Late Devonian fossils of New South Wales and early tetrapod habitats

Central New South Wales, Australia, has a rich fossil record of Late Devonian (Famennian) fossil fish (eight species, mostly Bothriolepis and Remigolepis) and a single tetrapod (Metaxygnathus). This paper presents, for the first time, evidence from trace fossils, fossil plants, and palaeosols of the Hervey Group for the palaeoenvironment and evolution of Devonian tetrapods and fish. Late Devonian palaeosols of the Hervey Group in New South Wales formed in a semiarid climate with low shrubby desert vegetation, but at two levels including one with a tetrapod, there is evidence of subhumid woodland. That double spike to subhumid climate matches palaeoclimatic spikes in Pennsylvania cued to global atmospheric spikes in carbon dioxide correlated with the Annulata event of marine black shales dated at 365 Ma. This evidence supports the woodland hypothesis of tetrapod origins rather than the idea that they evolved from fish escaping shrinking desert ponds, or evolved in tidal flats. The Canowindra fish bed of mass mortality in a desiccated billabong (oxbow lake) is a stunning example of what happened in drying desert ponds. New South Wales has no clear evidence of intertidal vertebrates, and trackways which inspired this hypothesis are now controversial. In otherwise aquatic Late Devonian tetrapods, limbs may have been adaptations to negotiating or hiding from predators in streams choked with woody debris, and their necks allowed feeding on land, or in water shallower than their bodies.