Oldest pathology in a tetrapod bone illuminates the origin of terrestrial vertebrates.
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.
Ancient Environments Program, Queensland Museum, 122 Gerler Rd, Hendra, Queensland, 4011, Australia; School of Earth, Environmental and Biological Sciences, Queensland University of Technology, Brisbane, Queensland, 4000, Australia; Centre for Musculoskeletal Research, Griffith University, Southport, Queensland, 4222, Australia.
Peter J
PJ
Bishop
Department of Anatomy and Developmental Biology, Monash University, Clayton, Victoria, 3800, Australia.
Christopher W
CW
Walmsley
School of Earth, Environmental and Biological Sciences, Queensland University of Technology, Brisbane, Queensland, 4000, Australia.
Matthew J
MJ
Phillips
Department of Anatomy and Developmental Biology, Monash University, Clayton, Victoria, 3800, Australia.
Michelle R
MR
Quayle
Australian Regenerative Medicine Institute, Monash University, Clayton, Victoria, 3800, Australia.
Catherine A
CA
Boisvert
Department of Anatomy and Developmental Biology, Monash University, Clayton, Victoria, 3800, Australia.
Colin R
CR
McHenry
D000818:Animals; D001842:Bone and Bones / Q000000981:diagnostic imaging / Q000473:pathology*; D002146:Bony Callus / Q000000981:diagnostic imaging / Q000473:pathology; D020342:Finite Element Analysis; D005580:Fossils; D050723:Fractures, Bone / Q000000981:diagnostic imaging / Q000473:pathology; D007091:Image Processing, Computer-Assisted; D010802:Phylogeny; D011884:Radius / Q000000981:diagnostic imaging / Q000473:pathology; D014057:Tomography, X-Ray Computed; D014714:Vertebrates / Q000033:anatomy & histology*