Cretaceous stem chondrichthyans survived the end-Permian mass extinction

Area of Science:

• Paleontology
• Marine Biology
• Evolutionary Biology

Background:

• Cladodontomorph sharks, an ancient group of stem chondrichthyans, were believed to have gone extinct during the end-Permian mass extinction event.
• This extinction event marked a significant turning point, preceding the major diversification of modern shark lineages (euselachians).
• The fossil record for cladodontomorphs has a substantial gap, leaving their evolutionary history and survival strategies largely unknown.

Purpose of the Study:

• To describe a newly discovered assemblage of cladodontomorph shark teeth from the Early Cretaceous period.
• To extend the known fossil record of cladodontomorphs by approximately 120 million years.
• To investigate the survival mechanisms of this ancient shark lineage through major extinction events.

Main Methods:

• Detailed morphological analysis of shark teeth found in an outer-platform environment.
• Histological examination of tooth structures to confirm identification and gather new data.
• Comparative analysis with existing fossil records of chondrichthyans.

Main Results:

• Discovery of a cladodontomorph shark tooth assemblage from the Early Cretaceous of southern France.
• The findings represent a significant extension of the cladodontomorph fossil record, bridging a gap of about 120 million years.
• New histological and morphological evidence supports the identification of these ancient shark teeth.
• The survival of this lineage suggests a strategy of habitat contraction into deep-sea environments during catastrophic events.

Conclusions:

• Cladodontomorph sharks persisted beyond the end-Permian extinction, surviving through utilizing deep-sea refuges.
• The extended fossil record highlights the longest known gap for an extinct marine vertebrate group.
• This discovery underscores the critical role of deep-sea environments and their poorly understood biodiversity in marine fish evolutionary history.