Meeting Abstract
Among teleost fishes, upper jaw protrusion is a key contributor to their ecological success and evolutionary diversity. This feat involves numerous functional components of the craniofacial skeleton and associated muscles. Extreme protrusion, ~ 30% of head length, has evolved in a handful of Perciform lineages, and can enhance the capture of elusive prey. Here we explore the morphological alterations to the craniofacial skeleton that underlie this radical behavior. We focus on Caquetaia spectabilis, a South American cichlid known for its extreme jaw protrusion. Using µCT scans and 2D morphometrics, we compare craniofacial morphology and ontogeny of C. spectabilis to other cichlids. We document conspicuous, and predictable shifts in anatomy, including accelerated growth of the ascending arm of the premaxilla and length of the maxilla. In addition, we find that C. spectabilis experience delayed suture closure between the frontal components of the neurocranium, resulting in the retention of a fissure between frontal bones well beyond the developmental stage when sutures normally close. Cranial suture closure is a critical event in vertebrate development that is orchestrated by a complex genetic pathway. Deviations in the timing of suture closure can result in severe birth defects, detrimental to organismal fitness. We suggest that this unexpected osteological adaptation has evolved to accommodate growth of the ascending arm of the premaxilla in C. spectabilis. If true, this would mean that a major developmental process has been altered to accommodate extreme jaw protrusion in this lineage.
