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2005: Ph.D. Anatomical Science, Stony Brook University
2000: M.S. Basic Health Sciences, Stony Brook University
2000: M.Phil. Anatomical Sciences, Stony Brook University
1997: B.A. Anthropology, minor Biology, Univ. of California at Santa Cruz
Curriculum Vitae (PDF,24KB) | Endnote Überfile | Publications | Links
My research focuses on the functional morphology and biomechanics of complex, integrated functional systems, and specifically the vertebrate feeding system. I address questions of function, evolution and mechanics of the feeding system using in vivo experimental techniques, including bone strain, electromyography, and high-speed videography/videofluoroscopy.
At Brown University, I am working in the Functional Morphology & Biomechanics Laboratory with Dr. Elizabeth Brainerd on projects that utilize a newly-developed three-dimensional videofluoroscopy technology, called CTX. This experimental technique makes it possible to dynamically visualize the movements of skeletal tissues in three dimensions during various activities. I am directing two research projects using the CTX system: analysis of dental occlusion during mastication in miniature pigs and evaluation of the movements of cranial bones (cranial kinesis) during feeding in ducks. Both projects involve the surgical placement of tantalum markers in the skull (as well as the teeth of the pigs), followed by 3D videofluoroscopic recordings. CT scans of the experimental subjects are then superimposed upon the calibrated 3D recordings, resulting in an animated skeletal "model" from which movement data can be extracted.
The occlusion project has implications for understanding the mechanics of tooth contact during mastication. Although the kinematics of mastication have been studied in a variety of species, our knowledge of how the teeth actually come together is much less precise. Additionally, this project will evaluate the effect of tooth eruption on occlusion and the feasibility of using CTX technology to examine very small skeletal motions such as the movement of teeth within their sockets through tension and compression of the periodontal ligaments.
The cranial kinesis project is the first 3D examination of these types of movements in any vertebrate. Cranial kinesis involves movement of numerous cranial "segments" through the action of a complicated linkage system. Evaluation of these motions will give us mechanical insight into skull mobility, a feature that is shared by numerous groups of vertebrates.
My dissertation research, conducted at Stony Brook University and the University of Antwerp, Belgium, investigated functional and morphological trade-offs in lizards related to prey transport, or the movement of prey items through the oral cavity.
Prey Transport in Lizards
My dissertation research investigated functional and morphological trade-offs in lizards related to prey transport, or the movement of prey items through the oral cavity. This work has helped to elucidate the fundamental dichotomy in lizards between the use of the tongue as a sensory organ and its use as a means of food transport. Several clades of lizards with highly developed chemosensory systems have modified the morphology of the tongue, rendering it relatively ineffective for prey transport. However, instead of sacrificing overall transport ability, these groups of lizards have convergently evolved an alternative means of prey transport called inertial transport, during which rapid movements of the head and neck are coordinated with jaw opening and closing in order to transport prey. In addition to investigating this trade-off, my dissertation work was the first quantitative description of this type of feeding behavior in lizards. Additionally, it addressed the role of prey properties (e.g., prey type, prey mass, prey hardness) in the modulation of feeding behavior.
For a video (1.8MB) of Tupinambis merianae, a large teiid lizard, using inertial transport, please click here (MPG,1.6MB). The reflective markers on the animal's head are used by the Vicon system to identify and reconstruct 3-D coordinates.
Biomechanics of the Crocodilian Skull
An additional portion of my research program has focused on the biomechanics of feeding in crocodilians, and in 2001 I started a project with Dr. Callum Ross using bone strain analysis, electromyography and bite force measurement techniques to address a number of questions regarding cranial function. The original goal of this research was to examine the biomechanical behavior of the alligator mandible, but it has since expanded to include a number of different aspects of musculoskeletal biology.
One aspect of this research, conducted in collaboration with Dr. William Daniel, examined how in vivo strain magnitudes and orientations correspond to those obtained when the skull is modeled using basic beam theory and a finite-element model (FEM). Finite-element analysis (FEA) is a powerful technique that is becoming increasingly important in functional morphology. It permits the analysis of stress and strain within complex or irregular structures and allows for variation in the nature of external forces applied to these structures without the need for invasive in vivo experiments. However, extremely few confirmation studies using naturalistic in vivo data have been conducted to quantitatively examine the accuracy of finite-element and beam models in predicting strain regimes in skulls. The results of this study indicate that while the beam and finite-element model provide generally accurate predictions for in vivo strain orientations, patterns of strain magnitude in the models differ dramatically from the in vivo data. A portion of this work is being continued in collaboration with Dr. Emily Rayfield using a detailed FEM of the alligator mandible in order to better understand the function of sutures (collagenous junctions between cranial elements) in feeding.
Cranial Kinesis
I am also interested in cranial kinesis in both extant and extinct taxa, with an emphasis on extant lizards. Cranial kinesis refers to movement between or within the bones of the skull besides that in the articulation with the mandible. Different forms of kinesis are found in extant avian and squamate groups, as well as in a variety of extinct taxa. Cranial kinesis has traditionally been analyzed using a purely descriptive approach. However, by incorporating experimental techniques, such as videofluoroscopy and the ones mentioned above, the exact forms and mechanisms of cranial kinesis in various vertebrate forms can be elucidated and this knowledge applied to extant taxa. I am working with Dr. Anthony Herrel, from the University of Antwerp, to assess the degree of cranial kinesis in many different types of lizards, using a high-speed, high-resolution X-ray video system.
