A live coelacanth, a fish thought to be extinct, was caught in 1938.

Life finds a way.

—Jeff Goldblum as Ian Malcolm in Jurassic Park

There are many organisms represented in the fossil record. Most have become extinct, dying off long ago. Around 65 million years ago, a major cataclysmic event took place—today believed to have been the impact of a giant meteor—which appears to have caused the extinction of a huge number of species, including the dinosaurs. Such was believed to have been the case with the coelacanth (Latimeria chalumnae), a fish present in the fossil record from between 360 and 80 million years ago. In 1938, off the coast of South Africa, the scientific world was stunned when a fishing crew caught a live coelacanth (pronounced "see-la-kanth") in their shark net. This discovery was equivalent to finding a living dinosaur. Of course, if there was one coelacanth, there had to be more, and soon, a population was discovered near the Comoros Islands, off the southeastern coast of Africa. For nearly six decades, this was believed to be the only population, until a coelacanth was caught off the coast of Sulawesi, Indonesia. Interestingly, the local people of the island were already familiar with the species, and they even had a name for it—raja laut, or “king of the sea.” It was later determined that there were some small differences in the coelacanths from Sulawesi, and in 1999, they were determined to be a new species, Latimeria menadoensis.

A number of explanations exist for why the coelacanth disappeared from the fossil record for so long. One theory is that the ancient coelacanths lived in areas that favored the process of fossilization, whereas modern populations do not. The discovery of the coelacanth has led to some important revisions in evolutionary theories. Once thought to be one of the organisms directly linking land and sea animals in the evolutionary chain, examination of living coelacanths has suggested that the lungfish is more likely to occupy that place. Nonetheless, the coelacanth was considered the most incredible zoological find of the 20th century.

Science NetLinks
Zapping Fish (6–12) explores an interesting fact about fish. The audio interview and lesson suggestion focus on why fish do not normally get electrocuted when lightning strikes the water within which they are swimming. With the help of Don MacGorman, a physicist at the National Severe Storms Laboratory in Norman, Oklahoma, students gain a better understanding of electricity, conductors and insulators.

Water Fleas (6–12), another Science Update, focuses on the dangers associated with the introduction of foreign species into local ecosystems. Through examination of the work of Hugh MacIssac, an aquatic ecologist at the Great Lakes Institute for Environmental Research, students learn of the threat posed by an Asian water flea to local fish populations.

Xpeditions
In Aquatic Invaders (6–8), students explore the ways that native species interact in ecosystems. They then learn about some of the ways that exotic or invasive species can threaten the balance of the ecosystem. Students discover how the various elements of the Chesapeake Bay ecosystem are interconnected and investigate some of the issues associated with invasive species.

Illuminations
Students use fish-shaped crackers to learn about subtraction in the seven-lesson unit How Many More Fish? (Pre-K–2). The unit focuses on comparative subtraction as students explore all five meanings for the operations of subtraction (counting, sets, number line, balance and inverse of addition). In these lessons, the students use reasoning and then represent and communicate their findings.