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, 228 (3), 414-29

Morphology and Function of the Palatal Dentition in Choristodera

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Morphology and Function of the Palatal Dentition in Choristodera

Ryoko Matsumoto et al. J Anat.

Abstract

Choristoderes are a group of extinct freshwater reptiles that were distributed throughout Laurasia from the Middle Jurassic to the Miocene. They are inferred to have had a lifestyle similar to that of extant gavialid crocodiles, but they differed from crocodiles in retaining an extensive palatal dentition. All choristoderes had teeth on the vomers, palatines and pterygoids, and teeth are rarely present on the parasphenoid. Palatal teeth are conical, as in the marginal dentition, and form longitudinal and transverse rows. Detailed examination of different genera shows that the orientation of the palatal tooth crowns changes with their position on the palate, supporting the view that they are involved in intra-oral food transportation, presumably in combination with a fleshy tongue. Moreover, observed variation in palatal tooth shape and the width of palatal tooth batteries may provide additional clues about diet. The European Simoedosaurus lemoinei has sharper palatal teeth than its North American counterpart, S. dakotensis, suggesting a preference for softer prey - a conclusion consistent with the more gracile teeth and narrower snout.

Keywords: Champsosaurus; Simoedosaurus; function; morphology; palatal dentition; subthecodont.

