An Investigation into the Occurrence of Plicidentine in the Teeth of Squamate Reptiles

Despite its use as a diagnostic taxonomic feature, the occurrence and distribution of plicidentine in the teeth of squamate reptiles is unclear. This appears to be due to several factors: the various kinds of folding, wrinkling, and striation that occur within different dental tissues; difficulty of interpreting conditions in poorly preserved extinct taxa; and incomplete knowledge of tooth development. We investigated tooth development and morphology in extant and fossil squamate reptiles using skeletal preparations, histological sections, and CT-scanning data. Among squamates, we found plicidentine only in the teeth of varanoid lizards and note that much more anatomical complexity exists than previously thought in the dental and attachment tissues of these groups. Degree of development of plicidentine is variable within varanoids, with the strongest development occurring in some species of Varanus. In contrast to some reports, we found no evidence for the occurrence of plicidentine in the teeth of mosasauroid lizards or snakes. Some mosasaurs exhibit raised ridges on the enamel surface that extend from the base to the tip of the tooth, as well as occasional striation of the tooth bases built from bone of attachment; neither of these features is considered homologous to plicidentine infolding. Some snakes exhibit weak wrinkling of the tooth base that corresponds closely to the pattern of wrinkling in the overlying bone of attachment. This condition occurs infrequently in snakes, and details of tooth development and attachment also do not support its homology with plicidentine. Our results indicate that plicidentine is best interpreted as a synapomorphy of Varanoidea.

Figure 1

Transverse section through developing dentary tooth in Crotaphytus collaris (FMNH 210169).

Figure 2

Diagrammatic representation of cross-sectioned tooth base with (top) presence of plicidentine and (bottom) absence of plicidentine.

Figure 3

Varanid dental features. (A) Lingual view of mandibular teeth in Varanus sp. (FMNH 195576); (B) Ventral view of bases of three maturing teeth (maturing from left to right) in Varanus komodoensis (FMNH no number); (C) Bone of attachment tooth base in mandible of Varanus sp. (FMNH 195576); and (D) Transverse section through maxillary tooth of Varanus salvator (no data specimen).

Figure 4

Helodermatid dental features. (A) Lingual view of right dentary teeth in Heloderma horridum (FMNH 31366); (B) Ventral view of base of mature tooth in Heloderma suspectum (FMNH 229925); (C) Broken tooth base in contact with attachment tissue base in Heloderma horridum (FMNH 31366); and (D) Horizontal CT section revealing mandibular tooth bases in Heloderma horridum (TNHC 64380).

Figure 5

Lanthanotid dental features. (A, B) Scanning electron micrograph of right dentary teeth in lingual view in Lanthanotus borneensis (FMNH 134711); and (C) Transverse section through dentary tooth of Lanthanotus borneensis (FMNH 151714).

Figure 6

Mosasauroid dental features. (A) Ankylosed tooth in Clidastes propython (FMNH PR 139); (B) Lingual view of right dentary of Clidastes propython (FMNH PR 495); and (C) Transverse section through isolated tooth of Clidastes propython (FMNH PR 150).

Figure 7

Snake dental features. (A) Scanning electron micrograph of isolated maxillary tooth of the colubrid snake Enhydris doriae (FMNH 129420); (B) Scanning electron micrograph of left dentary teeth (lingual view) in the aniliid snake Anilius scytale (FMNH 35683); (C) Scanning electron micrograph of dentary (ventrolingual view) in the aniliid snake Anilius scytale (FMNH 35683); and (D) Sagittal section through dentary tooth of Anilius scytale (FMNH 35687).

Figure 8

Tooth structure in the fossil snake Yurlunggur sp. (QMF 36441). (A) Medial view of right dentary fragment; and (B) Detailed view of tooth base and attachment site.

Contributor Notes

(MK) Department Of Zoology, Field Museum Of Natural History, Chicago, Illinois 60605; and (OR) Department of Geology, Field Museum of Natural History, Chicago, Illinois 60605. E-mail: mkearney@fieldmuseum.org; and (OR) orieppel@fieldmuseum.org. Send reprint requests to MK.

Received: 24 Apr 2005

Accepted: 05 Apr 2006