The present study of Lepisosteus osseus dimorphism expands upon previous work by examining a broader array of morphometric characters while removing the bias associated with overall body length. A stepwise discriminant function analyses (swDFA) found that five characters best
distinguish the sexes: head width, mid‐snout width, anal‐fin height, anal‐fin width and prepectoral‐fin length. Discriminant function analyses (DFA) with the five characters yields misclassification rates of 23·5% for females and 9·7% for males. Subsequent
DFA using these five characters plus standard length yields misclassification rates of only 8·8% for females and 6·2% for males. The data presented here reveal differences in head and anal‐fin shape between male and female L. osseus that may have evolved to enhance
predatory abilities or competitive abilities during reproduction. This study is the first to find that L. osseus exhibits sexual dimorphism in characters without the biases of overall size.