The evolution of parrotfish saw two morphological innovations, pharyngeal jaw modification and the novel intramandibular joint. The pharyngeal jaw, a characteristic of all parrotfish, is basically a second set of jaws in addition to the primary jaw. Kind of like a mouth in a mouth. Didn’t the creature from Alien have a pharyngeal jaw? In contrast, not all parrotfish possess the intramandibular joint, a “unique jaw linkage [that allows] for increased control of the lower jaw” and allows for a larger mouth gape. Both of these modifications are presumed to be adaptive to allow for better scraping of algae off corals. In the evolution of the parrot fishes the pharyngeal jaw came first and was followed by the intramandibular joint.
Samantha Price presented today on research testing the extent that these morphological innovations potentially created new niche space and thereby increased diversification, i.e. the proliferation of new species. Prices examined several different morphological metrics as a measure key aspects of this diversification, e.g. gape size, protrusion, body size, and the very sophisticated sounding jaw kinematic transmission. Overall, her results are both intriguing and complex. The evolution of the pharyngeal jaw was not matched by significantly faster rates diversification in of the morphological metrics. Indeed some appeared to actually slow down. However, with the intramandibular joint came increased diversification, i.e. an adaptive radiation.