Origin of tetrapods based on a broken bone

Bishop et al. (2015) claimed to push the date for the origin of terrestrial tetrapods back into the Carboniferous (333 mya) by two million years. This is an odd assertion when the first tetrapod footprints date to 395 mya. And the first amniotes (reptiles) are known from 340 mya, also in the Viséan.

From the abstract: “The origin of terrestrial tetrapods was a key event in vertebrate evolution, yet how and when it occurred remains obscure, due to scarce fossil evidence. Here, we show that the study of palaeopathologies, such as broken and healed bones, can help elucidate poorly understood behavioural transitions such as this. Using high-resolution finite element analysis, we demonstrate that the oldest known broken tetrapod bone, a radius of the primitive stem tetrapod Ossinodus pueri from the mid-Viséan (333 million years ago) of Australia, fractured under a high-force, impact-type loading scenario. The nature of the fracture suggests that it most plausibly occurred during a fall on land. Augmenting this are new osteological observations, including a preferred directionality to the trabecular architecture of cancellous bone. Together, these results suggest that Ossinodus, one of the first large (>2m length) tetrapods, spent a significant proportion of its life on land. Our findings have important implications for understanding the temporal, biogeographical and physiological contexts under which terrestriality in vertebrates evolved. They push the date for the origin of terrestrial tetrapods further back into the Carboniferous by at least two million years. Moreover, they raise the possibility that terrestriality in vertebrates first evolved in large tetrapods in Gondwana rather than in small European forms, warranting a re-evaluation of this important evolutionary event.”

References
Bishop PJ, et al. 2015. Oldest Pathology in a Tetrapod Bone Illuminates the Origin of Terrestrial Vertebrates. PLoS ONE 10(5): e0125723. doi:10.1371/journal.pone.0125723

 

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