Cranial suture biomechanics in Metoposaurus krasiejowensis (Temnospondyli, Stereospondyli) from the upper Triassic of Poland

Abstract

Cranial sutures connect adjacent bones of the skull and play an important role in the absorption of stresses that may occur during different activities. The Late Triassic temnospondyl amphibian Metoposaurus krasiejowensis has been extensively studied over the years in terms of skull biomechanics, but without a detailed description of the function of cranial sutures. In the present study, 34 thin sections of cranial sutures were examined in order to determine their histovariability and interpret their biomechanical role in the skull. The histological model was compared with threedimensional-finite element analysis (FEA) simulations of the skull under bilateral and lateral biting as well as skull-raising loads for maximum and minimum principal stress. Histologically, only two sutural morphologies were recognised in the skull of Metoposaurus: interdigitated sutures (commonly associated with compressive stresses) are dominant along the entire length of the skull roof and palate; tongueand-groove sutures (commonly associated with tensile stresses) are present across the maxilla. FEA shows a much more complex picture of stress type and distribution than predicted by sutures. Common to both methods is a predominance of compressive stresses which act on the skull during biting. The methods predict different stress regimes during biting in the posterior part of the skull: where histological analysis suggests compression, FEA predicts tension. For lateral biting and skull raising, histological and digital reconstructions show similar general patterns but with some variations. K E Y W O R D S dermal bones, finite element analysis, histology, palaeoecology

Climatic influence on the growth pattern ofPanthasaurus maleriensisfrom the Late Triassic of India deduced from paleohistology

“…In general, the growth of Metoposaurus krasiejowensis consists of primary cortex built up of parallel-fibered bone, and sometimes even incipient fibrolamellar bone (Konietzko-Meier & Sander, 2013), which might be exclusively deposited in juvenile individuals (Konietzko-Meier & Sander, 2013). There is also a rich data set published on dermal bones in order to infer information about feeding ecology based on biomechanical reconstruction of metoposaurid skull (Gruntmejer, Konietzko-Meier & Bodzioch, 2016;Gruntmejer et al, 2019a;Gruntmejer et al, 2019b;Konietzko-Meier et al, 2018). Analyzes of vertebrae helped to establish histological ontogenetic stages, a method which allows a relative determination of individual age, based on various histological and microstructural characters of vertebrae, when the classical growth cycles are not developed (Konietzko-Meier, Bodzioch & Sander, 2012) and showed the variability between different temnospondyl groups which may be taxonomically important (Konietzko-Meier, Danto & Gądek, 2014).…”

Mandible histology in Metoposaurus krasiejowensis (Temnospondyli, Stereospondyli) from the Upper Triassic of Poland

“…The presence of well-mineralised and dense bundles in these areas suggests a strong skeletal muscle attachment of the skull to the vertebral column (Gruntmejer, Konietzko-Meier & Bodzioch, 2016). Moreover, numerous clusters of short Sharpey's fibres occur at sutural edges between adjacent bones (Gruntmejer et al, 2019b). Their presence along the lateral edges of dermal bones refers to the occurrence of collagen fibres within the sutural morphospace which bridged adjacent bones and increased the connections between them (Rafferty & Herring, 1999).…”

“…Metoposaurids were cosmopolitan temnospondyls in freshwater Sharpey's fibres shows that the skull was a robust structure which enabled the animal to bite actively on prey. Computational simulation of the skull of Metoposaurus krasiejowensis using FEA (Fortuny, Marcé-Nogué & Konietzko-Meier, 2017) and histological analysis of cranial sutures (Gruntmejer, 2012;Gruntmejer et al, 2019b) have documented that metoposaurids specialised in direct biting during ambush and active hunting. Moreover, previous studies which focused on skull biomechanics in Metoposaurus krasiejowensis, had already shown that histology and the computed Finite Elements (FE) method were not flawless research techniques.…”

“…It has been confirmed in a skull of Metoposaurus that even the same bone may show various microstructures in different areas (Gruntmejer, Konietzko-Meier & Bodzioch, 2016). In a computational approach, FEA results are very often based on some simplifications and may thus mask significant biomechanical features, i.e., bone porosity or ornamentation (Bright, 2014;Konietzko-Meier et al, 2018;Gruntmejer et al, 2019b). However, applying both methodologies in parallel to a wider extent may provide a larger data set and more reliable results.…”

“…However, applying both methodologies in parallel to a wider extent may provide a larger data set and more reliable results. Merged histological and computational FE studies have revealed that metoposaurids were well adapted to life in Late Triassic ecosystems and used two foraging techniques of prey capture, i.e., bilateral and lateral biting during active swimming and bilateral biting, while remaining buried in mud and attacking prey in ambush (Konietzko-Meier et al, 2018;Gruntmejer et al, 2019b).…”