Research Interests

The lab’s research focuses on the functional morphology and evolution of the vertebrate head. The lab’s primary goal is to understand the structural, biomechanical, and evolutionary patterns of the feeding apparatus in reptiles. Data gathered from extant taxa are used to understand not only how living animals function but also how these animals evolved; therefore, incorporating fossil taxa into comparative and historical analyses is a common practice. Classical anatomical techniques used include dissection, vascular injection, and histology. These are coupled with CT scanning, MRI, and other imaging modalities that are analyzed with software packages that enable 3D visualization, reconstruction, and analysis of anatomical structures.

Illustration of research goals of the Holliday lab using the inverted pyramid of inference (Witmer, 1995) as a heuristic device. Basically, the lab relies on understanding anatomy, which forms the foundation for inferences of function and behavior.

Currently there are two active projects underway:

Archosaur feeding evolution: Understanding feeding functional morphology is critical to gaining insight into how animals interact with their food and environment. We are currently reconstructing and analyzing jaw muscle morphology in living and fossil archosaurs (a group which includes birds, crocodilians, and dinosaurs) to not only understand feeding behavior and evolution in particular fossil groups (e.g., tyrannosaurs and early crocodyliforms), but to also understand how the highly-derived, modern avian and crocodylian conditions arose. Computer models of the head skeletomuscular system are developed and validated using living animals using dissection. These data are then be incorporated into finite element models (FEA) and 3D-animated kinematic models used to explore feeding functional hypotheses in collaboration with researchers from several different institutions.

Reptilian connective tissues biology: Reptile heads are composed of a number of complicated bony and soft-tissue structures including sutures, fibrocartilaginous sesamoids, and synovial joints. For the most part however, little is known about the responses of reptile connective tissues to epigenetic (e.g., mechanical) and anthropogenic (e.g., pollutant) stimuli and the genetic and regulatory mechanisms responsible for reptilian cranial tissues is largely unexplored (with the exception of birds). Therefore the potential applicability of reptilian models to biomedical sciences remains untested, though insights into arthritis and osteoporosis appear possible. Particular joints and tissues are being harvested from alligators, birds, and lizards and analyzed using CT, material properties testing, and histology to understand the structure and function of sutures, synovial joints, cartilage, ligaments, and tendons of the head.

Opportunities for Students

   —Learn anatomical techniques including dissection, vascular injection, and histology
             — Collect and analyze data from CT scanning for use in research and education
             —Use cutting edge 3D visualization and animation software to reconstruct the anatomy of living and fossil animals
             —Learn histology of skeletal tissues (e.g., bone, cartilage, muscle)

Ongoing projects for students

           Dinosaur and crocodilian feeding evolution
                            reconstruct jaw muscles, nerves, and other tissues in 3D models of extinct animals

                    Reptilian bone biology
                            generate histological and imaging data from reptiles for studies on suture growth, bone density, and joint function

                    Human Gross Anatomy and Radiology
                           reconstruct and label human anatomy in 3D using CT and MRI data

Projects (click titles to ink to separate pages) all images © Casey M Holliday 2006 unless otherwise noted
Flamingo Head Vasculature (Holliday, Ridgely, Balanoff, & Witmer, 2006 Anat Rec)		Archosaur Adductor Chamber Homology (Holliday & Witmer, 2007, J Morph)

Diapsid Orbitotemporal Evolution (Holliday & Witmer)		Effects of PCBs on Turtle Bone Density (DK Holliday & CM Holliday)

Crocodyliform Braincase Evolution (Holliday & Witmer)		Limb Articular Cartilage in Extant and Fossil Archosaurs (Holliday, Ridgely, Sedlmayr, & Witmer)

Hadrosaur Anatomy & Feeding Mechanics (Rybczinski, Tirabasso, Cuthburton, & Holliday)		A Critical Appraisal of Dinosaur Cranial Kinesis (Holliday & Witmer)

Diapsid Intracranial Joint and Skull Functional Morphology

Frontal suture morphology	Crocodyliform and diapsid symphyseal morphometrics	FEA of joint and skull function in Varanus

Basal joint structure and histology

Publications
Holliday, Casey M., Ryan C. Ridgely, Amy M. Balanoff, and Lawrence M. Witmer. 2006. Cephalic vascular anatomy in flamingos (Phoenicopterus ruber) based on novel vascular injection and computed tomographic imaging analyses. Anatomical Record 288A(10):1031–1041.	PDF	Link to page
Holliday, Casey M. and Lawrence M. Witmer. 2007. Archosaur adductor chamber homology: integration of musculoskeletal and topological criteria in jaw muscle homology. Journal of Morphology.268:457-484.	PDF	Link to page
Holliday, Casey M. and Lawrence M. Witmer. In Review. Cranial kinesis in dinosaurs: intracranial joints, protractor muscles, and their significance for cranial evolution and function in diapsids. Journal of Vertebrate Paleontology.	PDF	Link to page