The mosasaur tooth attachment apparatus as paradigm for the evolution of the gnathostome periodontium

Abstract

Vertebrate teeth are attached to jaws by a variety of mechanisms, including acrodont, pleurodont, and thecodont modes of attachment. Recent studies have suggested that various modes of attachment exist within each sub-category. Especially squamates feature a broad diversity of modes of attachment. Here we have investigated tooth attachment tissues in the late cretaceous mosasaur Clidastes and compared mosasaur tooth attachment with modes of attachment found in other extant reptiles. Using histologic analysis of ultrathin ground sections, four distinct mineralized tissues that anchor mosasaur teeth to the jaw were identified: (i) an acellular cementum layer at the interface between root and cellular cementum, (ii) a massive cone consisting of trabecular cellular cementum, (iii) the mineralized periodontal ligament containing mineralized Sharpey's fibers, and (iv) the interdental ridges connecting adjacent teeth. The complex, multilayered attachment apparatus in mosasaurs was compared with attachment tissues in extant reptiles, including Iguana and Caiman. Based on our comparative analysis we postulate the presence of a quadruple-layer tissue architecture underlying reptilian tooth attachment, comprised of acellular cementum, cellular cementum, mineralized periodontal ligament, and interdental ridge (alveolar bone). We propose that the mineralization status of the periodontal ligament is a dynamic feature in vertebrate evolution subject to functional adaptation.

The last European varanid: demise and extinction of monitor lizards (Squamata, Varanidae) from Europe

“…Trenchant and keeled or globular teeth, provided with spongy tissue for the connection with their tooth-bearing bone, and striation of the surface of the teeth near their base (indicating the presence of plicidentine, i.e., the infolding of the dentine and enamel at the basal portion of the tooth) are typical features of the clade Varanoidea (e.g., Estes, 1983;Bailon, 1991;Kearney and Rieppel, 2006;Pianka et al, 2004;Luan et al, 2009). Moreover, certain features of the new Greek material exclude its referral to the non-varanid varanoids (helodermatids, necrosaurids, and lanthanotids).…”

Mandibular histology and growth of the nonmammaliaform cynodont Tritylodon

“…The size of the osteocyte lacunae appear to be more globular in the alveolar bone than the mandibular bone [in mosasaurs, the opposite pattern occurs (Luan et al, 2009)], although we are cautious in making this statement as there are many factors such as orientation of the lacunae and diagenesis that can affect their appearance and size.…”

Tooth histology, attachment, and replacement in the Ichthyopterygia reviewed in an evolutionary context

“…The goal of research on this topic was to describe the diversity of tooth shape, structure, and attachment in a wide variety of taxa, and to identify commonalities in amniote dentition. Interest in both of these aspects of tooth histology persists to the present day, and now also includes data on tooth development and gene expression (e.g., Caldwell et al 2003;Delgado et al 2005;Luan et al 2009;McIntosh et al 2002). However, such detailed information remains limited to a handful of genera, and current research does not emphasize differences in the quantity and arrangement of tooth tissues between closely related organisms.…”