating back to the Devonian Period (415 to 360 ma).
A long fossil record and present day abundance and diversity of gastropods attests to their evolutionary success. Over time, they have withstood several major extinction events that wiped out many other species.
Broward College A. Hugh Adams Central Campus |
A. Hugh Adams Central Campus
3501 SW Davie Road
John H. Payne Hall, Building 7
Davie, FL 33314