Thinopus and a Critical Review of Devonian Tetrapod Footprints

Abstract

Devonian tetrapod tracks and trackways can be recognized by three criteria: morphology of the manus and pes impressions that matches known Devonian tetrapod skeletal morphology, manus smaller than pes, and the alternating trackway pattern that results from lateral sequence walking in quadrupedal tetrapod locomotion. The first reported Devonian tetrapod track, named Thinopus antiquus, from Pennsylvania, is not a tetrapod track and is likely an impression of a fish coprolite(s). A critical review of the published Devonian track record indicates only three can be verified as produced by a tetrapod trackmaker—Genoa River, Australia; Easter Ross, Scotland; and Valentia Island, Ireland. The supposed tetrapod tracks from the Middle Devonian of the Zachełmie quarry, Poland, fail the criteria for identification as Devonian tetrapod tracks. Indeed, no convincing case has been made that the Zachełmie structures are tetrapod tracks. Instead, they are reinterpreted as fish nests/feeding traces (ichnogenus Piscichnus). The oldest Devonian tetrapod trackway is Givetian and this is the oldest record of a tetrapod, but the sparse record of Devonian tetrapod tracks is of no other biostratigraphic and little paleobiogeographic significance. Bona fide Devonian tetrapod tracks are from nonmarine facies, so they do not support a marginal marine origin of tetrapods. They indicate lateral sequence walking and pelvic-limb-propelled, fully terrestrial (subaerial) locomotion in freshwater environments by at least some Devonian tetrapods.

Keywords:

• Thinopus
• Tetrapod
• Track
• Trackway
• Lateral sequence walking
• Devonian
• Piscichnus

ACKNOWLEDGMENTS

I am grateful to Dan Brinkman and Walter Joyce for access to the holotype of Thinopus antiquus. Discussions with Ted Daeschler regarding Devonian tetrapod footprints are appreciated, and Bill DiMichele and Patricia Gensel provided paleobotanical advice. Grzegorz Niedźwiedzki generously provided photographs of some of the Zachełmie quarry structures, and Murray Gingras provided the image in Figure 13. Comments by an anonymous reviewer and Ted Daeschler, as well as the editorial oversight of Murray Gingras, much improved the manuscript. It is a pleasure to dedicate this article to my good friend and mentor Martin Lockley, to honor his many contributions to vertebrate ichnology.