A large coelacanth, †Whiteia giganteus sp. nov., from the Triassic of Texas, USA, establishes a Pangean radiation of early Mesozoic actinistians

Abstract

An intriguing pattern among extant lineages of vertebrates is the existence of depauperons: clades that have remained species-poor over huge time spans (i.e., >100 million years ago). Among these are so-called living fossil fishes like gars, sturgeons, bichirs, and lungfishes. Perhaps the most famous of these are the coelacanths, which are today represented by only two species yet are known from a fossil record comprising over 400 million years of evolution. Despite the high morphological and body size disparity observable in extinct coelacanths, the total number of species belonging to the coelacanth lineage Actinistia remains very low. Here, I describe the skull of a new species of large-bodied coelacanth from the Late Triassic Dockum Group of Texas. †Whiteia giganteus sp. nov. is the most massive member of its genus and one of the largest known Triassic actinistians. Phylogenetic analysis shows that this clade is stemward of the divergence-Latimerioidei-that produced almost all coelacanth diversity after the Triassic. In turn, †W. giganteus substantiates a new episode of body size increase in the coelacanth total clade and suggests an unsampled degree of coelacanth diversity in the Triassic of the United States, which has previously produced only latimerioid fossils.