Biology of the Sauropod Dinosaurs: Understanding the Life of Giants

By Nicole Klein; Kristian Remes et al. | Go to book overview

5
Structure and Function of the Sauropod Respiratory System

STEVEN F. PERRY, THOMAS BREUER, AND NADINE PAJOR

BECAUSE DINOSAUR LUNGS do not fossilize, reconstruc-
tion of the sauropod respiratory system must rely on
indirect evidence. We combine extant phylogenetic
bracketing and functional morphological approximation
to draw conclusions on the structure and function of the
sauropod respiratory system. The combination of these
techniques leads to strong evidence for the presence of
lungs that consisted of two parts: a gas exchange region
that was attached to the ribs and vertebrae, and a sac-like
region below the exchange region, close to the liver and
intestine. This respiratory system is similar to the effi-
cient lung–air sac system of birds. It is highly adaptable
and could have served to supply oxygen, remove carbon
dioxide, and help with temperature control.


Introduction

Indirect evidence for the reconstruction of the respiratory system of extinct animals can come from the skeleton itself, mainly from the ribs and the rib cage. Most interesting here is the morphology of the uncinate processes, the course and density of Sharpey’s fibers within the ribs, and the heads of the ribs and their articulation to the vertebrae.

Extant phylogenetic bracketing (Witmer 1995) is used to deduce the possible structural type of the respiratory system, whereas functional morphological approximation (Perry & Sander 2004) is applied in a second step to give information on the functional/physiological implications of these structures.

In this chapter, we first give an overview of general lung structure and function in amniotes. We then focus on differences in lung systems of the closest living relatives of dinosaurs: birds and reptiles. Finally, we discuss the indirect evidence for the presence of an avian-like structural type of lung in sauropod dinosaurs. This structure has functional implications, which in turn either limit or make possible certain metabolic strategies. It is capable of supporting a broad scope of metabolic demands, including the high demand of a rapidly growing and highly active juvenile and the relatively low demand of a resting adult. Furthermore, an avian-like lung system could have helped in thermoregulation by providing large heat-transfer surfaces. Finally, the presence of air sacs lowers the overall density and thus the mass of an animal of a given size, resulting in lower energy requirement and mechanical advances compared to models with nonavian lung structures. We conclude that the lung structure in sauropods contributed to making gigantism possible (see also Sander et al. 2010).

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