Ancient sharks' rapid tooth replacement sheds light on ecosystem's recovery during Triassic Period

A team of researchers studied the tooth replacement rate of ancient hybodont sharks and its role in the recovery of the marine ecosystem during the Middle Triassic period. The ancient sharks, some of the most successful chondrichthyan lineages of all time, first appeared in the Devonian era and survived until the Late Cretaceous, according to a study published in May by Science Direct.

The study, led by Wen Wen and Qiyue Zhang, along with Jürgen Kriwet, Shixue Hu, Changyong Zhou, Jinyuan Huang, Xindong Cui, Xiao Min, and Michael J. Benton, found that the end-Permian mass extinction, which devastated much of life on Earth, had a surprisingly limited effect on hybodont sharks. Researchers noted that there are fewer records of hybodonts in the Triassic compared to the Jurassic and Cretaceous periods in China, which could hint at a shift in the marine ecosystem during this period. Actinopterygian fishes thrived in the time after this, with an impressive diversity of 31 taxa, including Halecomorphi and Ginglymodi. Chondrichthyan fishes, such as hybodont sharks, were relatively scarce, the report read.

"Our study offers a unique glimpse into the dynamics of ancient marine life after a catastrophic extinction event," Co-researcher Qiyue Zhang said. "The recovery of marine ecosystems during the Middle Triassic period was a complex process, and the role of hybodontid sharks was undoubtedly essential."

The researchers' breakthrough came with the discovery of three taxa of hybodontid sharks based on teeth, a first for the Mesozoic era in China. One of the taxa belongs to the Lonchidiidae family, christened Luopingselache striata gen. et sp. nov., while the other two were identified as belonging to Acrodus. The preserved dentition of Luopingselache striata provided valuable insights, showing pronounced monognathic heterodonty, a feature that distinguished this ancient shark. The study delved further into the tooth replacement rate of Luopingselache striata, revealing a surprisingly rapid rate of 2.6 days/row on average. According to the researchers, this rapid replacement might have been an adaptation to replace broken teeth and maintain an adequate dentition, vital for the survival of these sharks, the researchers wrote.

"The rapid tooth replacement rate we observed in Luopingselache striata is truly remarkable," lead researcher Wen Wen said. "It speaks to the resilience and adaptability of these ancient creatures during a crucial period of marine ecosystem recovery."

The researchers believe that these new insights into ancient sharks' tooth replacement rates provide valuable data for understanding the adaptive strategies of marine life during a time of ecological upheaval. Moreover, the study contributes to a better understanding of the recovery of marine ecosystems following major extinction events, which has implications for understanding current and future patterns of ecological recovery in the face of environmental challenges.