The fossil record of Gonorynchiformes

The fossil record of gonorynchiform fishes provides key information on the diversity, palaeobiogeography, and phylogeny of the group. The first mention of fossil Gonorynchiformes dates back to Cuvier in the early 19th century, and there is still a need for a critical review of the earliest descriptions and of some key taxa today. Fossil gonorynchiform fishes are known from the earliest Cretaceous (Berriasian-Valanginian) to the earliest Miocene, and the clade has several extant representatives. To date, the fossil record has yielded only about 18 genera and 35 species of Gonorynchiformes. With only 46 known localities, their fossil record is relatively poor compared to that of other groups of Ostariophysi. The distribution of these localities is heterogeneous in both space and time. Debates on the phylogenetic status of Gonorynchiformes have mainly focused on the identity of the basal-most members of the clade and on its sister group. Unfortunately, very few large-scale phylogenetic studies have included the fossil representatives of the clade. Using known fossil occurrences and several phylogenetic proposals, we conducted an exploratory diversity analysis. A traditional taxic approach shows that gonorynchiform diversity rose steadily during the Early Cretaceous and reached a peak in the Aptian-Cenomanian interval. It then declined slightly towards the end of the Cretaceous and it decreased further at the dawn of the Cenozoic. This apparent low diversity level is only interrupted by relative diversity peaks in the first half of the Eocene and in the Oligocene. In the absence of fossils after the earliest Miocene, diversity estimates are conjectural for most of the Neogene. We found a close similarity of the estimates obtained with alternative phylogenetic hypotheses, meaning that the differences among these phylogenies have virtually no impact on inferred diversity patterns. Our diversity analysis points to some major gaps in the known fossil record, and it calls for the integration of most (if not all) fossil taxa in phylogenetic analyses.