MORPHOLOGICAL CHANGES OF VERTEBRAL CENTRA IN THE EXTANT NORTHERN PIKE (ESOX LUCIUS) AND ITS PALEONTOLOGICAL SIGNIFICANCE

The microfossil sites (for example, Ravenscrag Formation) in Canada preserves one of the best microfossil assemblages which have been a focus of paleontological research since the 1970s. Amongst fishes, one of the most frequently documented microfossils are vertebral centra. They are quite robust, subcircular in shape, and are greater in quantity as compared to other delicate fish bones. Proper identification of these centra can greatly contribute to faunal and paleoenvironmental analyses. However, they differ in their morphology along the column even in the same species, which makes it difficult to assign them to a particular taxon. Due to this, it becomes challenging to study commonly found fishes in these sites. The Northern pike, Esox lucius belonging to the order Esociformes is very common in Holoarctic fresh water of Canada, but a complete study on its vertebral column has never been done. Apart from being commonly found, northern pikes for its specific feeding and predating mechanisms can significantly aid in deciphering the paleoenvironment of these sites. Centra that are thought to belong to Esox sp. have been documented from microfossil localities but their ural caudal centra have never been described. Fossil pikes, specifically Paleocene pikes do not differ much in structure from the extant pikes, hence, an approach towards the better identification of centra of E. lucius is to compare the fossil material to the extant material. Thus, this study includes an examination of the complete vertebral column of an individual specimen of the extant E. lucius to document the changes in morphology of vertebrae along the column. There are 19 significant morphological changes documented along the entire length of the vertebral column. The results demonstrate that two centra which look different from one another could in fact belong to the same species. Thus, allowing the isolated elements to be confidently sorted from mixed and diverse micro vertebrate fossil assemblages to specific taxa. In addition, the documentation of the morphological variation helps in assigning an isolated centrum to a specific region in the column. This is the first study which provides information and detailed descriptions about morphological changes in centra along the column in E. lucius and also describes their ural centra.