Functional Morphology of Animals

by

Duncan J. Irschick

• LAST REVIEWED: 16 August 2022
• LAST MODIFIED: 23 May 2012
• DOI: 10.1093/obo/9780199830060-0034

Introduction

As a field, functional morphology aims to understand how morphological form is related to function in the broadest sense. The goals of functional morphology are twofold. The first goal is to understand whether different body forms and physical structures (e.g., bone dimensions) match in a logical way with the functions that they appear well suited for (e.g., locomotion, feeding), and whether such matching makes sense in an evolutionary and ecological context. A second goal is mechanistic; namely, to understand how basic functions, such as locomotion, occur by examining lower-level components, such as muscles, bones, and heart tissue. However, the field of functional morphology is heterogeneous and has several subfields, each of which has its own history and traditions, and each of which adds generally to the broad goal of relating form to function. These subfields include functional anatomy, biomechanics, ecomorphology, and evolutionary functional morphology. Functional anatomy predominated for many centuries, and it aimed to infer function from structure. While it remains today as a conceptual tool, it has largely been supplanted by direct measurements of animal function. Biomechanics unites the science of material properties and physics to understand animal movement. Ecomorphology represents an infusion of functional morphological techniques into the field of ecology, and it is useful for understanding specializations to different habitats. Finally, evolutionary functional morphology integrates principles of evolutionary theory with functional morphology. Evolutionary functional morphology has blossomed in particular over the last several decades. The field of functional morphology in its present form came fully into existence in the 1950s and 1960s, but underlying ideas about how form relates to function have been in existence at least since the time of Aristotle. An exact timeline is challenging, but the field was dominated for many years by anatomists, who inferred how form related to function. The advent of technological innovations in the 1950s and 1960s that allowed the visualization of movement and the monitoring of internal structures such as muscles allowed the field to mature such that both form and function could be empirically studied. Whereas research in the 1960s and 1970s was limited to a few model species that could be examined using only a few techniques, the modern field employs a wide array of techniques, both in the field and in the laboratory, and examines many kinds of animal species. The field has evolved from simple descriptions of external form, anatomy, or movement to highly detailed empirical analyses of body movements using high-speed video (kinematics), and force plates (kinetics). Functional morphology is inherently comparative, and it examines many kinds of species (e.g., birds, lizards, mammals) that occur in different environments (e.g., aquatic, terrestrial).

General Overviews

There is no single original classic work, for the field of functional morphology is heterogeneous and was cobbled together across many years by many independent researchers. However, several early syntheses are notable. Gans 1974 is an influential early source that explained the overarching goals of biomechanics, a subfield of functional morphology. R. McNeill Alexander has written many seminal overviews, including Alexander 1992, which is a well-written and readable account of biomechanics. Hildebrand, et al. 1985 is an edited volume that stands as a landmark in the field by providing a coherent and practical set of chapters written by experts on different functions (e.g., climbing, locomotion). Lauder 1995 is a book chapter that nicely explains why we expect form and function should (or should not) be related among individuals or among species. Two relatively recent and thorough books on locomotion, Alexander 2003 and Biewener 2003, encapsulate many of the techniques and concepts that are relevant for other functions, such as feeding. Irschick and Henningsen 2009 provides a recent overview of the state of the field, and while concise, it provides several case studies that are exemplars of the modern approach.

• Alexander, R. McNeill. 1992. Exploring biomechanics: Animals in motion. New York: Scientific American Library.

  This book covers all kinds of animal movements, ranging from running to flying, and answers some of the most basic mysteries surrounding animal movement, such as how cheetahs can run so fast, or whether flying lizards can actually “fly.”

• Alexander, R. McNeill. 2003. Principles of animal locomotion. Princeton, NJ: Princeton Univ. Press.

  Provides an extensive source of references on all aspects of locomotion, but focuses on the mechanistic and biomechanical determinants of locomotion rather than the ecological or evolutionary causes.

• Biewener, Andrew A. 2003. Animal locomotion. Oxford: Oxford Univ. Press.

  This book differs from Alexander 2003 in being more focused on muscles, nerves, and bones as important elements driving locomotion. It has an excellent chapter on the neural basis of locomotion that is worth reading.

• Gans, Carl. 1974. Biomechanics: An approach to vertebrate biology. Ann Arbor: Univ. of Michigan Press.

  One of the first books to comprehensively synthesize the range of techniques used in biomechanics, such as EMGs. The author is greatly interested in reptiles, and they are heavily represented in this book.

• Hildebrand, Martin, Dennis F. Bramble, Karl F. Liem, and David B. Wake. 1985. Functional vertebrate morphology. Cambridge, MA: Belknap Press of Harvard Univ. Press.

  A classic compendium of chapters that covers topics ranging from climbing to flight, each written by an expert. While some chapters tend to infer function from form, this remains a must-read for any budding functional morphologist.

• Irschick, Duncan J., and Justin P. Henningsen. 2009. Functional morphology: Muscles, elastic mechanisms, and animal performance. In Princeton guide to ecology. Edited by Simon Levin, 27–37. Princeton, NJ: Princeton Univ. Press.

  A concise (10-page) book chapter that provides key definitions for terms such as performance and kinematics, and provides several key examples that describe the range of techniques used in functional morphology, such as studies of flight kinematics in bees, and X-rays of breathing in lizards.

• Lauder, George V. 1995. On the inference of function from structure. In Functional morphology in vertebrate paleontology. Edited by Jeffrey J. Thomason, 1–18. Cambridge, UK: Cambridge Univ. Press.

  A conceptual book chapter that argues that inferring function from structure has some shortcomings; a valuable cautionary paper.