Dental structures originally emerged as components of the exoskeleton of ancestral vertebrates. Throughout evolution, these structures started being built inside the oral cavity, allowing these ancestral vertebrates to switch to a more predatory lifestyle and opening a vast diversity of new ecological niches. However, to date, the evolutionary and developmental processes by which dental structures can be built in new areas of the body plan are not clear. One of the main limitations for investigating this question is the lack of informative model organisms that show a clear gain of dental structures in new areas of the body. In this study, I focus my studies on catfish (Teleostei: Silurifomes): a highly diverse group of fish that contains a lineage of denticulate catfish (Loricarioidei) in which dental structures presumably emerged de novo on extra-oral body surfaces. I use the Loricarioidei to study the evolutionary and developmental mechanisms through which dentition can be built in new areas of the vertebrate body plan. Because this lineage has never been studied in the context of dental evolution, I must take a multidisciplinary approach at this question to have a broad perspective of the factors related to the gain of dental structures in the loricarioid body. In this work I integrate information that I recovered through studies in the fields of molecular phylogenetics, morphology, evolutionary biology and developmental biology. I begin by determining the phylogenetic landscape in which these denticles emerged, and start by placing the Loricarioidei within the catfish phylogeny. However, the fast molecular evolution of this group and the general diversity of evolutionary rates among catfish species raise methodological challenges for inferring this phylogeny correctly. I address these challenges and propose two new methods, LS³ and LS⁴, to improve any phylogeny inference in which extreme heterogeneous evolutionary rates may be a source of bias. I apply LS⁴ as implemented in a software I produced for this work, LSX, on a new molecular dataset to address the position of the Loricarioidei, and I am able to place this lineage nested within Siluriformes, among groups of catfish that have a naked skin. These results confirm that dental structures indeed emerged de novo in the extra-oral regions of loricarioids.