Andrew H. Lee, PhD

Associate Professor of Anatomy

Midwestern University
Arizona College of Osteopathic Medicine
Department of Anatomy
Agave 201R
19555 N 59th Ave.
Glendale, AZ 85308

Office: (623) 572-3732
Lab: (623) 572-6088
e-mail: alee2 at midwestern dot edu


Project 1: I am interested in understanding the physiological and ecological context for the bone histology of dinosaurs.  Because dinosaurs show bone tissue that has a blend of avian and reptilian traits (highly vascularized yet punctuated with annual growth lines), their physiology is presumably intermediary as well.  Studies to assess how intermediate are possible because bone histology records some aspects of physiology such as growth rate.  By using the annual growth lines preserved in dinosaur long bones to estimate growth rates (Lee & Werning, 2008; Cooper, Lee, et al., 2008; Lee et al., 2013; Lee & O'Connor, 2013), my work shows that large dinosaurs reached reproductive size at about five times faster than living reptiles scaled to comparable size (Lee & Werning, 2008).  Even at small body sizes, dinosaurs grew about 40% faster than living reptiles (Lee & O'Connor, 2013).  At least some dinosaurs reached sexual maturity well before they reached full-size, as demonstrated in half-grown specimens by the presence of avian-like reproductive bone tissues (medullary bone) (Lee & Werning, 2008). A potential ecological advantage of rapid growth and early sexual maturity, especially for prey species of dinosaurs, is the increase in lifetime reproductive success (Cooper, Lee, et al., 2008).  These findings clarify how dinosaurs were successful for 150 million years and the evolutionary precedents for rapid growth and reproduction in descendants of dinosaurs (birds).

Project 2: Paleophysiological inferences as described above must be grounded on data from living species.  Surprisingly, we know more about the bone histology of extinct species than of living ones.  To address this deficit, I also study on how bone histology in living species is governed by internal (e.g., growth and historical) and external (e.g., mechanical and ecological) factors.  Early in my career, I showed that mechanical factors do not always account for the vascular organization in bony tissue; despite experiencing a great deal of twisting during locomotion, femora of alligators do not show a histological feature thought to resist twisting loads (Lee, 2004).  However, this feature (laminar tissue) is prevalent in some of the wing bones of birds.  To test if laminar tissue is specifically a flight adaptation, I looked at the wing bones of bats and found that laminar tissue is completely absent (Lee & Simons, 2015).  The absence of laminar tissue in bats is best explained by relatively slow growth rates compared to birds (Lee & Simons, 2015).  This work suggests that growth rate is an important constraint on the expression of bone histology.  To test this idea further, students in my lab are currently tracking the development of laminar tissue in the wing bones of birds.

Project 3:  A developmental approach is also critical to understand the origin of mammalian headgear (i.e., horns, ossicones, antlers, and pronghorns).  With a team of collaborators, I synthesized the scattered literature on the evolution of mammalian headgear and identified the general need for data on early cranial development (Davis, Brakora, & Lee, 2011).  In particular, early pronghorn development is woefully understudied.  Future work may clarify the evolutionary tree of mammals and explain how mammalian headgear became so diverse.  Beyond the fields of phylogenetics and evolution, this contribution may also generate insight into biomedical fields investigating skin-bone interactions and regenerative medicine.