During the summer of 2001, I participated in two paleontological expeditions in Madagascar. The first was an expedition to Southern Madagascar in search of Cenozoic terrestrial deposits and cave sites. The end of the summer was spent as a member of Dr. David Krause's crew in northwestern Madagascar where we excavated sites of Late Cretaceous age. During the later expedition, we participated in the dedication of the first school in Madagascar built with money from the Ankizy Fund, a non-profit organization founded by Dr. Krause with the goal of providing education and health care to Malagasy children in more rural regions of the country.
During August of 2002, I rode my bicycle from Seattle, WA to San Francisco, CA. I hope to complete a cross-country ride at some point in the future. Outside of academics, I enjoy competitive swimming, bicycling, and cooking.
I have compiled a number of Endnote reference files from various people and institutions. The file is relatively broad, including references for articles and book chapters in the fields of evolutionary biology, biomechanics, functional morphology, and paleontology. The file is available in zipped format (5.5 Mb) and includes a MS-Word document with more detailed information on the Überfile. If you have an Endnote reference file that you would like to contribute, please contact me.
Download uberfile.zip (5.5MB)
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Metzger, K.A. and A. Herrel (2006) Utility of skeletal mass as a measure of body size in lizards. Journal of Herpetology 40(3): 381-384. Full-text available (PDF,124KB).
Metzger, K.A. and A. Herrel (2005) Correlations between lizard cranial shape and diet: a quantitative, phylogenetically informed analysis. Biological Journal of the Linnean Society 86: 433-466. Full-text available (PDF,704KB).
Metzger, K.A., W.J.T. Daniel, and C. Ross (2005) Comparison of beam theory and finite-element analysis to in vivo bone strain in the alligator cranium. The Anatomical Record, Part A 283A (2): 331-348. Full-text available (PDF,560KB).
Ross, C.F. and K.A. Metzger (2004) Bone strain gradients and optimization in vertebrate skulls. Annals of Anatomy 186 (5-6) 387-396. Full-text available (PDF,880KB).
Metzger, K.A. (2002) Cranial Kinesis in Lepidosaurs: Skulls in Motion. In: Topics in Vertebrate Functional and Ecological Morphology, pp. 15-46. (P. Aerts, A. Herrel, K. D'Aout, and R. Van Damme eds.). Shaker Publishing, Maastricht. Full-text available (PDF,1.5MB).
Metzger, K.A. (2000) Society of Vertebrate Paleontology's fifty-ninth annual meeting. Evolutionary Anthropology 9(4): 149-150. Full-text available (PDF,172KB).
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Metzger, K.A. and C.F. Ross (2004) In vivo loading patterns in the alligator mandible. Journal of Morphology 260(3): 313. Abstract available (PDF,52KB).
Ross, C.F., B. Demes, and K.A. Metzger (2004) Bone strain in the cranial and postcranial skeletons of tetrapods. Journal of Morphology 260(3): 323. Abstract available (PDF,56KB).
Metzger, K.A., C.F. Ross, and M. Spencer (2003) Does the constrained lever model describe an optimality criterion in crocodilian jaw mechanics? Integrative and Comparative Biology 43(6): 825. Abstract available (PDF,68KB).
Ross, C.F. and K.A. Metzger (2003) Strain gradients and optimality criteria in vertebrate skulls. Integrative and Comparative Biology 43(6): 827. Abstract available (PDF,16KB).
Demes, B., K. Metzger and S. Larson (2003) The functional signficance of the primate fibula. American Journal of Physical Anthropology Supplement 120(S36): 87. Abstract available (PDF,128KB).
Metzger, K.A. and C. Ross (2002) Adaptive value of the intramandibular joint in archosaurs: In vivo evidence from crocodilians. Journal of Vertebrate Paleontology 22 (S3): 87A-88A. Abstract available (PDF,8KB).
Metzger, K.A. and C.F. Ross (2001) Strain patterns in the lower jaw of the caiman (Caiman crocodilus): implications for the function and evolution of the intramandibular joint in archosaurs. Journal of Morphology 248(3): 261-262. Abstract available (PDF,112KB).
Metzger, K.A. and A. Herrel (2001) Inertial feeding in reptiles: the role of skull mass reduction. American Zoologist 41(6): 1525. Abstract available (PDF,8KB).
Metzger, K.A. and C. Lacoste (1998) Sexual dimorphism in the modern human femur: application of linear and areal data. American Journal of Physical Anthropology 105(S26): 161-162. Abstract available (PDF,268KB).
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Ross, C. and K. Metzger (2003) Along comes Mr. Alligator, as quiet as can be . . . Case studies in suboptimal skull design. Key Note Lecture at 1st International Workshop on Evolutionary Changes in the Craniofacial Morphology of Primates,September 18-23, 2003. Greifswald, Germany. Abstract available (PDF,112KB).
Metzger, K.A. and C. Ross (2002) Patterns of strain across the intramandibular joint in crocodilians. Society for Integrative and Comparative Biology, Division of Vertebrate Morphology, 2002 Northeast Regional Meeting. Cambridge, Massachusetts.
Metzger, K.A. (1999) Fiber typing in the mammalian masseter complex. Society for Integrative and Comparative Biology, Division of Vertebrate Morphology, 1999 Northeast Regional Meeting. Providence, Rhode Island.
Metzger, K.A. and C. Lacoste (1998) Sexual dimorphism and discriminant analysis of the modern human femur. American Association of Forensic Sciences 50th Annual Meeting. San Francicso, California. Abstract available (PDF,24KB).
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Society for Integrative and Comparative Biology (SICB)
Society of Vertebrate Paleontology
EMBL Reptile Database
Crocodilian, Tuatara, and Turtle Species of the World, Florida Museum of Natural History
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