The morphology, development, and evolution of the head of fishes: Foundational studies for a renaissance of comparative morphology

Abstract

Acta Zoologica has played a key role as a publishing outlet for advancing zoological knowledge since its foundation in 1920 by Nils Holmgren. With the journal celebrating its centennial, we have assembled a virtual issue that celebrates some of the morphological highlights from the history of Acta Zoologica, which has been a venue for precise and detailed anatomical descriptions of the morphology and ontogeny of major vertebrate taxa. Because our own focus of research has been the evolution of the musculoskeletal system of fishes, a bias toward these topics in our selection is readily apparent. However, these papers also reflect the tradition established by Holmgren's "Studies on the Heads of Fishes," published in Acta Zoologica. We hope that by bringing together Holmgren's "Studies," along with a selection of other papers from across the history of the journal will inspire the continued growth of comparative vertebrate anatomy, especially in an era where advanced technologies are available. We discuss various author's approaches to morphology, including Holmgren (1877-1954), Torsten Pehrson (1887-1970), and Alexej Nikolajevich Sewertzoff (1866-1936. The foundation that was laid by these and other workers offers the basis for continued investigation and testing of hypotheses. We feel that the true testament to the power of comparative anatomy is that even after so much study and the volume of baseline data available, new and important findings continue to be made from the careful observation of anatomical form.The observer, basing on the data of palaeontology, comparative anatomy and embryology, will try to reconstruct as closely as possible the evolution of all members of the given group… A.N. Sewertzoff, 1928, p. 59-60

Heads and tails: The notochord develops differently in the cranium and caudal fin of Atlantic Salmon (Salmo salar, L.)

“…Given that the heads of fishes have been studied carefully for over 100 years (for review, see Hilton, Warth, & Konstantinidis, 2019 )—and that the study of fish heads continues at the vanguard of research on vertebrate origins (Martik et al, 2019 )—we find it remarkable that there is more to learn about the cranial notochord. But while the notochord is present and accounted for in early chondrocranial basal plate development, we learn of its demise without details, even in classic papers (Bertmar, 1959 ): “The anterior end of the notochord [in Hepsetus ] has just begun to reduce … a process that will proceed at the next stages.” Moreover, in Salmo salar , Holmgren's ( 1943 ) remarkable tome treats the notochord as a transient landmark (see his figs.…”