Amniote faunal revision of the Pictou Group (Permo-Carboniferous), Prince Edward Island, Canada

Recent histological studies have revealed a diversity of dental features in Permo-Carboniferous tetrapods. Here, we report on the occurrence of plicidentine (infolded dentine around the base of the tooth root) in Sphenacodontia, the first such documentation in Synapsida, the clade that includes mammals. Five taxa were examined histologically, Ianthodon schultzei, Sphenacodon ferocior, Dimetrodon limbatus, Dimetrodon grandis, and Secodontosaurus obtusidens. The tooth roots of Ianthodon possess multiple folds, which is generally viewed as the primitive condition for amniotes. Sphenacodon and D. limbatus have distinctive "four-leaf clover"-shaped roots in cross section, whereas Secodontosaurus has an elongate square shape with only subtle folding. The most derived and largest taxon examined in this study, D. grandis, has rounded roots in cross section and therefore no plicidentine. This pattern of a loss of plicidentine in sphenacodontids supports previous functional hypotheses of plicidentine, where teeth with shallow roots require folds to increase the area of attachment to the tooth-bearing element, whereas teeth with long roots do not. This pattern may also reflect differences in diet between co-occurring sphenacodontids as well as changes in feeding niche through time, specifically in the apex predator Dimetrodon.

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First record of plicidentine in Synapsida and patterns of tooth root shape change in Early Permian sphenacodontians

Brink

LeBlanc

Reisz

2014

Naturwissenschaften

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Dimetrodon (Synapsida: Sphenacodontidae) from the cave system at Richards Spur, OK, USA, and a comparison of Early Permian–aged vertebrate paleoassemblages

Brink

MacDougall

Reisz

2019

Sci Nat

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Re-evaluation of the historic Canadian fossil Bathygnathus borealis from the Early Permian of Prince Edward Island

et al. 2015

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Abstract:The holotype and only known specimen of Bathygnathus borealis is a partial snout with maxillary dentition of a presumed sphenacodontid from the Lower Permian (Artinskian 283-290 Ma) redbeds of Prince Edward Island, Canada. Due to its incomplete nature, assessment of the taxon's systematic position within a cladistic analysis had never been performed. However, recent recognition of the phylogenetic utility of tooth characters in sphenacodontids now allows for a modern phylogenetic evaluation of B. borealis. Results show that B. borealis is the sister taxon of Dimetrodon grandis, which is supported by dental characters: crowns with mesial and distal denticles and roots elongate, lacking plicidentine. An autapomorphy of B. borealis is the large facial exposure of the septomaxilla. As Bathygnathus has priority over Dimetrodon in the scientific literature, we suggest a reversal of precedence is required to preserve the familiar name Dimetrodon and to maintain universality, thus recognizing the new species Dimetrodon borealis. Résumé : L'holotype et seul spécimen connu de Bathygnathus borealis consiste en un museau partiel avec dentition maxillaire d'un sphénacodontidé présumé des couches rouges du Permien inférieur (Artinskien 283-290 Ma) de l'Île-du-Prince-Édouard (Canada). En raison du caractère incomplet du spécimen, une évaluation de la position systématique de ce taxon dans le cadre d'une analyse cladistique n'avait jamais été effectuée, mais la reconnaissance récente de l'utilité phylogénétique des caractères dentaires chez les sphénacodontidés rend maintenant possible une évaluation phylogénétique moderne de B. borealis. Les résultats démontrent que B. borealis est le taxon frère de Dimetrodon grandis, une interprétation appuyée par des caractères dentaires dont des couronnes avec denticules mésiaux et distaux et des racines allongées, exemptes de plicidentine. La grande exposition faciale du septomaxillaire est une autapomorphie de B. borealis. Comme Bathygnathus a priorité sur Dimetrodon dans la documentation scientifique, nous proposons qu'une inversion de la préséance est nécessaire afin de préserver le nom familier Dimetrodon et de maintenir l'universalité, en reconnaissant ainsi la nouvelle espèce Dimetrodon borealis. [Traduit par la Rédaction]

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Amniote faunal revision of the Pictou Group (Permo-Carboniferous), Prince Edward Island, Canada

Cited by 5 publications

References 50 publications

First record of plicidentine in Synapsida and patterns of tooth root shape change in Early Permian sphenacodontians

First record of plicidentine in Synapsida and patterns of tooth root shape change in Early Permian sphenacodontians

Dimetrodon (Synapsida: Sphenacodontidae) from the cave system at Richards Spur, OK, USA, and a comparison of Early Permian–aged vertebrate paleoassemblages

Re-evaluation of the historic Canadian fossil Bathygnathus borealis from the Early Permian of Prince Edward Island

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