Cretaceous stem chondrichthyans survived the end-Permian mass extinction

Abstract

Cladodontomorph sharks are Palaeozoic stem chondrichthyans thought to go extinct at the end-Permian mass extinction. This extinction preceded the diversification of euselachians, including modern sharks. Here we describe an outer-platform cladodontomorph shark tooth assemblage from the Early Cretaceous of southern France, increasing the fossil record of this group by circa 120 million years. Identification of this material rests on new histological observations and morphological evidence. Our finding shows that this lineage survived mass extinctions most likely by habitat contraction, using deep-sea refuge environments during catastrophic events. The recorded gap in the cladodontomorph lineage represents the longest gap in the fossil record for an extinct marine vertebrate group. This discovery demonstrates that the deep-sea marine diversity, poorly known during most of the fish evolutionary history, contains essential data for a complete understanding of the long-term evolution of marine fish paleobiodiversity.

Chondrichthyan tooth enameloid: past, present, and future

“…A more complex tooth enameloid microstructure was recently described in the ctenacanth N. flagstaffensis from the mid‐Permian of Arizona (Guinot et al ., ). Below a thick SCE, loosely packed bundles of crystallites oriented apicobasally are observed, except near the cutting edges where they become normal to the cutting edge axis.…”

“…First, Guinot et al . () demonstrated the presence of a PBE in the ctenacanth N. flagstaffensis , whereas Glikmanius (Fig. A, B) lacks any degree of microstructural differentiation.…”

“…Instead, some taxa were shown to possess a two-layered enameloid, an observation that obviously raises issues on the homology of these layers within neoselachians. Finally, a PBE was recently identified in Neosaivodus flagstaffensis Hodnett, Elliott, Olson & Wittke, 2012, a ctenacanthiform from the Permian of Arizona (Guinot et al, 2013), which suggests that the distribution of the parallel-bundled enameloid within chondrichthyans is more complex than previously assumed.…”

“…Novel data (Enault, Cappetta & Adnet, ; Guinot et al ., ) have hinted at unsuspected diversity in the enameloid microstructure of some chondrichthyan lineages. These works underline the urgent need for a complete reassessment of the diversity and distribution of chondrichthyan enameloid microstructures.…”

Early Triassic Marine Biotic Recovery: The Predators' Perspective

“…Fishes, especially actinopterygians, generally exhibit an increase in diversity at the beginning of the Mesozoic, and reach their first peak in the Middle Triassic [26]–[28], [51], [52]. A specific radiation event has been recently proposed for neoselachian and hybodont chondrichthyans at the Permo-Triassic boundary, partly as a response to the extinction of previously abundant Palaeozoic stem chondrichthyans (e.g., Stethacanthidae) [53], although some clades such as cladodontomorph chondrichthyans might have survived into the Triassic utilizing deep-sea refugia [54].…”