. Bonner zoologische Monographien. Zoology. 148 Flatfishes as models The concept of the establishment of ecological zones was developed by von Wahlert (1961) in a case study of the peculiarly asymmetric Pleuronectiformes, or flatfishes. The ''ethological key innovation" in the ancestral lineage of flat- fishes involves the sleeping posture, where the fish lies on one side on the bottom. This trait, which is also known in the closely-related symmetrical carnivorous Serranidae, began to be retained by Pleuronectiformes when awake. These fish therefore extended the functional context of &quo
. Bonner zoologische Monographien. Zoology. 148 Flatfishes as models The concept of the establishment of ecological zones was developed by von Wahlert (1961) in a case study of the peculiarly asymmetric Pleuronectiformes, or flatfishes. The ''ethological key innovation" in the ancestral lineage of flat- fishes involves the sleeping posture, where the fish lies on one side on the bottom. This trait, which is also known in the closely-related symmetrical carnivorous Serranidae, began to be retained by Pleuronectiformes when awake. These fish therefore extended the functional context of "lying on the side". This opened the way to a new mode of life for those fishes when hunting, allowing them to lie in wait for prey in ambush, buried in the sand. Structural adaptations to this behavior followed in the course of evolution and represent "morphological key innovations" which acted to channelize this mode of life: the body is laterally compressed, the two sides have diverged into a functional underside and a func- tional upperside, the eye from the functional underside has migrated to the margin of the head and then to the functional upperside to enable binocular vision, and in the flounders (Pleuronectoidei) the fish is camouflaged and adapted to a benthic life by its physiological ability to alter its color. By this new mode of life the sandy ocean bottom now could be exploited. The stem species with this new body plan radiated to more than 500 recent species. These species have in no way replaced the representatives of the original (plesiomorphic) mode of life. Instead, they've just added a new ecological layer or stratum (see below). The evolution of the Teleostei zone The evolution of different groups of fish is mainly characterized by transforaia- tions of the feeding apparatus (Fig. 6). Fishes with relationships to the epibenthos such as sharks have mouths which are located beneath the rostrum. The morpho- logical key innovation of the bony
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