Figures

Figure 1
Figure 1
Choristoderan phylogenetic tree with palatal tooth arrangement; phylogenetic tree based on Matsumoto et al. (2013). Dentition on each palatal element marked in a different color; red, vomerine teeth; yellow, palatine teeth; green, longitudinal pterygoid tooth row; blue, pterygoid flange tooth row.
Figure 2
Figure 2
Marginal and palatal tooth morphology: (a) juvenile Monjurosuchus sp. (IVPP V14261) dentary teeth in medial view; (b) Cteniogenys sp. dentary (UCL uncataloged) in lateral view, SEM; (c) Champsosaurus gigas (SMM P77.33.24) left dentary teeth in lateral view; (d, e) Champsosaurus gigas (SMM P77.33.24) right maxillary teeth in lateral view, image reflected for ease of comparison; (f) Simoedosaurus lemoinei (MNHN BR 1935) replacement maxillary teeth in medial view; (g) Cteniogenys sp. (BMNH R11759), right pterygoid tooth; (h) Champsosaurus sp. isolated right palatine teeth (RTMP 92.36.270) in medial view. Tooth position is uncertain in (b), (g), (h) due to incompleteness of specimens.
Figure 3
Figure 3
Pterygoid teeth in Cteniogenys sp. (BMNH R11759) from the Middle Jurassic of Kirtlington, Oxfordshire, UK; (a) reconstructed skull in palatal view (Evans, 1990); color coding of the different regions of the palatal dentition are the same as in Fig. 2; (b) anterior longitudinal tooth row; (c) posterior pterygoid teeth; (d) isolated pterygoid from UCL uncataloged specimens (magnification × 50); (e) enlarged image of (b), worn tooth crown from the longitudinal pterygoid tooth row in medial view; (f) enlarged image of (d), complete crown on the longitudinal pterygoid tooth row in medial view (magnification × 500); (g) enlarged image of (d), posterior pterygoid tooth (magnification × 500).
Figure 4
Figure 4
Hyphalosaurus lingyuanensis holotype from the Early Cretaceous of the Yixian Formation of China (IVPP V11075): (a) photograph of the skull in palatal view; (b) line drawing of (a); color coding of the different regions of the palatal dentition are the same as in Fig. 2.
Figure 5
Figure 5
(a) Monjurosuchus sp. (IVPP V14261) from the Early Cretaceous of China, skull in palatal view: (b) photographs of the skull, enlarged view of palatal tooth area in (a); (c) line drawing of (b); color coding of the different regions of the palatal dentition are the same as in Fig. 2.
Figure 6
Figure 6
Ikechosaurus sunailinae from the Early Cretaceous Chabu‐Sumu locality, Inner Mongolia (IVPP V9611‐3), skull in palatal view: (a) photograph and line drawing of the skull in ventral view. Black circles indicate alveoli of palatal teeth; white circles showing presence of the teeth; color coding of the different regions of the palatal dentition are the same as in Fig. 2; gray zone indicating nasopalatal trough; arrows on tooth row showing orientation of tooth crowns. (b) Enlarged image of pterygoid and parasphenoid regions; (c) enlarged image of the longitudinal pterygoid tooth row (posterior); (d) pterygoid flange teeth in posterior view (image inverted for comparison).
Figure 7
Figure 7
Comparison of the palatal dentition in Champsosaurus; (a–d) from the Late Cretaceous; (e, f) from the Late Cretaceous and the Paleocene; (g–i) from the Paleocene. (a) Semi‐adult C. lindoei (RTMP 87.36.41); (b) juvenile C. lindoei (RTMP 94.163.01); (c) C. albertensis (RTMP 86.12.11), pterygoid flange teeth incomplete; (d) C. natator (NMC8919) pterygoid flange teeth incomplete; (e) C. ambulator (modified from Sigogneau‐Russell, 1979); (f) C. laramiensis (redrawn based on Brown, 1905 and Sigogneau‐Russell, 1979); (g) C. gigas (SMM P77.33.24); (h) C. dolloi (IRSNB R21) pterygoid flange teeth incomplete; (i) C. tenuis (SMM P79.14.1) pterygoid flange teeth and pterygoid longitudinal tooth rows are incomplete. Scale bars: 50 mm, but scale is unknown in (e). Blue colored area marks the distribution of the palatal dentition, and gray colored area marks nasopalatal trough extending from the choana.
Figure 8
Figure 8
Palatal dentition of Simoedosaurus sp. (SMNS 59026) (a–e) and S. lemoinei (f–i) from Mont Berru Reims, France: (a) photograph and line drawing of the skull (SMNS 59026) in palatal view; color coding of the different regions of the palatal dentition is the same as in Fig. 2; (b) lateral view of the snout (a); (c) enlarged image of anterior vomerine teeth of (b); (d) enlarged image of anterior palatine teeth of (b); (e) enlarged image of pterygoid teeth of (b) (reflected image); (f) isolated left vomer with teeth in lateral view, image inverted (MNHN BL9947); (g) isolated left palatine, image inverted (MNHN BR728); (h) posterior palatine dentition (MNHN BR 1935; neotype of S. lemoinei); (i) enlarged image of (h).
Figure 9
Figure 9
Simoedosaurus dakotensis (SMM P76.10.1) from the Paleocene of western North Dakota (near top of Slope Formation), USA: (a) skull in palatal view, digital image above and line drawing below (the letters b–h correspond to the following close‐up images below); color coding of the different regions of the palatal dentition is the same as in Fig. 2; (b) anterior vomerine teeth; (c) anterior palatine teeth; (d) posterior pterygoid, lateral tooth row; (e) posterior pterygoid, medial tooth row; (f) pterygoid flange in lateral view; (g) pterygoid flange in posterior view; (h) pterygoid flange teeth in lateral view.
Figure 10
Figure 10
(a) CT image of Champsosaurus lindoei (NMC 8920) without scale; the numbers on the skull corresponding to slice images 1–4. Red arrows showing nasopalatal trough. (b) Diagram of skull and lower jaw in anterior section (Champsosaurus as the model), the palatine teeth lie on the ridge, soft tissues are drawn in dashed‐lines.
Figure 11
Figure 11
Champsosaurus gigas (SMM P77.33.24) from the Paleocene of western North Dakota: (a) skull in lateral view; (b) line drawing and photograph of palatal dentition; (c) anterior vomerine teeth (reflected image); (d) palatine tooth row (reflected image); (e) anterior palatal dentition; (f) pterygoid, lateral tooth row; (g) pterygoid, medial tooth row; (h) pterygoid flange tooth row in lateral view. Black circles indicate alveoli of palatal teeth; color coding of the different regions of the palatal dentition is the same as in Fig. 2.
Figure 12
Figure 12
Late Cretaceous Champsosaurus; (a–c) C. albertensis (RTMP 86.12.11) from the Horseshoe Canyon Formation at Drumheller, Canada; (a) photo and line drawing of C. albertensis in palatal view; (b) right vomerine teeth in lateral view; (c) right palatine teeth in medial view, reflected image. (d–f) C. lindoei (RTMP 94.163.01) from the Oldman Formation Alberta, Canada; (d) photo and line drawing of C. lindoei in palatal view; (e) right vomerine teeth in lateral view; (f) right anterior palatine teeth in lateral view. Black circles indicate alveoli of palatal teeth; color coding of the different regions of the palatal dentition is the same as in Fig. 2.
Figure 13
Figure 13
Summary of the morphological variation in the palatal dentition of neochoristoderes corresponding to feeding stages; color coding of the different regions of the palatal dentition is the same as in Fig. 2.

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