Justin S. Sipla jsipla@ic.sunysb.edu Ph.M. Anatomical Sciences, Stony Brook University (2004) M.S. Basic Health Sciences, Stony Brook University (2004) B.A. Anthropology, University of California at Los Angeles (2001) Major Advisor: Catherine Forster

My research focuses on understanding the relationship between locomotor behavior and vestibular function in tetrapods, specifically theropod dinosaurs and birds, both from a comparative and functional perspective. The semicircular canal system of the inner ear responds to rotational movement of the head during locomotion. This information is used by the brain to reflexively control eye position, maintain equilibrium, and adjust posture. Differences in the size and shape of the semicircular canals affect the biomechanical and hydrodynamic properties of the system, and are thought to correlate with preferred modes of locomotion.

My dissertation work examines this link in theropods and birds, using computed tomography and x-ray microtomography to peer inside the otic capsules of extant birds and extinct dinosaurs. 3-D imaging and surface rendering are used to model the canal system, brain, and associated cranial structures. Measurements are obtained using morphometric tools such as VoxBlast (VayTek). A large comparative database of extant bird morphology has been generated for use in evaluating the flight capabilities of primitive birds. In collaboration with Justin Georgi and Cathy Forster, similar techniques are being applied to Dinosauria in general. Recent work has demonstrated that the semicircular canal dimensions of dinosaurs are tightly correlated with locomotor preference, such that in bipedal species the anterior semicircular canals are vertically enlarged relative to quadrupedal species, providing clues about the locomotor functions of dinosaurs with debated postures.

In the experimental domain, my work focuses on documenting patterns of head movements in primates and crocodiles, using kinematics, cineradiography, and electromyography to evaluate the motor control mechanisms underlying head stabilization during locomotion.

3D reconstruction of the skull of the ornithischian dinosaur Psittacosaurus mongoliensis (IGM 100/1132) in transparent right lateral view, showing orientation and relative size of right semicircular canal system (in red).	3D reconstruction of Metallura tyrianthina, a small hummingbird, showing the left medial wall of the braincase and associated semicircular canal sytem.	Virtual endocast of the brain and left semicircular canal system of Buteo jamaicensis, the red-tailed hawk, reconstructed from CT scans.

Sipla, J.S., J.A. Georgi, and C.A. Forster (2005) The semicircular canals of dinosaurs: Tracking major transitions in locomotion. Submitted.

Sipla, J.S., F. Spoor (2005) The physics and physiology of balance. In Senses on the Threshold (eds. J.G.M. Thewissen and S. Nummela). In press.

Georgi, J.A. and J. S. Sipla (2005) Balance: comparative anatomy and physiology in secondarily aquatic reptiles and birds. In Senses on the Threshold (eds. J.G.M. Thewissen and S. Nummela). In press.

Sipla, J.S., J.A. Georgi, and C.A. Forster (2004) The semicircular canals of dinosaurs: Tracking major transitions in locomotion. Journal of Vertebrate Paleontology. Suppl. 24:113.

Sipla, J.S., J.A. Georgi, and C.A. Forster (2003) The semicircular canal dimensions of birds and crocodilians: Implications for the origin of flight. Journal of Vertebrate Paleontology. Suppl. 23:97.

Sipla, J.S., C.F. Ross, and S.G. Larson (2002) Kinematics and EMG activation of head-neck muscles during locomotion in Erythrocebus patas. American Journal of Physical Anthropology. Suppl. 36:193.

Sipla, J.S. (2002) Kinematics of head posture during galloping locomotion in Erythrocebus patas. Journal of Vestibular Research. Suppl. 11: 193.

Head Games Show Whether Dinos Went on Two Legs or Four, Erik Stokstad, Science 306: 1466.

Peering Into Ancient Ears, Erik Stokstad, Science 302: 770-771.