When Tradition Meets Technology: Systematic Morphology of Fishes in the Early 21st Century
Many of the primary groups of fishes currently recognized have been established through an iterative process of anatomical study and comparison of fishes that has spanned a time period approaching 500 years. In this paper we give a brief history of the systematic morphology of fishes, focusing on some of the individuals and their works from which we derive our own inspiration. We further discuss what is possible at this point in history in the anatomical study of fishes and speculate on the future of morphology used in the systematics of fishes. Beyond the collection of facts about the anatomy of fishes, morphology remains extremely relevant in the age of molecular data for at least three broad reasons: 1) new techniques for the preparation of specimens allow new data sources to be broadly compared; 2) past morphological analyses, as well as new ideas about interrelationships of fishes (based on both morphological and molecular data) provide rich sources of hypotheses to test with new morphological investigations; and 3) the use of morphological data is not limited to understanding phylogeny and evolution of fishes, but rather is of broad utility to understanding the general biology (including phenotypic adaptation, evolution, ecology, and conservation biology) of fishes. Although in some ways morphology struggles to compete with the lure of molecular data for systematic research, we see the anatomical study of fishes entering into a new and exciting phase of its history because of recent technological and methodological innovations. With each new advance of technology and with each new generation of researcher, systematic morphology becomes a new and vibrant science.
Illustrations from the early history of the morphology of fishes, showing concepts of homology and archetypes. (A) Illustration from Belon (1555; modified from Grande, 2010:fig. 557) showing homology of the vertebrate skeleton. (B) Illustration from Geoffroy Saint-Hilaire (1818) showing homology among the axial skeletons of vertebrates. Image courtesy of T. W. Pietsch. (C) The archetype of the vertebrate (Owen, 1849; also used by Owen, 1848). (D) Conceptualized/simplified schematic of the vertebrate head; modified from Liem et al. (2001:fig. 7.3) by William E. Bemis.
Illustration from Haeckel’s Antropogenie oder Entwicklungsgeschichte des Menschen (1877). The image shows early ontogenetic stages of four mammals (human, bat, cat, and sheep). Although not directly associated with the biogenetic law, the illustration clearly yet artistically shows Haeckel’s hypothesis of repeating ontogenetic stages across phylogeny.
Title page of Agassiz (1857) in which he outlined his views on the congruence between comparative anatomy, embryology, stratigraphy, and biogeography.
Illustrations showing a specimen (A, B) and reconstructions (C–G) of the head of the coccosteomorph arthrodire †Tapinosteus heintzi Stensiö, 1959. From Stensiö (1963:pl. 7 figs. 2, 3, and figs. 70, 76, 47, 71A, 62A, respectively).
Caudal skeletons of actinopterygian fishes, showing different numbering schemes and inferences of homology. (A) Amia calva, VIMS 19093. (B) Hiodon alosoides, UMA F10592. (C) Channa argus, VIMS 19091. (D) Astroscopus guttatus, VIMS 19094. (E) Caranx crysos, UMA F11596. (F) Zaprora silenus, VIMS 19093. Scale bars equal 10 mm. Anatomical abbreviations: h, hypural; phy, parhypural. Institutional abbreviations: UMA, University of Massachusetts Amherst; VIMS, Nunnally Ichthyology Collection, Virginia Institute of Marine Science.
Different morphological techniques used in early ontogenetic stages of the paddlefish, Polyodon spatula. (A, B) Reconstructions of a micro-CT scan. (A) Reconstruction of musculature (red) and skeletal structures (blue and gray) with an overlay of the actual CT scan. (B) Reconstruction as a standalone model. (C) Image of the cranial musculature stained with an antibody specific for muscle tissue. (D) Classical clearing-and-staining method for skeletal structures (bone stained red, cartilage stained blue). Scale bars equal 0.5 mm.
Computed tomography images of sturgeons. (A) Dorsal and (B) ventral views of the skull of Huso huso (MCZ 54269). (C) Dorsal and (D) ventral views of the skull of Scaphirhynchus platorynchus (FMNH 45024). (E) Dorsal and (F) ventral views of the skull of Pseudoscaphirhynchus kaufmanni (UAIC 13265.01). Institutional abbreviations: FMNH, Field Museum of Natural History; MCZ, Museum of Comparative Zoology, Harvard University; UAIC, University of Alabama Ichthyology Collection. Scale bars equal 1 cm.
Confocal microscopy of antibody stained specimens of tetraodontiform fishes showing early stages of development of cranial musculature. (A–C) Ontogenetic series of Balistapus undulatus. (D) An unidentified monacanthid larva. (E, F) Two different stages of the freshwater pufferfish Monotrete suvattii. Abbreviations represent different muscle portions of the musculus adductor mandibulae.
Contributor Notes
Associate Editor: G. Arratia.