COMPARISONS OF ARCHITECTURAL AND SURFICIAL BURROW MORPHOLOGIES WITHIN AND BETWEEN FOSSIL AND EXTANT VERTEBRATES TO AID IN IDENTIFICATION OF FOSSIL VERTEBRATE BURROWS

Excavators of fossil burrows are commonly identified based on body fossils, whereas the architectural and surficial burrow morphologies are interpreted for their paleoenvironmental and paleoecological significance. Burrow morphologies can also be used to identify the excavator in the rock record and test their biogenic origin. Comparisons of burrow morphologies between and within fossil and extant groups of vertebrates are limited. With an increasing number of fossil burrows discovered, the study of fossil and extant burrow morphologies is important to help identify burrows, especially when body fossils within them are absent. Burrowing is a behavioral adaptation of animals in response to environmental conditions. Burrows are used for living, feeding, brooding, or temporary refuge from extreme conditions or predators. Modern vertebrates that commonly excavate burrows comprise fish, amphibians, reptiles, and mammals, all of which have ancestral examples. Fossil burrows are also known from extinct groups, such as the Therapsida. The architecture of fossil and extant vertebrate burrows vary between groups for many reasons, including the animal’s anatomy, social structure, purpose for burrowing, as well as the environment. For example, aestivation and hibernation burrows represent a transient presence in soil. Burrows used only for reproduction or in conjunction with hibernation represent a temporary presence in soil. Burrows used as dwellings that involve the complete life cycle with above ground activity represent a periodic presence in soil. Burrows used for all aspects of the life cycle with little or no aboveground activity represent a permanent presence in soil. Fossil burrows from a particular group also share many of the same architectural morphologies as their descendants. For example, lungfish burrows in Devonian fluvial deposits represent the oldest record of vertebrate burrows, interpreted based on their similarity to younger and extant lungfish burrows.