The discovery of a new Devonian tetrapod trackway in SW Ireland

Abstract

A tetrapod trackway has been discovered in Devonian sedimentary rocks of SW Ireland. It is the first discovery of its kind in Europe. Details of the footprints are not preserved, probably because of strong Variscan pressure solution cleavage. However, after removing the effect of Variscan deformation, the large number of footprints (more than 150) makes it possible to calculate the original dimensions of the footprint pattern: stride (approximately 34 cm) and pace (approximately 35 cm). These values are higher than those for other traces of comparable age. The total length of the tetrapod is estimated to be 1 m. Lithostratigraphical and biostratigraphical arguments indicate an age of Mid- to Late Devonian.

Behavioral evidence for the evolution of walking and bounding before terrestriality in sarcopterygian fishes

“…We have shown here that gaits similar to those indicated by some early fossil trackways attributed to early tetrapods (1,3,9,14) can be produced by nontetrapod sarcopterygians. Trackways lacking unambiguous evidence of digits, particularly those from the Devonian, when sarcopterygian fishes were diverse and abundant (8,32), are now open to question.…”

“…Many fossil trackways from the Devonian are indicative of quadrupedal and bipedal gaits very similar to those used by modern terrestrial tetrapods (1,3,9,13,14). That tracks were preserved demonstrates that these animals were walking on a substrate.…”

“…Trackways lacking unambiguous evidence of digits, particularly those from the Devonian, when sarcopterygian fishes were diverse and abundant (8,32), are now open to question. Examples include Valentia Island tracks (14), Kap Graah tracks (1), and Glen Isla 4. Location of lungs and center of mass in P. annectens.…”

“…One essential adaptation in the evolution of tetrapods was the ability to locomote on land, a trait that required significant morphological and functional changes in the appendicular system. Many of these morphological changes can be observed in the fossil record (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). Work on basal tetrapod fossils has revealed that even those with digited limbs can be aquatic (5,7).…”

Possible hominin footprints from the late Miocene (c. 5.7 Ma) of Crete?

“…It is therefore not surprising that ichnologists practice parataxonomy in classifying traces; only where there is sufficient data to infer a trackmaker do they make a more formal link to conventional palaeontological taxonomy. Where such linkages are made they can have controversial implications, especially where body fossils are absent from comparable locations and stratigraphic intervals (e.g., Stössel, 1995;Niedzwiedzki et al, 2010;Voigt and Ganzelewski, 2010;Brusatte et al, 2011;Lichtig et al, 2017). Here, we report an example of the challenges of making such inferences when the implications run counter to conventional views on human evolution: hominin-like footprints from the late Miocene of Crete, at least 5.6 million years old and thus approximately 2 million years older than the hominin trackways from Laetoli in Tanzania (Leakey and Hay, 1979;Leakey and Harris, 1987;White and Suwa, 1987;Deino, 2011).…”