Sandbar shark (C. plumbeus): The sandbar shark has a snout that is shorter than the width of its mouth and a large first dorsal fin originating over the axis of the pectoral fin (the Caribbean reef shark’s first dorsal fin is further from the head than the sandbar shark). Unlike the Caribbean reef shark, the sandbar shark has widely spaced non-overlapping dermal denticles that lack defined teeth on their free edges.
One useful definition distinguishes reefs from mounds as follows: Both are considered to be varieties of organosedimentary buildups – sedimentary features, built by the interaction of organisms and their environment, that have synoptic relief and whose biotic composition differs from that found on and beneath the surrounding sea floor. Reefs are held up by a macroscopic skeletal framework. Coral reefs are an excellent example of this kind. Corals and calcareous algae grow on top of one another and form a three-dimensional framework that is modified in various ways by other organisms and inorganic processes. By contrast, mounds lack a macroscopic skeletal framework (see stromatolite). Mounds are built by microorganisms or by organisms that don't grow a skeletal framework. A microbial mound might be built exclusively or primarily by cyanobacteria. Excellent examples of biostromes formed by cyanobacteria occur in the Great Salt Lake in Utah, and in Shark Bay on the coast of Western Australia.
The Caribbean reef shark (Carcharhinus perezi) is a species of requiem shark, belonging to the family Carcharhinidae. It is found in the tropical waters of the western Atlantic Ocean from Florida to Brazil, and is the most commonly encountered reef shark in the Caribbean Sea. With a robust, streamlined body typical of the requiem sharks, this species is difficult to tell apart from other large members of its family such as the dusky shark (C. obscurus) and the silky shark (C. falciformis). Distinguishing characteristics include dusky-colored fins without prominent markings, a short free rear tip on the second dorsal fin, and tooth shape and number.
Ancient reefs buried within stratigraphic sections are of considerable interest to geologists because they provide paleo-environmental information about the location in Earth's history. In addition, reef structures within a sequence of sedimentary rocks provide a discontinuity which may serve as a trap or conduit for fossil fuels or mineralizing fluids to form petroleum or ore deposits.