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

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. Keywords Temnospondyli · Metoposaurus · Mandible · Sutures · BiomechanicsResumen Se ha examinado la morfología de las suturas mandibulares del temnospóndilo del Triásico Superior Metoposaurus krasiejowensis para determinar su papel en la biomecánica mandibular. Hasta la fecha, no se han realizado estudios histológicos de las suturas mandibulares de vertebrados fósiles, en contraste con los estudios histológicos en suturas craneales. Como consecuencia, las interpretaciones sobre las suturas mandibulares están aquí basadas en la comparación con estudios previos en suturas craneales y con análisis 3D de elementos finitos para esta misma especie. En total 32 laminas delgadas estándares fueron estudiadas con observaciones de microscopio petrográfico con el fin de diferenciar la morfología de las suturas mandibulares. Cinco tipos de suturas mandibulares son presentes en este taxón: interdigitales, levemente interdigitales, superposición, lengua, ranura y lindante. En base a estudios previos, se ha asumido generalmente que las suturas levemente interdigitales, lengua, ranura y lindantes se asocian con cargas de tensión, mientras que las de tipo interdigitales se asocian con compresión y el tipo sutural de superposición con distintas cargas de absorción y neutralización. Las suturas asociadas con tensión ocurren mayormente en la parte...

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

“…The present histological analysis of the cranial sutures in Metoposaurus krasiejowensis skull revealed the presence of only two sutural morphologies: interdigitated (deep and smooth) and tongue‐and‐groove, in comparison with the mandible of this taxon where five different suture types occur (Gruntmejer et al, ). The skull of Metoposaurus krasiejowensis is dominated by interdigitated sutures both on the skull roof and palate.…”

“…In sutures located at the midline of the skull, Sharpey's fibres are rarer. A similar pattern of Sharpey's fibre arrangements also occurs at the lateral edges of mandibular sutures, that is, they are numerous in interdigitated sutures, whereas in shallow interdigitated, overlapping, and tongue‐and‐groove sutures they are rarer and even difficult to follow (Gruntmejer et al, ). Moreover, well‐mineralised Sharpey's fibres occur numerously in all dermal bones of Metoposaurus krasiejowensis and they are not limited to sutural edges.…”

“…Recent histological and computational FEA have revealed that, similar to most of the large temnospondyls (particularly, stereospondyls; e.g., Fortuny, Marcé‐Nogué, De Esteban‐Trivigno, Gil, & Galobart, ; Fortuny, Marcé‐Nogué, Gil, & Galobart, , Fortuny et al, ; Lautenschlager, Witzmann, & Werneburg, ; Marcé‐Nogué et al, ), metoposaurids were capable of active hunting as well as ambush predation (Fortuny et al, ; Konietzko‐Meier et al, ). Moreover, preliminary interpretation of mandibular suture biomechanics in Metoposaurus krasiejowensis (Gruntmejer et al, ) confirms the ability to engage in strong biting. Based on these considerations, Metoposaurus krasiejowensis is an excellent candidate on which to test palaeobiological hypotheses.…”

“…The extensive record of osteohistological and 3D‐computational studies on the Late Triassic temnospondyl amphibian Metoposaurus krasiejowensis is a good example in this respect. This taxon has been well described in terms of osteology (Dzik, Sulej, Kaim, & Niedźwiedzki, ; Barycka, ; Sulej, , ; Dzik & Sulej, ; Konietzko‐Meier & Wawro, ; Antczak & Bodzioch, ), histology (Gruntmejer, ; Gruntmejer et al, ; Gruntmejer, Konietzko‐Meier, Bodzioch, & Fortuny, ; Konietzko‐Meier et al, ; Konietzko‐Meier, Bodzioch, & Sander, ; Konietzko‐Meier, Danto, & Gądek, ; Konietzko‐Meier & Klein, ; Konietzko‐Meier & Sander, ; Teschner, Sander, & Konietzko‐Meier, ), and computational biomechanics (Fortuny, Marcé‐Nogué, & Konietzko‐Meier, ; Konietzko‐Meier et al, ). From these studies, a picture has emerged that describes Metoposaurus as an elongate, aquatic, animal that used its long and flattened tail for swimming (Konietzko‐Meier et al, ).…”

New insights into the evolution of temnospondyls

“…As previously mentioned, during the Late Triassic the capitosaurids share nonmarine environments with other groups such as the metoposaurids. The latters are the topics of the contributions of Gruntmejer et al (2019) and Chakravorti and Sengupta (2019) who used different approaches (taxonomy, paleobiology, etc.) and multiple taxa to investigate this enigmatic group: Gruntmejer et al…”