# Diversity of tooth mineralisation patterns at the base of crown chondrichthyans

## TL;DR

This study examines ancient shark teeth to reveal early diversity in tooth structure and mineralization patterns among early jawed fish.

## Contribution

It identifies significant histological and developmental disparity in tooth mineralization at the base of crown chondrichthyans.

## Key findings

- Thin sections and CT data show high histological diversity in early chondrichthyan teeth.
- Mineralization patterns vary widely, with no clear phylogenetic signal among the studied taxa.
- Tooth size differences suggest varying replacement rates, with implications for holocephalan evolution.

## Abstract

The highly specialised dentitions of modern sharks enable them to exploit a wide range of food sources. Exceptional fossil preservation of three Late Devonian basal chondrichthyan taxa from the Anti-Atlas, Morocco, provides the unique opportunity to study these dentitions in detail, including their tooth histology, replacement patterns, and mineralisation sequences. Thin sections and CT-data of tooth files reveal a high histological diversity and evidence a noticeable disparity in mineralisation patterns early in chondrichthyan evolution. The presence of similar tooth histology and mineralisation patterns in phylogenetically and chronostratigraphically distant chondrichthyan taxa opposes a phylogenetic signal. Although the pseudoosteodont histotype is considered plesiomorphic, we found a high disparity regarding the arrangement of dental tissues in early chondrichthyans. Tooth size differences indicate slow tooth replacement rates for Ctenacanthus and Maghriboselache. Smaller differences in Phoebodus suggest an elevated rate. Tooth retention in Maghriboselache might constitute a precursor for the holocephalan evolution of tooth plates.

The study of three in situ preserved chondrichthyan tooth files reveals histological and developmental disparity at the stem of crown chondrichthyans and provides insights into tooth replacement and the evolution of holocephalan tooth plates.