Research Training Program

The Characidae is a family of South American fishes that is one of the most diverse groups known. However, the evolutionary relationships among many of its various subfamilies, genera, and species remain uncertain. One example is the genus Brittanichthys. Once classified in the subfamily Cheirodontinae, Brittanichthys and several genera that together comprise a group of small, herring-like characids are now incertae sedis genera whose relationships among each other and to other characids are in need of investigation. A cladistic analysis of this group of genera based on a specialized jaw anatomy and other characters of the skeleton suggests that the three genera Brittanichthys, Leptobrycon, and Thrissobrycon form a monophyletic clade with Microschemobrycon as a sister group. This specialized jaw anatomy consists of reduction in the size of premaxillae, enlargement of the maxillae, and reduction of size and number of moth. These derived features may indicate a pelagic, plankton-feeding lifestyle. There is also a possible association of Brittanichthys to the characid subfamily Glandulocaudinae that is suggested by caudal fin structures. Difficulties in resolving phylogenetic relationships can result from problematic choices in establishing outgroups for poorly studied taxa.