Phylogenetic relationships between living and fossil spinicaudatan taxa (Branchiopoda Spinicaudata): reconsidering the evidence

Abstract

In order to understand relationships between living and fossil groups of spinicaudatan clam shrimp, it is important to review historical and contemporary attempts at evaluating the evolutionary history of the group. A comprehensive review of previous phylogenetic and paleontological work is presented here and considered in an evolutionary context in an attempt to bridge the gap between neontological and fossil works and to present a foundation upon which future studies may contribute to the understanding of spinicaudatan evolutionary history. This study is broken into three discrete sections dealing with various aspects of spinicaudatan neontology and paleontology. First, a brief review of the current state of branchiopod systematics is presented. Second, we offer reviews of contemporary efforts in the paleontological study of fossil Spinicaudata with familial and super-familial descriptions of major fossil groups. Finally, an effort to establish biologically sound hypotheses of relatedness between fossil and living lineages of ‘clam shrimp’ is presented. We conclude that attempts to integrate modern and extinct representatives of the spinicaudatans in a holistic approach result in many of the fossil families becoming paraphyletic or polyphyletic, highlighting the persistent rift between biological and palaeontological studies of the group. It is our hope that the hypotheses presented here will aid in a more synthetic studies of Spinicaudata and also allow biological patterns to be investigated across the groups over geologic time.