Morphology and preliminary biomechanical interpretation of mandibular sutures in Metoposaurus krasiejowensis (Temnospondyli, Stereospondyli) from the Upper Triassic of Poland

Kamil Gruntmejer,Dorota Konietzko-Meier,Josep Fortuny,Adam Bodzioch

doi:10.1007/s41513-018-0072-4

Abstract

The morphology of the mandibular sutures in the Late Triassic temnospondyl Metoposaurus krasiejowensis has been examined in order to determine their role in mandible biomechanics. Until now, no histological studies of mandibular sutures in extinct vertebrates were performed, in contrast to cranial sutures. As a consequence, mandibular suture interpretations herein are based mainly on comparisons with previous studies of cranial sutures and with 3D cranial finite element analysis of this species. A total of 32 standard thin sections were studied under standard petrographic microscope observations in order to differentiate the morphology of mandibular sutures. Five mandibular suture types are present in this taxon: interdigitated, shallowly interdigitated, overlapping, tongue and groove and abutting. Based on previous work, it has generally been assumed that the shallowly interdigitated, tongue, groove and abutting suture types are associated with tension, the interdigitated type with compression and the overlapping type with absorption and counteraction of variable loads. The sutures associated with tension occur mainly in the anterior part of the mandible, principally in the dentary; overlapping sutures have been noted in medial portions of the mandible and sutures associated with compression mainly in posterior portions, i.e., in the angular and prearticular. The variability of suture types along the mandible suggests a complex loading regime of compression and tension. Sutures associated with tension and a flexible symphysis potentially allowed an increase of oral volume during gape opening, whereas sutures associated with compression represent adaptations for strong bite forces.

Highlights

With the exception of the small-sized taxon Apachesaurus, metoposaurids were large, around 2–3-m-long, aquatic temnospondyl amphibians with dorso-ventrally flattened bodies and large and parabolic skulls (Hunt 1993; Schoch and Milner 2000)
The main goal of the present study is to investigate, for the first time, mandibular sutural morphology in the Late Triassic temnospondyl Metoposaurus krasiejowensis using histological thin sections
The mandible sutures in Metoposaurus krasiejowensis are of different types: interdigitated, shallowly interdigitated, overlapping, tongue and groove and abutting

Summary

Introduction

With the exception of the small-sized taxon Apachesaurus, metoposaurids were large, around 2–3-m-long, aquatic temnospondyl amphibians with dorso-ventrally flattened bodies and large and parabolic skulls (Hunt 1993; Schoch and Milner 2000). Dzik et al (2000) proposed that prey was captured by suction, whereas 3D-computational finite element analysis (FEA) of large temnospondyl taxa (e.g., capitosaurids) has revealed that these animals were active hunters, able to attack their prey by direct biting during swimming as well. It is because of the limited comparisons with extant taxa and demonstrating the peculiar ecological niche occupied by gigantic temnospondyl taxa (Fortuny et al 2011, 2012, 2016; Marcé-Nogué et al 2015). Dutuit (1976) illustrated a cross section of the posterior part of the mandible of Dutuitosaurus ouazzoui, focusing on the articulation between the skull and mandible; no detailed information on the structure of the suture was provided

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