Comparative Osteology and Phylogenetic Relationships of Fossil and Living Sturgeons (Actinopterygii, Acipenseriformes)

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ABSTRACT Sturgeons, paddlefishes and their fossil relatives form a smallgroup of fishes from the Northern hemisphere called Acipenseriformes thatis believed to have split off from other ray-finned fishes (theactinopterygians) some 150 million years ago. The morphology of livingsturgeons (25 species) has remained largely unchanged since they firstevolved. Although there have been many studies of sturgeon morphology,there never has been a study that is detailed or comprehensive enough toallow modern studies of their evolution. The new study of the skeleton offossil and living sturgeons by Hilton, Grande and Bemis has two main goals.The first objective is to describe in detail the skeleton of the shortnosesturgeon (Acipenser brevirostrum), a small species of sturgeon found incoastal rivers of eastern North America. This study will be based onseveral types of specimens, including dry skeletons, hand cleaned skeletonsthat are stored in alcohol, and cleared and stained skeletons (in which thesoft tissue is made clear, cartilage is stained blue and bone is stainedred). Specimens representing all life history stages will be studied, fromthe earliest embryos to the oldest specimens available. Such an approachallows observations of changes of morphology due to growth and developmentof the skeleton. The results of this study will be published in a largeformat monograph, illustrated with photographs for documentation and linedrawings for interpretation, accompanied by clear text descriptions. Theintention is that this monograph will serve as a lasting contribution tothe knowledge of the anatomy of sturgeons and a standard reference foranatomical studies of primitive ray-finned fishes. The second part of this study concerns tracing evolutionaryrelationships among living and fossil sturgeons. Most fossils that areidentified as sturgeons are very fragmentary, and only after a detailedstudy of the living members of a group can such specimens be properlyinterpreted. Additionally, new comparative data generated during the firstpart of the study will be used to formulate new hypotheses ofrelationships. All previous morphological studies of the relationships ofsturgeons are inadequate for various reasons. For instance, many studieshave looked only at relationships of sturgeons from a particular geographicregion or country. Evolution has not occurred within political boundaries,and Hilton, Grande and Bemis' study will be the first to incorporatemorphological data for all sturgeons on a worldwide scale. All species ofsturgeons are afforded some form of protection, with many listed asendangered. The precarious conservation status of many sturgeons makestudies of their evolutionary history even more critical.