# A new teleosaurid (Crocodylomorpha, Thalattosuchia) from the Sibumasu Terrane of Southeast Asia and a taxonomic reassessment of Indosinosuchus

## TL;DR

A new species of teleosaurid crocodile is discovered in Thailand, offering insights into the diversity and habitat preferences of these ancient marine reptiles in Southeast Asia.

## Contribution

The paper introduces a new teleosaurid species and revises the taxonomy of Indosinosuchus, enhancing understanding of teleosaurid diversity and paleobiogeography.

## Key findings

- Indosinosuchus peninsularensis sp. nov. is characterized by unique cranial and postcranial features.
- Phylogenetic analysis supports a monophyletic Teleosauroidea and positions the new species within a polytomy.
- The new species provides evidence for ecological plasticity and dispersal of teleosaurids in Southeast Asia.

## Abstract

We describe teleosaurid remains from the Middle to Upper Jurassic Khlong Min Formation at Ban Nam Pun in southern Thailand and define Indosinosuchus peninsularensis sp. nov. This new species is diagnosed by a unique combination of cranial and postcranial features, including the nasal reaching anteriorly at the level of the 18th maxillary alveolus, absence of an incisive foramen, oval-shaped external nares, and broad ornamented osteoderms. Phylogenetic analysis positions I. peninsularensis within a polytomy alongside Mystriosaurus laurillardi and other Asian teleosaurids, supporting a monophyletic Teleosauroidea. In addition, the revision of Indosinosuchus kalasinensis as a junior synonym of I. potamosiamensis also strengthens the taxonomic framework of the genus Indosinosuchus. Indosinosuchus peninsularensis sp. nov., discovered in a low-energy lagoonal environment, offers significant insights on the ecological preferences of teleosaurids. In contrast to the fluvially deposited Phu Kradung Formation of northeastern Thailand, the lagoonal and marginal marine sediments of the Khlong Min Formation are considered indicative of a broad spectrum of habitat occupation by Asian teleosauroids. Based on these observations, a high degree of ecological plasticity has been inferred for Thai teleosaurids, and their extensive dispersal across both the Sibumasu and Indochina terranes during the Middle to Late Jurassic has been further substantiated. The recognition of I. peninsularensis sp. nov. contributes to our understanding of teleosaurid diversity and paleobiogeography in Southeast Asia.