Casey M. Holliday

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Vertebrate Functional Morphology & Evolution

 

Microanatomy of the mandibular symphysis in lizards: patterns in fiber orientation and Meckel's cartilage and their significance in cranial evolution

CM Holliday, NM Gardner, SM Paesani, M Douthitt, JL Ratliff. 2010. The Anatomical Record. 293:1350-1359.

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Soft tissue morphology of the mandibular symphysis

Although the mandibular symphysis is a functionally and evolutionarily important feature of the vertebrate skull, little is known about the soft-tissue morphology of the joint in squamate reptiles. Lizards evolved a diversity of skull shapes and feeding behaviors, thus it is expected that the morphology of the symphysis will correspond with functional patterns. Here we present new histological data illustrating the morphology of the joint in a number of taxa including iguanians, geckos, scincomorphs, lacertoids, and anguimorphs. The symphyses of all taxa exhibit dorsal and ventral fibrous portions of the joints that possess an array of parallel and woven collagen fibers. The middle and ventral portions of the joints are complemented by contributions of Meckelís cartilage. Kinetic taxa have more loosely-built symphyses with large domains of parallel-oriented fibers whereas hard biting and akinetic taxa have symphyses primarily composed of dense, woven fibers. Whereas most taxa maintain unfused Meckelís cartilages, iguanians and geckos independently evolved fused Meckelís cartilages however the jointís morphologies suggest different developmental mechanisms. Fused Meckelís cartilages may be associated with the apomorphic lingual behaviors exhibited by iguanians (tongue translation) and geckos (drinking). These morphological data shed new light on the functional, developmental, and evolutionary patterns displayed by the heads of lizards.

Funded by: WV NASA Space Grant Consortium; Marshall University; Ohio University; and University of Missouri. Acknowledgments to Steve Reilly (OU Biological Sciences) Larry Witmer (OU Biomedical Sciences), Jessie Maisano (UTCT; NSF Deep Scaly National Science Foundation); and Phil Allman (Florida Gulf Coast University): University of Missouri Department of Pathology and Anatomical Sciences.

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FIGURE 1. Phylogenetic relationships and head structure of lepidosaur taxa used in this study. Cladogram based on Conrad (2008). FIGURE 2. Anatomical organization of the mandibular symphysis of Varanus exanthematicus and V. niloticus. (A) CT model of mandibles in dorsal view; (B) Right mandible in medial view; (C) Close-up view of symphysis in A depicting osteological structures of symphysis and the correlates of soft tissues; (D) Close-up view of symphysis in B depicting location of sections in E-H. (E) Axial section of symphysis in Varanus exanthematicus (Varanidae)(Goldnerís Trichrome); (F) Axial section of symphysis of V. exanthematicus (Von Kossa/MacNealís Tetrachrome); (G) Horizontal section of middle portion of symphysis in V. niloticus (Goldnerís Trichrome); (H) Horizontal section of dorsal portion of symphysis in V. niloticus (Goldnerís Trichrome). Scale bar = 50Ķm. FIGURE 3. Fiber orientation in the symphyses of select taxa using circular polarized light and image analysis software. (A, B) Varanus niloticus; (C, D) Pogona vitticeps (Iguania); (E, F) Eumeces schneideri (Scincidae); (B, D, F) 0 degrees; (A, C, E) 45 degrees.
FIGURE 4. Anatomical organization of the mandibular symphyses in representative squamate taxa. (A, B) Eumeces; (C, D) Oplurus cuvierii (Iguania); (E, F) Gerrhosaurus major (Gerrhosauridae); (G, H) Pogona; (I) Lepidophyma flavimaculatum (Xantusiidae); (J) Tupinambis teguixin (Teiidae); (K) Hemitheconyx caudicinctus (Gekkota); (L) Nerodia sipedon (Serpentes). (A, F, L) Von Kossa/MacNealís tetrachrome. (B, E, G, H, I, J, K) Goldnerís Trichrome. Scale bar = 50Ķm. FIGURE 5. Anatomy of Meckelís cartilages and ossification fronts in representative squamate taxa. (A) Ctenosaura similis (Iguania); (B) Callisaurus draconoides (Iguania); (C) Pogona; (D) Gerrhosaurus; (E, F) Eumeces; (G) Hemitheconyx; (H, I) Higher magnification of cartilage-bone transition in Pogona; (J) V. niloticus. (A, C, I) Safranin O/Fast Green; (B, D, F, H) Von Kossa/MacNealís tetrachrome; (E, G) Goldnerís trichrome. (A-I) axial sections. (J) horizontal section. FIGURE 6. Evolutionary morphology of the mandibular symphysis in lepidosaurs with key soft tissue structures and behavioral regimes. (A) Pogona (Iguania); (B) Hemitheconyx (Gekkota); (C) Eumeces (Scincidae); (D) Lepidophyma (Xantusiidae); (E) Tupinambis (Teiidae); (F) Varanus exanthematicus (Varanidae).

 

Lizard 3D Database

Investigations into the structure of lizard mandibular symphyses

This page was constructed by Nick Gardner, Marshall University Undergraduate during 2009.

 

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Histology

Hemitheconyx caudicinctus

OUVC 10411

Hemitheconyx caudicinctus

Skull
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Hemitheconyx caudicinctus

Mandibles
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Oedura lesueurii

OUVC 10412

Oedura lesueurii

Skull
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Oedura lesueurii

Mandibles
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Lepidophyma flavimaculatum

OUVC 10418

Lepidophyma flavimaculatum

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Lepidophyma flavimaculatum

Mandibles
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Gerrhosaurus major

OUVC 10410

Gerrhosaurus major

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Gerrhosaurus major

Mandibles
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Eumeces schneideri

OUVC 10415

Eumeces schneideri

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Eumeces schneideri

Mandibles
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Tupinambis teguixin

OUVC 10413

Tupinambis teguixin

Skull
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Tupinambis teguixin

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Varanus exanthematicus

OUVC 10416

 

Varanus exanthematicus

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Varanus exanthematicus

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Pogona vitticeps

ROM 22699 courtesy of UTCT


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Pogona vitticeps

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Pogona vitticeps

Mandibles
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