For Immediate Release Media contact: The Field Museum Nancy O'Shea 312/665-7100 media@fieldmuseum.org Something old, something new More than 500 species of modern flatfishes live in fresh and salt water. All have an unusual flattened body form that is well adapted to life at the bottom. Some families of flatfishes have both eyes on the right side of their head while other families have both eyes on the left side. Typically, the undersides of flatfishes are white or pale, but their uppersides are camouflaged to fit in with the surroundings. Some species are able to change the color of their upperside. Weighing up to 720 pounds, these carnivorous bottom-feeders vary considerably in size from 4 inches to 7 feet. Many are important game and food fishes. The Nature study examined several specimens of two kinds of fossil fishes from the Eocene (about 50 million years ago) of northern Italy. One of these is a newly described genus that Friedman has named Heteronectes (meaning “different swimmer”). He discovered it in a museum drawer at the Naturhistorisches Museum in Vienna, Austria, and prepared the fossil at The Field Museum with the assistance of the museum’s expert preparators. The other fossil, Amphistium, is known from several specimens from the same Italian site as Heteronectes and a single fossil from France. It has been known to science but incorrectly classified for more than 100 years. All previous studies of Amphistium mistakenly concluded that it had a symmetrical skull. Examining the anatomy of Amphistium and Heteronectes with a diverse range of techniques (including CAT scanning and chemical preparation, which dissolves the rock surrounding the fossil skeleton), Friedman discovered that both represent primitive flatfishes with a somewhat asymmetrical skull. Nevertheless, in both cases the eyes remain on opposite sides of the head in adults. In other words, the fossils show incomplete asymmetry, displaying an intermediate condition between what is found in ordinary symmetrical fishes and extraordinary asymmetrical flatfishes. This discovery rejects the notion that flatfishes must have arisen suddenly as “hopeful monsters” and documents two steps in the gradual assembly of one of the most bizarre body plans found among vertebrates. The position of Amphistium and Heteronectes within the fish evolutionary tree is confirmed by many aspects of their anatomy. Features unrelated to asymmetry link these fossils with flatfishes, but the specimens also show characters more primitive than those found in any living form. Adding a further twist to the story, the right eye migrated in some specimens of Amphistium, while the left eye moved in other specimens. This is unlike most living species of flatfishes, where individuals are always right- or left-eyed. It also indicates that that mixed ‘handedness’ is primitive for flatfishes. Continue >>